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Author name code: gopalswamy
ADS astronomy entries on 2022-09-14
author:"Gopalswamy, Nat"
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Title: Effect of the Heliospheric State on CME Evolution
Authors: Dagnew, Fithanegest Kassa; Gopalswamy, Nat; Tessema, Solomon
Belay; Akiyama, Sachiko; Yashiro, Seiji
2022ApJ...936..122D Altcode:
The culmination of solar cycle 24 by the end of 2019 has created
the opportunity to compare the differing properties of coronal mass
ejections (CMEs) between two whole solar cycles: solar cycle 23 (SC 23)
and solar cycle 24 (SC 24). We report on the width evolution of limb
CMEs in SCs 23 and 24 in order to test the suggestion by Gopalswamy et
al. that CME flux ropes attain pressure balance at larger heliocentric
distances in SC 24. We measure CME width as a function of heliocentric
distance for a significantly large number of limb CMEs (~1000) and
determine the distances where the CMEs reach constant width in each
cycle. We introduced a new parameter, the transition height (hc) of a
CME, defined as the critical heliocentric distance beyond which the CME
width stabilizes to a quasi-constant value. Cycle and phase-to-phase
comparisons are based on this new parameter. We find that the average
value of hc in SC 24 is 62% higher than that in SC 23. SC 24 CMEs
attain their peak width at larger distances from the Sun than SC 23
CMEs do. The enhanced transition height in SC 24 is new observational
ratification of the anomalous expansion. The anomalous expansion of
SC 24 CMEs, which is caused by the weak state of the heliosphere,
accounts for the larger heliocentric distance where the pressure
balance between CME flux rope and the ambient medium is attained.
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Title: What Is Unusual About the Third Largest Geomagnetic Storm of
Solar Cycle 24?
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Xie, H.; Mäkelä,
P.; Fok, M. -C.; Ferradas, C. P.
2022JGRA..12730404G Altcode: 2022arXiv220711630G
We report on the solar and interplanetary (IP) causes of the
third largest geomagnetic storm (26 August 2018) in solar cycle
24. The underlying coronal mass ejection (CME) originating from
a quiescent filament region becomes a 440 km/s magnetic cloud
(MC) at 1 au after ∼5 days. The prolonged CME acceleration (for
∼24 hr) coincides with the time profiles of the post-eruption
arcade intensity and reconnected flux. Chen et al. (2019, <A
href="https://doi.org/10.3847/1538-4357/ab3f36">https://doi.org/10.3847/1538-4357/ab3f36</A>)
obtain a lower speed since they assumed that the CME does not
accelerate after ∼12 hr. The presence of multiple coronal holes near
the filament channel and the high-speed wind from them seem to have
the combined effect of producing complex rotation in the corona and
IP medium resulting in a high-inclination MC. The Dst time profile
in the main phase steepens significantly (rapid increase in storm
intensity) coincident with the density increase (prominence material)
in the second half of the MC. Simulations using the Comprehensive Inner
Magnetosphere-Ionosphere model show that a higher ring current energy
results from larger dynamic pressure (density) in MCs. Furthermore,
the Dst index is highly correlated with the main-phase time integral
of the ring current injection that includes density, consistent with
the simulations. A complex temporal structure develops in the storm
main phase if the underlying MC has a complex density structure during
intervals of southward IP magnetic field. We conclude that the high
intensity of the storm results from the prolonged CME acceleration,
complex rotation of the CME flux rope, and the high density in the
1-au MC.
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Title: Effect of the Heliospheric State on CME Evolution
Authors: Kassa Dagnew, Fithanegest; Gopalswamy, Nat; Belay Tessema,
Solomon; Akiyama, Sachiko; Yashiro, Seiji
2022arXiv220803536K Altcode:
The culmination of solar cycle 24 by the end of 2019 has created
the opportunity to compare the differing properties of coronal mass
ejections (CMEs) between two whole solar cycles: Solar cycle 23 (SC 23)
and Solar cycle 24 (SC 24). We report on the width evolution of limb
CMEs in SC 23 and 24 in order to test the suggestion by Gopalswamy
et al. (2015a) that CME flux ropes attain pressure balance at larger
heliocentric distances in SC 24. We measure CME width as a function
of heliocentric distance for a significantly large number of limb CMEs
(~1000) and determine the distances where the CMEs reach constant width
in each cycle. We introduced a new parameter: the transition height (hc)
of a CME defined as the critical heliocentric distance beyond which the
CME width stabilizes to a quasi-constant value. Cycle and phase-to-phase
comparisons are based on this new parameter. We find that the average
value of hc in SC 24 is 62% higher than in SC 23. SC 24 CMEs attain
their peak width at larger distances from the Sun as compared to SC
23 CMEs. The enhanced transition height in SC 24 is new observational
ratification of the anomalous expansion. The anomalous expansion of SC
24 CMEs which is caused by the weak state of the heliosphere, accounts
for the larger heliocentric distance where the pressure balance between
CME flux rope and the ambient medium is attained.
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Title: Capacity Building Workshop on Coronal and Interplanetary
Shocks in Kodaikanal
Authors: D'Amicis, Raffaella; Kathiravan, C.; Chellasamy Edwin,
Ebenezer; Gopalswamy, Nat
2022cosp...44.3079D Altcode:
Space-based white-light coronagraph observations, radio spectral
and imaging observations from space and ground are powerful tools to
study and characterize interplanetary shocks driven by coronal mass
ejections (CMEs). To encourage the scientific use of a wealth of data
accumulated at the CDAW Data Center at NASA Goddard Space Flight Center
including space missions (SOHO, GOES, SDO, STEREO, ACE), images of
type II radio bursts from the Gauribidanur Radioheliograph (GRAPH),
ground based radio data from the e-CALLISTO network and the Radio
Solar Telescope Network around the globe, a two-week COSPAR Capacity
Building Workshop was held in Kodaikanal, India, in 2020. This workshop
was intended for scientists and students in developing countries (with
particular reference to people from India, Pakistan, Africa, Malaysia,
Indonesia, and Sri Lanka) where the e-CALLISTO instruments are deployed
to perform joint studies using their data in conjunction with space
data to investigate geoeffective solar transient phenomena. The workshop
consisted of a series of introductory lectures on the Sun, Solar Corona,
Interplanetary medium, Solar Eruptions, Shocks, and Solar Radio Bursts
and also on Python software for data analysis. Several projects were
undertaken by teams consisting of lecturers and students. In this
presentation, we report about this successful workshop.
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Title: Halo coronal mass ejections, solar energetic particles,
and sustained gamma-ray emission
Authors: Gopalswamy, Nat; Xie, Hong; Makela, Pertti; Yashiro, Seiji;
Akiyama, Sachiko
2022cosp...44.1167G Altcode:
Halo coronal mass ejections (CMEs) are fast and wide and hence are
very energetic. CMEs that produce space weather events such as intense
geomagnetic storms and large solar energetic particle (SEP) events
have high proportion of halo CMEs. One CME population has 100 percent
halos: the CMEs associated with sustained gamma-ray emission (SGRE)
from the Sun that last for at least 3 hours. CMEs associated with
SGRE are ultrafast (average speed ~2000 km/s), very similar to CMEs
that produce ground level enhancement (GLE) events. The SGRE - halo CME
connection supports the idea that high-energy protons accelerated at the
CME shock precipitate back to the solar surface, interact with ambient
protons, and produce pion decay continuum observed as SGRE. In order
to further clarify the relationship, we start with all ultrafast halo
CMEs (sky-plane speed at least 1800 km/s) observed in solar cycles
24 that had simultaneous gamma-ray observations from the Sun. We
identified 20 such CMEs that have an average sky-plane speed of ~2142
km/s, fourteen of which were frontsided. The soft X-ray flare sizes
ranged from M3.7 to X8.2. We determined the CME kinematics using the
graduated cylindrical shell model applied to SOHO and STEREO coronagraph
data. The three-dimensional speed from the graduated cylindrical shell
(GCS) model peaks at ≥2000 km/s (average 2698 km/s). The initial
acceleration of the CMEs is >1 km s-2 (average 3.5 km s-2). These
speeds and accelerations are typical of GLE events, indicating strong
shocks close to the Sun accelerating highest energy particles. When
we examined the Fermi Large Area Telescope (Fermi/LAT) >100 MeV
gamma-ray data, we found that all but one of the 14 frontsided halo
CMEs are associated with an SGRE event. The lone halo without SGRE had
a Fermi/LAT data gap, so we cannot rule out the possibility of SGRE
association. Among the 6 backside halo CMEs, one was associated with
an SGRE, which is the famous 2014 September 1 event originating about
40 degrees behind the limb. Two events had backside location similar
to that of the 2014 September 1 event, but the flux rope orientation
is north-south indicating a smaller longitudinal extent of the source
region, so no SGRE is observed on the frontside. The remaining three
events were too far behind the limb. We present additional information
on the properties of the SEP events and interplanetary type II radio
bursts that further support the CME-SGRE connection.
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Title: Flux Rope from Eruption Data (FRED) method applied to
Earth-directed CMEs from solar cycles 23 and 24
Authors: Gopalswamy, Nat; Xie, Hong; Makela, Pertti; Yashiro, Seiji;
Akiyama, Sachiko
2022cosp...44.2427G Altcode:
Only a fraction of an active region magnetic flux participates in a
typical eruption. The total reconnected flux within the eruption area
underlying post eruption arcades (PEAs) represents this fraction. The
"flux rope from eruption data" or FRED refers to a technique that
defines a coronal mass ejection (CME) flux rope based on the total
reconnected flux during the eruption and geometric modeling of the
white-light CMEs. One of the key features of FRED is that we know
the axial magnetic field strength of the flux rope in the corona. If
the flux rope expands self similarly, one can obtain its magnetic
field components at any location in the heliosphere. This technique
was applied previously to Earth-arriving CMEs of solar cycle 23 with
encouraging results. Now that solar cycle 24 is complete, we apply the
FRED technique to cycle 24 events and compare the results with those
obtained for cycle 23.
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Title: Modeling the East-West Asymmetry of Energetic Particle Fluence
in Large Solar Energetic Particle Events Using the iPATH Model
Authors: Ding, Zheyi; Li, Gang; Ebert, Robert W.; Dayeh, Maher A.;
Fe-Dueñas, Adolfo Santa; Desai, Mihir; Xie, Hong; Gopalswamy, N.;
Bruno, A.
2022JGRA..12730343D Altcode:
It has been noted that in large solar energetic particle (SEP) events,
the peak intensities show an East-West asymmetry with respect to the
source flare locations. Using the 2D improved Particle Acceleration and
Transport in the Heliosphere (iPATH) model, we investigate the origin
of this longitudinal trend. We consider multiple cases with different
solar wind speeds and eruption speeds of the coronal mass ejections
(CMEs) and fit the longitudinal distributions of time-averaged fluence
by symmetric/asymmetric Gaussian functions with three time intervals of
8, 24 and 48 hr after the flare onset time respectively. The simulation
results are compared with a statistical study of three-spacecraft
events. We suggest that the East-West asymmetry of SEP fluence and
peak intensity can be primarily caused the combined effect of an
extended shock acceleration process and the evolution of magnetic
field connection to the shock front. Our simulations show that the
solar wind speed and the CME speed are important factors determining
the East-West fluence asymmetry.
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Title: Interhemispheric Asymmetries in Ionospheric Electron Density
Responses During Geomagnetic Storms: A Study Using Space-Based and
Ground-Based GNSS and AMPERE Observations
Authors: Swarnalingam, N.; Wu, D. L.; Gopalswamy, N.
2022JGRA..12730247S Altcode:
We utilize Total Electron Content (TEC) measurements and electron
density (Ne) retrieval profiles from Global Navigation Satellite System
(GNSS) receivers onboard multiple Low Earth Orbit (LEO) satellites
to characterize large-scale ionosphere-thermosphere system responses
during geomagnetic storms. We also analyze TEC measurements from GNSS
receivers in a worldwide ground-based network. Measurements from four
storms during June and July 2012 (boreal summer months), December 2015
(austral summer month), and March 2015 (equinoctial month) are analyzed
to study global ionospheric responses and the interhemispheric asymmetry
of these responses. We find that the space-based and ground-based TECs
and their responses are consistent in all four geomagnetic storms. The
global 3D view from GNSS-Radio Occultation (RO) Ne observations captures
enhancements and the uplifting of Ne structures at high latitudes
during the initial and main phases. Subsequently, Ne depletion occurs
at high latitudes and starts progressing into midlatitude and low
latitude as the storm reaches its recovery phase. A clear time lag
is evident in the storm-induced Ne perturbations at high latitudes
between the summer and winter hemispheres. The interhemispheric
asymmetry in TEC and Ne appears to be consistent with the magnitudes
of the Active Magnetosphere and Planetary Electrodynamics Response
Experiment (AMPERE) high latitude integrated field-aligned currents
(FACs), which are 3-4 MA higher in the summer hemisphere than in the
winter hemisphere during these storms. The ionospheric TEC and Ne
responses combined with the AMPERE-observed FACs indicate that summer
preconditioning in the ionosphere-thermosphere system plays a key role
in the interhemispheric asymmetric storm responses.
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Title: The Relation between Type III Radio Storms and CIR Energetic
Particles
Authors: Gopalswamy, Nat; Mäkelä, Pertti; Yashiro, Seiji; Akiyama,
Sachiko; Xie, Hong
2022arXiv220515852G Altcode:
We report on a study that compares energetic particle fluxes in
corotating interaction regions (CIRs) associated with type III radio
storm with those in nonstorm CIRs. In a case study, we compare the
CIR particle events on 2010October 21 and 2005 November 2. The two
events have similar solar and solar wind circumstances, except that
the former is associated with a type III radio storm and has a higher
CIR particle flux and fluence. We also perform a statistical study,
which shows that the proton and electron fluences are higher in the
storm associated CIRs by factor of about 6 and 8, respectively than
those in the storm-free CIRs.
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Title: Can Type III Radio Storms be a Source of Seed Particles to
Shock Acceleration?
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Mäkelä, Pertti; Yashiro,
Seiji; Xie, Hong
2022arXiv220515233G Altcode:
An intense type III radio storm has been disrupted by a fast halo
coronal mass ejection (CME) on 2000 April 4. The CME is also associated
with a large solar energetic particle (SEP) event. The storm recovers
after about10 hrs. We identified another CME that occurs on 2003
November 11 with similar CME properties but there is no type III storm
in progress. The 2003 November 11 CME is also not associated with an SEP
event above the background (less than 2 pfu), whereas the one with type
III storm has an intense SEP event (about 56 pfu). One of the factors
affecting the intensity of SEP events is the presence of seed particles
that are accelerated by CME-driven shocks. We suggest that the type
III storm source, which accelerates electrons to produce the storm,
also accelerates ions that serve as seed particles to the CME shock.
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Title: Study of the Mass-loss Rate from the Sun
Authors: Michalek, Grzegorz; Gopalswamy, Nat; Yashiro, Seiji
2022ApJ...930...74M Altcode:
We investigate the temporal evolution of the yearly total mass-loss
rate (YTMLR) from the Sun through coronal mass ejections (CMEs) over
solar cycles 23 and 24. The mass determination of CMEs can be subject
to significant uncertainty. To minimize this problem, we have used
extensive statistical analysis. For this purpose, we employed data
included in the Coordinated Data Analysis Workshop (CDAW) catalog. We
estimated the contributions to mass loss from the Sun from different
subsamples of CMEs (selected on the basis of their masses, angular
widths, and position angles). The temporal variations of the YTMLR
were compared to those of the sunspot number (SSN), X-ray flare flux,
and the Disturbance Storm Time (Dst) index. We show that the CME mass
included in the CDAW catalog reflects with high accuracy the actual
mass-loss rate from the Sun through CMEs. Additionally, it is shown
that the CME mass distribution in the log-lin representation reflects
the Gaussian distribution very well. This means that the CMEs included
in the CDAW catalog form one coherent population of ejections that
have been correctly identified. Unlike the CME occurrence rate, it
turns out that the YTMLR is a very good indicator of solar activity
(e.g., SSN) and space weather (e.g., Dst index) consequences. These
results are very important, since the YTMLR, unlike the mass loss
through solar wind, significantly depends on solar cycles.
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Title: Modern Faraday Rotation Studies to Probe the Solar Wind
Authors: Kooi, Jason E.; Wexler, David B.; Jensen, Elizabeth A.;
Kenny, Megan N.; Nieves-Chinchilla, Teresa; Wilson, Lynn B., III; Wood,
Brian E.; Jian, Lan K.; Fung, Shing F.; Pevtsov, Alexei; Gopalswamy,
Nat; Manchester, Ward B.
2022FrASS...941866K Altcode:
For decades, observations of Faraday rotation have provided unique
insights into the plasma density and magnetic field structure of
the solar wind. Faraday rotation (FR) is the rotation of the plane
of polarization when linearly polarized radiation propagates through
a magnetized plasma, such as the solar corona, coronal mass ejection
(CME), or stream interaction region. FR measurements are very versatile:
they provide a deeper understanding of the large-scale coronal magnetic
field over a range of heliocentric distances (especially ≈1.5 to
20 R⊙) not typically accessible to in situ spacecraft observations;
detection of small-timescale variations in FR can provide information
on magnetic field fluctuations and magnetohydrodynamic wave activity;
and measurement of differential FR can be used to detect electric
currents. FR depends on the integrated product of the plasma
density and the magnetic field component along the line of sight
to the observer; historically, models have been used to distinguish
between their contributions to FR. In the last two decades, though,
new methods have been developed to complement FR observations with
independent measurements of the plasma density based on the choice
of background radio source: calculation of the dispersion measure
(pulsars), measurement of Thomson scattering brightness (radio
galaxies), and application of radio ranging and apparent-Doppler
tracking (spacecraft). New methods and new technology now make it
possible for FR observations of solar wind structures to return not
only the magnitude of the magnetic field, but also the full vector
orientation. In the case of a CME, discerning the internal magnetic
flux rope structure is critical for space weather applications.
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Title: Periodic Oscillations in LASCO Coronal Mass Ejection Speeds:
Space Seismology
Authors: Michalek, Grzegorz; Gopalswamy, Nat; Yashiro, Seiji
2022ApJ...927L..16M Altcode:
Coronal mass ejections (CMEs) are energetic eruptions of organized
magnetic structures from the Sun. Therefore, the reconnection of the
magnetic field during ejection can excite periodic speed oscillations
of CMEs. A previous study showed that speed oscillations are frequently
associated with CME propagation. The Solar and Heliospheric Observatory
mission's white-light coronagraphs have observed about 30,000 CMEs from
1996 January to the end of 2019 December. This period of time covers two
solar cycles (23 and 24). In the present study, the basic attributes of
speed oscillations during this period of time were analyzed. We showed
that the oscillation parameters (period and amplitude) significantly
depend not only on the phase of a given solar cycle but also on the
intensity of individual cycles as well. This reveals that the basic
attributes of speed oscillation are closely related to the physical
conditions prevailing inside the CMEs as well as in the interplanetary
medium in which they propagate. Using this approximation, we estimated
that, on average, the CME internal magnetic field varies from 18 up
to 25 mG between minimum and maximum solar activity. The obtained
results show that a detailed analysis of speed oscillations can be a
very efficient tool for studying not only the physical properties of
the ejections themselves but also the condition of the interplanetary
medium in which they expand. This creates completely new perspectives
for studying the physical parameters of CMEs shortly after their
eruption in the Sun's environment (space seismology).
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Title: Eruption of the EUV Hot Channel from the Solar Limb and
Associated Moving Type IV Radio Burst
Authors: Vemareddy, P.; Démoulin, P.; Sasikumar Raja, K.; Zhang,
J.; Gopalswamy, N.; Vasantharaju, N.
2022ApJ...927..108V Altcode: 2022arXiv220106899V
Using the observations from the Solar Dynamics Observatory, we study
an eruption of a hot-channel flux rope (FR) near the solar limb on 2015
February 9. The pre-eruptive structure is visible mainly in EUV 131 Å
images, with two highly sheared loop structures. They undergo a slow
rising motion and then reconnect to form an eruptive hot channel,
as in the tether-cutting reconnection model. The J-shaped flare
ribbons trace the footpoint of the FR that is identified as the hot
channel. Initially, the hot channel is observed to rise slowly at 40
km s<SUP>-1</SUP>, followed by an exponential rise from 22:55 UT at a
coronal height of 87 ± 2 Mm. Following the onset of the eruption at
23:00 UT, the flare reconnection then adds to the acceleration process
of the coronal mass ejection (CME) within 3 R <SUB>⊙</SUB>. Later
on, the CME continues to accelerate at 8 m s<SUP>-2</SUP> during its
propagation period. Further, the eruption also launched type II radio
bursts, which were followed by type III and type IVm radio bursts. The
start and end times of the type IVm burst correspond to the CME's
core height of 1.5 and 6.1 R <SUB>⊙</SUB>, respectively. Also, the
spectral index is negative, suggesting that nonthermal electrons are
trapped in the closed loop structure. Accompanied by this type IVm
burst, this event is unique in the sense that the flare ribbons are
very clearly observed together with the erupting hot channel, which
strongly suggests that the hooked parts of the J-shaped flare ribbons
outline the boundary of the erupting FR.
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Title: VizieR Online Data Catalog: Solar coronal mass ejections with
SOHO/LASCO (Dagnew+, 2020)
Authors: Dagnew, F. K.; Gopalswamy, N.; Tessema, S. B.; Akiyama, S.;
Yashiro, S.; Tesfu, T. Y.
2022yCat..19030118D Altcode:
We used data (Gopalswamy+, 2010SunGe...5....7G) from the catalog
that compiles all halo coronal mass ejections (HCMEs) manually
identified from the Solar and Heliospheric Observatory Large Angle
and Spectrometric Coronagraph Experiment (SOHO/LASCO) images within
the C2 and C3 field of view (FOV). <P />(1 data file).
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Title: Solar activity and space weather
Authors: Gopalswamy, Nat; Mäkelä, Pertti; Yashiro, Seiji; Akiyama,
Sachiko; Xie, Hong
2022JPhCS2214a2021G Altcode: 2022arXiv220102724G
After providing an overview of solar activity as measured by the sunspot
number (SSN) and space weather events during solar cycles (SCs) 21-24,
we focus on the weak solar activity in SC 24. The weak solar activity
reduces the number of energetic eruptions from the Sun and hence the
number of space weather events. The speeds of coronal mass ejections
(CMEs), interplanetary (IP) shocks, and the background solar wind
all declined in SC 24. One of the main heliospheric consequences of
weak solar activity is the reduced total (magnetic + gas) pressure,
magnetic field strength, and Alfvén speed. There are three groups
of phenomena that decline to different degrees in SC 24 relative to
the corresponding ones in SC 23: (i) those that decline more than
SSN does, (ii) those that decline like SSN, and (iii) those that
decline less than SSN does. The decrease in the number of severe
space weather events such as high-energy solar energetic particle
(SEP) events and intense geomagnetic storms is deeper than the
decline in SSN. The reduction in the number of severe space weather
events can be explained by the backreaction of the weak heliosphere
on CMEs. CMEs expand anomalously and hence their magnetic content is
diluted resulting in weaker geomagnetic storms. The reduction in the
number of intense geomagnetic storms caused by corotating interaction
regions is also drastic. The diminished heliospheric magnetic field
in SC 24 reduces the efficiency of particle acceleration, resulting in
fewer high-energy SEP events. The numbers of IP type II radio bursts,
IP socks, and high-intensity energetic storm particle events closely
follow the number of fast and wide CMEs (and approximately SSN) because
all these phenomena are closely related to CME-driven shocks. The number
of halo CMEs in SC 24 declines less than SSN does, mainly due to the
weak heliospheric state. Phenomena such as IP CMEs and magnetic clouds
related to frontside halos also do not decline significantly. The mild
space weather is likely to continue in SC 25, whose strength has been
predicted to be not too different from that of SC 24.
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Title: Arrival Time Estimates of Earth-Directed CME-Driven Shocks
Authors: Suresh, K.; Gopalswamy, N.; Shanmugaraju, A.
2022SoPh..297....3S Altcode:
We report on the travel times of 19 interplanetary (IP) shocks driven by
Earth-directed coronal mass ejections (CMEs) that occurred from 2010 to
2017. We track the shocks ahead of CMEs using the graduated cylindrical
shell (GCS) model constructed from multiple-view observations from
the Solar TErrestrial RElations Observatory (STEREO) and Solar
and Heliospheric Observatory (SOHO) coronagraphs. We calculate the
Earthward speed of the shocks from the height-time data obtained from
the GCS fit that we use as input to the Empirical Shock Arrival (ESA)
model to predict the shock travel times to 1 AU. We find that the mean
absolute deviation (MAD) of the predicted IP shock travel time from
the observed travel time is about 6.1 hours. The prediction error
ranges from −14.3 hours to +13.1 hours with a standard deviation
of 7.5 hours. The MAD and RMS errors are significantly smaller than
those in the previous report (Gopalswamy et al., Space Weather11, 661,
2013), which used SOHO-STEREO quadrature observations to obtain the
Earthward speed of halo CMEs. The χ<SUP>2</SUP>-test confirms the high
consistency level between predicted and observed travel times. These
results suggest that the three-dimensional speeds of shocks can be
derived using the GCS model outside of quadrature intervals and can
be used in the determination of shock travel times.
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Title: Hemisphere-Asymmetric Responses of the Ionosphere to
Geomagnetic Storms as Observed by GNSS and AMPERE
Authors: Swarnalingam, Nimalan; Wu, Dong; Gopalswamy, Nat
2021AGUFMSA24B..05S Altcode:
To characterize global ionosphere-thermosphere (IT) system responses
during geomagnetic storms, we use electron density (Ne) and Total
Electron Content (TEC) observations from space and ground for multiple
storms, occurring in the boreal and austral summer months, as well
as equinoctial month. The storm-induced Ne response in the summer
and winter hemispheres appears to be different and asymmetric. The
summer hemisphere shows a stronger response compared to the winter
hemisphere. On the other hand, the response during the equinoctial
month storm is more symmetric. The global 3D view from GNSS Radio
Occultation (RO) Ne observation captures enhancements and uplifting of
Ne structures at high latitudes during the initial and main phases. A
clear time lag is evident in the storm-induced perturbation at high
latitudes between the summer and winter hemispheres. Subsequently,
Ne depletions occur at high latitudes. Time lag between high and mid
latitudes is also evident, as the storm reaches its recovery phase. The
observed hemispheric asymmetry in the ionospheric response appears to
be consistent with AMPERE Field-Aligned Current (FAC) measurements. The
integrated FACs in the summer hemisphere is a 4 - 5 MA higher than
the winter hemisphere during these storms.
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Title: The Structural Connection between CME Flux Ropes near the
Sun and at 1 AU
Authors: Xie, Hong; Gopalswamy, Nat; Akiyama, Sachiko
2021AGUFMSH35B2058X Altcode:
We preformed the first comprehensive statistical analysis comparing flux
rope structures of coronal mass ejections (CMEs) near the Sun and at 1
AU, using SOHO and STEREO measurements for the two full solar cycles
of 23 and 24. The study aims to investigate the physical connection
of 102 magnetic flux ropes (FR) among solar source regions, CMEs in
the extended corona, and magnetic clouds (MCs) near Earth. Our main
results include: 1) We confirmed that the hemispheric helicity rule
holds true for $\sim$ 87\% of our 102 events. For the thirteen events
that do not follow this rule, the FR axis directions and helicity signs
can be inferred from soft X-ray and EUV images and magnetogram data in
the source regions (e.g., coronal arcade skews, sigmoids, and magnetic
tongues). 2) Around 25\% of the 102 events have rotations $>$
40\dg between the MC and CME--FR axial orientations. 3) For $\sim$56\%
of these rotational events, the flux rope rotations occurred within
the COR2 FOV, which can be predicted from the CME tilts obtained from
flux rope fitting models. In addition, we found that for 89\% of the
nineteen stealth CMEs under study, we can use the CNL locations and
tilts to predict the flux rope helicity and its axial direction in
the MCs. The above results would help to improve the prediction of the
flux rope structures in situ. We discuss their implications on space
weather forecasts.
---------------------------------------------------------
Title: Novel Magnetic Field and Electron Density Measurements of
CMEs (within AU) with the Proposed Multiview Observatory for Solar
Terrestrial Science (MOST) Mission
Authors: Jensen, P. E., C. S. P., Elizabeth; Manchester, Ward; Fung,
Shing; Gopalswamy, Nat; Jian, Lan; Kenny, Megan; Kooi, Jason; Lazio,
Joseph; Li, Lihua; Nieves-Chinchilla, Teresa; Pevtsov, Alexei; Wexler,
David; Wilson, Lynn; Wood, Brian; Bale, Stuart; Bastian, Tim
2021AGUFMSH33A..08J Altcode:
The Multiview Observatory for Solar Terrestrial Science (MOST) mission
concept will be the most advanced solar observatory to date (Gopalswamy
et al, SH0001, 2021). Comprising four spacecraft, two located in the L4
and ahead of L4 position and two located in the L5 and behind of the L5
position, the four lines-of-sight (LOSs) form the basis for the unique
Faraday Effect Tracker of Coronal and Heliospheric Structures (FETCH)
instrument (Wexler et al, SH0019, 2021). We report on our modeling
into the expected Faraday rotation (FR) caused by an Earth-directed
CME crossing the MOST/FETCH radio-sensing paths using a heliospheric
3-D MHD model to obtain the necessary LOS data on electron density
and magnetic field components (see example image). Specifically, we
utilized simulation data of the 2005 May 13 CME (Manchester IV et al.,
2014, Plasma Phys. Control. Fusion), which erupted from the north-south
polarity inversion line of AR 10759 at 16:03 UT, reaching speeds around
2000 km/s in the corona. The trajectory of the CME at an acute angle
to the Earth-Sun line crosses each FETCH LOS at a different time. Two
LOSs are at different viewing angles with little overlap between
the CME sheath and magnetic flux rope core. A blind test fitting of
the Faraday rotation functions (Figures 6 and 7 in Jensen et al.,
2010, Sol. Phys.) to the simulated FETCH observations reproduced the
orientation of the CME for its handedness as well as its associated
complementary degenerate solution. In conclusion, one of the four
LOSs will be more sensitive to observing CME flux rope structure of
Earthward CMEs, depending on their trajectory. We find that two of the
four LOSs enable analyzing CME evolution, whereas the other two LOSs
enable analyzing the average magnetic field vector in the corresponding
high density regions dominating the measurements at that time. For
example, the average sheath magnetic field vector can be partially
measured in the plane of the ecliptic due to the angular differences
between 2 LOSs. We discuss future work as this effort develops.
---------------------------------------------------------
Title: A Study on the Near-Sun Speed and Acceleration of CMEs
Associated with Sustained Gamma-Ray Emission Events Observed by
FERMI-LAT
Authors: Makela, Pertti; Gopalswamy, Nat; Xie, Hong; Akiyama, Sachiko;
Yashiro, Seiji
2021AGUFMSH35E2118M Altcode:
Sustained gamma-ray emission (SGRE) events, also called late-phase
gamma-ray emission (LPGRE) events, are solar eruptive events that
produce long-lasting >100 MeV gamma-ray flux. Enhanced gamma-ray
emission can extend several hours after the impulsive phase of
the associated solar flare. SGRE events have been detected since
1980s, but the highly sensitive Large Area Telescope (LAT) on the
FERMI spacecraft has observed SGREs more frequently since 2010. The
>100 MeV gamma-ray emission is generated by >300 MeV protons via
neutral pion production and decay. Flare-related processes or shock
waves driven by coronal mass ejections (CMEs) have been suggested as
possible acceleration mechanisms of the >300 MeV protons. Previous
studies have shown that SGRE events are associated with fast and wide
halo CMEs. We describe in detail the near-Sun speed and acceleration of
SGRE-event-associated CMEs and compare them with other CME populations
without SGRE events. Fast acceleration suggests early shock formation
with high speeds that are typical of ground level enhancement events
and SGRE events indicating acceleration of high-energy particles. The
height-time profiles are obtained by fitting 3D flux rope and shock
wave models to the EUV and white-light images of the CME.
---------------------------------------------------------
Title: FETCH Concept: Investigating Quiescent and Transient Magnetic
Structures in the Inner Heliosphere using Faraday Rotation of
Spacecraft Radio Signals
Authors: Wexler, David; Jensen, Elizabeth; Gopalswamy, Nat; Wilson,
Lynn; Fung, Shing; Nieves-Chinchilla, Teresa; Jian, Lan; Bastian,
Tim; Pevtsov, Alexei; Manchester, Ward; Kenny, Megan; Lazio, Joseph;
Wood, Brian; Kooi, Jason
2021AGUFMSH31A..05W Altcode:
The Faraday Effect Tracker of Coronal and Heliospheric structures
(FETCH) is a new instrument concept being developed to probe coronal
and interplanetary magnetic field structures in the ambient solar wind,
corotating interaction regions and coronal mass ejections (CMEs) as
they evolve in the inner heliosphere. FETCH is one of the instruments
that constitute the Multiview Observatory for Solar Terrestrial (MOST)
science mission. FETCH will measure Faraday rotation (FR) of linearly
polarized spacecraft radio signals transmitted along four lines of sight
provided by the four MOST spacecraft: two large spacecraft deployed
at Sun-Earth Lagrange points 4 and 5 and two smaller spacecraft, one
ahead of L4 and the other behind L5. FETCH will transmit and receive at
selected radio frequencies in the 1-100 MHz range for lines of sight
with solar impact parameters < 0.5 AU. FR yields the line-of-sight
(LOS) integrated product of electron number density and LOS-projected
magnetic field strengths. The FR measurements will be obtained from
the Stokes polarization parameters while additional plasma parameters,
such as electron column density, will be extracted from other signal
diagnostics. The multifrequency FR data and four lines-of-sight
will be used to constrain the magnetic field topology and dynamics of
interplanetary plasma structures upstream from Earth. Unique to this FR
experiment, the FETCH transmitter-receiver instrumentation is positioned
such that the entire sensing path remains in interplanetary space, thus
avoiding the complications of trans-ionospheric FR observations. The
FETCH key science objectives include: (1) characterizing CME magnetic
field structure and flux rope orientation, (2) tracking CME propagation
and shock signatures, (3) understanding the magnetic field features
of corotating interaction regions in the extended corona and inner
heliosphere, and (4) determination of large-scale MHD wave organization
in regions of developed ambient solar wind and its evolution during
perturbed flows. The MOST mission will build upon the achievements of
the Solar Heliospheric Observatory (SOHO) and the Solar Terrestrial
Relations Observatory (STEREO) missions during the last couple of
decades. FETCH will help fill the long-standing measurement gap of
magnetic field data in the inner heliosphere.
---------------------------------------------------------
Title: The Multiview Observatory for Solar Terrestrial Science (MOST)
Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall,
Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe,
Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung,
Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward;
Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy;
DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen,
P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi,
Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal;
DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran;
Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei;
Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan
2021AGUFMSH12A..07G Altcode:
The Multiview Observatory for Solar Terrestrial Science (MOST) is a
comprehensive mission concept targeting the magnetic coupling between
the solar interior and the heliosphere. The wide-ranging imagery and
time series data from MOST will help understand the solar drivers and
the heliospheric responses as a system, discerning and tracking 3D
magnetic field structures, both transient and quiescent in the inner
heliosphere. MOST will have seven remote-sensing and three in-situ
instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate
surface and subsurface magnetism by exploiting the combination of
helioseismic and magnetic-field measurements in the photosphere; (2)
Inner Coronal Imager in EUV (ICIE) to study large-scale structures
such as active regions, coronal holes and eruptive structures by
capturing the magnetic connection between the photosphere and the
corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image
the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to
seamlessly study transient and quiescent large-scale coronal structures
extending from the ICIE field of view (FOV); (5) Faraday Effect
Tracker of Coronal and Heliospheric structures (FETCH), a novel radio
package to determine the magnetic field structure and plasma column
density, and their evolution within 0.5 au; (6) Heliospheric Imager
with Polarization (HIP) to track solar features beyond the WCOR FOV,
study their impact on Earth, and provide important context for FETCH;
(7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams
and shocks propagating into the heliosphere via passive radio emission;
(8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra
of electrons, and ions from H to Fe at multiple spatial locations
and use energetic particles as tracers of magnetic connectivity; (9)
Solar Wind Magnetometer (MAG) to characterize magnetic structures at
1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma
structures at 1 au. MOST will have two large spacecraft with identical
payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4
and behind L5 to carry additional FETCH elements. MOST will build upon
SOHO and STEREO achievements to expand the multiview observational
approach into the first half of the 21st Century.
---------------------------------------------------------
Title: Earth-affecting solar transients: a review of progresses in
solar cycle 24
Authors: Zhang, Jie; Temmer, Manuela; Gopalswamy, Nat; Malandraki,
Olga; Nitta, Nariaki V.; Patsourakos, Spiros; Shen, Fang; Vršnak,
Bojan; Wang, Yuming; Webb, David; Desai, Mihir I.; Dissauer, Karin;
Dresing, Nina; Dumbović, Mateja; Feng, Xueshang; Heinemann, Stephan
G.; Laurenza, Monica; Lugaz, Noé; Zhuang, Bin
2021PEPS....8...56Z Altcode: 2020arXiv201206116Z
This review article summarizes the advancement in the studies of
Earth-affecting solar transients in the last decade that encompasses
most of solar cycle 24. It is a part of the effort of the International
Study of Earth-affecting Solar Transients (ISEST) project, sponsored
by the SCOSTEP/VarSITI program (2014-2018). The Sun-Earth is an
integrated physical system in which the space environment of the
Earth sustains continuous influence from mass, magnetic field, and
radiation energy output of the Sun in varying timescales from minutes to
millennium. This article addresses short timescale events, from minutes
to days that directly cause transient disturbances in the Earth's
space environment and generate intense adverse effects on advanced
technological systems of human society. Such transient events largely
fall into the following four types: (1) solar flares, (2) coronal mass
ejections (CMEs) including their interplanetary counterparts ICMEs,
(3) solar energetic particle (SEP) events, and (4) stream interaction
regions (SIRs) including corotating interaction regions (CIRs). In
the last decade, the unprecedented multi-viewpoint observations of
the Sun from space, enabled by STEREO Ahead/Behind spacecraft in
combination with a suite of observatories along the Sun-Earth lines,
have provided much more accurate and global measurements of the size,
speed, propagation direction, and morphology of CMEs in both 3D and over
a large volume in the heliosphere. Many CMEs, fast ones, in particular,
can be clearly characterized as a two-front (shock front plus ejecta
front) and three-part (bright ejecta front, dark cavity, and bright
core) structure. Drag-based kinematic models of CMEs are developed to
interpret CME propagation in the heliosphere and are applied to predict
their arrival times at 1 AU in an efficient manner. Several advanced
MHD models have been developed to simulate realistic CME events from
the initiation on the Sun until their arrival at 1 AU. Much progress
has been made on detailed kinematic and dynamic behaviors of CMEs,
including non-radial motion, rotation and deformation of CMEs, CME-CME
interaction, and stealth CMEs and problematic ICMEs. The knowledge
about SEPs has also been significantly improved. An outlook of how to
address critical issues related to Earth-affecting solar transients
concludes this article.
---------------------------------------------------------
Title: High latitude coronal mass ejections during the solar
maximum 24
Authors: Yashiro, Seiji; Gopalswamy, Nat; Akiyama, Sachiko
2021AGUFMSH35B2052Y Altcode:
We examined high latitude CMEs using a catalog of prominence
eruptions (PEs) detected automatically in the SDO/AIA 304 Å
Images (https://cdaw.gsfc.nasa.gov/CME_list/autope/). The source
locations are listed in the prominence catalog, so we could exclude
the low-latitude CMEs but appeared in the high latitude due to the
projection effects. There are 115 high latitude PEs (Latitude>= 60
degree), but we could identify 60 CMEs only. The CME association rate
is similar to the that of prominence eruptions observed by microwave
(Gopalswamy et al. 2003, ApJ, 586, 562). Yashiro et al. (2020, JASTP,
205, 105324) reported that the high-latitude PE speed decreased with
decreasing average polar magnetic field strength, but we could not find
such a clear relationship in the CME speed. The speed of high latitude
CMEs are typically 400 km/s, but the CME speeds were occasionally high
(e.g., ~700 km/s) when the prominence became jet-like CMEs. Because of
the difference of the CME widths, the CME speed is not enough parameter
to describe the CME kinematics. On the other hand, we found that the
kinetic energy of the high latitude CMEs decreased with decreasing
average magnetic field strength. Weaker field strengths indicate
smaller amount of energy available to power the eruptions.
---------------------------------------------------------
Title: Spotless days and geomagnetic index as the predictors of
solar cycle 25
Authors: Burud, Dipali S.; Jain, Rajmal; Awasthi, Arun K.; Chaudhari,
Sneha; Tripathy, Sushanta C.; Gopalswamy, Nat; Chamadia, Pramod;
Kaushik, Subhash C.; Vhatkar, Rajiv
2021RAA....21..215B Altcode: 2021arXiv210511448B
We study the sunspot activity in relation to spotless days (SLDs)
during the descending phase of solar cycles 11-24 to predict the
amplitude of sunspot cycle 25. For this purpose, in addition to
SLD, we also consider the geomagnetic activity (aa index) during the
descending phase of a given cycle. A very strong correlation of the SLD
(0.68) and aa index (0.86) during the descending phase of a given cycle
with the maximum amplitude of next solar cycle has been estimated. The
empirical relationship led us to deduce the amplitude of cycle 25 to be
99.13± 14.97 and 104.23± 17.35 using SLD and aa index, respectively
as predictors. Both the predictors provide comparable amplitude for
solar cycle 25 and reveal that solar cycle 25 will be weaker than cycle
24. Further, we predict that the maximum of cycle 25 is likely to occur
between February and March 2024. While the aa index has been utilized
extensively in the past, this work establishes SLDs as another potential
candidate for predicting the characteristics of the next cycle.
---------------------------------------------------------
Title: The Structural Connection between Coronal Mass Ejection Flux
Ropes near the Sun and at 1 au
Authors: Xie, H.; Gopalswamy, N.; Akiyama, S.
2021ApJ...922...64X Altcode:
We have performed the first comprehensive statistical analysis comparing
flux rope (FR) structures of coronal mass ejections (CMEs) near the
Sun and at 1 au, using Solar and Heliospheric Observatory and Solar
Terrestrial Relations Observatory measurements for the two full solar
cycles 23 and 24. This study aims to investigate the physical connection
of 102 magnetic FRs among solar source regions, CMEs in the extended
corona, and magnetic clouds (MCs) near Earth. Our main results are as
follows: (1) We confirmed that the hemispheric-helicity rule holds true
for ~87% of our 102 events. For the 13 events that do not follow this
rule, the FR axis directions and helicity signs can be inferred from
soft X-ray and extreme ultraviolet images and magnetogram data in the
source regions (e.g., coronal arcade skews, Fe XII stalks, sigmoids,
and magnetic tongues). (2) Around 25% of the 102 events have rotations
>40° between the MC and CME-FR axial orientations. (3) For ~56%
of these rotational events, the FR rotations occurred within the COR2
field of view, which can be predicted from the CME tilts obtained from
FR fitting models. In addition, we found that for 89% of the 19 stealth
CMEs under study, we were able to use coronal neutral line locations and
tilts to predict the FR helicity and its axial direction in the MCs. The
above results should help improve the prediction of FR structures in
situ. We discuss their implications on space weather forecasts.
---------------------------------------------------------
Title: Total Solar Irradiance Variability on the Evolutionary
Timescale and its Impact on the Earth's Mean Surface Temperature
Authors: Shukure, N. T.; Tessema, S. B.; Gopalswamy, N.
2021ApJ...917...86S Altcode: 2021arXiv210603657S
The Sun is the primary source of energy for the Earth. The small changes
in total solar irradiance (TSI) can affect our climate on the longer
timescale. In the evolutionary timescale, the TSI varies by a large
amount and hence its influence on the Earth's mean surface temperature
(T<SUB>s</SUB>) also increases significantly. We develop a mass loss
dependent analytical model of TSI in the evolutionary timescale
and evaluated its influence on the T<SUB>s</SUB>. We determined
the numerical solution of TSI for the next 8.23 Gyr to be used as
an input to evaluate the T<SUB>s</SUB> which formulated based on a
zero-dimensional energy balance model. We used the present-day albedo
and bulk atmospheric emissivity of the Earth and Mars as initial and
final boundary conditions, respectively. We found that the TSI increases
by 10% in 1.42 Gyr, by 40% in about 3.4 Gyr, and by 120% in about 5.229
Gyr from now, while the T<SUB>s</SUB> shows an insignificant change in
1.644 Gyr and increases to 298.86 K in about 3.4 Gyr. The T<SUB>s</SUB>
attains the peak value of 2319.2 K as the Sun evolves to the red giant
and emits the enormous TSI of 7.93 × 10<SUP>6</SUP> W m<SUP>-2</SUP>
in 7.676 Gys. At this temperature Earth likely evolves to be a liquid
planet. In our finding, the absorbed and emitted flux equally increases
and approaches the surface flux in the main sequence, and they are
nearly equal beyond the main sequence, while the flux absorbed by the
cloud shows the opposite trend.
---------------------------------------------------------
Title: Particle Acceleration and Transport at the Sun Inferred from
Fermi/LAT Observations of >100 MeV Gamma-rays
Authors: Gopalswamy, Nat; Mäkelä, Pertti; Yashiro, Seiji
2021arXiv210811286G Altcode:
The sustained gamma-ray emission (SGRE) events from the Sun are
associated with an ultrafast (2000 km/s or greater) halo coronal mass
ejection (CME) and a type II radio burst in the decameter-hectometric
(DH) wavelengths. The SGRE duration is linearly related to the type
II burst duration indicating that >300 MeV protons required for
SGREs are accelerated by the same shock that accelerates tens of keV
electrons that produce type II bursts. When magnetically well connected,
the associated solar energetic particle (SEP) event has a hard spectrum,
indicating copious acceleration of high-energy protons. In one of the
SGRE events observed on 2014 January 7 by Fermi/LAT, the SEP event
detected by GOES has a very soft spectrum with not many particles
beyond 100 MeV. This contradicts the presence of the SGRE, implying the
presence of significant number of >300 MeV protons. Furthermore, the
durations of the type II burst and the SGRE agree with the known linear
relationship between them (Gopalswamy et al. 2018, ApJ 868, L19). We
show that the soft spectrum is due to poor magnetic connectivity
of the shock nose to an Earth observer. Even though the location of
the eruption (S15W11) is close to the disk center, the CME propagated
non-radially making the CME flank crossing the ecliptic rather than the
nose. High-energy particles are accelerated near the nose, so they do
not reach GOES but they do precipitate to the vicinity of the eruption
region to produce SGRE. This study provides further evidence that SGRE
is caused by protons accelerated in shocks and propagating sunward to
interact with the atmospheric ions.
---------------------------------------------------------
Title: The Common Origin of High-energy Protons in Solar Energetic
Particle Events and Sustained Gamma-Ray Emission from the Sun
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Xie, H.;
Akiyama, S.
2021ApJ...915...82G Altcode: 2021arXiv210501206G
We report that the number of >500 MeV protons (N<SUB>g</SUB>)
inferred from sustained gamma-ray emission (SGRE) from the Sun is
significantly correlated with that of protons propagating into space
(N<SUB>SEP</SUB>) as solar energetic particles (SEPs). Under the
shock paradigm for SGRE, shocks driven by coronal mass ejections
(CMEs) accelerate high-energy protons sending them toward the Sun to
produce SGRE by interacting with the atmospheric particles. Particles
also escape into the space away from the Sun to be detected as SEP
events. Therefore, the significant N<SUB>SEP</SUB>-N<SUB>g</SUB>
correlation (correlation coefficient 0.77) is consistent with the
common shock origin for the two proton populations. Furthermore, the
underlying CMEs have properties akin to those involved in ground level
enhancement events indicating the presence of high-energy (up to ~GeV)
particles required for SGRE. We show that the observed gamma-ray flux is
an underestimate in limb events (central meridian distance >60°)
because SGRE sources are partially occulted when the emission is
spatially extended. With the assumption that the SEP spectrum at the
shock nose is hard and that the 100 MeV particles are accelerated
throughout the shock surface (half width in the range 60°-120°)
we find that the latitudinal widths of SEP distributions are energy
dependent with the smallest width at the highest energies. Not using the
energy-dependent width results in an underestimate of N<SUB>SEP</SUB>
in SGRE events occurring at relatively higher latitudes. Taking
these two effects into account removes the apparent lack of
N<SUB>SEP</SUB>-N<SUB>g</SUB> correlation reported in previous studies.
---------------------------------------------------------
Title: The Common Origin of High-energy Protons in Solar Energetic
Particle Events and Sustained Gamma-ray Emission from the Sun
Authors: Gopalswamy, N.; Yashiro, S.; Makela, P.; Xie, H.; Akiyama, S.
2021AAS...23832208G Altcode:
We report on the correlation between the number of >500 MeV
protons (N<SUB>g</SUB>) deduced from the Fermi/LAT >100 MeV
sustained gamma-ray emission (SGRE) and the number of protons at 1
au (N<SUB>SEP</SUB>) estimated from PAMELA mission's solar energetic
particle (SEP) measurements. The correlation is highly significant with
a correlation coefficient of 0.77 and hence supports the shock origin
of >300 MeV protons that interact with the solar chromosphere and
resulting in pion decay observed as SGRE. The lack of correlation
previously reported has been shown to be due to (i) a systematic
underestimate of N<SUB>g</SUB> in events originating close to the limb
owing to the spatially-extended nature of SGRE, and (ii) a systematic
underestimate of N<SUB>SEP</SUB> in events originating at higher
latitudes as a consequence of poor latitudinal connectivity. Correcting
for these to effects, we find that the regression line is close to
the N<SUB>g </SUB>= N<SUB>SEP</SUB> line. The close correlation found
between N<SUB>SEP</SUB> and N<SUB>g</SUB> indicating their common
origin (the CME-driven shock) is consistent with other significant
correlations: (i) between the SGRE duration and the duration of the
associated interplanetary type II radio burst, and (ii) between the
SGRE fluence and CME speed.
---------------------------------------------------------
Title: Diffuse Interplanetary Radio Emission from a Polar Coronal
Mass Ejection
Authors: Gopalswamy, N.; Makela, P.; Yashiro, S.; Akiyama, S.
2021arXiv210501216G Altcode:
We report on the first detection of nonthermal radio emission associated
with a polar coronal mass ejection. We call the radio emission as
diffuse interplanetary radio emission (DIRE), which occurs in the
decameter-hectometric wavelengths. The radio emission originates from
the shock flanks that interact with nearby streamers.
---------------------------------------------------------
Title: A Weak Fermi Gamma-ray Event Associated with a Halo CME and
a Type II Radio Burst
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.
2021arXiv210501212G Altcode:
We report on the 2015 June 25 sustained gamma-ray emission (SGRE) event
associated with a halo coronal mass ejection and a type II radio burst
in the decameter-hectometric (DH) wavelengths. The duration and ending
frequency of the type II burst are linearly related to the SGRE duration
as found in previous works involving intense gamma-ray events. This
study confirms that the SGRE event is due to protons accelerated in
the shock that produced the DH type II burst.
---------------------------------------------------------
Title: Investigating width distribution of slow and fast CMEs in
solar cycles 23 and 24
Authors: Pant, V.; Majumdar, S.; Patel, R.; Chauhan, A.; Banerjee,
D.; Gopalswamy, N.
2021FrASS...8...73P Altcode: 2021arXiv210412850P
Coronal Mass Ejections (CMEs) are highly dynamic events originating in
the solar atmosphere, that show a wide range of kinematic properties
and are the major drivers of the space weather. The angular width of the
CMEs is a crucial parameter in the study of their kinematics. The fact
that whether slow and fast CMEs (as based on their relative speed to
the average solar wind speed) are associated with different processes at
the location of their ejection is still debatable. Thus, in this study,
we investigate their angular width to understand the differences between
the slow and fast CMEs. We study the width distribution of slow and fast
CMEs and find that they follow different power law distributions, with
a power law indices ($\alpha$) of -1.1 and -3.7 for fast and slow CMEs
respectively. To reduce the projection effects, we further restrict
our analysis to only limb events as derived from manual catalog and
we find similar results. We then associate the slow and fast CMEs to
their source regions, and classified the sources as Active Regions
(ARs) and Prominence Eruptions (PEs). We find that slow and fast CMEs
coming from ARs and PEs, also follow different power laws in their
width distributions. This clearly hints towards a possibility that
different mechanisms might be involved in the width expansion of slow
and fast CMEs coming from different sources.These results are also
crucial from the space weather perspective since the width of the CME
is an important factor in that aspect.
---------------------------------------------------------
Title: Imaging and Spectral Observations of a Type-II Radio Burst
Revealing the Section of the CME-Driven Shock That Accelerates
Electrons
Authors: Majumdar, Satabdwa; Tadepalli, Srikar Paavan; Maity,
Samriddhi Sankar; Deshpande, Ketaki; Kumari, Anshu; Patel, Ritesh;
Gopalswamy, Nat
2021SoPh..296...62M Altcode: 2021arXiv210309536M
We report on a multi-wavelength analysis of the 26 January 2014 solar
eruption involving a coronal mass ejection (CME) and a Type-II radio
burst, performed by combining data from various space and ground-based
instruments. An increasing standoff distance with height shows the
presence of a strong shock, which further manifests itself in the
continuation of the metric Type-II burst into the decameter-hectometric
(DH) domain. A plot of speed versus position angle (PA) shows different
points on the CME leading edge traveled with different speeds. From the
starting frequency of the Type-II burst and white-light data, we find
that the shock signature producing the Type-II burst might be coming
from the flanks of the CME. Measuring the speeds of the CME flanks,
we find the southern flank to be at a higher speed than the northern
flank; further the radio contours from Type-II imaging data showed that
the burst source was coming from the southern flank of the CME. From
the standoff distance at the CME nose, we find that the local Alfvén
speed is close to the white-light shock speed, thus causing the Mach
number to be small there. Also, the presence of a streamer near the
southern flank appears to have provided additional favorable conditions
for the generation of shock-associated radio emission. These results
provide conclusive evidence that the Type-II emission could originate
from the flanks of the CME, which in our study is from the southern
flank of the CME.
---------------------------------------------------------
Title: On the Connection between Solar Surface Magnetic Flux and
the Total Solar Irradiance
Authors: Shukure, N. T.; Tessema, S. B.; Gopalswamy, N.
2021ApJ...907...39S Altcode:
Solar surface magnetic flux evolution plays a dominant role in the
variability of total solar irradiance (TSI). Different proxies of
magnetic activity have been introduced to correlate solar variability
and TSI. We present the daily strong flux densities (SFDs) and
weak flux densities (WFDs) defined with three magnetic thresholds
calculated from the Solar Dynamic Observatory/Helioseismic Magnetic
Imager. TSI measurements are from the radiometers of the Variability of
Solar Irradiance and Gravity Oscillations experiment on the Solar and
Heliosphere Observatory, and sunspot area (SSA) is from the National
Oceanic and Atmospheric Administration. We characterize the influence
of the magnetic flux density variation on the TSI using the Pearson,
Spearman, and percentage bend correlations and wavelet analysis between
the TSI and the flux density. The Pearson's correlation shows that the
TSI is negatively and strongly correlated with SFD and moderately with
SSA; Spearman and 20% bend correlation shows that the TSI is moderately
correlated with SFD and weakly with SSA on solar maximum, but weakly
correlated on solar minimum. However, the TSI is not correlated with
WFD during solar maximum and minimum. The bootstrapping tests also
confirm that the influence of SFD on TSI is more significant than that
of SSA. Finally, a wavelet analysis supports the idea that the SFD and
TSI have a causality linkage and that the SFD dominantly influences
the TSI variability on the rotational timescale.
---------------------------------------------------------
Title: INterplanetary Flux ROpe Simulator (INFROS): Predicting the
magnetic-field vectors of ICMEs
Authors: Srivastava, Nandita; Gopalswamy, Nat; Sarkar, Ranadeep
2021cosp...43E1029S Altcode:
We have developed an observationally constrained analytical model,
the INterplanetary Flux ROpe Simulator (INFROS), for predicting
the magnetic-field vectors of interplanetary coronal mass ejections
(ICMEs). The main architecture of INFROS uses the near-Sun flux rope
properties obtained from the observational parameters that are evolved
through the model to estimate the magnetic field vectors of ICMEs
at any heliocentric distance. As a proof of concept, we present the
case study of an Earth-impacting CME which occurred on 2013 April
11. The predicted magnetic field profiles of the associated ICME
show good agreement with those observed by the in-situ spacecraft. We
further validated INFROS model for the ICMEs detected by the radially
aligned multiple spacecraft orbiting the Sun at different heliocentric
distances. The in-situ observations of those ICMEs as detected in
MESSENGER at ∼ 0.3 AU or VEX at ~0.7 AU and STEREO at ~1 AU , help
us to constrain the INFROS model parameters in order to predict the
magnetic field-vectors of the ICME at 1 AU. INFROS shows promising
results in the forecasting of Bz in near real-time. It is a simple less
time-consuming and computationally inexpensive compared to other models
and has the potential to be implemented as a practical space-weather
forecasting tool.
---------------------------------------------------------
Title: Magnetic Field Strength in and Around Coronal Flux Ropes
Authors: Gopalswamy, Nat
2021cosp...43E1027G Altcode:
It is clear from observations and modeling perspectives that all
interplanetary coronal mass ejections (ICMEs) may have a flux rope
structure. At the Sun, flux ropes are inferred from post eruption
arcades (PEAs), which are thought to be part staying with the Sun,
while the other part, viz., the flux rope is ejected into space. The
total reconnected flux can be derived from the magnetic flux underlying
the PEA or the swept-up flare ribbon area. The reconnected flux
has important quantitative information on the magnetic content of
the ejected flux rope (the poloidal flux of the flux rope). This
information, when coupled with the geometrical properties of the flux
rope derived from white-light coronagraph images, can be used to derive
the axial field strength of the flux rope near the Sun. Under the
assumption of a force-free flux rope, one can get all the components
of the flux rope magnetic field, including the one that causes
geomagnetic storms. Coupled with the fact that the axial magnetic
field direction can be obtained from a number of techniques, we have
full information on the coronal flux ropes. The internal structure
of the flux rope is key to predict its geoeffectiveness. The flux
rope propagates through the ambient medium and often drives a shock
if super-Alfvenic. Shock-driving CMEs have an additional source of
southward magnetic field that can result in geomagnetic storms. The
presence of a shock near the Sun can often be inferred from type
II radio bursts and white-light observations. The white-light shock
structure can be used to infer the ambient magnetic field strength
because the shock standoff distance and the radius of curvature of the
driving flux rope are related to the shock Mach number. Since the shock
speed can be measured from coronagraph observations, it is possible
to derive the ambient Alfven speed and magnetic field strength. This
talk illustrates the techniques to derive the flux-rope and ambient
field strengths with specific examples.
---------------------------------------------------------
Title: The COSPAR Capacity Building Workshops in Solar Terrestrial
Science
Authors: Gopalswamy, Nat
2021cosp...43E2156G Altcode:
The main objective of COSPAR Capacity-Building Workshops (CBWs) is
to train young scientists and students from developing countries in
using space data obtained by current and past missions. The training
involves accessing data from various sources and processing them using
free software tools available online. The COSPAR CBW activities enhance
the scientific return from many space missions by addressing problems
that were not originally considered by the mission teams. For solar
terrestrial science, there are several data bases dealing with solar
variability and its terrestrial and heliospheric impact. For example,
large arrays of data have been accumulated at the CDAW Data Center
of NASA's Goddard Space Flight Center from missions such as the
ESA/NASA Solar and Heliospheric Observatory (SOHO) mission, NASA's
Solar Terrestrial Relations Observatory (STEREO), Wind, and Advanced
Composition Explorer (ACE). There are uniform and extended data sets
on solar flares and coronal mass ejections that have interesting
implications for magnetic energy release on the Sun and societal
implications for humans. There are many data sets from ground-based
observations that complement the space data and help address many
problems in solar terrestrial science. This talk summarizes my
experience is serving as the science lead in a couple of workshops
that focused on coronal mass ejections and their relation to shocks
in the inner heliosphere.
---------------------------------------------------------
Title: Space Weather Capacity Building Activities by the International
Space Weather Initiative
Authors: Gopalswamy, Nat
2021cosp...43E2435G Altcode:
The International Space Weather Initiative (ISWI) is a grassroots
organization involved in creating and developing space-weather-literate
communities around the globe. ISWI activities include deployment of
space weather instrumentation, space weather science research, and
capacity building. ISWI was formed to continue the International
Heliophysical Year (IHY 2007) activities focusing on the space
weather aspects in the near-Earth space. Since 2013, ISWI is aligned
with the permanent space weather agenda of the Science and Technology
Subcommittee (STSC) formed by the United Nations Committee on Peaceful
Uses of Outer Space (UNCOPUOS). The governance of ISWI involves the
secretariat and a steering committee constituted by experts from
the space weather community. Information on ISWI activities and space
weather in general is distributed via the ISWI Newsletter issued once a
month. The ISWI web site (http://iswi-secretariat.org) is a repository
of documents related to ISWI activities including ISWI instrument
networks, lectures from schools, workshop presentations, and the ISWI
Newsletter issues. The capacity building and educational activities
of ISWI are (i) running space science schools, mainly in developing
countries, (ii) deployment of space weather instruments around the
world, and (iii) participating in efforts by other international
organizations such as COSPAR. The space science schools involve teaching
all topics from the solar interior to the surface of Earth to graduate
students and young scientists. These schools are run in collaboration
with other international organizations such as SCOSTEP and COSPAR
that have overlapping interest in capacity building. The instrument
deployment is also a capacity building activity because students are
involved in the deployment and operations. The data from the space
weather instruments are combined with data from other sources including
space missions to address space weather problems. ISWI conducts space
weather workshops in collaboration with the United Nations Office of
Outer Space Affairs (UNOOSA) in which ISWI instrument providers and
hosts attend to present their science results. Young scientists and
students are provided with travel support to attend these workshops. The
lecturers of ISWI schools/workshops often visit local high schools
to interact with students and science teachers to inspire the next
generation scientists.
---------------------------------------------------------
Title: Properties of High-Frequency Type II Radio Bursts and Their
Relation to the Associated Coronal Mass Ejections
Authors: Umuhire, A. C.; Gopalswamy, N.; Uwamahoro, J.; Akiyama, S.;
Yashiro, S.; Mäkelä, P.
2021SoPh..296...27U Altcode:
Solar radio bursts are often early indicators of space weather events
such as coronal mass ejections (CMEs). In this study, we determined
the properties of a sample of 40 high-starting-frequency (≥ 150 MHz)
type II radio bursts and the characteristics of the associated CMEs
such as width, location and speed during 2010-2016. The high starting
frequency implies shock formation closer to the solar surface, which
has important ramifications for the analysis of particle acceleration
near the Sun. We found the CME heliocentric distances at the onset
time of metric type II bursts range from 1.16 to 1.90 solar radii
(Rs). The study was also extended to 128 metric type II bursts to
include lower-starting-frequency events for further analysis. The
projected CME heights range from 1.15 to 2.85 Rs. The lower starting
frequency correspond to shocks forming at larger heights. A weak
correlation was found between the type-II starting frequency and
CME heights, which is consistent with the density decline in the
inner corona. The analysis confirmed a good correlation between the
drift rate and the starting frequency of type II bursts (correlation
coefficient ∼ 0.8). Taking into account the radial variation of CMEs
speeds from the inner corona to the interplanetary medium, we observed
the deviations from the universal drift-rate spectrum of type II bursts
and confirmed the previous results relating type II bursts to CMEs.
---------------------------------------------------------
Title: The impact of CMEs on the critical frequency of F2-layer
ionosphere (foF2)
Authors: Seyoum, Alene; Gopalswamy, Nat; Nigussie, Melessew; Mezgebe,
Nigusse
2021IAUS..356..400S Altcode: 2020arXiv200408278S
The ionospheric critical frequency (foF2) from ionosonde measurements
at geographic high, middle, and low latitudes are analyzed with the
occurrence of coronal mass ejections (CMEs) in long term variability
of the solar cycles. We observed trends of monthly maximum foF2 values
and monthly averaged values of CME parameters such as speed, angular
width, mass, and kinetic energy with respect to time. The impact of CMEs
on foF2 is very high at high latitudes and low at low latitudes. The
time series for monthly maximum foF2 and monthly-averaged CME speed
are moderately correlated at high and middle latitudes.
---------------------------------------------------------
Title: The Balloon-Borne Investigation of Temperature and Speed of
Electrons in the Corona (BITSE): Mission Description and Preliminary
Results
Authors: Gopalswamy, N.; Newmark, J.; Yashiro, S.; Mäkelä, P.;
Reginald, N.; Thakur, N.; Gong, Q.; Kim, Y. -H.; Cho, K. -S.; Choi,
S. -H.; Baek, J. -H.; Bong, S. -C.; Yang, H. -S.; Park, J. -Y.; Kim,
J. -H.; Park, Y. -D.; Lee, J. -O.; Kim, R. -S.; Lim, E. -K.
2021SoPh..296...15G Altcode: 2020arXiv201106111G
We report on the Balloon-borne Investigation of Temperature and Speed of
Electrons in the corona (BITSE) mission launched recently to observe the
solar corona from ≈3 Rs to 15 Rs at four wavelengths (393.5, 405.0,
398.7, and 423.4 nm). The BITSE instrument is an externally occulted
single stage coronagraph developed at NASA's Goddard Space Flight Center
in collaboration with the Korea Astronomy and Space Science Institute
(KASI). BITSE used a polarization camera that provided polarization
and total brightness images of size 1024 ×1024 pixels. The Wallops
Arc Second Pointer (WASP) system developed at NASA's Wallops Flight
Facility (WFF) was used for Sun pointing. The coronagraph and WASP were
mounted on a gondola provided by WFF and launched from the Fort Sumner,
New Mexico station of Columbia Scientific Balloon Facility (CSBF) on
September 18, 2019. BITSE obtained 17,060 coronal images at a float
altitude of ≈128,000 feet (≈39 km) over a period of ≈4 hrs. BITSE
flight software was based on NASA's core Flight System, which was
designed to help develop flight quality software. We used EVTM (Ethernet
Via Telemetry) to download science data during operations; all images
were stored on board using flash storage. At the end of the mission,
all data were recovered and analyzed. Preliminary analysis shows that
BITSE imaged the solar minimum corona with the equatorial streamers
on the east and west limbs. The narrow streamers observed by BITSE are
in good agreement with the geometric properties obtained by the Solar
and Heliospheric Observatory (SOHO) coronagraphs in the overlapping
physical domain. In spite of the small signal-to-noise ratio (≈14 )
we were able to obtain the temperature and flow speed of the western
steamer. In the heliocentric distance range 4 - 7 Rs on the western
streamer, we obtained a temperature of ≈1.0 ±0.3 MK and a flow
speed of ≈260 km s<SUP>−1</SUP> with a large uncertainty interval.
---------------------------------------------------------
Title: Comparing Solar Minimum 24/25 with Historical Solar Wind
Records at 1 AU
Authors: Jian, L.; Gopalswamy, N.; Luhmann, J. G.; Russell, C. T.
2020AGUFMSH021..04J Altcode:
Following the study of previous deep solar minimum 23/24 in Jian et
al. (2011), we choose a one-year interval at each solar minimum from the
beginning of the acquisition of solar wind measurements in the ecliptic
plane and at 1 AU, to compare the solar and solar wind parameters at
the most recent solar minimum 24/25 with previous solar minima. In
addition, combining the continuous solar wind measurements near 1 AU
from Wind/ACE and STEREO A/B missions, we survey and characterize
the large-scale solar wind structures during 1995-2019, including
slow-to-fast stream interaction regions (SIRs), interplanetary coronal
mass ejections (ICMEs), and interplanetary shocks. We study their
solar cycle variations comprehensively, focusing on the comparison
of solar cycles 23 and 24, as well as the comparison of solar minima
22/23, 23/24, and 24/25. Through the study, we describe the long-term
variations of space environment for other WHPI investigations.
---------------------------------------------------------
Title: The Coronal Diagnostic Experiment (CODEX)
Authors: Newmark, J. S.; Gopalswamy, N.; Kim, Y. H.; Viall, N. M.;
Cho, K. S. F.; Reginald, N. L.; Bong, S. C.; Gong, Q.; Choi, S.;
Strachan, L.; Yashiro, S.
2020AGUFMSH0280011N Altcode:
Understanding solar wind sources and acceleration mechanisms
is an overarching solar physics goal. Current models are highly
under-constrained due to the limitations of the existing data,
particularly in the ~3-10 Rs range. COronal Diagnostic EXperiment
(CODEX) is designed to deliver the first global, comprehensive
data sets that will impose crucial constraints and answer targeted
essential questions, including: Are there signatures of hot plasma
released into the solar wind from previously closed fields? What are
the velocities and temperatures of the density structures that are
observed so ubiquitously within streamers and coronal holes? <P />To
provide these crucial measurements, NASA's Goddard Space Flight Center,
in collaboration with the Korea Astronomy and Space Science Institute,
will develop a next-generation coronagraph for the International
Space Station. This imaging coronagraph uses multiple filters to obtain
simultaneous measurements of electron density, temperature, and velocity
within a single instrument. This will be the first time all three
have been measured simultaneously for this critical field-of-view,
and CODEX achieves these measurements multiple times a day.
---------------------------------------------------------
Title: Acceleration of >300 MeV particles by interplanetary shocks
evidenced by sustained gamma-ray emission from the Sun
Authors: Gopalswamy, N.; Makela, P.; Yashiro, S.; Akiyama, S.
2020AGUFMSH008..02G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Intercycle and Intracycle Variation of Halo CME Rate Obtained
from SOHO/LASCO Observations
Authors: Dagnew, Fithanegest Kassa; Gopalswamy, Nat; Tessema, Solomon
Belay; Akiyama, Sachiko; Yashiro, Seiji; Tesfu, Tesfay Yemane
2020ApJ...903..118D Altcode:
We report on the properties of halo coronal mass ejections (HCMEs)
in solar cycles 23 and 24. We compare the HCME properties between the
corresponding phases (rise, maximum, and declining) in cycles 23 and
24 and compare those between the whole cycles. Despite the significant
decline in the sunspot number (SSN) in cycle 24, which dropped by 46%
with respect to cycle 23, the abundance of HCMEs is similar in the two
cycles. The HCME rate per SSN is 44% higher in cycle 24. In the maximum
phase, cycle 24 rate normalized to SSN increased by 127%, while the
SSN dropped by 43%. The source longitudes of cycle 24 HCMEs are more
uniformly distributed than those in cycle 23. We found that the average
sky-plane speed in cycle 23 is ∼16% higher than that in cycle 24. The
size distributions of the associated flares between the two cycles and
the corresponding phases are similar. The average speed at a central
meridian distance (CMD) ≥ 60<SUP>0</SUP> for cycle 23 is ∼28% higher
than that of cycle 24. We discuss the unusual bump in HCME activity
in the declining phase of cycle 23 as being due to exceptional active
regions that produced many CMEs during 2003 October-2005 October. The
differing HCME properties in the two cycles can be attributed to the
anomalous expansion of cycle 24 CMEs. Considering the HCMEs in the
rise, maximum, and declining phases, we find that the maximum phase
shows the highest contrast between the two cycles.
---------------------------------------------------------
Title: Diffuse Interplanetary Radio Emission: Shock Emission or a
Type III storm?
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Mäkelä, Pertti;
Yashiro, Seiji
2020URSL....2...49G Altcode: 2020arXiv201112763G
We present a clear case of a Diffuse Interplanetary Radio Emission
(DIRE) event observed during 2002 March 11-12 in association with a
fast coronal mass ejection (CME). In the previous event reported [1],
there were two CMEs, and a detailed analysis was required to pin down
the underlying CME. In the event presented here, the CME association
is unambiguous, and the DIRE is found to originate from the flanks of
the CME-driven shock. We also provide quantitative explanation for
not observing radio emission from the shock nose. We also clarify
that DIRE is not a type III storm because the latter occurs outside
of solar eruptions.
---------------------------------------------------------
Title: The Energetic Particle Detector. Energetic particle instrument
suite for the Solar Orbiter mission
Authors: Rodríguez-Pacheco, J.; Wimmer-Schweingruber, R. F.; Mason,
G. M.; Ho, G. C.; Sánchez-Prieto, S.; Prieto, M.; Martín, C.;
Seifert, H.; Andrews, G. B.; Kulkarni, S. R.; Panitzsch, L.; Boden,
S.; Böttcher, S. I.; Cernuda, I.; Elftmann, R.; Espinosa Lara, F.;
Gómez-Herrero, R.; Terasa, C.; Almena, J.; Begley, S.; Böhm, E.;
Blanco, J. J.; Boogaerts, W.; Carrasco, A.; Castillo, R.; da Silva
Fariña, A.; de Manuel González, V.; Drews, C.; Dupont, A. R.;
Eldrum, S.; Gordillo, C.; Gutiérrez, O.; Haggerty, D. K.; Hayes,
J. R.; Heber, B.; Hill, M. E.; Jüngling, M.; Kerem, S.; Knierim,
V.; Köhler, J.; Kolbe, S.; Kulemzin, A.; Lario, D.; Lees, W. J.;
Liang, S.; Martínez Hellín, A.; Meziat, D.; Montalvo, A.; Nelson,
K. S.; Parra, P.; Paspirgilis, R.; Ravanbakhsh, A.; Richards, M.;
Rodríguez-Polo, O.; Russu, A.; Sánchez, I.; Schlemm, C. E.; Schuster,
B.; Seimetz, L.; Steinhagen, J.; Tammen, J.; Tyagi, K.; Varela, T.;
Yedla, M.; Yu, J.; Agueda, N.; Aran, A.; Horbury, T. S.; Klecker, B.;
Klein, K. -L.; Kontar, E.; Krucker, S.; Maksimovic, M.; Malandraki,
O.; Owen, C. J.; Pacheco, D.; Sanahuja, B.; Vainio, R.; Connell,
J. J.; Dalla, S.; Dröge, W.; Gevin, O.; Gopalswamy, N.; Kartavykh,
Y. Y.; Kudela, K.; Limousin, O.; Makela, P.; Mann, G.; Önel, H.;
Posner, A.; Ryan, J. M.; Soucek, J.; Hofmeister, S.; Vilmer, N.;
Walsh, A. P.; Wang, L.; Wiedenbeck, M. E.; Wirth, K.; Zong, Q.
2020A&A...642A...7R Altcode:
After decades of observations of solar energetic particles from
space-based observatories, relevant questions on particle injection,
transport, and acceleration remain open. To address these scientific
topics, accurate measurements of the particle properties in the inner
heliosphere are needed. In this paper we describe the Energetic Particle
Detector (EPD), an instrument suite that is part of the scientific
payload aboard the Solar Orbiter mission. Solar Orbiter will approach
the Sun as close as 0.28 au and will provide extra-ecliptic measurements
beyond ∼30° heliographic latitude during the later stages of the
mission. The EPD will measure electrons, protons, and heavy ions with
high temporal resolution over a wide energy range, from suprathermal
energies up to several hundreds of megaelectronvolts/nucleons. For
this purpose, EPD is composed of four units: the SupraThermal
Electrons and Protons (STEP), the Electron Proton Telescope (EPT),
the Suprathermal Ion Spectrograph (SIS), and the High-Energy Telescope
(HET) plus the Instrument Control Unit that serves as power and data
interface with the spacecraft. The low-energy population of electrons
and ions will be covered by STEP and EPT, while the high-energy
range will be measured by HET. Elemental and isotopic ion composition
measurements will be performed by SIS and HET, allowing full particle
identification from a few kiloelectronvolts up to several hundreds
of megaelectronvolts/nucleons. Angular information will be provided
by the separate look directions from different sensor heads, on the
ecliptic plane along the Parker spiral magnetic field both forward
and backwards, and out of the ecliptic plane observing both northern
and southern hemispheres. The unparalleled observations of EPD will
provide key insights into long-open and crucial questions about the
processes that govern energetic particles in the inner heliosphere.
---------------------------------------------------------
Title: A comparison of CME expansion speeds between solar cycles 23
and 24
Authors: Dagnew, Fithanegest K.; Gopalswamy, Nat; Tessema, Solomon B.
2020JPhCS1620a2003D Altcode:
We report on a comparison of the expansion speeds of limb coronal mass
ejections (CMEs) between solar cycles 23 and 24. We selected a large
number of limb CME events associated with soft X-ray flare size greater
than or equal to M1.0 from both cycles. We used data and measurement
tools available at the online CME catalog (https://cdaw.gsfc.nasa.gov)
that consists of the properties of all CMEs detected by the Solar
and Heliospheric Observatory’s (SOHO) Large Angle and Spectrometric
Coronagraph (LASCO). We found that the expansion speeds in cycle 24
are higher than those in cycle 23. We also found that the relation
between radial and expansion speeds has different slopes in cycles 23
and 24. The cycle 24 slope is 45% higher than that in cycle 23. The
expansion speed is also higher for a given radial speed. The difference
increases with speed. For a 2000 km/s radial speed, the expansion
speed in cycle 24 is ∼48% higher. These results present additional
evidence for the anomalous expansion of cycle 24-CMEs, which is due
to the reduced total pressure in the heliosphere.
---------------------------------------------------------
Title: Intercycle and intracycle variation of halo CME rate obtained
from SOHO/LASCO observations
Authors: Kassa Dagnew, Fithanegest; Gopalswamy, Nat; Belay Tessema,
Solomon; Akiyama, Sachiko; Yashiro, Seiji; Yemane Tesfu, Tesfay
2020arXiv200906033K Altcode:
We report on the properties of halo coronal mass ejections (HCMEs)
in solar cycles 23 and 24. We compare the HCMEs properties between the
corresponding phases (rise, maximum, and declining) in cycles 23 and
24 in addition to comparing those between the whole cycles. Despite
the significant decline in the sunspot number (SSN) in cycle 24, which
dropped by 46% with respect to cycle 23, the abundance of HCMEs is
similar in the two cycles. The HCME rate per SSN is 44% higher in cycle
24. In the maximum phase, cycle-24 rate normalized to SSN increased by
127% while the SSN dropped by 43%. The source longitudes of cycle-24
HCMEs are more uniformly distributed than those in cycle 23. We found
that the average sky-plane speed in cycle 23 is ~16% higher than that
in cycle 24. The size distributions of the associated flares between
the two cycles and the corresponding phases are similar. The average
speed at a central meridian distance (CMD) = 600 for cycle 23 is ~28%
higher than that of cycle 24. We discuss the unusual bump in HCME
activity in the declining phase of cycle 23 as due to exceptional
active regions that produced many CMEs during October 2003 to October
2005. The differing HCME properties in the two cycles can be attributed
to the anomalous expansion of cycle-24 CMEs. Considering the HCMEs
in the rise, maximum and declining phases, we find that the maximum
phase shows the highest contrast between the two cycles.
---------------------------------------------------------
Title: A catalog of prominence eruptions detected automatically in
the SDO/AIA 304 Å images
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.; Mäkelä, P. A.
2020JASTP.20505324Y Altcode: 2020arXiv200511363Y
We report on a statistical study of prominence eruptions (PEs) using
a catalog of these events routinely imaged by the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in the
304 Å pass band. Using an algorithm developed as part of an LWS
project, we have detected PEs in 304 Å synoptic images with 2-min
cadence since May 2010. A catalog of these PEs is made available
online (https://cdaw.gsfc.nasa.gov/CME_list/autope/). The 304 Å
images are polar-transformed and divided by a background map (pixels
with minimum intensity during one day) to get the ratio maps above
the limb. The prominence regions are defined as pixels with a ratio
≥2. Two prominence regions with more than 50% of pixels overlapping
are considered the same prominence. If the height of a prominence
increases monotonically in 5 successive images, it is considered
eruptive. All the PEs seen above the limb are detected by the routine,
but only PEs with width ≥15° are included in the catalog to eliminate
polar jets and other small-scale mass motions. The identifications are
also cross-checked with the PEs identified in Nobeyama Radioheliograph
images (http://solar.nro.nao.ac.jp/norh/html/prominence/). The catalog
gives the date, time, central position angle, latitude, and width of
the eruptive prominence. The catalog also provides links to JavaScript
movies that combine SDO/AIA images with GOES soft X-ray data to identify
the associated flares, and with SOHO/LASCO C2 images to identify
the associated coronal mass ejections. We examined the statistical
properties of the PEs and found that (1) the surges generally occur only
in the active region belt while prominences are found in all latitudes,
and (2) the high-latitude PE speed decreased with the decreasing of
the average polar magnetic field strength of the previous cycle.
---------------------------------------------------------
Title: Effect of the Weakened Heliosphere in Solar Cycle 24 on the
Properties of Coronal Mass Ejections
Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Michalek, G.; Xie,
H.; Mäkelä, P.
2020JPhCS1620a2005G Altcode: 2020arXiv200708291G
Solar cycle (SC) 24 has come to an end by the end of 2019, providing
the opportunity to compare two full cycles to understand the
manifestations of SC 24 - the smallest cycle in the Space Age that
has resulted in a weak heliospheric state indicated by the reduced
pressure. The backreaction of the heliospheric state is to make the
coronal mass ejections (CMEs) appear physically bigger than in SC
23, but their magnetic content has been diluted resulting in a lower
geoeffectiveness. The heliospheric magnetic field is also lower in SC
24, leading to the dearth of high-energy solar energetic particle (SEP)
events. These space-weather events closely follow fast and wide (FW)
CMEs. All but FW CMEs are higher in number in SC 24. The active region
potential energy is lower in SC 24, consistent with the reduced rate
of FW CMEs. The CME rate - sunspot number (SSN) correlation is high in
both cycles but the rate increases faster in SC 24. We find that limb
CMEs are slower in SC 24 as in the general population but wider. Limb
halo CMEs also follow the same trend of slower SC-24 CMEs. However, the
SC-24 CMEs become halos at a shorter distance from the Sun. Thus, slower
CMEs becoming halos sooner is a clear indication of the backreaction
of the weaker heliospheric state on CMEs. We can further pin down the
heliospheric state as the reason for the altered CME properties because
the associated flares have similar distributions in the two cycles -
unaffected by the heliospheric state.
---------------------------------------------------------
Title: Interplanetary Radio Emission: A Summary of Recent Results
Authors: Gopalswamy, Nat
2020arXiv200809222G Altcode:
This paper summarizes some recent results in the low-frequency radio
physics of the Sun. The spatial domain covers the space from the outer
corona to the orbit of Earth. The results obtained make use of radio
dynamic spectra and white-light coronagraph images and involve radio
bursts associated with solar eruptions and those occurring outside solar
eruptions. In particular, the connection between type II radio bursts
and the sustained gamma-ray emission from the Sun is highlighted. The
directivity of interplanetary type IV bursts found recently is discussed
to understand the physical reason behind it. A new event showing the
diffuse interplanetary radio emission (DIRE) is introduced and its
properties are compared with those of regular type II bursts. The DIRE
is from the flanks of a CME-driven shock propagating through nearby
streamer. Finally, a new noise storm observed by two spacecraft is
briefly discussed to highlight its evolution over two solar rotations
including the disruption and recovery by solar eruptions.
---------------------------------------------------------
Title: The State of the Heliosphere Revealed by Limb-halo Coronal
Mass Ejections in Solar Cycles 23 and 24
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Yashiro, Seiji
2020ApJ...897L...1G Altcode: 2020arXiv200605844G
We compare the properties of halo coronal mass ejections (CMEs)
that originate close to the limb (within a central meridian distance
range of 60°-∼90°) during solar cycles 23 and 24 to quantify the
effect of the heliospheric state on CME properties. There are 44 and
38 limb halos in cycles 23 and 24, respectively. Normalized to the
cycle-averaged total sunspot number, there are 42% more limb halos in
cycle 24. Although the limb halos as a population are very fast (average
speed ∼1464 km s<SUP>-1</SUP>), cycle-24 halos are slower by ∼26%
than the cycle-23 halos. We introduce a new parameter, the heliocentric
distance of the CME leading edge at the time a CME becomes a full halo;
this height is significantly shorter in cycle 24 (by ∼20%) and has
a lower cutoff at ∼6 R<SUB>s</SUB>. These results show that cycle-24
CMEs become halos sooner and at a lower speed than the cycle-23 ones. On
the other hand, the flare sizes are very similar in the two cycles,
ruling out the possibility of eruption characteristics contributing
to the differing CME properties. In summary, this study reveals the
effect of the reduced total pressure in the heliosphere that allows
cycle-24 CMEs to expand more and become halos sooner than in cycle
23. Our findings have important implications for the space-weather
consequences of CMEs in cycle 25 (predicted to be similar to cycle 24)
and for understanding the disparity in halo counts reported by automatic
and manual catalogs.
---------------------------------------------------------
Title: A comparison of CME expansion speeds between solar cycles 23
and 24
Authors: Kassa Dagnew, Fithanegest; Gopalswamy, Nat; Belay Tessema,
Solomon
2020arXiv200713204K Altcode:
We report on a comparison of the expansion speeds of limb coronal mass
ejections (CMEs) between solar cycles 23 and 24. We selected a large
number of limb CME events associated with soft X-ray flare size greater
than or equal to M1.0 from both cycles. We used data and measurement
tools available at the online CME catalog (https://cdaw.gsfc.nasa.gov)
that consists of the properties of all CMEs detected by the Solar
and Heliospheric Observatory's (SOHO) Large Angle and Spectrometric
Coronagraph (LASCO). We found that the expansion speeds in cycle 24
are higher than those in cycle 23. We also found that the relation
between radial and expansion speeds has different slopes in cycles 23
and 24. The cycle 24 slope is 45% higher than that in cycle 23. The
expansion speed is also higher for a given radial speed. The difference
increases with speed. For a 2000 km/s radial speed, the expansion
speed in cycle 24 is ~48% higher. These results present additional
evidence for the anomalous expansion of cycle 24-CMEs, which is due
to the reduced total pressure in the heliosphere.
---------------------------------------------------------
Title: Interplanetary shocks as a source of sustained gamma-ray
emission from the Sun
Authors: Gopalswamy, Nat; Mäkelä, Pertti
2020EGUGA..2221334G Altcode:
It has recently been shown that the sustained gamma-ray emission
(SGRE) from the Sun that lasts for hours beyond the impulsive phase
of the associated flare is closely related to radio emission from
interplanetary shocks (Gopalswamy et al. 2019, JPhCS, 1332, 012004,
2019). This relationship supports the idea that >300 MeV protons
accelerated by CME-driven shocks propagate toward the Sun, collide
with chromospheric protons and produce neutral pions that promptly
decay into >80 MeV gamma-rays. There have been two challenges
to this idea. (i) Since the location of the shock can be halfway
between the Sun and Earth at the SGRE end time, it has been suggested
that magnetic mirroring will not allow the high energy protons to
precipitate. (ii) Lack of correlation between the number protons
involved in the production of >100 MeV gamma-rays (Ng) and the
number of protons (Nsep) in the associated solar energetic particle
(SEP) event has been reported. In this paper, we show that the mirror
ratio problem is no different from that in flare loops where electrons
and protons precipitate to produce impulsive phase emissions. We also
suggest that the lack of Ng - Nsep correlation is due to two reasons:
(1) Nsep is underestimated in the case of eruptions happening at large
ecliptic latitudes because the high-energy protons accelerated near
the nose do not reach the observer. (2) In the case of limb events,
the Ng is underestimated because gamma-rays from some part of the
extended gamma-ray source do not reach the observer.
---------------------------------------------------------
Title: A Modified Spheromak Model Suitable for Coronal Mass Ejection
Simulations
Authors: Singh, Talwinder; Yalim, Mehmet S.; Pogorelov, Nikolai V.;
Gopalswamy, Nat
2020ApJ...894...49S Altcode: 2020arXiv200210409S
Coronal mass ejections (CMEs) are some of the primary drivers of
extreme space weather. They are large eruptions of mass and magnetic
field from the solar corona and can travel the distance between Sun
and Earth in half a day to a few days. Predictions of CMEs at 1 au,
in terms of both its arrival time and magnetic field configuration,
are very important for predicting space weather. Magnetohydrodynamic
modeling of CMEs, using flux rope-based models, is a promising tool
for achieving this goal. In this study, we present one such model for
CME simulations, based on spheromak magnetic field configuration. We
have modified the spheromak solution to allow for independent input
of poloidal and toroidal fluxes. The motivation for this is the
possibility of estimating these fluxes from solar magnetograms and
extreme ultraviolet data from a number of different approaches. We
estimate the poloidal flux of CME using post-eruption arcades and
toroidal flux from the coronal dimming. In this modified spheromak,
we also have the option to control the helicity sign of flux ropes,
which can be derived from the solar disk magnetograms using the
magnetic tongue approach. We demonstrate the applicability of this
model by simulating the 2012 July 12 CME in the solar corona.
---------------------------------------------------------
Title: Positron Processes in the Sun
Authors: Gopalswamy, Nat
2020Atoms...8...14G Altcode: 2020arXiv200404280G
Positrons play a major role in the emission of solar gamma-rays at
energies from a few hundred keV to >1 GeV. Although the processes
leading to positron production in the solar atmosphere are well
known, the origin of the underlying energetic particles that interact
with the ambient particles is poorly understood. With the aim of
understanding the full gamma-ray spectrum of the Sun, I review the
key emission mechanisms that contribute to the observed gamma-ray
spectrum, focusing on the ones involving positrons. In particular, I
review the processes involved in the 0.511 MeV positron annihilation
line and the positronium continuum emissions at low energies, and
the pion continuum emission at high energies in solar eruptions. It
is thought that particles accelerated at the flare reconnection and
at the shock driven by coronal mass ejections are responsible for
the observed gamma-ray features. Based on some recent developments I
suggest that energetic particles from both mechanisms may contribute
to the observed gamma-ray spectrum in the impulsive phase, while the
shock mechanism is responsible for the extended phase.
---------------------------------------------------------
Title: Impact of space weather on climate and habitability of
terrestrial-type exoplanets
Authors: Airapetian, V. S.; Barnes, R.; Cohen, O.; Collinson,
G. A.; Danchi, W. C.; Dong, C. F.; Del Genio, A. D.; France, K.;
Garcia-Sage, K.; Glocer, A.; Gopalswamy, N.; Grenfell, J. L.; Gronoff,
G.; Güdel, M.; Herbst, K.; Henning, W. G.; Jackman, C. H.; Jin, M.;
Johnstone, C. P.; Kaltenegger, L.; Kay, C. D.; Kobayashi, K.; Kuang,
W.; Li, G.; Lynch, B. J.; Lüftinger, T.; Luhmann, J. G.; Maehara, H.;
Mlynczak, M. G.; Notsu, Y.; Osten, R. A.; Ramirez, R. M.; Rugheimer,
S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.; Sousa-Silva, C.;
Stamenković, V.; Strangeway, R. J.; Usmanov, A. V.; Vergados, P.;
Verkhoglyadova, O. P.; Vidotto, A. A.; Voytek, M.; Way, M. J.; Zank,
G. P.; Yamashiki, Y.
2020IJAsB..19..136A Altcode: 2019arXiv190505093A
The current progress in the detection of terrestrial type exoplanets has
opened a new avenue in the characterization of exoplanetary atmospheres
and in the search for biosignatures of life with the upcoming
ground-based and space missions. To specify the conditions favorable for
the origin, development and sustainment of life as we know it in other
worlds, we need to understand the nature of astrospheric, atmospheric
and surface environments of exoplanets in habitable zones around
G-K-M dwarfs including our young Sun. Global environment is formed by
propagated disturbances from the planet-hosting stars in the form of
stellar flares, coronal mass ejections, energetic particles, and winds
collectively known as astrospheric space weather. Its characterization
will help in understanding how an exoplanetary ecosystem interacts
with its host star, as well as in the specification of the physical,
chemical and biochemical conditions that can create favorable and/or
detrimental conditions for planetary climate and habitability along with
evolution of planetary internal dynamics over geological timescales. A
key linkage of (astro) physical, chemical, and geological processes can
only be understood in the framework of interdisciplinary studies with
the incorporation of progress in heliophysics, astrophysics, planetary
and Earth sciences. The assessment of the impacts of host stars on the
climate and habitability of terrestrial (exo)planets will significantly
expand the current definition of the habitable zone to the biogenic zone
and provide new observational strategies for searching for signatures
of life. The major goal of this paper is to describe and discuss the
current status and recent progress in this interdisciplinary field and
to provide a new roadmap for the future development of the emerging
field of exoplanetary science and astrobiology.
---------------------------------------------------------
Title: ICME Evolution in the Inner Heliosphere
Authors: Luhmann, J. G.; Gopalswamy, N.; Jian, L. K.; Lugaz, N.
2020SoPh..295...61L Altcode:
ICMEs (interplanetary coronal mass ejections), the heliospheric
counterparts of what is observed with coronagraphs at the Sun as CMEs,
have been the subject of intense interest since their close association
with geomagnetic storms was established in the 1980s. These major
interplanetary plasma and magnetic field transients, often preceded
and accompanied by solar energetic particles (SEPs), interact with
planetary magnetospheres, ionospheres, and upper atmospheres in
now fairly well-understood ways, although their details and context
affect their overall impacts. The term ICME as it is used here refers
to the complete solar-wind plasma and field disturbance, including the
leading shock (if present), the compressed, deflected solar-wind plasma
and the field behind the shock ("sheath"), and the coronal ejecta (the
"driver") - often called a magnetic cloud. Many uncertainties remain in
understanding both the relationship to what is observed at the Sun and
the variety of local outcomes suggested by in-situ observations. This
impacts our abilities to interpret events and to forecast effects based
on solar observations. Here, we briefly consider what is known about
ICMEs and their evolution en route from the Sun from the combination of
available observations and interpretive models that have been developed
up to now. The included references are only representative of the large
body of work that has been published on this subject. Our aim is to
provide the reader with an updated synthesis of research results in
this still active area of heliophysics at the dawn of the Parker Solar
Probe (PSP) and Solar Orbiter (SO) mission era.
---------------------------------------------------------
Title: Space, time and velocity association of successive coronal
mass ejections
Authors: Lara, Alejandro; Gopalswamy, Nat; Niembro, Tatiana;
Pérez-Enríquez, Román; Yashiro, Seiji
2020A&A...635A.112L Altcode:
<BR /> Aims: Our aim is to investigate the possible physical association
between consecutive coronal mass ejections (CMEs). <BR /> Methods:
Through a statistical study of the main characteristics of 27 761 CMEs
observed by SOHO/LASCO during the past 20 years. <BR /> Results: We
found the waiting time (WT) or time elapsed between two consecutive
CMEs is < 5 h for 59% and < 25 h for 97% of the events, and
the CME WTs follow a Pareto Type IV statistical distribution. The
difference of the position-angle of a considerable population of
consecutive CME pairs is less than 30°, indicating the possibility
that their source locations are in the same region. The difference
between the speed of trailing and leading consecutive CMEs follows a
generalized Student t-distribution. The fact that the WT and the speed
difference have heavy-tailed distributions along with a detrended
fluctuation analysis shows that the CME process has a long-range
dependence. As a consequence of the long-range dependence, we found
a small but significative difference between the speed of consecutive
CMEs, with the speed of the trailing CME being higher than the speed
of the leading CME. The difference is largest for WTs < 2 h and
tends to be zero for WTs > 10 h, and it is more evident during the
ascending and descending phases of the solar cycle. We suggest that
this difference may be caused by a drag force acting over CMEs closely
related in space and time. <BR /> Conclusions: Our results show that
the initiation and early propagation of a significant population of
CMEs cannot be considered as a "pure" stochastic process; instead they
have temporal, spatial, and velocity relationship.
---------------------------------------------------------
Title: Source of Energetic Protons in the 2014 September 1 Sustained
Gamma-ray Emission Event
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.; Akiyama, S.; Xie,
H.; Thakur, N.
2020SoPh..295...18G Altcode: 2020arXiv200103816G
We report on the source of >300 MeV protons during the SOL2014-09-01
sustained gamma-ray emission (SGRE) event based on multi-wavelength data
from a wide array of space- and ground-based instruments. Based on the
eruption geometry we provide concrete explanation for the spatially and
temporally extended γ -ray emission from the eruption. We show that
the associated flux rope is of low inclination (roughly oriented in
the east-west direction), which enables the associated shock to extend
to the frontside. We compare the centroid of the SGRE source with the
location of the flux rope's leg to infer that the high-energy protons
must be precipitating between the flux rope leg and the shock front. The
durations of the SOL2014-09-01 SGRE event and the type II radio burst
agree with the linear relationship between these parameters obtained
for other SGRE events with duration ≥3 hrs. The fluence spectrum of
the SEP event is very hard, indicating the presence of high-energy
(GeV) particles in this event. This is further confirmed by the
presence of an energetic coronal mass ejection with a speed >2000
kms−<SUP>1</SUP>, similar to those in ground level enhancement (GLE)
events. The type II radio burst had emission components from metric to
kilometric wavelengths as in events associated with GLE events. All
these factors indicate that the high-energy particles from the shock
were in sufficient numbers needed for the production of γ -rays via
neutral pion decay.
---------------------------------------------------------
Title: A Study of the Observational Properties of Coronal Mass
Ejection Flux Ropes near the Sun
Authors: Sindhuja, G.; Gopalswamy, N.
2020ApJ...889..104S Altcode:
We present the observational properties of coronal mass ejection
(CME) flux ropes (FRs) near the Sun based on a set of 35 events from
solar cycle 24 (2010-2017). We derived the CME FR properties using the
Flux Rope from Eruption Data technique. According to this technique,
the geometrical properties are obtained from a flux-rope fit to CMEs
and the magnetic properties from the reconnected flux in the source
region. In addition, we use the magnetic flux in the dimming region
at the eruption site. Geometric properties like radius of the FR and
the aspect ratio are derived from the FR fitting. The reconnected
flux exhibits a positive correlation with flare fluence in soft
X-rays (SXRs), peak flare intensity in SXRs, CME speed, and kinetic
energy, with correlation coefficients (cc) 0.78, 0.6, 0.48, and 0.55,
respectively. We found a moderate positive correlation between magnetic
flux in the core dimming regions and the toroidal flux obtained from
the Lundquist solution for a force-free FR (cc = 0.43). Furthermore,
we correlate the core dimming flux and CME mass (cc = 0.34). The area
of the core dimming region shows a moderate correlation with the radius
of the FR (cc = 0.4). Thus, we infer that greater magnetic content
(poloidal and toroidal fluxes) indicates a more energetic eruption in
terms of flare size, CME speed, kinetic energy, mass, and radius of
the FR, suggesting important implications for space weather predictions.
---------------------------------------------------------
Title: The shock driving capability of a CME inferred from
multiwavelength observations
Authors: Kassa Dagnew, Fithanegest; Gopalswamy, Nat; Belay Tessema,
Solomon; Umuhire, Ange Cynthia; Yashiro, Seiji; Mäkelä, Pertti;
Xie, Hong
2020arXiv200204056K Altcode:
The radial speed of a coronal mass ejection (CME) determines the
shock-driving capability of a CME as indicated by the presence of a
type II radio burst. Here we report on the April 18, 2014 CME that was
associated with a type II radio burst in the metric and interplanetary
domains. We used the radio-burst data provided by the San Vito Solar
Observatory of the Radio Solar Telescope Network and data from the
Wind spacecraft. The CME is a full halo in the field of view of
the coronagraphs on board the Solar and Heliospheric Observatory
(SOHO). The CME was also observed by the coronagraphs on board the
Solar Terrestrial Relations Observatory (STEREO). We computed the CME
shock and flux rope speeds based on the multi-view observations by the
different coronagraphs and by EUV instruments. We determined the shock
speed from metric and interplanetary radio observations and found them
to be consistent with white-light observations, provided the metric type
II burst and its continuation into the decameter-hectometric domain are
produced at the shock flanks, where the speed is still high enough to
accelerate electrons that produce the type II bursts. Interestingly,
there was an interplanetary type II burst segment consistent with an
origin at the shock nose suggesting that the curved shock was crossing
plasma levels separated by a few solar radii. We conclude that the
CME speed is high enough to produce the interplanetary Type II burst
and a solar energetic particle (SEP) event. However, the speed is
not high enough to produce a ground level enhancement (GLE) event,
which requires the shock to form at a height of ~1.5 Rs.
---------------------------------------------------------
Title: An Observationally Constrained Analytical Model for Predicting
the Magnetic Field Vectors of Interplanetary Coronal Mass Ejections
at 1 au
Authors: Sarkar, Ranadeep; Gopalswamy, Nat; Srivastava, Nandita
2020ApJ...888..121S Altcode: 2019arXiv191203494S
We report on an observationally constrained analytical model, the
INterplanetary Flux ROpe Simulator (INFROS), for predicting the magnetic
field vectors of coronal mass ejections (CMEs) in the interplanetary
medium. The main architecture of INFROS involves using the near-Sun
flux rope properties obtained from the observational parameters that
are evolved through the model in order to estimate the magnetic field
vectors of interplanetary CMEs (ICMEs) at any heliocentric distance. We
have formulated a new approach in INFROS to incorporate the expanding
nature and the time-varying axial magnetic field strength of the flux
rope during its passage over the spacecraft. As a proof of concept,
we present the case study of an Earth-impacting CME which occurred on
2013 April 11. Using the near-Sun properties of the CME flux rope,
we have estimated the magnetic vectors of the ICME as intersected
by the spacecraft at 1 au. The predicted magnetic field profiles
of the ICME show good agreement with those observed by the in situ
spacecraft. Importantly, the maximum strength (10.5 ± 2.5 nT) of the
southward component of the magnetic field (Bz) obtained from the model
prediction is in agreement with the observed value (11 nT). Although our
model does not include the prediction of the ICME plasma parameters, as
a first-order approximation, it shows promising results in forecasting
of Bz in near real time, which is critical for predicting the severity
of the associated geomagnetic storms. This could prove to be a simple
space-weather forecasting tool compared to the time-consuming and
computationally expensive MHD models.
---------------------------------------------------------
Title: On the properties of solar energetic particle events associated
with metric type II radio bursts
Authors: Mäkelä, Pertti; Gopalswamy, Nat; Xie, Hong; Akiyama,
Sachiko; Yashiro, Seiji; Thakur, Neeharika
2020arXiv200110506M Altcode:
Metric type II solar radio bursts and solar energetic particles (SEPs)
are both associated with shock fronts driven by coronal mass ejections
(CMEs) in the solar corona. Recent studies of ground level enhancements
(GLEs), regular large solar energetic particle (SEP) events and filament
eruption (FE) associated large SEP events have shown that SEP events are
organized by spectral index of proton fluence spectra and by the average
starting frequencies of the associated type II radio bursts. Both these
results indicate a hierarchical relationship between CME kinematics
and SEP event properties. In this study, we expand the investigations
to fluence spectra and the longitudinal extent of metric type II
associated SEP events including low-intensity SEP events. We utilize
SEP measurements of particle instruments on the Solar and Heliospheric
Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO)
spacecraft together with radio bursts observations by ground-based
radio observatories during solar cycle 24. Our results show that
low-intensity SEP events follow the hierarchy of spectral index or
the hierarchy of the starting frequency of type II radio bursts. We
also find indications of a trend between the onset frequency of metric
type II bursts and the estimated longitudinal extent of the SEP events
although the scatter of data points is quite large. These two results
strongly support the idea of SEP acceleration by shocks. Stronger
shocks develop closer to the Sun.
---------------------------------------------------------
Title: The Shock-Driving Capability of a CME Inferred from
Multiwavelength Observations
Authors: Dagnew, F.; Gopalswamy, N.; Tessema, S.; Umuhire, A.; Yashiro,
S.; Mäkelä, P.; Xie, H.
2019SunGe..14..105D Altcode: 2019SunGe..14...105
The radial speed of a coronal mass ejection (CME) determines the
shock-driving capability of a CME as indicated by the presence of a
type II radio burst. Here we report on the April 18, 2014 CME that was
associated with a type II radio burst in the metric and interplanetary
domains. We used the radio-burst data provided by the San Vito Solar
Observatory of the Radio Solar Telescope Network and data from the
Wind spacecraft. The CME is a full halo in the field of view of
the coronagraphs on board the Solar and Heliospheric Observatory
(SOHO). The CME was also observed by the coronagraphs on board the
Solar Terrestrial Relations Observatory (STEREO). We computed the CME
shock and flux rope speeds based on the multi-view observations by the
different coronagraphs and by EUV instruments. We determined the shock
speed from metric and interplanetary radio observations and found them
to be consistent with white-light observations, provided the metric type
II burst and its continuation into the decameter-hectometric domain are
produced at the shock flanks, where the speed is still high enough to
accelerate electrons that produce the type II bursts. Interestingly,
there was an interplanetary type II burst segment consistent with an
origin at the shock nose suggesting that the curved shock was crossing
plasma levels separated by a few solar radii. We conclude that the
CME speed is high enough to produce the interplanetary Type II burst
and a solar energetic particle (SEP) event. However, the speed is
not high enough to produce a ground level enhancement (GLE) event,
which requires the shock to form at a height of ~1.5 Rs.
---------------------------------------------------------
Title: Low Frequency Radio Bursts Observed by the Wind Spacecraft
and their Contribution to the Understanding of Coronal Mass Ejections
Authors: Gopalswamy, N.; Makela, P.; Yashiro, S.
2019AGUFMSH43C3379G Altcode:
At frequencies below the ionospheric cutoff, only three types of solar
radio bursts caused by nonthermal electrons are observed: type II,
type III, and type IV bursts. A quarter century of radio observations
from the Radio and Plasma Wave (WAVES) experiment and white light
observations from the Large Angle and Spectrometric Coronagraph
(LASCO) have contributed enormously to our understanding of solar
eruptions and their heliospheric consequences. In particular, type II
bursts provide information on shocks driven by coronal mass ejections
(CMEs), including the locations of particle acceleration along the
shock surface and their ability to identify shocks accelerating solar
energetic particle (SEP) events. The ending frequencies of type II
bursts have become an important indicator of the heliocentric distance
over which shocks remain as efficient particle accelerators evidenced
by high-energy SEP events and sustained gamma-ray emission (SGRE)
events. This paper highlights some major results regarding CMEs and
low-frequency radio bursts and summarize some outstanding problems
that are being investigated.
---------------------------------------------------------
Title: Solar Sources of Coronal Mass Ejections
Authors: Akiyama, S.; Gopalswamy, N.; Yashiro, S.; Michalek, G.
2019AGUFMSH11D3389A Altcode:
Coronal Mass Ejections (CMEs) are one of the important phenomena
in space weather research. The SOHO/LASCO CME catalog has listed
more than 29,000 CMEs since January 1996 and is extensively used in
the community. The catalog provides the basic CME properties, e.g.,
speed, angular width, mass, and kinetic energy. However the CME source
information is not included since it is difficult to examine the source
of all CMEs listed in the CME catalog. Here we describe two special
CME lists that include CME source information: (i) a list of wide CMEs
whose angular width is ≥ 60⁰, and (ii) list of CMEs associated
with ≥ C3.0 flares. To determine the source location, we use all
available eruptive signatures near the surface, such as solar flares,
filament eruptions, EUV waves, and coronal dimmings. The X-ray flare
class and the flare start/peak times are also listed if available. We
have assigned six confidence levels to the source identification:
0 - no source was identified, 5 - source was identified without
doubt. We were able to identify the source locations of 6,870 wide
CMEs out of 8,420 that occurred during 1996 to 2018. We found that 48%
of wide CMEs originated from the active regions and 52% were from the
quiet Sun. Solar flares and CMEs are closely related but there is no
one-to-one correspondence. During 1996 to 2018, there are 7,658 ≥
C3 flares. From these, we find that ~90% of X-class, 50% of M-class,
and 20% of C3-C9 class flares were associated with CMEs. Statistical
relationship between the flares and the CMEs will be presented.
---------------------------------------------------------
Title: On the Shock Source of Sustained Gamma-Ray Emission from
the Sun
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.; Lara, A.; Akiyama,
S.; Xie, H.
2019JPhCS1332a2004G Altcode: 2019arXiv190713318G
It has recently been shown that the spatially and temporally extended
γ-ray emission in solar eruptions are caused by >300 MeV protons
precipitating on the Sun from shocks driven by coronal mass ejections
(CMEs). The γ-rays result from the decay of neutral pions produced
in the proton-proton interaction when the >300 MeV protons collide
with those in the chromosphere. The evidence comes from the close
correlation between the durations of the sustained gamma-ray emission
(SGRE) and the associated interplanetary (IP) type II radio bursts. In
this paper, we provide further evidence that support the idea that
protons accelerated in IP shocks driven by CMEs propagate toward the
Sun, precipitate in the chromosphere to produce the observed SGRE. We
present the statistical properties of the SGRE events and the associated
CMEs, flares, and type II radio bursts. It is found that the SGRE
CMEs are similar to those associated with ground level enhancement
events. The CME speed is well correlated with the SGRE fluence. High
CME speed is an important requirement for the occurrence of SGRE,
while the flare size is not. Based on these results, we present a
schematic model illustrating the spatially and temporally extended
nature of SGRE related to the CME flux rope-shock structure.
---------------------------------------------------------
Title: Statistical Survey of Coronal Mass Ejections and Interplanetary
Type II Bursts
Authors: Krupar, V.; Magdalenić, J.; Eastwood, J. P.; Gopalswamy,
N.; Kruparova, O.; Szabo, A.; Němec, F.
2019ApJ...882...92K Altcode:
Coronal mass ejections (CMEs) are responsible for most severe
space weather events, such as solar energetic particle events and
geomagnetic storms at Earth. Type II radio bursts are slow drifting
emissions produced by beams of suprathermal electrons accelerated at
CME-driven shock waves propagating through the corona and interplanetary
medium. Here, we report a statistical study of 153 interplanetary
type II radio bursts observed by the two STEREO spacecraft between
2008 March and 2014 August. The shock associated radio emission was
compared with CME parameters included in the Heliospheric Cataloguing,
Analysis and Techniques Service catalog. We found that faster CMEs
are statistically more likely to be associated with the interplanetary
type II radio bursts. We correlate frequency drifts of interplanetary
type II bursts with white-light observations to localize radio sources
with respect to CMEs. Our results suggest that interplanetary type II
bursts are more likely to have a source region situated closer to CME
flanks than CME leading edge regions.
---------------------------------------------------------
Title: Are Solar Energetic Particle Events and Type II Bursts
Associated with Fast and Narrow Coronal Mass Ejections?
Authors: Kahler, S. W.; Ling, A. G.; Gopalswamy, N.
2019SoPh..294..134K Altcode:
Gradual solar energetic (E >10 MeV) particle (SEP) events and
metric through kilometric wavelength type II radio bursts are usually
associated with shocks driven by fast (V ≥900 kms−<SUP>1</SUP>)
and wide (W ≥60<SUP>∘</SUP>) coronal mass ejections (FW CMEs). This
criterion was established empirically by several studies from solar
cycle 23. The characteristic Alfvén speed in the corona, which ranges
over 500 - 1500 km s<SUP>−1</SUP> at heights ≥2 R<SUB>o</SUB>,
provides the minimum V requirement for a CME to drive a shock, but the
general absence of SEP events or type II bursts with fast and narrow
(W <60<SUP>∘</SUP>) CMEs has not been explained. We review and
confirm the earlier studies with a more comprehensive comparison of SEP
events and type II bursts with fast and narrow (FN) CMEs. We offer an
explanation for the lack of SEP event and type II burst associations
with FN CMEs in terms of recent heuristic arguments and modeling that
show that the response of a magnetized plasma to the propagation of
a CME depends on the CME geometry as well as on its speed. A clear
distinction is made between a projectile that propagates through
the medium to produce a bow shock, and a 3D piston that everywhere
accumulates material to produce a broad shock and sheath. The bow
shock is unfavorable for producing SEP events and type II bursts,
but the 60<SUP>∘</SUP> cut-off is not explained.
---------------------------------------------------------
Title: Statistical Study on Multispacecraft Widespread Solar Energetic
Particle Events During Solar Cycle 24
Authors: Xie, H.; St. Cyr, O. C.; Mäkelä, P.; Gopalswamy, N.
2019JGRA..124.6384X Altcode:
We conduct a statistical study on the large three-spacecraft widespread
solar energetic particle (SEP) events. Longitudinal distributions
of the peak intensities, onset delays, and relation between the SEP
intensity, coronal mass ejection (CME) shock speed, width, and the
kinetic energy of the CME have been investigated. We apply a Gaussian
fit to obtain the SEP intensity I<SUB>0</SUB> and distribution width
σ and a forward-modeling fit to determine the true shock speed and
true CME width. We found a good correlation between σ and connection
angle to the flare site and I<SUB>0</SUB> and the kinetic energy
of the CME. By including the true shock speed and true CME widths,
we reduce root-mean-square errors on the predicted SEP intensity
by ∼41% for protons compared to Richardson et al.'s (2014, <A
href="https://doi.org/10.1007/s11207-014-0524-8">https://doi.org/10.1007/s11207-014-0524-8</A>)
prediction. The improved correlation between the CME kinetic energy and
SEP intensity provides strong evidence for the CME-shock acceleration
theory of SEPs. In addition, we found that electron and proton release
time delays (DTs) relative to Type II radio bursts increase with
connection angles. The average electron (proton) DT is ∼14 (32)
min for strongly anisotropic events and ∼2.5 (4.4) hr for weakly
anisotropic events. Poor magnetic connectivity and large scattering
effects are two main reasons to cause large delays.
---------------------------------------------------------
Title: Direct Estimates of the Solar Coronal Magnetic Field
Using Contemporaneous Extreme-ultraviolet, Radio, and White-light
Observations
Authors: Kumari, Anshu; Ramesh, R.; Kathiravan, C.; Wang, T. J.;
Gopalswamy, N.
2019ApJ...881...24K Altcode: 2019arXiv190709721K
We report a solar coronal split-band type II radio burst
that was observed on 2016 March 16 with the Gauribidanur Radio
Spectro-Polarimeter in the frequency range ≈90-50 MHz, and the
Gauribidanur RadioheliograPH at two discrete frequencies, viz. 80 and
53.3 MHz. Observations around the same epoch in extreme ultraviolet
(EUV) and white light show that the above burst was associated with a
flux-rope structure and a coronal mass ejection (CME), respectively. The
combined height-time plot generated using EUV, radio, and white-light
data suggests that the different observed features (i.e., the flux rope,
type II burst, and the CME) are all closely associated. We constructed
an empirical model for the coronal electron density distribution
(N <SUB> e </SUB>(r), where r is the heliocentric distance) from
the above set of observations themselves and used it to estimate the
coronal magnetic field strength (B) over the range of r values in which
the respective events were observed. The B values are consistent with
each other. They vary as B(r) = 2.61 × r <SUP>-2.21</SUP> G in the
range r ≈ 1.1-2.2R <SUB>⊙</SUB>. As far as we know, similar direct
estimates of B in the near-Sun corona without assuming a model for N
<SUB> e </SUB>(r), and by combining cotemporal set of observations in
two different regions (radio and white-light) of the electromagnetic
spectrum, have rarely been reported. Further, the present work is a
novel attempt where the characteristics of a propagating EUV flux-rope
structure, considered to be the signature of a CME close to the Sun,
have been used to estimate B(r) in the corresponding distance range.
---------------------------------------------------------
Title: On the Coronal Mass Ejection Detection Rate during Solar
Cycles 23 and 24
Authors: Michalek, Grzegorz; Gopalswamy, Nat; Yashiro, Seiji
2019ApJ...880...51M Altcode:
The Solar and Heliospheric Observatory (SOHO) mission’s white light
coronagraphs have observed more than 25,000 coronal mass ejections
(CMEs) from 1996 January to the end of 2015 July. This period of time
covers almost two solar cycles (23 and 24). The basic attributes of
CMEs, reported in the SOHO/Large Angle and Spectrometric Coronagraph
(LASCO) catalog, during these solar cycles were statistically
analyzed. The question of the CME detection rate and its connection
to the solar cycles was considered in detail. Based on the properties
and detection rate, CMEs can be divided into two categories: regular
and specific events. The regular events are pronounced and follow the
pattern of sunspot number. On the other hand, the special events are
poorer and more correlated with the general conditions of heliosphere
and corona. Nevertheless, both groups of CMEs are the result of the
same physical phenomenon, viz. release of magnetic energy from closed
field regions. It was demonstrated that the enhanced CME rate, since the
solar cycle 23 polar-field reversal, is due to a significant decrease
of total (magnetic and plasma) heliospheric pressure as well as the
changed magnetic pattern of solar corona. CMEs expel free magnetic
energy and helicity from the Sun; therefore, they are related to
complex solar magnetic field structure. It is also worth emphasizing
that the CMEs listed in the SOHO/LASCO catalog are real ejections
(not false identification). Their detection rate reflects the global
evolution of the magnetic field on the Sun, and not only changes in
the magnetic structures associated with sunspots.
---------------------------------------------------------
Title: Global Energetics of Solar Flares. VII. Aerodynamic Drag in
Coronal Mass Ejections
Authors: Aschwanden, Markus J.; Gopalswamy, Nat
2019ApJ...877..149A Altcode: 2019arXiv190605804A
The free energy that is dissipated in a magnetic reconnection process
of a solar flare, generally accompanied by a coronal mass ejection
(CME), has been considered as the ultimate energy source of the global
energy budget of solar flares in previous statistical studies. Here
we explore the effects of the aerodynamic drag force on CMEs, which
supplies additional energy from the slow solar wind to a CME event,
besides the magnetic energy supply. For this purpose, we fit the
analytical aerodynamic drag model of Cargill and Vršnak et al. to
the height-time profiles r(t) of LASCO/SOHO data in 14,316 CME events
observed during the first 8 yr (2010-2017) of the Solar Dynamics
Observatory era (ensuring EUV coverage with AIA). Our main findings
are (1) a mean solar wind speed of w = 472 ± 414 km s<SUP>-1</SUP>,
(2) a maximum drag-accelerated CME energy of E <SUB>drag</SUB> ≲
2 × 10<SUP>32</SUP> erg, (3) a maximum flare-accelerated CME energy
of E <SUB>flare</SUB> ≲ 1.5 × 10<SUP>33</SUP> erg, (4) the ratio
of the summed kinetic energies of all flare-accelerated CMEs to the
drag-accelerated CMEs amounts to a factor of 4, (5) the inclusion
of the drag force slightly lowers the overall energy budget of CME
kinetic energies in flares from ≈7% to ≈4%, and (6) the arrival
times of CMEs at Earth can be predicted with an accuracy of ≈23%.
---------------------------------------------------------
Title: Reconstructing Extreme Space Weather From Planet Hosting Stars
Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander,
D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz,
M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.;
Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage,
K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy,
N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen,
A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.;
Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.;
Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.;
Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian,
A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.;
Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville,
V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.;
Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.;
Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.;
Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova,
S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T.
2019BAAS...51c.564A Altcode: 2019astro2020T.564A; 2019arXiv190306853A
The goal of this white paper is to identify and describe promising key
research goals to aid the theoretical characterization and observational
detection of ionizing radiation from quiescent and flaring upper
atmospheres of planet hosts as well as properties of stellar coronal
mass ejections (CMEs) and stellar energetic particle (SEP) events.
---------------------------------------------------------
Title: Obituary: Mukul R. Kundu (1930-2010)
Authors: Gopalswamy, Nat
2019BAAS...51b0314G Altcode:
Renowned solar physicist and radio astronomer Mukul Ranjan Kundu
died on 17 June 2010 near College Park, Maryland, from complications
after an automobile accident that occurred when he was returning home
from work. A recipient of the American Astronomical Society's 2007
George Ellery Hale Prize, Mukul spent his entire career studying
the radiophysics of the Sun. His work significantly advanced the
understanding of the interactions between accelerated electrons and the
magnetized solar corona and of the myriad nonthermal radio phenomena
that resulted.
---------------------------------------------------------
Title: Explicit IMF B<SUB>y</SUB>-Effect Maximizes at Subauroral
Latitudes (Dedicated to the Memory of Eigil Friis-Christensen)
Authors: Holappa, L.; Gopalswamy, N.; Mursula, K.
2019JGRA..124.2854H Altcode: 2019arXiv190404568H
The most important parameter in the coupling between solar wind
and geomagnetic activity is the B<SUB>z</SUB>-component of the
interplanetary magnetic field (IMF). However, recent studies have
shown that IMF B<SUB>y</SUB> is an additional, independent driver of
geomagnetic activity. We use here local geomagnetic indices from a large
network of magnetic stations to study how IMF B<SUB>y</SUB> affects
geomagnetic activity at different latitudes for all solar wind and,
separately, during coronal mass ejections. We show that geomagnetic
activity, for all solar wind, is 20% stronger for B<SUB>y</SUB> >
0 than for B<SUB>y</SUB> < 0 at subauroral latitudes of about
60° corrected geomagnetic latitude. During coronal mass ejections,
the B<SUB>y</SUB>-effect is larger, about 40%, at slightly lower
latitudes of about 57° (corrected geomagnetic) latitude. These results
highlight the importance of the IMF B<SUB>y</SUB>-component for space
weather at different latitudes and must be taken into account in space
weather modeling.
---------------------------------------------------------
Title: Simulating Solar Coronal Mass Ejections Constrained by
Observations of Their Speed and Poloidal Flux
Authors: Singh, T.; Yalim, M. S.; Pogorelov, N. V.; Gopalswamy, N.
2019ApJ...875L..17S Altcode: 2019arXiv190400140S
We demonstrate how the parameters of a Gibson-Low flux-rope-based
coronal mass ejection (CME) can be constrained using remote
observations. Our Multi-Scale Fluid-Kinetic Simulation Suite has
been used to simulate the propagation of a CME in a data-driven solar
corona background computed using the photospheric magnetogram data. We
constrain the CME model parameters using the observations of such
key CME properties as its speed, orientation, and poloidal flux. The
speed and orientation are estimated using multi-viewpoint white-light
coronagraph images. The reconnected magnetic flux in the area covered
by the post-eruption arcade is used to estimate the poloidal flux in
the CME flux rope. We simulate the partial halo CME on 2011 March 7
to demonstrate the efficiency of our approach. This CME erupted with
the speed of 812 km s<SUP>-1</SUP> and its poloidal flux, as estimated
from source active region data, was 4.9 × 10<SUP>21</SUP> Mx. Using
our approach, we were able to simulate this CME with the speed 840
km s<SUP>-1</SUP> and the poloidal flux of 5.1 × 10<SUP>21</SUP> Mx,
in remarkable agreement with the observations.
---------------------------------------------------------
Title: On the Properties of Solar Energetic Particle Events Associated
with Metric Type II Radio Bursts
Authors: Mäkelä, P.; Gopalswamy, N.; Xie, H.; Akiyama, S.; Yashiro,
S.; Thakur, N.
2019SunGe..14..123M Altcode: 2019SunGe..14...123
Metric type II solar radio bursts and solar energetic particles (SEPs)
are both associated with shock fronts driven by coronal mass ejections
(CMEs) in the solar corona. Recent studies of ground level enhancements
(GLEs), regular large solar energetic particle (SEP) events and filament
eruption (FE) associated large SEP events have shown that SEP events are
organized by spectral index of proton fluence spectra and by the average
starting frequencies of the associated type II radio bursts. Both these
results indicate a hierarchical relationship between CME kinematics
and SEP event properties. In this study, we expand the investigations
to fluence spectra and the longitudinal extent of metric type II
associated SEP events including low-intensity SEP events. We utilize
SEP measurements of particle instruments on the Solar and Heliospheric
Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO)
spacecraft together with radio bursts observations by ground-based
radio observatories during solar cycle 24. Our results show that
low-intensity SEP events follow the hierarchy of spectral index or
the hierarchy of the starting frequency of type II radio bursts. We
also find indications of a trend between the onset frequency of metric
type II bursts and the estimated longitudinal extent of the SEP events
although the scatter of data points is quite large. These two results
strongly support the idea of SEP acceleration by shocks. Stronger
shocks develop closer to the Sun.
---------------------------------------------------------
Title: A Catalog of Type II radio bursts observed by Wind/WAVES and
their Statistical Properties
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.
2019SunGe..14..111G Altcode: 2019arXiv191207370G; 2019SunGe..14...111
Solar type II radio bursts are the signature of particle acceleration by
shock waves in the solar corona and interplanetary medium. The shocks
originate in solar eruptions involving coronal mass ejections (CMEs)
moving at super-Alfvenic speeds. Type II bursts occur at frequencies
ranging from hundreds of MHz to tens of kHz, which correspond to
plasma frequencies prevailing in the inner heliosphere from the
base of the solar corona to the vicinity of Earth. Type II radio
bursts occurring at frequencies below the ionospheric cutoff are
of particular importance, because they are due to very energetic
CMEs that can disturb a large volume of the heliosphere. The
underlying shocks accelerate not only electrons that produce the
type II bursts, but also protons and heavy ions that have serious
implications for space weather. The type II radio burst catalog
(https://cdaw.gsfc.nasa.gov/CME_list/radio/waves_type2.html) presented
here provides detailed information on the bursts observed by the Radio
and Plasma Wave Experiment (WAVES) on board the Wind Spacecraft. The
catalog is enhanced by compiling the associated flares, CMEs, and solar
energetic particle (SEP) events including their basic properties. We
also present the statistical properties of the radio bursts and the
associated phenomena, including solar-cycle variation of the occurrence
rate of the type II bursts.
---------------------------------------------------------
Title: Evidence for Shock Source of Solar Sustained Gamma-ray
Emission: Fermi, Wind, and SOHO Observations
Authors: Gopalswamy, N.; Mäkelä, Pertti; Yashiro, Seiji; Lara
Sanchez, Alejandro; Xie, Hong; Akiyama, Sachiko; MacDowall, Robert J.
2019AAS...23340106G Altcode:
Fermi Large Area Telescope (Fermi/LAT) observations have shown that
sustained gamma-ray emission (SGRE) from the Sun is rather common. Such
events are now called sustained gamma ray emission (SGRE) events. Some
SGRE events last for almost a day. SGRE is thought to be pion continuum
resulting from the impact of >300 MeV protons impacting the solar
chromosphere. Two sources of the high-energy protons have been discussed
in the literature: (i) continued acceleration/trapping of protons in
large-scale magnetic structures in the associated solar eruption and
(ii) precipitation of sunward propagating protons accelerated in
CME-driven shocks. One of the best observational signatures of CME
shocks is the interplanetary type II radio emission due to nonthermal
electrons accelerated in the shock front. Shocks start accelerating
particles very close to the Sun and often continue to do so far into
the IP medium resulting in kilohertz radio emission. We examined the
type II burst properties such as the duration and ending frequencies
and compared them with the SGRE durations. The SGRE duration has a
significant linear relationship with the duration and ending frequency
of type II bursts. This result strongly supports the idea that protons
accelerated at the shock front travel back to the Sun to precipitate and
produce SGRE. The protons must be traveling along field lines threading
the shock front and lying at the periphery of the CME flux rope. Initial
estimates show that the shocks at a distance of several tens of solar
radii when the SGRE and type II bursts end. The required >300 MeV
proton events are not observed at Earth in most of the events. This can
be explained by the fact that SEP events need magnetic connectivity
to the observer, whereas type II bursts and SGRE are electromagnetic
emissions and hence do not have the connectivity requirement.
---------------------------------------------------------
Title: Interplanetary Type II Radio Bursts from Wind/WAVES and
Sustained Gamma-Ray Emission from Fermi/LAT: Evidence for Shock Source
Authors: Gopalswamy, Nat; Mäkelä, Pertti; Yashiro, Seiji; Lara,
Alejandro; Xie, Hong; Akiyama, Sachiko; MacDowall, Robert J.
2018ApJ...868L..19G Altcode:
We present quantitative evidence that interplanetary type II radio
bursts and sustained gamma-ray emission (SGRE) events from the Sun
are closely related. Out of about 30 SGRE events reported in Share
et al. we consider 13 events that had a duration exceeding ∼5 hr to
exclude any flare-impulsive phase gamma-rays. The SGRE duration also
has a linear relation with the ending frequency of the bursts. The
synchronism between the ending times of SGRE and the type II emission
strongly supports the idea that the same shock accelerates electrons to
produce type II bursts and protons (>300 MeV) that propagate from
the shock to the solar surface to produce SGRE via pion decay. The
acceleration of high-energy particles is confirmed by the associated
solar energetic particle (SEP) events detected at Earth and/or at the
Solar Terrestrial Relations Observatory spacecraft. Furthermore, the
presence of >300 MeV protons is corroborated by the fact that the
underlying coronal mass ejections (CMEs) had properties identical to
those associated with ground-level enhancement events: they had speeds
of >2000 km s<SUP>-1</SUP> and all were full-halo CMEs. Many SEP
events did not have detectable flux at Earth in the >300 MeV energy
channels, presumably because of poor magnetic connectivity.
---------------------------------------------------------
Title: Coronal flux ropes and their interplanetary counterparts
Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Xie, H.
2018JASTP.180...35G Altcode: 2017arXiv170508912G
We report on a study comparing coronal flux ropes inferred from
eruption data with their interplanetary counterparts constructed
from in situ data. The eruption data include the source-region
magnetic field, post-eruption arcades, and coronal mass ejections
(CMEs). Flux ropes were fit to the interplanetary CMEs (ICMEs)
considered for the 2011 and 2012 Coordinated Data Analysis Workshops
(CDAWs). We computed the total reconnected flux involved in each of
the associated solar eruptions and found it to be closely related to
flare properties, CME kinematics, and ICME properties. By fitting flux
ropes to the white-light coronagraph data, we obtained the geometric
properties of the flux ropes and added magnetic properties derived
from the reconnected flux. We found that the CME magnetic field in the
corona is significantly higher than the ambient magnetic field at a
given heliocentric distance. The radial dependence of the flux-rope
magnetic field strength is faster than that of the ambient magnetic
field. The magnetic field strength of the coronal flux ropes is also
correlated with that in interplanetary flux ropes constructed from
in situ data, and with the observed peak magnetic field strength in
ICMEs. The physical reason for the observed correlation between the
peak field strength in ICMEs is the higher magnetic field content in
faster coronal flux ropes and ultimately the higher reconnected flux
in the eruption region. The magnetic flux ropes constructed from the
eruption data and coronagraph observations provide a realistic input
that can be used by various models to predict the magnetic properties
of ICMEs at Earth and other destination in the heliosphere.
---------------------------------------------------------
Title: Very narrow coronal mass ejections producing solar energetic
particles
Authors: Bronarska, K.; Wheatland, M. S.; Gopalswamy, N.; Michalek, G.
2018A&A...619A..34B Altcode:
<BR /> Aims: Our main aim is to study the relationship between
low-energy solar particles (energies below 1 MeV) and very narrow
coronal mass ejections ("jets" with angular width ≤ 20°). <BR />
Methods: For this purpose, we considered 125 very narrow coronal mass
ejections (CMEs) from 1999 to 2003 that are potentially associated
with low-energy solar particles (LESPs). These events were chosen on
the basis of their source location. We studied only very narrow CMEs at
the western limb, which are expected to have good magnetic connectivity
with Earth. <BR /> Results: We found 24 very narrow CMEs associated
with energetic particles such as ions (protons and <SUP>3</SUP>He),
electrons, or both. We show that arrival times at Earth of energetic
particles are consistent with onset times of the respective CMEs, and
that in the same time intervals, there are no other potential sources
of energetic particles. We also demonstrate statistical differences
for the angular width distributions using the Kolmogorov-Smirnov
test for angular widths for these 24 events. We consider a coherent
sample of jets (mostly originating from boundaries of coronal holes)
to identify properties of events that produce solar energetic particles
(velocities, widths, and position angles). Our study presents a new
approach and result: very narrow CMEs can generate low-energy particles
in the vicinity of Earth without other activity on the Sun. The results
could be very useful for space weather forecasting.
---------------------------------------------------------
Title: Sun-to-earth propagation of the 2015 June 21 coronal mass
ejection revealed by optical, EUV, and radio observations
Authors: Gopalswamy, N.; Mäkelä, P.; Akiyama, S.; Yashiro, S.; Xie,
H.; Thakur, N.
2018JASTP.179..225G Altcode: 2018arXiv180710979G
We investigate the propagation of the 2015 June 21 CME-driven shock
as revealed by the type II bursts at metric and longer wavelengths
and coronagraph observations. The CME was associated with the second
largest geomagnetic storm of solar cycle 24 and a large solar energetic
particle (SEP) event. The eruption consisted of two M-class flares,
with the first one being confined, with no metric or interplanetary
radio bursts. However, there was intense microwave burst, indicating
accelerated particles injected toward the Sun. The second flare was
eruptive that resulted in a halo CME. The CME was deflected primarily
by an equatorial coronal hole that resulted in the modification of
the intensity profile of the associated SEP event and the duration of
the CME at Earth. The interplanetary type II burst was particularly
intense and was visible from the corona all the way to the vicinity of
the Wind spacecraft with fundamental-harmonic structure. We computed
the shock speed using the type II drift rates at various heliocentric
distances and obtained information on the evolution of the shock that
matched coronagraph observations near the Sun and in-situ observations
near Earth. The depth of the geomagnetic storm is consistent with the
1-AU speed of the CME and the magnitude of the southward component.
---------------------------------------------------------
Title: Direction-finding Analysis of the 2012 July 6 Type II Solar
Radio Burst at Low Frequencies
Authors: Mäkelä, Pertti; Gopalswamy, Nat; Akiyama, Sachiko
2018ApJ...867...40M Altcode:
The 2012 July 6 X1.1 flare at S13W59 and a halo coronal mass ejection
(CME) with a space speed of ∼1900 km s<SUP>-1</SUP> were associated
with type III and type II radio bursts. The metric-to-decametric type
II radio burst extended down to ∼5 MHz. Simultaneously, a slowly
drifting feature with a harmonic structure was observed by Wind and
Solar Terrestrial Relations Observatory radio receivers around and below
1 MHz, above the strong type III radio burst at lower frequencies. The
radio direction-finding analysis of this lower-frequency interplanetary
(IP) type II radio burst indicates that the radio source was located
near the nose and possibly toward the southern flank of the CME-driven
shock. These results provide an independent confirmation of the previous
suggestions that when the metric and IP type II bursts are overlapping,
the lower-frequency IP type II radio burst originates near the shock
nose, whereas the source of the higher-frequency metric type II burst
is closer to the Sun in the shock flank region. These results further
support the idea that the coronal and IP type II bursts are produced
by the same CME-driven shock.
---------------------------------------------------------
Title: Fermi, Wind, and SOHO Observations of Sustained Gamma-Ray
Emission from the Sun
Authors: Gopalswamy, N.; Makela, P.; Yashiro, S.; Lara, A.; Xie, H.;
Akiyama, S.; MacDowall, R. J.
2018arXiv181008958G Altcode:
We report on the linear relationship between the durations of two types
of electromagnetic emissions associated with shocks driven by coronal
mass ejections: sustained gamma-ray emission (SGRE) and interplanetary
type II radio bursts. The relationship implies that shocks accelerate
about 10 keV electrons (for type II bursts) and greater than 300 MeV
protons (for SGRE) roughly over the same duration. The SGRE events are
from the Large Area Telescope (LAT) on board the Fermi satellite, while
the type II bursts are from the Radio and Plasma Wave Experiment (WAVES)
on board the Wind spacecraft. Here we consider five SGRE events that
were not included in a previous study of events with longer duration
(greater than 5 hours). The five events are selected by relaxing the
minimum duration to 3 hours. We found that some SGRE events had a tail
that seems to last until the end of the associated type II burst. We
pay special attention to the 2011 June 2 SGRE event that did not
have a large solar energetic particle event at Earth or at the STEREO
spacecraft that was well connected to the eruption. We suggest that
the preceding CME acted as a magnetic barrier that mirrored protons
back to Sun.
---------------------------------------------------------
Title: Properties of DH Type II Radio Bursts and Their Space Weather
Implications
Authors: Gopalswamy, N.; Mäkelä, P.
2018arXiv181011173G Altcode:
We report on the properties of type II radio bursts observed by the
Radio and Plasma Wave Experiment (WAVES) on board the Wind spacecraft
over the past two solar cycles. We confirm that the associated coronal
mass ejections (CMEs) are fast and wide, more than half the CMEs
being halos. About half of the type II bursts extend down to 0.5 MHz,
corresponding to a heliocentric distance of tens of solar radii. The
DH type II bursts are mostly confined to the active region belt and
their occurrence rate follows the solar activity cycle. Type II burst
occurring on the western hemisphere of the Sun and extending to lower
frequencies are good indicators of a solar energetic particle event.
---------------------------------------------------------
Title: The Effects of Uncertainty in Initial CME Input Parameters
on Deflection, Rotation, B<SUB>z</SUB>, and Arrival Time Predictions
Authors: Kay, C.; Gopalswamy, N.
2018JGRA..123.7220K Altcode:
Understanding the effects of coronal mass ejections (CMEs)
requires knowing if and when they will impact and their properties
upon impact. Of particular importance is the strength of a CME's
southward magnetic field component (B<SUB>z</SUB>). Kay et al. (2013, <A
href="https://doi:10.1088/0004-637X/775/1/5">https://doi:10.1088/0004-637X/775/1/5</A>,
2015, <A href="https://doi:10.1088/948
0004-637X/805/2/168">https://doi:10.1088/948 0004-637X/805/2/168</A>)
have shown that the simplified analytic model Forecasting a
CME's Altered Trajectory (ForeCAT) can reproduce the deflection
and rotation of CMEs. Kay, Gopalswamy, Reinard, and Opher (2017, <A
href="https://doi.org/10.3847/1538-4357/835/2/117">https://doi.org/10.3847/1538-4357/835/2/117</A>)
introduced ForeCAT In situ Data Observer, which uses ForeCAT results
to simulate magnetic field profiles. ForeCAT In situ Data Observer
reproduces the in situ observations on roughly hourly time scales,
suggesting that these models could be extremely useful for predictions
of B<SUB>z</SUB>. However, as with all models, both models are
sensitive to their input parameters, which may not be precisely known
for predictions. We explore this sensitivity using ensembles having
small changes in the initial latitude, longitude, and orientation
of the erupting CME. We explore the effects of different background
magnetic field models and find that the changes in deflection and
rotation resulting from the uncertainty in the initial parameters
tend to exceed the changes from different magnetic backgrounds. The
range in the in situ profiles tends to scale with the range in the
deflection and rotation. We also consider a simple arrival time model
using ForeCAT results and find an average absolute error of only 3
hr. We show that an uncertainty in the CME position of 8.1° ± 6.9°
leads to variations of 6 hr in the arrival time. This measure depends
strongly on the location of impact within the CME with the arrival
time changing less for impacts near the nose.
---------------------------------------------------------
Title: Long-term solar activity studies using microwave imaging
observations and prediction for cycle 25
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.; Akiyama, S.
2018JASTP.176...26G Altcode: 2018arXiv180402544G
We use microwave imaging observations from the Nobeyama Radioheliograph
at 17 GHz for long-term studies of solar activity. In particular,
we use the polar and low-latitude brightness temperatures as proxies
to the polar and active-region magnetic fields, respectively. We also
use the locations of prominence eruptions as a proxy to the filament
locations to study their time variation. We show that the polar
microwave brightness temperature is highly correlated with the polar
magnetic field strength and the fast solar wind speed. We also show that
the polar microwave brightness in one solar cycle is correlated with
the low latitude brightness with a lag of about half a solar cycle. We
use this correlation to predict the strength of the solar cycle 25:
the smoothed sunspot numbers in the southern and northern hemispheres
can be predicted as 89 and 59, respectively. These values indicate that
cycle 25 will not be too different from cycle 24 in its strength. We
also combined the rush-to-the-pole data from Nobeyama prominences with
historical data going back to 1860 to study the north-south asymmetry
of sign reversal at solar poles. We find that the reversal asymmetry
has a quasi-periodicity of 3-5 cycles.
---------------------------------------------------------
Title: A small satellite mission for solar coronagraphy
Authors: Gopalswamy, N.; Gong, Qian
2018SPIE10769E..0XG Altcode:
We present on a concept study of the Goddard Miniature Coronagraph
(GMC) mission for measuring the plasma flow in the solar corona in
the form of solar wind and coronal mass ejections (CMEs). These mass
flows can dramatically alter the near-Earth space environment to
hazardous conditions posing danger to human technology in space. The
primary science objective of the mission is to measure the properties
of CMEs, coronal structures, and the solar wind near the Sun. The
miniaturization of the coronagraph involves using a single-stage
optics and a polarization camera, both of which reduce the size of the
coronagraph. GMC will be accommodated in a small satellite that can
be built with cubesat material to minimize cost. The development of
the Dellingr mission at NASA/GSFC has provided expertise and a clear
pathway to build the GMC mission. The hardware and software used for
the Dellingr mission are technically sound, so the GMC mission can be
fully defined. Software, pointing, control and communications systems
developed for GSFC CubeSats can be readily adapted to cut costs. We
present orbit options such as an ISS orbit or a Sun synchronous dawndusk
polar orbit with the aim of maximizing solar observations.
---------------------------------------------------------
Title: Dependence of Coronal Mass Ejection Properties on Their
Solar Source Active Region Characteristics and Associated Flare
Reconnection Flux
Authors: Pal, Sanchita; Nandy, Dibyendu; Srivastava, Nandita;
Gopalswamy, Nat; Panda, Suman
2018ApJ...865....4P Altcode: 2018arXiv180804144P
The near-Sun kinematics of coronal mass ejections (CMEs) determine
the severity and arrival time of associated geomagnetic storms. We
investigate the relationship between the deprojected speed and
kinetic energy of CMEs and magnetic measures of their solar sources,
reconnection flux of associated eruptive events, and intrinsic
flux-rope characteristics. Our data covers the period 2010-2014 in
solar cycle 24. Using vector magnetograms of source active regions,
we estimate the size and nonpotentiality. We compute the total
magnetic reconnection flux at the source regions of CMEs using
the post-eruption arcade method. By forward modeling the CMEs,
we find their deprojected geometric parameters and constrain their
kinematics and magnetic properties. Based on an analysis of this
database, we report that the correlation between CME speed and their
source active region size and global nonpotentiality is weak, but not
negligible. We find the near-Sun velocity and kinetic energy of CMEs to
be well correlated with the associated magnetic reconnection flux. We
establish a statistically significant empirical relationship between
the CME speed and reconnection flux that may be utilized for prediction
purposes. Furthermore, we find CME kinematics to be related with the
axial magnetic field intensity and relative magnetic helicity of their
intrinsic flux ropes. The amount of coronal magnetic helicity shed by
CMEs is found to be well correlated with their near-Sun speeds. The
kinetic energy of CMEs is well correlated with their intrinsic magnetic
energy density. Our results constrain processes related to the origin
and propagation of CMEs and may lead to better empirical forecasting
of their arrival and geoeffectiveness.
---------------------------------------------------------
Title: Extreme Kinematics of the 2017 September 10 Solar Eruption
and the Spectral Characteristics of the Associated Energetic Particles
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Xie, H.; Akiyama,
S.; Monstein, C.
2018ApJ...863L..39G Altcode: 2018arXiv180709906G
We report on the 2017 September 10 ground-level enhancement (GLE)
event associated with a coronal mass ejection whose initial acceleration
(∼9.1 km s<SUP>-2</SUP>) and initial speed (∼4300 km s<SUP>-1</SUP>)
were among the highest observed in the Solar and Heliospheric
Observatory era. The GLE event was of low intensity (∼4.4% above
background) and softer-than-average fluence spectrum. We suggest that
poor connectivity (longitudinal and latitudinal) of the source to Earth
compounded by the weaker ambient magnetic field contributed to these GLE
properties. Events with similar high initial speed either lacked GLE
association or had softer fluence spectra. The shock-formation height
inferred from the metric type II burst was ∼1.4 Rs, consistent with
other GLE events. The shock height at solar particle release (SPR)
was ∼4.4 ± 0.38 Rs, consistent with the parabolic relationship
between the shock height at SPR and source longitude. At SPR, the
eastern flank of the shock was observed in EUV projected on the disk
near the longitudes magnetically connected to Earth: W60 to W45.
---------------------------------------------------------
Title: A New Technique to Provide Realistic Input to CME Forecasting
Models
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Yashiro, Seiji; Xie, Hong
2018IAUS..335..258G Altcode: 2017arXiv170903160G
We report on a technique to construct a flux rope (FR) from eruption
data at the Sun. The technique involves line-of-sight magnetic fields,
post-eruption arcades in the corona, and white-light coronal mass
ejections (CMEs) so that the FR geometric and magnetic properties can
be fully defined in addition to the kinematic properties. We refer to
this FR as FRED (Flux Rope from Eruption Data). We illustrate the FRED
construction using the 2012 July 12 eruption and compare the coronal
and interplanetary properties of the FR. The results indicate that the
FRED input should help make realistic predictions of the components
of the FR magnetic field in the heliosphere.
---------------------------------------------------------
Title: Globally Coordinated Space Weather Education and Outreach
Initiative
Authors: Chulaki, Anna; Glover, Alexi; Nandi, Dibyendu; Gopalswamy,
Nat; Di Pippo, Simonetta
2018cosp...42E.656C Altcode:
The poster will summarize outcome from thePSW.5-Panel 2: Capacity
building in space weather: Globally coordinated space weather
education and outreach initiativesWe will provide summaries of ongoing
international educational activities in space weather and discuss
needs and opportunities for global coordination in space weather
awareness, education and outreach. <P />What aspects of space weather
education/outreach require special attention? <P />What type of novel
education initiatives should we undertake? <P />Do we need a framework
for coordinating international space weather educational initiatives? <P
/>What should be the role of COSPAR PSW in space weather education?
---------------------------------------------------------
Title: Relationship between SEP peak intensity and shock speed,
CME width and acceleration; no
Authors: Xie, Hong; St. Cyr, O. C.; Makela, P.; Gopalswamy, N.
2018shin.confE.112X Altcode:
We study the large solar energetic particle (SEP) events that were
detected by GOES in the >10 MeV energy channel during December 2006
to January 2016. Data used in this study includes the Solar Electron
Proton Telescope (SEPT) and High Energy Telescopes (HET) on STEREO
A and B, the Electron, Proton, and Alpha Monitor (EPAM) on ACE,
and the Energetic and Relativistic Nuclei and Electron instrument
(ERNE) on SOHO. From multi-spacecraft observations we obtained the
peak intensity I0 at the center of the Gausssian function using the
Gausssian fit. We then study the relationship between electron and
proton peak intensity and shock speed and CME width. We found that
the correlation between electron and proton peak intensity and shock
speed can be improved by taking into account the effects of CME width
and SEP connection angle. We also found that SEP onset and peak delays
relative to type III onset are closely related to the CME accelerations
at the main and residual acceleration phases. The implication for the
SEP forecast of our obtained results will be discussed.
---------------------------------------------------------
Title: The Effects of Uncertainty on Deflection, Rotation, Bz and
Arrival Time Predictions
Authors: Kay, Christina; Gopalswamy, Nat
2018shin.confE.195K Altcode:
Understanding the effects of coronal mass ejections (CMEs) requires
knowing not only if and when they will impact, but also their
properties upon impact. Of particular importance is the strength of
a CME's southward magnetic field component (Bz). Kay et al. (2013,
2015) have shown that the simplified analytic model ForeCAT can
be used to reproduce the deflection and rotation of CMEs. Kay et
al. (2017) introduced FIDO, which uses the position and orientation
from ForeCAT to simulate magnetic field profiles. FIDO reproduces the
in situ observations on roughly hourly time scales, suggesting that
the combination of ForeCAT and FIDO could be extremely useful for
predictions of Bz. However, as with all models, both ForeCAT and FIDO
are sensitive to their input parameters, which may not be precisely
known for actual predictions. We explore the sensitivity of both
models using ensembles with small changes in the initial latitude,
longitude, and orientation of the erupting CME. Additionally, thus
far ForeCAT has only been run using a Potential Field Source Surface
(PFSS) magnetic background driven by a synoptic map. We explore the
effects of different magnetic backgrounds - the Schatten Current Sheet
model and synchronic maps. We find that the changes in deflection and
rotation resulting from the uncertainty in the initial parameters tend
to exceed the changes from different magnetic backgrounds. The range
in the in situ profiles tends to scale with the range in the deflection
and rotation. We also consider the effects of these changes in a simple
arrival time model and show that accurate arrival times can only be
achieved if the CME position and orientation are precisely known.
---------------------------------------------------------
Title: Unusual Polar Conditions of the Sun during Solar Cycle 24
and its Iplications for Cycle 25
Authors: Gopalswamy, Nat; Masuda, Satoshi; Yashiro, Seiji; Akiyama,
Sachiko; Shibasaki, Kiyoto
2018cosp...42E1250G Altcode:
Polar field strength in one solar cycle is known to indicate the
strength (e.g., Sunspot number) and phase of the next cycle. In
particular the polar field strength (or its proxies such as the
polar coronal hole area and microwave polar brightness) during the
minimum phase of a given cycle seem to be well correlated with the
maximum sunspot number of the next cycle. Polar prominence eruptions
and coronal mass ejections have also been found to be indicators
of low polar field; their cessation signals the time of polarity
reversal. While these indicators are present in the current cycle,
significant differences are found regarding the phase lag between the
two hemispheres and the duration of polar eruptions. We use data from
the Nobeyama Radioheliograph, the Solar Dynamics Observatory, SOLIS,
and Wilcox Solar Observatory to highlight these differences. We find
that the north polar region of the Sun has near-zero field strength for
more than three years. This is unusually long and caused by surges of
both polarities heading toward the north pole that prevent the buildup
of the polar field. This seems to be due to anti-Hale active regions
that appeared around the 2012 peak sunspot activity in the northern
hemisphere. The unusual condition is consistent with (i) the continued
high-latitude prominence eruption, (ii) the extended period of high
tilt angle of the heliospheric current sheet, (iii) the weak microwave
polar brightness, and (iv) the lack of north polar coronal hole. On
the other hand, the south polar field has started building up and the
coronal hole has appeared in early 2015 because of large active regions
of the correct tilt in the southern hemisphere during the 2014 peak of
sunspot activity. The extended period of near-zero field in the north
polar region should result in very weak and delayed sunspot activity
in the northern hemisphere in cycle 25. On the other hand the south
polar field has already increased significantly, suggesting that the
activity in the southern hemisphere should start early; the amplitude
will depend on how the south polar fields will evolve in the declining
phase of cycle 24.
---------------------------------------------------------
Title: Towards a global space weather community hub and a network of
International Space Weather Action Teams (ISWAT) aiming to advance
space weather capabilities and to facilitate Global Space Weather
Roadmap updates
Authors: Kuznetsova, Maria; Glover, Alexi; Gopalswamy, Nat; Di Pippo,
Simonetta
2018cosp...42E1899K Altcode:
Panel 3: COSPAR space weather action teams: A bottom-up component
of global coordination in space weather.14:00-17:30, Thursday,
19 July, Room: SR 29 (HH) - Santa Clara Chairs: Masha Kuznetsova
(NASA, USA), Hermann Opgenoorth (Swedish Institute of Space Physics,
Sweden)One of the key challenges identified in the COSPAR-ILWS space
weather roadmap [Schrijver et al., 2015] is a transformation into an
effectively functioning, information-sharing, global space weather
community. To address this challenge and to demonstrate the critical
value of a global coordination the COSPAR Panel on Space Weather will
coordinate an active network of topical scientific action teams (a.k.a.,
International Space Weather Action Teams). Action teams will address
space weather roadmap recommendations, provide a bottom-up push for
coordination and innovation, serve as a channel for a global community
voice, assess progress in various areas of space weather, and propose
regular updates for guiding documents. Moderators of ISWAT clusters
(action teams grouped by space environment domains and/or impacts)
and organizers of PSW.1-4 events will present their outlook on the
ISWAT concept, plans for topical action teams activities for the
next two years, approaches to Roadmap updates, and invite community
input and active participation.14:00 - 14:10 Introduction of the
ISWAT concept. 14:10 - 14:40 Updates from PSW.1-4 (5-7 min)14:40 -
15:30: ISWAT moderators presentations, Q&A (5-7 min)16:00 - 17:30:
Panel discussion, Q&A, community feedback Panelists: Jon Linker
(Predictive Science Inc., USA)Manuela Temmer (University of Gratz,
Austria)Mario Bisi (RAL SFTC, UK)Robert Wimmer-Schweingruber (University
of Kiel, Germany)Hermann Opgenoorth (Swedish Institute of Space Physics,
Sweden)Ian Mann (University of Alberta, Canada)Sean Bruinsma (CNES,
France)Anna Belehaki (NOA, Greece)Alexi Glover (ESA)Daniel Heynderickx
(DH Consultancy, Belgium)Norbert Jakowski (DLR, Germany)Manuel Grande
(Aberystwyth University, UK)
---------------------------------------------------------
Title: Accurate prediction and testing of CME arrival and properties
from Sun to Earth
Authors: Cairns, Iver; Van der Holst, Bart; Lobzin, Vasili; Schmidt,
Joachim; Neudegg, Dave; Gopalswamy, Nat; Parkinson, Murray; Steward,
Graham; Kelly, Andrew
2018cosp...42E.492C Altcode:
Most major space weather events are due to fast CMEs and their shocks
interacting with Earth's magnetosphere. Accurate prediction of CME
arrival, propagation, and properties is thus vital for prediction of
space weather at Earth as well as elsewhere in the solar system. In
particular, it is important to accurately predict the CME velocity,
shape, and evolution as functions of position and time, as well as the
flow velocity and magnetic field vector in the coronal and solar wind
plasma, downstream of the CME shock, and inside the CME. We report the
results of simulating 4 separate CMEs from the Sun to 1 AU with the
Space Weather Modelling Framework (SWMF; 2015 and 2016 versions). The
simulations are set up carefully using Wilcox photospheric magnetogram
data and coronagraph images and height-time data below 10 solar radii
from coronagraphs. Outstanding agreement between the observations
and simulations is found for the CME on 29 November 2013 that was
directed primarily towards STEREO A. In particular, the CME's arrival
at STEREO A, deceleration of the CME in agreement with the Gopalswamy
et al. [2011] model, and the time-varying plasma and field (including
B_{z}) agree extremely well. from upstream of the CME shock to within
the CME. Similarly, the results of the simulations to the Earth-directed
CMEs of 4, 6, and 7 September 2017 range from excellent to very good
for the arrival time and for the 1-hour averaged density, radial speed,
B_{z}, and magnetic field strength from the shock to well into the
CME. These results provide strong evidence that we have the capability
with the Space Weather Modeling Framework, when sufficiently carefully
initialized, to accurately predict the properties and evolution of
CMEs and the interplanetary magnetic field and plasma from the Sun to
1 AU. This suggests that we are very close to being able to accurately
predict the triggers for CME-driven space weather at Earth.
---------------------------------------------------------
Title: Metric Type II Onset Frequency and the Longitudinal Extent
of SEP Events
Authors: Makela, Pertti; Gopalswamy, N.; Yashiro, S.; Thakur, N.;
Akiyama, S.; Xie, H.
2018shin.confE.116M Altcode:
Average starting frequencies of the type II bursts
observed during ground level enhancements (GLEs), regular and
filament-eruption-associated solar energetic particle (SEP) events
have distinct, but overlapping, distributions (Gopalswamy et al. 2017,
J. Phys. Conf. Ser., Proc. 16th AIAC). Based on these results, we
studied a possible dependence between the onset frequency of metric
type II radio bursts and the longitudinal spread of the >25 MeV
SEP events from the list of Richardson et al. (2014, Sol. Phys. 289)
covering the first seven years of the STEREO mission. We have used
radio data available online, mainly from the Radio Solar Telescope
Network (RSTN) and e-CALLISTO international network of solar radio
spectrometers, to estimate the type II onset frequencies. We find
a linear trend between the extent of the SEP events and the onset
frequency of the metric type II bursts, but the scatter of data points
is quite large, and correlations are modest.
---------------------------------------------------------
Title: Observational Signatures of CME Structure near the Sun
Authors: Gopalswamy, Nat
2018shin.confE.204G Altcode:
Coronagraphic observations tell us about the electron density
distribution in the CME structure. The famous three-part structure
is determined by the dense prominence core surrounded by a magnetic
structure that appears less dense (void) and forms a bright front by
pushing against the ambient medium. Super-Alfvenic CMEs have another
overlying structure, the shock sheath that became clear in SOHO/LASCO
observations, and is now routinely observed in STEREO images. The
basic magnetic structure underlying CMEs observed in the solar wind
has been determined to be a flux rope, which is identified with the
void structure in coronagraphic images. When an eruption happens, what
is left behind on the Sun is the post-eruption arcade (PEA), which
is formed over the neutral line from which the prominence erupted as
part of the CME. The PEA properties provide important clues to the
understanding of the flux rope structure of CMEs. Coronal dimming is
another key signature, which helps understand the geometry of the flux
rope with respect to the PEA and the direction of axial magnetic flux
rope: PEA and the flux rope are formed due to the same reconnection
process. Forward modeling CMEs observed in coronagraphic images provides
the geometrical properties of flux ropes, while the reconnected flux
in the eruption provides their magnetic properties. The flux rope from
eruption data (FRED) represents the culmination of the CME research
over the past half a century.
---------------------------------------------------------
Title: Panel Discussion: Capacity building in space weather: Globally
coordinated space weather education and outreach initiatives
Authors: Gopalswamy, Nat
2018cosp...42E1249G Altcode:
Panel 2: Capacity building in space weather: Globally coordinated space
weather education and outreach initiatives12:20-13:00, Thursday, 19
July, Room: SR 29 (HH) -Santa Clara Convener: Dibyendu Nandi (CESSI
/ IISER Kolkata, India)Chair: Nat Gopalswamy (NASA, USA)This panel
discussion will bring together diverse organizations involved in space
weather education and outreach activities, provide brief summaries of
ongoing activities and discuss opportunities for new initiatives of the
COSPAR Space Weather Panel towards global coordination in space weather
awareness, education and outreach. 12:20 - 12:40: Opening Statements
(5 min)12:40 - 13:00: Q&A, Discussion PanelPanelists: Simonetta Di
Pippo (UNOOSA), Anna Chulaki (CCMC, USA), Alexi Glover (ESA, COSPAR's
Panel on Capacity Building)Suggested questions to panelists:What aspects
of space weather education/outreach require special attention? What
type of novel education initiatives should we undertake?Do we need a
framework for coordinating international space weather educational
initiatives?What should be the role of COSPAR PSW in space weather
education? The scientific committee on solar terrestrial physics
(SCOSTEP) is an interdisciplinary body of the International Council
for Science (ICSU) collaborating with five scientific unions unions
(IAMAS, IAU, IUGG/IAGA, IUPAP, URSI) and three interdisciplinary bodies
(COSPAR, SCAR, and WDS). SCOSTEP is actively involved in the science,
capacity building, and public outreach activities related to solar
terrestrial physics. By design, space weather is a significant part of
solar terrestrial physics dealing with the short-term variability of
the Sun and how it affects Earth's space environment. The space weather
activities of SCOSTEP are conducted via the scientific programs such
as the current VarSITI (variability of the Sun and Its Terrestrial
Impact). Of particular interest for space weather is the ISEST
(International Study of Earth-affecting Solar Transients) project
directly deals with the two sources of space weather at Earth, viz.,
coronal mass ejections and high speed solar wind and their consequences
(geomagnetic storms and solar energetic particle events). As part
of this project, daily alerts are issued whenever a space-weather
causing feature such as a filament or a coronal hole appears near the
disk center of the Sun. SCOSTEP also collaborates with COSPAR, URSI,
and the International Space Weather Initiative (ISWI) to run Space
Science Schools for PhD students and young postdocs. These capacity
building activities enhances space weather literacy among researchers
in developing countries. SCOSTEP also runs a visiting scholar program
that provides short-term (1-3 months) training in solar terrestrial
relationship in advanced laboratories for students from developing
counties.
---------------------------------------------------------
Title: The COSPAR Capacity Building Workshop at Mekelle University
in Ethiopia
Authors: Gopalswamy, Nat
2018cosp...42E1251G Altcode:
This talk summarizes the experience in organizing the COSPAR
Capacity-Building Workshop "Coronal and Interplanetary Shocks:
Analysis of Data from SOHO, Wind, and e-CALLISTO" in Mekelle University,
Ethiopia. The main objective of the COSPAR Capacity-Building Workshops
is to encourage the scientific use of space data by scientists in
developing countries. In particular, in view of the large number
of extensive archives of data from past and current space missions,
and the ready access to these and the associated analysis software
via the internet, the typical workshop aims to provide a highly
practical training in the use of one or more of these, based on current
missions. In line with this objective, a two-week workshop introduces
data analysis of space-based white-light coronagraph observations
and radio spectral observations from space and ground to study shocks
driven by coronal mass ejections. In particular, the wealth of data
accumulated at the CDAW Data Center at NASA Goddard Space Flight
Center from the ESA/NASA Solar and Heliospheric Observatory (SOHO)
mission, NASA's Solar Terrestrial Relations Observatory (STEREO),
NASA's Wind and Advanced Composition Explorer (ACE) missions are
used. In addition, ground based radio data from the e-CALLISTO network
and the Radio Solar Telescope Network (RSTN) around the globe are used
for the study. Context information from NOAA's GOES mission and NASA's
Solar Dynamics Observatory (SDO) missions are also used. This workshop
enables scientists and students in developing countries where the e-
CALLISTO instruments are deployed to use their data in conjunction
with space data to study Earth- affecting solar transient phenomena.
---------------------------------------------------------
Title: Solar Energetic Particle Events Associated with Prominence
Eruptions: A Case Study
Authors: Thakur, Neeharika; Gopalswamy, N.; Akiyama, S.; Mäkelä,
P.; Yashiro, S.; Xie, H.; Cohen, C.
2018shin.confE.229T Altcode:
We investigated the characteristics the 2015 June 18 large solar
energetic particle (SEP) event (GOES >10 MeV particle flux was
>10 particles/(cm^2 s sr)) associated with a prominence eruption
from the Sun. Recent work (Gopalswamy et al. 2015 ApJ 806, 8) reported
on a set of large SEP events associated with filament eruption (FE)
events occurring outside of active regions. The FE-associated SEPs are
produced by coronal mass ejections (CMEs) that are accelerating and
forming a shock at large distances from the Sun. Such SEPs exhibit a
soft energy spectrum with the spectral index >4 in the 10-100 MeV
range. The 2015 June 18 eruption was associated with an M1.3 flare
and a prominence eruption from the west limb observed by SDO. The
associated CME was fast (speed 1714 km/s), and it was accelerating in
the LASCO field of view (acceleration 27.7 m/s^2). The CME did not
produce a metric type II radio burst but it was associated with an
interplanetary (IP) type II radio burst, implying that a strong shock
formed in the interplanetary medium. We present our initial findings
of this case study of prominence-associated SEPs.
---------------------------------------------------------
Title: Why was the Fluence Spectrum of the 2017 September 10 GLE
So Soft?
Authors: Gopalswamy, Nat; Makela, P.; Yashiro, S.; Xie, H.; Akiyama, S.
2018shin.confE.110G Altcode:
The 2017 September 10 solar energetic particle (SEP) event with ground
level enhancement (GLE) from NOAA AR 12673 was the fourth largest event
in solar cycle 23 in terms of the >10 MeV intensity (1490 pfu). In
spite of the ultra-high initial speed of 3100 km/s and an initial
acceleration of 9.4 km s-2, the GLE was rather weak with an intensity
of only 4.4% above background, much smaller than that of the 2012 May
17 GLE (18.6%) and only slightly higher than the sub-GLE event of 2014
January 6 (2.5%). The 10-100 MeV fluence spectrum (fitted to a power
law) was the third softest among the GLEs of cycles 23 and 24 combined
(Gopalswamy et al. 2016, ApJ 833, 216). The fluence spectral index was
3.17±.06, indicating it is softer than the 2012 May 17 GLE (2.48±0.12)
and the sub-GLE of 2014 January 6 (2.54±0.11). The two GLEs with
spectra softer than that of the 2017 September 10 event are the ones
on 1998 August 24 (3.79±0.12) and 2003 November 2 (3.50±0.12). We
show that poor latitudinal connectivity was the primary reason for
the soft spectrum in these events: the ecliptic distance was larger
than the average value (±13?, Gopalswamy et al. ApJ 765, L30) for
GLE events. If the GeV particles are accelerated near the shock nose,
a larger ecliptic distance would not be favorable for these particles
to reach Earth. In the 2017 September 17 event, the flank connected
to Earth was 20?.3 away from the nose. Since the nose speed of the
shock was >3000 km/s, the flank speed was still large (>2800
km/s), so GeV particles were still produced at the flanks. The lower
energy particles are accelerated over a much larger area of the shock
resulting in a soft spectrum.
---------------------------------------------------------
Title: Sun-to-Earth simulation of the July 12, 2012 geo-effective
CME with EUHFORIA+OpenGGCM
Authors: Scolini, Camilla; Verbeke, Christine; Chané, Emmanuel;
Zuccarello, Francesco; Poedts, Stefaan; Rodriguez, Luciano; Pomoell,
Jens; Cramer, William D.; Raeder, Joachim; Gopalswamy, Nat
2018tess.conf10903S Altcode:
In this work we perform a Sun-to-Earth comprehensive analysis of the
July 12, 2012 CME with the aim of testing the space weather predictive
capabilities of the newly developed EUHFORIA heliospheric model
integrated with a flux rope model. In order to achieve this goal,
we make use of a model chain approach by using EUHFORIA outputs at
Earth as input parameters for the OpenGGCM magnetospheric model. <P
/>We first reconstruct the CME kinematic parameters by means of single-
and multi- spacecraft reconstruction methods based on coronagraphic and
heliospheric CME observations. The magnetic field-related parameters
of the flux-rope are estimated based on imaging observations of the
photospheric and low coronal source region of the eruption. We then
simulate the event with EUHFORIA, using both a cone and a flux-rope CME
model in order to compare the effect of the different CME kinematical
and magnetic input parameters on simulation results at L1. We compare
simulations outputs with in-situ observations of the Interplanetary
CME and we use them as input for the OpenGGCM model, so to investigate
the magnetospheric response to ICME-driven solar wind perturbations
modelled with EUHFORIA. We study the ICME-driven geomagnetic storm
focusing on the predicted geomagnetic activity and compare it with
actual data records. Finally, we discuss the forecasting capabilities
of such kind of approach and its future improvements.
---------------------------------------------------------
Title: Interplanetary type II radio bursts: STEREO observations and
Monte Carlo Simulations
Authors: Krupar, Vratislav; Eastwood, Jonathan P.; Magdalenic, Jasmina;
Gopalswamy, Nat; Kruparova, Oksana; Szabo, Adam
2018EGUGA..20.9950K Altcode:
Coronal mass ejections (CMEs) are responsible for most severe space
weather events such as solar energetic particle events and geomagnetic
storms at Earth. Type II radio bursts are slow drifting emissions
produced by beams of suprathermal electrons accelerated at CME-driven
MHD shock waves propagating through the corona and interplanetary
medium. Here, we report a statistical study of 153 interplanetary
type II radio bursts observed by the two STEREO spacecraft between
March 2008 and August 2014. The shock associated radio emission
was compared with CMEs from the HELCATS (Heliospheric Cataloguing,
Analysis and Techniques Service) catalogue. We found that fast CMEs are
statistically more likely to be associated with the interplanetary type
II radio bursts. We have correlated frequency drifts with white-light
observations in order to localize radio sources with a respect to a CME
geometry. Our results suggest that interplanetary type II bursts are
more likely to have a source region situated close to CME flanks than
close to the CME nose. Finally, we performed Monte Carlo simulations
to study a role of propagation on a visibility of interplanetary type
II radio bursts.
---------------------------------------------------------
Title: Sun-to-Earth simulations of geo-effective Coronal Mass
Ejections with EUHFORIA: a heliospheric-magnetospheric model chain
approach
Authors: Scolini, Camilla; Verbeke, Christine; Poedts, Stefaan;
Rodriguez, Luciano; Mierla, Marilena; Pomoell, Jens; Cramer, William;
Raeder, Jimmy; Gopalswamy, Nat
2018EGUGA..20.6441S Altcode:
In this work we perform a Sun-to-Earth comprehensive analysis of the
July 12, 2012 CME with the aim of testing the space weather predictive
capabilities of the newly developed EUHFORIA heliospheric model
integrated with a flux rope model. In order to achieve this goal,
we make use of a model chain approach by using EUHFORIA outputs at
Earth as input parameters for the OpenGGCM magnetospheric model. We
first reconstruct the CME kinematic parameters by means of single- and
multi- spacecraft reconstruction methods based on coronagraphic and
heliospheric CME observations. The magnetic field-related parameters
of the flux-rope are estimated based on imaging observations of the
photospheric and low coronal source region of the eruption. We then
simulate the event with EUHFORIA, using both a cone and a flux-rope CME
model in order to compare the effect of the different CME kinematical
and magnetic input parameters on simulation results at L1. We compare
simulations outputs with in-situ observations of the Interplanetary
CME and we use them as input for the OpenGGCM model, so to investigate
the magnetospheric response to ICME-driven solar wind perturbations
modelled with EUHFORIA. We study the ICME-driven geomagnetic storm
focusing on the predicted geomagnetic activity and compare it with
actual data records. Finally, we discuss the forecasting capabilities
of such kind of approach and its future improvements.
---------------------------------------------------------
Title: Coronal mass ejections as a new indicator of the active Sun
Authors: Gopalswamy, Nat
2018IAUS..340...95G Altcode: 2018arXiv180411112G
Coronal mass ejections (CMEs) have become one of the key indicators
of solar activity, especially in terms of the consequences of the
transient events in the heliosphere. Although CMEs are closely related
to the sunspot number (SSN), they are also related to other closed
magnetic regions on the Sun such as quiescent filament regions. This
makes CMEs a better indicator of solar activity. While sunspots mainly
represent the toroidal component of solar magnetism, quiescent filaments
(and hence CMEs associated with them) connect the toroidal and poloidal
components via the rush-to-the-pole (RTTP) phenomenon. Taking the end of
RTTP in each hemisphere as an indicator of solar polarity reversal, it
is shown that the north-south reversal asymmetry has a quasi-periodicity
of 3-5 solar cycles. Focusing on the geospace consequences of CMEs, it
is shown that the maximum CME speeds averaged over Carrington rotation
period show good correlation with geomagnetic activity indices such
as Dst and aa.
---------------------------------------------------------
Title: Physical Conditions in the Solar Corona Derived from the
Total Solar Eclipse Observations obtained on 2017 August 21 Using
a Polarization Camera
Authors: Gopalswamy, N.; Yashiro, Seiji; Reginald, Nelson; Thakur,
Neeharika; Thompson, Barbara J.; Gong, Qian
2018AAS...23122008G Altcode:
We present preliminary results obtained by observing the solar corona
during the 2017 August 21 total solar eclipse using a polarization
camera mounted on an eight-inch Schmidt-Cassegrain telescope. The
observations were made from Madras Oregon during 17:19 to 17:21
UT. Total and polarized brightness images were obtained at four
wavelengths (385, 398.5, 410, and 423 nm). The polarization camera had a
polarization mask mounted on a 2048x2048 pixel CCD with a pixel size of
7.4 microns. The resulting images had a size of 975x975 pixels because
four neighboring pixels were summed to yield the polarization and total
brightness images. The ratio of 410 and 385 nm images is a measure
of the coronal temperature, while that at 423 and 398.5 nm images
is a measure of the coronal flow speed. We compared the temperature
map from the eclipse observations with that obtained from the Solar
Dynamics Observatory’s Atmospheric Imaging Assembly images at six EUV
wavelengths, yielding consistent temperature information of the corona.
---------------------------------------------------------
Title: A Study of the Interplanetary Signatures of Earth-Arriving CMEs
Authors: Akiyama, S.; Yashiro, S.; Gopalswamy, N.; Xie, H.; Makela,
P. A.; Kay, C.
2017AGUFMSH51E..06A Altcode:
We studied interplanetary (IP) signatures associated with coronal mass
ejections (CMEs) that are likely to reach Earth. In order to find Earth-
arriving CMEs, we started with disk-center CMEs originating within 30
degrees from the central meridian and the equator. Using the side-view
images from the STEREO mission, we excluded CMEs that faded out before
reaching the Earth orbit, or were captured by other CMEs, or erupted
away from the ecliptic plane. We found 61 Earth- arriving CMEs during
2009/10/01 - 2012/07/31 (inclusive). Though all events were observed
to reach Earth in the STEREO/HI2 field of view, only 34 out of 61
events (56%) were associated with magnetic cloud (MC) or ejecta (EJ)
observed by ACE or Wind. We compared the CME characteristics associated
with 9 MCs, 25 EJs, and 27 no- clear- signature (NCS) events to find
out what might cause the difference in the IP signatures. To avoid
projection effects, we used coronagraph images obtained by the STEREO
mission. The average speed (width) of CMEs associated with MCs, EJs,
and NCSs are 484 km/s (104°), 663 km/s (135°), and 595 km/s (144°),
respectively. CMEs associated with MCs tend to be less energetic than
other types in our dataset. We also checked the coronal holes (CHs)
near the CME source to examine the effect of the CME deflection. In the
case of MCs and EJs, only 22% (2/9) and 28% (7/25) events have CHs near
the source, while 48% (13/27) NCS events have nearby CHs. We discuss
what factors near the Sun cause the observed differences at Earth.
---------------------------------------------------------
Title: Sun-to-Earth simulations of geo-effective Coronal Mass
Ejections with EUHFORIA: a heliospheric-magnetospheric model chain
approach
Authors: Scolini, C.; Verbeke, C.; Gopalswamy, N.; Wijsen, N.; Poedts,
S.; Mierla, M.; Rodriguez, L.; Pomoell, J.; Cramer, W. D.; Raeder, J.
2017AGUFMSH31A2716S Altcode:
Coronal Mass Ejections (CMEs) and their interplanetary counterparts
are considered to be the major space weather drivers. An accurate
modelling of their onset and propagation up to 1 AU represents a
key issue for more reliable space weather forecasts, and predictions
about their actual geo-effectiveness can only be performed by coupling
global heliospheric models to 3D models describing the terrestrial
environment, e.g. magnetospheric and ionospheric codes in the
first place. In this work we perform a Sun-to-Earth comprehensive
analysis of the July 12, 2012 CME with the aim of testing the space
weather predictive capabilities of the newly developed EUHFORIA
heliospheric model integrated with the Gibson-Low (GL) flux rope
model. In order to achieve this goal, we make use of a model chain
approach by using EUHFORIA outputs at Earth as input parameters for the
OpenGGCM magnetospheric model. We first reconstruct the CME kinematic
parameters by means of single- and multi- spacecraft reconstruction
methods based on coronagraphic and heliospheric CME observations. The
magnetic field-related parameters of the flux rope are estimated based
on imaging observations of the photospheric and low coronal source
regions of the eruption. We then simulate the event with EUHFORIA,
testing the effect of the different CME kinematic input parameters on
simulation results at L1. We compare simulation outputs with in-situ
measurements of the Interplanetary CME and we use them as input for
the OpenGGCM model, so to investigate the magnetospheric response to
solar perturbations. From simulation outputs we extract some global
geomagnetic activity indexes and compare them with actual data records
and with results obtained by the use of empirical relations. Finally,
we discuss the forecasting capabilities of such kind of approach and
its future improvements.
---------------------------------------------------------
Title: A Statistical Study of Interplanetary Type II Bursts: STEREO
Observations
Authors: Krupar, V.; Eastwood, J. P.; Magdalenic, J.; Gopalswamy,
N.; Kruparova, O.; Szabo, A.
2017AGUFMSH41B2774K Altcode:
Coronal mass ejections (CMEs) are the primary cause of the most severe
and disruptive space weather events such as solar energetic particle
(SEP) events and geomagnetic storms at Earth. Interplanetary type II
bursts are generated via the plasma emission mechanism by energetic
electrons accelerated at CME-driven shock waves and hence identify
CMEs that potentially cause space weather impact. As CMEs propagate
outward from the Sun, radio emissions are generated at progressively
at lower frequencies corresponding to a decreasing ambient solar
wind plasma density. We have performed a statistical study of 153
interplanetary type II bursts observed by the two STEREO spacecraft
between March 2008 and August 2014. These events have been correlated
with manually-identified CMEs contained in the Heliospheric Cataloguing,
Analysis and Techniques Service (HELCATS) catalogue. Our results confirm
that faster CMEs are more likely to produce interplanetary type II radio
bursts. We have compared observed frequency drifts with white-light
observations to estimate angular deviations of type II burst propagation
directions from radial. We have found that interplanetary type II bursts
preferably arise from CME flanks. Finally, we discuss a visibility of
radio emissions in relation to the CME propagation direction.
---------------------------------------------------------
Title: Relationship between SEP Peak intensity and CME Acceleration,
Speed and Width
Authors: Xie, H.; St Cyr, O. C.; Makela, P. A.; Gopalswamy, N.
2017AGUFMSH33C..01X Altcode:
We study the large solar energetic particle (SEP) events that were
detected by GOES in the >10 MeV energy channel during December 2006
to January 2016. Data used in this study includes the Solar Electron
Proton Telescope (SEPT) and High Energy Telescopes (HET) on STEREO
A and B, the Electron, Proton, and Alpha Monitor (EPAM) on ACE,
and the Energetic and Relativistic Nuclei and Electron instrument
(ERNE) on SOHO. By choosing the smallest connection angles between
SEP solar locations and magnetic foot-points of each spacecraft, we
divide SEP events as SOHO SEPs or STEREO SEPs. We then compute the SEP
peak intensity I0 at the center of the Gausssian using the Gausssian
expression from Richardson et al. (2014) and study the relationship
between SEP electron and proton peak intensity and CME acceleration,
speed and width. By using I0 derived from multi-spacecraft observations
we found that the correlations between SEP peak intensity and CME
acceleration and speed improved. We also found that this correlation
can be further improved by taking into account the effects of CME width
and its solar source latitude. The implication for the SEP forecast
of our obtained results will be discussed.
---------------------------------------------------------
Title: Using the Coronal Evolution to Successfully Forward Model CMEs'
In Situ Magnetic Profiles
Authors: Kay, C.; Gopalswamy, N.
2017JGRA..12211810K Altcode: 2017arXiv171003825K
Predicting the effects of a coronal mass ejection (CME) impact requires
knowing if impact will occur, which part of the CME impacts, and its
magnetic properties. We explore the relation between CME deflections
and rotations, which change the position and orientation of a CME,
and the resulting magnetic profiles at 1 AU. For 45 STEREO-era,
Earth-impacting CMEs, we determine the solar source of each CME,
reconstruct its coronal position and orientation, and perform a
ForeCAT (Forecasting a CME's Altered Trajectory) simulation of the
coronal deflection and rotation. From the reconstructed and modeled
CME deflections and rotations, we determine the solar cycle variation
and correlations with CME properties. We assume no evolution between
the outer corona and 1 AU and use the ForeCAT results to drive the
ForeCAT In situ Data Observer (FIDO) in situ magnetic field model,
allowing for comparisons with ACE and Wind observations. We do not
attempt to reproduce the arrival time. On average FIDO reproduces
the in situ magnetic field for each vector component with an error
equivalent to 35% of the average total magnetic field strength when the
total modeled magnetic field is scaled to match the average observed
value. Random walk best fits distinguish between ForeCAT's ability to
determine FIDO's input parameters and the limitations of the simple flux
rope model. These best fits reduce the average error to 30%. The FIDO
results are sensitive to changes of order a degree in the CME latitude,
longitude, and tilt, suggesting that accurate space weather predictions
require accurate measurements of a CME's position and orientation.
---------------------------------------------------------
Title: On the Onset Frequency of Metric Type II Radio Bursts and
the Longitudinal Extent of the Associated SEP Events
Authors: Makela, P. A.; Gopalswamy, N.; Yashiro, S.; Thakur, N.;
Akiyama, S.; Xie, H.
2017AGUFMSH33C..04M Altcode:
In a recent study Gopalswamy et al. (2017, J. Phys. Conf. Ser.,
Proc. 16th AIAC) found that the ground level enhancements (GLEs),
regular solar energetic particle (SEP) events and filament eruption
(FE) associated SEP events have distinct average starting frequencies of
the associated type II bursts, although the distributions overlap. They
also found that the initial acceleration of the coronal mass ejections
(CMEs) associated with the three groups were distinct. Based on
these earlier results emphasizing a hierarchical relationship of CME
kinematics and SEP events, we studied the possible dependence between
the longitudinal spread of the SEP events and the onset frequency of
metric type II. The studied >25 MeV SEP events are from the list
of Richardson et al. (2014, Sol. Phys. 289) covering the first seven
years of the STEREO mission. However, our preliminary results show
only a weak correlation between the extent of the SEP event and the
onset frequency of the metric type II radio burst.
---------------------------------------------------------
Title: Prediction of CMEs and Type II Bursts from Sun to Earth
Authors: Cairns, I. H.; Schmidt, J. M.; Gopalswamy, N.; van der
Holst, B.
2017AGUFMSH31D..06C Altcode:
Most major space weather events are due to fast CMEs and their
shocks interacting with Earth's magnetosphere. SImilarly, type II
solar radio bursts are well-known signatures of CMEs and their shocks
moving through the corona and solar wind. The properties of the space
weather events and the type II radio bursts depend sensitively on the
CME velocity, shape, and evolution as functions of position and time,
as well as on the magnetic field vector in the coronal and solar
wind plasma, downstream of the CME shock, and inside the CME. We
report simulations of CMEs and type II bursts from the Sun to Earth
with the Space Weather Modelling Framework (2015 and 2016 versions),
set up carefully using relevant data, and a kinetic radio emission
theory. Excellent agreement between observations, simulations, and
theory are found for the coronal (metric) type II burst of 7 September
2014 and associated CME, including the lack of radio emission in the
solar wind beyond about 10 solar radii. Similarly, simulation of a CME
and type II burst from the Sun to 1 AU over the period 29 November -
1 December 2013 yield excellent agreement for the radio burst from 10
MHz to 30 kHz for STEREO A and B and Wind, arrival of the CME at STEREO
A within 1 hour reported time, deceleration of the CME in agreement with
the Gopalswamy et al. [2011] observational analyses, and B<SUB>z</SUB>
rotations at STEREO A from upstream of the CME shock to within the
CME. These results provide strong support for the type II theory and
also that the Space WeatherModeling Framework can accurately predict the
properties and evolution of CMEs and the interplanetary magnetic field
and plasma from the Sun to 1 AU when sufficiently carefully initialized.
---------------------------------------------------------
Title: Reproducing the Magnetic Field of Near-Earth ICMEs
Authors: Kay, C.; Gopalswamy, N.
2017AGUFMSH34B..03K Altcode:
Understanding the magnetic profile of an ICME is critical for
predicting its potential effects near Earth. Kay et al. (2017)
introduced the ForeCAT In situ Data Observer (FIDO), which uses the
results of a coronal CME deflection and rotation model to orient
a simple Lundquist force-flux rope, which is then propagated over a
synthetic spacecraft. This work showed the potential of the FIDO model
for predicting ICME magnetic field on roughly hourly time scales,
and that the in situ profiles are very sensitive to precise location
and orientation of the ICME flux rope. We expand upon this work with a
recent study of 45 STEREO-era near-Earth CMEs and consider the circular
flux rope (Nieves-Chinchilla et al. 2016) in addition to the Lundquist
flux rope. We quantitatively analyze the goodness-of-fit of the FIDO
fits and determine the circumstances under which the FIDO model performs
best. Finally, we explore the limitations of the flux rope model itself
to reproduce the data, versus our ability to determine the appropriate
values of its free parameters.
---------------------------------------------------------
Title: Deflection and Rotation of STEREO-Era CMEs
Authors: Kay, C.; Gopalswamy, N.
2017AGUFMSH51E..03K Altcode:
Understanding the location and orientation of CMEs is critical for
predicting whether they will impact Earth, and what their magnetic
orientation may be upon impact. This requires accounting for any
deflection or rotation that may occur as the CME propagates away from
the Sun. For 45 Earth-directed CMEs occurring between 2007 and 2014,
all observed by both STEREO spacecraft, we use EUV observations to
determine the precise initial location, then reconstruct the position
and orientation in COR1 and COR2 using the GCS technique. Using a
model for the in situ magnet field we also determine the location and
orientation near 1 AU. We then simulate the deflection and rotation
of these CMEs using the ForeCAT model (Kay et al. 2015). We find
good agreement between the observed and simulated CME deflections and
rotations. These CMEs span the end of Solar Cycle 23 to the maximum of
Solar Cycle 24 allowing us to investigate the changes in CME deflection
and rotation. We find that the magnitude and direction of the deflection
and rotation are determined by a balance between the changes in the
background magnetic field and the changes in the CME properties,
such as the mass and velocity.
---------------------------------------------------------
Title: A Sun-to-Earth Analysis of Magnetic Helicity of the 2013
March 17-18 Interplanetary Coronal Mass Ejection
Authors: Pal, Sanchita; Gopalswamy, Nat; Nandy, Dibyendu; Akiyama,
Sachiko; Yashiro, Seiji; Makela, Pertti; Xie, Hong
2017ApJ...851..123P Altcode: 2017arXiv171201114P
We compare the magnetic helicity in the 2013 March 17-18 interplanetary
coronal mass ejection (ICME) flux rope at 1 au and in its solar
counterpart. The progenitor coronal mass ejection (CME) erupted on
2013 March 15 from NOAA active region 11692 and is associated with
an M1.1 flare. We derive the source region reconnection flux using
the post-eruption arcade (PEA) method that uses the photospheric
magnetogram and the area under the PEA. The geometrical properties of
the near-Sun flux rope is obtained by forward-modeling of white-light
CME observations. Combining the geometrical properties and the
reconnection flux, we extract the magnetic properties of the CME
flux rope. We derive the magnetic helicity of the flux rope using its
magnetic and geometric properties obtained near the Sun and at 1 au. We
use a constant-α force-free cylindrical flux rope model fit to the
in situ observations in order to derive the magnetic and geometric
information of the 1 au ICME. We find a good correspondence in both
amplitude and sign of the helicity between the ICME and the CME,
assuming a semi-circular (half torus) ICME flux rope with a length of
π au. We find that about 83% of the total flux rope helicity at 1 au
is injected by the magnetic reconnection in the low corona. We discuss
the effect of assuming flux rope length in the derived value of the
magnetic helicity. This study connecting the helicity of magnetic flux
ropes through the Sun-Earth system has important implications for the
origin of helicity in the interplanetary medium and the topology of
ICME flux ropes at 1 au and hence their space weather consequences.
---------------------------------------------------------
Title: Prominence Eruption Initiated by Helical Kink Instability of
an Embedded Flux Rope
Authors: Vemareddy, P.; Gopalswamy, N.; Ravindra, B.
2017ApJ...850...38V Altcode: 2017arXiv170910035V
We study the triggering mechanism of a limb-prominence eruption and
the associated coronal mass ejection (CME) near AR 12342 using Solar
Dynamics Observatory and Large Angle and Spectrometric Coronagraph/Solar
Heliospheric Observatory observations. The prominence is seen with an
embedded flux thread (FT) at one end and bifurcates from the middle to
a different footpoint location. The morphological evolution of the FT
is similar to that of an unstable flux rope (FR), which we regard as
a prominence-embedded FR. The FR twist exceeds the critical value. In
addition, the morphology of the prominence plasma in 304 Å images marks
the helical nature of the magnetic skeleton, with a total of 2.96 turns
along arc length. The potential field extrapolation model indicates that
the critical height of the background magnetic field gradient falls
within the inner corona (105 Mm), which is consistent with the extent
of coronal plasma loops. These results suggest that the helical kink
instability in the embedded FR caused the slow rise of the prominence to
the height of the torus instability domain. Moreover, the differential
emission measure analysis unveils heating of the prominence plasma to
coronal temperatures during an eruption, suggesting reconnection-related
heating underneath the upward rising embedded FR. The prominence starts
with a slow rise motion of 10 km s<SUP>-1</SUP>, which is followed by
fast and slow acceleration phases that have an average acceleration of
28.9 m s<SUP>-2 </SUP>and 2.4 m s<SUP>-2</SUP> in C2 and C3 field of
view, respectively. As predicted by previous numerical simulations, the
observed synchronous kinematic profiles of the CME leading edge and the
core support the involved FR instability in the prominence initiation.
---------------------------------------------------------
Title: Toward a Next Generation Solar Coronagraph: Development of
a Compact Diagnostic Coronagraph on the ISS
Authors: Cho, K. -S.; Bong, S. -C.; Choi, S.; Yang, H.; Kim, J.;
Baek, J. -H.; Park, J.; Lim, E. -K.; Kim, R. -S.; Kim, S.; Kim,
Y. -H.; Park, Y. -D.; Clarke, S. W.; Davila, J. M.; Gopalswamy, N.;
Nakariakov, V. M.; Li, B.; Pinto, R. F.
2017JKAS...50..139C Altcode:
The Korea Astronomy and Space Science Institute plans to develop
a coronagraph in collaboration with National Aeronautics and Space
Administration (NASA) and to install it on the International Space
Station (ISS). The coronagraph is an externally occulted one-stage
coronagraph with a field of view from 3 to 15 solar radii. The
observation wavelength is approximately 400 nm, where strong Fraunhofer
absorption lines from the photosphere experience thermal broadening and
Doppler shift through scattering by coronal electrons. Photometric
filter observations around this band enable the estimation of
2D electron temperature and electron velocity distribution in the
corona. Together with a high time cadence (<12 min) of corona images
used to determine the geometric and kinematic parameters of coronal
mass ejections, the coronagraph will yield the spatial distribution
of electron density by measuring the polarized brightness. For the
purpose of technical demonstration, we intend to observe the total
solar eclipse in August 2017 with the filter system and to perform a
stratospheric balloon experiment in 2019 with the engineering model
of the coronagraph. The coronagraph is planned to be installed on the
ISS in 2021 for addressing a number of questions (e.g., coronal heating
and solar wind acceleration) that are both fundamental and practically
important in the physics of the solar corona and of the heliosphere.
---------------------------------------------------------
Title: Extreme Solar Eruptions and their Space Weather Consequences
Authors: Gopalswamy, Nat
2017arXiv170903165G Altcode:
Solar eruptions generally refer to coronal mass ejections (CMEs)
and flares. Both are important sources of space weather. Solar flares
cause sudden change in the ionization level in the ionosphere. CMEs
cause solar energetic particle (SEP) events and geomagnetic storms. A
flare with unusually high intensity and/or a CME with extremely
high energy can be thought of examples of extreme events on the
Sun. These events can also lead to extreme SEP events and/or geomagnetic
storms. Ultimately, the energy that powers CMEs and flares are stored in
magnetic regions on the Sun, known as active regions. Active regions
with extraordinary size and magnetic field have the potential to
produce extreme events. Based on current data sets, we estimate the
sizes of one-in-hundred and one-in-thousand year events as an indicator
of the extremeness of the events. We consider both the extremeness in
the source of eruptions and in the consequences. We then compare the
estimated 100-year and 1000-year sizes with the sizes of historical
extreme events measured or inferred.
---------------------------------------------------------
Title: A Hierarchical Relationship between the Fluence Spectra and
CME Kinematics in Large Solar Energetic Particle Events: A Radio
Perspective
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.; Thakur, N.;
Akiyama, S.; Xie, H.
2017JPhCS.900a2009G Altcode: 2017arXiv170700209G
We report on further evidence that solar energetic particles are
organized by the kinematic properties of coronal mass ejections
(CMEs)[1]. In particular, we focus on the starting frequency of type II
bursts, which is related to the distance from the Sun where the radio
emission starts. We find that the three groups of solar energetic
particle (SEP) events known to have distinct values of CME initial
acceleration, also have distinct average starting frequencies of the
associated type II bursts. SEP events with ground level enhancement
(GLE) have the highest starting frequency (107 MHz), while those
associated with filament eruption (FE) in quiescent regions have the
lowest starting frequency (22 MHz); regular SEP events have intermediate
starting frequency (81 MHz). Taking the onset time of type II bursts as
the time of shock formation, we determine the shock formation heights
measured from the Sun center. We find that the shocks form on average
closest to the Sun (1.51 Rs) in GLE events, farthest from the Sun
in FE SEP events (5.38 Rs), and at intermediate distances in regular
SEP events (1.72 Rs). Finally, we present the results of a case study
of a CME with high initial acceleration (∼3 km s<SUP>-2</SUP>) and
a type II radio burst with high starting frequency (∼200 MHz) but
associated with a minor SEP event. We find that the relation between
the fluence spectral index and CME initial acceleration continues to
hold even for this minor SEP event.
---------------------------------------------------------
Title: CME Velocity and Acceleration Error Estimates Using the
Bootstrap Method
Authors: Michalek, Grzegorz; Gopalswamy, Nat; Yashiro, Seiji
2017SoPh..292..114M Altcode:
The bootstrap method is used to determine errors of basic attributes of
coronal mass ejections (CMEs) visually identified in images obtained by
the Solar and Heliospheric Observatory (SOHO) mission's Large Angle and
Spectrometric Coronagraph (LASCO) instruments. The basic parameters of
CMEs are stored, among others, in a database known as the SOHO/LASCO
CME catalog and are widely employed for many research studies. The
basic attributes of CMEs (e.g. velocity and acceleration) are obtained
from manually generated height-time plots. The subjective nature of
manual measurements introduces random errors that are difficult to
quantify. In many studies the impact of such measurement errors is
overlooked. In this study we present a new possibility to estimate
measurements errors in the basic attributes of CMEs. This approach is
a computer-intensive method because it requires repeating the original
data analysis procedure several times using replicate datasets. This
is also commonly called the bootstrap method in the literature. We
show that the bootstrap approach can be used to estimate the errors
of the basic attributes of CMEs having moderately large numbers of
height-time measurements. The velocity errors are in the vast majority
small and depend mostly on the number of height-time points measured
for a particular event. In the case of acceleration, the errors are
significant, and for more than half of all CMEs, they are larger than
the acceleration itself.
---------------------------------------------------------
Title: Comparison of the coronal mass ejection shock acceleration
of three widespread SEP events during solar cycle 24
Authors: Xie, H.; Mäkelä, P.; St. Cyr, O. C.; Gopalswamy, N.
2017JGRA..122.7021X Altcode:
We studied three solar energetic particle (SEP) events observed on 14
August 2010, 3 November 2011, and 5 March 2013 by Solar Terrestrial
Relations Observatory (STEREO) A, B, and near-Earth (L1) spacecraft
with a longitudinal distribution of particles >90°. Using
a forward modeling method combined with extreme ultraviolet and
white-light images, we determined the angular extent of the shock,
the time and location (cobpoint) of the shock intersection with
the magnetic field line connecting to each spacecraft, and compute
the shock speed at the cobpoint of each spacecraft. We then examine
whether the observations of SEPs at each spacecraft were accelerated
and injected by the spatially extended shocks or whether another
mechanism such as cross-field transport is required for an alternative
explanation. Our analyses results indicate that the SEPs observed
at the three spacecraft on 3 November, STEREO B (STB) and L1 on 14
August, and the 5 March SEP event at STEREO A (STA) can be explained
by the direct shock acceleration. This is consistent with the observed
significant anisotropies, short time delays between particle release
times and magnetic connection times, and sharp rises in the SEP
time profiles. Cross-field diffusion is the likely cause for the 14
August SEP event observed by STA and the 5 March SEPs observed by STB
and L1 spacecraft, as particle observations featured weak electron
aniotropies and slow rising intensity profiles. Otherwise, the wide
longitudinal spread of these SEP increases would require an existence
of a circumsolar shock, which may not be a correct assumption in the
corona and heliosphere.
---------------------------------------------------------
Title: New Evidence for a Coronal Mass Ejection-driven High Frequency
Type II Burst near the Sun
Authors: Kumari, Anshu; Ramesh, R.; Kathiravan, C.; Gopalswamy, N.
2017ApJ...843...10K Altcode:
We report observations of the high frequency type II radio burst
(≈430-30 MHz) that occurred in the solar corona on 2015 November
4. The drift rate of the burst, estimated close to the start frequency
of its fundamental component (≈215 MHz), is unusually high (≈2
MHz s<SUP>-1</SUP>). Our analysis shows that the estimated speed
of the magnetohydrodynamic shock driver of the burst varies with
time. The peak speed and acceleration are very large, ≈ 2450
{km} {{{s}}}<SUP>-1</SUP> and ≈ 17 {km} {{{s}}}<SUP>-2</SUP>,
respectively. There is spatio-temporal correlation between the type II
burst and the associated coronal mass ejection (CME) in the whitelight
and extreme-ultraviolet images. The time profile of the shock speed and
the light curve of the associated soft X-ray flare correlate well. These
results indicate that in the present case, (I) the magnetohydrodynamic
shock responsible for the high frequency coronal type II burst is driven
by the CME and (II) the time profile of the type II burst shock speed
represents the near-Sun kinematics of the CME.
---------------------------------------------------------
Title: Direction Finding Analysis of the 2012 July 6 Radio Burst
Authors: Makela, Pertti; Gopalswamy, Nat; Akiyama, Sachiko
2017shin.confE.141M Altcode:
The 2012 July 6 X1.1 flare at S13W59 and a halo CME with a space
speed of 1900 km/s were associated with type III and type II radio
bursts. The metric-to-decametric type II radio burst extended down to 5
MHz. Simultaneously a slowly drifting feature with a harmonic structure
was observed by Wind and STEREO radio receivers around and below 1 MHz,
above the strong type III radio burst at lower frequencies. The radio
direction finding analysis of this interplanetary (IP) type II radio
burst indicates that the radio source was located near the nose and
towards the southern flank of the CME-driven shock. This results is
in accordance with previous suggestions that when the metric and IP
type II burst are overlapping, the IP type II radio burst originates
near the shock nose, whereas the source of the metric type II burst
is closer to the Sun in the shock flank region.
---------------------------------------------------------
Title: Observations and Simulations of the Sun-to-Earth Evolution
of a STEREO-Era Set of Earth-Impacting CMEs and their In Situ
Magnetic Field
Authors: Kay, Christina; Gopalswamy, Nat
2017shin.confE..20K Altcode:
Coronal mass ejections (CMEs) drive extreme space weather events
throughout the solar system. Predicting the effects of a CME impact
requires knowing not only if a CME will impact a given point, but also
which part of the CME impacts, and what its magnetic properties are upon
impact. We explore the relation between CME deflections and rotations,
which change the position and orientation of a CME, and the resulting
magnetic profiles at 1 AU. For 45 STEREO-era, Earth-impacting CMEs, we
determine the region from which each CME erupts, reconstruct its coronal
position and orientation, and perform a ForeCAT (Kay et al. 2015)
simulation of the coronal deflection and rotation. From this large set
of reconstructed and modeled CME deflections and rotations we determine
variations in the behavior over the solar cycle as well as correlations
with CME properties. We then couple the ForeCAT results with the FIDO in
situ magnetic field model (Kay et al. 2017), allowing for comparisons
with ACE and Wind observations. FIDO successfully reproduces the in
situ magnetic field for all but three of the CMEs. From random walk best
fits, we distinguish between ForeCAT's ability to determine FIDO's input
parameters, and the limitations of using a simple flux rope model to
reproduce complicated in situ structures. We find that the FIDO results
are quite sensitive to changes of order a degree in the CME latitude,
longitude, and tilt, suggesting that accurate space weather predictions
require accurate measurements of a CME's position and orientation.
---------------------------------------------------------
Title: Deflection and Rotation of CMEs from Active Region 11158
Authors: Kay, Christina; Gopalswamy, Nat; Xie, Hong; Yashiro, Seiji
2017SoPh..292...78K Altcode: 2017arXiv170407694K
Between 13 and 16 February 2011, a series of coronal mass ejections
(CMEs) erupted from multiple polarity inversion lines within
active region 11158. For seven of these CMEs we employ the graduated
cylindrical shell (GCS) flux rope model to determine the CME trajectory
using both Solar Terrestrial Relations Observatory (STEREO) extreme
ultraviolet (EUV) and coronagraph images. We then use the model called
Forecasting a CME's Altered Trajectory (ForeCAT) for nonradial CME
dynamics driven by magnetic forces to simulate the deflection and
rotation of the seven CMEs. We find good agreement between ForeCAT
results and reconstructed CME positions and orientations. The
CME deflections range in magnitude between 10<SUP>∘</SUP> and
30<SUP>∘</SUP>. All CMEs are deflected to the north, but we find
variations in the direction of the longitudinal deflection. The
rotations range between 5<SUP>∘</SUP> and 50<SUP>∘</SUP> with both
clockwise and counterclockwise rotations. Three of the CMEs begin with
initial positions within 2<SUP>∘</SUP> from one another. These three
CMEs are all deflected primarily northward, with some minor eastward
deflection, and rotate counterclockwise. Their final positions and
orientations, however, differ by 20<SUP>∘</SUP> and 30<SUP>∘</SUP>,
respectively. This variation in deflection and rotation results from
differences in the CME expansion and radial propagation close to the
Sun, as well as from the CME mass. Ultimately, only one of these seven
CMEs yielded discernible in situ signatures near Earth, although the
active region faced toward Earth throughout the eruptions. We suggest
that the differences in the deflection and rotation of the CMEs can
explain whether each CME impacted or missed Earth.
---------------------------------------------------------
Title: Cataloguing radio emission associated with coronal mass
ejections: results from the HELCATS project
Authors: Eastwood, Jonathan; Krupar, Vratislav; Magdalenic, Jasmina;
Bisi, Mario; Gopalswamy, Nat; Davies, Jackie; Harrison, Richard;
Barnes, David
2017EGUGA..19.5249E Altcode:
The goal of the Heliospheric Cataloguing, Analysis and Techniques
Service (HELCATS) is to add value to the STEREO dataset by cataloguing
the properties of coronal mass ejections and corotating interaction
regions observed by STEREO. As part of this work, the complementary
nature of radio measurements and white light observations has been
assessed. Here we report on the cataloguing of slowly-drifting radio
emission observed by STEREO WAVES in conjunction with events identified
in the HELCATS manually-generated coronal mass ejection catalogue. We
present preliminary statistical results derived from the catalogue,
in particular the extent to which radio emission is more likely to
occur in conjunction with fast coronal mass ejections. We further use
the catalogue to make an initial assessment of the angular deviation
between radio emission and coronal mass ejection motion, in order to
determine which part of the coronal mass ejection contributes most to
the radio emission. HELCATS is project 606692 of the European Union's
Seventh Framework Programme.
---------------------------------------------------------
Title: Estimation of Reconnection Flux Using Post-eruption Arcades
and Its Relevance to Magnetic Clouds at 1 AU
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Xie, H.
2017SoPh..292...65G Altcode: 2017arXiv170101943G
We report on a new method to compute the flare reconnection (RC)
flux from post-eruption arcades (PEAs) and the underlying photospheric
magnetic fields. In previous works, the RC flux has been computed using
the cumulative flare ribbon area. Here we obtain the RC flux as the flux
in half of the area underlying the PEA in EUV imaged after the flare
maximum. We apply this method to a set of 21 eruptions that originated
near the solar disk center in Solar Cycle 23. We find that the RC flux
from the arcade method (Φ<SUB>rA</SUB>) has excellent agreement with
the flux from the flare-ribbon method (Φ<SUB>rR</SUB>) according to
Φ<SUB>rA</SUB>=1.24 (Φ<SUP>r<SUB>R</SUB>) 0.99</SUP>. We also find
Φ<SUB>rA</SUB> to be correlated with the poloidal flux (Φ<SUB>P</SUB>)
of the associated magnetic cloud at 1 AU: Φ<SUB>P</SUB>=1.20
(Φ<SUP>r<SUB>A</SUB>) 0.85</SUP>. This relation is nearly identical
to that obtained by Qiu et al. (Astrophys. J. 659, 758, 2007) using
a set of only 9 eruptions. Our result supports the idea that flare
reconnection results in the formation of the flux rope and PEA as a
common process.
---------------------------------------------------------
Title: A Close Connection between Flares and Coronal Mass Ejections
Revealed by the Reconnected Flux in the Solar Source Region
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Yashiro, Seiji; Xie, Hong
2017EGUGA..1918101G Altcode:
We report on a study of the properties of flares and coronal mass
ejections (CMEs) associated with interplanetary CMEs (ICMEs) detected
close to Earth. The study is based on a set of magnetic clouds (MCs)
and non-cloud ejecta (EJ) originating very close to the solar disk. We
computed the total reconnected flux in each of the associated solar
eruptions and compared it with the CME, flare, and ICME properties. We
find that the reconnection flux is closely related to the parameters
describing the three phenomena. By fitting flux ropes to the coronagraph
data, we show that the CME magnetic field in the corona is significantly
higher than the ambient magnetic field. The radial dependence of the
Flux-rope magnetic field is faster than that of the ambient magnetic
field. This technique provides a simple method to predict the magnetic
properties of ICMEs at various destination in the heliosphere.
---------------------------------------------------------
Title: Predicting the Magnetic Field of Earth-impacting CMEs
Authors: Kay, C.; Gopalswamy, N.; Reinard, A.; Opher, M.
2017ApJ...835..117K Altcode:
Predicting the impact of coronal mass ejections (CMEs) and the southward
component of their magnetic field is one of the key goals of space
weather forecasting. We present a new model, the ForeCAT In situ Data
Observer (FIDO), for predicting the in situ magnetic field of CMEs. We
first simulate a CME using ForeCAT, a model for CME deflection and
rotation resulting from the background solar magnetic forces. Using
the CME position and orientation from ForeCAT, we then determine the
passage of the CME over a simulated spacecraft. We model the CME’s
magnetic field using a force-free flux rope and we determine the in
situ magnetic profile at the synthetic spacecraft. We show that FIDO
can reproduce the general behavior of four observed CMEs. FIDO results
are very sensitive to the CME’s position and orientation, and we
show that the uncertainty in a CME’s position and orientation from
coronagraph images corresponds to a wide range of in situ magnitudes
and even polarities. This small range of positions and orientations
also includes CMEs that entirely miss the satellite. We show that two
derived parameters (the normalized angular distance between the CME
nose and satellite position and the angular difference between the
CME tilt and the position angle of the satellite with respect to the
CME nose) can be used to reliably determine whether an impact or miss
occurs. We find that the same criteria separate the impacts and misses
for cases representing all four observed CMEs.
---------------------------------------------------------
Title: A Hierarchical Relationship between CME Properties and the
Fluence Spectral Index of Large Solar Energetic Particle Events
Authors: Gopalswamy, N.; Yashiro, Seiji; Thakur, Neeharika; Makela,
Pertti; Xie, Hong; Akiyama, Sachiko
2017AAS...22932503G Altcode:
We report on a hierarchical relationship found between properties of
white-light coronal mass ejections (CMEs) and the fluence spectral
indices of the associated Large Solar Energetic Particle (SEP)
Events. We consider 74 large SEP events from the western hemisphere
in solar cycles 23 and 24 by multiple spacecraft (SAMPEX, GOES, and
STEREO). The associated CMEs are observed by SOHO. We find that CMEs
with high initial acceleration are associated with SEP events with the
hardest fluence spectra, while those with lowest initial acceleration
have SEP events with the softest fluence spectra; CMEs with intermediate
initial acceleration result in SEP events with moderately hard fluence
spectra. Impulsive acceleration leading to high CME speeds close to
the Sun results in shock formation close to the Sun, where the ambient
magnetic field and density are high and the particles are energized more
efficiently. Slowly accelerating CMEs drive shocks at large distances
from the Sun, where the magnetic field and density have fallen off
significantly, reducing the efficiency of shock acceleration. These
opposite extremes are represented by ground level enhancement (GLE)
events that have high speeds early on (high initial acceleration) and
the SEP events associated with CMEs from quiescent filament region
that have low early speeds (low initial acceleration). This finding
strongly supports the idea that CME-driven shocks accelerate SEPs and
the heliocentric distance where the acceleration takes place decides
the hardness of the SEP fluence spectrum.
---------------------------------------------------------
Title: CME association rate of solar flares in cycles 23 and 24
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.; Makela, P. A.;
Masuda, S.
2016AGUFMSH13C2320Y Altcode:
We report on the solar cycle variation of coronal mass ejection (CME)
association rate of solar flares in cycles 23 and 24. There were 1,442
and 707 M flares in the cycles 23 and 24, respectively. We examine the
CME associations of these flares using SOHO/LASCO and STEREO/SECCHI/COR1
images. Because the CME association rate increases with the soft X-ray
flare size, we examined the CME association rate for a given flare
size. We found that the CME association of the M1 flares was 43% in
the cycle 23 and decreased to 33% in the cycle 24. The same trend was
found in the M2 (57% vs 50%) and M3-M5 flares (61% vs 55%). A supporting
observation is that the average decay time of the M1 flares was 14.3
min in the cycle 23 and 12.2 min in the cycle 24, indicating a decrease
of long-duration-event (LDE) flares, which are closely related to the
CMEs. We also found that the fraction of CME-poor active regions (ARs)
was 13% (11 out of 87 ARs) in the cycle 23 and 22% (10 out of 45 ARs)
in the cycle 24. These results suggest that the performance of the CME
prediction algorithms based on the cycle 23 data could be degraded in
the cycle 24.
---------------------------------------------------------
Title: Statistical Analysis of Periodic Oscillations in LASCO Coronal
Mass Ejection Speeds
Authors: Michalek, G.; Shanmugaraju, A.; Gopalswamy, N.; Yashiro,
S.; Akiyama, S.
2016SoPh..291.3751M Altcode: 2016SoPh..tmp..165M
A large set of coronal mass ejections (CMEs, 3463) has been selected to
study their periodic oscillations in speed in the Solar and Heliospheric
Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph
(LASCO) field of view. These events, reported in the SOHO/LASCO catalog
in the period of time 1996 - 2004, were selected based on having at
least 11 height-time measurements. This selection criterion allows us
to construct at least ten-point speed-distance profiles and evaluate
kinematic properties of CMEs with a reasonable accuracy. To identify
quasi-periodic oscillations in the speed of the CMEs a sinusoidal
function was fitted to speed-distance profiles and the speed-time
profiles. Of the considered events 22 % revealed periodic velocity
fluctuations. These speed oscillations have on average amplitude
equal to 87 kms−<SUP>1</SUP> and period 7.8 R<SUB>⊙</SUB>/241 min
(in distance/time). The study shows that speed oscillations are a
common phenomenon associated with CME propagation implying that all
the CMEs have a similar magnetic flux-rope structure. The nature of
oscillations can be explained in terms of magnetohydrodynamic (MHD)
waves excited during the eruption process. More accurate detection of
these modes could, in the future, enable us to characterize magnetic
structures in space (space seismology).
---------------------------------------------------------
Title: Erratum: Erratum to: Dynamics of CMEs in the LASCO Field
of View
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.; Bronarska, K.
2016SoPh..291.3869M Altcode: 2016SoPh..tmp..159M
No abstract at ADS
---------------------------------------------------------
Title: The 2012 July 23 Backside Eruption: An Extreme Energetic
Particle Event?
Authors: Gopalswamy, N.; Yashiro, S.; Thakur, N.; Mäkelä, P.; Xie,
H.; Akiyama, S.
2016ApJ...833..216G Altcode: 2016arXiv161005790G
The backside coronal mass ejection (CME) of 2012 July 23 had a
short Sun-to-Earth shock transit time (18.5 hr). The associated solar
energetic particle (SEP) event had a >10 MeV proton flux peaking at
∼5000 pfu, and the energetic storm particle event was an order of
magnitude larger, making it the most intense event in the space era
at these energies. By a detailed analysis of the CME, shock, and SEP
characteristics, we find that the July 23 event is consistent with
a high-energy SEP event (accelerating particles to gigaelectronvolt
energies). The times of maximum and fluence spectra in the range 10-100
MeV were very hard, similar to those of ground-level enhancement (GLE)
events. We found a hierarchical relationship between the CME initial
speeds and the fluence spectral indices: CMEs with low initial speeds
had SEP events with the softest spectra, while those with the highest
initial speeds had SEP events with the hardest spectra. CMEs attaining
intermediate speeds result in moderately hard spectra. The July 23 event
was in the group of hard-spectrum events. During the July 23 event,
the shock speed (>2000 km s<SUP>-1</SUP>), the initial acceleration
(∼1.70 km s<SUP>-2</SUP>), and the shock-formation height (∼1.5
solar radii) were all typical of GLE events. The associated type II
burst had emission components from meter to kilometer wavelengths,
suggesting a strong shock. These observations confirm that the 2012
July 23 event is likely to be an extreme event in terms of the energetic
particles it accelerated.
---------------------------------------------------------
Title: HELCATS: Statistical results on interplanetary type II bursts
observed by STEREO/Waves
Authors: Krupar, V.; Eastwood, J. P.; Magdalenic, J.; Gopalswamy,
N.; Bisi, M. M.; Davies, J. A.; Harrison, R. A.; Barnes, D.
2016AGUFMSH11C2246K Altcode:
Heliospheric Cataloguing, Analysis and Techniques Service (HELCATS)
is a project of the European Union's Seventh Framework Programme. The
current version of the HELCATS manually-generated Coronal Mass Ejection
(CME) catalogue contains more than 1,300 CMEs observed between 2007
and 2014. CMEs are sometimes associated with the so called type II
bursts which are considered to be radio signatures of fast electrons
accelerated at the CME-driven shock front. We present statistical
results on 153 type II bursts associated with manually-identified
CMEs in the HELCATS catalogue. We found that faster CMEs are more
likely to produce radio emissions. By comparing frequency drifts with
white-light observations we calculated angular deviations of type II
burst propagation directions from radial. Our results confirm that
type II bursts statistically arise from CME flanks. We also discuss
the use of interplanetary radio emission in the context of space
weather forecasting.
---------------------------------------------------------
Title: Comparison on the CME-shock Acceleration of Three Widespread
SEPs during Solar Cycle 24
Authors: St Cyr, O. C.; Xie, H.; Pertti, M.; Gopalswamy, N.
2016AGUFMSH41B2534S Altcode:
Using forward-modeling of three-dimensional (3D) flux rope plus oblate
spheroid shock model, we analyze three solar energetic particle (SEP)
events observed in three views by STEREO and SOHO spacecraft. The three
SEP events occurred on August 14, 2010, November 03, 2011, and March 05,
2013. All three SEP events show widespread distribution in longitude
(> 90 degree) but with different onset delays, rate of flux increase,
and electron anisotropies. By fitting the 3D flux rope + shock model
to white-light and EUV images from STEREO, SOHO and SDO, we are able to
best determine the 3D shape of the CME shock wave. The forward-modeling
technique constrained with multi-spacecraft observations allowed
us to determine the locations where the shock fronts intersect the
magnetic footpoints of three spacecraft (STA, B and ACE/Wind), and
compute the shock speeds and expansion speeds at the intersecting
points. Our fitting results show that the November 03, 2011 SEP has
the fastest expansion speed among three events, which is consistent
with the rapid flux rises at all three spacecraft and small onset
delay between well-connected STA and poor-connected STB and ACE/Wind
( 30 min). On the other hand, the March 05, 2013 SEP has the largest
shock leading-edge speed thus the largest electron intensity. However,
due to its relatively weak expansion, the shock ceased expanding at 100
degree. The intensity observed by ACE/EPAM and Wind/3DP ( 140 degree
away from the SEP solar source) rose very slowly with a large delay
of 5 hr, which cannot be explained by the shock acceleration. For the
Aug. 14, 2010 event, the SEP observed at STB and ACE/Wind are shown
to be accelerated and injected by the shock and consistent with the
large anisotropies observed at these two locations. The cross-field
diffusion is the likely cause of the Aug. 14, 2010 SEP event observed
by STA and the March 05, 2013 event observed by STB and ACE/Wind,
which show almost no anisotropy. This investigation helps explore the
relative importance of the various mechanisms of SEP acceleration.
---------------------------------------------------------
Title: The ForeCAT In Situ Data Observer and the Effects of Deflection
and Rotation on CME Geoeffectiveness
Authors: Kay, C.; Gopalswamy, N.; Reinard, A.; Opher, M.;
Nieves-Chinchilla, T.
2016AGUFMSH13B2298K Altcode:
CMEs drive the strongest space weather events at Earth and throughout
the solar system. At Earth, the amount of southward magnetic field in a
CME is a major component in determining the severity of an impact. We
present results from ForeCAT (Forecasting a CME's Altered Trajectory,
Kay et al. 2015), which predicts the deflection and rotation of
CMEs based on magnetic forces determined by the background magnetic
field. Understanding these deflections and rotations is essential to
understanding the geoeffectiveness of CMEs as it determines whether a
CME will hit Earth and the orientation of the flux rope magnetic field
upon impact. Using the CME location and orientation from ForeCAT and
simple flux rope models we show that we can reproduce the in situ
magnetic profiles of Earth-impacting CMEs with the new ForeCAT In
situ Data Observer (FIDO). We compare these results with the in situ
profiles obtained assuming that no deflection or rotation occurs, and
find that including these nonradial effects is essential for accurate
space weather forecasting. For several observed cases we comment on
how the deflection and rotation affects the southward component of
the CME's magnetic field, and therefore the CME's geoeffectiveness.
---------------------------------------------------------
Title: Shock Formation, Energetic Particle Release, and Kinematics
of Coronal Mass Ejections
Authors: Gopalswamy, N.; Yashiro, S.; Thakur, N.; Makela, P. A.; Xie,
H.; Akiyama, S.
2016AGUFMSH32A..06G Altcode:
There are many source and environmental parameters that affect the
characteristics of large solar energetic particle (SEP) events. We
report on three primary characteristics that seem to determine whether
a CME-driven shock can accelerate particles to very high energies. The
first one is the height of shock formation, as indicated by type II
radio bursts. For SEP events with GeV particles, the shocks form
very close to the Sun, about half a solar radius above the solar
surface. For events from filament eruptions (FEs) outside active
regions, the shock forms at much larger heights - either in the outer
corona or in the interplanetary medium. The second characteristic
is the acceleration profile of CMEs. In high-energy particle events,
the associated CMEs accelerate impulsively (initial acceleration is 2
km/s/s), ensuring strong shocks very close to the solar surface where
the ambient magnetic field is high. In FE SEP events, the acceleration
is typically an order of magnitude smaller, consistent with shock
formation at large distances from the Sun. The third factor is the
Alfven speed profile in the ambient medium. It is well known that the
Alfven speed (or magnetosonic speed) in the corona increases from 300
km/s in the region where shocks typically form to several hundred km/s
around 3 solar radii. After that the characteristic speed steadily
declines. The behavior of the CME speed profile with respect to the
Alfven speed profile essentially determines the true strength of the
shock. One of the observational consequences of these three factors
is the 10-100 MeV spectral index of the SEP events. We show that the
high-energy SEP events and FE SEP events fall on the opposite ends of
the distribution of the spectral index: 2 and >4, respectively.
---------------------------------------------------------
Title: History and development of coronal mass ejections as a key
player in solar terrestrial relationship
Authors: Gopalswamy, N.
2016GSL.....3....8G Altcode: 2016arXiv160203665G
Coronal mass ejections (CMEs) are relatively a recently discovered
phenomenon—in 1971, some 15 years into the Space Era. It took another
two decades to realize that CMEs are the most important players in
solar terrestrial relationship as the root cause of severe weather
in Earth's space environment. CMEs are now counted among the major
natural hazards because they cause large solar energetic particle
(SEP) events and major geomagnetic storms, both of which pose danger
to humans and their technology in space and ground. Geomagnetic storms
discovered in the 1700s, solar flares discovered in the 1800s, and SEP
events discovered in the 1900s are all now found to be closely related
to CMEs via various physical processes occurring at various locations
in and around CMEs, when they interact with the ambient medium. This
article identifies a number of key developments that preceded the
discovery of white-light CMEs suggesting that CMEs were waiting to be
discovered. The last two decades witnessed an explosion of CME research
following the launch of the Solar and Heliospheric Observatory mission
in 1995, resulting in the establishment of a full picture of CMEs.
---------------------------------------------------------
Title: Constraining the Solar Coronal Magnetic Field Strength using
Split-band Type II Radio Burst Observations
Authors: Kishore, P.; Ramesh, R.; Hariharan, K.; Kathiravan, C.;
Gopalswamy, N.
2016ApJ...832...59K Altcode:
We report on low-frequency radio (85-35 MHz) spectral observations
of four different type II radio bursts, which exhibited
fundamental-harmonic emission and split-band structure. Each of the
bursts was found to be closely associated with a whitelight coronal
mass ejection (CME) close to the Sun. We estimated the coronal magnetic
field strength from the split-band characteristics of the bursts, by
assuming a model for the coronal electron density distribution. The
choice of the model was constrained, based on the following criteria:
(1) when the radio burst is observed simultaneously in the upper and
lower bands of the fundamental component, the location of the plasma
level corresponding to the frequency of the burst in the lower band
should be consistent with the deprojected location of the leading edge
(LE) of the associated CME; (2) the drift speed of the type II bursts
derived from such a model should agree closely with the deprojected
speed of the LE of the corresponding CMEs. With the above conditions,
we find that: (1) the estimated field strengths are unique to each
type II burst, and (2) the radial variation of the field strength in
the different events indicate a pattern. It is steepest for the case
where the heliocentric distance range over which the associated burst
is observed is closest to the Sun, and vice versa.
---------------------------------------------------------
Title: Determining ICME Magnetic Field Orientation with the ForeCAT
In Situ Data Observer
Authors: Kay, Christina; Gopalswamy, N.; Reinard, A.; Opher, M.
2016usc..confE..20K Altcode:
CMEs drive the strongest space weather events at Earth and throughout
the solar system. At Earth, the amount of southward magnetic field in a
CME is a major component in determining the severity of an impact. We
present results from ForeCAT (Forecasting a CME's Altered Trajectory,
Kay et al. 2015), which predicts the deflection and rotation of
CMEs based on magnetic forces determined by the background magnetic
field. Using HMI magnetograms to reconstruct the background magnetic
field and AIA images to constrain the early evolution of CMEs, we show
that we can reproduce the deflection and rotation of CMEs observed
in the corona. Using this CME location and orientation from ForeCAT
results and a simple force-free flux rope model we show that we can
reproduce the in situ magnetic profiles of Earth-impacting CMEs. We
compare these results with the in situ profiles obtained assuming
that no deflection or rotation occurs, and find that including these
nonradial effects is essential for accurate space weather forecasting.
---------------------------------------------------------
Title: The Complex Solar Polarity Reversal during Cycle 24
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2016usc..confE..37G Altcode:
The polarity reversal at solar poles is an important event
with important implications for solar magnetism, the polarity
of interplanetary coronal mass ejections, and even cosmic ray
modulation. The poles often do not reverse simultaneously. During the
several recent cycles, the north pole reversed first, followed by the
south. During cycle 24, this trend has been broken in that the south
pole reversed first. The polarity reversal is typically marked by
the cessation of high-latitude eruptive activities such coronal mass
ejections and prominence eruptions. Even though polar prominences
started appearing as early as 2011, the reversal in the north was
completed only by the end of 2015. On the other hand the south polar
region behaved as in previous cycles and reversed over a shorter time
scale, about a year before the reversal in the north. By combining
prominence eruption detected automatically (Nobeyama Radioheliograph
and SDO), the polar microwave brightness (Nobeyama Radioheliograph),
and the magnetic butterfly diagram (SDO and NSO) we show that the
complexity can be attributed to the emergence of active regions that
violated the Hale polarity rule and Joy's law. The extended period of
near-zero field in the north polar region should result in very weak
and delayed sunspot activity in the northern hemisphere in cycle 25,
the southern hemispheric activity should start early; the amplitude
will depend on how the south polar fields will evolve in the declining
phase of cycle (24).
---------------------------------------------------------
Title: Coronal magnetic field profiles from shock-CME standoff
distances
Authors: Schmidt, J. M.; Cairns, Iver H.; Gopalswamy, N.; Yashiro, S.
2016JGRA..121.9299S Altcode:
Coronagraphs observe coronal mass ejections (CMEs) and driven
shocks in white light images. From these observations the shock's
speed and the shock's standoff distance from the CME's leading edge
can be derived. Using these quantities, theoretical relationships
between the shock's Alfvénic Mach number MA and standoff distance,
and empirical radial profiles for the solar wind velocity and number
density, the radial magnetic field profile upstream of the shock can
be calculated. These profiles cannot be measured directly. We test the
accuracy of this method for estimating the radial magnetic field profile
upstream of the shock by simulating a sample CME that occurred on 29
November 2013 using the three-dimensional (3-D) magnetohydrodynamic
Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme code, retrieving
shock-CME standoff distances from the simulation, and comparing the
estimated and simulated radial magnetic field profiles. We find good
agreement between the two profiles (within ±30%) between 1.8 and 10
R<SUB>⊙</SUB>. Our simulations confirm that a linear relationship
exists between the standoff distance and the inverse compression ratio
at the shock. We also find very good agreement between the empirical
and simulated radial profiles of the number density and speed of the
solar wind and inner corona.
---------------------------------------------------------
Title: On the reduced geoeffectiveness of solar cycle 24: A moderate
storm perspective
Authors: Selvakumaran, R.; Veenadhari, B.; Akiyama, S.; Pandya, Megha;
Gopalswamy, N.; Yashiro, S.; Kumar, Sandeep; Mäkelä, P.; Xie, H.
2016JGRA..121.8188S Altcode:
The moderate and intense geomagnetic storms are identified for
the first 77 months of solar cycles 23 and 24. The solar sources
responsible for the moderate geomagnetic storms are indentified during
the same epoch for both the cycles. Solar cycle 24 has shown nearly 80%
reduction in the occurrence of intense storms whereas it is only 40%
in case of moderate storms when compared to previous cycle. The solar
and interplanetary characteristics of the moderate storms driven by
coronal mass ejection (CME) are compared for solar cycles 23 and 24
in order to see reduction in geoeffectiveness has anything to do with
the occurrence of moderate storm. Though there is reduction in the
occurrence of moderate storms, the Dst distribution does not show much
difference. Similarly, the solar source parameters like CME speed, mass,
and width did not show any significant variation in the average values
as well as the distribution. The correlation between VB<SUB>z</SUB>
and Dst is determined, and it is found to be moderate with value of
0.68 for cycle 23 and 0.61 for cycle 24. The magnetospheric energy
flux parameter epsilon (ɛ) is estimated during the main phase of all
moderate storms during solar cycles 23 and 24. The energy transfer
decreased in solar cycle 24 when compared to cycle 23. These results
are significantly different when all geomagnetic storms are taken into
consideration for both the solar cycles.
---------------------------------------------------------
Title: Source Regions of the Type II Radio Burst Observed During a
CME-CME Interaction on 2013 May 22
Authors: Mäkelä, P.; Gopalswamy, N.; Reiner, M. J.; Akiyama, S.;
Krupar, V.
2016ApJ...827..141M Altcode: 2016arXiv160606989G
We report on our study of radio source regions during the type
II radio burst on 2013 May 22 based on direction-finding analysis
of the Wind/WAVES and STEREO/WAVES (SWAVES) radio observations at
decameter-hectometric wavelengths. The type II emission showed an
enhancement that coincided with the interaction of two coronal
mass ejections (CMEs) launched in sequence along closely spaced
trajectories. The triangulation of the SWAVES source directions
posited the ecliptic projections of the radio sources near the line
connecting the Sun and the STEREO-A spacecraft. The WAVES and SWAVES
source directions revealed shifts in the latitude of the radio source,
indicating that the spatial location of the dominant source of the
type II emission varies during the CME-CME interaction. The WAVES
source directions close to 1 MHz frequencies matched the location
of the leading edge of the primary CME seen in the images of the
LASCO/C3 coronagraph. This correspondence of spatial locations at
both wavelengths confirms that the CME-CME interaction region is
the source of the type II enhancement. Comparison of radio and
white-light observations also showed that at lower frequencies
scattering significantly affects radio wave propagation.
---------------------------------------------------------
Title: A small mission concept to the Sun-Earth Lagrangian L5 point
for innovative solar, heliospheric and space weather science
Authors: Lavraud, B.; Liu, Y.; Segura, K.; He, J.; Qin, G.; Temmer,
M.; Vial, J. -C.; Xiong, M.; Davies, J. A.; Rouillard, A. P.; Pinto,
R.; Auchère, F.; Harrison, R. A.; Eyles, C.; Gan, W.; Lamy, P.;
Xia, L.; Eastwood, J. P.; Kong, L.; Wang, J.; Wimmer-Schweingruber,
R. F.; Zhang, S.; Zong, Q.; Soucek, J.; An, J.; Prech, L.; Zhang,
A.; Rochus, P.; Bothmer, V.; Janvier, M.; Maksimovic, M.; Escoubet,
C. P.; Kilpua, E. K. J.; Tappin, J.; Vainio, R.; Poedts, S.; Dunlop,
M. W.; Savani, N.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard, T.;
DeForest, C.; Webb, D.; Lugaz, N.; Fuselier, S. A.; Dalmasse, K.;
Tallineau, J.; Vranken, D.; Fernández, J. G.
2016JASTP.146..171L Altcode:
We present a concept for a small mission to the Sun-Earth Lagrangian L5
point for innovative solar, heliospheric and space weather science. The
proposed INvestigation of Solar-Terrestrial Activity aNd Transients
(INSTANT) mission is designed to identify how solar coronal magnetic
fields drive eruptions, mass transport and particle acceleration that
impact the Earth and the heliosphere. INSTANT is the first mission
designed to (1) obtain measurements of coronal magnetic fields from
space and (2) determine coronal mass ejection (CME) kinematics with
unparalleled accuracy. Thanks to innovative instrumentation at a vantage
point that provides the most suitable perspective view of the Sun-Earth
system, INSTANT would uniquely track the whole chain of fundamental
processes driving space weather at Earth. We present the science
requirements, payload and mission profile that fulfill ambitious science
objectives within small mission programmatic boundary conditions.
---------------------------------------------------------
Title: The Interaction between Coronal Mass Ejections (CMEs) and
Coronal Holes (CHs) during the Solar Cycle 23 and its Geomagnetic
Consequences
Authors: Mohamed, Amaal; Gopalswamy, Nat
2016cosp...41E1319M Altcode:
The interactions between the two large scale phenomena, coronal holes
(CHs) and coronal mass ejections (CMEs) maybe considered as one of the
most important relations that having a direct impact not only on space
weather but also on the relevant plasma physics. Many observations have
shown that throughout their propagation from the Sun to interplanetary
space, CMEs interact with the heliospheric structures (e.g., other CMEs,
Corotating interaction regions (CIRs), helmet streamers, and CHs). Such
interactions could enhance the southward magnetic field component, which
has important implications for geomagnetic storm generation. These
interactions imply also a significant energy and momentum transfer
between the interacting systems where magnetic reconnection is taking
place. When CHs deflect CMEs away from or towards the Sun-Earth line,
the geomagnetic response of the CME is highly affected. Gopalswamy et
al. [2009] have addressed the deflection of CMEs due to the existence
of CHs that are in close proximity to the eruption regions. They
have shown that CHs can act as magnetic barriers that constrain CMEs
propagation and can significantly affect their trajectories. Here,
we study the interaction between coronal holes (CHs) and coronal mass
ejections (CMEs) using a resultant force exerted by all coronal holes
present on the disk and is defined as the coronal hole influence
parameter (CHIP). The CHIP magnitude for each CH depends on the CH
area, the distance between the CH centroid and the eruption region,
and the average magnetic field within the CH at the photospheric
level. The CHIP direction for each CH points from the CH centroid
to the eruption region. We focus on Solar Cycle 23 CMEs originating
from the disk center of the Sun (central meridian distance < 15
°). We present an extensive statistical study via compiling data
sets of observations of CMEs and their interplanetary counterparts;
known as interplanetary CMEs (ICMEs). There are 2 subsets of ICMEs:
magnetic cloud (MC) and non-magnetic cloud (non-MC) ICMEs. MCs are
identified by a smooth change of the magnetic field as measured with
spacecraft at 1 AU, using ACE and Wind spacecraft. It is found that the
maximum phase has the largest CHIP value (2.9 G) for non-MCs. The CHIP
is the largest (5.8 G) for driverless (DL) shocks, which are shocks at
1 AU with no discernible MC or non-MC. These results suggest that the
behavior of non-MCs is similar to that of the DL shocks and different
from that of MCs. In other words, the CHs may deflect the CMEs away
from the Sun-Earth line and force them to behave like limb CMEs with
DL shocks. This finding supports the idea that all CMEs may be flux
ropes if viewed from an appropriate vantage point.
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.721G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.728G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.729G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.714G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.723G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.727G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.726G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.716G Altcode:
Discussion
---------------------------------------------------------
Title: The differences between CME-rich and CME-poor Active Regions
Authors: Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat; Mäkelä,
Pertti
2016shin.confE.159A Altcode:
We studied the association of coronal mass ejections (CMEs) with large
X-ray flares occurring in flare-productive active regions (ARs). The
flare-productive ARs are defined as those which produce more than five
M1-class flares during their passage from the east to west limb. A
total of 1236 large X-ray flares were produced from 132 such ARs in
the period 1996 to 2015. We examined the CME association rate (RCME)
for each AR as an index of AR"s CME-productivity using by LASCO/SOHO
and SECCHI/STEREO. It is reasonable to expect that average RCME of the
flare-productive ARs is 50%, because about half of M1 class flares
have CME association. However, out of the 132 ARs, 20 were CME-rich
(RCME > 80%) and 21 were CME-poor (RCME < 20%). AR size and
magnetic potential energy do not seem to differ significantly between
CME-rich and CME-poor ARs. We did find a significant difference in the
recurrence time of flares in CME-rich ARs (average = 21.6 h) and hose
in CME-poor them (14.7 h). We discuss additional differences between
the two types of ARs.
---------------------------------------------------------
Title: Interaction between Coronal Mass Ejections: Limited Spatial
Extent Revealed by SOHO Observations
Authors: Gopalswamy, Nat; Reiner, Mike J.; Makela, Pertti; Yashiro,
Seiji
2016cosp...41E.711G Altcode:
A spectacular CME interaction event was observed on 2013 May 22 by
the Large Angle and Spectrometric Coronagraph (LASCO) on board the
Solar and Heliospheric Observatory (SOHO) mission as confirmed by
the radio signature detected by the Radio and Plasma Wave experiment
(WAVES) on board the Wind spacecraft. The interaction event was also
associated with an intense solar energetic particle event, typical of
such events in solar cycles 23 and 24. Detailed height-time plots of
the interacting CMEs at various position angles revealed a surprising
result: only a limited spatial extent of the primary CME was affected
by the interaction. The speed of the primary CME showed a sharp
decline in the position angle range where it interacted with the
preceding CME. At these position angles, the speed of the preceding
CME increased. At position angles away from the interaction region,
the speed of the primary CME remained roughly the same except for the
usual drag deceleration. This result has important implications to
theories on CME collision: treating the interacting CMEs to be rigid
bodies and using the whole mass of the CMEs may not be correct.
---------------------------------------------------------
Title: Energy dependence of SEP electron and proton onset times
Authors: Xie, H.; Mäkelä, P.; Gopalswamy, N.; St. Cyr, O. C.
2016JGRA..121.6168X Altcode: 2016arXiv160908171X
We study the large solar energetic particle (SEP) events that were
detected by GOES in the >10 MeV energy channel during December 2006
to March 2014. We derive and compare solar particle release (SPR)
times for the 0.25-10.4 MeV electrons and 10-100 MeV protons for
the 28 SEP events. In the study, the electron SPR times are derived
with the time-shifting analysis (TSA) and the proton SPR times are
derived using both the TSA and the velocity dispersion analysis
(VDA). Electron anisotropies are computed to evaluate the amount of
scattering for the events under study. Our main results include (1)
near-relativistic electrons and high-energy protons are released at
the same time within 8 min for most (16 of 23) SEP events. (2)There
exists a good correlation between electron and proton acceleration,
peak intensity, and intensity time profiles. (3) The TSA SPR times
for 90.5 MeV and 57.4 MeV protons have maximum errors of 6 min and
10 min compared to the proton VDA release times, respectively, while
the maximum error for 15.4 MeV protons can reach to 32 min. (4) For
7 low-intensity events of the 23, large delays occurred for 6.5 MeV
electrons and 90.5 MeV protons relative to 0.5 MeV electrons. Whether
these delays are due to times needed for the evolving shock to be
strengthened or due to particle transport effects remains unsolved.
---------------------------------------------------------
Title: Unusual Polar Activity of the Sun in the Northern Hemisphere
and Its Implications for Solar Cycle 25
Authors: Gopalswamy, Nat; Masuda, Satoshi; Yashiro, Seiji; Akiyama,
Sachiko; Shibasaki, Kiyoto
2016cosp...41E.712G Altcode:
Polar field strength in one solar cycle is known to indicate the
strength (e.g., Sunspot number) and phase of the next cycle. In
particular the polar field strength (or its proxies such as the
polar coronal hole area and microwave polar brightness) during the
minimum phase of a given cycle seem to be well correlated with the
maximum sunspot number of the next cycle. Polar prominence eruptions
and coronal mass ejections have also been found to be indicators
of low polar field; their cessation signals the time of polarity
reversal. While these indicators are present in the current cycle,
significant differences are found regarding the phase lag between the
two hemispheres and the duration of polar eruptions. We use data from
the Nobeyama Radioheliograph, the Solar Dynamics Observatory, SOLIS,
and Wilcox Solar Observatory to highlight these differences. We find
that the north polar region of the Sun has near-zero field strength for
more than three years. This is unusually long and caused by surges of
both polarities heading toward the north pole that prevent the buildup
of the polar field. This seems to be due to anti-Hale active regions
that appeared around the 2012 peak sunspot activity in the northern
hemisphere. The unusual condition is consistent with (i) the continued
high-latitude prominence eruption, (ii) the extended period of high
tilt angle of the heliospheric current sheet, (iii) the weak microwave
polar brightness, and (iv) the lack of north polar coronal hole. On
the other hand, the south polar field has started building up and the
coronal hole has appeared in early 2015 because of large active regions
of the correct tilt in the southern hemisphere during the 2014 peak of
sunspot activity. The extended period of near-zero field in the north
polar region should result in very weak and delayed sunspot activity
in the northern hemisphere in cycle 25. On the other hand the south
polar field has already increased significantly, suggesting that the
activity in the southern hemisphere should start early; the amplitude
will depend on how the south polar fields will evolve in the declining
phase of cycle (24).
---------------------------------------------------------
Title: Deflection and Rotation of CMEs from AR 11158
Authors: Kay, Christina Danielle; Gopalswamy, N.; Xie, H.; Yashiro, S.
2016shin.confE..41K Altcode:
Between the 13th and 16th of February 2011 a series of CMEs erupted
from multiple polarity inversion lines within AR 11158. For seven of
these CMEs we use the Graduated Cylindrical Shell (GCS) flux rope model
to determine the CME trajectory using both STEREO EUV and coronagraph
images. We then use ForeCAT, a model for nonradial CME dynamics driven
by magnetic forces, to simulate the deflection and rotation of the
seven CMEs. We find good agreement between the ForeCAT results and the
reconstructed CME positions and orientations. The CME deflections range
in magnitude between 10 and 30 degrees. All CMEs deflect to the north
but we find variation in direction of the longitudinal deflection. The
rotations range between 5 degrees and 50 degrees with both clockwise and
counterclockwise rotation occurring. Four of the CMEs begin with initial
positions within 2 degrees of one another. These four CMEs all deflect
primarily northward, with some minor eastward deflection, and rotate
counterclockwise. Their final positions and orientations, however,
respectively differ by 20 degrees and 30 degrees. This variation in
deflection and rotation results from differences in the CME expansion
and radial propagation close to the Sun, as well as the CME mass.
---------------------------------------------------------
Title: Kinematics of slow and fast CMEs in soar cycle 23 and 24
Authors: Banerjee, Dipankar; Gopalswamy, Nat; Pant, Vaibhav
2016cosp...41E.140B Altcode:
CMEs are episodic expulsion of plasma and magnetic fields from Sun into
heliosphere. CMEs can be classified, based on their speeds, as slow CMEs
and fast CMEs. We find that slow CMEs and fast CMEs behave differently
in two cycles. While fast CMEs seem to follow the sunspot variations,
slow CMEs have much flatter distribution. Thus the distribution of
total CMEs is affected by slow CME populations. We find double peak
behaviour in fast CMEs, since they follow the sunspot distribution, in
both the cycles without any significant delay from sunspot variation. It
suggests that most of the fast CMEs originates from active regions
associated with sunspots. We also find double peak behaviour in slow
CMEs in cycle 24 but not in cycle 23. In addition to this the number of
slow CMEs are far more than in cycle 23. These findings point towards
the fact that in cycle 24 slow CMEs to some extent are associated with
sunspots and due to weak heliospheric field they could somehow escape
easily thus giving double peak behaviour and larger distribution in
cycle 24. Apart from this we also find that slow and fast CMEs follow
different power laws. This may shed light on their origin as well.
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.717G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.715G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.720G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.722G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.719G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.730G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.718G Altcode:
Discussion
---------------------------------------------------------
Title: Smaller Forbush Decreases in Solar Cycle 24: Effect of the
Weak CME Field Strength?
Authors: Thakur, Neeharika; Gopalswamy, N.; Yashiro, S.; Akiyama,
S.; Xie, H.; Mäkelä, P.
2016shin.confE.172T Altcode:
A Forbush decrease (FD) is a sudden depression in the intensity
of galactic cosmic ray (GCR) background, followed by a gradual
recovery. One of the major causes of FDs is the presence of magnetic
structures such as magnetic clouds (MCs) or corotating interaction
regions (CIRs) that have enhanced magnetic field, which can scatter
particles away reducing the observed GCR intensity. Recent work
(Gopalswamy et al. 2014, GRL 41, 2673) suggests that coronal mass
ejections (CMEs) are expanding anomalously in solar cycle 24 due to the
reduced total pressure in the ambient medium. One of the consequences
of the anomalous expansion is the reduced magnetic content of MCs,
so we expect subdued FDs in cycle 24. In this paper, we present
preliminary results from a survey of FDs during MC events in cycle
24 in comparison with those in cycle 23. We find that only 17% FDs in
cycle 24 had an amplitude >3%, as compared to 31% in cycle 23. This
result is consistent with the difference in the maximum magnetic field
intensities (Bmax) of MCs in the two cycles: only 10% of MCs in cycle
24 have Bmax>20nT, compared to 22% in cycle 23, confirming that MCs
of cycle 24 have weaker magnetic field content. Therefore, we suggest
that weaker magnetic field intensity in the magnetic clouds of cycle
24 has led to FDs with smaller amplitudes.
---------------------------------------------------------
Title: The 2012 July 23 Backside Event: An Extreme Energetic
Particle Event?
Authors: Gopalswamy, Nat; Makela, Pertti; Yashiro, Seiji
2016shin.confE.173G Altcode:
The backside coronal mass ejection (CME) of 2012 July 23 has received
considerable attention because many of its characteristics place
it among the historical extreme solar events. For example, the
shock transit time from Sun to 1 au was 18.5 hours, similar to the
two 2003 Halloween events on October 28 and 29. The CME speed well
exceeded 2000 km/s as observed from three views: the STEREO-Ahead,
STEREO-Behind, and SOHO. The CME erupted from S17W141 and was heading
roughly towards STEREO-A. The solar energetic particle (SEP) event
had a peak value of 5000 pfu in the >10 MeV channel. The energetic
storm particle (ESP) event was an order of magnitude larger, placing
it among the most intense events in the space era. In this paper, we
examine whether the CME in this event could have accelerated particles
to GeV energies. The STEREO particle detectors do not have energy
channels higher than 100 MeV, so we determine the SEP spectrum in
the range 10-100 MeV and compare it with that of other ground level
enhancement (GLE) events. We find that the spectrum of the 2012 July
23 event is very hard (power law index 1.66), harder than that of all
GLE events in cycles 23 and 24. Only the most intense GLE of cycle 23
(2005 January 20), had a 10-100 MeV spectral index of 1.66. The two
GLE events of cycle 24 had spectral indices of 2.14 (2012 May 17) and
2.18 (2014 January 6). Thus we conclude that the 2012 July 23 event is
likely to be an extreme event in terms of the energetic particles it
accelerated. We also discuss additional characteristics of the event,
which support this conclusion.
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.724G Altcode:
Discussion
---------------------------------------------------------
Title: Discussion
Authors: Gopalswamy, Nat
2016cosp...41E.725G Altcode:
Discussion
---------------------------------------------------------
Title: Investigation on source locations of interplanetary type II
radio bursts using radio direction finding
Authors: Makela, Pertti; Gopalswamy, Nat; Akiyama, Sachiko
2016shin.confE.167M Altcode:
Source locations of interplanetary (IP) type II radio bursts can be
studied by comparing radio source directions obtained using direction
finding (DF) techniques with the white-light images of the associated
coronal mass ejections (CMEs). Previously this method has been used
to confirm that a CME-CME interaction event is the source of the
concurrently observed type II enhancement. These IP type II enhancements
are well suited for DF studies, because the signal-to-noise ratio of
the radio emission is sufficiently high. Regular IP type II bursts
are often fainter, especially so during solar cycle 24, which is
characterized by a lower solar activity level and a smaller number of
intense solar eruptions compared to solar cycle 23. In addition, it
is known that radio wave scattering affects the DF source directions
at lower frequencies. We report on our investigation on locating the
radio source of regular IP type II radio bursts by comparing the DF
source directions with the white-light images of the associated CMEs.
---------------------------------------------------------
Title: Detection of Nonthermal Radio Emission from a Polar coronal
mass ejection
Authors: Gopalswamy, Nat; Reiner, Mike J.; Makela, Pertti; Yashiro,
Seiji; Akiyama, Sachiko
2016cosp...41E.713G Altcode:
High-latitude coronal mass ejections from the polar crown region are
generally of low energy and hence thought to be not responsible for
driving shocks. However, the eruption of such CMEs are associated with
weak post eruption arcades suggesting that particle acceleration does
happen in the reconnection region beneath the erupting filaments. An
unusually fast CME erupted from the southern polar crown on 1999 June
14 observed by the Large Angle and Spectrometric Coronagraph (LASCO)
on board the Solar and Heliospheric Observatory (SOHO) mission. The
post eruption arcade was observed by the Soft X-ray Telescope on board
the Yohkoh mission and the Extreme-ultraviolet imaging Telescope
(EIT) on board SOHO. A diffuse radio emission was observed below 1
MHz by the Radio and Plasma Wave experiment (WAVES) on board the Wind
spacecraft. The good temporal association between the radio burst and
the CME suggests that the CME must be the source of energy for the
radio emission. The drift rate of the radio burst was much smaller
than that of a typical interplanetary type II burst. We suggest that
the radio burst is produced by a flank of the CME-driven shock passing
through a streamer located close to the east limb of the Sun. Such
an interaction is likely to have caused the slow drift of the burst
because the shock flank passes roughly parallel to the solar surface
in the flank region. The enhanced density in the streamer makes the
local Alfven speed lower, making the shock sufficiently strong to
accelerate a few keV electrons that lead to the radio emission. The
diffuse feature also contains a series of spikes, which suggest
possible escape of nonthermal electrons along open field lines. We
use the radio direction finding to confirm the results. This result
has important implications for particle acceleration by shock flanks,
where the geometry is expected to be quasi-perpendicular.
---------------------------------------------------------
Title: Low-Frequency Radio Bursts and Space Weather
Authors: Gopalswamy, Nat
2016arXiv160502218G Altcode:
Low-frequency radio phenomena are due to the presence of nonthermal
electrons in the interplanetary (IP) medium. Understanding these
phenomena is important in characterizing the space environment near
Earth and other destinations in the solar system. Substantial progress
has been made in the past two decades, because of the continuous and
uniform data sets available from space-based radio and white-light
instrumentation. This paper highlights some recent results obtained
on IP radio phenomena. In particular, the source of type IV radio
bursts, the behavior of type III storms, shock propagation in the
IP medium, and the solar-cycle variation of type II radio bursts are
considered. All these phenomena are closely related to solar eruptions
and active region evolution. The results presented were obtained by
combining data from the Wind and SOHO missions.
---------------------------------------------------------
Title: Solar Activity Studies using Microwave Imaging Observations
Authors: Gopalswamy, Nat
2016arXiv160502221G Altcode:
We report on the status of solar cycle 24 based on polar prominence
eruptions (PEs) and microwave brightness enhancement (MBE) information
obtained by the Nobeyama radioheliograph. The north polar region of
the Sun had near-zero field strength for more than three years (2012
to 2015) and ended only in September 2015 as indicated by the presence
of polar PEs and the lack of MBE. The zero-polar-field condition in
the south started only around 2013, but it ended by June 2014. Thus
the asymmetry in the times of polarity reversal switched between cycle
23 and 24. The polar MBE is a good proxy for the polar magnetic field
strength as indicated by the high degree of correlation between the
two. The cross-correlation between the high- and low-latitude MBEs is
significant for a lag of ~5.5 to 7.3 years, suggesting that the polar
field of one cycle indicates the sunspot number of the next cycle in
agreement with the Babcock-Leighton mechanism of solar cycles. The
extended period of near-zero field in the north-polar region should
result in a weak and delayed sunspot activity in the northern hemisphere
in cycle 25.
---------------------------------------------------------
Title: On the Directivity of Low-Frequency Type IV Radio Bursts
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Mäkelä, Pertti; Yashiro,
Seiji; Cairns, Iver H.
2016arXiv160502223G Altcode:
An intense type IV radio burst was observed by the STEREO Behind
(STB) spacecraft located about 144 degres behind Earth. The burst was
associated with a large solar eruption that occurred on the backside
of the Sun (N05E151) close to the disk center in the STB view. The
eruption was also observed by the STEREO Ahead (STA) spacecraft
(located at 149 degrees ahead of Earth) as an eruption close to the
west limb (N05W60) in that view. The type IV burst was complete in STB
observations in that the envelope reached the lowest frequency and then
receded to higher frequencies. The burst was partial viewed from STA,
revealing only the edge coming down to the lowest frequency. The type
IV burst was not observed at all near Earth because the source was
61 degrees behind the east limb. The eruption was associated with a
low-frequency type II burst observed in all three views, although it
was not very intense. Solar energetic particles were also observed at
both STEREOs and at SOHO, suggesting that the shock was much extended,
consistent with the very high speed of the CME (about 2048 km/s). These
observations suggest that the type IV emission is directed along a
narrow cone above the flare site. We confirm this result statistically
using the type IV bursts of solar cycle 23.
---------------------------------------------------------
Title: Minifilament Eruptions that Drive Coronal Jets in a Solar
Active Region
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David;
Panesar, Navdeep; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat
2016SPD....47.0334S Altcode:
Solar coronal jets are common in both coronal holes and in active
regions. Recently, Sterling et al. (2015), using data from Hinode/XRT
and SDO/AIA, found that coronal jets originating in polar coronal holes
result from the eruption of small-scale filaments (minifilaments). The
jet bright point (JBP) seen in X-rays and hotter EUV channels off to one
side of the base of the jet's spire develops at the location where the
minifilament erupts, consistent with the JBPs being miniature versions
of typical solar flares that occur in the wake of large-scale filament
eruptions. Here we consider whether active region coronal jets also
result from the same minifilament-eruption mechanism, or whether they
instead result from a different mechanism, such as the hitherto popular
“emerging flux” model for jets. We present observations of an on-disk
active region that produced numerous jets on 2012 June 30, using data
from SDO/AIA and HMI, and from GOES/SXI. We find that several of these
active region jets also originate with eruptions of miniature filaments
(size scale ~20”) emanating from small-scale magnetic neutral lines
of the region. This demonstrates that active region coronal jets are
indeed frequently driven by minifilament eruptions. Other jets from the
active region were also consistent with their drivers being minifilament
eruptions, but we could not confirm this because the onsets of those
jets were hidden from our view. This work was supported by funding
from NASA/LWS, NASA/HGI, and Hinode.
---------------------------------------------------------
Title: Unusual Polar Conditions in Solar Cycle 24 and Their
Implications for Cycle 25
Authors: Gopalswamy, Nat; Yashiro, Seiji; Akiyama, Sachiko
2016ApJ...823L..15G Altcode: 2016arXiv160502217G
We report on the prolonged solar-maximum conditions until late 2015
at the north-polar region of the Sun indicated by the occurrence of
high-latitude prominence eruptions (PEs) and microwave brightness
temperature close to the quiet-Sun level. These two aspects of solar
activity indicate that the polarity reversal was completed by mid-2014
in the south and late 2015 in the north. The microwave brightness in
the south-polar region has increased to a level exceeding the level of
the Cycle 23/24 minimum, but just started to increase in the north. The
north-south asymmetry in the polarity reversal has switched from that
in Cycle 23. These observations lead us to the hypothesis that the
onset of Cycle 25 in the northern hemisphere is likely to be delayed
with respect to that in the southern hemisphere. We find that the
unusual condition in the north is a direct consequence of the arrival
of poleward surges of opposite polarity from the active region belt. We
also find that multiple rush-to-the-pole episodes were indicated by the
PE locations that lined up at the boundary between opposite-polarity
surges. The high-latitude PEs occurred in the boundary between the
incumbent polar flux and the insurgent flux of opposite polarity.
---------------------------------------------------------
Title: A Study of the 2012 January 19 Complex Type II Radio Burst
Using Wind, SOHO, and STEREO Observations
Authors: Teklu, T. B.; Gholap, A. V.; Gopalswamy, N.; Yashiro, S.;
Mäkelä, P.; Akiyama, S.; Thakur, N.; Xie, H.
2016arXiv160509644T Altcode:
We report on a case study of the complex type II radio burst of
2012 January 19 and its association with a white light coronal mass
ejection (CME). The complexity can be described as the appearance of an
additional type II burst component and strong intensity variation. The
dynamic spectrum shows a pair of type II bursts with fundamental
harmonic structures, one confined to decameter-hectometric (DH)
wavelengths and the other extending to kilometric (km) wavelengths. By
comparing the speeds obtained from white-light images with that speed
of the shock inferred from the drift rate, we show that the source of
the short-lived DH component is near the nose.
---------------------------------------------------------
Title: Minifilament Eruptions that Drive Coronal Jets in a Solar
Active Region
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.;
Panesar, Navdeep K.; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat
2016ApJ...821..100S Altcode:
We present observations of eruptive events in an active region adjacent
to an on-disk coronal hole on 2012 June 30, primarily using data from
the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA),
SDO/Helioseismic and Magnetic Imager (HMI), and STEREO-B. One eruption
is of a large-scale (∼100″) filament that is typical of other
eruptions, showing slow-rise onset followed by a faster-rise motion
starting as flare emissions begin. It also shows an “EUV crinkle”
emission pattern, resulting from magnetic reconnections between
the exploding filament-carrying field and surrounding field. Many
EUV jets, some of which are surges, sprays and/or X-ray jets, also
occur in localized areas of the active region. We examine in detail
two relatively energetic ones, accompanied by GOES M1 and C1 flares,
and a weaker one without a GOES signature. All three jets resulted
from small-scale (∼20″) filament eruptions consistent with a slow
rise followed by a fast rise occurring with flare-like jet-bright-point
brightenings. The two more-energetic jets showed crinkle patters, but
the third jet did not, perhaps due to its weakness. Thus all three jets
were consistent with formation via erupting minifilaments, analogous
to large-scale filament eruptions and to X-ray jets in polar coronal
holes. Several other energetic jets occurred in a nearby portion of
the active region; while their behavior was also consistent with their
source being minifilament eruptions, we could not confirm this because
their onsets were hidden from our view. Magnetic flux cancelation
and emergence are candidates for having triggered the minifilament
eruptions.
---------------------------------------------------------
Title: CME flux rope and shock identifications and locations:
Comparison of white light data, Graduated Cylindrical Shell model,
and MHD simulations
Authors: Schmidt, J. M.; Cairns, Iver H.; Xie, Hong; St. Cyr, O. C.;
Gopalswamy, N.
2016JGRA..121.1886S Altcode:
Coronal mass ejections (CMEs) are major transient phenomena in the
solar corona that are observed with ground-based and spacecraft-based
coronagraphs in white light or with in situ measurements by
spacecraft. CMEs transport mass and momentum and often drive shocks. In
order to derive the CME and shock trajectories with high precision,
we apply the graduated cylindrical shell (GCS) model to fit a flux
rope to the CME directed toward STEREO A after about 19:00 UT on 29
November 2013 and check the quality of the heliocentric distance-time
evaluations by carrying out a three-dimensional magnetohydrodynamic
(MHD) simulation of the same CME with the Block Adaptive Tree Solar-Wind
Roe Upwind Scheme (BATS-R-US) code. Heliocentric distances of the
CME and shock leading edges are determined from the simulated white
light images and magnetic field strength data. We find very good
agreement between the predicted and observed heliocentric distances,
showing that the GCS model and the BATS-R-US simulation approach
work very well and are consistent. In order to assess the validity of
CME and shock identification criteria in coronagraph images, we also
compute synthetic white light images of the CME and shock. We find
that the outer edge of a cloud-like illuminated area in the observed
and predicted images in fact coincides with the leading edge of the
CME flux rope and that the outer edge of a faint illuminated band in
front of the CME leading edge coincides with the CME-driven shock front.
---------------------------------------------------------
Title: Two Exceptions in the Large SEP Events of Solar Cycles 23
and 24
Authors: Thakur, N.; Gopalswamy, N.; Mäkelä, P.; Akiyama, S.;
Yashiro, S.; Xie, H.
2016SoPh..291..513T Altcode: 2016SoPh..tmp...21T
We discuss our findings from a survey of all large solar energetic
particle (SEP) events of Solar Cycles 23 and 24, i.e. the SEP events
where the intensity of > 10 MeV protons observed by GOES was > 10
pfu. In our previous work (Gopalswamy et al. in Geophys. Res. Lett. 41,
2673, 2014) we suggested that ground level enhancements (GLEs) in Cycles
23 and 24 also produce an intensity increase in the GOES > 700 MeV
proton channel. Our survey, now extended to include all large SEP events
of Cycle 23, confirms this to be true for all but two events: i) the
GLE of 6 May 1998 (GLE57) for which GOES did not observe enhancement
in > 700 MeV protons intensities and ii) a high-energy SEP event
of 8 November 2000, for which GOES observed > 700 MeV protons
but no GLE was recorded. Here we discuss these two exceptions. We
compare GLE57 with other small GLEs, and the 8 November 2000 SEP event
with those that showed similar intensity increases in the GOES >
700 MeV protons but produced GLEs. We find that, because GOES >
700 MeV proton intensity enhancements are typically small for small
GLEs, they are difficult to discern near solar minima due to higher
background. Our results also support that GLEs are generally observed
when shocks of the associated coronal mass ejections (CMEs) form at
heights 1.2 - 1.93 solar radii [R<SUB>⊙</SUB>] and when the solar
particle release occurs between 2 - 6 R<SUB>⊙</SUB>. Our secondary
findings support the view that the nose region of the CME-shock may
be accelerating the first-arriving GLE particles and the observation
of a GLE is also dependent on the latitudinal connectivity of the
observer to the CME-shock nose. We conclude that the GOES > 700 MeV
proton channel can be used as an indicator of GLEs excluding some rare
exceptions, such as those discussed here.
---------------------------------------------------------
Title: Special issue "International CAWSES-II Symposium"
Authors: Yamamoto, Mamoru; Shiokawa, Kazuo; Nakamura, Takuji;
Gopalswamy, Nat
2016EP&S...68...26Y Altcode:
This special issue gathered papers from the International
CAWSES-II Symposium (November 18-22, 2013 at Nagoya University,
Japan). Climate and Weather of the Sun-Earth System II (CAWSES-II)
is an international scientific program sponsored by Scientific
Committee on Solar-Terrestrial Physics (SCOSTEP) that continued from
2009 to 2013. The program was established with the aim of significantly
enhancing our understanding of the space environment and its impacts on
life and society. The International CAWSES-II Symposium was successful
with 388 presentations; and from that, 38 papers were published in
this special issue. In this preface, we briefly discuss the contents
of the special issue as well as the CAWSES-II review papers published
in Progress in Earth and Planetary Science (PEPS) in 2014-2015.
---------------------------------------------------------
Title: Current Polar Activity of the Sun and Its implications for
Solar Cycle 25
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2015AGUFMSH23A2424G Altcode:
Polar activity of one solar cycle is known to indicate certain
characteristics of the subsequent cycle in terms of strength (e.g.,
Sunspot number) and phase. In particular the polar field strength
(or its proxies such as the microwave polar brightness) during the
minimum phase of seem to be well correlated with the maximum sunspot
number of the next cycle. Polar prominence eruptions and coronal
mass ejections have also been found to be important indicators of the
time of polarity reversal. While these indicators are present in the
current cycle, significant differences are found regarding the phase
lag between the two hemispheres and the duration of polar eruptions. We
use prominence eruption data from the Nobeyama Radioheliograph and the
Solar Dynamics Observatory to highlight these differences. We also use
the polar microwave brightness variation and discuss the implications
to solar cycle 25.
---------------------------------------------------------
Title: Energy Dependence of SEP Electron and Proton Onset Times
Authors: Makela, P. A.; Xie, H.; Gopalswamy, N.; St Cyr, O. C.
2015AGUFMSH33B2468M Altcode:
We study the large solar energetic particle (SEP) events that were
detected by GOES in the > 10 MeV energy channel during December 2006
to March 2014. Using multi-spacecraft observations from STEREO A, B and
SOHO, we are able to determine accurately the solar particle release
(SPR) time of SEP electrons and protons. We first compute connection
angles (CA) between the solar events and magnetic foot-points connecting
to each spacecraft. By choosing the smallest CA, we derive the electron
and proton SPRs using electron fluxes from the SOHO Electron Proton
and Helium Instrument (EPHIN), proton fluxes from the SOHO Energetic
and Relativistic Nuclei and Electron instrument (ERNE), and from the
High Energy Telescope (HET) on STEREO. It is found that: 1) the 0.25
MeV-0.7 MeV electron SPRs are ~10 min earlier than 2.64 MeV - 10.4 Mev
electron SPRs; 2) the proton SPRs inferred from high-energy channels
(> 50 MeV) are similar to electron SPRs; 3) the proton SPRs inferred
from lower energy channel (10 - 16.9 MeV) can be either ~ 7 min earlier
than or delayed from the electron SPRs for tens of minutes to hours,
especially for SEPs with large pre-event background flux levels. In
this study, we evaluated the effects of large scattering and high
background levels on SPRs and made suggested corrections for the
background effect on SPR times. We also find that for some large SEP
events, the observed EPHIN electron and ERNE proton intensity profiles
show a double-peak feature. The onset of the first peak corresponds
well to the associated Type III and metric Type II onset and tends to
be nearly scattering-free.
---------------------------------------------------------
Title: A Comparative Study of Confined and Eruptive Solar Flares
using Microwave Observations
Authors: Yashiro, S.; Akiyama, S.; Masuda, S.; Shimojo, M.; Asai,
A.; Imada, S.; Gopalswamy, N.
2015AGUFMSH43B2447Y Altcode:
It is well known that about 10% X-class solar flares are not associated
with coronal mass ejections (CMEs). These flares are referred to
as confined flares, which are not associated with mass or energetic
particles leaving the Sun. However, electrons are accelerated to MeV
energies as indicated by the presence of microwave emission with a
turnover frequency of ~15 GHz (Gopalswamy et al. 2009, IAU Symposium
257, p. 283). In this paper, we extend the study of confined flares to
lower soft X-ray flare sizes (M and above) that occurred in the time
window of the Nobeyama Radioheliograph (NoRH). We also make use of the
microwave spectral information from the Nobeyama Radio Polarimeters
(NoRP). During 1996 - 2014, NoRH and NoRP observed 663 flares with
size M1.0 or larger. Using the CME observations made by SOHO/LASCO
and STEREO/SECCHI, we found 215 flares with definite CME association
(eruptive flares) and 202 flares that definitely lacked CMEs (confined
flares). The remaining 146 flares whose CME association is unclear are
excluded from the analysis. We examined the peak brightness temperature
and the spatial size obtained by NoRH. Although there is a large
overlap between the two populations in these properties, we found
that microwave sources with the largest spatial extent and highest
brightness temperature are associated with eruptive flares. Spectral
analysis using NoRP data showed a tendency that more confined flares
had higher turnover frequency (≥17 GHz). We also compare the NoRH
images with the photospheric magnetograms to understand the difference
in the magnetic structure of the two types of flare sources.
---------------------------------------------------------
Title: CMEs during the Two Activity Peaks in Cycle 24 and their
Space Weather Consequences
Authors: Gopalswamy, N.; Makela, P.; Akiyama, S.; Yashiro, S.;
Thakur, N.
2015SunGe..10..111G Altcode: 2015arXiv150904216G
We report on a comparison between space weather events that occurred
around the two peaks in the sunspot number (SSN) during solar cycle
24. The two SSN peaks occurred in the years 2012 and 2014. Even
though SSN was larger during the second peak, we find that there were
more space weather events during the first peak. The space weather
events we considered are large solar energetic particle (SEP) events
and major geomagnetic storms associated with coronal mass ejections
(CMEs). We also considered interplanetary type II radio bursts, which
are indicative of energetic CMEs driving shocks. When we compared the
CME properties between the two SSN peaks, we find that more energetic
CMEs occurred during the 2012 peak. In particular, we find that CMEs
accompanying IP type II bursts had an average speed of 1543 km/s
during the 2012 peak compared to 1201 km/s during the 2014 peak. This
result is consistent with the reduction in the average speed of the
general population of CMEs during the second peak. All SEP events
were associated with the interplanetary type II bursts, which are
better than halo CMEs as indicators of space weather. The comparison
between the two peaks also revealed the discordant behavior between
the CME rate and SSN was more pronounced during the second peak. None
of the 14 disk-center halo CMEs was associated with a major storm in
2014. The lone major storm in 2014 was due to the intensification of
the (southward) magnetic field in the associated magnetic cloud by a
shock that caught up and propagated into the magnetic cloud.
---------------------------------------------------------
Title: Short-term variability of the Sun-Earth system: an overview
of progress made during the CAWSES-II period
Authors: Gopalswamy, Nat; Tsurutani, Bruce; Yan, Yihua
2015PEPS....2...13G Altcode: 2015PESS....2...13G; 2015arXiv150406332G
This paper presents an overview of results obtained during the CAWSES-II
period on the short-term variability of the Sun and how it affects
the near-Earth space environment. CAWSES-II was planned to examine
the behavior of the solar-terrestrial system as the solar activity
climbed to its maximum phase in solar cycle 24. After a deep minimum
following cycle 23, the Sun climbed to a very weak maximum in terms
of the sunspot number in cycle 24 (MiniMax24), so many of the results
presented here refer to this weak activity in comparison with cycle
23. The short-term variability that has immediate consequence to Earth
and geospace manifests as solar eruptions from closed-field regions and
high-speed streams from coronal holes. Both electromagnetic (flares)
and mass emissions (coronal mass ejections - CMEs) are involved in
solar eruptions, while coronal holes result in high-speed streams that
collide with slow wind forming the so-called corotating interaction
regions (CIRs). Fast CMEs affect Earth via leading shocks accelerating
energetic particles and creating large geomagnetic storms. CIRs
and their trailing high-speed streams (HSSs), on the other hand,
are responsible for recurrent small geomagnetic storms and extended
days of auroral zone activity, respectively. The latter leads to the
acceleration of relativistic magnetospheric `killer' electrons. One
of the major consequences of the weak solar activity is the altered
physical state of the heliosphere that has serious implications for
the shock-driving and storm-causing properties of CMEs. Finally,
a discussion is presented on extreme space weather events prompted
by the 23 July 2012 super storm event that occurred on the backside
of the Sun. Many of these studies were enabled by the simultaneous
availability of remote sensing and in situ observations from multiple
vantage points with respect to the Sun-Earth line.
---------------------------------------------------------
Title: Influence of the Solar Wind Speed on the Propagation of
Coronal Mass Ejections
Authors: Yashiro, S.; Tokumaru, M.; Fujiki, K.; Iju, T.; Akiyama,
S.; Makela, P. A.; Gopalswamy, N.
2015AGUFMSH53B2497Y Altcode:
We investigate the influence of the solar wind (SW) on the propagation
of a set of 191 coronal mass ejections (CMEs) near the Sun during
the period 1996-2013. The CMEs were observed by LASCO on board SOHO
and their source regions were identified using the CME-associated
eruptive features (flares, filament eruptions, dimmings) in X-ray, EUV,
microwave, and Hα observations. The SW speeds above the CME source
regions were estimated from the interplanetary scintillation (IPS)
observations from the Solar Terrestrial Environ Laboratory, Nagoya
University. We considered only CMEs from close to the limb in order to
avoid the projection effects. We also considered CMEs with at least 10
height-time measurements in order to avoid the large uncertainty in the
acceleration measurements. We confirm the well-known CME-SW relationship
that the CMEs propagating faster (slower) than the ambient solar wind
are likely to decelerate (accelerate). The correlation between the
acceleration and the difference of the CME and the SW speeds is high
with a correlation coefficient of -0.74, slightly lower compared to the
one for CMEs associated with interplanetary radio bursts (Gopalswamy
et al. 2001, JGR, 106, 29219). There are many accelerating CMEs in
our sample with a speed similar to the ambient solar wind speed. This
could be due to selection effect because accelerating CMEs tend to
remain visible longer than decelerating ones. We also found that CMEs
originating from around the sources of the fast solar wind tend to be
faster, indicating that the open magnetic fields above the CME source
regions affect the CME propagation.
---------------------------------------------------------
Title: Comparison of the 26 May 2012 SEP Event with the 3 November
2011 SEP Event
Authors: Makela, P. A.; Gopalswamy, N.; Thakur, N.; Xie, H.
2015AGUFMSH33B2465M Altcode:
We compare the solar and interplanetary events associated with two
large solar energetic particle (SEP) events on 26 May 2012 and 3
November 2011. Both SEP events were detected at three longitudinally
widely separated locations by STEREO A and B spacecraft (more than 100
deg away from Earth) and the Wind and SOHO spacecraft near Earth. In
Earth view, the November 2011 eruption occurred far behind the east
limb at N09E154, whereas the May 2012 eruption occurred closer to the
west limb at N15W121, suggesting that SEPs accelerated during the 2012
event might have easier access to Earth. Even though the 2012 event
was more intense in the GOES >10 MeV proton channel (peak intensity
14 pfu) than the 2011 event (peak intensity 4 pfu), we find that the
latter event was more intense at higher energies (> 40 MeV). Also,
the initial rise at lower energies was slightly faster for the 2011
event as measured by SOHO/ERNE. In addition, the CME associated with
the May 2012 event was faster with an estimated space speed of ~2029
km/s than that in the November 2011 event (1188 km/s). STEREO/EUVI
images of the associated post-eruption arcades (PEAs) indicate that
their orientations were different: the PEA of the May 2012 event had
a high inclination (north-south), while the inclination of the PEA
of the 2011 event was more moderate. Differences in the flux rope
orientation may also have effect on the longitudinal extent of the
SEP events. These observations suggest that the dependence of solar
proton intensities on the observer's longitudinal distance from the
solar source is more complex than traditionally assumed.
---------------------------------------------------------
Title: Diffuse Interplanetary Radio Emission (DIRE) Accompanying
Type II Radio Bursts
Authors: Teklu, T. B.; Gopalswamy, N.; Makela, P. A.; Yashiro, S.;
Akiyama, S.; Xie, H.
2015AGUFMSH51A2441T Altcode:
We report on an unusual drifting feature in the radio dynamic spectra
at frequencies below 14 MHz observed by the Radio and Plasma Wave
(WAVES) experiment on board the Wind spacecraft. We call this
feature as "Diffuse Interplanetary Radio Emission (DIRE)". The DIRE
events are generally associated with intense interplanetary type
II radio bursts produced by shocks driven by coronal mass ejections
(CMEs). DIREs drift like type II bursts in the dynamic spectra, but
the drifting feature consist of a series of short-duration spikes
(similar to a type I chain). DIREs occur at higher frequencies than
the associated type II bursts, with no harmonic relationship with the
type II burst. The onset of DIREs is delayed by several hours from
the onset of the eruption. Comparing the radio dynamic spectra with
white-light observations from the Solar and Heliospheric Observatory
(SOHO) mission, we find that the CMEs are generally very energetic
(fast and mostly halos). We suggest that the DIRE source is typically
located at the flanks of the CME-driven shock that is still at lower
heliocentric distances.
---------------------------------------------------------
Title: Type II Radio Bursts as Indicators of Space Weather Drivers
Authors: Gopalswamy, N.
2015AGUFMSH41F..04G Altcode:
Interplanetary type II radio bursts are important indicators of
shock-driving coronal mass ejections (CMEs). CME-driven shocks
are responsible for large solar energetic particle (SEP) events
and sudden commencement/sudden impulse events recorded by ground
magnetometers. The excellent overlap of the spatial domains probed
by SOHO/STEREO coronagraphs with the spectral domains of Wind/WAVES
and STEREO/WAVES has contributed enormously in understanding CMEs and
shocks as space weather drivers. This paper is concerned with type II
bursts of solar cycle 23 and 24 that had emission components down to
kilometric wavelengths. CMEs associated with these bursts seem to be the
best indicators of large SEP events, better than the halo CMEs. However,
there are some differences between the type II bursts of the two cycles,
which are explained based on the different states of the heliosphere
in the two cycles. Finally, the type II burst characteristics of some
recent extreme events are discussed.
---------------------------------------------------------
Title: Advancing the understanding of the Sun-Earth interaction—the
Climate and Weather of the Sun-Earth System (CAWSES) II program
Authors: Tsuda, Toshitaka; Shepherd, Marianna; Gopalswamy, Nat
2015PEPS....2...28T Altcode: 2015PESS....2...28T
The Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) of the
International Council for Science (ICSU) implemented an international
collaborative program called Climate and Weather of the Sun-Earth System
(CAWSES), which was active from 2004 to 2008; this was followed by the
CAWSES II program during the period of 2009-2013. The CAWSES program was
aimed at improving the understanding of the coupled solar-terrestrial
system, with special emphasis placed on the short-term (weather) and
long-term (climate) variability of solar activities and their effects
on and responses of Geospace and Earth's environment. Following the
successful implementation of CAWSES, the CAWSES II program pursued
four fundamental questions addressing the way in which the coupled
Sun-Earth system operates over time scales ranging from minutes to
millennia, namely, (1) What are the solar influences on the Earth's
climate? (2) How will Geospace respond to an altered climate? (3) How
does short-term solar variability affect the Geospace environment? and
(4) What is the Geospace response to variable inputs from the lower
atmosphere? In addition to these four major tasks, the SCOSTEP and
CAWSES promoted E-science and informatics activities including the
creation of scientific databases and their effective utilization in
solar-terrestrial physics research. Capacity building activities were
also enhanced during CAWSES II, and this represented an important
contribution of SCOSTEP to the world's solar-terrestrial physics
community. This introductory paper provides an overview of CAWSES
II activities and serves as a preface to the dedicated review papers
summarizing the achievements of the program's four task groups (TGs)
and the E-science component.
---------------------------------------------------------
Title: a Roadmap to Advance Understanding of the Science of Space
Weather
Authors: Schrijver, K.; Kauristie, K.; Aylward, A.; De Nardin, C. M.;
Gibson, S. E.; Glover, A.; Gopalswamy, N.; Grande, M.; Hapgood, M. A.;
Heynderickx, D.; Jakowski, N.; Kalegaev, V. V.; Lapenta, G.; Linker,
J.; Liu, S.; Mandrini, C. H.; Mann, I. R.; Nagatsuma, T.; Nandy, D.;
Obara, T.; O'Brien, T. P., III; Onsager, T. G.; Opgenoorth, H. J.;
Terkildsen, M. B.; Valladares, C. E.; Vilmer, N.
2015AGUFMSH12A..01S Altcode:
There is a growing appreciation that the environmental conditions that
we call space weather impact the technological infrastructure that
powers the coupled economies around the world. With that comes the need
to better shield society against space weather by improving forecasts,
environmental specifications, and infrastructure design. A COSPAR/ILWS
team recently completed a roadmap that identifies the scientific focus
areas and research infrastructure that are needed to significantly
advance our understanding of space weather of all intensities and of
its implications and costs for society. This presentation provides a
summary of the highest-priority recommendations from that roadmap.
---------------------------------------------------------
Title: Low-Frequency Type II Radio Detections and Coronagraph Data
to Describe and Forecast the Propagation of 71 CMEs/Shocks
Authors: St Cyr, O. C.; Cremades, H.; Iglesias, F. A.; Xie, H.;
Kaiser, M. L.; Gopalswamy, N.
2015AGUFMSH21B2401S Altcode:
Motivated by improving predictions of arrival times at Earth of
shocks driven by coronal mass ejections (CMEs), we have analyzed 71
Earth-directed events in different stages of their propagation. The
study is primarily based on approximated locations of interplanetary
(IP) shocks derived from Type-II radio emissions detected by the
Wind/WAVES experiment during 1997-2007. Distance-time diagrams resulting
from the combination of white-light corona, IP Type-II radio, and
in situ data lead to the formulation of descriptive profiles of each
CME's journey toward Earth. Furthermore, two different methods to track
and predict the location of CME-driven IP shocks are presented. The
linear method, solely based on Wind/WAVES data, arises after key
modifications to a pre-existing technique that linearly projects the
drifting low-frequency Type-II emissions to 1 AU. This upgraded method
improves forecasts of shock arrival time by almost 50%. The second
predictive method is proposed on the basis of information derived from
the descriptive profiles, and relies on a single CME height-time point
and on low-frequency Type-II radio emissions to obtain an approximate
value of the shock arrival time at Earth. In addition, we discuss
results on CME-radio emission associations, characteristics of IP
propagation, and the relative success of the forecasting methods.
---------------------------------------------------------
Title: Requirements for an Operational Coronagraph
Authors: Howard, R.; Vourlidas, A.; Harrison, R. A.; Bisi, M. M.;
Plunkett, S. P.; Socker, D. G.; Eyles, C. J.; Webb, D. F.; DeForest,
C. E.; Davies, J. A.; Howard, T. A.; de Koning, C. A.; Gopalswamy,
N.; Davila, J. M.; Tappin, J.; Jackson, B. V.
2015AGUFMSH14A..02H Altcode:
Coronal mass ejections (CMEs) have been shown to be the major driver
of the non-recurrent space weather events and geomagnetic storms. The
utility of continuously monitoring such events has been very effectively
demonstrated by the LASCO experiment on the SOHO mission. However SOHO
is aging, having been launched 20 years ago on Dec 2, 1995. The STEREO
mission, in which two spacecraft in orbits about the sun are drifting
away from earth, has shown the utility of multiple viewpoints off the
sun-earth line. Up to now the monitoring of CMES has been performed
by scientific instruments such as LASCO and SECCHI with capabilities
beyond those required to record the parameters that are needed to
forecast the impact at earth. However, there is great interest within
the US NOAA and the UK Met Office to launch operational coronagraphs
to L1 and L5. An ad-hoc group was formed to define the requirements
of the L5 coronagraph. In this paper we present some requirements that
must be met by operational coronagraphs. The Office of Naval Research
is gratefully acknowledged.
---------------------------------------------------------
Title: Properties and geoeffectiveness of magnetic clouds during
solar cycles 23 and 24
Authors: Gopalswamy, N.; Yashiro, S.; Xie, H.; Akiyama, S.; Mäkelä,
P.
2015JGRA..120.9221G Altcode: 2015arXiv151000906G
We report on a study that compares the properties of magnetic clouds
(MCs) during the first 73 months of solar cycles 23 and 24 in order
to understand the weak geomagnetic activity in cycle 24. We find that
the number of MCs did not decline in cycle 24, although the average
sunspot number is known to have declined by ~40%. Despite the large
number of MCs, their geoeffectiveness in cycle 24 was very low. The
average Dst index in the sheath and cloud portions in cycle 24 was -33
nT and -23 nT, compared to -66 nT and -55 nT, respectively, in cycle
23. One of the key outcomes of this investigation is that the reduction
in the strength of geomagnetic storms as measured by the Dst index
is a direct consequence of the reduction in the factor VB<SUB>z</SUB>
(the product of the MC speed and the out-of-the-ecliptic component of
the MC magnetic field). The reduction in MC-to-ambient total pressure
in cycle 24 is compensated for by the reduction in the mean MC speed,
resulting in the constancy of the dimensionless expansion rate at 1
AU. However, the MC size in cycle 24 was significantly smaller, which
can be traced to the anomalous expansion of coronal mass ejections near
the Sun reported by Gopalswamy et al. (2014a). One of the consequences
of the anomalous expansion seems to be the larger heliocentric distance
where the pressure balance between the CME flux ropes and the ambient
medium occurs in cycle 24.
---------------------------------------------------------
Title: High-energy solar particle events in cycle 24
Authors: Gopalswamy, N.; Mäkelä, P.; Yashiro, S.; Xie, H.; Akiyama,
S.; Thakur, N.
2015JPhCS.642a2012G Altcode: 2015arXiv150706162G
The Sun is already in the declining phase of cycle 24, but the
paucity of high-energy solar energetic particle (SEP) events continues
with only two ground level enhancement (GLE) events as of March 31,
2015. In an attempt to understand this, we considered all the large SEP
events of cycle 24 that occurred until the end of 2014. We compared
the properties of the associated CMEs with those in cycle 23. We
found that the CME speeds in the sky plane were similar, but almost
all those cycle-24 CMEs were halos. A significant fraction of (16%)
of the frontside SEP events were associated with eruptive prominence
events. CMEs associated with filament eruption events accelerate slowly
and attain peak speeds beyond the typical GLE release heights. When we
considered only western hemispheric events that had good connectivity
to the CME nose, there were only 8 events that could be considered as
GLE candidates. One turned out to be the first GLE event of cycle 24
(2012 May 17). In two events, the CMEs were very fast (>2000 km/s)
but they were launched into a tenuous medium (high Alfven speed). In the
remaining five events, the speeds were well below the typical GLE CME
speed (∼2000 km/s). Furthermore, the CMEs attained their peak speeds
beyond the typical heights where GLE particles are released. We conclude
that several factors contribute to the low rate of high-energy SEP
events in cycle 24: (i) reduced efficiency of shock acceleration (weak
heliospheric magnetic field), (ii) poor latitudinal and longitudinal
connectivity), and (iii) variation in local ambient conditions (e.g.,
high Alfven speed).
---------------------------------------------------------
Title: Low-Frequency Type-II Radio Detections and Coronagraph Data
Employed to Describe and Forecast the Propagation of 71 CMEs/Shocks
Authors: Cremades, H.; Iglesias, F. A.; St. Cyr, O. C.; Xie, H.;
Kaiser, M. L.; Gopalswamy, N.
2015SoPh..290.2455C Altcode: 2015arXiv150501730C; 2015SoPh..tmp..136C
Motivated by improving predictions of arrival times at Earth of
shocks driven by coronal mass ejections (CMEs), we have analyzed 71
Earth-directed events in different stages of their propagation. The
study is primarily based on approximated locations of interplanetary
(IP) shocks derived from Type-II radio emissions detected by the
Wind/WAVES experiment during 1997 - 2007. Distance-time diagrams
resulting from the combination of white-light corona, IP Type-II radio,
and in-situ data lead to the formulation of descriptive profiles of
each CME's journey toward Earth. Furthermore, two different methods
for tracking and predicting the location of CME-driven IP shocks are
presented. The linear method, solely based on Wind/WAVES data, arises
after key modifications to a pre-existing technique that linearly
projects the drifting low-frequency Type-II emissions to 1 AU. This
upgraded method improves forecasts of shock-arrival times by almost 50
%. The second predictive method is proposed on the basis of information
derived from the descriptive profiles and relies on a single CME
height-time point and on low-frequency Type-II radio emissions to obtain
an approximate value of the shock arrival time at Earth. In addition,
we discuss results on CME-radio emission associations, characteristics
of IP propagation, and the relative success of the forecasting methods.
---------------------------------------------------------
Title: The Mild Space Weather in Solar Cycle 24
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Yashiro, Seiji; Xie,
Hong; Makela, Pertti; Michalek, Grzegorz
2015arXiv150801603G Altcode:
The space weather is extremely mild during solar cycle 24: the number
of major geomagnetic storms and high-energy solar energetic particle
events are at the lowest since the dawn of the space age. Solar wind
measurements at 1 AU using Wind and ACE instruments have shown that
there is a significant drop in the density, magnetic field, total
pressure, and Alfven speed in the inner heliosphere as a result of
the low solar activity. The drop in large space weather events is
disproportionately high because the number of energetic coronal mass
ejections that cause these events has not decreased significantly. For
example, the rate of halo CMEs, which is a good indicator of energetic
CMEs, is similar to that in cycle 23, even though the sunspot
number has declined by about 40%. The mild space weather seems to
be a consequence of the anomalous expansion of CMEs due to the low
ambient pressure in the heliosphere. The anomalous expansion results
in the dilution of the magnetic contents of CMEs, so the geomagnetic
storms are generally weak. CME driven shocks propagating through the
weak heliospheric field are less efficient in accelerating energetic
particles, so the particles do not attain high energies. Finally,
we would like to point out that extreme events such as the 2012 July
23 CMEs that occurred on the backside of the Sun and did not affect
Earth except for a small proton event.
---------------------------------------------------------
Title: Kinematic and Energetic Properties of the 2012 March 12 Polar
Coronal Mass Ejection
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2015ApJ...809..106G Altcode: 2015arXiv150704057G
We report on the energetics of the 2012 March 12 polar coronal mass
ejection (CME) originating from a southern latitude of ∼60°. The
polar CME is similar to low-latitude (LL) CMEs in almost all respects:
three-part morphology; post-eruption arcade (PEA), CME, and filament
kinematics; CME mass and kinetic energy; and the relative thermal energy
content of the PEA. From polarized brightness images, we estimate
the CME mass, which is close to the average mass of LL CMEs. The
CME kinetic energy (3.3 × 10<SUP>30</SUP> erg) is also typical of
the general population of CMEs. From photospheric magnetograms, we
estimate the free energy (1.8 × 10<SUP>31</SUP> erg) in the polar crown
source region, which we find is sufficient to power the CME and the
PEA. About 19% of the free energy went into the CME kinetic energy. We
compute the thermal energy content of the PEA (2.3 × 10<SUP>29</SUP>
erg) and find it to be a small fraction (6.8%) of the CME kinetic
energy. This fraction is remarkably similar to that in active region
CMEs associated with major flares. We also show that the 2012 March 12
is one among scores of polar CMEs observed during the maximum phase of
cycle 24. The cycle 24 polar crown prominence eruptions have the same
rate of association with CMEs as those from LLs. This investigation
supports the view that all CMEs are magnetically propelled from closed
field regions, irrespective of their location on the Sun (polar crown
filament regions, quiescent filament regions, or active regions).
---------------------------------------------------------
Title: GOES: An Indicator for GLEs?
Authors: Thakur, Neeharika; Gopalswamy, N.; Mäkelä, P.; Akiyama,
S.; Yashiro, S.; Xie, H.
2015shin.confE.149T Altcode:
We surveyed all large solar energetic particle (SEP) events (intensity
at least 10 pfu in the >10 MeV GOES channel) in solar cycles 23
and 24 to confirm the suggestion that ground level enhancements (GLEs)
produce an intensity increase in the GOES >700 MeV proton channel
(Gopalswamy et al. 2014). The survey confirms this in all but two
large SEP events: (1) the GLE of 6 May 1998 (GLE57) did not have GOES
>700 MeV protons and (2) the 8 November 2000 SEP event had GOES
>700 MeV protons but no GLE was recorded. We compare GLE57 with
other similar GLEs, and the 8 November 2000 SEP event with those that
showed similar intensity increases in the GOES >700 MeV protons but
produced GLEs. We find that because GOES >700 MeV proton intensity
enhancements are typically small for small GLEs; they are difficult to
discern near solar minima due to higher background. Our results are
consistent with previous findings that GLEs are generally observed
when CME-driven shocks form at heights 1.2-1.9 solar radii (Rs) (GLE
release occurs when the CMEs are at 2-6 Rs). Our study also supports
the view that the nose region of the CME-shock may be accelerating GeV
particles, but may not be detected due to poor latitudinal connectivity
of the observer to the shock nose. We conclude that GOES >700 MeV
proton channel can be used as an indicator for GLEs with some rare
exceptions. Use of GOES as a GLE indicator becomes especially important
because the observation of small GLEs may be missed by sparsely located
neutron monitors.
---------------------------------------------------------
Title: Observational Aspects of Particle Acceleration Resulting
in GLEs
Authors: Gopalswamy, Nat
2015shin.confE.146G Altcode:
Ground Level Enhancement (GLE) events in cycle 24 have been extremely
rare: only 2 events have been reported as of June 4, 2015, even though
solar activity is already in the declining phase. In an attempt to
understand this, we examined all the large SEP events of cycle 24
that occurred until the end of 2014. We compared the properties of
the SEP-associated CMEs with those in cycle 23. We found that the
CME speeds in the sky plane are similar, but almost all the cycle-24
CMEs were halos. A significant fraction of (13%) of the frontside SEP
events were associated with eruptive prominence events. CMEs associated
with filament eruption events accelerate slowly and attain peak speeds
beyond the typical GLE release heights. When we considered only western
hemispheric SEP events that had good latitudinal connectivity to the CME
nose, there were only 8 candidate GLE events. One turned out to be the
first GLE event of cycle 24 (17 May 2012). In two events, the CMEs were
very fast (>2000 km/s) but they were launched into a tenuous medium
(high Alfven speed). In the remaining five events, the speeds were well
below the average CME speed ( 2000 km/s) in GLE events. Furthermore,
the CMEs attained their peak speeds beyond the typical heights where
GLE particles are released. We conclude that there are several factors
that seem to be responsible for the very low rate of high-energy
SEP events in cycle 24: (i) reduced efficiency of shock acceleration
(weak heliospheric magnetic field), (ii) large-ecliptic distance to
solar sources of major eruptions (poor latitudinal connectivity), and
(iii) variation in local ambient conditions (e.g., high Alfven speed).
---------------------------------------------------------
Title: Hierarchical relationship of DH and mDH type II bursts using
the kinematic properties of the associated CMEs
Authors: Teklu, Tsega Berhane; Gopalswamy, N.; Mäkelä, P.; Yashiro,
S.; Akiyama, S.; Xie, H.; Thakur, N.
2015shin.confE..51T Altcode:
Using type II radio bursts from WIND WAVES and the associated CMEs from
SOHO LASCO, Gopalswamy et al., (2005) found a hierarchical relationship
between the wavelength range of the type II bursts and CME kinetic
energy. Under 'DH Type II bursts' they had included mDH, DH and DHkm
bursts. (DH: Decameter-hectometric; m: metric; km: kilometric). In
this work, we consider the pure DH and mDH subsets separately. We find
that mDH have slightly larger average speed, larger halo fraction,
and larger non-halo width. Despite these consistent relationships,
DH CMEs have slightly larger association rate with SEPs than mDH
CMEs. The DH CMEs in Gopalswamy et al. (2005) have a higher average
speed because they include DH km CMEs, which are more energetic. The
SEP association rate of DH and mDH type II bursts are much smaller than
that of mkm type II bursts. The SEP sources are generally located in
the western hemisphere because of magnetic connectivity requirement.
---------------------------------------------------------
Title: Filament Eruptions Outside of Active Regions as Sources of
Large Solar Energetic Particle Events
Authors: Kahler, S.; Gopalswamy, N.; Makela, P.; Akiyama, S.; Yashiro,
S.; Xie, H.; Thakur, N.
2015ICRC...34...48K Altcode: 2015PoS...236...48K
No abstract at ADS
---------------------------------------------------------
Title: Solar energetic particle association of fast and wide coronal
mass ejections
Authors: Yashiro, Seiji; Gopalswamy, N.; Akiyama, S.; Mäkelä, P.;
Xie, H.
2015shin.confE..47Y Altcode:
The occurrence of solar energetic particle (SEP) events in association
with fast (speed ∼900 km/s) and wide (width ∼) coronal mass
ejections (FW CMEs) was investigated. Source regions of the FW CMEs were
identified using SOHO/EIT, STEREO/EUVI, and SDO/AIA images. Using STEREO
EUV observations, we are able to determine the source locations of
CMEs that occurred behind the limb with a high degree of accuracy. The
>10 MeV proton flux at Earth was examined using GOES/SEM. The
>10 MeV proton flux at the STEREO spacecraft was estimated using
STEREO/HET, which detects energetic protons in 11 energy channels in
the range 13.6 to 100 MeV. By fitting a power law to the STEREO data,
we extrapolated the proton flux to the 10 - 150 MeV range as an estimate
of the >10 MeV proton flux. We examined the SEP associations of
196 FW CMEs that occurred during 2006 December to 2014 September and
found that (1) the SEP association rate peaked at the W61°, (2) the
magnetically well-connected longitudes range from W20°-W93°, (3)
the SEP association rate distribution is skewed: the eastern wing of
the rate distribution drops slowly compared to the western wing, (4)
all >1700 km/s CMEs originating from the well-connected longitude
are associated with the SEP events. We examined the preconditioning by
preceding CMEs and found that all but one huge SEP event (∼1000 pfu)
are preconditioned.
---------------------------------------------------------
Title: Energy Dependence of SEP Electron and Proton Onset Times
Authors: Xie, Hong; Makela, P.; Gopalswamy, N.; St. Cyr, O. C.
2015shin.confE..46X Altcode:
We study large solar energetic particle (SEP) events with >
10 MeV proton flux observed by GOES during solar cycle 24. Using
multi-spacecraft observations from STEREO A, B and SOHO, we are able
to determine accurately the solar particle release (SPR) time of
SEP electrons and protons. We first compute connection angles (CA)
between the solar events and magnetic foot-points connecting to each
spacecraft. By choosing the smallest CA, we derive the electron and
proton SPRs using electron fluxes from the SOHO Electron Proton and
Helium Instrument (EPHIN), proton fluxes from the SOHO Energetic and
Relativistic Nuclei and Electron instrument (ERNE), and from the High
Energy Telescope (HET) on STEREO. We find that the proton SPRs inferred
from high-energy channels (> 50 MeV) are similar to electron SPRs;
the proton SPRs inferred from lower energy channel (5.12 - 16.9 MeV)
can be delayed from the electron SPRs from tens of minutes to hours,
especially for SEPs with large pre-event flux levels, suggesting that
lower-energy protons might be trapped for a long time or suffer more
scattering than higher-energy protons. We also find that for some large
SEP events, the observed EPHIN electron and ERNE proton intensity
profiles show a double-peak feature. The onset of the first peak
corresponds well to the associated Type III and metric Type II onset.
---------------------------------------------------------
Title: Earth-arrival of Coronal Mass Ejections originating from
close to the Solar Disk Center
Authors: Akiyama, Sachiko; Yashiro, S.; Gopalswamy, N.; Mäkelä,
P.; Xie, H.
2015shin.confE..97A Altcode:
Not all coronal mass ejections (CMEs) that originate from close to the
solar disk center arrive at Earth due to various reasons. In order
to find the fraction of CMEs that do reach Earth, we investigated a
set of wide CMEs (width ∼ 60 degrees) originating from close to the
disk center (Central Meridian Distance < 30 degrees). Seventy such
CMEs were identified in 2011 using SOHO and STEREO coronagraphs and
heliospheric imagers. The solar sources of these CMEs were confirmed to
be close to the disk center using images from the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We found
that only about a third of the disk-center CMEs arrived at Earth. We
examined the possible reasons for the non-arrival of the remaining
CMEs and found that 1) 31% of CMEs faded out before reaching Earth,
2) 27% were captured by following faster CMEs, and 3) 7% of CMEs left
the ecliptic plane. The faded-out CMEs became invisible in STEREO/COR1
(32%), COR2 (32%), or HI1 (36%) fields of view. We also investigated
the geoeffectiveness of the Earth-arriving CMEs and found that only 17%
(4/22) of them produced at least a moderate geomagnetic storm (Dst
index < -50 nT). The Dst index of the largest geomagnetic storms
in our data set was -72 nT. In 2011 there were 3 intense geomagnetic
storms (Dst Index < -100 nT), but all of them were produced by
non-disk center CMEs and hence they are not in our sample. We also
found that the Earth-arriving CMEs are faster than the fading-out CMEs
( 700 km/s vs. 300 km/s) from COR1 to COR2 FOVs. We conclude that
only a tiny fraction of wide CMEs originating from the disk center
are geoeffective (4/70 or 6%). In the future work, we are planning to
expand study period to increase the sample size.
---------------------------------------------------------
Title: White-light and radio observations of CME interaction during
the 2013 May 22 solar energetic particle event
Authors: Mäkelä, Pertti; Gopalswamy, N.; Yashiro, S.; Xie, H.;
Reiner, M. J.
2015shin.confE..96M Altcode:
On 2013 May 22, the SOHO/LASCO coronagraph observed two coronal mass
ejections (CMEs) in close sequence at 08:48 UT and 13:25 UT originating
from the same NOAA AR11745 located at N15W70. The CMEs were associated
with a large increase of proton flux with a peak intensity of 1660
protons cm^-2 sr^-1 s^-1 in the GOES >10 MeV integral channel. During
the event, the following, faster CME with a sky-plane speed of 1466 km/s
overtook and interacted with the preceding, slower CME with a sky-plane
speed of 687 km/s. The LASCO white-light images clearly revealed that
during the interaction the preceding CME accelerated while the following
CME decelerated. The CME interaction also caused an enhancement of type
II radio emission detected at the decameter-hectometric wavelengths by
radio instruments on the Wind and STEREO spacecraft. The source location
of the type II enhancement estimated by direction finding technique
confirmed that the radio emission was coming from the interaction
region. The drift rate of the type II radio burst was also seen to be
different after the merger of the CMEs.
---------------------------------------------------------
Title: Estimating the Height of CMEs Associated with a Major SEP
Event at the Onset of the Metric Type II Radio Burst during Solar
Cycles 23 and 24
Authors: Mäkelä, P.; Gopalswamy, N.; Akiyama, S.; Xie, H.;
Yashiro, S.
2015ApJ...806...13M Altcode:
We studied the coronal mass ejection (CME) height at the onset of 59
metric type II radio bursts associated with major solar energetic
particle (SEP) events, excluding ground level enhancements (GLEs),
during solar cycles 23 and 24. We calculated CME heights using a simple
flare-onset method used by Gopalswamy et al. to estimate CME heights
at the metric type II onset for cycle 23 GLEs. We found the mean CME
height for non-GLE events (1.72 R<SUB>⊙</SUB>) to be ∼12% greater
than that (1.53 R<SUB>⊙</SUB>) for cycle 23 GLEs. The difference could
be caused by more impulsive acceleration of the GLE-associated CMEs. For
cycle 24 non-GLE events, we compared the CME heights obtained using the
flare-onset method and the three-dimensional spherical-shock fitting
method and found the correlation to be good (CC = 0.68). We found the
mean CME height for cycle 23 non-GLE events (1.79 R<SUB>⊙</SUB>) to be
greater than that for cycle 24 non-GLE events (1.58 R<SUB>⊙</SUB>),
but statistical tests do not definitely reject the possibility of
coincidence. We suggest that the lower formation height of the shocks
during cycle 24 indicates a change in the Alfvén speed profile because
solar magnetic fields are weaker and plasma density levels are closer
to the surface than usual during cycle 24. We also found that complex
type III bursts showing diminution of type III emission in the 7-14
MHz frequency range are more likely associated with events with a
CME height at the type II onset above 2 R<SUB>⊙</SUB>, supporting
suggestions that the CME/shock structure causes the feature.
---------------------------------------------------------
Title: Understanding space weather to shield society: A global road
map for 2015-2025 commissioned by COSPAR and ILWS
Authors: Schrijver, Carolus J.; Kauristie, Kirsti; Aylward, Alan D.;
Denardini, Clezio M.; Gibson, Sarah E.; Glover, Alexi; Gopalswamy,
Nat; Grande, Manuel; Hapgood, Mike; Heynderickx, Daniel; Jakowski,
Norbert; Kalegaev, Vladimir V.; Lapenta, Giovanni; Linker, Jon A.;
Liu, Siqing; Mandrini, Cristina H.; Mann, Ian R.; Nagatsuma, Tsutomu;
Nandy, Dibyendu; Obara, Takahiro; Paul O'Brien, T.; Onsager, Terrance;
Opgenoorth, Hermann J.; Terkildsen, Michael; Valladares, Cesar E.;
Vilmer, Nicole
2015AdSpR..55.2745S Altcode: 2015arXiv150306135S
There is a growing appreciation that the environmental conditions
that we call space weather impact the technological infrastructure
that powers the coupled economies around the world. With that comes
the need to better shield society against space weather by improving
forecasts, environmental specifications, and infrastructure design. We
recognize that much progress has been made and continues to be made
with a powerful suite of research observatories on the ground and
in space, forming the basis of a Sun-Earth system observatory. But
the domain of space weather is vast - extending from deep within the
Sun to far outside the planetary orbits - and the physics complex
- including couplings between various types of physical processes
that link scales and domains from the microscopic to large parts
of the solar system. Consequently, advanced understanding of space
weather requires a coordinated international approach to effectively
provide awareness of the processes within the Sun-Earth system through
observation-driven models. This roadmap prioritizes the scientific focus
areas and research infrastructure that are needed to significantly
advance our understanding of space weather of all intensities and
of its implications for society. Advancement of the existing system
observatory through the addition of small to moderate state-of-the-art
capabilities designed to fill observational gaps will enable significant
advances. Such a strategy requires urgent action: key instrumentation
needs to be sustained, and action needs to be taken before core
capabilities are lost in the aging ensemble. We recommend advances
through priority focus (1) on observation-based modeling throughout the
Sun-Earth system, (2) on forecasts more than 12 h ahead of the magnetic
structure of incoming coronal mass ejections, (3) on understanding
the geospace response to variable solar-wind stresses that lead to
intense geomagnetically-induced currents and ionospheric and radiation
storms, and (4) on developing a comprehensive specification of space
climate, including the characterization of extreme space storms to guide
resilient and robust engineering of technological infrastructures. The
roadmap clusters its implementation recommendations by formulating
three action pathways, and outlines needed instrumentation and research
programs and infrastructure for each of these. An executive summary
provides an overview of all recommendations.
---------------------------------------------------------
Title: Large Solar Energetic Particle Events Associated with Filament
Eruptions Outside of Active Regions
Authors: Gopalswamy, N.; Mäkelä, P.; Akiyama, S.; Yashiro, S.; Xie,
H.; Thakur, N.; Kahler, S. W.
2015ApJ...806....8G Altcode: 2015arXiv150400709G
We report on four large filament eruptions (FEs) from solar cycles 23
and 24 that were associated with large solar energetic particle (SEP)
events and interplanetary type II radio bursts. The post-eruption
arcades corresponded mostly to C-class soft X-ray enhancements,
but an M1.0 flare was associated with one event. However, the
associated coronal mass ejections (CMEs) were fast (speeds ∼ 1000
km s<SUP>-1</SUP>) and appeared as halo CMEs in the coronagraph field
of view. The interplanetary type II radio bursts occurred over a wide
wavelength range, indicating the existence of strong shocks throughout
the inner heliosphere. No metric type II bursts were present in
three events, indicating that the shocks formed beyond 2-3 Rs. In one
case, there was a metric type II burst with low starting frequency,
indicating a shock formation height of ∼2 Rs. The FE-associated SEP
events did have softer spectra (spectral index >4) in the 10-100
MeV range, but there were other low-intensity SEP events with spectral
indices ≥4. Some of these events are likely FE-SEP events, but were
not classified as such in the literature because they occurred close
to active regions. Some were definitely associated with large active
region flares, but the shock formation height was large. We definitely
find a diminished role for flares and complex type III burst durations
in these large SEP events. Fast CMEs and shock formation at larger
distances from the Sun seem to be the primary characteristics of the
FE-associated SEP events.
---------------------------------------------------------
Title: The Peculiar Behavior of Halo Coronal Mass Ejections in Solar
Cycle 24
Authors: Gopalswamy, N.; Xie, H.; Akiyama, S.; Mäkelä, P.; Yashiro,
S.; Michalek, G.
2015ApJ...804L..23G Altcode: 2015arXiv150401797G
We report on the remarkable finding that the halo coronal mass ejections
(CMEs) in cycle 24 are more abundant than in cycle 23, although the
sunspot number in cycle 24 has dropped by ∼40%. We also find that
the distribution of halo-CME source locations is different in cycle 24:
the longitude distribution of halos is much flatter with the number of
halos originating at a central meridian distance ≥slant 60{}^\circ
twice as large as that in cycle 23. On the other hand, the average
speed and associated soft X-ray flare size are the same in both cycles,
suggesting that the ambient medium into which the CMEs are ejected is
significantly different. We suggest that both the higher abundance and
larger central meridian longitudes of halo CMEs can be explained as
a consequence of the diminished total pressure in the heliosphere in
cycle 24. The reduced total pressure allows CMEs to expand more than
usual making them appear as halos.
---------------------------------------------------------
Title: Geometrical Relationship Between Interplanetary Flux Ropes
and Their Solar Sources
Authors: Marubashi, K.; Akiyama, S.; Yashiro, S.; Gopalswamy, N.;
Cho, K. -S.; Park, Y. -D.
2015SoPh..290.1371M Altcode: 2015SoPh..tmp...46M
We investigated the physical connection between interplanetary flux
ropes (IFRs) near Earth and coronal mass ejections (CMEs) by comparing
the magnetic field structures of IFRs and CME source regions. The
analysis is based on the list of 54 pairs of ICMEs (interplanetary
coronal mass ejections) and CMEs that are taken to be the most probable
solar source events. We first attempted to identify the flux rope
structure in each of the 54 ICMEs by fitting models with a cylinder
and torus magnetic field geometry, both with a force-free field
structure. This analysis determined the possible geometries of the
identified flux ropes. Then we compared the flux rope geometries with
the magnetic field structure of the solar source regions. We obtained
the following results: (1) Flux rope structures are seen in 51 ICMEs
out of the 54. The result implies that all ICMEs have an intrinsic
flux rope structure, if the three exceptional cases are attributed to
unfavorable observation conditions. (2) It is possible to find flux rope
geometries with the main axis orientation close to the orientation of
the magnetic polarity inversion line (PIL) in the solar source regions,
the differences being less than 25°. (3) The helicity sign of an IFR
is strongly controlled by the location of the solar source: flux ropes
with positive (negative) helicity are associated with sources in the
southern (northern) hemisphere (six exceptions were found). (4) Over
two-thirds of the sources in the northern hemisphere are concentrated
along PILs with orientations of 45° ± 30° (measured clockwise from
the east), and over two-thirds in the southern hemisphere along PILs
with orientations of 135° ± 30°, both corresponding to the Hale
boundaries. These results strongly support the idea that a flux rope
with the main axis parallel to the PIL erupts in a CME and that the
erupted flux rope propagates through the interplanetary space with
its orientation maintained and is observed as an IFR.
---------------------------------------------------------
Title: Dynamics of CMEs in the LASCO Field of View
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.; Bronarska, K.
2015SoPh..290..903M Altcode: 2015SoPh..tmp...20M
A large set (16 000) of coronal mass ejections (CMEs) observed during
1996 - 2011 was selected to study their dynamics in the LASCO field of
view (LFOV). These events were selected based on the criterion that at
least three height-time measurements were available for each CME. The
height-time measurements included in the SOHO/LASCO catalog were used
to determine velocities and accelerations of the respective CMEs at
successive distances from the Sun. Next, these parameters were sorted
into 30 subsamples depending on the distance from the Sun at which
they were determined. The mean velocities and accelerations calculated
for the successive distance-dependent subsamples of CMEs were used to
study their dynamics. We demonstrate that CMEs in the LFOV manifest
three distinct phases of propagation: (i) The propelling Lorentz
force dominates the dynamics of CMEs in the inner (C2 LASCO) FOV,
(ii) a stable propagation occurs as a result of the balance between
the propelling and drag forces, (iii) the drag force dominates at
the outer edge of the LFOV. When we considered different categories
of CME separately, we found different acceleration-distance profiles
for different categories.
---------------------------------------------------------
Title: The Dynamics of Eruptive Prominences
Authors: Gopalswamy, Nat
2015ASSL..415..381G Altcode: 2014arXiv1407.2594G
This chapter discusses the dynamical properties of eruptive prominences
in relation to coronal mass ejections (CMEs). The fact that eruptive
prominences are a part of CMEs is emphasized in terms of their
physical association and kinematics. The continued propagation of
prominence material into the heliosphere is illustrated using in-situ
observations. The solar-cycle variation of eruptive prominence locations
is discussed with a particular emphasis on the rush-to-the-pole (RTTP)
phenomenon. One of the consequences of the RTTP phenomenon is polar
CMEs, which are shown to be similar to the low-latitude CMEs. This
similarity is important because it provides important clues to
the mechanism by which CMEs erupt. The nonradial motion of CMEs
is discussed, including the deflection by coronal holes that have
important space weather consequences. Finally, the implications of
the presented observations for CME modeling are outlined.
---------------------------------------------------------
Title: Instant: An Innovative L5 Small Mission Concept for Coordinated
Science with Solar Orbiter and Solar Probe Plus
Authors: Lavraud, B.; Liu, Y. D.; Harrison, R. A.; Liu, W.;
Auchere, F.; Gan, W.; Lamy, P. L.; Xia, L.; Eastwood, J. P.;
Wimmer-Schweingruber, R. F.; Zong, Q.; Rochus, P.; Maksimovic, M.;
Temmer, M.; Escoubet, C. P.; Kilpua, E.; Rouillard, A. P.; Davies,
J. A.; Vial, J. C.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard,
T. A.; DeForest, C. E.
2014AGUFMSH21B4109L Altcode:
We will present both the science objectives and related instrumentation
of a small solar and heliospheric mission concept, INSTANT:
INvestigation of Solar-Terrestrial Activity aNd Transients. It will be
submitted as an opportunity to the upcoming ESA-China S-class mission
call later this year. This concept was conceived to allow innovative
measurements and unprecedented, early determination of key properties
of Earthbound CMEs from the L5 vantage point. Innovative measurements
will include magnetic field determination in the corona thanks to
Hanle measurement in Lyman-α and polarized heliospheric imaging
for accurate determination of CME trajectories. With complementary
in situ measurements, it will uniquely permit solar storm science,
solar storm surveillance, and synergy with Solar Orbiter and Solar
Probe Plus (the ESA-China S2 mission launch is planned in 2021).
---------------------------------------------------------
Title: The Relation Between Large-Scale Coronal Propagating Fronts
and Type II Radio Bursts
Authors: Nitta, Nariaki V.; Liu, Wei; Gopalswamy, Nat; Yashiro, Seiji
2014SoPh..289.4589N Altcode: 2014arXiv1409.4754N
Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and
type II radio bursts are often associated with coronal mass ejections
(CMEs). Both phenomena may signify shock waves driven by CMEs. Taking
EUV full-disk images at an unprecedented cadence, the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has
observed the so-called EIT waves or large-scale coronal propagating
fronts (LCPFs) from their early evolution, which coincides with the
period when most metric type II bursts occur. This article discusses the
relation of LCPFs as captured by AIA with metric type II bursts. We show
examples of type II bursts without a clear LCPF and fast LCPFs without
a type II burst. Part of the disconnect between the two phenomena may
be due to the difficulty in identifying them objectively. Furthermore,
it is possible that the individual LCPFs and type II bursts may reflect
different physical processes and external factors. In particular,
the type II bursts that start at low frequencies and high altitudes
tend to accompany an extended arc-shaped feature, which probably
represents the 3D structure of the CME and the shock wave around it,
and not just its near-surface track, which has usually been identified
with EIT waves. This feature expands and propagates toward and beyond
the limb. These events may be characterized by stretching of field
lines in the radial direction and may be distinct from other LCPFs,
which may be explained in terms of sudden lateral expansion of the
coronal volume. Neither LCPFs nor type II bursts by themselves serve
as necessary conditions for coronal shock waves, but these phenomena
may provide useful information on the early evolution of the shock
waves in 3D when both are clearly identified in eruptive events.
---------------------------------------------------------
Title: Vision for the Future of Lws TR&T
Authors: Schwadron, N.; Mannucci, A. J.; Antiochos, S. K.;
Bhattacharjee, A.; Gombosi, T. I.; Gopalswamy, N.; Kamalabadi, F.;
Linker, J.; Pilewskie, P.; Pulkkinen, A. A.; Spence, H. E.; Tobiska,
W. K.; Weimer, D. R.; Withers, P.; Bisi, M. M.; Kuznetsova, M. M.;
Miller, K. L.; Moretto, T.; Onsager, T. G.; Roussev, I. I.; Viereck,
R. A.
2014AGUFMSH33B..02S Altcode:
The Living With a Star (LWS) program addresses acute societal
needs for understanding the effects of space weather and developing
scientific knowledge to support predictive capabilities. Our society's
heavy reliance on technologies affected by the space environment,
an enormous number of airline customers, interest in space tourism,
and the developing plans for long-duration human exploration space
missions are clear examples that demonstrate urgent needs for space
weather models and detailed understanding of space weather effects and
risks. Since its inception, the LWS program has provided a vehicle
to innovate new mechanisms for conducting research, building highly
effective interdisciplinary teams, and ultimately in developing the
scientific understanding needed to transition research tools into
operational models that support the predictive needs of our increasingly
space-reliant society. The advances needed require broad-based
observations that cannot be obtained by large missions alone. The
Decadal Survey (HDS, 2012) outlines the nation's needs for scientific
development that will build the foundation for tomorrow's space weather
services. Addressing these goals, LWS must develop flexible pathways
to space utilizing smaller, more diverse and rapid development of
observational platforms. Expanding utilization of ground-based assets
and shared launches will also significantly enhance opportunities
to fulfill the growing LWS data needs. Partnerships between NASA
divisions, national/international agencies, and with industry will
be essential for leveraging resources to address increasing societal
demand for space weather advances. Strengthened connections to user
communities will enhance the quality and impact of deliverables from
LWS programs. Thus, we outline the developing vision for the future of
LWS, stressing the need for deeper scientific understanding to improve
forecasting capabilities, for more diverse data resources, and for
project deliverables that address the growing needs of user communities.
---------------------------------------------------------
Title: Association Rate of Major Sep Events As a Function of CME
Speed and Source Longitude
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.; Makela, P. A.;
Xie, H.
2014AGUFMSH43A4186Y Altcode:
We report on the fraction of fast and wide coronal mass ejections
(FW CMEs; speed>900 km/s; width>60°) that produce solar
energetic particle (SEP) events. Source regions of the FW CMEs were
identified using SOHO/EIT, STEREO/EUVI, and SDO/AIA. Using STEREO EUV
observations, we are able to determine the source locations behind
the west limb with a high degree of accuracy. The >10 MeV proton
flux at Earth was examined using GOES/SEM. The >10 MeV proton flux
at the STEREO spacecraft was estimated using STEREO/HET, which detects
energetic protons in 11 channels from 13.6 to 100 MeV. We extrapolated
the proton flux in the 10 - 150 MeV range with a power-law fit and
derived the corresponding >10 MeV proton flux. For each FW CME,
we have three proton flux values for three different relative source
longitudes with respect to the observer. The SEP association rate is
determined by dividing the number of SEP-producing CMEs by the total
number of events in each 20° bin of the relative source longitude. We
found that the SEP association rate peaked at the W60°-W80° bin and
the magnetically well-connected longitudes range from W20°-W100°. We
also found that the rate distribution is skewed: the eastern wing of
the rate distribution drops slowly compared to the western wing. This
indicates that the eastern CMEs (longitude < 0°) have a better
chance to reach the magnetic field line connected to Earth than the
far-behind-the-west-limb (longitude > 120°) CMEs.
---------------------------------------------------------
Title: Estimation of Reconnection Flux using Post-eruption Arcades
and Prediction of Bz at Earth
Authors: Gopalswamy, N.; Xie, H.; Yashiro, S.; Akiyama, S.
2014AGUFMSH21C4139G Altcode:
Coronal mass ejections (CMEs) and flares share the same eruption
process as has been confirmed from various aspects of the two
phenomena. In particular, the post-eruption arcade and the CME flux
rope are formed out of the same reconnection process. It is customary
to compute the flare reconnection flux from the flare-ribbon area and
photospheric/chromosphericmagnetic field strength. Here we report on a
new method to compute the reconnection flux from post-eruption arcades
(PEAs). Instead of counting the ribbon pixels in a series of images,
we simply measure the area under PEAs after the flare maximum and the
underlying photospheric magnetic field. The reconnection flux is then
half of the product of these two quantities. We illustrate this method
using specific examples and show that the ribbon and arcade methods
yield very similar results. We show that this method provides a simple
means of predicting the 1-AU flux rope magnetic field (including Bz)
from measurements made near the Sun.
---------------------------------------------------------
Title: Factors Affecting the Occurrence of Large Solar Energetic
Particle Events
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Xie, H.; Makela,
P. A.; Thakur, N.
2014AGUFMSH41D..07G Altcode:
In order to understand the paucity of high-energy solar energetic
particle (SEP) events in solar cycle 24, we examined all major eruptions
(soft X-ray flare size ≥M5.0) on the front side of the Sun during
the period from December 1, 2008 to January 31, 2014. There were 59
such eruptions that were associated with CMEs. When a flux rope was
fitted to the white-light CMEs observed by SOHO and STEREO it was found
that the CME sources were on the disk only for 55 eruptions. There
were 16 large SEP events (proton intensity ≥10 pfu in the >10
MeV channel) detected by GOES and 4 by STEREO-B in association with
these eruptions. When the CMEs were grouped according to their speeds
(<1500 km/s and ≥ 1500 km/s) it was found that only three of
the <1500 km/s CMEs (or 11%) were associated with large SEP events
compared to 17 or (61%) of the ≥ 1500 km/s CMEs. This result confirms
the importance of CME speed for SEP association. In fact there were
ten other large SEP events with flare size <M5.0, but associated
with fast CMEs, suggesting that the flare size does not determine SEP
association. In order to narrow down the properties of CMEs that produce
GLE events, we divided the SEP-associated CMEs into a different speed
range: ≥2000 km/s and 1500-1999 km/s. We also required that the CMEs
originated from the longitudinal range of W20 to W90 (traditional GLE
longitudes). There were sixteen such events, 6 with speed in the range
1500-1999 km/s and 10 with ≥2000 km/s. When we further applied the
criterion that the latitudinal distance of the CME sources from the
ecliptic must be within ±13o (Gopalswamy et al. 2013 ApJL 765, L30),
we found that there were only four CMEs that met this criterion. One
of the four was the GLE event of 2012 May 17 whose CME speed was only
slightly less than 2000 km/s. The 2011 August 9 CME was ejected into
a tenuous medium, which means the shock was likely weak due to higher
ambient Alfven speed, even though the CME speed was well above 2000
km/s. The speed of the 2011 June 7 CME (1680 km/s) was well below the
typical speed of GLE CMEs. The last one, the 2013 May 22 event was
an interacting CME event, but the speed of the primary CME was only
1880 km/s. Thus we conclude that the CME speed, the ecliptic distance
of the CME source, and the ambient conditions are all important in
deciding whether an SEP event would have GLE particles. Work supported
by NASA's Living with a Star Program.
---------------------------------------------------------
Title: High Energy Particle Events in Solar Cycles 23 and 24
Authors: Thakur, N.; Gopalswamy, N.; Makela, P. A.; Yashiro, S.;
Akiyama, S.; Xie, H.
2014AGUFMSH43A4190T Altcode:
We present a study of high-energy solar energetic particle (SEP) events
in solar cycles 23 and 24 using GOES data. We selected large SEP events,
which showed intensity enhancements in the >500 MeV and >700 MeV
GOES energy channels. A study of cycle 24 and the first half of cycle
23 ground level enhancements (GLEs) by Gopalswamy et al. 2014 showed
that typically, SEP events with intensity enhancement at >700 MeV
have been associated with GLEs. We have extended the survey to cover
the whole cycle 23. Our preliminary survey confirms this to be true
for all except for three cases. There were two GLEs (1998/05/06 and
2006/12/06) for which a clear increase in >700 MeV protons was not
observed by GOES. There was one high energy SEP event (2000/11/08), for
which GOES observed >700 MeV protons but no GLE was produced. Here
we compare all the high-energy particle events from cycles 23 and
24 with GLEs. We also compare energy spectra of all high-energy SEP
events with those that produced GLEs. Work supported by NASA's Living
with a Star Program. Ref.: Gopalswamy et al. 2014, GRL, 41, 2673
---------------------------------------------------------
Title: Major solar eruptions and high-energy particle events during
solar cycle 24
Authors: Gopalswamy, Nat; Xie, Hong; Akiyama, Sachiko; Mäkelä,
Pertti A.; Yashiro, Seiji
2014EP&S...66..104G Altcode: 2014arXiv1408.3617G
We report on a study of all major solar eruptions that occurred on
the frontside of the Sun during the rise to peak phase of cycle 24
(first 62 months) in order to understand the key factors affecting the
occurrence of large solar energetic particle events (SEPs) and ground
level enhancement (GLE) events. The eruptions involve major flares
with soft X-ray peak flux ≥ 5.0 x10<SUP>-5</SUP> Wm<SUP>-2</SUP>
(i.e., flare size ≥ M5.0) and accompanying coronal mass ejections
(CMEs). The selection criterion was based on the fact that the only
front-side GLE in cycle 24 (GLE 71) had a flare size of M5.1. Only
approximately 37% of the major eruptions from the western hemisphere
resulted in large SEP events. Almost the same number of large SEP
events was produced in weaker eruptions (flare size < M5.0),
suggesting that the soft X-ray flare is not a good indicator of SEP
or GLE events. On the other hand, the CME speed is a good indicator of
SEP and GLE events because it is consistently high supporting the shock
acceleration mechanism. We found the CME speed, magnetic connectivity
to Earth (in longitude and latitude), and ambient conditions as the
main factors that contribute to the lack of high-energy particle
events during cycle 24. Several eruptions poorly connected to Earth
(eastern-hemisphere or behind-the-west-limb events) resulted in very
large SEP events detected by the Solar Terrestrial Relations Observatory
(STEREO) spacecraft. Some very fast CMEs, likely to have accelerated
particles to GeV energies, did not result in a GLE event because of
poor latitudinal connectivity. The stringent latitudinal requirement
suggests that the highest-energy particles are likely accelerated
in the nose part of shocks, while the lower energy particles are
accelerated at all parts. There were also well-connected fast CMEs,
which did not seem to have accelerated high-energy particles due to
possible unfavorable ambient conditions (high Alfven speed, overall
reduction in acceleration efficiency in cycle 24).
---------------------------------------------------------
Title: Strategic Science to Address Current and Future Space
Weather Needs
Authors: Mannucci, A. J.; Schwadron, N.; Antiochos, S. K.;
Bhattacharjee, A.; Bisi, M. M.; Gopalswamy, N.; Kamalabadi, F.;
Pulkkinen, A. A.; Tobiska, W. K.; Weimer, D. R.; Withers, P.
2014AGUFMSM24A..09M Altcode:
NASA's Living With a Star (LWS) program has contributed a wealth of
scientific knowledge that is relevant to space weather and user needs. A
targeted approach to science questions has resulted in leveraging
new scientific knowledge to improve not only our understanding of the
Heliophysics domain, but also to develop predictive capabilities in key
areas of LWS science. This fascinating interplay between science and
applications promises to benefit both domains. Scientists providing
feedback to the LWS program are now discussing an evolution of the
targeted approach that explicitly considers how new science improves,
or enables, predictive capability directly. Long-term program goals
are termed "Strategic Science Areas" (SSAs) that address predictive
capabilities in six specific areas: geomagnetically induced currents,
satellite drag, solar energetic particles, ionospheric total electron
content, radio frequency scintillation induced by the ionosphere,
and the radiation environment. SSAs are organized around user needs
and the impacts of space weather on society. Scientists involved in
the LWS program identify targeted areas of research that reference
(or bear upon) societal needs. Such targeted science leads to new
discoveries and is one of the valid forms of exploration. In this
talk we describe the benefits of targeted science, and how addressing
societal impacts in an appropriate way maintains the strong science
focus of LWS, while also leading to its broader impacts.
---------------------------------------------------------
Title: Homologous flare-CME events and their metric type II radio
burst association
Authors: Yashiro, S.; Gopalswamy, N.; Mäkelä, P.; Akiyama, S.;
Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan,
P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.;
Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P.
2014AdSpR..54.1941Y Altcode:
Active region NOAA 11158 produced many flares during its disk
passage. At least two of these flares can be considered as homologous:
the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on February
14, 2011. Both flares occurred at the same location (eastern edge of
the active region) and have a similar decay of the GOES soft X-ray
light curve. The associated coronal mass ejections (CMEs) were slow
(334 and 337 km/s) and of similar apparent widths (43° and 44°), but
they had different radio signatures. The second event was associated
with a metric type II burst while the first one was not. The COR1
coronagraphs on board the STEREO spacecraft clearly show that the
second CME propagated into the preceding CME that occurred 50 min
before. These observations suggest that CME-CME interaction might be
a key process in exciting the type II radio emission by slow CMEs.
---------------------------------------------------------
Title: An Estimate of the Coronal Magnetic Field near a Solar Coronal
Mass Ejection from Low-frequency Radio Observations
Authors: Hariharan, K.; Ramesh, R.; Kishore, P.; Kathiravan, C.;
Gopalswamy, N.
2014ApJ...795...14H Altcode:
We report ground-based, low-frequency (<100 MHz) radio imaging,
spectral, and polarimeter observations of the type II radio burst
associated with the solar coronal mass ejection (CME) that occurred
on 2013 May 2. The spectral observations indicate that the burst has
fundamental (F) and harmonic (H) emission components with split-band
and herringbone structures. The imaging observations at 80 MHz indicate
that the H component of the burst was located close to leading edge
of the CME at a radial distance of r ≈ 2 R <SUB>⊙</SUB> in the
solar atmosphere. The polarimeter observations of the type II burst,
also at 80 MHz, indicate that the peak degree of circular polarization
(dcp) corresponding to the emission generated in the corona ahead
of and behind the associated MHD shock front are ≈0.05 ± 0.02 and
≈0.1 ± 0.01, respectively. We calculated the magnetic field B in
the above two coronal regions by adopting the empirical relationship
between the dcp and B for the harmonic plasma emission and the values
are ≈(0.7-1.4) ± 0.2 G and ≈(1.4-2.8) ± 0.1 G, respectively.
---------------------------------------------------------
Title: Coronal Mass Ejections and Non-recurrent Forbush Decreases
Authors: Belov, A.; Abunin, A.; Abunina, M.; Eroshenko, E.; Oleneva,
V.; Yanke, V.; Papaioannou, A.; Mavromichalaki, H.; Gopalswamy, N.;
Yashiro, S.
2014SoPh..289.3949B Altcode: 2014SoPh..tmp...73B
Coronal mass ejections (CMEs) and their interplanetary counterparts
(interplanetary coronal mass ejections, ICMEs) are responsible
for large solar energetic particle events and severe geomagnetic
storms. They can modulate the intensity of Galactic cosmic rays,
resulting in non-recurrent Forbush decreases (FDs). We investigate
the connection between CME manifestations and FDs. We used specially
processed data from the worldwide neutron monitor network to pinpoint
the characteristics of the recorded FDs together with CME-related data
from the detailed online catalog based upon the Solar and Heliospheric
Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO)
data. We report on the correlations of the FD magnitude to the CME
initial speed, the ICME transit speed, and the maximum solar wind
speed. Comparisons between the features of CMEs (mass, width, velocity)
and the characteristics of FDs are also discussed. FD features for halo,
partial halo, and non-halo CMEs are presented and discussed.
---------------------------------------------------------
Title: Ground Level Enhancement in the 2014 January 6 Solar Energetic
Particle Event
Authors: Thakur, N.; Gopalswamy, N.; Xie, H.; Mäkelä, P.; Yashiro,
S.; Akiyama, S.; Davila, J. M.
2014ApJ...790L..13T Altcode: 2014arXiv1406.7172T
We present a study of the 2014 January 6 solar energetic particle event
which produced a small ground level enhancement (GLE), making it the
second GLE of this unusual solar cycle 24. This event was primarily
observed by the South Pole neutron monitors (increase of ~2.5%) while a
few other neutron monitors recorded smaller increases. The associated
coronal mass ejection (CME) originated behind the western limb and
had a speed of 1960 km s<SUP>-1</SUP>. The height of the CME at the
start of the associated metric type II radio burst, which indicates
the formation of a strong shock, was measured to be 1.61 Rs using a
direct image from STEREO-A/EUVI. The CME height at the time of the GLE
particle release (determined using the South Pole neutron monitor data)
was directly measured as 2.96 Rs based on STEREO-A/COR1 white-light
observations. These CME heights are consistent with those obtained for
GLE71, the only other GLE of the current cycle, as well as cycle-23 GLEs
derived using back-extrapolation. GLE72 is of special interest because
it is one of only two GLEs of cycle 24, one of two behind-the-limb GLEs,
and one of the two smallest GLEs of cycles 23 and 24.
---------------------------------------------------------
Title: ISEST Program: International Stud of Earth-affecting Solar
Transients
Authors: Zhang, Jie; Temmer, Manuela; Gopalswamy, Nat
2014shin.confE...7Z Altcode:
A new international program: International Study of Earth-affecting
Solar Transients (IEST), is introduced. This program is one of
the four scientific elements supported by the VarSITI (Variability
of the Sun and Its Terrestrial Impact) project, a five-year long
international-cross-discipline-collaboration project from 2014-2018,
sponsored by the SCOSTEP (Scientific Committee of Solar-Terrestrial
Physics). The aim of ISEST is to understand the origin, propagation and
evolution of solar transients, including CMEs, CIRs and SEPs, through
the space between the Sun and the Earth, and improve the prediction
capability for space weather. Particular emphasis will be placed on the
weak solar activity prevailing in Solar Cycle 24 (MiniMax24). The ISEST
program consists of six working groups, encompassing data analysis,
theoretical interpretation, numerical modeling, B-south challenge,
event campaign study, and long-term MiniMax24 campaign studies. It
is anticipated that the ISEST will create a comprehensive online
database of Earth-affecting solar transients contributed by both
observers and modelers. By the end of the program It is expected that
the space weather prediction using solar observations will be improved
significantly.
---------------------------------------------------------
Title: An Investigation of the Interplanetary Type II Radio Bursts
Observed on 2012 January 19
Authors: Teklu, Tsega Berhane; Gopalswamy, N.; Mäkelä, P.; Yashiro,
S.; Akiyama, S.; Xie, H.
2014shin.confE.155T Altcode:
We report on the analysis of the 2012 January 19 type II radio bursts
observed by the Wind/WAVES experiment. The type II radio burst had two
components. The first was a short-lived burst in decameter-hectometric
(DH) while the second was long lived extending to kilometric (km)
wavelengths. The short-lived type II burst had a high drift rate
(- 5.4 kHz/s) while the long-lived one had a regular drift rate (-
2.7 kHz/s). The type II burst was associated with a halo CME observed
by SOHO/LASCO moving with a speed of 1120 km/s. The presence of two
type II bursts seems to be due to the interaction of the halo CME
with a proceeding CME, as indicated by SOHO and STEREO coronagrpahic
images. Analysis of the scale heights based on coronal density
variations confirms the interaction. We establish the connection
between CME height and the frequency of the type II bursts. The CME
was also associated with solar energetic particles, consistent with
the strong shock. The Earth arrival of the CME-driven shock was also
observed by Wind/TNR and SoHO/CELIAS Proton Monitor.
---------------------------------------------------------
Title: Understanding the Longitudinal Extent and Timing of SEP Onsets:
The November 3 2011 Event
Authors: Xie, Hong; St. Cyr, C.; Gopalswamy, N.
2014shin.confE..86X Altcode:
We study a multi-spacecraft solar energetic particle (SEP) event,
which occurred on November 3 2011. The CME associated with the
SEP event was observed as a behind the east-limb event (N06E152)
by SOHO/LASCO. The CME was observed to be at W102 and E50 in
STEREO-A and B views, respectively. This SEP event had a remarkable
prompt particle increase at all three spacecraft despite their
wide separation. Using a forward-fitting technique with an oblate
spheroid model, we study the evolution of the CME shock and EUV wave
in the low corona. Observations from STEREO and SOHO (white light),
and SDO (EUV) were used to constraint the 3D shock shape and the EUV
imprints on the solar surface. The combination of a full 3D model and
multi-wavelength observational constraints allowed us to determine
the radial and expansion speeds of the CME-shock and EUV wave in a
consistent way. We were also able to determine the timing and the
locations where the shock front intersects the magnetic footpoints
connected to each spacecraft. The Parker-spiral theory with the average
solar-wind speed measured in situ was used to estimate the location
of magnetic field lines connecting the Sun to each spacecraft. The
SEP onset time was determined by carrying out a velocity-dispersion
analysis on the particles arriving at each spacecraft. By comparing
the SEP onset delay with the time taken for the shock to expand to
the longitudes of the connecting magnetic field lines, we confirmed
that the wide spread SEP event was in fact a result of the expanding
shock and the EUV wave for this case.
---------------------------------------------------------
Title: Estimating the Height of CMEs at the Onset of Metric Type
II Bursts
Authors: Makela, Pertti; Gopalswamy, Nat
2014shin.confE.103M Altcode:
The onset of type II radio bursts indicates the moment when a shock
front ahead of a coronal mass ejection (CME) forms and starts to
accelerate electrons in the solar corona. Therefore, the onset of metric
type II bursts, which can be observed remotely by radio instruments,
provides us the first indication of the CME-driven shock front
propagating in the solar corona. Several methods have been suggested
to estimate the height of the associated CME. Here we estimate the
CME height by assuming that CMEs with an initial height of 1.25 Rs
accelerate from rest to final speed (the measured linear speed of the
CME) during a period starting at the flare onset time and ending at the
flare peak time, after which they propagate with a final speed. Using
this method Gopalswamy et al. (2012) found the CME height at metric
type II burst onset with mean and median values of 1.53 Rs and 1.47 Rs,
respectively for the cycle 23 ground level enhancement (GLE) events. We
have expanded this study to include all major non-GLE solar energetic
particle (SEP) events. We find that the average and median height of
non-GLE CMEs at the onset of the metric type II bursts to be 1.73 Rs
and 1.61 Rs, respectively. For cycle 23 (cycle 24) CMEs the average
height is 1.78 Rs (1.59 Rs) and the median height 1.61 Rs (1.45 Rs),
respectively. Because Alfven speed is proportional to magnetic field,
weaker solar magnetic fields during cycle 24 result in lower Alfven
speeds on average and hence shocks could form earlier, if we assume
that CME speed distributions are similar in cycle 23 and cycle 24.
---------------------------------------------------------
Title: Are Polar-crown Coronal Mass Ejections Similar to the
Low-latitude Counterparts?
Authors: Gopalswamy, N.; Yashiro, Seiji; Akiyama, Sachiko
2014AAS...22430306G Altcode:
Coronal mass ejections (CMEs) from the polar-crown filament
region originate above 60-degree latitude during solar activity
maxima. Polar-crown CMEs originate from bipolar magnetic regions,
whereas both bipolar and multipolar regions produce CMEs at low
latitudes. If polar CMEs are similar to the low-latitude ones,
then a single eruption mechanism can apply to all CMEs, the common
element being the magnetic free energy. We examine several polar-crown
CMEs to determine their three-part morphology, acceleration profile
including the height of peak acceleration, CME-flare relationship,
and energetics. We found that these properties are similar to those of
low-latitude CMEs. We use illustrative examples from the Solar Dynamics
Observatory images to show quantitatively that the polar-crown CMEs
are very similar to their low-latitude counterparts. Even though the
post eruption arcades are weak, we show that the peak thermal energy of
these arcades is a few percent of the CME kinetic energy, similar to
what is observed in large eruptive events. These observations suggest
that a bipolar configuration is sufficient for the production of CMEs.
---------------------------------------------------------
Title: Latitudinal Connectivity of Ground Level Enhancement Events
Authors: Gopalswamy, N.; Mäkelä, P.
2014ASPC..484...63G Altcode: 2013arXiv1310.8506G
We examined the source regions and coronal environment of the historical
ground level enhancement (GLE) events in search of evidence for
non-radial motion of the associated coronal mass ejection (CME). For
the 13 GLE events that had source latitudes >30° we found evidence
for possible non-radial CME motion due to deflection by large-scale
magnetic structures in nearby coronal holes, streamers, or pseudo
streamers. Polar coronal holes are the main source of deflection in
the rise and declining phases of solar cycles. In the maximum phase,
deflection by large-scale streamers or pseudo streamers overlying
high-latitude filaments seems to be important. The B0 angle reduced
the ecliptic distance of some GLE source regions and increased in
others with the net result that the average latitude of GLE events did
not change significantly. The non-radial CME motion is the dominant
factor that reduces the ecliptic distance of GLE source regions,
thereby improving the latitudinal connectivity to Earth. We further
infer that the GLE particles must be accelerated at the nose part of
the CME-driven shocks, where the shock is likely to be quasi-parallel.
---------------------------------------------------------
Title: Anomalous expansion of coronal mass ejections during solar
cycle 24 and its space weather implications
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Yashiro, Seiji; Xie,
Hong; Mäkelä, Pertti; Michalek, Grzegorz
2014GeoRL..41.2673G Altcode: 2014arXiv1404.0252G
The familiar correlation between the speed and angular width of
coronal mass ejections (CMEs) is also found in solar cycle 24, but
the regression line has a larger slope: for a given CME speed, cycle
24 CMEs are significantly wider than those in cycle 23. The slope
change indicates a significant change in the physical state of the
heliosphere, due to the weak solar activity. The total pressure in the
heliosphere (magnetic + plasma) is reduced by ~40%, which leads to the
anomalous expansion of CMEs explaining the increased slope. The excess
CME expansion contributes to the diminished effectiveness of CMEs in
producing magnetic storms during cycle 24, both because the magnetic
content of the CMEs is diluted and also because of the weaker ambient
fields. The reduced magnetic field in the heliosphere may contribute
to the lack of solar energetic particles accelerated to very high
energies during this cycle.
---------------------------------------------------------
Title: Do Solar Coronal Holes Affect the Properties of Solar Energetic
Particle Events?
Authors: Kahler, S. W.; Arge, C. N.; Akiyama, S.; Gopalswamy, N.
2014SoPh..289..657K Altcode:
The intensities and timescales of gradual solar energetic particle
(SEP) events at 1 AU may depend not only on the characteristics of
shocks driven by coronal mass ejections (CMEs), but also on large-scale
coronal and interplanetary structures. It has long been suspected
that the presence of coronal holes (CHs) near the CMEs or near the
1-AU magnetic footpoints may be an important factor in SEP events. We
used a group of 41 E≈ 20 MeV SEP events with origins near the solar
central meridian to search for such effects. First we investigated
whether the presence of a CH directly between the sources of the CME
and of the magnetic connection at 1 AU is an important factor. Then we
searched for variations of the SEP events among different solar wind
(SW) stream types: slow, fast, and transient. Finally, we considered the
separations between CME sources and CH footpoint connections from 1 AU
determined from four-day forecast maps based on Mount Wilson Observatory
and the National Solar Observatory synoptic magnetic-field maps and
the Wang-Sheeley-Arge model of SW propagation. The observed in-situ
magnetic-field polarities and SW speeds at SEP event onsets tested the
forecast accuracies employed to select the best SEP/CH connection events
for that analysis. Within our limited sample and the three analytical
treatments, we found no statistical evidence for an effect of CHs on SEP
event peak intensities, onset times, or rise times. The only exception
is a possible enhancement of SEP peak intensities in magnetic clouds.
---------------------------------------------------------
Title: Multiwavelength diagnostics of the precursor and main phases
of an M1.8 flare on 2011 April 22
Authors: Awasthi, A. K.; Jain, R.; Gadhiya, P. D.; Aschwanden, M. J.;
Uddin, W.; Srivastava, A. K.; Chandra, R.; Gopalswamy, N.; Nitta,
N. V.; Yashiro, S.; Manoharan, P. K.; Choudhary, D. P.; Joshi, N. C.;
Dwivedi, V. C.; Mahalakshmi, K.
2014MNRAS.437.2249A Altcode: 2013arXiv1310.6029A; 2013MNRAS.tmp.2720A
We study the temporal, spatial and spectral evolution of the M1.8 flare,
which occurred in the active region 11195 (S17E31) on 2011 April 22,
and explore the underlying physical processes during the precursor
phase and their relation to the main phase. The study of the source
morphology using the composite images in 131 Å wavelength observed by
the Solar Dynamics Observatory/Atmospheric Imaging Assembly and 6-14
keV [from the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI)] revealed a multiloop system that destabilized systematically
during the precursor and main phases. In contrast, hard X-ray emission
(20-50 keV) was absent during the precursor phase, appearing only from
the onset of the impulsive phase in the form of foot-points of emitting
loops. This study also revealed the heated loop-top prior to the loop
emission, although no accompanying foot-point sources were observed
during the precursor phase. We estimate the flare plasma parameters,
namely temperature (T), emission measure (EM), power-law index (γ)
and photon turn-over energy (ɛ<SUB>to</SUB>), and found them to be
varying in the ranges 12.4-23.4 MK, 0.0003-0.6 × 10<SUP>49</SUP>
cm<SUP>-3</SUP>, 5-9 and 14-18 keV, respectively, by forward fitting
RHESSI spectral observations. The energy released in the precursor
phase was thermal and constituted ≈1 per cent of the total energy
released during the flare. The study of morphological evolution of
the filament in conjunction with synthesized T and EM maps was carried
out, which reveals (a) partial filament eruption prior to the onset of
the precursor emission and (b) heated dense plasma over the polarity
inversion line and in the vicinity of the slowly rising filament during
the precursor phase. Based on the implications from multiwavelength
observations, we propose a scheme to unify the energy release during
the precursor and main phase emissions in which the precursor phase
emission was originated via conduction front that resulted due to the
partial filament eruption. Next, the heated leftover S-shaped filament
underwent slow-rise and heating due to magnetic reconnection and finally
erupted to produce emission during the impulsive and gradual phases.
---------------------------------------------------------
Title: INSTANT: INvestigation of Solar-Terrestrial Associated
Natural Threats
Authors: Lavraud, Benoit; Vial, Jean-Claude; Harrison, Richard; Davies,
Jackie; Escoubet, C. Philippe; Zong, Qiugang; Auchere, Frederic; Liu,
Ying; Bale, Stuart; Gopalswamy, Nat; Li, Gang; Maksimovic, Milan;
Liu, William; Rouillard, Alexis
2014cosp...40E1758L Altcode:
The INSTANT mission will tackle both compelling solar and heliospheric
science objectives and novel space weather capabilities. This is
allowed by combining innovative and state-of-the-art instrumentation
at an appropriate off-Sun-Earth line location on an orbit lagging
the Earth around the Sun, near the L5 Lagrangian point. It is an
affordable mission that tackles major objectives of the European and
Chinese communities in terms of space physics and space weather. The
science objectives are: 1. What is the magnetic field magnitude and
topology in the corona? 2. How does the magnetic field reconfigure
itself during CME eruptions? 3. What are the sources and links between
the slow and fast winds? 4. How do CMEs accelerate and interact in the
interplanetary medium? The mission will further allow the following
crucial space weather capabilities: 5. Three-days advance knowledge
of CIR properties that reach Earth. 6. Twelve hours to 2 days advance
warning of Earth-directed CMEs. 7. Thanks to Lyman-α observations,
first-ever capability of determining the magnetic field magnitude and
orientation of Earth-directed CMEs. The mission will be proposed in
the context of the upcoming ESA-China S-class call for mission.
---------------------------------------------------------
Title: Flare - Flux Rope Relationship using Post-eruption Arcades
Authors: Gopalswamy, Nat; Xie, Hong; Yashiro, Seiji; Akiyama, Sachiko
2014cosp...40E1047G Altcode:
A close connection between the coronal mass ejections (CME) and flare
in a given solar eruption has been confirmed from various aspects
of the two phenomena. The relation between the reconnection flux and
the poloidal flux of the associated 1-AU flux ropes is of particular
importance because it can be used for space weather predictions. It is
customary to compute the flare reconnection flux from the flare-ribbon
area and photospheric/chromospheric magnetic field strength. Here
we report on a new method to compute the reconnection flux from
post-eruption arcades (PEAs). Instead of counting the ribbon pixels in a
series of images, we simply measure the area under PEAs after the flare
maximum and the underlying photospheric magnetic field. The reconnection
flux is then half of the product of these two quantities. We illustrate
this method using specific examples and show that the ribbon and
arcade methods yield results, which are in good agreement. Finally,
we show that this provides a simple means of predicting the 1-AU flux
rope magnetic field from measurements made near the Sun.
---------------------------------------------------------
Title: Future L5 Missions for Solar Physics and Space Weather
Authors: Auchere, Frederic; Gopalswamy, Nat
2014cosp...40E.148A Altcode:
Coronal mass ejections (CMEs) and corotating interaction regions (CIR)
are the sources of intense space weather in the heliosphere. Most of
the current knowledge on CMEs accumulated over the past few decades
has been derived from observations made from the Sun-Earth line,
which is not the ideal vantage point to observe Earth-affecting
CMEs (Gopalswamy et al., 2011a,b). In this paper, the advantages of
remote-sensing and in-situ observations from the Sun-Earth L5 point
are discussed. Locating a mission at Sun-Earth L5 has several key
benefits for solar physics and space weather: (1) off the Sun-Earth
line view is critical in observing Earth-arriving parts of CMEs,
(2) L5 coronagraphic observations can also provide near-Sun space
speed of CMEs, which is an important input to models that forecast
Earth-arrival time of CMEs, (3) backside and frontside CMEs can be
readily distinguished even without inner coronal imagers, (4) preceding
CMEs in the path of Earth-affecting CMEs can be identified for a better
estimate of the travel time, (5) CIRs reach the L5 point a few days
before they arrive at Earth, and hence provide significant lead time
before CIR arrival, (6) L5 observations can provide advance knowledge
of CME and CIR source regions (coronal holes) rotating to Earth view,
and (7) magnetograms obtained from L5 can improve the surface magnetic
field distribution used as input to MHD models that predict the
background solar wind. The paper also discusses L5 mission concepts
that can be achieved in the near future. References Gopalswamy, N.,
Davila, J. M., St. Cyr, O. C., Sittler, E. C., Auchère, F., Duvall,
T. L., Hoeksema, J. T., Maksimovic, M., MacDowall, R. J., Szabo,
A., Collier, M. R. (2011a), Earth-Affecting Solar Causes Observatory
(EASCO): A potential International Living with a Star Mission from
Sun-Earth L5 JASTP 73, 658-663, DOI: 10.1016/j.jastp.2011.01.013
Gopalswamy, N., Davila, J. M., Auchère, F., Schou, J., Korendyke,
C. M. Shih, A., Johnston, J. C., MacDowall, R. J., Maksimovic, M.,
Sittler, E., et al. (2011b), Earth-Affecting Solar Causes Observatory
(EASCO): a mission at the Sun-Earth L5, Solar Physics and Space Weather
Instrumentation IV. Ed. Fineschi, S. & Fennelly, J., Proceedings
of the SPIE, Volume 8148, article id. 81480Z, DOI: 10.1117/12.901538
---------------------------------------------------------
Title: Obscuration of Flare Emission by an Eruptive Prominence
Authors: Gopalswamy, Nat; Yashiro, Seiji
2013PASJ...65S..11G Altcode: 2013arXiv1309.2046G
We report on the eclipsing of microwave flare emission by an eruptive
prominence from a neighboring region as observed by the Nobeyama
Radioheliograph at 17 GHz. The obscuration of the flare emission
appears as a dimming feature in the microwave flare light curve. We
use the dimming feature to derive the temperature of the prominence
and the distribution of heating along the length of the filament. We
find that the prominence is heated to a temperature above the quiet Sun
temperature at 17 GHz. The duration of the dimming is the time taken
by the eruptive prominence in passing over the flaring region. We also
find evidence for the obscuration in EUV images obtained by the Solar
and Heliospheric Observatory (SOHO) mission.
---------------------------------------------------------
Title: Solar energetic particle events during the rise phases of
solar cycles 23 and 24
Authors: Chandra, R.; Gopalswamy, N.; Mäkelä, P.; Xie, H.; Yashiro,
S.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Jain,
R.; Awasthi, A. K.; Manoharan, P. K.; Mahalakshmi, K.; Dwivedi, V. C.;
Choudhary, D. P.; Nitta, N. V.
2013AdSpR..52.2102C Altcode:
We present a comparative study of the properties of coronal mass
ejections (CMEs) and flares associated with the solar energetic particle
(SEP) events in the rising phases of solar cycles (SC) 23 (1996-1998)
(22 events) and 24 (2009-2011) (20 events), which are associated
with type II radio bursts. Based on the SEP intensity, we divided the
events into three categories, i.e. weak (intensity < 1 pfu), minor
(1 pfu < intensity < 10 pfu) and major (intensity ⩾ 10 pfu)
events. We used the GOES data for the minor and major SEP events and
SOHO/ERNE data for the weak SEP event. We examine the correlation
of SEP intensity with flare size and CME properties. We find that
most of the major SEP events are associated with halo or partial halo
CMEs originating close to the sun center and western-hemisphere. The
fraction of halo CMEs in SC 24 is larger than the SC 23. For the minor
SEP events one event in SC23 and one event in SC24 have widths <
120° and all other events are associated with halo or partial halo
CMEs as in the case of major SEP events. In case of weak SEP events,
majority (more than 60%) of events are associated with CME width <
120°. For both the SC the average CMEs speeds are similar. For major
SEP events, average CME speeds are higher in comparison to minor and
weak events. The SEP event intensity and GOES X-ray flare size are
poorly correlated. During the rise phase of solar cycle 23 and 24,
we find north-south asymmetry in the SEP event source locations: in
cycle 23 most sources are located in the south, whereas during cycle
24 most sources are located in the north. This result is consistent
with the asymmetry found with sunspot area and intense flares.
---------------------------------------------------------
Title: A Study of Coronal Holes Observed by SoHO/EIT and the Nobeyama
Radioheliograph
Authors: Akiyama, Sachiko; Gopalswamy, Nat; Yashiro, Seiji; Mäkelä,
Pertti
2013PASJ...65S..15A Altcode:
Coronal holes (CHs) are areas of reduced emission in EUV and X-ray
images that show bright patches of microwave enhancements (MEs) related
to magnetic network junctions inside the CHs. A clear correlation
between the CH size and the solar wind (SW) speed is well known, but we
have less information about the relationship between MEs and other CH
and SW properties. We studied the characteristics of 21 equatorial CHs
associated with corotating interaction regions (CIRs) during 1996 to
2005. Our CHs were divided into two groups according to the intensity
of the associated geomagnetic storms: Dst ≤ -100 nT (10 events) and
> -100 nT (11 events). Using EUV 284 Å images obtained by SOHO/EIT
and 17 GHz microwave images obtained by the Nobeyama Radioheliograph
(NoRH), we found a linear correlation not only between the maximum SW
speed and the area of EUV CH (r = 0.62), but also between the maximum
SW speed and the area of the ME (r = 0.79). We also compared the EUV
CH areas with and without an overlapping ME. The area of the CHs with
an ME is better correlated with the SW speed (r = 0.71) than the area
of those without an ME (r = 0.36). Therefore, the radio ME may play
an important role in understanding the origin of SW.
---------------------------------------------------------
Title: Testing the empirical shock arrival model using quadrature
observations
Authors: Gopalswamy, N.; Mäkelä, P.; Xie, H.; Yashiro, S.
2013SpWea..11..661G Altcode: 2013arXiv1310.8510G
The empirical shock arrival (ESA) model was developed based on
quadrature data from Helios (in situ) and P-78 (remote sensing)
to predict the Sun-Earth travel time of coronal mass ejections
(CMEs). The ESA model requires earthward CME speed as input, which
is not directly measurable from coronagraphs along the Sun-Earth
line. The Solar Terrestrial Relations Observatory (STEREO) and the
Solar and Heliospheric Observatory (SOHO) were in quadrature during
2010-2012, so the speeds of Earth-directed CMEs were observed with
minimal projection effects. We identified a set of 20 full halo CMEs
in the field of view of SOHO that were also observed in quadrature
by STEREO. We used the earthward speed from STEREO measurements as
input to the ESA model and compared the resulting travel times with the
observed ones from L1 monitors. We find that the model predicts the CME
travel time within about 7.3 h, which is similar to the predictions
by the ENLIL model. We also find that CME-CME and CME-coronal hole
interaction can lead to large deviations from model predictions.
---------------------------------------------------------
Title: Flux emergence, flux imbalance, magnetic free energy and
solar flares
Authors: Choudhary, Debi Prasad; Gosain, Sanjay; Gopalswamy, Nat;
Manoharan, P. K.; Chandra, R.; Uddin, W.; Srivastava, A. K.; Yashiro,
S.; Joshi, N. C.; Kayshap, P.; Dwivedi, V. C.; Mahalakshmi, K.;
Elamathi, E.; Norris, Max; Awasthi, A. K.; Jain, R.
2013AdSpR..52.1561C Altcode:
Emergence of complex magnetic flux in the solar active regions lead
to several observational effects such as a change in sunspot area
and flux embalance in photospheric magnetograms. The flux emergence
also results in twisted magnetic field lines that add to free energy
content. The magnetic field configuration of these active regions
relax to near potential-field configuration after energy release
through solar flares and coronal mass ejections. In this paper,
we study the relation of flare productivity of active regions with
their evolution of magnetic flux emergence, flux imbalance and free
energy content. We use the sunspot area and number for flux emergence
study as they contain most of the concentrated magnetic flux in the
active region. The magnetic flux imbalance and the free energy are
estimated using the HMI/SDO magnetograms and Virial theorem method. We
find that the active regions that undergo large changes in sunspot
area are most flare productive. The active regions become flary when
the free energy content exceeds 50% of the total energy. Although,
the flary active regions show magnetic flux imbalance, it is hard to
predict flare activity based on this parameter alone.
---------------------------------------------------------
Title: Understanding shock dynamics in the inner heliosphere with
modeling and type II radio data: A statistical study
Authors: Xie, H.; St. Cyr, O. C.; Gopalswamy, N.; Odstrcil, D.;
Cremades, H.
2013JGRA..118.4711X Altcode:
We study two methods of predicting interplanetary shock location and
strength in the inner heliosphere: (1) the ENLIL simulation and (2)
the kilometric type II (kmTII) prediction. To evaluate differences in
the performance of the first method, we apply two sets of coronal mass
ejections (CME) parameters from the cone-model fitting and flux-rope
(FR) model fitting as input to the ENLIL model for 16 halo CMEs. The
results show that the ENLIL model using the actual CME speeds from
FR-fit provided an improved shock arrival time (SAT) prediction. The
mean prediction errors for the FR and cone-model inputs are 4.90±5.92
h and 5.48±6.11 h, respectively. A deviation of 100 km s<SUP>-1</SUP>
from the actual CME speed has resulted in a SAT error of 3.46 h on
average. The simulations show that the shock dynamics in the inner
heliosphere agrees with the drag-based model. The shock acceleration
can be divided as two phases: a faster deceleration phase within 50
R<SUB>s</SUB> and a slower deceleration phase at distances beyond
50 R<SUB>s</SUB>. The linear-fit deceleration in phase 1 is about 1
order of magnitude larger than that in phase 2. When applying the
kmTII method to 14 DH-km CMEs, we found that combining the kmTII
method with the ENLIL outputs improved the kmTII prediction. Due to
a better modeling of plasma density upstream of shocks and the kmTII
location, we are able to provide a more accurate shock time-distance
and speed profiles. The mean kmTII prediction error using the ENLIL
model density is 6.7±6.4 h; it is 8.4±10.4 h when the average solar
wind plasma density is used. Applying the ENLIL density has reduced the
mean kmTII prediction error by ∼2 h and the standard deviation by 4.0
h. Especially when we applied the combined approach to two interacting
events, the kmTII prediction error was drastically reduced from 29.6 h
to -4.9 h in one case and 10.6 h to 4.2 h in the other. Furthermore,
the results derived from the kmTII method and the ENLIL simulation,
together with white-light data, provide a valuable validation of
shock formation location and strength. Such information has important
implications for solar energetic particle acceleration.
---------------------------------------------------------
Title: A multiwavelength study of eruptive events on January 23,
2012 associated with a major solar energetic particle event
Authors: Joshi, N. C.; Uddin, W.; Srivastava, A. K.; Chandra, R.;
Gopalswamy, N.; Manoharan, P. K.; Aschwanden, M. J.; Choudhary, D. P.;
Jain, R.; Nitta, N. V.; Xie, H.; Yashiro, S.; Akiyama, S.; Mäkelä,
P.; Kayshap, P.; Awasthi, A. K.; Dwivedi, V. C.; Mahalakshmi, K.
2013AdSpR..52....1J Altcode: 2013arXiv1303.1251J
We use multiwavelength data from space and ground based instruments
to study the solar flares and coronal mass ejections (CMEs) on January
23, 2012 that were responsible for one of the largest solar energetic
particle (SEP) events of solar cycle 24. The eruptions consisting of two
fast CMEs (≈1400 km s<SUP>-1</SUP> and ≈2000 km s<SUP>-1</SUP>) and
M-class flares that occurred in active region 11402 located at ≈N28
W36. The two CMEs occurred in quick successions, so they interacted
very close to the Sun. The second CME caught up with the first one
at a distance of ≈11-12 R<SUB>sun</SUB>. The CME interaction may be
responsible for the elevated SEP flux and significant changes in the
intensity profile of the SEP event. The compound CME resulted in a
double-dip moderate geomagnetic storm (Dst∼-73nT). The two dips are
due to the southward component of the interplanetary magnetic field in
the shock sheath and the ICME intervals. One possible reason for the
lack of a stronger geomagnetic storm may be that the ICME delivered
a glancing blow to Earth.
---------------------------------------------------------
Title: An Automatic Detection Technique for Prominence Eruptions
and Surges using SDO/AIA Images
Authors: Yashiro, Seiji; Gopalswamy, N.; Makela, P.; Akiyama, S.;
Sterling, A. C.
2013SPD....44...99Y Altcode:
We present an automatic technique to detect and characterize eruptive
events (EEs), e.g. prominence eruptions and surges, using SDO/AIA
304 Å images. The technique works as follows. 1) The SDO 304 Å
images are polar-transformed for easy handling of the outward motion
of EEs and for saving computer resources. 2) The transformed images
are divided by a background map, which is determined as the minimum
intensity of each pixel during 24 hours. 3) The EEs are defined as a
region in the ratio maps with pixels having a ratio >2. Because a
stationary prominence has relatively high background, the prominence
is detected only when it moves. 4) Pattern recognition is performed to
separate different EEs at different locations. 5) In successive images,
two EEs with more than 50% of pixels overlapping are considered to
be the same EE. 6) If the height of an EE increases monotonically
in 5 successive images, we consider it as a reliable eruption. The
technique detects 1428 prominence eruptions and 1921 surges from 2010
May to 2012 December. The locations of PEs identified by this technique
clearly indicated decayed onset of the maximum phase in the south with
respect to the north. This work was supported by NASA Living with a
Star TR&T programAbstract (2,250 Maximum Characters): We present
an automatic technique to detect and characterize eruptive events
(EEs), e.g. prominence eruptions and surges, using SDO/AIA 304 Å
images. The technique works as follows. 1) The SDO 304 Å images are
polar-transformed for easy handling of the outward motion of EEs and
for saving computer resources. 2) The transformed images are divided by
a background map, which is determined as the minimum intensity of each
pixel during 24 hours. 3) The EEs are defined as a region in the ratio
maps with pixels having a ratio >2. Because a stationary prominence
has relatively high background, the prominence is detected only when it
moves. 4) Pattern recognition is performed to separate different EEs at
different locations. 5) In successive images, two EEs with more than 50%
of pixels overlapping are considered to be the same EE. 6) If the height
of an EE increases monotonically in 5 successive images, we consider it
as a reliable eruption. The technique detects 1428 prominence eruptions
and 1921 surges from 2010 May to 2012 December. The locations of PEs
identified by this technique clearly indicated decayed onset of the
maximum phase in the south with respect to the north. This work was
supported by NASA Living with a Star TR&T program
---------------------------------------------------------
Title: Solar Sources of Wide Coronal Mass Ejections during the
Ascending Phase of Cycle 24
Authors: Akiyama, Sachiko; Gopalswamy, N.; Yashiro, S.; Makela, P.
2013SPD....44..130A Altcode:
It is well known that fast and wide CMEs are generally involved in large
solar energetic particle (SEP) events and are generally important in
affecting the heliosphere. We examined the solar sources of all wide
CMEs (width ≥ 60°) observed by SOHO/LASCO and STEREO/SECCHI in 2011
(ascending phase of solar cycle 24) by confirming the back-sided events
using STEREO data. We identified 600 wide CMEs, of which 323 (54%)
and 163 (27%) were associated with active region flares and eruptive
quiescent filaments, respectively. In 88 cases (15%) only EUV dimmings
were observed. The remaining 26 (4%) CMEs were of unknown origin,
including 7 stealth CMEs. It is significant that about 1% of all wide
CMEs do not have identifiable near-surface signatures. Considering only
the front side CMEs, the median X-ray intensity associated with ARs and
filament regions were C3.7 and C1.6, respectively. The average speeds of
AR and quiescent-filament CMEs were, 537 and 373 km/s. We conclude that
some the results of the previous solar cycles can be clarified because
of the availability of STEREO data.Abstract (2,250 Maximum Characters):
It is well known that fast and wide CMEs are generally involved in large
solar energetic particle (SEP) events and are generally important in
affecting the heliosphere. We examined the solar sources of all wide
CMEs (width ≥ 60°) observed by SOHO/LASCO and STEREO/SECCHI in 2011
(ascending phase of solar cycle 24) by confirming the back-sided events
using STEREO data. We identified 600 wide CMEs, of which 323 (54%)
and 163 (27%) were associated with active region flares and eruptive
quiescent filaments, respectively. In 88 cases (15%) only EUV dimmings
were observed. The remaining 26 (4%) CMEs were of unknown origin,
including 7 stealth CMEs. It is significant that about 1% of all wide
CMEs do not have identifiable near-surface signatures. Considering
only the front side CMEs, the median X-ray intensity associated with
ARs and filament regions were C3.7 and C1.6, respectively. The average
speeds of AR and quiescent-filament CMEs were, 537 and 373 km/s. We
conclude that some the results of the previous solar cycles can be
clarified because of the availability of STEREO data.
---------------------------------------------------------
Title: On the Solar Sources of Polar-crown Coronal Mass Ejections
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2013SPD....44...83G Altcode:
Coronal mass ejections (CMEs) from the polar crown filament
region originate above 60-degree latitude during solar activity
maxima. Cessation of these high-latitude CMEs marks the end of the
maximum phase when the solar poles reverse their polarity. The eruption
mechanism of these polar CMEs is not well understood: they originate
from bipolar magnetic regions in contrast to the low-latitude ones,
which may occur from both bipolar and multipolar regions. One of the
key questions is whether the polar CMEs are associated with flare-like
brightening and if so what the nature of the CME-flare relationship
is. We investigated a number of polar CMEs, which do have post-eruption
arcades (PEAs) observed in soft X-ray and EUV wavelengths. We combine
data from the Solar Dynamics Observatory (SDO), the Solar Terrestrial
Relations Observatory (STEREO), and the Solar Heliospheric Observatory
(SOHO) to examine the flare-CME relationship in the case of polar
crown CMEs. In particular, we measure the initial CME acceleration and
compare it with the time-derivative of the PEA intensity to demonstrate
a relationship akin to Neupert effect. The CME morphology, mass,
and kinematics are similar to the low-latitude CMEs. The ratio of the
thermal energy content of PEAs to the CME kinetic energy is very similar
to that from low-latitude CMEs. Finally, the free energy estimated from
photospheric magnetograms and the area covered by the PEAs, we find
that the free energy is sufficient to power the CMEs and PEAs. Thus,
we conclude that the polar-crown CMEs are fundamentally similar to
the low-latitude CMEs and hence may have similar eruption mechanism.
---------------------------------------------------------
Title: Connecting Near-Sun CME flux Ropes to the 1-AU Flux Ropes
using the Flare-CME Relationship
Authors: Gopalswamy, N.; Xie, H.; Yashiro, S.; Akiyama, S.
2013SPD....4430001G Altcode:
Coronal mass ejections (CMEs) and solar flares are closely related in
various ways because the two phenomena are different manifestations
of the same energy release in closed magnetic regions on the sun. Of
particular interest is the relation between flare reconnection flux
at the Sun and the poloidal flux of the 1-AU flux rope associated
with the flare. If a flux rope forms due to flare reconnection,
then the two fluxes are almost equal. The flare reconnection flux
is normally computed from the flare-ribbon area and the photospheric
field strength in the ribbon area. Here we report on another technique,
which makes use of the area under the post-eruption arcade (PEA). We
show that the reconnection flux derived from the PEA technique agrees
with the one derived from flare ribbons. We also fit a flux rope to the
white-light CME observations and derive the aspect ratio of the flux
rope. Assuming self-similar expansion of the flux rope, we show that
the magnetic content and size of the 1-AU flux rope can be predicted
from the flare magnetic field (the average photospheric field strength
within half of the PEA area) and the aspect ratio of the coronal flux
rope. We illustrate the method with several examples.
---------------------------------------------------------
Title: Effect of CME interactions on SEP intensity: modeling the
2012-March-07 SEP event with ENLIL
Authors: Xie, Hong; Gopalswamy, N.; St. Cyr, O. C.
2013SPD....44..125X Altcode:
We performed a case study on the effect of CME interactions on SEP
intensity for the 2012-March-07 SEP event. The 2012 March 07 SEP event
had the second largest intensity during solar cycle 24. The SEP/ESP peak
intensities peaked at 1500/6000 pfu. The event was associated with a
double X-ray flare and two CMEs in quick succession. In soft X-rays,
the flares reached peak flux levels of X5.4 (00:02 UT) and X1.1,
respectively, from AR1429 (N18E31). The flare peaks were at ~00:24
and ~01:14 UT, while the onset times were 00:02 UT and 01:05 UT. The
associated CMEs were very fast: 2376 km/s (CME1) and 2203 km/s (CME2)
and appeared < 1 hour apart. Two distinct type II radio bursts were
detected in the decameter-hectometric (DH) spectrum observed by the
Wind/WAVES experiment. The interaction of two CMEs was clearly seen
from STEREO COR2 B movie from West limb around 01:54 UT, with enhanced
signature in DH type II spectrum around the same time. The two CMEs
arrived at 21.5 Rs (inner boundary of ENLIL) at 01:55 UT and 02:40 UT,
respectively, with flux-rope fitted propagation directions of N17E27
and N00E17. Two ENLIL runs were performed: 1) only CME1 was inserted
at 21.5Rs and 2) both CME1 and CME2 were inserted in the simulation to
study the effect of CME interactions. Comparing the results of the two
runs, we found that both the shock intensity and shock speed of Run2
were higher than Run1, suggesting that the CME interaction have not
only enhanced shock intensity but also caused higher speed, therefore
resulting in larger SEP intensity. This work was supported by NASA
Living with a Star TR&T programAbstract (2,250 Maximum Characters):
We performed a case study on the effect of CME interactions on SEP
intensity for the 2012-March-07 SEP event. The 2012 March 07 SEP event
had the second largest intensity during solar cycle 24. The SEP/ESP peak
intensities peaked at 1500/6000 pfu. The event was associated with a
double X-ray flare and two CMEs in quick succession. In soft X-rays,
the flares reached peak flux levels of X5.4 (00:02 UT) and X1.1,
respectively, from AR1429 (N18E31). The flare peaks were at ~00:24
and ~01:14 UT, while the onset times were 00:02 UT and 01:05 UT. The
associated CMEs were very fast: 2376 km/s (CME1) and 2203 km/s (CME2)
and appeared < 1 hour apart. Two distinct type II radio bursts were
detected in the decameter-hectometric (DH) spectrum observed by the
Wind/WAVES experiment. The interaction of two CMEs was clearly seen
from STEREO COR2 B movie from West limb around 01:54 UT, with enhanced
signature in DH type II spectrum around the same time. The two CMEs
arrived at 21.5 Rs (inner boundary of ENLIL) at 01:55 UT and 02:40 UT,
respectively, with flux-rope fitted propagation directions of N17E27
and N00E17. Two ENLIL runs were performed: 1) only CME1 was inserted
at 21.5Rs and 2) both CME1 and CME2 were inserted in the simulation
to study the effect of CME interactions. Comparing the results of
the two runs, we found that both the shock intensity and shock speed
of Run2 were higher than Run1, suggesting that the CME interaction
have not only enhanced shock intensity but also caused higher speed,
therefore resulting in larger SEP intensity. This work was supported
by NASA Living with a Star TR&T program
---------------------------------------------------------
Title: Observations of CMEs and models of the eruptive corona
Authors: Gopalswamy, Nat
2013AIPC.1539....5G Altcode: 2013arXiv1304.0087G
Current theoretical ideas on the internal structure of CMEs
suggest that a flux rope is central to the CME structure, which
has considerable observational support both from remote-sensing and
in-situ observations. The flux-rope nature is also consistent with the
post-eruption arcades with high-temperature plasmas and the charge
states observed within CMEs arriving at Earth. The model involving
magnetic loop expansion to explain CMEs without flux ropes is not
viable because it contradicts CME kinematics and flare properties
near the Sun. The flux rope is fast, it drives a shock, so the global
picture of CMEs becomes complete if one includes the shock sheath to
the CSHKP model.
---------------------------------------------------------
Title: Height of shock formation in the solar corona inferred from
observations of type II radio bursts and coronal mass ejections
Authors: Gopalswamy, N.; Xie, H.; Mäkelä, P.; Yashiro, S.; Akiyama,
S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan,
P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.;
Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P.
2013AdSpR..51.1981G Altcode: 2013arXiv1301.0893G
Employing coronagraphic and EUV observations close to the solar surface
made by the Solar Terrestrial Relations Observatory (STEREO) mission,
we determined the heliocentric distance of coronal mass ejections
(CMEs) at the starting time of associated metric type II bursts. We
used the wave diameter and leading edge methods and measured the CME
heights for a set of 32 metric type II bursts from solar cycle 24. We
minimized the projection effects by making the measurements from a
view that is roughly orthogonal to the direction of the ejection. We
also chose image frames close to the onset times of the type II bursts,
so no extrapolation was necessary. We found that the CMEs were located
in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs),
with mean and median values of 1.43 and 1.38 Rs, respectively. We
conclusively find that the shock formation can occur at heights
substantially below 1.5 Rs. In a few cases, the CME height at type
II onset was close to 2 Rs. In these cases, the starting frequency
of the type II bursts was very low, in the range 25-40 MHz, which
confirms that the shock can also form at larger heights. The starting
frequencies of metric type II bursts have a weak correlation with the
measured CME/shock heights and are consistent with the rapid decline
of density with height in the inner corona.
---------------------------------------------------------
Title: Observations of the Highest Energy Particles from the Sun
and the Identification of their Acceleration Mechanism
Authors: Gopalswamy, Nat; Xie, H.; Yashiro, S.
2013shin.confE.142G Altcode:
The highest energy ( GeV) particles accelerated by the Sun are the
Ground Level Enhancement (GLE) in solar energetic particle (SEP) events
during large solar eruptions. Extensive observations of GLE-associated
coronal mass ejections (CMEs) during solar cycle 23 suggest that shocks
forming very close to the Sun have sufficient time to accelerate GeV
particles. The first GLE event of solar cycle 24 (on May 17, 2012)
is consistent with the shock acceleration mechanism because the CME
was very fast ( 2000 km/s), but the associated flare was rather weak
(M-class flare). Gopalswamy et al. (2013, ApJ 765, L30) showed that
the unfavorable B0 angle and non-radial motion of CMEs might have
rendered the shock nose poorly connected to Earth in other similar
or larger eruptions during solar cycle 24. In such non-GLE events,
the latitudinal distance of the source region to the ecliptic was
much larger than that in cycle-23 GLE events. In one case, even though
the connectivity was not an issue, the shock seemed to be rather weak
probably because of a higher Alfven speed in the ambient medium. Thus,
GLE events require special conditions in terms of CME kinematics,
coronal environment, and the magnetic connectivity of the solar source
to an Earth observer. In this work, we examined the source locations
of historical GLE events and found that the apparent higher-latitude
GLE events indeed have favorable B0 angle and coronal-hole deflection
toward the equator. We also examined additional large eruptions of
cycle 24 and confirmed the importance of connectivity to Earth.
---------------------------------------------------------
Title: Near-Sun Flux-Rope Structure of CMEs
Authors: Xie, H.; Gopalswamy, N.; St. Cyr, O. C.
2013SoPh..284...47X Altcode: 2012arXiv1212.1409X
We have used the Krall flux-rope model (Krall and St. Cyr,
Astrophys. J.2006, 657, 1740) (KFR) to fit 23 magnetic cloud (MC)-CMEs
and 30 non-cloud ejecta (EJ)-CMEs in the Living With a Star (LWS)
Coordinated Data Analysis Workshop (CDAW) 2011 list. The KFR-fit
results shows that the CMEs associated with MCs (EJs) have been
deflected closer to (away from) the solar disk center (DC), likely by
both the intrinsic magnetic structures inside an active region (AR)
and ambient magnetic structures (e.g. nearby ARs, coronal holes,
and streamers, etc.). The mean absolute propagation latitudes and
longitudes of the EJ-CMEs (18<SUP>∘</SUP>, 11<SUP>∘</SUP>) were
larger than those of the MC-CMEs (11<SUP>∘</SUP>, 6<SUP>∘</SUP>)
by 7<SUP>∘</SUP> and 5<SUP>∘</SUP>, respectively. Furthermore, the
KFR-fit widths showed that the MC-CMEs are wider than the EJ-CMEs. The
mean fitting face-on width and edge-on width of the MC-CMEs (EJ-CMEs)
were 87 (85)<SUP>∘</SUP> and 70 (63)<SUP>∘</SUP>, respectively. The
deflection away from DC and narrower angular widths of the EJ-CMEs
have caused the observing spacecraft to pass over only their flanks
and miss the central flux-rope structures. The results of this work
support the idea that all CMEs have a flux-rope structure.
---------------------------------------------------------
Title: On the Relationship Between Metric and DH Type II Bursts
Authors: Makela, P.; Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Xie, H.
2013AGUSMSH52A..01M Altcode:
The metric and decameter-hectometric (DH) type II radio bursts provide
an opportunity to remotely observe the formation and propagation of
shocks in the solar corona and in interplanetary (IP) space. However,
the radio spectral observations give only limited information on
the location of the source of the type II emission, which has led to
a long-held controversy over whether the metric type II bursts are
due to blast waves or CME-driven shocks. For example, metric type II
bursts are occasionally observed to be coincidental with DH type II
bursts. In these cases it has been suggested that the DH-component
could be associated with a CME-driven shock and the m-component with
a blast wave or unknown source, or that the DH-component originates
from the nose of the CME-driven shock and the m-component from the
shock flanks. In our presentation we use coronal Alfven speed profile,
CME kinematics, and type II drift rate characteristics to provide
a comprehensive explanation for the observed relationship between
coronal and IP type II bursts.
---------------------------------------------------------
Title: The Solar Connection of Enhanced Heavy Ion Charge States in
the Interplanetary Medium: Implications for the Flux-Rope Structure
of CMEs
Authors: Gopalswamy, N.; Mäkelä, P.; Akiyama, S.; Xie, H.; Yashiro,
S.; Reinard, A. A.
2013SoPh..284...17G Altcode: 2012arXiv1212.0900G
We investigated a set of 54 interplanetary coronal mass ejection
(ICME) events whose solar sources are very close to the disk center
(within ± 15<SUP>∘</SUP> from the central meridian). The ICMEs
consisted of 23 magnetic-cloud (MC) events and 31 non-MC events. Our
analyses suggest that the MC and non-MC ICMEs have more or less the
same eruption characteristics at the Sun in terms of soft X-ray flares
and CMEs. Both types have significant enhancements in ion charge
states, although the non-MC structures have slightly lower levels
of enhancement. The overall duration of charge-state enhancement is
also considerably smaller than that in MCs as derived from solar wind
plasma and magnetic signatures. We find very good correlation between
the Fe and O charge-state measurements and the flare properties such
as soft X-ray flare intensity and flare temperature for both MCs and
non-MCs. These observations suggest that both MC and non-MC ICMEs are
likely to have a flux-rope structure and the unfavorable observational
geometry may be responsible for the appearance of non-MC structures
at 1 AU. We do not find any evidence for an active region expansion
resulting in ICMEs lacking a flux-rope structure because the mechanism
of producing high charge states and the flux-rope structure at the
Sun is the same for MC and non-MC events.
---------------------------------------------------------
Title: Post-Eruption Arcades and Interplanetary Coronal Mass Ejections
Authors: Yashiro, S.; Gopalswamy, N.; Mäkelä, P.; Akiyama, S.
2013SoPh..284....5Y Altcode:
We compare the temporal and spatial properties of posteruption arcades
(PEAs) associated with coronal mass ejections (CMEs) at the Sun that
end up as magnetic cloud (MC) and non-MC events in the solar wind. We
investigate the length, width, area, tilt angle, and formation time
of the PEAs associated with 22 MC and 29 non-MC events and we find no
difference between the two populations. According to current ideas
on the relation between flares and CMEs, the PEA is formed together
with the CME flux-rope structure by magnetic reconnection. Our results
indicate that at the Sun flux ropes form during CMEs in association with
both MC and non-MC events; however, for non-MC events the flux-rope
structure is not observed in the interplanetary space because of the
geometry of the observation, i.e. the location of the spacecraft when
the structure passes through it.
---------------------------------------------------------
Title: Preface
Authors: Gopalswamy, N.; Nieves-Chinchilla, T.; Hidalgo, M.; Zhang,
J.; Riley, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.
2013SoPh..284....1G Altcode: 2013arXiv1304.0085G
This Topical Issue of Solar Physics, devoted to the study of flux-rope
structure in coronal mass ejections (CMEs), is based on two Coordinated
Data Analysis Workshops (CDAWs) held in 2010 (20 - 23 September in Dan
Diego, California, USA) and 2011 (September 5-9 in Alcala, Spain). The
primary purpose of the CDAWs was to address the question: Do all CMEs
have flux rope structure? There are 18 papers om this topical issue,
including this preface.
---------------------------------------------------------
Title: Propagation Characteristics of CMEs Associated with Magnetic
Clouds and Ejecta
Authors: Kim, R. -S.; Gopalswamy, N.; Cho, K. -S.; Moon, Y. -J.;
Yashiro, S.
2013SoPh..284...77K Altcode:
We have investigated the characteristics of magnetic cloud (MC)
and ejecta (EJ) associated coronal mass ejections (CMEs) based on
the assumption that all CMEs have a flux rope structure. For this,
we used 54 CMEs and their interplanetary counterparts (interplanetary
CMEs: ICMEs) that constitute the list of events used by the NASA/LWS
Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We
considered the location, angular width, and speed as well as the
direction parameter, D. The direction parameter quantifies the degree of
asymmetry of the CME shape in coronagraph images, and shows how closely
the CME propagation is directed to Earth. For the 54 CDAW events,
we found the following properties of the CMEs: i) the average value
of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49),
which indicates that the MC-associated CMEs propagate more directly
toward the Earth than the EJ-associated CMEs; ii) comparison between
the direction parameter and the source location shows that the majority
of the MC-associated CMEs are ejected along the radial direction, while
many of the EJ-associated CMEs are ejected non-radially; iii) the mean
speed of MC-associated CMEs (946 km s<SUP>−1</SUP>) is faster than
that of EJ-associated CMEs (771 km s<SUP>−1</SUP>). For seven very
fast CMEs (≥ 1500 km s<SUP>−1</SUP>), all CMEs with large D (≥
0.4) are associated with MCs and the CMEs with small D are associated
with EJs. From the statistical analysis of CME parameters, we found
the superiority of the direction parameter. Based on these results,
we suggest that the CME trajectory essentially determines the observed
ICME structure.
---------------------------------------------------------
Title: Coronal Mass Ejections and Ground Level Enhancement Events
Authors: Gopalswamy, N.
2013AGUSMSH33B..04G Altcode:
Ground level enhancement (GLE) in solar energetic particle (SEP)
events represent the production of GeV particles by the Sun during
large solar eruptions. Although the GLE events were first detected
in 1942 and reported by Scott Forbush (1946) a few years later, the
mechanism for the production of these high-energy particles is not fully
understood. GLEs were attributed to solar flares from the beginning,
but after the discovery of coronal mass ejections (CMEs) in 1971,
the possibility of CME-driven shocks accelerating GLE particles has
also gained importance. Extensive CME observations in association with
GLEs became available only during solar cycle 23, enabling a fresh look
at the importance of CME-driven shocks. This paper presents a summary
of CME properties obtained primarily from the Solar and Heliospheric
Observatory (SOHO), which are fully consistent with shock acceleration
of GLE particles. During solar cycle 24, there has been only one GLE
event (on May 17, 2012) as of this writing. This is the first GLE event
to be fully observed by the Solar Terrestrial Relations Observatory
(STEREO) mission, providing critical information on CME kinematics
that helped verify the results obtained for cycle 23 GLE events. In
particular, it is confirmed that (i) the shock forms very close to
the solar surface (within half a solar radius) and the GLE particles
are released ~10 minutes later, and (ii) GLE events require special
conditions in terms of CME kinematics, coronal environment, and the
magnetic connectivity of the solar source to an Earth observer. Forbush,
S. E., Three Unusual Cosmic-Ray Increases Possibly Due to Charged
Particles from the Sun, Physical Review, 70, 771, 1946
---------------------------------------------------------
Title: Comparison of Helicity Signs in Interplanetary CMEs and Their
Solar Source Regions
Authors: Cho, K. -S.; Park, S. -H.; Marubashi, K.; Gopalswamy, N.;
Akiyama, S.; Yashiro, S.; Kim, R. -S.; Lim, E. -K.
2013SoPh..284..105C Altcode:
If all coronal mass ejections (CMEs) have flux ropes, then the CMEs
should keep their helicity signs from the Sun to the Earth according to
the helicity conservation principle. This study presents an attempt to
answer the question from the Coordinated Data Analysis Workshop (CDAW),
"Do all CMEs have flux ropes?", by using a qualitative helicity sign
comparison between interplanetary CMEs (ICMEs) and their CME source
regions. For this, we select 34 CME-ICME pairs whose source active
regions (ARs) have continuous SOHO/MDI magnetogram data covering
more than 24 hr without data gap during the passage of the ARs near
the solar disk center. The helicity signs in the ARs are determined
by estimation of cumulative magnetic helicity injected through the
photosphere in the entire source ARs. The helicity signs in the ICMEs
are estimated by applying the cylinder model developed by Marubashi
(Adv. Space. Res., 26, 55, 2000) to 16 second resolution magnetic field
data from the MAG instrument onboard the ACE spacecraft. It is found
that 30 out of 34 events (88 %) are helicity sign-consistent events,
while four events (12 %) are sign-inconsistent. Through a detailed
investigation of the source ARs of the four sign-inconsistent events,
we find that those events can be explained by the local helicity
sign opposite to that of the entire AR helicity (28 July 2000 ICME),
incorrectly reported solar source region in the CDAW list (20 May 2005
ICME), or the helicity sign of the pre-existing coronal magnetic field
(13 October 2000 and 20 November 2003 ICMEs). We conclude that the
helicity signs of the ICMEs are quite consistent with those of the
injected helicities in the AR regions from where the CMEs erupted.
---------------------------------------------------------
Title: Coronal Hole Influence on the Observed Structure of
Interplanetary CMEs
Authors: Mäkelä, P.; Gopalswamy, N.; Xie, H.; Mohamed, A. A.;
Akiyama, S.; Yashiro, S.
2013SoPh..284...59M Altcode: 2013arXiv1301.2176M
We report on the coronal hole (CH) influence on the 54 magnetic
cloud (MC) and non-MC associated coronal mass ejections (CMEs)
selected for studies during the Coordinated Data Analysis Workshops
(CDAWs) focusing on the question if all CMEs are flux ropes. All
selected CMEs originated from source regions located between
longitudes 15E - 15W. Xie, Gopalswamy, and St. Cyr (2013, Solar Phys.,
doi:10.1007/s11207-012-0209-0) found that these MC and non-MC associated
CMEs are on average deflected towards and away from the Sun-Earth line,
respectively. We used a CH influence parameter (CHIP) that depends
on the CH area, average magnetic field strength, and distance from
the CME source region to describe the influence of all on-disk CHs
on the erupting CME. We found that for CHIP values larger than 2.6 G
the MC and non-MC events separate into two distinct groups where MCs
(non-MCs) are deflected towards (away) from the disk center. Division
into two groups was also observed when the distance to the nearest CH
was less than 3.2×10<SUP>5</SUP> km. At CHIP values less than 2.6 G
or at distances of the nearest CH larger than 3.2×10<SUP>5</SUP> km
the deflection distributions of the MC and non-MCs started to overlap,
indicating diminishing CH influence. These results give support to the
idea that all CMEs are flux ropes, but those observed to be non-MCs
at 1 AU could be deflected away from the Sun-Earth line by nearby CHs,
making their flux rope structure unobservable at 1 AU.
---------------------------------------------------------
Title: The First Ground Level Enhancement Event of Solar Cycle 24:
Direct Observation of Shock Formation and Particle Release Heights
Authors: Gopalswamy, N.; Xie, H.; Akiyama, S.; Yashiro, S.; Usoskin,
I. G.; Davila, J. M.
2013ApJ...765L..30G Altcode: 2013arXiv1302.1474G
We report on the 2012 May 17 ground level enhancement (GLE) event,
which is the first of its kind in solar cycle 24. This is the first GLE
event to be fully observed close to the surface by the Solar Terrestrial
Relations Observatory (STEREO) mission. We determine the coronal mass
ejection (CME) height at the start of the associated metric type
II radio burst (i.e., shock formation height) as 1.38 Rs (from the
Sun center). The CME height at the time of GLE particle release was
directly measured from a STEREO image as 2.32 Rs, which agrees well
with the estimation from CME kinematics. These heights are consistent
with those obtained for cycle-23 GLEs using back-extrapolation. By
contrasting the 2012 May 17 GLE with six other non-GLE eruptions from
well-connected regions with similar or larger flare sizes and CME
speeds, we find that the latitudinal distance from the ecliptic is
rather large for the non-GLE events due to a combination of non-radial
CME motion and unfavorable solar B0 angle, making the connectivity
to Earth poorer. We also find that the coronal environment may play
a role in deciding the shock strength.
---------------------------------------------------------
Title: A High-frequency Type II Solar Radio Burst Associated with
the 2011 February 13 Coronal Mass Ejection
Authors: Cho, K. -S.; Gopalswamy, N.; Kwon, R. -Y.; Kim, R. -S.;
Yashiro, S.
2013ApJ...765..148C Altcode:
We examine the relationship between the high-frequency (425 MHz) type II
radio burst and the associated white-light coronal mass ejection (CME)
that occurred on 2011 February 13. The radio burst had a drift rate of
2.5 MHz s<SUP>-1</SUP>, indicating a relatively high shock speed. From
SDO/AIA observations we find that a loop-like erupting front sweeps
across high-density coronal loops near the start time of the burst
(17:34:17 UT). The deduced distance of shock formation (0.06 Rs)
from the flare center and speed of the shock (1100 km s<SUP>-1</SUP>)
using the measured density from SDO/AIA observations are comparable
to the height (0.05 Rs, from the solar surface) and speed (700 km
s<SUP>-1</SUP>) of the CME leading edge observed by STEREO/EUVI. We
conclude that the type II burst originates even in the low corona
(<59 Mm or 0.08 Rs, above the solar surface) due to the fast CME
shock passing through high-density loops.
---------------------------------------------------------
Title: Extremely Impulsive Eruption associated with an X-class Flare
on 2012 October 23
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2013enss.confE.146G Altcode:
Typically about 10% X-class solar flares are confined, i.e., they are
not association with mass ejection or type II bursts in the metric and
longer wavelengths. Failed eruptions are known to occur occasionally,
indicating the weakness of the propelling force compared to the
overlying restraining forces. Here we report an event on 2012 October
23 that is closer to an eruptive event: it was associated with a metric
type II burst, EUV disturbance (SDO, STEREO) and an extremely brief
CME in the STEREO coronagraphic field of view. This paper presents an
analysis of the event showing that the EUV disturbance is close to
a blast wave, but not quite. Model fitting indicates that the speed
falls faster than that of a blast wave indicating a quick shutoff
of the propelling force. We also compare this event with another
eruptive event on 2012 January 27 that had a similar flare magnitude,
but was accompanied by a huge CME with all the usual interplanetary
disturbances.
---------------------------------------------------------
Title: Implications of Mass and Energy Loss due to Coronal Mass
Ejections on Magnetically Active Stars
Authors: Drake, Jeremy J.; Cohen, Ofer; Yashiro, Seiji; Gopalswamy, Nat
2013ApJ...764..170D Altcode: 2013arXiv1302.1136D
Analysis of a database of solar coronal mass ejections (CMEs)
and associated flares over the period 1996-2007 finds well-behaved
power-law relationships between the 1-8 Å flare X-ray fluence and CME
mass and kinetic energy. We extrapolate these relationships to lower
and higher flare energies to estimate the mass and energy loss due to
CMEs from stellar coronae, assuming that the observed X-ray emission
of the latter is dominated by flares with a frequency as a function
of energy dn/dE = kE <SUP>-α</SUP>. For solar-like stars at saturated
levels of X-ray activity, the implied losses depend fairly weakly on the
assumed value of α and are very large: \dot{M}∼ 5× 10^{-10} M_⊙
yr<SUP>-1</SUP> and \dot{E}∼ 0.1 L_⊙. In order to avoid such large
energy requirements, either the relationships between CME mass and speed
and flare energy must flatten for X-ray fluence >~ 10<SUP>31</SUP>
erg, or the flare-CME association must drop significantly below 1
for more energetic events. If active coronae are dominated by flares,
then the total coronal energy budget is likely to be up to an order of
magnitude larger than the canonical 10<SUP>-3</SUP> L <SUB>bol</SUB>
X-ray saturation threshold. This raises the question of what is the
maximum energy a magnetic dynamo can extract from a star? For an energy
budget of 1% of L <SUB>bol</SUB>, the CME mass loss rate is about 5
× 10<SUP>-11</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP>.
---------------------------------------------------------
Title: Multi-wavelength diagnostics of thermal and non-thermal
characteristics in 22 April 2011 confined flare
Authors: Awasthi, Arun K.; Jain, Rajmal; Aschwanden, Markus J.; Uddin,
Wahab; Srivastava, Abhishek K.; Chandra, Ramesh; Gopalswamy, Nat;
Nitta, Nariaki; Yashiro, Seiji; Manoharan, P. K.; Prasad Choudhary,
Debi; Joshi, N. C.; Dwivedi, Vidya Charan; Mahalakshmi, K.
2013ASInC...9...71A Altcode:
We study the spatial, spectral and temporal characteristics of thermal
and non-thermal emission in an M1.8 flare, which occurred in NOAA
AR 11195 (S17E31) on 22 April 2011. This study quantifies spatial
and temporal correlation of thermal and non-thermal emissions in
precursor, impulsive as well as gradual phase of energy release
employing multi-wavelength observation from SDO, HESSI and SOXS
missions. Based on spectral fitting analysis performed on the X-ray
emission observed by RHESSI as well as SOXS missions in low energy
and high energy respectively, we define that <20 keV emission
corresponds to thermal and >20 keV emission to be non-thermal
counterpart of the emission. Therefore, we construct X-ray images
employing RHESSI observation in energy bands 6-20 and 20-100 keV
over the time integration of 30s. We report co-spatial X-ray emission
in various phases of emission. We also report absence of non-thermal
counterpart in the X-ray emission in precursor phase however visible at
the commencement of main phase. To characterize thermal and non-thermal
signatures, we overlay the X-ray image contours on the Hα and EUV
observations from GONG and SDO/AIA respectively. We report thermal
emission in the precursor phase to be co-spatial to UV counterpart. In
contrast, we report absence of emission in the EUV wavebands i.e. 1600
and 1700 Å which, in principle, correspond to temperature minimum
zone and photosphere during the precursor phase. This confirms the
absence of non-thermal emission as appeared in X-ray emission during
the precursor phase. Further, during the impulsive as well as in
gradual phase, thermal and non-thermal emissions have been found to
be originated from a compact source, co-spatial in nature. Analysis
of Line of sight (LOS) magnetic field observations from SDO/HMI does
not reveal noticeable changes in the positive and negative fluxes
as well as magnetic-field gradient during this event. In contrast,
Hα emission observed by GONG has revealed the filament eruption as
the trigger of flare. This suggests filament eruption to be driver of
this event, consistent with the CSHKP model of solar flare.
---------------------------------------------------------
Title: STEREO and SOHO contributions to coronal mass ejection studies:
Some recent results
Authors: Gopalswamy, N.
2013ASInC..10...11G Altcode:
This paper summarizes some recent results on coronal mass ejections
(CMEs) obtained from the Solar Terrestrial Relations Observatory
(STEREO) that relate to previous results from the Solar and Heliospheric
Observatory (SOHO). Making use of the extended field of view of the
STEREO instruments and the capability to view solar eruptions from
vantage points away from the Sun-Earth line, this paper addresses CME
morphology and the early evolution of CMEs including shock formation
indicated by type II radio bursts and EUV disturbances. In situ
observations from STEREO locations and Sun-Earth L1 are used to provide
evidence to support the idea that all CMEs in the interplanetary medium
may be flux ropes. Finally, the use of shock-flux rope morphology to
determine the heliospheric magnetic field is discussed.
---------------------------------------------------------
Title: Erratum: "Behavior of Solar Cycles 23 and 24 Revealed by
Microwave Observations" <A href="/abs/2012ApJ...750L..42G">(2012,
ApJ, 750, L42)</A>
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Michalek, G.;
Shibasaki, K.; Hathaway, D. H.
2013ApJ...763L..24G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Homologous Flare-CME Events with and without a metric type
II radio burst
Authors: Yashiro, S.; Gopalswamy, N.; Makela, P. A.
2012AGUFMSH43A2139Y Altcode:
Active region NOAA 11158 produced many flares and CMEs during its disk
passage, out of which at least two can be considered as homologous. The
events are the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on
February 14, 2011. Both flares occurred at the same location (eastern
edge of the active region) and have a similar decay of the GOES soft
X-ray light curve. The associated CMEs were slow (319 km/s and 337
km/s) and of similar widths (63 and 64 degree), but they had different
radio signature. The second event was associated with a metric type
II burst while the first one was not. The COR1 coronagraphs on board
the STEREO spacecraft clearly show that the second CME propagated
into the aftermath a preceding CME. These observations suggest that
CME-CME interaction might be a key process in exciting the type II
radio emission by slow CMEs.
---------------------------------------------------------
Title: A Space Weather Mission to the Earth's 5th Lagrangian Point
(L5)
Authors: Howard, R. A.; Vourlidas, A.; Ko, Y.; Biesecker, D. A.;
Krucker, S.; Murphy, N.; Bogdan, T. J.; St Cyr, O. C.; Davila, J. M.;
Doschek, G. A.; Gopalswamy, N.; Korendyke, C. M.; Laming, J. M.;
Liewer, P. C.; Lin, R. P.; Plunkett, S. P.; Socker, D. G.; Tomczyk,
S.; Webb, D. F.
2012AGUFMSA13D..07H Altcode:
The highly successful STEREO mission, launched by NASA in 2006,
consisted of two spacecraft in heliocentric orbit, one leading and
one trailing the Earth and each separating from Earth at the rate
of about 22.5 degrees per year. Thus the two spacecraft have been
probing different probe/Sun/Earth angles. The utility of having remote
sensing and in-situ instrumentation away from the Sun-Earth line was
well demonstrated by STEREO. Here we propose the concept of a mission
at the 5th Lagrangian "point" in the Earth/Sun system, located behind
Earth about 60 degrees to the East of the Sun-Earth line. Such a mission
would enable many aspects affecting space weather to be well determined
and thus improving the prediction of the conditions of the solar wind
as it impinges on geospace. For example, Coronal Mass Ejections can
tracked for a significant distance toward Earth, new active regions
can be observed before they become visible to the Earth observer, the
solar wind can be measured before it rotates to Earth. The advantages
of such a mission will be discussed in this presentation.
---------------------------------------------------------
Title: Tracking Solar Wind Input from the Sun to the Magnetosphere:
2007-2011
Authors: St Cyr, O. C.; Mays, M. L.; Xie, H.; Gopalswamy, N.
2012AGUFMSH43C..02S Altcode:
During 2011 we were in the fortunate circumstance of having the twin
STEREO spacecraft (Kaiser et al., 2008) pass through quadrature with
the Sun-Earth line. As a result, the STEREO heliospheric imagers
offer the possibility to track solar wind density features (e.g.,
CMEs and CIRs) from the Sun-to-Earth. We have examined all instances
of Dst <-30 for this five year period, and we have identified the
solar wind sources of these magnetospheric disturbances using remote
sensing and in situ measurements.
---------------------------------------------------------
Title: Hot Precursor Ejecta and Other Peculiarities of the 2012 May
17 Ground Level Enhancement Event
Authors: Gopalswamy, N.; Xie, H.; Nitta, N. V.; Usoskin, I.; Davila,
J. M.
2012AGUFMSH21A2180G Altcode:
We report on the first Ground Level Enhancement (GLE) event of Solar
Cycle 24, which occurred on May 17, 2012 from a well-connected region
(NOAA AR 11476, N11W76) on the Sun. There has been a real dearth
of GLE events during cycle 24: even though the Sun has reached its
solar maximum phase, it has produced only this one GLE event. Over the
first 4.5 years of solar cycle 23, there were 5 GLE events, which is
roughly a third of all the events of that cycle. The recent GLE event
was associated with a moderate flare with an X-ray size of only M5.1,
well below the median flare size (X3.8) of cycle 23 GLE events. On
the other hand, the associated CME was very fast (~2000 km/s),
typical of GLE events. During cycle 23, the CME speeds in GLE events
ranged from 1203 km/s to 3675 km/s with an average value of 2083 km/s
(Gopalswamy et al., 2012). The speed of the cycle 24 GLE was measured
accurately because it was a limb event in the SOHO coronagraphic field
of view. The CME was also observed by the STEREO coronagraphs, which
helped derive the initial acceleration as 1.5 km/s/s, which is also
typical of GLE-producing CMEs. We were also able to directly determine
the heliocentric distance of the CME (2.3 solar radii (Rs)) at the
time of the release of GLE particles because there was a STEREO/COR1
image precisely at the time of the particle release. This result
is consistent with what was obtained for the cycle 23 GLE events,
including the distance of the CME at the time of metric type II burst
onset (1.3 Rs), indicating shock formation very close to the Sun
( ~0.3 Rs above the solar surface). We infer that the shock had to
travel an additional 1 Rs before the GLE particles were released. The
CME had a precursor in the form of a hot ejecta some tens of minutes
before the main eruption. The preceding ejecta is termed hot because
it was observed only in the 94 A images obtained by the Solar Dynamics
Observatory (SDO). The 94 A images correspond to coronal a temperature
of ~6MK. The lower temperature images such as at 193 A did not show
the ejecta. The hot ejecta was accelerating and attained a speed
of ~70 km/s before it was blasted by the big GLE-producing CMEs. We
suggest that the hot material of the precursor ejecta might have been
further accelerated by the CME-driven shock resulting in the GLE
event. Reference Gopalswamy, N.,Xie, H., Yashiro, S., Akiyama, S.,
Mäkelä, P., Usoskin, I. G., Properties of Ground Level Enhancement
Events and the Associated Solar Eruptions During Solar Cycle 23,
Space Science reviews, DOI: 10.1007/s11214-012-9890-4
---------------------------------------------------------
Title: Energetic particle and other space weather events of solar
cycle 24
Authors: Gopalswamy, Nat
2012AIPC.1500...14G Altcode: 2012arXiv1208.3951G
We report on the space weather events of solar cycle 24 in comparison
with those during a similar epoch in cycle 23. We find major differences
in all space weather events: solar energetic particles, geomagnetic
storms, and interplanetary shocks. Dearth of ground level enhancement
(GLE) events and major geomagnetic storms during cycle 24 clearly
standout. The space weather events seem to reflect the less frequent
solar eruptions and the overall weakness of solar cycle 24.
---------------------------------------------------------
Title: Properties of Ground Level Enhancement Events and the
Associated Solar Eruptions During Solar Cycle 23
Authors: Gopalswamy, N.; Xie, H.; Yashiro, S.; Akiyama, S.; Mäkelä,
P.; Usoskin, I. G.
2012SSRv..171...23G Altcode: 2012SSRv..tmp...38G; 2012arXiv1205.0688G
Solar cycle 23 witnessed the most complete set of observations
of coronal mass ejections (CMEs) associated with the Ground Level
Enhancement (GLE) events. We present an overview of the observed
properties of the GLEs and those of the two associated phenomena,
viz., flares and CMEs, both being potential sources of particle
acceleration. Although we do not find a striking correlation between
the GLE intensity and the parameters of flares and CMEs, the solar
eruptions are very intense involving X-class flares and extreme CME
speeds (average ∼2000 km/s). An M7.1 flare and a 1200 km/s CME are
the weakest events in the list of 16 GLE events. Most (80 %) of the CMEs
are full halos with the three non-halos having widths in the range 167
to 212 degrees. The active regions in which the GLE events originate are
generally large: 1290 msh (median 1010 msh) compared to 934 msh (median:
790 msh) for SEP-producing active regions. For accurate estimation of
the CME height at the time of metric type II onset and GLE particle
release, we estimated the initial acceleration of the CMEs using flare
and CME observations. The initial acceleration of GLE-associated CMEs
is much larger (by a factor of 2) than that of ordinary CMEs (2.3
km/s<SUP>2</SUP> vs. 1 km/s<SUP>2</SUP>). We confirmed the initial
acceleration for two events for which CME measurements are available
in the inner corona. The GLE particle release is delayed with respect
to the onset of all electromagnetic signatures of the eruptions:
type II bursts, low frequency type III bursts, soft X-ray flares
and CMEs. The presence of metric type II radio bursts some 17 min
(median: 16 min; range: 3 to 48 min) before the GLE onset indicates
shock formation well before the particle release. The release of GLE
particles occurs when the CMEs reach an average height of ∼3.09 R
<SUB> s </SUB> (median: 3.18 R <SUB> s </SUB>; range: 1.71 to 4.01
R <SUB> s </SUB>) for well-connected events (source longitude in the
range W20-W90). For poorly connected events, the average CME height at
GLE particle release is ∼66 % larger (mean: 5.18 R <SUB> s </SUB>;
median: 4.61 R <SUB> s </SUB>; range: 2.75-8.49 R <SUB> s </SUB>). The
longitudinal dependence is consistent with shock accelerations because
the shocks from poorly connected events need to expand more to cross
the field lines connecting to an Earth observer. On the other hand, the
CME height at metric type II burst onset has no longitudinal dependence
because electromagnetic signals do not require magnetic connectivity
to the observer. For several events, the GLE particle release is very
close to the time of first appearance of the CME in the coronagraphic
field of view, so we independently confirmed the CME height at particle
release. The CME height at metric type II burst onset is in the narrow
range 1.29 to 1.8 R <SUB> s </SUB>, with mean and median values of
1.53 and 1.47 R <SUB> s </SUB>. The CME heights at metric type II
burst onset and GLE particle release correspond to the minimum and
maximum in the Alfvén speed profile. The increase in CME speed between
these two heights suggests an increase in Alfvénic Mach number from
2 to 3. The CME heights at GLE particle release are in good agreement
with those obtained from the velocity dispersion analysis (Reames in
Astrophys. J. 693:812, 2009a; Astrophys. J. 706:844, 2009b) including
the source longitude dependence. We also discuss the implications of
the delay of GLE particle release with respect to complex type III
bursts by ∼18 min (median: 16 in; range: 2 to 44 min) for the flare
acceleration mechanism. A similar analysis is also performed on the
delay of particle release relative to the hard X-ray emission.
---------------------------------------------------------
Title: Determination of the Heliospheric Radial Magnetic Field from
the Standoff Distance of a CME-driven Shock Observed by the STEREO
Spacecraft
Authors: Poomvises, Watanachak; Gopalswamy, Nat; Yashiro, Seiji;
Kwon, Ryun-Young; Olmedo, Oscar
2012ApJ...758..118P Altcode:
We report on the determination of radial magnetic field strength in the
heliocentric distance range from 6 to 120 solar radii (R <SUB>⊙</SUB>)
using data from Coronagraph 2 (COR2) and Heliospheric Imager I (HI1)
instruments on board the Solar Terrestrial Relations Observatory
spacecraft following the standoff-distance method of Gopalswamy &
Yashiro. We measured the shock standoff distance of the 2008 April
5 coronal mass ejection (CME) and determined the flux-rope curvature
by fitting the three-dimensional shape of the CME using the Graduated
Cylindrical Shell model. The radial magnetic field strength is computed
from the Alfvén speed and the density of the ambient medium. We also
compare the derived magnetic field strength with in situ measurements
made by the Helios spacecraft, which measured the magnetic field at
the heliocentric distance range from 60 to 215 R <SUB>⊙</SUB>. We
found that the radial magnetic field strength decreases from 28 mG at
6 R <SUB>⊙</SUB> to 0.17 mG at 120 R <SUB>⊙</SUB>. In addition,
we found that the radial profile can be described by a power law.
---------------------------------------------------------
Title: Preface
Authors: Gopalswamy, N.; Nitta, N. V.
2012SSRv..171....1G Altcode: 2012SSRv..tmp...79G
No abstract at ADS
---------------------------------------------------------
Title: Deflections of Fast Coronal Mass Ejections and the Properties
of Associated Solar Energetic Particle Events
Authors: Kahler, S. W.; Akiyama, S.; Gopalswamy, N.
2012ApJ...754..100K Altcode:
The onset times and peak intensities of solar energetic particle (SEP)
events at Earth have long been thought to be influenced by the open
magnetic fields of coronal holes (CHs). The original idea was that a CH
lying between the solar SEP source region and the magnetic footpoint of
the 1 AU observer would result in a delay in onset and/or a decrease in
the peak intensity of that SEP event. Recently, Gopalswamy et al. showed
that CHs near coronal mass ejection (CME) source regions can deflect
fast CMEs from their expected trajectories in space, explaining the
appearance of driverless shocks at 1 AU from CMEs ejected near solar
central meridian (CM). This suggests that SEP events originating in
CME-driven shocks may show variations attributable to CH deflections
of the CME trajectories. Here, we use a CH magnetic force parameter
to examine possible effects of CHs on the timing and intensities of
41 observed gradual E ~ 20 MeV SEP events with CME source regions
within 20° of CM. We find no systematic CH effects on SEP event
intensity profiles. Furthermore, we find no correlation between the
CME leading-edge measured position angles and SEP event properties,
suggesting that the widths of CME-driven shock sources of the SEPs are
much larger than the CMEs. Independently of the SEP event properties,
we do find evidence for significant CME deflections by CH fields in
these events.
---------------------------------------------------------
Title: The Relationship Between the Expansion Speed and Radial Speed
of CMEs Confirmed Using Quadrature Observations of the 2011 February
15 CME
Authors: Gopalswamy, N.; Makela, P.; Yashiro, S.; Davila, J. M.
2012SunGe...7....7G Altcode: 2012arXiv1205.0744G
It is difficult to measure the true speed of Earth-directed CMEs
from a coronagraph along the Sun-Earth line because of the occulting
disk. However, the expansion speed (the speed with which the CME appears
to spread in the sky plane) can be measured by such coronagraph. In
order to convert the expansion speed to radial speed (which is
important for space weather applications) one can use empirical
relationship between the two that assumes an average width for all
CMEs. If we have the width information from quadrature observations,
we can confirm the relationship between expansion and radial speeds
derived by Gopalswamy et al. (2009a). The STEREO spacecraft were in
qudrature with SOHO (STEREO-A ahead of Earth by 87<SUP>o</SUP>and
STEREO-B 94<SUP>o</SUP>behind Earth) on 2011 February 15, when a fast
Earth-directed CME occurred. The CME was observed as a halo by the
Large-Angle and Spectrometric Coronagraph (LASCO) on board SOHO. The
sky-plane speed was measured by SOHO/LASCO as the expansion speed,
while the radial speed was measured by STEREO-A and STEREO-B. In
addition, STEREO-A and STEREO-B images measured the width of the
CME, which is unknown from Earth view. From the SOHO and STEREO
measurements, we confirm the relationship between the expansion
speed (V<SUB>exp</SUB>) and radial speed (V<SUB>rad</SUB>) derived
previously from geometrical considerations (Gopalswamy et al. 2009a):
V<SUB>rad</SUB>=1/2 (1 + cot w)V<SUB>exp</SUB>, where w is the half
width of the CME. STEREO-B images of the CME, we found that CME
had a full width of 7 6<SUP>o</SUP>, so w=3 8<SUP>o</SUP>. This
gives the relation as V<SUB>rad</SUB>=1.1 4 V<SUB>exp</SUB>. From
LASCO observations, we measured V<SUB>exp</SUB>=897 km/s, so we get
the radial speed as 10 2 3 km/s. Direct measurement of radial speed
yields 945 km/s (STEREO-A) and 105 8 km/s (STEREO-B). These numbers
are different only by 7.6 % and 3.4 % (for STEREO-A and STEREO-B,
respectively) from the computed value.
---------------------------------------------------------
Title: Dependence of solar proton events on their associated
activities: Coronal mass ejection parameters
Authors: Park, J.; Moon, Y. -J.; Gopalswamy, N.
2012JGRA..117.8108P Altcode: 2012JGRA..11708108P
In this study we have examined the occurrence probability of solar
proton events (SPEs) and their peak fluxes depending on coronal
mass ejection (CME) parameters, linear speed (V), angular width
(AW), and location (L). For this we used the NOAA SPE list and their
associated CME data from 1997 to 2006. We found that the probability
strongly depends on CME speed and angular width as follows. The
highest association (36.1%) is found for the full halo CMEs with V
≥ 1500 kms<SUP>-1</SUP> but the lowest association (0.9%) is found
for the partial halo CMEs with 400 kms<SUP>-1</SUP> ≤ V < 1000
kms<SUP>-1</SUP>. The SPE occurrence probabilities are different as
much as 4.9 to 23 times according to CME speed and 1.6 to 6.5 times to
angular width. The probabilities depending on CME speed and location
increase from the eastern region to the western region and with
speed. We have also examined the relationship between CME speed and
SPE flux as well as its dependence on angular width (partial halo and
full halo), longitude (east, center, and west) and direction parameter
(<0.4 and ≥0.4). Our results show that the relationships strongly
depend on longitude as well as direction parameter.
---------------------------------------------------------
Title: Radio-loud CMEs from the disk center lacking shocks at 1 AU
Authors: Gopalswamy, N.; MäKelä, P.; Akiyama, S.; Yashiro, S.; Xie,
H.; MacDowall, R. J.; Kaiser, M. L.
2012JGRA..117.8106G Altcode: 2012arXiv1207.0021G; 2012JGRA..11708106G
A coronal mass ejection (CME) associated with a type II burst and
originating close to the center of the solar disk typically results
in a shock at Earth in 2-3 days and hence can be used to predict
shock arrival at Earth. However, a significant fraction (about 28%)
of such CMEs producing type II bursts were not associated with
shocks at Earth. We examined a set of 21 type II bursts observed by
the Wind/WAVES experiment at decameter-hectometric (DH) wavelengths
that had CME sources very close to the disk center (within a central
meridian distance of 30 degrees), but did not have a shock at Earth. We
find that the near-Sun speeds of these CMEs average to ∼644 km/s,
only slightly higher than the average speed of CMEs associated with
radio-quiet shocks. However, the fraction of halo CMEs is only ∼30%,
compared to 54% for the radio-quiet shocks and 91% for all radio-loud
shocks. We conclude that the disk-center radio-loud CMEs with no
shocks at 1 AU are generally of lower energy and they drive shocks
only close to the Sun and dissipate before arriving at Earth. There
is also evidence for other possible processes that lead to the lack
of shock at 1 AU: (i) overtaking CME shocks merge and one observes a
single shock at Earth, and (ii) deflection by nearby coronal holes can
push the shocks away from the Sun-Earth line, such that Earth misses
these shocks. The probability of observing a shock at 1 AU increases
rapidly above 60% when the CME speed exceeds 1000 km/s and when the
type II bursts propagate to frequencies below 1 MHz.
---------------------------------------------------------
Title: On the Oscillatory and Non-oscillatory Loop Systems and
Dynamical Processes during the X2.1 Solar Flare on 06 September 2011
Authors: Srivastava, Abhishek K.; Jain, Rajmal; Prasad Choudhary, Debi;
Charan Dwivedi, Vidya; Aschwanden, Markus; Nitta, Nariaki; Gopalswamy,
Nat; Awasthi, Arun Kumar; Chandra, Ramesh; Kayshap, Pradeep; Joshi,
N. C.; Manoharan, P. K.; Norris, Max; Makela, Pertti; Mahalakshmi,
K.; Elamathi, E.
2012cosp...39.1882S Altcode: 2012cosp.meet.1882S
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Flux Imbalance in Active Regions NOAA 11283 and
NOAA 11302
Authors: Prasad Choudhary, Debi; Jain, Rajmal; Charan Dwivedi, Vidya;
Aschwanden, Markus; Nitta, Nariaki; Gopalswamy, Nat; Awasthi, Arun
Kumar; Chandra, Ramesh; Srivastava, Abhishek K.; Manoharan, P. K.;
Norris, Max; Mahalakshmi, K.; Elamathi, E.; Uddin, Wahab; Yashiro,
Seiji
2012cosp...39..334P Altcode: 2012cosp.meet..334P
We investigate the magnetic flux imbalance of two active regions NOAA
11302 and NOAA 11283 during their disk passage. The active region NOAA
11302 appeared in the east limb on September 23, 2011 as beta-gamma
complexity and produced 73 c-class, 27 M-class and 2 X-class flares
many of which were associated with CMEs during the disk passage. The
active region NOAA 11283 appeared on the east limb on September 1,
2011 as beta-gamma complexity and produced 16 c-class, 9 m-class and 2
x-class flares and CMEs. Both these active regions were of similar size
but the evolution of magnetic complexity during their disk passage
was very different. None of them made second disk passage. These
two active regions represent two different class of activity. Among
several reasons, the magnetic flux imbalance of the active regions
result due to the presence of electric current with in the active
regions. The high cadence full disk magnetograms obtained using the
GONG and SDO-HMI instruments serve as the primary data source of this
investigation. We relate the change in the magnetic flux imbalance
with the flare occurrence in these two contrasting active regions.
---------------------------------------------------------
Title: Height of Shock Formation in the Solar Corona Inferred from
Observations of Type II Radio Bursts and Coronal Mass Ejections
Authors: Gopalswamy, Nat; Jain, Rajmal; Prasad Choudhary, Debi;
Charan Dwivedi, Vidya; Aschwanden, Markus; Nitta, Nariaki; Awasthi,
Arun Kumar; Srivastava, Abhishek K.; Joshi, N. C.; Manoharan, P. K.;
Makela, Pertti; Mahalakshmi, K.; Elamathi, E.; Uddin, Wahab; Yashiro,
Seiji; Akiyam, Sachiko
2012cosp...39..653G Altcode: 2012cosp.meet..653G
No abstract at ADS
---------------------------------------------------------
Title: Multi-wavelength diagnostics of thermal and non-thermal
sources in the 22 April 2011 flare event
Authors: Awasthi, Arun Kumar; Jain, Rajmal; Prasad Choudhary, Debi;
Charan Dwivedi, Vidya; Aschwanden, Markus; Nitta, Nariaki; Gopalswamy,
Nat; Chandra, Ramesh; Srivastava, Abhishek K.; Kayshap, Pradeep; Joshi,
N. C.; Manoharan, P. K.; Norris, Max; Mahalakshmi, K.; Elamathi, E.;
Uddin, Wahab
2012cosp...39...75A Altcode: 2012cosp.meet...75A
No abstract at ADS
---------------------------------------------------------
Title: Coronal Mass Ejections and Type II Radio Bursts from Active
Region 11158
Authors: Yashiro, Seiji; Jain, Rajmal; Prasad Choudhary, Debi; Charan
Dwivedi, Vidya; Aschwanden, Markus; Nitta, Nariaki; Gopalswamy, Nat;
Awasthi, Arun Kumar; Chandra, Ramesh; Srivastava, Abhishek K.; Kayshap,
Pradeep; Joshi, N. C.; Manoharan, P. K.; Makela, Pertti; Mahalakshmi,
K.; Elam, E.
2012cosp...39.2205Y Altcode: 2012cosp.meet.2205Y
The NOAA active region (AR) 11158 emerged at around S20E50 on 2011
February 10 as two bipoles and quickly developed into a large complex
region. During 2011 February 13-17, AR 11158 produced 48 flares
(>C1 level) including the first X-class flare of 15 February,
2011 in solar cycle 24. The 48 flares can be divided into four groups
based on their location within the AR. We examined their associations
of coronal mass ejections (CMEs) and metric type II radio bursts in
order to find preferred locations of both the phenomena. We found that,
out of 48 flares, 15 had associated CMEs, occurring frequently at the
eastern edge of the AR. We also found that six flares were associated
with type II radio bursts and all of them were associated with CMEs
also. No type II was associated with the CME-less flare. This suggests
that the CME association is a necessary condition for a flare to be
associated with a metric type II burst.
---------------------------------------------------------
Title: The 3-D structure of CMEs as Inferred from Coronagraph
Observations
Authors: Gopalswamy, Nat
2012cosp...39..649G Altcode: 2012cosp.meet..649G
Although the 3-D nature of coronal mass ejections (CMEs) has been
suspected for a long time, it is only after the launch of the Solar
Terrestrial Relations Observatory (STEREO) mission that it became
possible to directly observe such structures. The twin instrument
suite of the STEREO mission combined with the Solar and Heliospheric
Observatory (SOHO) instruments helped enormously in obtaining the 3-D
structure of CMEs. One of the earliest revelations is the confirmation
that halo CMEs are like normal CMEs, except that they are viewed head on
(or tail on) and are generally more energetic than the normal CMEs. EUV
observations from STEREO and from the Solar Dynamics Observatory (SDO)
also reveal the hemispheric nature of the early-phase shock-driving
CMEs. STEREO coronagraphs provided broad-side views of such CMEs, so
it became possible to estimate the width of the halo CMEs and hence
validate CME cone models. In particular, the quadrature observations
that became possible in 2010 and 2011 when the STEREO spacecraft were
separated from the Sun-Earth line by about 90 degrees, revealed that
CMEs are generally cone-shaped. Current theoretical ideas on the
internal structure of CMEs suggest that a flux rope is central to
the CME structure, which has considerable observational support. The
cone model can be reconciled with the flux-rope structure with
certain requirements on the thickness of the rope legs. The quadrature
observations also helped us understand the relation between the radial
and expansion speeds of CMEs, which were only known from empirical
relations in the past. This paper highlights some key results obtained
using observations from the declining phase of solar cycle 23 and the
rise phase of solar cycle 24.
---------------------------------------------------------
Title: Inferences on the Behavior of Solar Cycle 24 from the Polar
Coronal Hole Enhancement and the Rate of Prominence Eruptions Observed
by the Nobeyama Radioheliograph
Authors: Gopalswamy, Nat; Yashiro, Seiji; Akiyama, Sachiko; Shibasaki,
Kiyoto
2012cosp...39..651G Altcode: 2012cosp.meet..651G
After a prolonged minimum at the end of the solar cycle 23, solar
activity picked up, but generally at low levels. One of the indicators
of the level of activity is the rate of prominence eruptions (PEs)
automatically detected in the images obtained by the Nobeyama
Radioheliograph (NoRH). The relation between PEs and coronal mass
ejections (CMEs) has a specific characteristic during solar minima:
The PE latitude is generally higher than that of the associated CME nose
indicating a general equatorward deflection of CMEs. The overall extent
of the offset seems to be similar during the rise phases of cycle 23
and 24, but there are far fewer PEs during cycle 24. The open field
lines emanating from the polar coronal hole are thought to deflect
CMEs away from the polar region. It is found that the offset starts
in the year 2007, roughly two years before the deepest solar minimum
and continued into the rise phase of the solar cycle 24. A significant
north-south asymmetry is observed in the deflection process, which can
be explained by the different behavior of the north and south polar
coronal holes. We also constructed NoRH microwave butterfly diagram
using 17 GHz images, which reveal that the solar activity has reached
the maximum phase in the north pole. This is further confirmed by the
latitudes of prominence eruptions reminiscent of the maximum phase.
---------------------------------------------------------
Title: A Study of the 12 June 2010 C6.1/SF flare associated with a
CME, surge and energetic particles
Authors: Uddin, Wahab; Jain, Rajmal; Manoharan, P. K.; Prasad
Choudhary, Debi; Charan Dwivedi, Vidya; Aschwanden, Markus; Nitta,
Nariaki; Gopalswamy, Nat; Awasthi, Arun Kumar; Chandra, Ramesh;
Srivastava, Abhishek K.; Kayshap, Pradeep; Joshi, N. C.; Norris, Max;
Makela, Pertti; Mahalaksh, K.
2012cosp...39.2026U Altcode: 2012cosp.meet.2026U
In this paper, we present the multiwavelength analysis of the C6.1/SF
flare on 12 June 2010 from NOAA AR 11081. The flare was observed by
various ground based (ARIES H-alpha; HIRAS Radio) and space borne
observatories (SDO, STEREO, SOHO, GOES). The flare was accompanied by
a spray/surge and a slow coronal mass ejection (CME) that propagated
with a speed of ~382 km/s. The eruption was associated with a weak
solar energetic particle (SEP) event. The solar source of the eruption
was a rapid emerging flux region. The eruption was also associated
with the three major types of radio bursts (type II, III and IV). The
interesting observation is the shock production (type II burst and
SEP event) by a relatively slow CME. We interpret the results in the
light of existing theories.
---------------------------------------------------------
Title: Global Cooperation in the Capacity Building Activities on
Sun-Earth Connection Studies
Authors: Gopalswamy, Nat; Davila, Joseph; Luebken, Franz-Josef;
Shepherd, Marianna; Tsuda, Toshitaka
2012cosp...39..650G Altcode: 2012cosp.meet..650G
The importance of global cooperation in Sun-Earth connection studies
can be readily seen in the formation of a number of international
collaborative programs such as the Climate and Weather of the
Sun Earth System (CAWSES) by SCOSTEP* and the International Space
Weather Initiative (ISWI). ISWI is the continuation of the successful
International Heliophysical Year (IHY) program. These programs have
brought scientists together to tackle issues of solar-terrestrial
phenomena. An important element of these organizations is capacity
building activities, which include deployment of low-cost ground
based instruments for Sun-Earth connection studies and training young
people (scientists and graduate students) from developing countries
to operate these instruments and become members of the international
solar-terrestrial scientific community. The training also helps young
people to make use of data from the vast array of space and ground based
instruments currently available for Sun-Earth connection studies. This
paper presents a summary of CAWSES and ISWI activities that promote
space Sun-Earth connection studies via complementary approaches in
international scientific collaborations, capacity building, and public
outreach. *Scientific Committee on Solar Terrestrial Physics (SCOSTEP)
is an Interdisciplinary Body of the International Council for Science
with representations from COSPAR, IAU, IUGG/IAGA, IUPAP, IAMAS, SCAR,
and URSI (http://www.yorku.ca/scostep)
---------------------------------------------------------
Title: The location of solar metric type II radio bursts with respect
to the associated coronal mass ejections
Authors: Ramesh, R.; Gopalswamy, Nat; Lakshmi, Anna M.; Kathiravan, C.
2012cosp...39.1549R Altcode: 2012cosp.meet.1549R
No abstract at ADS
---------------------------------------------------------
Title: A Global View of the Energetic Solar Eruptions during 2012
January 19-27
Authors: Gopalswamy, Nat; Davila, Joseph; Kaiser, Michael; Macdowall,
Robert; Cyr, Chris; Xie, Hong; Makela, Pertti; Yashiro, Seiji;
Poomvises, Watanachak
2012cosp...39..652G Altcode: 2012cosp.meet..652G
The rise phase of solar cycle was generally unremarkable and subdued in
terms of large solar eruptive events that had significant heliospheric
consequences. Towards the end of the rise phase, a series of three
coronal mass ejections (CMEs) originated from NOAA active region
11402 that were accompanied by M or X-class flares, significant solar
energetic particle events (including the largest event as of this
writing), interplanetary type II radio bursts, and shocks. While
the particle radiation was very intense in two events, the plasma
impact on the magnetosphere was moderate. This paper provides an
overview of the eruptive events, focusing on the kinematic evolution
of the CMEs in relation to the interplanetary type II radio bursts
and shocks. In particular we compare the drift rate variation of
the interplanetary type II bursts with the speed variation of the
CMEs obtained from heliospheric imaging. We make use of data from the
Solar and Heliospheric Observatory (SOHO), Solar Terrestrial Relations
Observatory (STEREO), Solar Dynamics Observatory (SDO), Wind, GOES,
and ground based observatories for this investigation.
---------------------------------------------------------
Title: Solar Energetic Particle Events and Associated CMEs during
the Rising Phases of Solar Cycle 23 and 24 - A Comparative study
Authors: Chandra, Ramesh; Jain, Rajmal; Prasad Choudhary, Debi; Charan
Dwivedi, Vidya; Aschwanden, Markus; Nitta, Nariaki; Gopalswamy, Nat;
Awasthi, Arun Kumar; Srivastava, Abhishek K.; Kayshap, Pradeep; Joshi,
N. C.; Manoharan, P. K.; Makela, Pertti; Mahalakshmi, K.; Elamathi,
E.; Uddi, Wahab
2012cosp...39..303C Altcode: 2012cosp.meet..303C
No abstract at ADS
---------------------------------------------------------
Title: Flare and CME Productivity of Active Region 11429
Authors: Yashiro, Seiji; Gopalswamy, N.; Akiyama, S.; Michalek, G.;
Makela, P.
2012shin.confE.161Y Altcode:
Active region NOAA 11429 produced 3 X- and 15 M-class flares
duringMarch 2 to 13. We examined their CME association using
SOHO/LASCO andSTEREO/COR1 and found that 8 flares were CME-associated
and theremaining 10 were CME-less. We found that the 10 CME-less
flaresoccurred successively between 19 UT on March 5 and 22 UT on
March 6. Theintensities of the flares were relatively low (range:
M1.0 - M2.1;median: M1.3), but the occurrence rate was very high
(at 3-hourintervals on average). During this period a CME erupted
from thesouthern edge of this region but the X-ray enhancement was
not detectedby GOES. The CME-associated flares are relatively intense
(range: M2.0 -X5.4; median M8.1), and the waiting times (intervals
between successiveflares) are longer ( 36 hours on average) than those
of the CME-lessflares. We present a comprehensive view of flare-CME
activities of theactive region 11429 and discuss the difference of
the CME-associated andCME-less flares.
---------------------------------------------------------
Title: The Location of Solar Metric Type II Radio Bursts with Respect
to the Associated Coronal Mass Ejections
Authors: Ramesh, R.; Lakshmi, M. Anna; Kathiravan, C.; Gopalswamy,
N.; Umapathy, S.
2012ApJ...752..107R Altcode:
Forty-one solar type II radio bursts located close to the solar limb
(projected radial distance r >~ 0.8 R <SUB>⊙</SUB>) were observed
at 109 MHz by the radioheliograph at the Gauribidanur observatory
near Bangalore during the period 1997-2007. The positions of the
bursts were compared with the estimated location of the leading edge
(LE) of the associated coronal mass ejections (CMEs) close to the
Sun. 38/41 of the type II bursts studied were located either at or
above the LE of the associated CME. In the remaining 3/41 cases, the
burst was located behind the LE of the associated CME at a distance
of <0.5 R <SUB>⊙</SUB>. Our results suggest that nearly all the
metric type II bursts are driven by the CMEs.
---------------------------------------------------------
Title: A study of cold-high density materials in ICMEs
Authors: Akiyama, Sachiko; Gopalswamy, Nat; Yashiro, Seiji; Kim,
Rok-Soon; Mäkelä, Pertti; Xie, Hong; Marubashi, Katsuhide
2012shin.confE.136A Altcode:
Eruptive prominence (EP) is dynamic and is well known as the core of
coronal mass ejections (CMEs) near the Sun. Reports of filament material
in in-situ observations are rare, even though EPs are identified as a
solar source of an interplanetary CMEs. We studied cold high-density
material in 54 ICMEs (1997 - 2006), whose solar source was located
within 15 degrees from the disk center. All events were part of the
Living with a Star (LWS) Coordinated Data-Analysis Workshop (CDAW) known
as the 'Flux Rope CDAW', which took place in 2012 and 2011. Using SXT,
EIT, TRACE and Ha data, we carefully checked the solar sources to see
whether EPs including filament disappearances were observed coincidently
or not. We found 33 (21) CME-ICME pairs associated with (without)
EPs. Then we selected cold high-density bumps within the overall
interval of the ICMEs, which satisfied the following conditions: 1)
There is a proton and He++ density increase for more than two hours. 2)
Maximum proton temperature remains lower than the average temperature of
the ICME. 3) Exclude density increases at the boundary between sheath
and ICME. 4) In cases where the ICME is followed by another ICME or
a corotating interaction region, exclude the density increase at the
rear boundary. With these criteria, we found 20 (10) cold high-density
material in ICMEs with (without) EPs. We found that the average proton
and He++ density increases in ICMEs associated with EP (15.8 and 0.56
/cm^3) are larger than in ICMEs associated with non-EPs (10.7 and 0.34
/cm^3). There is no preferred location of the density increase during
the ICME. Average location of increase is near the center of the ICME.
---------------------------------------------------------
Title: Behavior of Solar Cycles 23 and 24 Revealed by Microwave
Observations
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Michalek, G.;
Shibasaki, K.; Hathaway, D. H.
2012ApJ...750L..42G Altcode: 2012arXiv1204.2816G
Using magnetic and microwave butterfly diagrams, we compare the
behavior of solar polar regions to show that (1) the polar magnetic
field and the microwave brightness temperature during solar minimum
substantially diminished during the cycle 23/24 minimum compared to
the 22/23 minimum. (2) The polar microwave brightness temperature
(Tb) seems to be a good proxy for the underlying magnetic field
strength (B). The analysis indicates a relationship, B = 0.0067Tb -
70, where B is in G and Tb in K. (3) Both the brightness temperature
and the magnetic field strength show north-south asymmetry most of
the time except for a short period during the maximum phase. (4) The
rush-to-the-pole phenomenon observed in the prominence eruption (PE)
activity seems to be complete in the northern hemisphere as of 2012
March. (5) The decline of the microwave brightness temperature in the
north polar region to the quiet-Sun levels and the sustained PE activity
poleward of 60<SUP>o</SUP>N suggest that solar maximum conditions have
arrived at the northern hemisphere. The southern hemisphere continues
to exhibit conditions corresponding to the rise phase of solar cycle 24.
---------------------------------------------------------
Title: Comparison between Major Confined and Eruptive Flares
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Dennis, B. R.
2012AAS...22042402G Altcode:
Statistical studies have shown that a large fraction of major solar
flares (42% M-class and 15% X-class) are not associated with coronal
mass ejections (CMEs). The CME-less flares are confined flares as
opposed to the eruptive flares associated with CMEs. Confined flares
are certainly good particle accelerators as inferred from intense
microwave, hard X-ray, and gamma-ray emissions. Note that a single
acceleration mechanism operates in confined flares, whereas eruptive
flares can have both flare-resident and shock accelerations (the shock
acceleration is due to energetic CMEs). In this paper, we report on
a statistical study of more than two dozen confined flares with soft
X-ray flare size exceeding M5 in comparison with a control sample of
eruptive flares with similar soft X-ray flare size. We compare the
microwave and X-ray emission characteristics in the two populations;
these emissions correspond to sunward energy flow. For a given X-ray
flare size, the microwave flux is scattered over a wider range for
the eruptive flares when compared to the confined flares. We also
compare the metric and longer wavelength radio bursts between the two
populations; these emissions correspond to the flow of nonthermal
electrons away from the Sun. We find that almost all the confined
flares lack metric radio bursts, suggesting that there is very little
flow of energy into the interplanetary medium. On the other hand, there
is high degree of association between eruptive flares and metric radio
bursts. This suggests that in confined flares the accelerated electrons
have no access to open magnetic field lines. Finally, we examined the
association of EUV waves with the two flare populations. While we find
EUV waves in most of the eruptive flares, there was no confined flare
with EUV waves. This suggests that CMEs is a necessary condition for
the generation of global waves.
---------------------------------------------------------
Title: A Comparison of Solar Energetic Particle Events with 1 AU
Magnetic Field Connections to Solar Coronal Holes
Authors: Kahler, Stephen W.; Arge, C. N.; Akiyama, S.; Gopalswamy, N.
2012AAS...22020436K Altcode:
The observed properties of solar energetic particle (SEP) events are
known to depend on the source locations and speeds of their associated
coronal mass ejections (CMEs). However, the CME characteristics cannot
account for a great deal of the variability in SEP event intensities and
time scales. It has long been suspected that the presence of coronal
holes (CHs) near the CMEs or near the 1 AU magnetic footpoints may
be an important factor in SEP events. We use a group of E 20 MeV SEP
events with origins near solar central meridian to look for possible
CH effects. The CH connections from 1 AU are determined from the 4-day
forecast maps based on Mount Wilson Observatory and the National Solar
Observatory synoptic magnetic field maps and the Wang-Sheeley-Arge
model of solar wind propagation. The observed in situ magnetic field
polarities and solar wind speeds at SEP event onsets test the forecast
accuracies to select the best SEP/CH connection events for analysis. The
SEP event properties are then compared with the relative locations and
separations of the CMEs and the 1 AU footpoints to determine whether
and how the CHs may affect SEP events.
---------------------------------------------------------
Title: CME-associated Radio Bursts from Satellite Observations
Authors: Gopalswamy, Nat
2012AAS...22030403G Altcode:
Coronal mass ejections (CMEs) are closely associated with various types
of radio bursts from the Sun. All radio bursts are due to nonthermal
electrons, which are accelerated during the eruption of CMEs. Radio
bursts at frequencies below about 15 MHz are of particular interest
because they are associated with energetic CMEs that contribute to
severe space weather. The low-frequency bursts need to be observed
primarily from space because of the ionospheric cutoff. The main
CME-related radio bursts are associated are: type III bursts due to
accelerated electrons propagating along open magnetic field lines, type
II bursts due to electrons accelerated in shocks, and type IV bursts
due to electrons trapped in post-eruption arcades behind CMEs. This
paper presents a summary of results obtained during solar cycle 23
primarily using the white-light coronagraphic observations from the
Solar Heliospheric Observatory (SOHO) and the WAVES experiment on
board Wind. Particular emphasis will be placed on what we can learn
about particle acceleration in the coronal and interplanetary medium
by analyzing the CMEs and the associated radio bursts.
---------------------------------------------------------
Title: On the Relationship Between a High-frequency Type II Solar
Radio Burst and Coronal Mass Ejection on February 13, 2011
Authors: Cho, Kyung-Suk; Gopalswamy, N.; Kwon, R.; Kim, R.; Yashiro, S.
2012AAS...22052502C Altcode:
We examine the relationship between a metric type II radio burst that
started from an unusually high frequency of 425 MHz (fundamental
component) and the associated white-light coronal mass ejection on
2011 February 11. The radio burst had a drift rate of 3 MHz/sec,
indicating a relatively high shock speed. The question we would like
to answer is whether the high frequency type II burst is generated by
the CME. To avoid the ambiguity normally caused by the use of density
models in the analysis of type II bursts, we measure the coronal
electron density by applying automated emission measure analysis code
developed by Aschwanden et al. (2011) to AIA/SDO images in 6 coronal
filters. From SDO AIA observations we find that a loop-like erupting
front sweeps across high density coronal loops near the start time of
the burst (17:34:15 UT). The deduced height of shock formation (1.2
Rs) from the measured density is comparable to the height (1.15 Rs)
of the CME observed by STEREO/EUVI. Thus we conclude that the high
frequency type II burst could be generated at locations where the CME
passes through the high density loops in the low corona.
---------------------------------------------------------
Title: Propagation Characteristics of CMEs Associated Magnetic Clouds
and Ejecta
Authors: Kim, Roksoon; Gopalswamy, N.; Cho, K.; Moon, Y.; Yashiro, S.
2012AAS...22052108K Altcode:
We have investigated the characteristics of magnetic cloud (MC)
and ejecta (EJ) associated coronal mass ejections (CMEs) based on
the assumption that all CMEs have a flux rope structure. For this,
we used 54 CMEs and their interplanetary counter parts (interplanetary
CMEs: ICMEs) that constitute the list of events used by the NASA/LWS
Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We
considered the location, angular width, speed, and direction parameter,
D, that quantifies the propagation direction of a CME. For the 54
CDAW events, we found several properties of the CMEs as follows:
(1) the average value of D for the 23 MCs (0.62) is larger than that
for the 31 EJs (0.49), which indicates that the MC-associated CMEs
propagate more directly to the Earth than the EJ-associated CMEs; (2)
comparison between the direction parameter and the source location
shows that the majority of the MC-associated CMEs are ejected along
the radial direction, while many of the EJ-associated CMEs are ejected
non-radially; (3) the mean speed of MC-associated CMEs (946 km/s)
is faster than that of EJ-associated CMEs (771 km/s). For seven
very fast CMEs (> 1500 km/s), all CMEs with large D (> 0.4)
are associated with MCs and the CMEs with small D are associated with
EJs. On the basis of these results, we suggest that the CME trajectory
essentially decides the observed ICME structure.
---------------------------------------------------------
Title: Factors affecting the intensity of solar energetic particle
events
Authors: Gopalswamy, Nat
2012AIPC.1436..247G Altcode: 2011arXiv1109.2933G
This paper updates the influence of environmental and source factors
of shocks driven by coronal mass ejections (CMEs) that are likely to
influence the solar energetic particle (SEP) events. The intensity
variation due to CME interaction reported in [1] is confirmed by
expanding the investigation to all the large SEP events of solar cycle
23. The large SEP events are separated into two groups, one associated
with CMEs running into other CMEs, and the other with CMEs running
into the ambient solar wind. SEP events with CME interaction generally
have a higher intensity. New possibilities such as the influence of
coronal holes on the SEP intensity are also discussed. For example,
the presence of a large coronal hole between a well-connected eruption
and the solar disk center may render the shock poorly connected because
of the interaction between the CME and the coronal hole. This point is
illustrated using the 2004 December 3 SEP event delayed by about 12
hours from the onset of the associated CME. There is no other event
at the Sun that can be associated with the SEP onset. This event is
consistent with the possibility that the coronal hole interaction
influences the connectivity of the CMEs that produce SEPs, and hence
the intensity of the SEP event.
---------------------------------------------------------
Title: Erratum to: Relation Between Type II Bursts and CMEs Inferred
from STEREO Observations
Authors: Gopalswamy, N.; Thompson, W. T.; Davila, J. M.; Kaiser,
M. L.; Yashiro, S.; Mäkelä, P.; Michalek, G.; Bougeret, J. -L.;
Howard, R. A.
2012SoPh..277..459G Altcode: 2011SoPh..tmp..421G; 2011SoPh..tmp..425G
No abstract at ADS
---------------------------------------------------------
Title: Coronal mass ejection-driven shocks and the associated sudden
commencements/sudden impulses
Authors: Veenadhari, B.; Selvakumaran, R.; Singh, Rajesh; Maurya,
Ajeet K.; Gopalswamy, N.; Kumar, Sushil; Kikuchi, T.
2012JGRA..117.4210V Altcode: 2012JGRA..11704210V
Interplanetary (IP) shocks are mainly responsible for the sudden
compression of the magnetosphere, causing storm sudden commencement
(SC) and sudden impulses (SIs) which are detected by ground-based
magnetometers. On the basis of the list of 222 IP shocks compiled
by Gopalswamy et al. (2010), we have investigated the dependence of
SC/SIs amplitudes on the speed of the coronal mass ejections (CMEs)
that drive the shocks near the Sun as well as in the interplanetary
medium. We find that about 91% of the IP shocks were associated with
SC/SIs. The average speed of the SC/SI-associated CMEs is 1015 km/s,
which is almost a factor of 2 higher than the general CME speed. When
the shocks were grouped according to their ability to produce type II
radio burst in the interplanetary medium, we find that the radio-loud
(RL) shocks produce a much larger SC/SI amplitude (average ∼32 nT)
compared to the radio-quiet (RQ) shocks (average ∼19 nT). Clearly,
RL shocks are more effective in producing SC/SIs than the RQ shocks. We
also divided the IP shocks according to the type of IP counterpart of
interplanetary CMEs (ICMEs): magnetic clouds (MCs) and nonmagnetic
clouds. We find that the MC-associated shock speeds are better
correlated with SC/SI amplitudes than those associated with non-MC
ejecta. The SC/SI amplitudes are also higher for MCs than ejecta. Our
results show that RL and RQ type of shocks are important parameters
in producing the SC/SI amplitude.
---------------------------------------------------------
Title: Understanding shock dynamics in the inner heliosphere with
modeling and Type II radio data: The 2010-04-03 event
Authors: Xie, H.; Odstrcil, D.; Mays, L.; St. Cyr, O. C.; Gopalswamy,
N.; Cremades, H.
2012JGRA..117.4105X Altcode: 2012JGRA..11704105X
The 2010 April 03 solar event was studied using observations from STEREO
SECCHI, SOHO LASCO, and Wind kilometric Type II data (kmTII) combined
with WSA-Cone-ENLIL model simulations performed at the Community
Coordinated Modeling Center (CCMC). In particular, we identified the
origin of the coronal mass ejection (CME) using STEREO EUVI and SOHO
EIT images. A flux-rope model was fit to the SECCHI A and B, and LASCO
images to determine the CME's direction, size, and actual speed. J-maps
from STEREO COR2/HI-1/HI-2 and simulations from CCMC were used to study
the formation and evolution of the shock in the inner heliosphere. In
addition, we also studied the time-distance profile of the shock
propagation from kmTII radio burst observations. The J-maps together
with in-situ data from the Wind spacecraft provided an opportunity
to validate the simulation results and the kmTII prediction. Here we
report on a comparison of two methods of predicting interplanetary
shock arrival time: the ENLIL model and the kmTII method; and
investigate whether or not using the ENLIL model density improves
the kmTII prediction. We found that the ENLIL model predicted the
kinematics of shock evolution well. The shock arrival times (SAT)
and linear-fit shock velocities in the ENLIL model agreed well with
those measurements in the J-maps along both the CME leading edge and
the Sun-Earth line. The ENLIL model also reproduced most of the large
scale structures of the shock propagation and gave the SAT prediction
at Earth with an error of ∼1 ± 7 hours. The kmTII method predicted
the SAT at Earth with an error of ∼15 hours when using n<SUB>0</SUB> =
4.16 cm<SUP>-3</SUP>, the ENLIL model plasma density near Earth; but it
improved to ∼2 hours when using n<SUB>0</SUB> = 6.64 cm<SUP>-3</SUP>,
the model density near the CME leading edge at 1 AU.
---------------------------------------------------------
Title: Comparison of Dst forecast models for intense geomagnetic
storms
Authors: Ji, Eun-Young; Moon, Y. -J.; Gopalswamy, N.; Lee, D. -H.
2012JGRA..117.3209J Altcode: 2012JGRA..11703209J
We have compared six Dst forecast models using 63 intense geomagnetic
storms (Dst ≤ -100 nT) that occurred from 1998 to 2006. For
comparison, we estimated linear correlation coefficients and RMS
errors between the observed Dst data and the predicted Dst during the
geomagnetic storm period as well as the difference of the value of
minimum Dst (ΔDst<SUB>min</SUB>) and the difference in the absolute
value of Dst minimum time (Δt<SUB>Dst</SUB>) between the observed
and the predicted. As a result, we found that the model by Temerin
and Li (2002, 2006) gives the best prediction for all parameters when
all 63 events are considered. The model gives the average values:
the linear correlation coefficient of 0.94, the RMS error of 14.8
nT, the ΔDst<SUB>min</SUB> of 7.7 nT, and the absolute value of
Δt<SUB>Dst</SUB> of 1.5 hour. For further comparison, we classified
the storm events into two groups according to the magnitude of Dst. We
found that the model of Temerin and Lee (2002, 2006) is better than the
other models for the events having -100 ≤ Dst < -200 nT, and three
recent models (the model of Wang et al. (2003), the model of Temerin
and Li (2002, 2006), and the model of Boynton et al. (2011b)) are better
than the other three models for the events having Dst ≤ -200 nT.
---------------------------------------------------------
Title: Magnetic Field Strength in the Upper Solar Corona Using
White-light Shock Structures Surrounding Coronal Mass Ejections
Authors: Kim, R. -S.; Gopalswamy, N.; Moon, Y. -J.; Cho, K. -S.;
Yashiro, S.
2012ApJ...746..118K Altcode: 2011arXiv1112.0288K
To measure the magnetic field strength in the solar corona,
we examined 10 fast (>=1000 km s<SUP>-1</SUP>) limb coronal
mass ejections(CMEs) that show clear shock structures in Solar and
Heliospheric Observatory/Large Angle and Spectrometric Coronagraph
images. By applying the piston-shock relationship to the observed
CME's standoff distance and electron density compression ratio, we
estimated the Mach number, Alfvén speed, and magnetic field strength
in the height range 3-15 solar radii (R<SUB>s</SUB> ). The main results
from this study are as follows: (1) the standoff distance observed in
the solar corona is consistent with those from a magnetohydrodynamic
model and near-Earth observations; (2) the Mach number as a shock
strength is in the range 1.49-3.43 from the standoff distance ratio,
but when we use the density compression ratio, the Mach number is in
the range 1.47-1.90, implying that the measured density compression
ratio is likely to be underestimated owing to observational limits;
(3) the Alfvén speed ranges from 259 to 982 km s<SUP>-1</SUP> and
the magnetic field strength is in the range 6-105 mG when the standoff
distance is used; (4) if we multiply the density compression ratio by
a factor of two, the Alfvén speeds and the magnetic field strengths
are consistent in both methods; and (5) the magnetic field strengths
derived from the shock parameters are similar to those of empirical
models and previous estimates.
---------------------------------------------------------
Title: Interplanetary shocks lacking type II radio bursts.
Authors: Gopalswamy, N.; Xie, H.; Makela, P.; Akiyama, S.; Yashiro,
S.; Kaiser, M. L.; Howard, R. A.; Bougeret, J. -L.
2012yCat..17101111G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Magnetic Field Measurement from EUV Images Made by
the Solar Dynamics Observatory
Authors: Gopalswamy, Nat; Nitta, Nariaki; Akiyama, Sachiko; Mäkelä,
Pertti; Yashiro, Seiji
2012ApJ...744...72G Altcode: 2011arXiv1109.2925G
By measuring the geometrical properties of the coronal mass ejection
(CME) flux rope and the leading shock observed on 2010 June 13 by
the Solar Dynamics Observatory (SDO) mission's Atmospheric Imaging
Assembly we determine the Alfvén speed and the magnetic field strength
in the inner corona at a heliocentric distance of ~1.4 Rs. The basic
measurements are the shock standoff distance (ΔR) ahead of the CME
flux rope, the radius of curvature of the flux rope (R <SUB>c</SUB>),
and the shock speed. We first derive the Alfvénic Mach number (M) using
the relationship, ΔR/R <SUB>c</SUB> = 0.81[(γ-1) M <SUP>2</SUP> +
2]/[(γ+1)(M <SUP>2</SUP> - 1)], where γ is the only parameter that
needed to be assumed. For γ = 4/3, the Mach number declined from
3.7 to 1.5 indicating shock weakening within the field of view of the
imager. The shock formation coincided with the appearance of a type II
radio burst at a frequency of ~300 MHz (harmonic component), providing
an independent confirmation of the shock. The shock compression ratio
derived from the radio dynamic spectrum was found to be consistent
with that derived from the theory of fast-mode MHD shocks. From the
measured shock speed and the derived Mach number, we found the Alfvén
speed to increase from ~140 km s<SUP>-1</SUP> to 460 km s<SUP>-1</SUP>
over the distance range 1.2-1.5 Rs. By deriving the upstream plasma
density from the emission frequency of the associated type II radio
burst, we determined the coronal magnetic field to be in the range
1.3-1.5 G. The derived magnetic field values are consistent with other
estimates in a similar distance range. This work demonstrates that the
EUV imagers, in the presence of radio dynamic spectra, can be used as
coronal magnetometers.
---------------------------------------------------------
Title: Relation Between the 3D-Geometry of the Coronal Wave and
Associated CME During the 26 April 2008 Event
Authors: Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.
2012esrs.book..115T Altcode:
We study the kinematical characteristics and 3D geometry of
a large-scale coronal wave that occurred in association with the
26 April 2008 flare-CME event. The wave was observed with the EUVI
instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B)
with a mean speed of ∼ 240 km s<SUP>-1</SUP>. The wave is more
pronounced in the eastern propagation direction, and is thus, better
observable in STEREO-B images. From STEREO-B observations we derive
two separate initiation centers for the wave, and their locations fit
with the coronal dimming regions. Assuming a simple geometry of the
wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B
observations. We find that the wave structure is asymmetric with an
inclination toward East. The associated CME has a deprojected speed
of ∼ 750±50 km s<SUP>-1</SUP>, and it shows a non-radial outward
motion toward the East with respect to the underlying source region
location. Applying the forward fitting model developed by Thernisien,
Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the
CME flux rope position on the solar surface to be close to the dimming
regions. We conclude that the expanding flanks of the CME most likely
drive and shape the coronal wave.
---------------------------------------------------------
Title: The relation between coronal holes and coronal mass ejections
during the rise, maximum, and declining phases of Solar Cycle 23
Authors: Mohamed, A. A.; Gopalswamy, N.; Yashiro, S.; Akiyama, S.;
Mäkelä, P.; Xie, H.; Jung, H.
2012JGRA..117.1103M Altcode: 2012JGRA..11701103M
We study the interaction between coronal holes (CHs) and coronal mass
ejections (CMEs) using a resultant force exerted by all the coronal
holes present on the disk and is defined as the coronal hole influence
parameter (CHIP). The CHIP magnitude for each CH depends on the CH area,
the distance between the CH centroid and the eruption region, and the
average magnetic field within the CH at the photospheric level. The
CHIP direction for each CH points from the CH centroid to the eruption
region. We focus on Solar Cycle 23 CMEs originating from the disk
center of the Sun (central meridian distance ≤15°) and resulting
in magnetic clouds (MCs) and non-MCs in the solar wind. The CHIP is
found to be the smallest during the rise phase for MCs and non-MCs. The
maximum phase has the largest CHIP value (2.9 G) for non-MCs. The CHIP
is the largest (5.8 G) for driverless (DL) shocks, which are shocks at
1 AU with no discernible MC or non-MC. These results suggest that the
behavior of non-MCs is similar to that of the DL shocks and different
from that of MCs. In other words, the CHs may deflect the CMEs away
from the Sun-Earth line and force them to behave like limb CMEs with
DL shocks. This finding supports the idea that all CMEs may be flux
ropes if viewed from an appropriate vantage point.
---------------------------------------------------------
Title: CME Parameter Input to ENLIL: LASCO halo cone versus STEREO
measurements
Authors: St Cyr, O. C.; Orlove, M.; Xie, H.; Gilbert, H. R.; Odstrcil,
D.; Gopalswamy, N.; Mays, M. L.; Quirk, C. A.; Henning, C.
2011AGUFMSH33B2046S Altcode:
ENLIL is a well-known model in the solar-helio community (Odstrcil
and Pizzo, 1999) and is frequently used to predict the arrival of
coronal mass ejections (CMEs) at Earth based on observations from
the SOHO LASCO coronagraphs. The halo CME parameters needed to drive
ENLIL are the CME size, speed, and direction, and these are typically
derived from fitting a "cone model" to the LASCO CME images to drive
interplanetary disturbances through the inner heliosphere (Xie et al.,
2004). But as seen from a single vantage point along the Sun-Earth
line, it is difficult to determine these projected CME parameters
unambiguously (e.g., Gopalswamy et al., 2009). Over the past few years
we have been in the fortunate circumstance of having the twin STEREO
spacecraft (Kaiser et al., 2008) at quadrature with the Sun-Earth line,
so we can compare directly the validity of the cone model with actual
measurements of the CMEs heading toward Earth. We report here on a
comparison of more than twenty SOHO LASCO halo coronal mass ejections
that were also observed by STEREO between 2008 and mid-2011.
---------------------------------------------------------
Title: What Controls the Magnetic Field Configuration of
Interplanetary Coronal Mass Ejections ?
Authors: Moon, Y.; Gopalswamy, N.; Kim, R.; Xie, H.; Yashiro, S.
2011AGUFMSH51A1994M Altcode:
In this work we address the question of the classification of
interplanetary coronal mass ejections (ICMEs): magnetic cloud (MC)
or ejecta (EJ). Using 186 shock-associated ICMEs from 1997 to 2006,
we have examined three possible causes : (1) magnetic complexity
characterized by sunspot number, (2) CME direction characterized by
CME angular distance (the angle between the CME cone axis and the sky
plane), and (3) CME-CME interaction characterized by the number of
halo CMEs. First, the annual fraction of MC is poorly anti-correlated
(R=-0.36) with annual sunspot number. Second, more than half of
the CMEs that originated near the central meridian produced EJs
and the distribution of CME angular distance for 38 EJs is not much
different from that for 16 MCs. Third, the annual fraction of MC is
well anti-correlated (R=-0.78) with the annual number of halo CMEs. In
addition, we also searched for candidate of interacting CMEs according
to temporal and spatial closeness by considering all halo CMEs during
the same period. As a result, we find that the annual fraction of
interacting CMEs is well correlated (R=0.87) with the annual number
of the halo CMEs as well as anti-correlated (R=-0.85) with the annual
fraction of MCs. The contingency table between CME-CME interaction
and MC occurrence also shows a good statistical result (Prediction of
detection 'yes' is 0.88, and Critical Success Index is 0.62), which
is better than that for the halo CME-storm relationship. Our results
imply that the CME interaction is mainly responsible for their observed
structure (MC or EJ) in the interplanetary medium.
---------------------------------------------------------
Title: CME Productivity of Active Regions 11158 and 11166
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.; Makela, P. A.
2011AGUFMSH13B1965Y Altcode:
Active regions (ARs) 11158 and 11166 respectively produced an X-class
flare on 2011 Feb 15 and March 9. The former flare was associated with
a CME, but the latter one was not. We examined the CME productivity
of the two active regions. AR 11158 emerged at around 3 UT on 2011 Feb
10. The first major flare from the active region was the M6.6 flare at
17:28 on Feb 13 which was associated with a CME. The CME productivity
was very high on Feb 14 and 15. Out of 11 flares (>C3 level),
10 had an associated CMEs. The CME productivity suddenly dropped on
Feb 18. There were 2 M- and 4 C-class flares but none of them had
an associated CME. AR 11166 emerged on Feb 25 on the far side of the
Sun and appeared on the east limb on March 2. One X-, four M-, and 16
upper C-class (C3-C9) flares occurred during the disk passage. The CME
productivity of the AR was not low since 11 out of 20 M- and C-class
flares had an associated CME. The X1.5 flare lacking an associated CME
is very special in terms of the CME productivity of the AR 11166. We
discuss the reason why the X flare lacked a CME.
---------------------------------------------------------
Title: Type II Radio Bursts as an Indicator of CME Location
Authors: Quirk, C. A.; St Cyr, O. C.; Henning, C.; Xie, H.; Gilbert,
H. R.; Orlove, M.; Gopalswamy, N.; Odstrcil, D.
2011AGUFMSH33B2047Q Altcode:
We examined a subset of nine low-frequency radio events with type
II radio bursts that drifted below 2 megahertz and were detected by
the WAVES investigation on the WIND spacecraft. For each event,
we identified the associated coronal mass ejection (CME) and
derived the electron density using a model of solar wind plasma
frequency (f<SUB>p</SUB> ≈ 9 * n<SUB>e</SUB><SUP>1/2</SUP>, where
f<SUB>p</SUB> is plasma frequency in kHz and n<SUB>e</SUB> is electron
density in cm<SUP>-3</SUP>) . We also used the pb_inverter program
in SolarSoft developed by Howard and Hayes to examine the electron
density structure. Expanding on the Van De Hulst process of inverting
polarized brightness measurements, the program inverts total brightness
measurements from SOHO LASCO images to extract electron density
information. From the electron density inferred from radio spectra,
we derived the location of the CME using five standard electron density
to height models (Leblanc, 1996; Saito, 1977; Bougeret, 1984; Alvarez,
1973; and Fainberg, 1971). Using images from the LASCO instrument on
SOHO and the SECCHI instrument on STEREO, we extracted locations of
the leading edge of the CME and compared the heights and velocities to
those found using the frequency data. For the lowest frequency events,
we also compared our results to the outputs of ENLIL, a time-dependent,
three-dimensional, MHD model of the heliosphere hosted by the Community
Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center.
---------------------------------------------------------
Title: Location of Coronal and IP Type II Burst Source Regions from
Radio and White-light Observations
Authors: Makela, P. A.; Gopalswamy, N.; Yashiro, S.
2011AGUFMSH23A1947M Altcode:
We present our preliminary results on the locations of source regions
of the type II radio bursts in the metric (m) and dekameter-hectometric
(DH) wavelength range. Type II bursts are occasionally observed to
consist of two temporally overlapping lanes of metric and DH bursts. It
has been suggested that the DH-component could be associated with
a CME-driven shock and the m-component with a blast wave or unknown
source, or that the DH-component originates from the shock nose and
the m-component from the shock flanks. In our study we used time-height
measurements of the associated coronal mass ejections (CMEs) to estimate
speeds at various position angles (PAs) along the CME front. We also
estimated plasma densities at the same PAs in the corona from inversion
of polarized brightness (pB) images of SOHO/LASCO coronagraphs. These
measurements suggest that both the m and DH-components can be explained
reasonably well with a single CME-driven shock as their source.
---------------------------------------------------------
Title: Earth-Affecting Solar Causes Observatory (EASCO): A
Heliophysics Mission at the Sun-Earth L5
Authors: Gopalswamy, N.; Easco Team
2011AGUFMSH22A..04G Altcode:
The wealth of knowledge accumulated on coronal mass ejections
over the past decade primarily comes from the SOHO and
STEREO missions. Unfortunately, these missions lacked some key
measurements. For example, STEREO did not have a magnetograph and SOHO
did not have an in-situ magnetometer. From the Sun-Earth line, SOHO
was not well-suited for observing Earth-directed CMEs because of the
occulting disk. STEREO's angle with the Sun-Earth line is changing
constantly, so only a limited number of Earth-directed CMEs were
observed in profile. The next generation Heliophysics mission should
overcome these deficiencies and observe the Sun from a vantage point
different from the Sun-Earth line. The Sun-Earth Lagrange point L5 is
well suited for stationing such a mission. Such a mission would provide
broad-side view of Earth directed CMEs and the shocks if the CMEs
are fast enough. Additionally, corotating interaction regions (CIRs),
which also cause adverse space weather, first arrive at L5 and a few
days later at Earth, thus providing excellent prediction opportunity
based on in-situ measurements at L5. Solar sources (active regions,
coronal holes) of these large-scale disturbances can be observed more
than a week before they rotate to Earth View. A suite of ten instruments
(seven remote-sensing in X-ray, EUV, optical, and radio wavelengths
and 3 in situ for plasma, magnetic field, and energetic particles)
would constitute an ideal scientific payload. Recently an L5 mission
concept known as the Earth-Affecting Solar Causes Observatory (EASCO)
(Gopalswamy et al., 2011) was studied at the Mission Design Laboratory
(MDL) of NASA's Goddard Space Flight Center. The aim of the MDL study
was to see how the scientific payload consisting of ten instruments
can be accommodated in the spacecraft bus, what propulsion system can
transfer the payload to the Sun-Earth L5, and what launch vehicles
are appropriate. The study found that all the ten instruments can be
readily accommodated and can be launched using an intermediate size
vehicle such as Taurus II with enhanced faring. The study also found
that a hybrid propulsion system consisting of an ion thruster (using
~55 kg of Xenon) and hydrazine (~10 kg) is adequate to position the
spacecraft at L5. The transfer to L5 will take about 2 years and the
science mission will last for 4 years around the next solar maximum in
2025. The mission can be readily extended for another solar cycle to get
a solar-cycle worth of data on Earth-affecting CMEs and CIRs. This paper
describes the EASCO mission, the scientific payload, and the results of
the MDL study. Reference: Gopalswamy, N. et al., Earth-Affecting Solar
Causes Observatory (EASCO): A potential International Living with a
Star Mission from Sun-Earth L5, J. Atmospheric and Solar-Terrestrial
Physics, 73, 658, 2011
---------------------------------------------------------
Title: First direct observational evidence of a CME deflection by
coronal hole on 15 February 2011 and a comparison with computations
Authors: Mohamed, A. A.; Gopalswamy, N.
2011AGUFMSH23A1950M Altcode:
It has been shown that coronal holes (CHs) can deflect a coronal
mass ejection (CME) away or towards the Sun-Earth line depending on
their relative location (Gopalswamy et al., 2009). This effect can be
described using a coronal-hole influence parameter (CHIP), which depends
on the CH area, the distance between the CH and the eruption region, and
the magnetic field strength within the CH at the photospheric level. We
have direct observation of CME deflection during the 2011February 15
CME, which was associated with an X2.2 flare (S21W21) on 01:44 UT from
STEREO/COR1 and COR2 observations. The CHIP is computed for the 2011
February 15 CME to be 0.73 G with a deflection angle of 62o. We use
the 193 Å AIA image from the Solar Dynamics Observatory (SDO) for CH
identification and SDO/HMI for determining the magnetic field strength
inside the CH. The largest CH (centroid at S59W15)) was close to the
CME eruption region (S21W21). We measured the deflection angle as 38o,
using STEREO/COR2 images. This deflection angle is not too different
from that obtained from the coronal hole observations.
---------------------------------------------------------
Title: High Angular Resolution Imaging of Solar Radio Bursts from
the Lunar Surface
Authors: MacDowall, R. J.; Lazio, J.; Bale, S.; Burns, J. O.; Farrell,
W. M.; Gopalswamy, N.; Jones, D. L.; Kasper, J. C.; Weiler, K.
2011AGUFM.P13D1738M Altcode:
Locating low frequency radio observatories on the lunar surface has a
number of advantages, including positional stability and a very low
ionospheric radio cutoff. Here, we describe the Radio Observatory
on the Lunar Surface for Solar studies (ROLSS), a concept for a low
frequency, radio imaging interferometric array designed to study
particle acceleration in the corona and inner heliosphere. ROLSS
would be deployed during an early lunar sortie or by a robotic
rover as part of an unmanned landing. The preferred site is on
the lunar near side to simplify the data downlink to Earth. The
prime science mission is to image type II and type III solar radio
bursts with the aim of determining the sites at and mechanisms by
which the radiating particles are accelerated. Secondary science
goals include constraining the density of the lunar ionosphere by
measuring the low radio frequency cutoff of the solar radio emissions
or background galactic radio emission, measuring the flux, particle
mass, and arrival direction of interplanetary and interstellar dust,
and constraining the low energy electron population in astrophysical
sources. Furthermore, ROLSS serves a pathfinder function for larger
lunar radio arrays. Key design requirements on ROLSS include the
operational frequency and angular resolution. The electron densities
in the solar corona and inner heliosphere are such that the relevant
emission occurs below 10 MHz, essentially unobservable from Earth's
surface due to the terrestrial ionospheric cutoff. Resolving the
potential sites of particle acceleration requires an instrument with
an angular resolution of at least 2 deg at 10 MHz, equivalent to a
linear array size of approximately one kilometer. The major components
of the ROLSS array are 3 antenna arms, each of 500 m length, arranged
in a Y formation, with a central electronics package (CEP) at their
intersection. Each antenna arm is a linear strip of polyimide film
(e.g., Kapton) on which 16 single polarization dipole antennas are
located by depositing a conductor (e.g., silver). The arms also contain
transmission lines for carrying the radio signals from the science
antennas to the CEP. Operations would consist of data acquisition during
the lunar day, with data downlinks to Earth one or more times every
24 hours. This work is supported in part by the NASA Lunar Science
Institute via Cooperative Agreement NNA09DB30A with the LUNAR team.
---------------------------------------------------------
Title: From SOHO to STEREO: Understanding Propagation of Coronal
Mass Ejections
Authors: Gopalswamy, N.
2011AGUFMSH32A..08G Altcode:
Direct comparison between coronal mass ejections (CMEs) from near the
Sun and their solar wind counterparts became possible roughly a decade
after the discovery of CMEs (Lindsay et al. 1999). This comparison
revealed that fast CMEs decelerate and slow CMEs accelerate due
to the interaction with the solar wind. Gopalswamy et al. (2000)
quantified this interaction as an interplanetary acceleration
which is useful in predicting the arrival time and speed of CMEs
at 1 AU. The interplanetary acceleration is essentially due to the
aerodynamic drag between the CME and the solar wind because the
propelling force and the solar gravity are effective only near the
Sun. Combined remote-sensing and in situ observations from SOHO and
Wind/ACE have helped us estimate the influence of the solar wind on
the propagation of CMEs. However, these measurements have severe
limitations because the remote-sensed and in-situ observations
correspond to different portions of the CME. Furthermore, the true
speeds of Earth-directed CMEs cannot be measured accurately from a
spacecraft located along the Sun-Earth line. There have been attempts
to model the CME as a cone and get the space speed of the CME, which
did improve the travel time predictions. Instruments on board the
Solar Terrestrial Relations Observatory (STEREO) mission were able
to provide observations of Earth-arriving CMEs without projection
effects, while the same CMEs were observed at Sun-Earth L1 by Wind
and ACE spacecraft. The quadrature between STEREO and L1 spacecraft
presented an ideal situation to study the interplanetary evolution of
CMEs and test earlier model results. The quadrature observations did
improve the CME travel time predictions, but additional factors such
as the unusually slow solar wind, CME cannibalism, and coronal-hole
deflection need to be considered to reconcile the difference between
observed and predicted travel times. This point is illustrated using the
2011 February 15 CME. References Gopalswamy, N. et al., Interplanetary
acceleration of coronal mass ejections, Geophys. Res. Lett., 27, 145,
2000 Lindsay, G. et al., Relationships between coronal mass ejection
speeds from coronagraph images and interplanetary characteristics of
associated interplanetary coronal mass ejections, J. Geophys. Res.,
104, 12515, 1999
---------------------------------------------------------
Title: The Effects of Coronal Holes on the Time Profiles of Gradual
Solar Energetic Particle Events
Authors: Kahler, S. W.; Akiyama, S.; Gopalswamy, N.
2011AGUFMSH44A..06K Altcode:
The onset times and peak intensities of solar energetic particle (SEP)
events at Earth have long been thought to be influenced by the open
magnetic fields of coronal holes (CHs). The basic idea is that when
CHs lie between the solar SEP source region and the interplanetary
magnetic field lines connecting the Earth to the Sun, there will be
a delay in onset and/or a diminution in the peak intensity of the SEP
event. Shen et al.(2006) found that neither CH proximity nor CH relative
location produced any obvious effect on SEP peak intensities. However,
Gopalswamy et al.(2009) have used SOHO/EIT CHs and a defined CH
influence parameter to show that nearby CHs can deflect fast CMEs
from their expected directions in space, explaining the appearance
of driverless shocks at 1 AU from CMEs ejected near solar central
meridian. Recent work has looked at the relation between CHs and CMEs
over the rise, maximum, and declining phases of solar cycle 23. Here we
use the CH locations and influence parameters to examine the effects of
CHs on the timing and intensities of SEP events observed by the GOES and
Wind spacecraft. We also include cases of fast CMEs that drive shocks
but produce no or only weak SEP events at Earth. The goal is to use CH
locations to help predict the SEP events produced by fast and wide CMEs.
---------------------------------------------------------
Title: The Radio Observatory on the Lunar Surface for Solar studies
Authors: Lazio, T. Joseph W.; MacDowall, R. J.; Burns, Jack O.; Jones,
D. L.; Weiler, K. W.; Demaio, L.; Cohen, A.; Paravastu Dalal, N.;
Polisensky, E.; Stewart, K.; Bale, S.; Gopalswamy, N.; Kaiser, M.;
Kasper, J.
2011AdSpR..48.1942L Altcode:
The Radio Observatory on the Lunar Surface for Solar studies (ROLSS) is
a concept for a near-side low radio frequency imaging interferometric
array designed to study particle acceleration at the Sun and in the
inner heliosphere. The prime science mission is to image the radio
emission generated by Type II and III solar radio burst processes
with the aim of determining the sites at and mechanisms by which
the radiating particles are accelerated. Specific questions to be
addressed include the following: (1) Isolating the sites of electron
acceleration responsible for Type II and III solar radio bursts
during coronal mass ejections (CMEs); and (2) Determining if and the
mechanism(s) by which multiple, successive CMEs produce unusually
efficient particle acceleration and intense radio emission. Secondary
science goals include constraining the density of the lunar ionosphere
by searching for a low radio frequency cutoff to solar radio emission
and constraining the low energy electron population in astrophysical
sources. Key design requirements on ROLSS include the operational
frequency and angular resolution. The electron densities in the solar
corona and inner heliosphere are such that the relevant emission occurs
at frequencies below 10 MHz. Second, resolving the potential sites of
particle acceleration requires an instrument with an angular resolution
of at least 2°, equivalent to a linear array size of approximately
1000 m. Operations would consist of data acquisition during the lunar
day, with regular data downlinks. No operations would occur during
lunar night. ROLSS is envisioned as an interferometric array, because
a single aperture would be impractically large. The major components
of the ROLSS array are 3 antenna arms arranged in a Y shape, with
a central electronics package (CEP) located at the center. The Y
configuration for the antenna arms both allows for the formation of
reasonably high dynamic range images on short time scales as well
as relatively easy deployment. Each antenna arm is a linear strip
of polyimide film (e.g., Kapton™) on which 16 science antennas are
located by depositing a conductor (e.g., silver). The antenna arms can
be rolled for transport, with deployment consisting of unrolling the
rolls. Each science antenna is a single polarization dipole. The arms
also contain transmission lines for carrying the radio signals from
the science antennas to the CEP. The CEP itself houses the receivers
for the science antennas, the command and data handling hardware,
and, mounted externally, the downlink antenna. We have conducted
two experiments relevant to the ROLSS concept. First, we deployed a
proof-of-concept science antenna. Comparison of the impedance of the
antenna feed points with simulations showed a high level of agreement,
lending credence to the antenna concept. Second, we exposed a sample
of space-qualified polyimide film, with a silver coating on one side,
to temperature cycling and UV exposure designed to replicate a year on
the lunar surface. No degradation of the polyimide film's material or
electric properties was found. Both of these tests support the notion of
using polyimide-film based antennas. The prime science mission favors an
equatorial site, and a site on the limb could simplify certain aspects
of the instrument design. A site on the lunar near side is sufficient
for meeting the science goals. While the site should be of relatively
low relief topography, the entire site does not have to be flat as
the fraction of the area occupied by the antenna arms is relatively
small (∼0.3%). Further, the antenna arms do not have to lay flat
as deviations of ±1 m are still small relative to the observational
wavelengths. Deployment could be accomplished either with astronauts,
completely robotically, or via a combination of crewed and robotic
means. Future work for the ROLSS concept includes more exhaustive
testing of the radio frequency (RF) and environmental suitability of
polyimide film-based science antennas, ultra-low power electronics in
order to minimize the amount of power storage needed, batteries with
a larger temperature range for both survival and operation, and rovers
(robotic, crewed, or both) for deployment. The ROLSS array could also
serve as the precursor to a larger array on the far side of the Moon
for astrophysical and cosmological studies.
---------------------------------------------------------
Title: Understanding Shock Dynamics in the Inner Heliosphere with
Modeling and Type II Radio Data: the 2010-04-03 event
Authors: Xie, H.; Odstrcil, D.; Mays, M. L.; St Cyr, O. C.; Gopalswamy,
N.; Cremades, H.
2011AGUFMSH33B2050X Altcode:
The 2010 April 03 solar event was studied using observations from
STEREO A and B SECCHI, SOHO LASCO, and kilometric type II data
combined with the WSA-Cone-ENLIL model. In particular, we identified
the origin of the coronal mass ejection (CME) using STEREO EUVI
and SOHO EIT images. A flux-rope model fit to the SECCHI A and B,
and LASCO images were used to determine the CME's direction, size,
and actual speed. J-maps from STEREO COR2/HI-1/HI-2 and simulations
from the ENLIL model were used to study the formation and evolution of
the shock in the inner heliosphere. In addition, we also studied the
time-distance profile of the shock propagation from kilometric type II
(kmTII) radio burst observations. Here we report on a comparison of
two methods of predicting interplanetary shock arrival time: the ENLIL
model and the kmTII method; and investigate whether or not using the
ENLIL model density improves the kmTII rediction. We found that the
ENLIL model predicted the kinematics of shock evolution well. The shock
arrival times (SAT) and linear fit shock velocities in the ENLIL model
agreed well with those measurements in the J-maps along both the CME
leading edge and the Sun-Earth line. The model also reproduced most
of the large scale structures of the shock propagation and gave the
SAT prediction at Earth with an error of 1.5 hours. The kmTII method
predicted the SAT at Earth with an error of 8 hours when using the
ENLIL model plasma density at near Earth; but it improved to 3 hours
when using the model density near the CME leading edge at 1 AU.
---------------------------------------------------------
Title: Magnetic field strength in the upper solar corona using
white-light shock structures surrounding coronal mass ejections
Authors: Kim, R.; Gopalswamy, N.; Moon, Y.; Cho, K.; Yashiro, S.
2011AGUFMSH43B1955K Altcode:
To measure the magnetic field strength in the solar corona, we examined
12 fast (> 1000 km s-1) limb CMEs which show clear shock-like
structures in SOHO/LASCO observations. By applying piston-shock
relationship to the observed CME's standoff distance and electron
density compression ratio, we estimated the Mach number, Alfven speed,
and magnetic field strength in the height range 3 to 15 solar radii
(Rs). We found: (1) the standoff distance observed in the solar corona
is consistent with those from a magnetohydrodynamic (MHD) model and
near-Earth observations; (2) the Mach number as a shock strength is
in the range 1.49 to 3.52 from the standoff distance data, but when
we use the compression ratio, the Mach number is in the range 1.47 to
1.90, implying that the measured density compression ratio is likely
to be underestimated due to observational limit; (3) the Alfven speed
ranges from 259 to 982 km s-1 and the magnetic field strength is in
the range 6 to 120 mG when the standoff distance is used; (4) if we
multiply the density compression ratio by a factor of 2, the Alfven
speeds and the magnetic field strengths are consistent in both methods;
(5) the magnetic field strengths derived from the shock parameters are
similar to those of empirical models and previous estimates. This is a
new attempt to measure magnetic field strength in the upper corona up
to 15 Rs from coronagraph observations alone. Our observations support
the idea that the diffuse structures surrounding the CME front can be
interpreted as shock structures.
---------------------------------------------------------
Title: Determination of the heliospheric radial magnetic field from
the Standoff Distance of a CME-driven shock Observed by the STEREO
spacecraft
Authors: Poomvises, W.; Gopalswamy, N.; Yashiro, S.
2011AGUFMSH23A1948P Altcode:
Recent work by Gopalswamy and Yashiro (2011) determined the radial
coronal magnetic field strength from 6 to 23 solar radii (Rs) by
measuring the standoff distance of a CME-driven shock observed in the
coronagraphic field of view. We now extend their work to determine
radial magnetic field strength in the heliocentric distance range
6 - 100 Rs using data from COR2 and HI 1 instruments onboard the
STEREO spacecraft. We apply the Raytrace model (Thernisien 2006,
2009) to measure the shock standoff distance for the April 5, 2008
CME. In addition, we determine the flux rope curvature by fitting a
circle to the CME. The ratio of the standoff distance to the radius of
curvature is a known function of the shock Mach number and the adiabatic
index. Thus we can obtain the shock Mach number, assuming the value
of the adiabatic index. The Alfven velocity can then be calculated
using the ambient solar wind velocity, shock velocity obtained
from the height-time measurements, and the Mach number. Finally,
the radial magnetic field trength is computed from the Alfven speed
and the density of the ambient medium. We also compare the derived
magnetic field strength with the in-situ measurements made by the
Helios spacecraft, which measured the magnetic field in the distance
range 60 - 215 Rs. We found that the magnetic field strength decreases
from 17 mG at 6 Rs to 1 mG at 100 Rs. In addition, the radial profile
can be described by a power law.
---------------------------------------------------------
Title: United Nations Basic Space Science Initiative: 2010 Status
Report on the International Space Weather Initiative
Authors: Gadimova, S.; Haubold, H. J.; Danov, D.; Georgieva, K.;
Maeda, G.; Yumoto, K.; Davila, J. M.; Gopalswamy, N.
2011SunGe...6....7G Altcode: 2011arXiv1108.2247G
The UNBSSI is a long-term effort for the development of astronomy
and space science through regional and international cooperation in
this field on a worldwide basis. A series of workshops on BSS was
held from 1991 to 2004 (India 1991, Costa Rica and Colombia 1992,
Nigeria 1993, Egypt 1994, Sri Lanka 1995, Germany 1996, Honduras
1997, Jordan 1999, France 2000, Mauritius 2001, Argentina 2002, and
China 2004) Pursuant to resolutions of the United Nations Committee
on the Peaceful Uses of Outer Space (UNCOPUOS) and its Scientific
and Technical Subcommittee, since 2005, these workshops focused on
the International Heliophysical Year 2007 (UAE 2005, India 2006,
Japan 2007, Bulgaria 2008, Ro Korea 2009) Starting in 2010, the
workshops focus on the International Space Weather Initiative (ISWI)
as recommended in a three-year-work plan as part of the deliberations
of UNCOPUOS (www.iswi-secretariat.org/). Workshops on the ISWI have
been scheduled to be hosted by Egypt in 2010 for Western Asia, Nigeria
in 2011 for Africa, and Ecuador in 2012 for Latin America and the
Caribbean. Currently, fourteen IHY/ISWI instrument arrays with more
than five hundred instruments are operational in ninety countries.
---------------------------------------------------------
Title: Relation Between the 3D-Geometry of the Coronal Wave and
Associated CME During the 26 April 2008 Event
Authors: Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.
2011SoPh..273..421T Altcode: 2011SoPh..tmp...75T; 2011arXiv1103.0196T; 2011SoPh..tmp..227T;
2011SoPh..tmp..158T
We study the kinematical characteristics and 3D geometry of a
large-scale coronal wave that occurred in association with the 26
April 2008 flare-CME event. The wave was observed with the EUVI
instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B)
with a mean speed of ∼ 240 km s<SUP>−1</SUP>. The wave is more
pronounced in the eastern propagation direction, and is thus, better
observable in STEREO-B images. From STEREO-B observations we derive
two separate initiation centers for the wave, and their locations fit
with the coronal dimming regions. Assuming a simple geometry of the
wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B
observations. We find that the wave structure is asymmetric with an
inclination toward East. The associated CME has a deprojected speed
of ∼ 750±50 km s<SUP>−1</SUP>, and it shows a non-radial outward
motion toward the East with respect to the underlying source region
location. Applying the forward fitting model developed by Thernisien,
Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the
CME flux rope position on the solar surface to be close to the dimming
regions. We conclude that the expanding flanks of the CME most likely
drive and shape the coronal wave.
---------------------------------------------------------
Title: Earth-Affecting Solar Causes Observatory (EASCO): a mission
at the Sun-Earth L5
Authors: Gopalswamy, Nat; Davila, Joseph M.; Auchère, Frédéric;
Schou, Jesper; Korendyke, Clarence M.; Shih, Albert; Johnston, Janet
C.; MacDowall, Robert J.; Maksimovic, Milan; Sittler, Edward; Szabo,
Adam; Wesenberg, Richard; Vennerstrom, Suzanne; Heber, Bernd
2011SPIE.8148E..0ZG Altcode: 2011SPIE.8148E..30G; 2011arXiv1109.2929G
Coronal mass ejections (CMEs) and corotating interaction regions
(CIRs) as well as their source regions are important because of
their space weather consequences. The current understanding of CMEs
primarily comes from the Solar and Heliospheric Observatory (SOHO)
and the Solar Terrestrial Relations Observatory (STEREO) missions,
but these missions lacked some key measurements: STEREO did not have a
magnetograph; SOHO did not have in-situ magnetometer. SOHO and other
imagers such as the Solar Mass Ejection Imager (SMEI) located on the
Sun-Earth line are also not well-suited to measure Earth-directed
CMEs. The Earth-Affecting Solar Causes Observatory (EASCO) is a
proposed mission to be located at the Sun-Earth L5 that overcomes
these deficiencies. The mission concept was recently studied at the
Mission Design Laboratory (MDL), NASA Goddard Space Flight Center,
to see how the mission can be implemented. The study found that the
scientific payload (seven remote-sensing and three in-situ instruments)
can be readily accommodated and can be launched using an intermediate
size vehicle; a hybrid propulsion system consisting of a Xenon ion
thruster and hydrazine has been found to be adequate to place the
payload at L5. Following a 2-year transfer time, a 4-year operation
is considered around the next solar maximum in 2025.
---------------------------------------------------------
Title: Coronal magnetic field measurement using CME-driven shock
observations
Authors: Gopalswamy, N.; Nitta, N.; Yashiro, S.; Mäkelä, P.; Xie,
H.; Akiyama, S.
2011sdmi.confE..22G Altcode:
Collisionless shocks form ahead of coronal mass ejections (CMEs) when
the CME speed exceeds the Alfven speed of the ambient plasma in the
corona and interplanetary medium. The shock stands at a distance from
the CME flux rope that depends on the shock Mach number, the geometry
of the driver, and the adiabatic index. While the shock ahead of the
CME has been observed for a long time in the in situ data, it has
been identified recently near the Sun in the coronagraphic and EUV
images. Unlike in situ observations, the imaging observations are two
dimensional, so one can better discern the CME-shock relationship
near the Sun. Gopalswamy and Yashiro (2011) demonstrated that the
coronal magnetic field can be derived from the shock standoff distance
measured in coronagraphic images. The method involves measuring the
standoff distance, the radius of curvature of the flux rope, and
assuming the value of the adiabatic index and deriving the Alfvénic
Mach number. The next step is to derive the Alfvénic Mach number
from the measured shock speed and an estimate of the local solar
wind speed. The final step involves deriving the magnetic field from
the Alfven speed by measuring the local plasma density either from
coronagraphic (polarized brightness) images (Gopalswamy and Yashiro
2011) or from the band-splitting of type II radio bursts (Gopalswamy
et al., 2011). In this paper, we derive the combined magnetic field
profile from near the Sun to the edge of the LASCO field of view
(1.5 to 30 solar radii) and compare it with the current model profiles.
---------------------------------------------------------
Title: Energetic storm particle events in coronal mass ejection-driven
shocks
Authors: Mäkelä, P.; Gopalswamy, N.; Akiyama, S.; Xie, H.;
Yashiro, S.
2011JGRA..116.8101M Altcode:
We investigate the variability in the occurrence of energetic storm
particle (ESP) events associated with shocks driven by coronal mass
ejections (CMEs). The interplanetary shocks were detected during
the period from 1996 to 2006. First, we analyze the CME properties
near the Sun. The CMEs with an ESP-producing shock are faster
($\langle$V<SUB>CME</SUB>$\rangle$ = 1088 km/s) than those driving
shocks without an ESP event ($\langle$V<SUB>CME</SUB>$\rangle$ = 771
km/s) and have a larger fraction of halo CMEs (67% versus 38%). The
Alfvénic Mach numbers of shocks with an ESP event are on average 1.6
times higher than those of shocks without. We also contrast the ESP
event properties and frequency in shocks with and without a type II
radio burst by dividing the shocks into radio-loud (RL) and radio-quiet
(RQ) shocks, respectively. The shocks seem to be organized into a
decreasing sequence by the energy content of the CMEs: RL shocks with an
ESP event are driven by the most energetic CMEs, followed by RL shocks
without an ESP event, then RQ shocks with and without an ESP event. The
ESP events occur more often in RL shocks than in RQ shocks: 52% of RL
shocks and only ∼33% of RQ shocks produced an ESP event at proton
energies above 1.8 MeV; in the keV energy range the ESP frequencies
are 80% and 65%, respectively. Electron ESP events were detected in
19% of RQ shocks and 39% of RL shocks. In addition, we find that (1)
ESP events in RQ shocks are less intense than those in RL shocks; (2)
RQ shocks with ESP events are predominately quasi-perpendicular shocks;
(3) their solar sources are located slightly to the east of the central
meridian; and (4) ESP event sizes show a modest positive correlation
with the CME and shock speeds. The observation that RL shocks tend
to produce more frequently ESP events with larger particle flux
increases than RQ shocks emphasizes the importance of type II bursts
in identifying solar events prone to producing high particle fluxes
in the near-Earth space. However, the trend is not definitive. If
there is no type II emission, an ESP event is less likely but not
absent. The variability in the probability and size of ESP events
most likely reflects differences in the shock formation in the low
corona and changes in the properties of the shocks as they propagate
through interplanetary space and the escape efficiency of accelerated
particles from the shock front.
---------------------------------------------------------
Title: The Strength and Radial Profile of the Coronal Magnetic Field
from the Standoff Distance of a Coronal Mass Ejection-driven Shock
Authors: Gopalswamy, Nat; Yashiro, Seiji
2011ApJ...736L..17G Altcode: 2011arXiv1106.4832G
We determine the coronal magnetic field strength in the heliocentric
distance range 6-23 solar radii (Rs) by measuring the shock
standoff distance and the radius of curvature of the flux rope
during the 2008 March 25 coronal mass ejection imaged by white-light
coronagraphs. Assuming the adiabatic index, we determine the Alfvén
Mach number, and hence the Alfvén speed in the ambient medium using
the measured shock speed. By measuring the upstream plasma density
using polarization brightness images, we finally get the magnetic field
strength upstream of the shock. The estimated magnetic field decreases
from ~48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the
magnetic field can be described by a power law in agreement with other
estimates at similar heliocentric distances.
---------------------------------------------------------
Title: First direct observational evidence of a CME deflection by
coronal hole on 15 February 2011 and a comparison with computations
Authors: Mohamed, Amaal Abd-Alla; Gopalswamy, Nat
2011shin.confE.127M Altcode:
It has been shown that coronal holes (CHs) can deflect a coronal
mass ejection (CME) away or towards the Sun-Earth line depending on
their relative location (Gopalswamy et al., 2009). This effect can be
described using a coronal-hole influence parameter (CHIP), which depends
on the CH area, the distance between the CH and the eruption region, and
the magnetic field strength within the CH at the photospheric level. We
have direct observation of CME deflection during the 2011February 15
CME, which was associated with an X2.2 flare (S21W21) on 01:44 UT from
STEREO/COR1 and COR2 observations. The CHIP is computed for the 2011
February 15 CME to be 0.73 G with a deflection angle of 62o. We use
the 193 Å AIA image from the Solar Dynamics Observatory (SDO) for CH
identification and SDO/HMI for determining the magnetic field strength
inside the CH. The largest CH (centroid at S59W15)) was close to the
CME eruption region (S21W21). We measured the deflection angle as 38o,
using STEREO/COR2 images. This deflection angle is not too different
from that obtained from the coronal hole observations.
---------------------------------------------------------
Title: Halo CMEs: Comparing Observations and Models
Authors: Gilbert, Holly; St. Cyr, Matthew Orlove. C.; Xie, Hong;
Mays, Leila; Gopalswamy, N.; Quirk, Cori; Henning, Christina
2011shin.confE..49G Altcode:
Since 1996, the SOHO LASCO coronagraphs have detected 'halo' CMEs
that appear to be directed toward Earth, but information about the
size and speed of these events seen face-on has been limited. From a
single vantage point along the Sun-Earth line, the primary limitation
has been ambiguity in fitting the cone model (or other forward-modeling
techniques, e.g., Thernisian et al., 2006). But in the past few years,
the STEREO mission has provided a view of Earth-directed events from
the side. These events offer the opportunity to compare measurements
(width and speed) of halo CMEs observed by STEREO with models that
derive halo CME properties. We report here results of such a comparison
on a large sample of LASCO CMEs in the STEREO era
---------------------------------------------------------
Title: Effects of Refraction on Angles and Times of Arrival of Solar
Radio Bursts
Authors: Thejappa, G.; MacDowall, R. J.; Gopalswamy, N.
2011ApJ...734...16T Altcode:
Solar type III and type II radio bursts suffer severe bending and
group delay due to refraction while escaping from the source where
the refractive index μ can be as low as ~0 to the observer where μ ~
1. These propagation effects can manifest themselves as errors in the
observed directions and times of arrival at the telescope. We describe
a ray-tracing technique that can be used to estimate these errors. By
applying this technique to the spherically symmetric density model
derived using the data from the WIND/Waves experiment, we show that (1)
the fundamental and harmonic emissions escape the solar atmosphere in
narrow cones (at 625 kHz the widths of these escape cones are ~1fdg1
and ~8°, respectively), (2) the errors in the angles as well as the
times of arrival increase monotonically with the angle of arrival
(at 625 kHz these errors are 0fdg26 and ~17.2 s for the fundamental
and ~0fdg52 and ~7.6 s for the harmonic at the maximum possible angles
of arrival of ~0fdg55 and ~4°, respectively), and (3) the lower the
frequencies are, the higher the errors in both the angles and times of
arrival are. This implies that at 625 kHz the measured arrival angles
and arrival times of the fundamental and harmonic are off by ~50%
and ~13%, and ~3.4% and ~1.5%, respectively.
---------------------------------------------------------
Title: Relationship between the Expansion Speed and Radial Speed of
CMEs Confirmed Using Quadrature Observations from Soho and Stereo
Authors: Gopalswamy, N.; Makela, P.; Yashiro, S.
2011simi.conf....2G Altcode:
The STEREO spacecraft were in qudrature with SOHO (STEREO-A ahead of
Earth by 87o and STEREO-B 94o behind Earth) on 2011 February 15, when
a fast Earth-directed CME occurred. The CME was observed as a halo by
the Large-Angle and Spectrometric Coronagraph (LASCO) on board SOHO. The
sky-plane speed was measured by SOHO/LASCO as the expansion speed, while
the radial speed was measured by STEREO-A and STEREO-B. In addition,
STEREO-A and STEREO-B images measured the width of the CME, which
is unknown from Earth view. From the SOHO and STEREO measurements,
we confirm the relationship between the expansion speed (Vexp) and
radial speed (Vrad) derived previously from geometrical considerations
(Gopalswamy et al. 2009): Vrad = Ѕ (1 + cot w) Vexp, where w is the
half width of the CME. STEREO-B images of the CME, we found that CME
had a full width of 75 degrees, so w = 37.5 degrees. This gives the
relation as Vrad = 1.15 Vexp. From LASCO observations, we measured
Vexp = 897 km/s, so we get the radial speed as 1033 km/s. Direct
measurement of radial speed from STEREO gives 945 km/s (STEREO-A) and
1057 km/s (STEREO-B). These numbers are different only by 2.3% and 8.5%
(for STEREO-A and STEREO-B, respectively) from the computed value.
---------------------------------------------------------
Title: A Radio Observatory on the Lunar Surface for Solar studies
(ROLSS)
Authors: MacDowall, R. J.; Lazio, T. J.; Bale, S. D.; Burns, J.;
Farrell, W. M.; Gopalswamy, N.; Jones, D. L.; Weiler, K. W.
2011arXiv1105.0666M Altcode:
By volume, more than 99% of the solar system has not been imaged at
radio frequencies. Almost all of this space (the solar wind) can be
traversed by fast electrons producing radio emissions at frequencies
lower than the terrestrial ionospheric cutoff, which prevents
observation from the ground. To date, radio astronomy-capable space
missions consist of one or a few satellites, typically far from each
other, which measure total power from the radio sources, but cannot
produce images with useful angular resolution. To produce such images,
we require arrays of antennas distributed over many wavelengths
(hundreds of meters to kilometers) to permit aperture synthesis
imaging. Such arrays could be free-flying arrays of microsatellites
or antennas laid out on the lunar surface. In this white paper, we
present the lunar option. If such an array were in place by 2020,
it would provide context for observations during Solar Probe Plus
perihelion passes. Studies of the lunar ionosphere's density and time
variability are also important goals. This white paper applies to the
Solar and Heliospheric Physics study panel.
---------------------------------------------------------
Title: What Controls the Classification of Interplanetary Mass
Ejections
Authors: Moon, Yong-Jae; Gopalswamy, N.; Kim, R.; Xie, H.; Yashiro, S.
2011SPD....42.2401M Altcode: 2011BAAS..43S.2401M
In this paper we address a question what controls the classification
of interplanetary mass ejections (ICMEs): magnetic cloud (MC) or
ejecta (EJ). Using 186 shock-associated ICMEs from 1997 to 2006, we
have examined three possible causes : (1) magnetic complexity with a
proxy of sunspot number, (2) CME direction as a proxy of cone angle
(the angle between the CME cone axis and the plane of sky), and (3)
ICME-ICME interaction with a proxy of the number of halo CMEs. First,
the fraction of MC is poorly anti-correlated (R=-0.36) with annual
sunspot number. Second, the distribution of CME cone angle for 38
EJs is not much different from that for 16 MCs. Third, the annual
fraction of magnetic cloud is well anti-correlated (R=-0.78) with
the annual number of halo CMEs. To demonstrate such a relationship,
we consider all halo CMEs during the same period and statistically
searched the candidate of interacting ICMEs according to temporal
and spatial closeness. As a result, we find that the annual fraction
of interacting ICME candidates is well correlated (R=0.87) with the
annual number of the halo CMEs as well as anti-correlated (R=-0.85)
with the annual fraction of MCs. The contingency table between ICME-ICME
interaction and MC occurrence also shows a good statistical result:
Hit (110), False Alarm (53), Prediction of detection 'yes' (0.88), and
Critical Success Index (0.62). Our results imply that the interaction
of ICMEs is mainly responsible for their classification.
---------------------------------------------------------
Title: Magnetic Field Strength in the Upper Solar Corona Using
White-light Shock Structures Surrounding Coronal Mass Ejections
Authors: Kim, Roksoon; Gopalswamy, N.; Moon, Y.; Cho, K.; Yashiro, S.
2011SPD....42.2306K Altcode: 2011BAAS..43S.2306K
To measure the magnetic field strength in the solar corona, we examined
12 fast (> 1000 km s-1) limb CMEs which show clear shock-like
structures in SOHO/LASCO observations. By applying piston-shock
relationship to the observed CME's standoff distance and electron
density compression ratio, we estimated the Mach number, Alfven speed,
and magnetic field strength in the height range 3 to 15Rs. Main
results from this study are: (1) the standoff distance observed in
the solar corona is consistent with those from a magnetohydrodynamic
(MHD) model and near-Earth observations; (2) the Mach number as a shock
strength is in the range 1.49 to 3.52 from the standoff distance data,
but when we use the compression ratio, the Mach number is in the
range 1.47 to 1.90, implying that the measured density compression
ratio is likely to be underestimated due to projection effects; (3)
the Alfven speeds range from 259 to 982 km s-1 and the magnetic field
strength is in the range 0.04 to 0.35 G when the standoff distance
is used; (4) if we multiply the compression ratio by a factor of 2,
the Alfven speeds and the magnetic field strengths are consistent in
both methods; (5) the derived magnetic field strengths in the inner
corona are similar to those of empirical models but noticeably higher
in the upper corona. This is a new attempt to measure magnetic field
strength from coronagraph observation alone. These observations are
consistent with the idea that the diffuse structures surrounding the
CME front can be interpreted as shock structures.
---------------------------------------------------------
Title: Understanding Interplanetary Shock Dynamics In The Inner
Heliosphere:The 2010 April 03 and August 01 Events
Authors: Xie, Hong; May, L.; St Cyr, C. O.; Gopalswamy, N.; Odstrcil,
D.; Cremades, H.
2011SPD....42.2312X Altcode: 2011BAAS..43S.2312X
The 2010 April 03 and 2010 August 01 CMEs were studied using
observations from STEREO A and B, and SOHO LASCO, combined with
ENLIL+Cone model simulations preformed at the Community Coordinated
Modelling Center (CCMC). In particular, we identified the origin of CMEs
using STEREO EUVI and/or SDO images. A flux-rope model fitting to the
SECCHI A and B, SOHO/LASCO images was used to determine CME directions
and actual speeds. J-maps from COR2/HI-1/HI-2 and simulations from CCMC
were used to study the formation and evolution of the shocks in the
inner heliosphere. We compared the simulation results with the observed
height-time profiles of the shock from white light and kilometric
type II (KmTII) burst (Wind/WAVES) observations. The predicted shock
arrival at Earth is compared with in-situ observations from ACE. It
is found that that ENLIL+cone model predicts the kinematics of shock
evolution well for both cases and the KmTII method is more successful
when using ENLIL model plasma density.
---------------------------------------------------------
Title: The 2011 February 15 Coronal Mass Ejection: Reconciling SOHO
and STEREO Observations in Quadrature
Authors: Gopalswamy, N.; Yashiro, S.; Makela, P.; Kaiser, M. L.
2011SPD....42.2322G Altcode: 2011BAAS..43S.2322G
The Large-Angle and Spectrometric Coronagraph (LASCO) on board SOHO
observed a fast halo coronal mass ejection on 2011 February 15. The
STEREO spacecraft were in qudrature with SOHO (STEREO-A ahead of Earth
by 87 deg and STEREO-B 94 deg behind Earth), enabling CME measurement
using the three spacecraft. The sky-plane speed measured by SOHO/LASCO
is closely related to the expansion speed of the CME, while the
radial speed was measured by STEREO-A and STEREO-B. In addition,
STEREO-A and STEREO-B images measured the width of the CME, which
is unknown from Earth view. From the SOHO and STEREO measurements,
we confirm the relationship between the expansion speed (Vexp) and
radial speed (Vrad) derived previously from geometrical considerations
(Gopalswamy et al. 2009): = Vrad = ½ (1 + cot w) Vexp, where w is the
half width of the CME. We can also measure the Earthward speed of the
CME directly from the STEREO measurements. The travel time to Earth
predicted from the Earthward speed using the Empirical Shock Arrival
model is 12 hours shorter than the actual travel time obtained from in
situ measurements at L1. The primary reason for this discrepancy seems
to be the interaction with the two preceding CMEs that slowed down
the CME in question. The CME interaction is also confirmed from the
radio enhancement observed by Wind/WAVES and STEREO WAVES experiments.
---------------------------------------------------------
Title: Earth-Affecting Solar Causes Observatory (EASCO): Results of
the Mission Concept Study
Authors: Gopalswamy, N.; EASCO Team
2011SPD....42.1518G Altcode: 2011BAAS..43S.1518G
Coronal mass ejections (CMEs) corotating interaction regions (CIRs)
are two large-scale structures that originate from the Sun and affect
the heliosphere in general and Earth in particular. While CIRs are
generally detected by in-situ plasma signatures, CMEs are remote-sensed
when they are still close to the Sun. The current understanding of
CMEs primarily come from the SOHO and STEREO missions. In spite of
the enormous progress made, there are some serious deficiencies in
these missions. For example, these missions did not carry all the
necessary instruments (STEREO did not have a magnetograph; SOHO did
not have in-situ magnetometer). From the Sun-Earth line, SOHO was not
well-suited for observing Earth-directed CMEs because of the occulting
disk. STEREO's angle with the Sun-Earth line is changing constantly,
so only a limited number of Earth-directed CMEs were observed in
profile. In order to overcome these difficulties, we proposed a news L5
mission concept known as the Earth-Affecting Solar Causes Observatory
(EASCO). The mission concept was recently studied at the Mission
Design Laboratory (MDL), NASA Goddard Space Flight Center. The aim of
the MDL study was to see how the scientific payload consisting of ten
instruments can be accommodated in the spacecraft bus, what propulsion
system can transfer the payload to the Sun-Earth L5, and what launch
vehicles are appropriate. The study found that all the ten instruments
can be readily accommodated and can be launched using an intermediate
size vehicle such as Taurus II with enhanced faring. The study also
found that a hybrid propulsion system consisting of an ion thruster
(using 55 kg of Xenon) and hydrazine ( 10 kg) is adequate to place the
payload at L5. The transfer will take about 2 years and the science
mission will last for 4 years around the next solar maximum in 2025.
---------------------------------------------------------
Title: Comparison between Linear and Quadratic Drag Models for
ICME Propagation
Authors: Moon, Yong-Jae; Vrsnak, B.; Gopalswamy, N.; Yashiro, S.
2011SPD....42.2318M Altcode: 2011BAAS..43S.2318M
In this paper, we have examined a recent issue what kinds of drag
form (linear or quadratic drag) is proper for interplanetary coronal
mass ejections (ICMEs). For this work, we have examined well-observed
LASCO CMEs associated with DH Type II bursts satisfying the following
conditions: (1) the CMEs speeds are larger than 600 km/s, (2) their
longitudes are larger than 60 degrees, (3) the numbers of their LASCO
data points are larger than 6, and (4) their accelerations are smaller
than -1 m/s<SUP>2</SUP>. We find that their accelerations (Log a) in
the LASCO field of view has a very good quadratic relationship with
the CME relative speeds Log (Vcme-400) with the correlation coefficient
of R=0.83, supporting the quadratic drag force. Another test has been
made by applying two drag models to two well-observed STEREO/SECCHI
events. As a result, we found that (1) while two speed profiles are
well fitted by the quadratic drag model, one speed profile can not be
fitted by the linear model; (2) while the physical parameters for the
quadratic model are well consistent with observations, the kinematic
viscosity for the linear model should be four orders larger than its
observed value. From this study, we conclude that the quadratic drag
model for ICME propagation should be proper than the linear drag model.
---------------------------------------------------------
Title: Halo Coronal Mass Ejections: Comparing Observations to Models
Authors: Gilbert, Holly; Orlove, M.; St. Cyr, O.; Xie, H.; Mays,
L. M.; Gopalswamy, N.
2011SPD....42.2310G Altcode: 2011BAAS..43S.2310G
Since 1996, the SOHO LASCO coronagraphs have detected "halo” CMEs
that appear to be directed toward Earth, but information about the
size and speed of these events seen face-on has been limited. From a
single vantage point along the Sun-Earth line, the primary limitation
has been ambiguity in fitting the cone model (or other forward-modeling
techniques, e.g., Thernisian et al., 2006). But in the past few years,
the STEREO mission has provided a view of Earth-directed events from
the side. These events offer the opportunity to compare measurements
(width and speed) of halo CMEs observed by STEREO with models that
derive halo CME properties. We report here results of such a comparison
on a large sample of LASCO CMEs in the STEREO era.
---------------------------------------------------------
Title: Association of EUV Waves and Coronal Mass Ejections
Authors: Yashiro, Seiji; Gopalswamy, N.
2011SPD....42.2317Y Altcode: 2011BAAS..43S.2317Y
The association between EUV waves and coronal mass ejections (CMEs)
is difficult to establish for disk flares using observations from the
Sun-Earth line because of visibility issues. The other possibility is
the real absence of mass motion in flares. This issue can be effectively
addressed by the twin spacecraft of the Solar Terrestrial Relations
Observatory (STEREO) mission. The Ahead and Behind spacecraft of the
STEREO mission were located around ±90° from the Sun-Earth line
from 2010 to 2012. This is the first opportunity to investigate
the connection between CMEs and EUV waves with a high degree of
accuracy. During January 28 - March 9, 2011, two X- and 28 M-class
flares occurred. We examined their CME associations using STEREO/SECCHI
and SOHO/LASCO observations, and EUV wave associations using SDO/AIA
data. We found that 10 out of 30 flares were associated with clear
flux-rope CMEs (FRCMEs) while 16 did not have any erupting features
above the flaring regions in the coronagraph images. The remaining
four flares had narrow CMEs or outflow above the flaring regions but
their connection to the flares is unclear. We also found all of the
FRCME-associated flares had clear EUV waves, while the flares without
CMEs also lacked EUV waves. We found one-to-one correspondence between
EUV waves and FRCMEs.
---------------------------------------------------------
Title: Source of Coronal and IP Type II Bursts Inferred from Radio
and White-light Observations
Authors: Makela, Pertti; Gopalswamy, N.; Yashiro, S.
2011SPD....42.2316M Altcode: 2011BAAS..43S.2316M
We report on a study of the speeds of type II radio bursts in the metric
(m) and dekameter-hectometric (DH) wavelength range constrained by
the time-height measurements of the associated coronal mass ejections
(CMEs). Dynamic spectra of type II bursts show occasionally a clear
discontinuity in frequency and temporal overlap of metric and DH
type II bursts. This has been interpreted to signify either (1) a
different origin of the type II components, i.e., the DH-component is
caused by a CME-driven shock and the m-component by a blast wave or
unknown source, or (2) same source but a different location, i.e.,
the DH-component originates from the shock nose and the m-component
from the shock flanks. Our preliminary results suggest that the single
CME-driven shock scenario can match both m and DH-component of type
II bursts reasonably well, assuming that true space speeds of the CMEs
and shocks are utilized.
---------------------------------------------------------
Title: Cme Evolution In The Interplanetary Space Based On Stereo
Observations.
Authors: Poomvises, Watanachak; Gopalswamy, N.; Zhang, J.
2011SPD....42.2311P Altcode: 2011BAAS..43S.2311P
STEREO/SECCHI observations help identify the true 3-D geometric
structure of CMEs and track their true evolution in the inner
heliosphere. Using STEREO observations, it is possible to obtain the
true speed of CMEs, which is key in predicting the arrival time of CMEs
at Earth (Gopalswamy et al. 2001). From the STEREO data, we are able to
track and measure CMEs in 3-D by using Raytrace model (Thernisien et
al 2006, 2009), which is free from projection effects and thus result
in true CME velocities. Studied study 5 CME events, we found that the
acceleration/deceleration of CMEs occur within 50 Rs from the Sun,
after that the CME velocity converges to the narrow range (Poomvises
et al 2010). Additionally, we found that expansion velocity of CMEs
also converges to a narrow range after 50 Rs. <P />The observations are
consistent with the theoretical flux rope model. The CME evolution can
be explained by different forces that act on the CME: Lorentz force,
thermal pressure force, gravity force, aero-dynamic drag force, and the
magnetic drag force. The drag coefficient typically varies between 2.5
to 3.0, which is much smaller than the factor of twelve suggested by
earlier studies. Moreover, the value of the polytropic index has been
found to be between 1.35 to 1.60. Therefore, we have been able to narrow
down the range of values for the drag coefficient and the polytropic
index, which help in improve the prediction of CME travel time.
---------------------------------------------------------
Title: Earth-Affecting Solar Causes Observatory (EASCO): A potential
International Living with a Star Mission from Sun-Earth L5
Authors: Gopalswamy, N.; Davila, J. M.; St. Cyr, O. C.; Sittler,
E. C.; Auchère, F.; Duvall, T. L.; Hoeksema, J. T.; Maksimovic, M.;
MacDowall, R. J.; Szabo, A.; Collier, M. R.
2011JASTP..73..658G Altcode:
This paper describes the scientific rationale for an L5 mission
and a partial list of key scientific instruments the mission should
carry. The L5 vantage point provides an unprecedented view of the
solar disturbances and their solar sources that can greatly advance
the science behind space weather. A coronagraph and a heliospheric
imager at L5 will be able to view CMEs broadsided, so space speed
of the Earth-directed CMEs can be measured accurately and their
radial structure discerned. In addition, an inner coronal imager
and a magnetograph from L5 can give advance information on active
regions and coronal holes that will soon rotate on to the solar
disk. Radio remote sensing at low frequencies can provide information
on shock-driving CMEs, the most dangerous of all CMEs. Coordinated
helioseismic measurements from the Sun-Earth line and L5 provide
information on the physical conditions at the base of the convection
zone, where solar magnetism originates. Finally, in situ measurements
at L5 can provide information on the large-scale solar wind structures
(corotating interaction regions (CIRs)) heading towards Earth that
potentially result in adverse space weather.
---------------------------------------------------------
Title: Coronal mass ejections and their heliospheric consequences
Authors: Gopalswamy, N.
2011ASInC...2..241G Altcode:
This paper is concerned with the properties of coronal mass ejections
(CMEs) that affect the heliosphere. The special populations of CMEs
that drive shocks, accelerate solar energetic particles, and produce
geomagnetic storms are discussed in comparison with the general
population (all CMEs of cycle 23). It is shown that the average CME
speeds of the special populations are larger than that of the general
population by a factor in the range 2--3. The angular width of these
CMEs is also generally large because most of the CMEs were halos. The
October -- November 2003 period produced a large number of energetic
CMEs, two of which were of historical proportions. These extreme events
are discussed in order to understand what one might expect from the
Sun as the largest event, given the maximum area and magnetic field
strength of the source active regions.
---------------------------------------------------------
Title: Universal Heliophysical Processes
Authors: Gopalswamy, Nat
2011sswh.book....9G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Mass Ejections and Solar Radio Emissions
Authors: Gopalswamy, N.
2011pre7.conf..325G Altcode:
Three types of low-frequency nonthermal radio bursts are associated
with coronal mass ejections (CMEs): Type III bursts due to accelerated
electrons propagating along open magnetic field lines, type II bursts
due to electrons accelerated in shocks, and type IV bursts due to
electrons trapped in post-eruption arcades behind CMEs. This paper
presents a summary of results obtained during solar cycle 23 primarily
using the white-light coronagraphic observations from the Solar
Heliospheric Observatory (SOHO) and the WAVES experiment on board Wind.
---------------------------------------------------------
Title: Observing Solar Radio Bursts from the Lunar Surface
Authors: MacDowall, R. J.; Lazio, T. J.; Bale, S. D.; Burns, J.;
Gopalswamy, N.; Jones, D. L.; Kaiser, M. L.; Kasper, J. C.; Weiler,
K. W.
2011pre7.conf..541M Altcode:
Locating low frequency radio observatories on the lunar surface has a
number of advantages, including fixed locations for the antennas and no
terrestrial inteference on the far side of the moon. Here, we describe
the Radio Observatory on the Lunar Surface for Solar studies (ROLSS),
a concept for a near-side, low frequency, interferometric radio imaging
array designed to study particle acceleration in the corona and inner
heliosphere. ROLSS would be deployed during an early lunar sortie or
by a robotic rover as part of an unmanned landing. The prime science
mission is to image intense type II and type III solar radio bursts
with the aim of determining the sites at and mechanisms by which the
radiating particles are accelerated. Secondary science goals include
constraining the density of the lunar ionosphere by searching for a low
radio frequency cutoff of the solar radio emissions and detecting the
low energy electron population in astrophysical sources. Furthermore,
ROLSS serves as a pathfinder for larger, far-side lunar radio arrays,
designed for faint sources.
---------------------------------------------------------
Title: The International Space Weather Initiative (ISWI)
Authors: Davila, Joseph M.; Gopalswamy, Nat; Thompson, Barbara J.;
Bogdan, Tom; Hapgood, Mike
2011sswh.book..375D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Heliocentric Distance of Coronal Mass Ejections at the Time of
Energetic Particle Release: Revisiting the Ground Level experiments
and instrumentation
Authors: Gopalswamy, Nat
2011ICRC...10..159G Altcode: 2011ICRC...32j.159G
No abstract at ADS
---------------------------------------------------------
Title: Low-frequency type III radio bursts and solar energetic
particle events
Authors: Gopalswamy, N.; Mäkelä, P.
2011CEAB...35...71G Altcode:
Complex type III bursts at low-frequencies (<14 MHz) are thought
to indicate large solar energetic particle (SEP) events. We analysed
six complex type III bursts from the same active region, one of which
was not accompanied by a SEP event. This event was accompanied by a
fast and wide coronal mass ejection (CME), but lacked a type II burst
and an interplanetary shock. When we examined the evolution and the
magnetic configuration of the active region, we did not find anything
peculiar. The lowest frequency of type III emission occurred at the
local plasma frequency in the vicinity of the Wind spacecraft that
observed the type III, which confirms that the magnetic connectivity of
the source region was good. We conclude that the lack of SEPs is due to
the lack of production rather than due to poor magnetic connectivity. We
also show that neither the type III burst duration nor the burst
intensity was able to distinguish between SEP and non-SEP events. The
lack of SEP event can be readily explained under the shock-acceleration
paradigm, but not under the flare-acceleration paradigm.
---------------------------------------------------------
Title: Maximum Coronal Mass Ejection Speed as an Indicator of Solar
and Geomagnetic Activities
Authors: Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.;
Gopalswamy, N.; Ozguc, A.; Rozelot, J. P.
2011ApJ...727...44K Altcode: 2011arXiv1111.4000K
We investigate the relationship between the monthly averaged maximal
speeds of coronal mass ejections (CMEs), international sunspot number
(ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008
time interval (solar cycle 23). Our new findings are as follows. (1)
There is a noteworthy relationship between monthly averaged maximum CME
speeds and sunspot numbers, Ap and Dst indices. Various peculiarities
in the monthly Dst index are correlated better with the fine structures
in the CME speed profile than that in the ISSN data. (2) Unlike the
sunspot numbers, the CME speed index does not exhibit a double peak
maximum. Instead, the CME speed profile peaks during the declining
phase of solar cycle 23. Similar to the Ap index, both CME speed and
the Dst indices lag behind the sunspot numbers by several months. (3)
The CME number shows a double peak similar to that seen in the sunspot
numbers. The CME occurrence rate remained very high even near the
minimum of the solar cycle 23, when both the sunspot number and the
CME average maximum speed were reaching their minimum values. (4) A
well-defined peak of the Ap index between 2002 May and 2004 August was
co-temporal with the excess of the mid-latitude coronal holes during
solar cycle 23. The above findings suggest that the CME speed index may
be a useful indicator of both solar and geomagnetic activities. It may
have advantages over the sunspot numbers, because it better reflects
the intensity of Earth-directed solar eruptions.
---------------------------------------------------------
Title: Understanding Interplanetary Shock Dynamics in the Inner
Heliosphere with New Observations and Modeling Techniques
Authors: St Cyr, O. C.; Henning, C.; Xie, H.; Odstrcil, D.; Mays,
L.; Cremades, H.; Iglesias, F.; Gopalswamy, N.; Kaiser, M. L.
2010AGUFMSH23B1850S Altcode:
This is a status report of our work predicting interplanetary shock
location and strength throughout the inner heliosphere. Coronal mass
ejection (CME) shocks accelerate energetic particles, and CME sheaths
and ejecta are the primary cause of severe geomagnetic storms. We have
evaluated an empirical prediction technique against ENLIL model runs
produced at the Community Coordinated Modelling Center (CCMC). The
prediction method is a technique based on the kilometric wavelength
interplanetary Type II radio emissions measured by Wind/WAVES
and described by Cremades, et al., 2007 (hereafter called "kmTII"
technique). For a subset of Earth-directed CMEs that were also observed
by SOHO LASCO, we have produced multiple ENLIL+cone model predictions
of the location of the shock and compared the predicted arrival of at
Earth with both the actual arrival and the kmTII prediction. We will
report the preliminary results of the comparison in this poster.
---------------------------------------------------------
Title: Aspects of Coronal Mass Ejections Related to Space Weather
Authors: Gopalswamy, N.
2010AGUFMSH52A..03G Altcode:
Solar cycle 23 witnessed an unprecedented array of space- and
ground-based instruments observing the violent eruptions from the
Sun that had huge impact on the heliosphere. It was possible to
characterize coronal mass ejections (CMEs) that cause extreme solar
energetic particle events and geomagnetic storms, the two aspects that
concern the space weather community. In this paper I discuss the special
populations of CMEs that have significant interplanetary consequences:
shock-driving CMEs identified based on their association with type II
radio bursts and in-situ shocks, SEP-producing CMEs, and geoeffective
CMEs (those that produce geomagnetic storms). I discuss the kinematic
and solar-source properties of these populations and how they vary
with the solar activity cycle. I also compare their properties with
the general population of CMEs, so one can recognize when and where
these events occur on the Sun.
---------------------------------------------------------
Title: Relation between CME Speed and Magnetic Helicity in Solar
Source Regions
Authors: Jung, H.; Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Xie, H.
2010AGUFMSH51C1686J Altcode:
Coronal mass ejections (CMEs) are thought to be powered by the free
energy in the solar source regions. The magnetic helicity in the source
regions is one of the indicators of this free energy. In order to see
the relationship between the magnetic helicity of CME source regions and
CME energy, we considered a set of 41 solar source regions (from solar
cycle 23) from which CMEs erupted and ended up as magnetic clouds near
Earth. Using EUV and magnetogram data from the Solar and Heliospheric
Observatory (SOHO) mission, we determined the most probable linear
force-free magnetic structure and its magnetic helicity for each CME
source region. The magnetograms taken just prior to the CME eruption
were used to compute the magnetic helicity. The CME speeds were obtained
from the SOHO/LASCO CME catalog (http://cdaw.gsfc.nasa.gov). We found
that the magnetic helicity is positively correlated with the speed of
CMEs. This result suggests that the magnetic helicity of CME source
regions maybe useful for predicting CME speed.
---------------------------------------------------------
Title: Statistical Study of Solar Activity Associated with SOHO UVCS
Coronal Mass Ejections
Authors: O'Neill, J. F.; St Cyr, O. C.; Mays, L.; Gopalswamy, N.;
Raymond, J. C.; Ciaravella, A.; Yashiro, S.; Xie, H.; Giordano, S.;
Quirk, C.
2010AGUFMSH23B1838O Altcode:
Recently a preliminary catalogue of coronal mass ejections (CMEs)
detected by the SOHO ultraviolet coronal spectrometer (UVCS) has been
made available to the scientific community through the online LASCO CME
catalogue (http://cdaw.gsfc.nasa.gov/). We have undertaken an initial
study to identify solar activity associated with the UVCS CMEs with
radio Type II events, and EUV and X-ray flares. Over 800 CMEs have
been identified in UVCS data, and we have found associated activity
for 185 events. In this poster we report the basic statistics as a
function of time, longitude, latitude, CME speed, etc.
---------------------------------------------------------
Title: An Earth-Directed CME not Observed in LASCO Images
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.
2010AGUFMSH23A1835Y Altcode:
The COR1 coronagraphs on STEREO-A and -B observed an Earth-directed
CME originating from N09W15 at 02:20 UT on 2010/07/09. The apparent
CME speed is only 291 km/s, and the angular width is 60 degrees. The
CME is somewhat slower than the average LASCO CME (average speed ~450
km/s) but not narrow. The CME was expected to be seen as a halo CME
because of the geometry and large width. However, the CME could not
be identified in the LASCO running difference movie because of the
visibility of the white-light coronagraph. On the other hand, EUV
images taken by SDO/AIA show a clear dimming to the northwest of the
source region and a wave-like feature propagating to the east. Faint
Earth-directed CMEs, seem to be better indicated by surface eruptive
signatures such as dimming and EUV waves. We discuss how to estimate
CME parameters using the EUV data alone.
---------------------------------------------------------
Title: Radio-Loud Coronal Mass Ejections without Shocks near Earth
Authors: Akiyama, S.; Gopalswamy, N.; Xie, H.; Yashiro, S.; Makela,
P. A.; St Cyr, O. C.; MacDowall, R. J.; Kaiser, M. L.
2010AGUFMSH32A..07A Altcode:
Type II radio bursts are produced by low energy electrons accelerated
in shocks driven by coronal mass ejections (CMEs). One can infer shocks
near the Sun, in the Interplanetary medium, and near Earth depending
on the wavelength range in which the type II bursts are produced. In
fact, type II bursts are good indicators of CMEs that produce solar
energetic particles. If the type II burst occurs from a source on the
Earth-facing side of the solar disk, it is highly likely that a shock
arrives at Earth in 2-3 days and hence can be used to predict shock
arrival at Earth. However, a significant fraction of CMEs producing
type II bursts were not associated shocks at Earth, even though the
CMEs originated close to the disk center. There are several reasons
for the lack of shock at 1 AU. CMEs originating at large central
meridian distances (CMDs) may be driving a shock, but the shock may
not be extended sufficiently to reach to the Sun-Earth line. Another
possibility is CME cannibalism because of which shocks merge and one
observes a single shock at Earth. Finally, the CME-driven shock may
become weak and dissipate before reaching 1 AU. We examined a set
of 30 type II bursts observed by the Wind/WAVES experiment that had
the solar sources very close to the disk center (within a CMD of 15
degrees), but did not have shock at Earth. We find that the near-Sun
speeds of the associated CMEs average to ~600 km/s, only slightly
higher than the average speed of CMEs associated with radio-quiet
shocks. However, the fraction of halo CMEs is only ~28%, compared
to 40% for radio-quiet shocks and 72% for all radio-loud shocks. We
conclude that the disk-center radio loud CMEs with no shocks at 1 AU are
generally of lower energy and they drive shocks only close to the Sun.
---------------------------------------------------------
Title: The Relation between Coronal Holes and CMEs during the Rise,
Maximum and Declining Phases of the Solar Cycle 23
Authors: Mohamed, A. A.; Gopalswamy, N.; Yashiro, S.; Akiyama, S.;
Makela, P. A.; Xie, H.; Jung, H.
2010AGUFMSH23B1852M Altcode:
We investigate the influence of coronal holes (CHs) on the propagation
of CMEs considering both magnetic clouds (MCs) and non-magnetic clouds
(non-MCs), during the three phases of the solar cycle 23. We consider
events originating within a central meridian distance of 15○. The
influence of the CHs is computed as a fictitious force that depends
on the CH area, the distance between the CH and the eruption region,
and the magnetic field within the CH at the photospheric level. We find
that the influence parameter is the smallest during the rise phase of
the cycle and increases during the maximum and then in the declining
phases. The largest influence parameter was observed to be for non-MCs
in the Maximum phase F= 2.9 G. However, the average influence parameter
is only about half of what was computed for driverless shocks F= 5.8
G. The CH effect on the non-MCs is found to be larger than that for MCs
during maximum phase; this may suggest that non-MCs may also have flux
rope structure which is hidden from observation due to the deflection by
the nearby CHs as has been suggested in the case of driverless shocks
(Gopalswamy et al., 2009, JGR). reference: Gopalswamy, N., p. Makela,
H. Xie, S. Akiyama, and S. Yashiro, (2009), "CME Interaction with
coronal holes and their interplanetary consequences" , J. Geophys. Res.,
114,A00A22 doi:10.1029/2008JA013686.
---------------------------------------------------------
Title: On the Occurrence of Energetic Storm Particle Events and Type
II Radio Bursts in CME-driven Shocks
Authors: Makela, P. A.; Gopalswamy, N.; Akiyama, S.; Xie, H.;
Yashiro, S.
2010AGUFMSH23B1847M Altcode:
We discuss correlations between energetic storm particle (ESP) events
and type II radio emission associated with coronal mass ejection-driven
shocks detected during 1996-2006. Shocks that could not be associated
with any type II radio emission within metric-to-kilometric wavelength
range were defined to be radio-quiet (RQ). All other shocks were defined
to be radio-loud (RL). ESP events were identified from the 66 keV-50
MeV proton intensities measured by the Electron, Proton and Alpha
Monitor (EPAM) instrument on the Advanced Composition Explorer (ACE)
spacecraft and the Energetic and Relativistic Nuclei and Electron (ERNE)
experiment on the Solar and Heliospheric Observatory (SOHO). Electron
ESP events were identified in the 38-53 keV energy channel of EPAM. It
is remarkable that a large fraction (32%) of RQ shocks produced a
particle flux increase at energies above 1.8 MeV. On the other hand,
only 52% of RL shocks produced ESP events. Electron ESP events were
observed in 20% of RQ shocks and 39% of RL shocks. We also find that
ESP events during RQ shocks are less intense than those associated
with RL shocks. Among RQ shocks, those with an ESP event have slightly
more eastern source longitudes (median longitude E07), whereas those
without have more western longitudes (median longitude W03). This
difference probably reflects the asymmetry in the relative size of ESP
events between the eastern and western flanks of the shock. Our results
indicate that type II emission is important for the occurrence of ESP
events. RL shocks produce frequently ESP events, and the associated ESP
events are also more intense than those observed during RQ shocks. The
variability in the occurrence of ESP events and type II radio bursts is
probably due to differences in the shock formation in the low corona
and changes in the properties of the shocks as they propagate through
interplanetary space, and the escape efficiency of accelerated particles
from the shock front.
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Title: International Space Weather Initiative (ISWI)
Authors: Gopalswamy, N.; Davila, J. M.
2010nspm.conf..160G Altcode:
The International Space Weather Initiative (ISWI) is an international
scientific program to understand the external drivers of space
weather. The science and applications of space weather has been
brought to prominence because of the rapid development of space based
technology that is useful for all human beings. The ISWI program has
its roots in the successful International Heliophysical Year (IHY)
program that ran during 2007 - 2009. The primary objective of the ISWI
program is to advance the science space weather by a combination of
instrument deployment, analysis and interpretation of space weather
data from the instruments deployed in conjunction with space data,
and communicate the results to the public and students. Like the IHY,
the ISWI will be a grass roots organization with key participation
from national coordinators with cooperation in an international
steering committee. This talk outlines the ISWI program including its
organization and proposed activities.
---------------------------------------------------------
Title: Opportunities for Ionospheric Science as Part of the
International Space Weather Initiative (ISWI) (Invited)
Authors: Davila, J. M.; Gopalswamy, N.; Haubold, H.
2010AGUFMSA43C..01D Altcode:
The International Heliophysical Year (IHY), which lasted for
approximately two years and involved the effort of thousands of
scientists from over 70 countries, ended in February 2009. The
major objectives of the IHY included over 60 collaborative studies
of universal physical processes in the solar system, the deployment
of arrays of small instruments to observe heliophysical processes, a
unique program of educational and public outreach, and the preservation
of the history of the IGY. The International Space Weather Initiative
(ISWI), an international effort fully supported by the United Nations,
is designed to build on the momentum developed during the IHY to
develop the capability to observe, understand, and predict space
weather phenomena, and provide the opportunity for the deployment
of new instrumentation in Africa and other regions. In this talk the
basic elements of the ISWI will be discussed, and the opportunities
for the deployment of new instrument will be discussed.
---------------------------------------------------------
Title: Understanding Interplanetary Shock Dynamics in the Inner
Heliosphere with New Observations and Modeling Techniques: Case
studies on the 2010-04-03 and 2010-08-01 events
Authors: Xie, H.; Mays, L.; St Cyr, O. C.; Gopalswamy, N.; Odstrcil,
D.; Cremades, H.
2010AGUFMSH23B1858X Altcode:
The 2010 April 03 and August 01 CMEs were studied using observations
from STEREO A and B, and SOHO LASCO, combined with ENLIL+Cone model
simulations preformed at the Community Coordinated Modelling Center
(CCMC). In particular, we identified the origin of CMEs using STEREO
EUVI and/or SDO images. A flux-rope model fitting to the SECCHI A
and B, SOHO/LASCO images was used to reconstruct the 3D structures
of CMEs and determine their actual speeds. J-maps were obtained from
COR-2/HI-1/HI-2 and simulations using ENLIL+cone model were conducted
to study the formation and evolution of the CME-driven shocks in the
inner heliosphere. We compared the simulation results with the observed
height-time profiles of the shocks from white light and kilometric
type II burst (Wind/WAVES) observations. The predicted shock arrival
at Earth is compared with in-situ observations from ACE and Wind. We
report the preliminary results of the study in this poster.
---------------------------------------------------------
Title: Corona Mass Ejections: a Summary of Recent Results
Authors: Gopalswamy, N.
2010nspm.conf..108G Altcode:
Corona mass ejections (CMEs) have been Recognized as the most energetic
phenomenon in the heliosphere, deriving their energy from the stressed
magnetic fields on the Sun. This paper highlights some of the recent
results obtained on CMEs from the Solar and Heliospheric Observatory
(SOHO) and the Solar Terrestrial Relations Observatory (STEREO)
missions. The summary of follows the talk. SOHO observations revealed
that the CME rate is almost a factor of: Two larger than previously
thought and varied with the solar activity cycle in a complex way
(eg, high-latitude CMEs occurred in great abundance during the solar
years maximum). CMEs were found to interact with other CMEs as well
as with other large-scale structures (corona holes), Resulting in
deflections and additional particle acceleration. STEREO observations
have confirmed the three-dimensional nature of CMEs and shocks the
surrounding them. The EUV signatures (flare arcades, Corona dimming,
filament Eruption, and EUV waves) associated with CMEs have become vital
in the identification of sources from Which solar CMEs erupt. CMEs
with speeds exceeding the characteristic speeds of the corona and
the interplanetary medium drive shocks, which produce type II radio
bursts. The wavelength range of type II bursts depends on the CME
kinetic energy: type II bursts with emission components at all
wavelengths (metric to kilometric) due to CMEs are of the highest
kinetic energy. Some CMEs, as fast as 1600 km / s do not produce
type II bursts, while slow CMEs (400 km / s) occasionally produce
type II bursts. These observations can be explained as the variation
in the ambient flow speed (solar wind) speed and the Alfvén. Not
all CME-driven shocks produce type II bursts because they are either
subcritical Or do not have the appropriate geometry. The same shocks
that produce type II bursts also produce solar energetic particles
(SEPS), Whose release near the Sun seems to be delayed with respect to
the onset of type II bursts. This may indicate a subtle difference in
the acceleration of the ions and ~ 10 keV electrons needed to produce
type II bursts. Surprisingly, some shocks lacking type II bursts are
associated with energetic storm particle events (ESPs), pointing to the
importance of electron escape from the shock for producing the radio
emission. CMEs slow down or accelerate in the interplanetary medium
because of the drag force, which modifies the transit time of CMEs
and shocks. Halo CMEs that appear to surround the occulting disk were
known before the SOHO era, and occasional events. During the SOHO era,
they became very prominent because of their ability to impact Earth and
producing geomagnetic storms. Halo CMEs are generally more energetic
than ordinary CMEs, which means they can produce north of the impact
on Earth's magnetosphere. Their origin close to the center disk of the
Sun ensures direct impact on the magnetosphere, although their internal
magnetic structure is crucial in causing storms. The solar sources of
CMEs that produce SEP events at Earth, on the other hand, are generally
in the western hemisphere because of the magnetic connectivity. Thus,
CMEs are very interesting from the point of view of plasma physics as
well as practical implications because of their space weather impact.
---------------------------------------------------------
Title: A Catalog of Halo Coronal Mass Ejections from SOHO
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Xie, H.; Mäkelä,
P.; Vourlidas, A.; Howard, R. A.
2010SunGe...5....7G Altcode:
Coronal mass ejections (CMEs) that appear to surround the occulting
disk of the observing coronagraph are known as halo CMEs. Halos
constitute a subset of energetic CMEs that have important heliospheric
consequences. Here we describe an on-line catalog that contains all
the halo CMEs that were identified in the images obtained by the
Solar and Heliospheric Observatory (SOHO) mission's Large Angle and
Spectrometric Coronagraph (LASCO) since 1996. Until the end of 2007,
some 396 halo CMEs were recorded. For each halo CME, we identify
the solar source (heliographic coordinates), the soft X-ray flare
importance, and the flare onset time. From the sky-plane speed
measurements and the solar source information we obtain the space
speed of CMEs using a cone model. In addition to the description of
the catalog (http://cdaw.gsfc.nasa.gov/CME_list/HALO/halo.html), we
summarize the statistical properties of the halo CMEs. We confirm that
halo CMEs are twice faster than ordinary CMEs and are associated with
major flares on the average. We also compared the annual rate of halo
CMEs with that obtained by automatic detection methods and found that
most of these methods have difficulty in identifying full halo CMEs.
---------------------------------------------------------
Title: Long-duration Low-frequency Type III Bursts and Solar Energetic
Particle Events
Authors: Gopalswamy, Nat; Mäkelä, Pertti
2010ApJ...721L..62G Altcode:
We analyzed the coronal mass ejections (CMEs), flares, and type II
radio bursts associated with a set of three complex, long-duration,
low-frequency (<14 MHz) type III bursts from active region 10588
in 2004 April. The durations were measured at 1 and 14 MHz using data
from Wind/WAVES and were well above the threshold value (>15 minutes)
normally used to define these bursts. One of the three type III bursts
was not associated with a type II burst, which also lacked a solar
energetic particle (SEP) event at energies >25 MeV. The 1 MHz
duration of the type III burst (28 minutes) for this event was near
the median value of type III durations found for gradual SEP events
and ground level enhancement events. Yet, there was no sign of an SEP
event. On the other hand, the other two type III bursts from the same
active region had similar duration but were accompanied by WAVES type
II bursts; these bursts were also accompanied by SEP events detected
by SOHO/ERNE. The CMEs for the three events had similar speeds, and
the flares also had similar size and duration. This study suggests
that the occurrence of a complex, long-duration, low-frequency type
III burst is not a good indicator of an SEP event.
---------------------------------------------------------
Title: Type III Radio Burst Duration and SEP events
Authors: Gopalswamy, Nat; Makela, P.; Xie, H.
2010shin.confE..19G Altcode:
Long-duration (>15 min), low-frequency (<14 MHz) type III radio
bursts have been reported to be indicative of solar energetic particle
(SEP) events. We measured the durations of type III bursts associated
with large SEP events of solar cycle 23. The Type III durations are
distributed symmetrically at 1 MHz yielding a mean value of 34 min
(median = 33 min) for the large SEP events. When the SEP events with
ground level enhancement (GLE) are considered, the distribution is
essentially unchanged (mean = 32 min; median = 30 min). To test the
importance of type III bursts in indicating SEP events, we considered a
set of six type III bursts from the same active region (AR 10588) whose
durations fit the 'long duration' criterion. We analyzed the coronal
mass ejections (CMEs), flares, and type II radio bursts associated
with the type III bursts. The CMEs were of similar speeds and the
flares are also of similar size and duration. All but one of the type
III bursts was not associated with a type II burst in the metric or
longer wavelength domains. The burst without type II burst also lacked
a SEP event at energies >25 MeV. The 1-MHz duration of the type III
burst (28 min) is near the median value of type III durations found
for gradual SEP events and ground level enhancement (GLE) events. Yet,
there was no sign of SEP events. On the other hand, two other type III
bursts from the same active region had similar duration but accompanied
by WAVES type II bursts; these bursts were also accompanied by SEP
events detected by SOHO/ERNE. This study suggests that the type III
burst duration may not be a good indicator of an SEP event, consistent
with the statistical study of Cliver and Ling (2009, ApJ).
---------------------------------------------------------
Title: Shock-driving CMEs near the Sun, in the Interplanetary Medium,
and near Earth.
Authors: Gopalswamy, Nat; Xie, H.; Makela, P.; Akiyama, S.; Yashiro,
S.; Kaiser, M. L.; Howard, R. A.; Bougeret, J. -L.
2010shin.confE.133G Altcode:
The excellent correspondence between type II radio bursts and
solar energetic particles (SEPs) made it clear that the same shock
accelerates ions and electrons. A recent investigation involving a
large number of IP shocks revealed that about 35% of IP shocks do not
produce type II bursts (radio quiet) or SEPs. Comparing the RQ shocks
with the radio loud (RL) ones revealed some interesting results,
which will be summarized in this poster. (1) There is no evidence
for blast waves. (2) Even a small fraction (20%) of RQ shocks is
associated with ion enhancements at the shock when the shock passes
the spacecraft. (3) The primary difference between the RQ and RL
shocks can be traced to the different kinematic properties of the
associated CMEs, although the shock properties measured at 1 AU are
not too different for the RQ and RL cases. This can be attributed
to the interaction with the IP medium, which seems to erase the
difference. More details can be found in Astrophysical Journal 710,
1111, 2010 (http://adsabs.harvard.edu/abs/2009arXiv0912.4719G).
---------------------------------------------------------
Title: The Relation Between Coronal Holes and CMEs During the Rise,
Maximum and Declining Phases of the Solar Cycle 23
Authors: Mohamed, Amaal Abd-Alla; Gopalswamy, N.; Yashiro, S.; Akiyama,
S.; Makela, P.; Xie, H.; Jung, H.
2010shin.confE.141M Altcode:
We investigate the influence of coronal holes on the propagation of
CMEs considering both magnetic clouds (MCs) and non-magnetic clouds
(non-MCs), during the three phases of the solar cycle 23. We consider
events originating within a central meridian distance of 15o. The
influence of the CHs is computed as a fictitious force that depends
on the CH area, the distance between the CH and the eruption region,
and the magnetic field within the CH at the photospheric level. We find
that the influence parameter is the smallest during the rise phase of
the cycle and increases during the maximum and then in the declining
phases. The largest influence parameter was observed in the declining
phase. However, the average influence parameter is only about half of
what was computed for driverless shocks (Gopalswamy et al., 2009, JGR).
---------------------------------------------------------
Title: Relation between Magnetic Helicity and CME Speed in Solar
Source Regions
Authors: Jung, Hyewon; Gopalswamy, Nat; Akiyama, Sachiko; Yashiro,
Seiji; Xie, Hong
2010shin.confE..88J Altcode:
Coronal mass ejections (CMEs) are thought to be powered by the free
energy in the solar source regions. The magnetic helicity in the source
regions is one of the indicators of this free energy. In order to
see the relationship between the magnetic helicity and CME energy, we
considered a set of 41 solar source regions (from solar cycle 23) from
which CMEs erupted and ended up as magnetic clouds near Earth. Using
EUV and magnetogram data from the Solar and Heliospheric Observatory
(SOHO) mission, we determined the most probable linear force free
magnetic structure and its magnetic helicity for each CME source
region. The magnetograms taken just prior to the CME eruption were
used to compute the magnetic helicity. The CME speeds were obtained
from the SOHO/LASCO CME catalog (http://cdaw.gsfc.nasa.gov). We found
that the magnetic helicity is positively correlated with the speed of
CMEs. This result suggests that the magnetic helicity of CME source
regions maybe useful for predicting CME speed.
---------------------------------------------------------
Title: X-ray Flare Durations and CME Associations
Authors: Yashiro, Seiji; Gopalswamy, N.; Akiyama, S.; Kahler, S.
2010shin.confE..86Y Altcode:
We report on a statistical study assessing how the soft X-ray flare
durations affect the flare-CME relationship. To this end, we considered
245 limb flares (central meridian distance > 60 degrees) that had
soft X-ray importance in the narrow range M1.0 to M3.0. We chose the
limb flares to avoid projection effects and the CME visibility issues;
the medium flares were considered to avoid the influence of flare peak
intensity on CME parameters. We examined the CME association of these
flares using coronal images obtained by SOHO/LASCO. We found that the
CME association rate of flares slowly increases with increasing flare
durations. All the flares with very long duration (T>100 min) were
associated with CMEs. However, 40% of the impulsive flares (T<10
min) were associated with CMEs, and 30% of the long-duration flares
(60<T<100 min) did not have CME association. The duration
distribution of flares with and without CMEs had a high degree of
overlap. We conclude that the soft X-ray flare duration is not a good
indicator of the CME association.
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Title: Type II radio emission and ESP events
Authors: Makela, Pertti; Gopalswamy, Nat; Akiyama, Sachiko; Xie,
Hong; Yashiro, Seiji
2010shin.confE..87M Altcode:
We report on a survey of energetic storm particle (ESP) events
associated with radio-quiet (RQ) and radio-loud (RL) interplanetary
(IP) shocks observed during 1996-2006. Shocks were classified into
RL or RQ events based on the existence of type II radio bursts. We
consider only shocks driven by coronal mass ejections (CMEs). Particle
observations are provided by the Electron, Proton and Alpha Monitor
(EPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft
and the Energetic and Relativistic Nuclei and Electron (ERNE) experiment
on the Solar and Heliospheric Observatoty (SOHO). We find that 32%
of RQ shocks produced an ESP event at energies >1.8 MeV, compared
to 52% of RL shocks. Electron enhancements were detected in 20% of RQ
shocks and 39% of RL shocks. The ESP events associated with RQ shocks
are less intense than those associated with RL shocks. In addition, RQ
shocks with ESP events are predominately quasi-perpendicular shocks,
and their solar sources located generally to the east of the central
meridian. The size of ESP increases showed a modest positive correlation
with the CME and shock speeds and with the Alfvenic Mach number. Our
results indicate that some RQ shocks can accelerate particles at 1 AU,
but less efficiently than RL shocks, even though they do not produce
observable type II radio bursts. This variability is probably related
to differences in the shock formation in the low corona, changes in the
properties of the shocks as they propagate through interplanetary space,
and the escape efficiency of accelerated particles from the shock front.
---------------------------------------------------------
Title: Expansion speed of Coronal Mass Ejections
Authors: Michalek, Grzegorz; Gopalswamy, Nat; Yashiro, Seiji
2010EGUGA..12.5142M Altcode:
A large set of limb CMEs has been used to determine the accurate
relationship between radial (V rad) and expansion (V exp) speeds of
CMEs. It was demonstrated that this relation is exceptionally well
described by the function f(w)= 1/2 (1 + cot (w)) representing a full
cone model for the CME with a half width, w. We also demonstrated that
this relation for the halo CMEs could be very simple V rad = V exp.
---------------------------------------------------------
Title: Large Geomagnetic Storms Associated with Limb Halo Coronal
Mass Ejections
Authors: Gopalswamy, Nat; Yashiro, Seiji; Xie, Hong; Akiyama, Sachiko;
Mäakelä, Pertti
2010aogs...21...71G Altcode: 2009arXiv0903.2776G
Solar cycle 23 witnessed the observation of hundreds of halo coronal
mass ejections (CMEs), thanks to the high dynamic range and extended
field of view of the Large Angle and Spectrometric Coronagraph (LASCO)
on board the Solar and Heliospheric Observatory (SOHO) mission. More
than two thirds of halo CMEs originating on the front side of the Sun
have been found to be geoeffective (Dst ≤ -50 nT). The delay time
between the onset of halo CMEs and the peak of ensuing geomagnetic
storms has been found to depend on the solar source location
(Gopalswamy et al., 2007). In particular, limb halo CMEs (source
longitude > 45°) have a 20% shorter delay time on the average. It
was suggested that the geomagnetic storms due to limb halos must be
due to the sheath portion of the interplanetary CMEs (ICMEs) so that
the shorter delay time can be accounted for. We confirm this suggestion
by examining the sheath and ejecta portions of ICMEs from Wind and ACE
data that correspond to the limb halos. Detailed examination showed
that three pairs of limb halos were interacting events. Geomagnetic
storms following five limb halos were actually produced by other disk
halos. The storms followed by four isolated limb halos and the ones
associated with interacting limb halos, were all due to the sheath
portions of ICMEs.
---------------------------------------------------------
Title: Polar Chromospheric Signatures of the Subdued Cycle 23/24
Solar Minimum
Authors: Gopalswamy, N.; Yashiro, S.; Makela, P.; Shibasaki, K.;
Hathaway, D.
2010AAS...21640103G Altcode: 2010BAAS...41..857G
Coronal holes appear brighter than the quiet Sun in microwave images,
with a brightness enhancement of 500 to 2000 K. The brightness
enhancement corresponds to the upper chromosphere, where the
plasma temperature is about 10000 K. We constructed a microwave
butterfly diagram using the synoptic images obtained by the Nobeyama
radioheliograph (NoRH) showing the evolution of the polar and low
latitude brightness temperature. While the polar brightness reveals the
chromospheric conditions, the low latitude brightness is attributed to
active regions in the corona. When we compared the microwave butterfly
diagram with the magnetic butterfly diagram, we found a good correlation
between the microwave brightness enhancement and the polar field
strength. The microwave butterfly diagram covers part of solar cycle
22, whole of cycle 23, and part of cycle 24, thus enabling comparison
between the cycle 23/24 and cycle 22/23 minima. The microwave brightness
during the cycle 23/24 minimum was found to be lower than that during
the cycle 22/23 minimum by 250 K. The reduced brightness temperature
is consistent with the reduced polar field strength during the cycle
23/24 minimum seen in the magnetic butterfly diagram. We suggest that
the microwave brightness at the solar poles is a good indicator of
the speed of the solar wind sampled by Ulysses at high latitudes.
---------------------------------------------------------
Title: Radioheliograph Observations of Metric Type II Bursts and
the Kinematics of Coronal Mass Ejections
Authors: Ramesh, R.; Kathiravan, C.; Kartha, Sreeja S.; Gopalswamy, N.
2010ApJ...712..188R Altcode:
Assuming that metric type II radio bursts from the Sun are due to
magnetohydrodynamic shocks driven by coronal mass ejections (CMEs),
we estimate the average CME acceleration from its source region up to
the position of the type II burst. The acceleration values are in the
range ≈600-1240 m s^{-2}, which are consistent with values obtained
using non-radio methods. We also find that (1) CMEs with comparatively
larger acceleration in the low corona are associated with soft X-ray
flares of higher energy; the typical acceleration of a CME associated
with X1.0 class soft X-ray flare being ≈ 1020 m s^{-2}, and (2)
CMEs with comparatively higher speed in the low corona slow down
quickly at large distances from the Sun—the deceleration of a CME
with a typical speed of 1000 km s<SUP>-1</SUP> being ≈ -15 m s^{-2}
in the distance range of ≈3-32 R <SUB>sun</SUB>.
---------------------------------------------------------
Title: Solar Sources of “Driverless” Interplanetary Shocks
Authors: Gopalswamy, N.; Mäkelä, P.; Xie, H.; Akiyama, S.;
Yashiro, S.
2010AIPC.1216..452G Altcode:
We identify the solar sources of a large number of interplanetary
(IP) shocks that do not have a discernible driver as observed by
spacecraft along the Sun-Earth line. At the Sun, these “driverless”
shocks are associated with fast and wide CMEs. Most of the CMEs were
also driving shocks near the Sun, as evidenced by the association of
IP type II radio bursts. Thus, all these shocks are driven by CMEs
and they are not blast waves. Normally limb CMEs produce driverless
shocks at 1 AU. But some disk-center CMEs also result in driverless
shocks because of deflection by nearby coronal holes. We estimate the
angular deflection to be in the range 20°-60°. We also compared the
influence of nearby coronal holes on a set of CMEs that resulted in
magnetic clouds. The influence is nearly three times larger in the
case of driverless shocks, confirming the large deflection required.
---------------------------------------------------------
Title: The CME link to geomagnetic storms
Authors: Gopalswamy, Nat
2010IAUS..264..326G Altcode:
The coronal mass ejection (CME) link to geomagnetic storms stems from
the southward component of the interplanetary magnetic field contained
in the CME flux ropes and in the sheath between the flux rope and the
CME-driven shock. A typical storm-causing CME is characterized by (i)
high speed, (ii) large angular width (mostly halos and partial halos),
and (iii) solar source location close to the central meridian. For
CMEs originating at larger central meridian distances, the storms
are mainly caused by the sheath field. Both the magnetic and energy
contents of the storm-producing CMEs can be traced to the magnetic
structure of active regions and the free energy stored in them.
---------------------------------------------------------
Title: Interplanetary Shocks Lacking Type II Radio Bursts
Authors: Gopalswamy, N.; Xie, H.; Mäkelä, P.; Akiyama, S.; Yashiro,
S.; Kaiser, M. L.; Howard, R. A.; Bougeret, J. -L.
2010ApJ...710.1111G Altcode: 2009arXiv0912.4719G
We report on the radio-emission characteristics of 222 interplanetary
(IP) shocks detected by spacecraft at Sun-Earth L1 during solar cycle
23 (1996 to 2006, inclusive). A surprisingly large fraction of the IP
shocks (~34%) was radio quiet (RQ; i.e., the shocks lacked type II radio
bursts). We examined the properties of coronal mass ejections (CMEs)
and soft X-ray flares associated with such RQ shocks and compared them
with those of the radio-loud (RL) shocks. The CMEs associated with the
RQ shocks were generally slow (average speed ~535 km s<SUP>-1</SUP>)
and only ~40% of the CMEs were halos. The corresponding numbers for
CMEs associated with RL shocks were 1237 km s<SUP>-1</SUP> and 72%,
respectively. Thus, the CME kinetic energy seems to be the deciding
factor in the radio-emission properties of shocks. The lower kinetic
energy of CMEs associated with RQ shocks is also suggested by the
lower peak soft X-ray flux of the associated flares (C3.4 versus
M4.7 for RL shocks). CMEs associated with RQ CMEs were generally
accelerating within the coronagraph field of view (average acceleration
~+6.8 m s<SUP>-2</SUP>), while those associated with RL shocks were
decelerating (average acceleration ~-3.5 m s<SUP>-2</SUP>). This
suggests that many of the RQ shocks formed at large distances from the
Sun, typically beyond 10 Rs, consistent with the absence of metric and
decameter—hectometric (DH) type II radio bursts. A small fraction
of RL shocks had type II radio emission solely in the kilometric
(km) wavelength domain. Interestingly, the kinematics of the CMEs
associated with the km type II bursts is similar to those of RQ shocks,
except that the former are slightly more energetic. Comparison of
the shock Mach numbers at 1 AU shows that the RQ shocks are mostly
subcritical, suggesting that they were not efficient in accelerating
electrons. The Mach number values also indicate that most of these are
quasi-perpendicular shocks. The radio-quietness is predominant in the
rise phase and decreases through the maximum and declining phases of
solar cycle 23. About 18% of the IP shocks do not have discernible
ejecta behind them. These shocks are due to CMEs moving at large
angles from the Sun-Earth line and hence are not blast waves. The solar
sources of the shock-driving CMEs follow the sunspot butterfly diagram,
consistent with the higher-energy requirement for driving shocks.
---------------------------------------------------------
Title: Prediction of the interplanetary Coronal Mass Ejection and
it's associated shock by using neural network
Authors: Mahrous, Ayman; Radi, Amr; Youssef, Mohamed; Faheem, Amin;
Ahmed, Safinaz; Gopalswamy, Nat
2010cosp...38.1905M Altcode: 2010cosp.meet.1905M
We determined the effective parameter that can be used to predict the
estimated arrival time for both Interplanetary Coronal Mass Ejection
(ICME) and its associated shock (using the list of Richardson/Cane ICMEs
in 1996-2007). Neural network model is used to predict ICME/shock
and its arrival time. The set of CME-IP shock pairs obtain from
Richardson/Cane ICMEs list is used to construct our neural model from
(1996-2005). Concurrently, we determined the effective parameter that
used CME-IP shock pairs from (2005-2007) to test our neural networks
model. We found that the model succeeded to predict 97
---------------------------------------------------------
Title: Quasi-Periodic Oscillations in Lasco Coronal Mass Ejection
Speeds
Authors: Shanmugaraju, A.; Moon, Y. -J.; Cho, K. -S.; Bong, S. C.;
Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Umapathy, S.; Vrsnak, B.
2010ApJ...708..450S Altcode:
Quasi-periodic oscillations in the speed profile of coronal mass
ejections (CMEs) in the radial distance range 2-30 solar radii are
studied. We considered the height-time data of the 307 CMEs recorded
by the Large Angle and Spectrometric Coronagraph (LASCO) during 2005
January-March. In order to study the speed-distance profile of the CMEs,
we have used only 116 events for which there are at least 10 height-time
measurements made in the LASCO field of view. The instantaneous CME
speed is estimated using a pair of height-time data points, providing
the speed-distance profile. We found quasi-periodic patterns in at
least 15 speed-distance profiles, where the speed amplitudes are larger
than the speed errors. For these events we have determined the speed
amplitude and period of oscillations. The periods of quasi-periodic
oscillations are found in the range 48-240 minutes, tending to
increase with height. The oscillations have similar properties as
those reported by Krall et al., who interpreted them in terms of the
flux-rope model. The nature of forces responsible for the motion of
CMEs and their oscillations are discussed.
---------------------------------------------------------
Title: Coronal Mass Ejections from Sunspot and Non-Sunspot Regions
Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Mäkelä, P.
2010ASSP...19..289G Altcode: 2009arXiv0903.1087G; 2010mcia.conf..289G
Coronal mass ejections (CMEs) originate from closed magnetic field
regions on the Sun, which are active regions and quiescent filament
regions. The energetic populations such as halo CMEs, CMEs associated
with magnetic clouds, geoeffective CMEs, CMEs associated with
solar energetic particles and interplanetary type II radio bursts,
and shock-driving CMEs have been found to originate from sunspot
regions. The CME and flare occurrence rates are found to be correlated
with the sunspot number, but the correlations are significantly weaker
during the maximum phase compared to the rise and declining phases. We
suggest that the weaker correlation results from high-latitude CMEs
from the polar crown filament regions that are not related to sunspots.
---------------------------------------------------------
Title: Estimation of coronal magnetic field using the type II radio
burst associated with a fast CME
Authors: Gopalswamy, Nat; Yashiro, Seiji; Akiyama, Sachiko; Freeland,
Samuel; Davila, Joseph; Howard, Russell; Bougeret, J. -L.
2010cosp...38.1808G Altcode: 2010cosp.meet.1808G
The 2008 March 25 coronal mass ejection (CME) was the second
fastest among the 10 type II producing CMEs in the STEREO era. The
CME was accompanied by a EUV wave and a shock discernible in the
white-light data. The type II burst was observed in the metric and
decameter-hectometer (DH) wavelength domains. The type II burst ended in
the DH domain when the CME speed started declining at a heliocentric
distance where the Alfven speed reached its peak value. Under the
scenario that the type II burst was caused by a CME-driven shock,
we see that the end of the type II burst corresponds to a significant
weakening of the shock, making it subcritical. The standoff distance
between the flux rope structure and the shock significantly increased at
the time of the shock weakening. From the observed standoff distance,
we estimated the upstream Alfvenic Mach number and hence the coronal
magnetic field. The magnetic field derived (0.04 G) is consistent with
typical quiet solar atmosphere at 7 solar radii.
---------------------------------------------------------
Title: Investigating the relation between Coronal Holes and CMEs
during the Rise, Maximum and Declining Phases of the Solar Cycle 23
Authors: Shahin, Amaal; Gopalswamy, Nat
2010cosp...38.1918S Altcode: 2010cosp.meet.1918S
In a study on the interaction between Coronal holes (CHs) and inter
planetary coronal mass ejections (ICMEs) during the declining phase
of solar cycle 23, Gopalswamy et al. [2009] showed that coronal holes
(CHs) act as a magnetic wall that constrains the CME propagation. The
CME trajectories are significantly affected when the eruptions
occur in close proximity to CHs. Here, we investigate the influence
of coronal holes on the propagation of CMEs through considering both
ICMEs categories with and without flux rope structures during the rise
and maximum phases of the solar cycle 23. We also, compare the results
obtained with that of the declining phase and of the driverless shocks
reported previously by Gopalswamy et al. [2009]. A list of ICMEs that
are not classified as MCs has been developed from the Interplanetary
(IP) shock list of the solar cycle 23 via selecting all disk center
events (central meridian distance 15o ) that have been observed
to be (MC s) which leaves us with another list includes the non MC
events. The influence of the CHs is computed as a fictitious force
that depends on the CH area, the distance between the CH and the
eruption region, and the magnetic field within the CH at photospheric
level. The open magnetic field distribution on the Sun is obtained for
the MCs and non MCs solar events studied during the rise and maximum
phases in addition to four magnetic cloud events were not included
in Goplaswamy et al. [2009]. This open filed distribution is obtained
through performing a potential field source surface extrapolation to
the corona up to a heliocentric distance of 2.5 Rs. The Correlation
Coefficient (CC) between the duration of the ICMEs and the resultant
influence parameter F of the coronal holes is determined in the case
of MCs and non MCs for rise, maximum and declining phases. The results
show that the correlation coefficient in the case of magnetic cloud
(MCs) events is very high at the rise phase ( 0.84) which confirms the
correspondence between the non radial motion during the rise phase of
the solar cycle and the higher magnetic field strength in the solar
regions of the polar coronal holes existed in this phase. The difference
between measured position angle (MPA) and the influence position angle
(FPA) where F is pointing, () for the non MCs in the rise and maximum
phases is found to be 34o and 35o ; respectively which is consistent
with that for driverless shocks given by Gopalswamy et al. [2009] (where
37o ). These results together with the average influence parameter
value (F av 2.53 G) for the declining phase which is found to be the
highest compared to the other two phases and also to the MCs average
values suggest that the non MCs are resembling in their behavior the
driverless shocks (which have been proven by Gopalswamy et al., 2009
to be deflected by the near by CH s away from the Sun-Earth line) and
that the non MCs may have flux rope structure as the MCs do have but
this structure is hidden from observation due to the deflection by CH
s. This finding may have bearing on the idea that all CMEs may be flux
ropes and the difference is only due to the viewing angle variation.
---------------------------------------------------------
Title: The International Space Weather Initiative
Authors: Davila, Joseph; Gopalswamy, Nat
2010cosp...38.4192D Altcode: 2010cosp.meet.4192D
The International Space Weather Initiative (ISWI) is an international
program of scientific collaboration to understand the external drivers
of space weather. One of the major thrusts of the ISWI is to deploy
arrays of small instruments such as magnetometers, radio antennas, GPS
receivers, all-sky cameras, particle detectors, etc. around the world to
provide global measurements of heliospheric phenomena. Scientists from
approximately 70 countries now participate in the instrument operation,
data collection, analysis, and publication of scientific results,
working at the forefront of science research. The purpose of the ISWI is
to continue the scientific study of universal processes in the solar
system that affect space weather and the terrestrial environment,
and to continue to coordinate the deployment and operation of new and
existing instrument arrays aimed at understanding the impacts of Space
Weather on Earth and the near-Earth environment. This project provides
an excellent opportunity for potential instrument providers to engage
collaborators from specific geographical locations, and to broaden
the coverage of existing instrument arrays. By deploying instruments
in strategically chosen locations new science and a more global view
of heliophysical processes is obtained. These data will also provide
new inputs for global ionospheric models in the future.
---------------------------------------------------------
Title: Recent STEREO Observations of Coronal Mass Ejections
Authors: St Cyr, O. C.; Xie, H.; Mays, M. L.; Davila, J. M.; Gilbert,
H. R.; Jones, S. I.; Pesnell, W. D.; Gopalswamy, N.; Gurman, J. B.;
Yashiro, S.; Wuelser, J.; Howard, R. A.; Thompson, B. J.; Thompson,
W. T.
2009AGUFMSH11A1491S Altcode:
Over 400 CMEs have been observed by STEREO SECCHI COR1 during
the mission's three year duration (2006-2009). Many of the solar
activity indicators have been at minimal values over this period,
and the Carrington rotation-averaged CME rate has been comparable to
that measured during the minima between Cycle 21-22 (SMM C/P) and
Cycle 22-23 (SOHO LASCO). That rate is about 0.5 CMEs/day. During
the current solar minimum (leading to Cycle 24), there have been
entire Carrington rotations where no sunspots were detected and the
daily values of the 2800 MHz solar flux remained below 70 sfu. CMEs
continued to be detected during these exceptionally quiet periods,
indicating that active regions are not necessary to the generation of
at least a portion of the CME population. In the past, researchers were
limited to a single view of the Sun and could conclude that activity
on the unseen portion of the disk might be associated with CMEs. But
as the STEREO mission has progressed we have been able to observe an
increasing fraction of the Sun's corona with STEREO SECCHI EUVI and
were able to eliminate this possibility. Here we report on the nature
of CMEs detected during these exceptionally-quiet periods, and we
speculate on how the corona remains dynamic during such conditions.
---------------------------------------------------------
Title: Expansion Speed of Coronal Mass Ejections
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.
2009SoPh..260..401M Altcode:
A large set of limb coronal mass ejections (CMEs) are used to
determine the accurate relationship between radial (V<SUB>rad</SUB>)
and expansion (V<SUB>exp</SUB>) speeds of CMEs. It is demonstrated
that this relation is exceptionally well described by the function
f(w)=1/2(1+cot w), representing a full cone model for the CME with
a half-width, w. We also demonstrate that for extremely fast CMEs
(V<SUB>exp</SUB>>3000 km s<SUP>−1</SUP>), it is better to use the
approximation V<SUB>rad</SUB>≈V<SUB>LE</SUB>. This implies that such
CMEs expand spherically above the solar surface.
---------------------------------------------------------
Title: Relation between Magnetic Helicity and CME Speed in Source
Active Regions
Authors: Jung, H.; Gopalswamy, N.; Akiyama, S.; Yashiro, S.
2009AGUFMSH41B1669J Altcode:
We report on a study linking the speed of coronal mass ejections
(CMEs) to the magnetic helicity in the source active regions. The
motivation comes from the fact that the CME speed may depend on the
active region free magnetic energy, which in turn may be represented
by the helicity, a proxy for the nonpotentiality. We selected a set
of active regions from solar cycle 23, measured their helicity, and
identified CMEs from the CME catalog (http://cdaw.gsfc.nasa.gov). Using
EUV and magnetogram data from the Solar and Heliospheric Observatory
(SOHO) mission, we measured the coronal helicity content before CME
eruptions. We extrapolated the photospheric magnetic field to the
corona to obtain the coronal helicity that fits a EUV image before
each CME eruption. The CME speeds used here corresponds to the average
speed within the SOHO coronagraphic field of view. We found that
magnetic helicity is positively correlated with the speed of CME. We
cross-checked the helicity values using the principle of magnetic
helicity conservation connecting helicity obtained from the Local
Correlation Tracking (LCT) method, the helicity of the associated
magnetic clouds and the coronal helicity.
---------------------------------------------------------
Title: The 26 April 2008 CME; a Case Study Tracking a CME into
the Heliosphere
Authors: Webb, D. F.; Galvin, A. B.; Gopalswamy, N.; Howard, T. A.;
Reinard, A. A.; Jackson, B.; Davis, C.
2009AGUFMSH41A1640W Altcode:
With the current unique constellation of spacecraft, we are studying
the origins of CMEs, their 3D structure and how they propagate through
the heliosphere. Here we present the results of a case study of one
well observed event that occurred during the Whole Heliosphere Interval
(WHI), originating at the Sun on 26 April 2008. The event arose from a
cluster of 3 active regions that evolved over several solar rotations
centered on WHI. The CME was moderately fast with evidence of a shock
and was associated with a coronal arcade, coronal dimming and an EUV
wave. The April 26 CME originated from disk center for STEREO-B and
apparently caused a small SEP event and shock and possible magnetic
cloud at STEREO-B on April 29. A brief IP type II suggests that
this event had the lowest starting frequency ever observed, which has
implications for the medium through which the shock propagates. Possible
ejecta was detected in situ at STEREO-B. The Fe charge states suggest
that there was a CIR-type interface with some bidirectional electron
streaming present. This is confirmed by SMEI 3D reconstructions of
density indicating that the ICME interacted with a preexisting CIR. The
ICME was also imaged by the SECCHI HI imagers; both the SMEI and HI
data permit us to track the dense material from the Sun past 1 AU.
---------------------------------------------------------
Title: Interplanetary Proton and Electron Enhancements Associated
with Radio-loud and Radio-quiet CME-driven Shocks
Authors: Makela, P. A.; Gopalswamy, N.; Xie, H.; Akiyama, S.;
Yashiro, S.
2009AGUFMSH33A1477M Altcode:
We present the results on electron and proton acceleration in
association with radio-quiet (RQ) and radio-loud (RL) shocks driven by
coronal mass ejections (CMEs) during 1996-2006. The CME-driven shocks
are classified into RL or RQ shocks based on the presence or the
lack of type II radio bursts in the metric and decameter-hectometric
wavelength range. We studied proton flux enhancements at L1 in the
66 keV - 50 MeV energy range observed by the ACE/EPAM and SOHO/ERNE
instruments. Electron flux enhancements were studied in the 38-53~keV
energy channel of EPAM. In general, the RL shocks are more likely
to be associated with an energetic storm particle (ESP) event than
RQ shocks. Approximately one third of RQ shocks and slightly over a
half of RL shocks produced an ESP event at energies above 1.8 MeV. In
overall both RQ and RL electron ESP events are rarer, but they follow
a similar pattern to the proton observations, i.e. ESP events are
observed in approximately one fifth versus two fifths of shocks,
respectively. We also studied correlations of ESP event size with CME
and shock properties. As expected, the ESP events associated with the RQ
shocks are less intense than those with RL shocks. In addition, particle
acceleration in RQ shocks occurs predominately in quasi-perpendicular
shocks. There is a modest positive correlation between ESP event size
and the CME and shock speed and the Mach number. Again, the correlations
are stronger for the RL shocks. It appears that shocks can accelerate
particles, although less efficiently, even when they do not produce
observable type II radio bursts. The variation between the presence
of type IIs and ESP events is probably connected to variations in the
coronal conditions of shock formation and to the consequent evolution
of the shock as it travels through diverse coronal and interplanetary
plasmas.
---------------------------------------------------------
Title: The subdued solar cycle 23/24 minimum revealed by microwave
butterfly diagram
Authors: Gopalswamy, N.; Yashiro, S.; Makela, P. A.; Shibasaki, K.
2009AGUFMSH13C..02G Altcode:
The 17 GHz microwave brightness temperature in coronal holes
is typically enhanced by 500 to 2000 K with respect to the quiet
Sun. This is considered to be a property of the upper chromosphere,
where the plasma temperature is ~10000 K. We constructed a microwave
butterfly diagram using the synoptic images obtained by the Nobeyama
Radioheliograph and compared it with the magnetic butterfly diagram. We
found a good correlation between the microwave brightness enhancement
and the polar field strength. We also performed a rotation-by-rotation
comparison between the two data sets to obtain the correlation
between the magnetic field strength and the microwave brightness
temperature. The microwave butterfly diagram covers part of cycle
22, whole of cycle 23, and part of cycle 24, thus enabling comparison
between the cycle 23/24 and cycle 22/23 minima. The microwave brightness
during the cycle 23/24 minimum was found to be lower than that during
the cycle 22/23 minimum by ~250 K. The reduced brightness temperature
is consistent with the reduced polar field strength during the cycle
23/24 minimum seen e.g., in the SOHO/MDI magnetic butterfly diagram. We
suggest that the microwave brightness at the solar poles is a good
indicator of the speed of the solar wind sampled by Ulysses at high
latitudes.
---------------------------------------------------------
Title: The relation between solar active region location and the
lowest frequency of type III emission
Authors: Kuroda, N.; Gopalswamy, N.
2009AGUFMSH23A1522K Altcode:
We have investigated the relation between the lowest frequencies of type
III bursts and the locations of source active regions from which the
causal electron beams originate. We chose several active regions that
produced coronal mass ejections (CMEs) and flares during their disk
passage. The type III bursts considered in this study originated from
these eruptions. The CMEs were detected by the Solar and Heliospheric
Observatory (SOHO) mission’s Large Angle and Spectrometric coronagraph
(LASCO). The type III bursts were observed by the Radio and Plasma
Wave Experiment (WAVES) on board Wind. By tracking the type III bursts
into the spectral range covered by the Thermal Noise Receiver (TNR)
on board Wind, we were able to measure the lowest frequency reached
by 104 type III bursts from 17 active regions. In addition, we were
able to measure the frequency separation between the type III bursts
and the local plasma frequency at the Wind spacecraft as measured by
TNR. Because the type III bursts were produced when the source active
regions were at various central meridian distances, we could study the
lowest frequency at which the type III bursts occurred as a function
of the source longitude. We found that the type III emission occurs
at frequencies close to the local plasma frequency at the spacecraft
when the source active regions are at the disk center or in the western
hemisphere. Type III bursts from active regions close to the east limb
of the Sun have a higher cutoff frequency. This can be explained by the
fact that type III bursts from eastern active regions cannot propagate
to the Wind spacecraft because of the intervening denser plasma regions
Further investigation is needed to understand the large scatter in the
data points, especially those that do not follow the expected tendency:
a closer examination would reveal the condition of interplanetary medium
and the state of solar wind at the time of these irregular points.
---------------------------------------------------------
Title: On the Origin, 3D Structure and Dynamic Evolution of CMEs
Near Solar Minimum
Authors: Xie, H.; St. Cyr, O. C.; Gopalswamy, N.; Yashiro, S.; Krall,
J.; Kramar, M.; Davila, J.
2009SoPh..259..143X Altcode:
We have conducted a statistical study 27 coronal mass ejections
(CMEs) from January 2007 - June 2008, using the stereoscopic views
of STEREO SECCHI A and B combined with SOHO LASCO observations. A
flux-rope model, in conjunction with 3D triangulations, has been used
to reconstruct the 3D structures and determine the actual speeds of
CMEs. The origin and the dynamic evolution of the CMEs are investigated
using COR1, COR2 and EUVI images. We have identified four types of
solar surface activities associated with CMEs: i) total eruptive
prominence (totEP), ii) partially eruptive prominence (PEP), iii)
X-ray flare, and iv) X-type magnetic structure (X-line). Among the
27 CMEs, 18.5% (5 of 27) are associated with totEPs, 29.6% (8 of 27)
are associated with PEPs, 26% (7 of 27) are flare related, and 26%
(7 of 27) are associated with X-line structures, and 43% (3 of 7)
are associated with both X-line structures and PEPs. Three (11%)
could not be associated with any detectable activity. The mean actual
speeds for totEP-CMEs, PEP-CMEs, flare-CMEs, and X-line-CMEs are 404
km s<SUP>−1</SUP>,247 km s<SUP>−1</SUP>,909 km s<SUP>−1</SUP>,
and 276 km s<SUP>−1</SUP>, respectively; the average mean values of
edge-on and broadside widths for the 27 CMEs are 52 and 85 degrees,
respectively. We found that slow CMEs (V≤400 km s<SUP>−1</SUP>) tend
to deflect towards and propagate along the streamer belts due to the
deflections by the strong polar magnetic fields of corona holes, while
some faster CMEs show opposite deflections away from the streamer belts.
---------------------------------------------------------
Title: Relation Between Type II Bursts and CMEs Inferred from STEREO
Observations
Authors: Gopalswamy, N.; Thompson, W. T.; Davila, J. M.; Kaiser,
M. L.; Yashiro, S.; Mäkelä, P.; Michalek, G.; Bougeret, J. -L.;
Howard, R. A.
2009SoPh..259..227G Altcode:
The inner coronagraph (COR1) of the Solar Terrestrial Relations
Observatory (STEREO) mission has made it possible to observe CMEs in
the spatial domain overlapping with that of the metric type II radio
bursts. The type II bursts were associated with generally weak flares
(mostly B and C class soft X-ray flares), but the CMEs were quite
energetic. Using CME data for a set of type II bursts during the
declining phase of solar cycle 23, we determine the CME height when
the type II bursts start, thus giving an estimate of the heliocentric
distance at which CME-driven shocks form. This distance has been
determined to be ∼1.5R<SUB>s</SUB> (solar radii), which coincides
with the distance at which the Alfvén speed profile has a minimum
value. We also use type II radio observations from STEREO/WAVES and
Wind/WAVES observations to show that CMEs with moderate speed drive
either weak shocks or no shock at all when they attain a height where
the Alfvén speed peaks (∼3R<SUB>s</SUB> - 4R<SUB>s</SUB>). Thus
the shocks seem to be most efficient in accelerating electrons in the
heliocentric distance range of 1.5R<SUB>s</SUB> to 4R<SUB>s</SUB>. By
combining the radial variation of the CME speed in the inner corona
(CME speed increase) and interplanetary medium (speed decrease) we
were able to correctly account for the deviations from the universal
drift-rate spectrum of type II bursts, thus confirming the close
physical connection between type II bursts and CMEs. The average height
(∼1.5R<SUB>s</SUB>) of STEREO CMEs at the time of type II bursts
is smaller than that (2.2R<SUB>s</SUB>) obtained for SOHO (Solar and
Heliospheric Observatory) CMEs. We suggest that this may indicate,
at least partly, the density reduction in the corona between the
maximum and declining phases, so a given plasma level occurs closer
to the Sun in the latter phase. In two cases, there was a diffuse
shock-like feature ahead of the main body of the CME, indicating a
standoff distance of 1R<SUB>s</SUB> - 2R<SUB>s</SUB> by the time the
CME left the LASCO field of view.
---------------------------------------------------------
Title: Investigating the relation between coronal holes and CMEs
during the rise phase of the solar cycle 23
Authors: Shahin, Amaal Abd-Alla; Gopalswamy, N.; Yashiro, S.; Akiyama,
S.; Makela, P.; Xie, H.; Jung, H.
2009shin.confE.126S Altcode:
In a study on the interaction between CHs and ICMEs during the
declining phase of solar cycle 23, Gopalswamy et al., (2009) showed
that coronal holes (CHs) act as a magnetic wall that constrains the
CME propagation. The CME trajectories are significantly affected when
the eruptions occur in close proximity to CHs. Here, we extend this
study to the rise phase of cycle 23. We consider the disk center CMEs
(central meridian distance ?15o) that produced interplanetary shocks
near Earth. We compute the influence of the CHs as a fictitious force
that depends on the CH area, the distance between the CH and the
eruption region, and the magnetic field within the CH at photospheric
level. We compare the fictitious force acting on the CMEs to see if
the appearance of the interplanetary counterparts of CMEs (ICMEs)
is affected by the CHs.
---------------------------------------------------------
Title: Flux Rope CMEs Associated with Total and Partial Eruptive
Prominences
Authors: Xie, Hong; Gilbert, H.; Gopalswamy, N.; St Cyr, O. C.
2009shin.confE.168X Altcode:
We present a statistical study involving 17 flux rope coronal mass
ejections (CMEs) associated with 1) total eruptive prominence (TEP)
and 2) partial eruptive prominence (PEP), observed by STEREO A and B. A
flux rope model in conjunction with 3D triangulations has been used
to reconstruct the 3D structures and determine the actual speeds of
CMEs. The origins and the dynamic evolution of the CMEs are investigated
using COR1 and COR2 coronagraphic images and EUVI images. Among the
17 CMEs, 29% (5 of 17) are associated with TEPs, 71% (12 of 17)
are associated with PEPs, and 58 % (7 of 12) are associated with
both the X-line magnetic structures and PEPs. It is the first direct
observations of the X-line structures in EUV images. For comparison,
we also study 7 flare related CMEs, which occurred during January 2007
- June 2008,;a CME is classified as a flare CME only when an A-class
(or above) X-ray flare is reported by GOES. The mean actual speeds
for TEP-CMEs, PEP-CMEs, X_line-CMEs, and flare CMEs are 404 km/s,
255 km/s, 276 km/s, and 909 km/s respectively. It is found that the
mean speed of TEP-CMEs is greater than that of PEP-CMEs but smaller
than that of flare-CMEs. In addition, we found that there is a good
anti- correlation between mass and speed among the 17 EP-CMEs with
correlation coefficient r = -0.63. However, no such correlation exists
among the 7 flare-CMEs. The results of this study are preliminary and
we intend to extend this work for a larger number of events.
---------------------------------------------------------
Title: Numerical simulation of interchange reconnection based on
the May 12, 1997 CME event
Authors: Cohen, Ofer; Schwadron, Nathan; Crooker, Nancy; Owens,
Mathew; Gombosi, Tamas; Connick, D. E.; St Cyr, O. C.; Gopalswamy,
N.; Yashiro, S.; Xie, H.
2009shin.confE.184C Altcode:
We perform a high-resolution MHD simulation of the May 12, 1997 CME
event. We focus on the detailed three-dimensional evolution of the
coronal magnetic field as the CME propagates through. Our goal is
to identify interchange reconnection events between the CME and the
ambient field and in particular, we try to quantify the the change in
the distribution of the open magnetic flux due to the interaction of
magnetic flux carried by the CME with the ambient open flux.
---------------------------------------------------------
Title: Erratum to “Solar sources and geospace consequences of
interplanetary magnetic clouds observed during solar cycle 23—Paper
1” [J. Atmos. Sol.-Terr. Phys. 70(2-4) (2008) 245-253]
Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Michalek, G.;
Lepping, R. P.
2009JASTP..71.1005G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of Solar Active Regions and Their Relationship
with Solar Eruption: a Statistical Study
Authors: Liu, Yang; Akiyama, S.; Gopalswamy, N.; Mason, J.; Nitta,
N.; Tylka, A.; Yashiro, S.; Yurchyshyn, V.
2009SPD....40.0920L Altcode:
Using magnetograms taken by SOHO/MDI, we have calculated some parameters
for solar active regions, and explored possible relationships between
them and solar eruptions. The parameters of active regions we studied
are magnetic flux, net flux, potential field energy, orientation
and separation. We also estimated decay index of magnetic field
overlying the neutral line, and the configuration of ambient field
under which the active region sits. The data used were taken from
1996 to 2005. With these results as a reference, we studied the active
regions that produced the large solar energetic particle (SEP) events,
or produced ground level enhancement (GLE) events. Comparison is also
made between the active regions that produced full eruption and confine
eruption (based on an event list published by Yashiro et al 2005, JGR,
11012S05Y). We present our results here, together with a discussion.
---------------------------------------------------------
Title: Coronal mass ejections and space weather
Authors: Gopalswamy, N.
2009cwse.conf...77G Altcode:
Solar energetic particles (SEPs) and geomagnetic storms are the
two primary space weather consequences of coronal mass ejections
(CMEs) and their interplanetary counterparts (ICMEs). I summarize the
observed properties of CMEs and ICMEs, paying particular attention to
those properties that determine the ability of CMEs in causing space
weather. Then I provide observational details of two the central issues:
(i) for producing geomagnetic storms, the solar source location and
kinematics along with the magnetic field structure and intensity are
important, and (ii) for SEPs, the shock-driving ability of CMEs, the
Alfven speed in the ambient medium, and the connectivity to Earth are
crucial parameters
---------------------------------------------------------
Title: Halo coronal mass ejections and geomagnetic storms
Authors: Gopalswamy, Nat
2009EP&S...61..595G Altcode: 2009EP&S...61L.595G
In this letter, I show that the discrepancies in the geoeffectiveness of
halo coronal mass ejections (CMEs) reported in the literature arise due
to the varied definitions of halo CMEs used by different authors. In
particular, I show that the low geoeffectiveness rate is a direct
consequence of including partial halo CMEs. The geoeffectiveness of
partial halo CMEs is lower because they are of low speed and likely
to make a glancing impact on Earth.
---------------------------------------------------------
Title: The SOHO/LASCO CME Catalog
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Stenborg, G.;
Vourlidas, A.; Freeland, S.; Howard, R.
2009EM&P..104..295G Altcode: 2009EM&P..tmp....8G
Coronal mass ejections (CMEs) are routinely identified in the images
of the solar corona obtained by the Solar and Heliospheric Observatory
(SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO)
since 1996. The identified CMEs are measured and their basic attributes
are cataloged in a data base known as the SOHO/LASCO CME Catalog. The
Catalog also contains digital data, movies, and plots for each CME,
so detailed scientific investigations can be performed on CMEs and
the related phenomena such as flares, radio bursts, solar energetic
particle events, and geomagnetic storms. This paper provides a brief
description of the Catalog and summarizes the statistical properties
of CMEs obtained using the Catalog. Data products relevant to space
weather research and some CME issues that can be addressed using the
Catalog are discussed. The URL of the Catalog is: <ExternalRef>
<RefSource>http://cdaw.gsfc.nasa.gov/CME_list</RefSource>
<RefTarget Address="http://cdaw.gsfc.nasa.gov/CME_list"
TargetType="URL"/> </ExternalRef>.
---------------------------------------------------------
Title: Preface to the Proceedings of the European General Assembly
and the United Nations Workshop
Authors: Gopalswamy, N.; Eichhorn, G.; Sakurai, T.; Haubold, H. J.
2009EM&P..104..139G Altcode: 2009EM&P..tmp....4G
No abstract at ADS
---------------------------------------------------------
Title: Statistical relationship between solar flares and coronal
mass ejections
Authors: Yashiro, Seiji; Gopalswamy, Nat
2009IAUS..257..233Y Altcode:
We report on the statistical relationships between solar flares and
coronal mass ejections (CMEs) observed during 1996-2007 inclusively. We
used soft X-ray flares observed by the Geostationary Operational
Environmental Satellite (GOES) and CMEs observed by the Large Angle and
Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric
Observatory (SOHO) mission. Main results are (1) the CME association
rate increases with flare's peak flux, fluence, and duration, (2) the
difference between flare and CME onsets shows a Gaussian distribution
with the standard deviation σ = 17 min (σ = 15 min) for the first
(second) order extrapolated CME onset, (3) the most frequent flare site
is under the center of the CME span, not near one leg (outer edge) of
the CMEs, (4) a good correlation was found between the flare fluence
versus the CME kinetic energy. Implications for flare-CME models
are discussed.
---------------------------------------------------------
Title: Modeling and prediction of fast CME/shocks associated with
type II bursts
Authors: Xie, H.; Gopalswamy, N.; Cyr, O. C. St.
2009IAUS..257..489X Altcode:
A numerical simulation with ENLIL+Cone model was carried out to study
the propagation of the shock driven by the 2005 May 13 CME. We then
conducted a statistical analysis on a subset of similar events, where
a decameter-hectometric (DH) type II radio burst and a counterpart
kilometric type II have been observed to be associated with each CME
(DHkm CME). The simulation results show that fast CME-driven shocks
experienced a rapid deceleration as they propagated through the
corona and then kept a nearly constant speed traveling out into the
heliosphere. Two improved methods are proposed to predict the fast
CME-driven shock arrival time, which give the prediction errors of
3.43 and 6.83 hrs, respectively.
---------------------------------------------------------
Title: SEPs and CMEs during cycle 23
Authors: Mäkelä, Pertti; Gopalswamy, Nat; Yashiro, Seiji; Akiyama,
Sachiko; Xie, Hong; Valtonen, Eino
2009IAUS..257..475M Altcode:
We present a study of solar energetic particles (SEPs) in association
with coronal mass ejections (CMEs) and type II radio bursts. The
particle and CME observations cover the years 1996-2007. We find that
heavy-ion events in association with type II bursts and proton events
are produced in more western and most energetic CMEs. In addition,
the source distribution of type II associated proton events with heavy
ions reminds the source distribution expected for events with flare
particles. Therefore, the estimation of relative contributions by
flares and shocks in SEP events and separation of suggested different
particle acceleration models is complicated.
---------------------------------------------------------
Title: CME interactions with coronal holes and their interplanetary
consequences
Authors: Gopalswamy, N.; Mäkelä, P.; Xie, H.; Akiyama, S.;
Yashiro, S.
2009JGRA..114.0A22G Altcode: 2009JGRA..11400A22G
A significant number of interplanetary shocks (~17%) during cycle
23 were not followed by drivers. The number of such “driverless”
shocks steadily increased with the solar cycle with 15%, 33%, and
52% occurring in the rise, maximum, and declining phase of the solar
cycle. The solar sources of 15% of the driverless shocks were very
close the central meridian of the Sun (within ~15°), which is quite
unexpected. More interestingly, all the driverless shocks with their
solar sources near the solar disk center occurred during the declining
phase of solar cycle 23. When we investigated the coronal environment
of the source regions of driverless shocks, we found that in each case
there was at least one coronal hole nearby, suggesting that the coronal
holes might have deflected the associated coronal mass ejections (CMEs)
away from the Sun-Earth line. The presence of abundant low-latitude
coronal holes during the declining phase further explains why CMEs
originating close to the disk center mimic the limb CMEs, which normally
lead to driverless shocks due to purely geometrical reasons. We also
examined the solar source regions of shocks with drivers. For these,
the coronal holes were located such that they either had no influence on
the CME trajectories, or they deflected the CMEs toward the Sun-Earth
line. We also obtained the open magnetic field distribution on the
Sun by performing a potential field source surface extrapolation to
the corona. It was found that the CMEs generally move away from the
open magnetic field regions. The CME-coronal hole interaction must be
widespread in the declining phase and may have a significant impact
on the geoeffectiveness of CMEs.
---------------------------------------------------------
Title: Introduction to special section on Large Geomagnetic Storms
Authors: Gopalswamy, N.
2009JGRA..114.0A00G Altcode: 2009JGRA..11400A00G
Solar cycle 23 witnessed the accumulation of rich data sets that reveal
various aspects of geomagnetic storms in unprecedented detail both at
the Sun where the storm-causing disturbances originate and in geospace
where the effects of the storms are directly felt. During two recent
coordinated data analysis workshops (CDAWs) the large geomagnetic
storms (Dst <= -100 nT) of solar cycle 23 were studied in order to
understand their solar, interplanetary, and geospace connections. This
special section grew out of these CDAWs with additional contributions
relevant to these storms. Here I provide a brief summary of the results
presented in the special section.
---------------------------------------------------------
Title: Major solar flares without coronal mass ejections
Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.
2009IAUS..257..283G Altcode:
We examine the source properties of X-class soft X-ray flares that
were not associated with coronal mass ejections (CMEs). All the flares
were associated with intense microwave bursts implying the production
of high energy electrons. However, most (85%) of the flares were not
associated with metric type III bursts, even though open field lines
existed in all but two of the active regions. The X-class flares seem
to be truly confined because there was no material ejection (thermal
or nonthermal) away from the flaring region into space.
---------------------------------------------------------
Title: Universal processes in heliophysics
Authors: Davila, Joseph M.; Gopalswamy, Nat; Thompson, Barbara J.
2009IAUS..257...11D Altcode:
The structure of the Universe is determined primarily by the interplay
of gravity which is dominant in condensed objects, and the magnetic
force which is dominant in the rarefied medium between condensed
objects. Each of these forces orders the matter into a set of
characteristic structures each with the ability to store and release
energy in response to changes in the external environment. For the
most part, the storage and release of energy proceeds through a number
of Universal Processes. The coordinated study of these processes in
different settings provides a deeper understanding of the underlying
physics governing Universal Processes in astrophysics.
---------------------------------------------------------
Title: Universal Heliophysical Processes
Authors: Gopalswamy, N.; Webb, D. F.
2009IAUS..257.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evolution of the anemone AR NOAA 10798 and the related
geo-effective flares and CMEs
Authors: Asai, Ayumi; Shibata, Kazunari; Ishii, Takako T.; Oka,
Mitsuo; Kataoka, Ryuho; Fujiki, Ken'ichi; Gopalswamy, Nat
2009JGRA..114.0A21A Altcode: 2009JGRA..11400A21A; 2008arXiv0812.2063A
We present a detailed examination of the features of the active region
(AR) NOAA 10798. This AR generated coronal mass ejections (CMEs) that
caused a large geomagnetic storm on 24 August 2005 with the minimum Dst
index of -216 nT. We examined the evolution of the AR and the features
on/near the solar surface and in the interplanetary space. The AR
emerged in the middle of a small coronal hole, and formed a sea anemone
like configuration. Hα filaments were formed in the AR, which have
southward axial field. Three M class flares were generated, and the
first two that occurred on 22 August 2005 were followed by Halo-type
CMEs. The speeds of the CMEs were fast, and recorded about 1200 and
2400 km s<SUP>-1</SUP>, respectively. The second CME was especially
fast, and caught up and interacted with the first (slower) CME during
their travelings toward Earth. These acted synergically to generate
an interplanetary disturbance with strong southward magnetic field of
about -50 nT, which was followed by the large geomagnetic storm.
---------------------------------------------------------
Title: EUV Wave Reflection from a Coronal Hole
Authors: Gopalswamy, N.; Yashiro, S.; Temmer, M.; Davila, J.; Thompson,
W. T.; Jones, S.; McAteer, R. T. J.; Wuelser, J. -P.; Freeland, S.;
Howard, R. A.
2009ApJ...691L.123G Altcode:
We report on the detection of EUV wave reflection from a coronal
hole, as observed by the Solar Terrestrial Relations Observatory
mission. The EUV wave was associated with a coronal mass ejection
(CME) erupting near the disk center. It was possible to measure the
kinematics of the reflected waves for the first time. The reflected
waves were generally slower than the direct wave. One of the important
implications of the wave reflection is that the EUV transients are
truly a wave phenomenon. The EUV wave reflection has implications for
CME propagation, especially during the declining phase of the solar
cycle when there are many low-latitude coronal holes.
---------------------------------------------------------
Title: The Expansion and Radial Speeds of Coronal Mass Ejections
Authors: Gopalswamy, N.; Dal Lago, A.; Yashiro, S.; Akiyama, S.
2009CEAB...33..115G Altcode:
We show the relation between radial (V_{rad}) and expansion (V_{exp})
speeds of coronal mass ejections (CMEs) depends on the CME width. As
CME width increases, {V_{rad}/V_{exp}} decreases from a value >1
to <1. For widths approaching 180°, the ratio approaches 0 if the
cone has a flat base, while it approaches 0.5 if the base has a bulge
(ice cream cone). The speed difference between the limb and disk halos
and the spherical expansion of super fast CMEs can be explained by
the width dependence.
---------------------------------------------------------
Title: On the Characteristics of Shocks driven by limb CMEs
Authors: Xie, H.; Gopalswamy, N.; Stcyr, C.
2008AGUFMSH23B1650X Altcode:
We investigate the characteristics of bow shocks driven by limb
CMEs near the Sun, including speed, width, compression ratio, and
the relationshipof the standoff distance with CME size (the radius
of curvature of a CME) and shock Mach number. We choose a subset of
limb CMEs with distinct association of the decameter- hectometric (DH)
type II burst, which is a good evidence of the existence CME-driven
shock. The DH spectral domain corresponds to plasma frequencies within
the field view of the SOHO/LASCO coronagraphs. Choosing limb events
has several advantages: 1) there is no projection effects for CME
speed measurements, 2) it is easier to determine the width of a CME
and the front bow shock, 3) there is high confidence level for the
plasma density determination from the white-light CME brightness. By
studying the shock stand off distance and compression ratio, we obtain
the shock Mach number and the Alfven speed profile in the corona.
---------------------------------------------------------
Title: Difference Between Magnetic Clouds and Non-cloud Ejecta in
the Interplanetary Medium
Authors: Gopalswamy, N.
2008AGUFMSH22A..01G Altcode:
Solar cycle 23 has witnessed the accumulation of data on an
unprecedented number of coronal mass ejections (CMEs) at the Sun and in
the interplanetary (IP) medium, thanks to the large array of spaceborne
observatories such as SOHO, Wind, and ACE. These observations have
helped us make significant progress on the structure and evolution of
CMEs in the inner heliosphere. One important question is whether the
magnetic cloud (MC) and non-cloud ejecta have any difference in their
solar origin. The ubiquitous nature of post-eruption arcades suggests
that there should not be any difference. However, CMEs associated
with MCs all originate from very close to the solar disk center
(both in latitude and longitude). To zeroth order, the non-cloud
ejecta seem to originate at larger central meridian distances
(CMDs). In the extreme case of shocks without discernible ejecta,
the corresponding CMEs have their solar sources near the limb. These
observations suggest that whether one observes a flux rope (MC) or
not depends mainly on the location of the observer with respect to the
Sun-Earth line. Observations from solar cycle 23 indicate that there
are significant deviations from the zeroth order picture, especially
for non-cloud ejecta and the "driverless shocks": their solar sources
near the disk center. The question is whether these ejecta do not have
flux-rope structure by birth or they somehow got deflected away from the
Sun-Earth line by other large- scale structures in the IP medium. The
latter seems to be true for at least a subset of events, which seems to
be affected by coronal holes located between the eruption center and
the Sun-Earth line. This needs to be checked for all the events that
deviate from the zeroth order picture. Charge-state signatures of MCs
and non-cloud ejecta also support such a picture: the solar sources of
IP CMEs with high charge states seem to originate close to the disk
center, similar to the MC-associated CMEs. Another piece of evidence
comes from the high correspondence between halo CMEs and MCs, both of
which are highly geoeffective. Halo CMEs originating at larger CMDs
produce geomagnetic storms via their sheath fields, again pointing to
the importance of geometry. Contrary to importance of internal structure
of CMEs for geoeffectiveness, the production of gradual solar energetic
particle (SEP) should not depend on the internal structure of CMEs if
the particles are accelerated by CME-driven shocks. In fact, there is
a significant difference in the source distribution of SEP-producing
CMEs (western sources) and MC CMEs (close to disk center). This paper
illustrates these results using coronal and IP data.
---------------------------------------------------------
Title: Relation between Coronal Mass Ejection, Type II Radio Burst,
and EUV Wave during the 2008 March 25 STEREO Event
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Freeland, S.;
Thompson, W. T.; Davila, J. M.; Howard, R. A.; Kaiser, M. L.; Bougeret,
J. -
2008AGUFMSH12A..02G Altcode:
STEREO and SOHO observations of the March 25, 2008 coronal mass ejection
(CME) provide an excellent opportunity to study its early evolution
from multiple view points. The CME was fast (980 km/s) and wide (112
degrees) from the east limb of the Sun as viewed by SOHO. The STEREO
spacecraft were separated by about 50 degrees, so the CME was a disk
event for the STEREO-behind spacecraft and a behind-the-limb event
for STEREO-ahead. The CME was associated with a well defined EUV wave
as observed by the STEREO/EUVI instrument, a metric type II burst,
and a multi-component type II burst observed by the STEREO/WAVES and
Wind/WAVES instruments. One of the important aspect of this CME is
that it was well observed by STEREO/SECCHI inner coronagraph (COR1)
when the metric type II burst was in progress, so we are able to obtain
the shock height with respect t the CME. This enabled us to infer the
connection the coronal shock driven by the CME (inferred from type II
burst) and the EUV wave. It appears that the EUV wave steepened into
a shock and produced the type II burst. The multiple components of
the type II burst were not harmonically related, so we examined the
circumstances of the eruption. CME was ejected in the region between
two streamers, so the CME-driven shock is likely to simultaneously
encounter high and low- density regions of the corona, thus producing
type II bursts at widely separated frequencies. This paper summarizes
these observations and explains how the CME, type II radio burst,
and EUV waves all fit together.
---------------------------------------------------------
Title: Outreach activities during the 2006 total solar eclipse
sponsored by the International Heliophysical Year
Authors: Rabello Soares, M. C.; Rabiu, A. B.; Gopalswamy, N.; Thompson,
B. J.; Davila, J. M.; Sobrinho, A. A.
2008AdSpR..42.1792R Altcode:
The International Heliophysical Year (IHY) is an international program
of scientific research to advance our understanding of the physical
processes that govern the Sun, Earth and heliosphere. It has a strong
educational component, linking research and education. Here, we describe
the outreach activities during the 2006 total solar eclipse sponsored
by IHY.
---------------------------------------------------------
Title: Conservation of open solar magnetic flux and the floor in
the heliospheric magnetic field
Authors: Owens, M. J.; Crooker, N. U.; Schwadron, N. A.; Horbury,
T. S.; Yashiro, S.; Xie, H.; St. Cyr, O. C.; Gopalswamy, N.
2008AGUFMSH12A..05O Altcode:
The near-Earth heliospheric magnetic field intensity, |B|, exhibits a
strong solar cycle variation, but returns to the same "floor" value each
solar minimum. The current minimum, however, has seen |B| drop below
previous minima, bringing in to question the existence of a floor, or
at the very least requiring a re-assessment of its value. In this study
we assume heliospheric flux consists of a constant open flux component
and a time-varying contribution from CMEs. In this scenario, the true
floor is |B| with zero CME contribution. Using observed CME rates over
the solar cycle, we estimate the "no-CME" |B| floor at ~4.2± 0.5 nT,
lower than previous floor estimates and below |B| observed this solar
minimum. We speculate that the drop in |B| observed this minimum may be
due to a persistently lower CME rate than the previous minimum, though
there are large uncertainties in the supporting observational data.
---------------------------------------------------------
Title: Solar connections of geoeffective magnetic structures
Authors: Gopalswamy, N.
2008JASTP..70.2078G Altcode:
Coronal mass ejections (CMEs) and high-speed solar wind streams
(HSS) are two solar phenomena that produce large-scale structures in
the interplanetary (IP) medium. CMEs evolve into interplanetary CMEs
(ICMEs) and the HSS result in corotating interaction regions (CIRs) when
they interact with preceding slow solar wind. This paper summarizes the
properties of these structures and describes their geoeffectiveness. The
primary focus is on the intense storms of solar cycle 23 because
this is the first solar cycle during which simultaneous, extensive,
and uniform data on solar, IP, and geospace phenomena exist. After
presenting illustrative examples of coronal holes and CMEs, I discuss
the internal structure of ICMEs, in particular the magnetic clouds
(MCs). I then discuss how the magnetic field and speed correlate in the
sheath and cloud portions of ICMEs. CME speed measured near the Sun also
has significant correlations with the speed and magnetic field strengths
measured at 1 AU. The dependence of storm intensity on MC, sheath, and
CME properties is discussed pointing to the close connection between
solar and IP phenomena. I compare the delay time between MC arrival
at 1 AU and the peak time of storms for the cloud and sheath portions
and show that the internal structure of MCs leads to the variations
in the observed delay times. Finally, we examine the variation of
solar-source latitudes of IP structures as a function of the solar
cycle and find that they have to be very close to the disk center.
---------------------------------------------------------
Title: Conservation of open solar magnetic flux and the floor in
the heliospheric magnetic field
Authors: Owens, M. J.; Crooker, N. U.; Schwadron, N. A.; Horbury,
T. S.; Yashiro, S.; Xie, H.; St. Cyr, O. C.; Gopalswamy, N.
2008GeoRL..3520108O Altcode:
The near-Earth heliospheric magnetic field intensity, |B|, exhibits
a strong solar cycle variation, but returns to the same “floor”
value each solar minimum. The current minimum, however, has seen |B|
drop below previous minima, bringing in to question the existence of a
floor, or at the very least requiring a re-assessment of its value. In
this study we assume heliospheric flux consists of a constant open
flux component and a time-varying contribution from CMEs. In this
scenario, the true floor is |B| with zero CME contribution. Using
observed CME rates over the solar cycle, we estimate the “no-CME”
|B| floor at ~4.0 +/- 0.3 nT, lower than previous floor estimates and
below |B| observed this solar minimum. We speculate that the drop in
|B| observed this minimum may be due to a persistently lower CME rate
than the previous minimum, though there are large uncertainties in
the supporting observational data.
---------------------------------------------------------
Title: International Heliophysical Year 2007: A Report from the
UN/NASA Workshop Bangalore, India, 27 November 1 December 2006
Authors: Davila, Joe; Gopalswamy, Nat; Thompson, Barbara; Haubold,
Hans J.
2008EM&P..103....9D Altcode: 2008EM&P..tmp...19D
The IHY Secretariat and the United Nations Basic Space Science
Initiative (UNBSSI) assist scientists and engineers from all over the
world in participating in the International Heliophysical Year (IHY)
2007. A major thrust of IHY/UNBSSI is to deploy arrays of small,
inexpensive instruments such as magnetometers, radio telescopes,
GPS receivers, all-sky cameras, etc. around the world to allow
global measurements of ionospheric and heliospheric phenomena. The
small instrument programme is envisioned as a partnership between
instrument providers and instrument hosts in developing nations. The
IHY/UNBSSI can facilitate the deployment of several of these networks
world-wide. Existing data bases and relevant software tools will
be identified to promote space science activities in developing
nations. Extensive data on space science have been accumulated by a
number of space missions. Similarly, long-term data bases are available
from ground-based observations. These data can be utilized in ways
different from originally intended for understanding the heliophysical
processes. This paper provides a comprehensive overview of IHY/UNBSSI,
its achievements, future plans, and outreach to the 192 Member States
of the United Nations as recorded in the UN/NASA workshop in India.
---------------------------------------------------------
Title: Coronal mass ejections, type II radio bursts, and solar
energetic particle events in the SOHO era
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Mäkelä, P.; Xie,
H.; Kaiser, M. L.; Howard, R. A.; Bougeret, J. L.
2008AnGeo..26.3033G Altcode:
Using the extensive and uniform data on coronal mass ejections (CMEs),
solar energetic particle (SEP) events, and type II radio bursts during
the SOHO era, we discuss how the CME properties such as speed, width
and solar-source longitude decide whether CMEs are associated with type
II radio bursts and SEP events. We discuss why some radio-quiet CMEs
are associated with small SEP events while some radio-loud CMEs are
not associated with SEP events. We conclude that either some fast and
wide CMEs do not drive shocks or they drive weak shocks that do not
produce significant levels of particle acceleration. We also infer
that the Alfvén speed in the corona and near-Sun interplanetary
medium ranges from <200 km/s to ~1600 km/s. Radio-quiet fast
and wide CMEs are also poor SEP producers and the association rate
of type II bursts and SEP events steadily increases with CME speed
and width (i.e. energy). If we consider western hemispheric CMEs,
the SEP association rate increases linearly from ~30% for 800 km/s
CMEs to 100% for ≥1800 km/s. Essentially all type II bursts in the
decametre-hectometric (DH) wavelength range are associated with SEP
events once the source location on the Sun is taken into account. This
is a significant result for space weather applications, because if a
CME originating from the western hemisphere is accompanied by a DH type
II burst, there is a high probability that it will produce an SEP event.
---------------------------------------------------------
Title: A comparison of coronal mass ejections identified by manual
and automatic methods
Authors: Yashiro, S.; Michalek, G.; Gopalswamy, N.
2008AnGeo..26.3103Y Altcode:
Coronal mass ejections (CMEs) are related to many phenomena
(e.g. flares, solar energetic particles, geomagnetic storms), thus
compiling of event catalogs is important for a global understanding
these phenomena. CMEs have been identified manually for a long time,
but in the SOHO era, automatic identification methods are being
developed. In order to clarify the advantage and disadvantage of the
manual and automatic CME catalogs, we examined the distributions of
CME properties listed in the CDAW (manual) and CACTus (automatic)
catalogs. Both catalogs have a good agreement on the wide CMEs
(width>120°) in their properties, while there is a significant
discrepancy on the narrow CMEs (width≤30°): CACTus has a larger
number of narrow CMEs than CDAW. We carried out an event-by-event
examination of a sample of events and found that the CDAW catalog
have missed many narrow CMEs during the solar maximum. Another
significant discrepancy was found on the fast CMEs (speed>1000
km/s): the majority of the fast CDAW CMEs are wide and originate from
low latitudes, while the fast CACTus CMEs are narrow and originate
from all latitudes. Event-by-event examination of a sample of events
suggests that CACTus has a problem on the detection of the fast CMEs.
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Title: Comment on “Prediction of the 1-AU arrival times of
CME-associated interplanetary shocks: Evaluation of an empirical
interplanetary shock propagation model” by K.-H. Kim et al.
Authors: Gopalswamy, N.; Xie, H.
2008JGRA..11310105G Altcode:
No abstract at ADS
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Title: Type II Radio Emission and Solar Energetic Particle Events
Authors: Gopalswamy, Nat
2008AIPC.1039..196G Altcode:
Type II radio bursts, solar energetic particle (SEP) events, and
interplanetary (IP) shocks all have a common cause, viz., fast and
wide (speed >=900 km/s and width >=60°)) coronal mass ejections
(CMEs). Deviations from this general picture are observed as (i) lack
of type II bursts during many fast and wide CMEs and IP shocks, (ii)
slow CMEs associated with type II bursts and SEP events, and (iii)
lack of SEP events during many type II bursts. I examine the reasons
for these deviations. I also show that ground level enhancement (GLE)
events are consistent with shock acceleration because a type II burst
is present in every event well before the release of GLE particles
and SEPs at the Sun.
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Title: Synthetic radio maps of CME-driven shocks below 4 solar radii
heliocentric distance
Authors: Schmidt, J. M.; Gopalswamy, N.
2008JGRA..113.8104S Altcode:
We present 2 1/2 D numerical MagnetoHydroDynamic (MHD) simulations of
coronal mass ejections (CMEs) in conjunction with plasma simulations
of radio emission from the CME-driven shocks. The CME-driven shock
extends to an almost spherical shape during the temporal evolution of
the CME. Our plasma simulations can reproduce the dynamic spectra
of coronal type II radio bursts, with the frequency drift rates
corresponding to the shock speeds. We find further, that the CME-driven
shock is an effective radio emitter at metric wavelengths, when the
CME has reached a heliocentric distance of about two solar radii
(?). We apply our simulation results to explain the radio images of
type II bursts obtained by radio heliographs, in particular to the
banana-shaped images of radio sources associated with fast CMEs.
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Title: Investigation of CME dynamics in the LASCO field of view
Authors: Shanmugaraju, A.; Moon, Y. -J.; Cho, K. -S.; Gopalswamy,
N.; Umapathy, S.
2008A&A...484..511S Altcode:
Context: The speed-distance profile of CMEs is important for
understanding the propagation of CMEs. <BR />Aims: Our main aim is
to study the initial speed of CMEs in the LASCO field of view and
its role in subsequent CME propagation using the acceleration-speed
profile. The secondary aim is to obtain the speed growth rate. <BR
/>Methods: We considered the height-time data of 307 CMEs observed by
SOHO/LASCO during January-March 2005. To study the CME speed profile,
we used only 116 events for which there were at least 10 height-time
measurements in the LASCO field of view. Using this data, we obtained
their initial speed, extrapolated initial speed, and growth rate. <BR
/>Results: The following results were found from this analysis. (i)
The initial speed obtained from the first two data points is in the
range 24-1208 km s<SUP>-1</SUP>, which is nearly similar to the
range of linear speed (67-920 km s<SUP>-1</SUP>) obtained from a
least squares fit through the entire h-t data set for each CME. (ii)
However, the initial speed or extrapolated initial speed is much
better correlated with acceleration and growth rate than the linear
speed. (iii) Nearly two thirds of the events (74/116) are found to be
accelerating. (iv) The speed growth rate is within the range -0.058
to 0.061 × 10<SUP>-3</SUP> s<SUP>-1</SUP>, and it decreases with the
distance. (v) The final observed distance in the LASCO field of view
depends very weakly upon the initial speed, or extrapolated initial
speed whereas it depends strongly on the linear speed. The above
results demonstrate the role played by the initial speed of the CMEs.
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Title: Plasma Radiation and Acceleration Effectiveness of CME-driven
Shocks
Authors: Gopalswamy, N.; Schmidt, J. M.
2008AGUSMSH41A..18G Altcode:
CME-driven shocks are effective radio radiation generators and
accelerators for Solar Energetic Particles (SEPs). We present simulated
3 D time-dependent radio maps of second order plasma radiation generated
by CME- driven shocks. The CME with its shock is simulated with the
3 D BATS-R-US CME model developed at the University of Michigan. The
radiation is simulated using a kinetic plasma model that includes
shock drift acceleration of electrons and stochastic growth theory of
Langmuir waves. We find that in a realistic 3 D environment of magnetic
field and solar wind outflow of the Sun the CME-driven shock shows a
detailed spatial structure of the density, which is responsible for
the fine structure of type II radio bursts. We also show realistic
3 D reconstructions of the magnetic cloud field of the CME, which
is accelerated outward by magnetic buoyancy forces in the diverging
magnetic field of the Sun. The CME-driven shock is reconstructed by
tomography using the maximum jump in the gradient of the entropy. In the
vicinity of the shock we determine the Alfven speed of the plasma. This
speed profile controls how steep the shock can grow and how stable
the shock remains while propagating away from the Sun. Only a steep
shock can provide for an effective particle acceleration.
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Title: Geoeffective Solar Activity: Coronal Mass Ejections, SEP
Events and Geomagnetic Storms Over Solar Cycle 23
Authors: M P; Gopalswamy, N.; Yashiro, S.; Akiyama, S.; Xie, H.;
Valtonen, E.
2008AGUSMSH43A..07M Altcode:
We present updated results for solar cycle 23 on coronal mass ejections
(CMEs) and solar energetic particle (SEP) events and their correlations
with solar sources and ensuing interplanetary disturbances and
geomagnetic storms. The main data set consists of observations over
the years 1996--2007 by the LASCO coronagraph and the ERNE particle
detector, both on board the SOHO spacecraft. We study the properties
of CMEs and the associated geomagnetic storms and the evolution of the
properties during solar cycle 23. Especially we are interested with
CMEs that are both geoeffective and SEPeffective. Special emphasis will
be given to halo CMEs which are the most likely CMEs to be geoeffective.
---------------------------------------------------------
Title: Effects of solar wind dynamic pressure and preconditioning
on large geomagnetic storms
Authors: Xie, H.; Gopalswamy, N.; Stcyr, C.; Yashiro, S.
2008AGUSMSM31C..02X Altcode:
We investigate the effects of solar wind dynamic pressure, Pdyn, and
preconditioning in 88 large magnetic storms occurring during solar
cycle 23. We have developed an improved model of the Dst profile,
based on a modified Burton equation, where additional effects of
Pdyn and diminished Dst pressure-correction have been taking into
account. On the average, our model predicts the Dst peak values within
9% of observations and gives an overall RMS error of 11%, which is an
improvement over those models whose injection functions only depend on
the solar wind electric field. The results demonstrate that there is
an increase in the Dst peak value when there is a large enhancement
of Pdyn during the main phase of a storm. The average increase of
the storm intensity is estimated to be 26% for 15 storms with the max
(Pdyn) > 15 nPa. We find that the preconditioning in multi-step Dst
storms plays no significant role in strengthening the storm intensity,
but increases the storm duration.
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Title: Properties of Coronal Holes Associated With Large Geomagnetic
Storms
Authors: Akiyama, S.; Gopalswamy, N.; Yashiro, S.
2008AGUSMSP51A..15A Altcode:
We study the characteristics of 11 equatorial coronal holes (CHs),
which resulted in large (minimum Dst index < - 100 nT) geomagnetic
storms in the interval 1996 to 2005. These storms were part of the
Living with a Star (LWS) Coordinated Data-Analysis Workshop (CDAW)
held in March 2005. Using 17 GHz microwave images obtained by the
Nobeyama Radio Heliograph (NoRH) and EUV images obtained by the
Extreme-ultraviolet Imaging Telescope (EIT), we find the EUV CH area
and the CH radio enhancement area are linearly correlated with the solar
wind speed. The solar wind speed is also related to the flux expansion
factor obtained as the ratio between areas of radio enhancement and EUV
CH. We study the temporal sequences of the solar wind parameters and
show that the time of CH central meridian passage, peak total magnetic
field strength, peak temperature, and peak speed are delayed by -2.5,
0.1, 0.6, 1.1 days from the time of peak CIR density, respectively.
---------------------------------------------------------
Title: Heating and Kinematics of an Eruptive Prominence Associated
with a Fast Coronal Mass Ejection
Authors: Gopalswamy, N.; Yashiro, S.; Shibasaki, K.
2008AGUSMSH31C..07G Altcode:
The fast (1800 km/s) coronal mass ejection (CME) on 2005 July 27
had a bright bubble-shaped prominence core observed by the Nobeyama
Radioheliograph (NoRH) in microwaves (17 and 34 GHz), TRACE at 171 A,
and the Extreme-ultraviolet Imaging Telescope (EIT) on board SOHO. NoRH
has the largest field of view among the non- white light instruments,
so the prominence could be tracked until it reached a height of about
0.75 solar radii from the limb. The prominence remained optically thick
at both 17 and GHz, even though it was significantly heated. Comparison
with TRACE observations suggest that the prominence was heated in
individual fibers within the prominence, making it multi-thermal
plasma. The prominence maintained its overall shape as it entered into
the field of view of SOHO/LASCO coronagraphs with a speed of about 1400
km/s, so the height-time history could be studied over a distance of
more than 20 solar radii from the Sun. NoRH data indicated that the
initial acceleration was extremely high (about1.4 km/s/s). During the
slow-rise phase of the prominence, EUV loops overlying the prominence
also moved out, which when combines with CME leading-edge measurements
from LASCO/C2 yielded an acceleration of about 300 m/s/s. This was
comparable to the average acceleration of the prominence over the same
height range. When we consider the just the LASCO field of view, both
the prominence core and the CME leading edge showed deceleration, but to
vastly different extents (-32 m/s/s for the CME leading edge compared to
-3 m/s/s for the prominence core). Our preliminary conclusion is that
the prominence was insulated from interacting with the non-CME ambient
medium, which might explain the weaker slowing down of the prominence.
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Title: Poor CME Productivity in Active Region 10960
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.
2008AGUSMSH31A..03Y Altcode:
Larger flares are generally likely to be associated with coronal mass
ejections (CMEs), but there are some CME- poor active regions, which
produce many large flares without associated CMEs. We present once such
active region NOAA 10960, which produced 10 M-class flares during the
disk passage. We examined their CME associations using coronagraph
observations obtained by LASCO on SOHO and SECCHI on STEREO. The
three coronagraph observations help us to determine whether or not
a flare has the associated CME. We found that two out of 10 M-class
flares were associated with the CMEs. The rate (20%) is low compared
to the average CME association rate (50%) of M-class flares during the
solar cycle 23. In addition, the associated CMEs are slow (337 km/s
and 208 km/s); further strengthening the conclusion that AR 10960 is
CME-poor. We consider various possibilities to explain why the active
region is CME-poor.
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Title: Space Weather Application Using Projected Velocity Asymmetry
of Halo CMEs
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.
2008SoPh..248..113M Altcode: 2008arXiv0801.1977M; 2008SoPh..tmp...24M
Halo coronal mass ejections (HCMEs) originating from regions close
to the center of the Sun are likely to be responsible for severe
geomagnetic storms. It is important to predict geoeffectiveness of HCMEs
by using observations when they are still near the Sun. Unfortunately,
coronagraphic observations do not provide true speeds of CMEs because
of projection effects. In the present paper, we present a new technique
to allow estimates of the space speed and approximate source location
using projected speeds measured at different position angles for a
given HCME (velocity asymmetry). We apply this technique to HCMEs
observed during 2001 - 2002 and find that the improved speeds are
better correlated with the travel times of HCMEs to Earth and with
the magnitudes of ensuing geomagnetic storms.
---------------------------------------------------------
Title: Average Thickness of Magnetosheath Upstream of Magnetic Clouds
at 1 AU versus Solar Longitude of Source
Authors: Lepping, R. P.; Wu, C. -C.; Gopalswamy, N.; Berdichevsky,
D. B.
2008SoPh..248..125L Altcode: 2008SoPh..tmp...35L
Starting with a large number (N=100) of Wind magnetic clouds (MCs)
and applying necessary restrictions, we find a proper set of N=29
to investigate the average ecliptic plane projection of the upstream
magnetosheath thickness as a function of the longitude of the solar
source of the MCs, for those cases of MCs having upstream shock waves. A
few of the obvious restrictions on the full set of MCs are the need for
there to exist a driven upstream shock wave, knowledge of the MC's solar
source, and restriction to only MCs of low axial latitudes. The analysis
required splitting this set into two subsets according to average
magnetosheath speed: slow/average (300 - 500 km s<SUP>−1</SUP>) and
fast (500 - 1100 km s<SUP>−1</SUP>) speeds. Only the fast set gives
plausible results, where the estimated magnetosheath thickness (ΔS)
goes from 0.042 to 0.079 AU (at 1 AU) over the longitude sector of 0°
(adjusted source-center longitude of the average magnetic cloud) to
40° off center (East or West), based on N=11 appropriate cases. These
estimates are well determined with a sigma (σ) for the fit of 0.0055
AU, where σ is effectively the same as \sqrt{} (chi-squared) for the
appropriate quadratic fit. The associated linear correlation coefficient
for ΔS versus |Longitude| was very good (c.c.=0.93) for the fast
range, and ΔS at 60° longitude is extrapolated to be 2.7 times the
value at 0°. For the slower speeds we obtain the surprising result
that ΔS is typically more-or-less constant at 0.040±0.013 AU at all
longitudes, indicating that the MC as a driver, when moving close to
the normal solar wind speed, has little influence on magnetosheath
thickness. In some cases, the correct choice between two candidate
solar-source longitudes for a fast MC might be made by noting the value
of the observed ΔS just upstream of the MC. Also, we point out that,
for the 29 events, the average sheath speed was well correlated with
the quantity ΔV[=(«V<SUB>MC</SUB>»−«V<SUB>UPSTREAM</SUB>»)],
and also with both «V<SUB>MC</SUB>» and «V<SUB>MC,T</SUB>», where
«V<SUB>MC</SUB>» is the first one-hour average of the MC speed,
«V<SUB>MC,T</SUB>» is the average MC speed across the full MC,
and «V<SUB>UPSTREAM</SUB>» is a five-hour average of the solar wind
speed just upstream of the shock.
---------------------------------------------------------
Title: Effects of solar wind dynamic pressure and preconditioning
on large geomagnetic storms
Authors: Xie, H.; Gopalswamy, N.; St. Cyr, O. C.; Yashiro, S.
2008GeoRL..35.6S08X Altcode:
We investigate the effects of solar wind dynamic pressure, P <SUB>
dyn </SUB>, and preconditioning in 88 large magnetic storms (Dst
< -100 nT) occurring during solar cycle 23. We have developed an
improved model of the Dst profile, based on a modified Burton equation,
where additional effects of P <SUB> dyn </SUB> and diminished Dst
pressure-correction have been taking into account. On the average,
our model predicts the Dst peak values within 9% of observations
and gives an overall RMS error of 11%, which is an improvement over
those models whose injection functions only depend on the solar wind
electric field. The results demonstrate that there is an increase
in the Dst peak value when there is a large enhancement of P <SUB>
dyn </SUB> during the main phase of a storm. The average increase of
the storm intensity is estimated to be 26% for 15 storms with the max
(P <SUB> dyn </SUB>) > 15 nPa. We find that the preconditioning in
multi-step Dst storms plays no significant role in strengthening the
storm intensity, but increases the storm duration.
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Title: Radio-Quiet Fast and Wide Coronal Mass Ejections
Authors: Gopalswamy, N.; Yashiro, S.; Xie, H.; Akiyama, S.;
Aguilar-Rodriguez, E.; Kaiser, M. L.; Howard, R. A.; Bougeret, J. -L.
2008ApJ...674..560G Altcode:
We report on the properties of radio-quiet (RQ) and radio-loud (RL)
coronal mass ejections (CMEs) that are fast and wide (FW). RQ CMEs
lack type II radio bursts in the metric and decameter-hectometric (DH)
wavelengths. RL CMEs are associated with metric or DH type II bursts. We
found that ~40% of the FW CMEs from 1996 to 2005 were RQ. The RQ CMEs
had an average speed of 1117 km s<SUP>-1</SUP> compared to 1438 km
s<SUP>-1</SUP> for the RL, bracketing the average speed of all FW CMEs
(1303 km s<SUP>-1</SUP>). The fraction of full halo CMEs (apparent width
= 360°) was the largest for the RL CMEs (60%), smallest for the RQ CMEs
(16%), and intermediate for all FW CMEs (42%). The median soft X-ray
flare size for the RQ CMEs (C6.9) was also smaller than that for the RL
CMEs (M3.9). About 55% of RQ CMEs were back sided, while the front-sided
ones originated close to the limb. The RL CMEs originated generally on
the disk with only ~25% being back sided. The RQ FW CMEs suggest that
the Alfvén speed in the low-latitude outer corona can often exceed
1000 km s<SUP>-1</SUP> and can vary over a factor of >=3. None of
the RQ CMEs was associated with large solar energetic particle events,
which is useful information for space weather applications.
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Title: Solar sources and geospace consequences of interplanetary
magnetic clouds observed during solar cycle 23
Authors: Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Michalek, G.;
Lepping, R. P.
2008JASTP..70..245G Altcode:
We present results of a statistical investigation of 99 magnetic
clouds (MCs) observed during 1995-2005. The MC-associated coronal mass
ejections (CMEs) are faster and wider on the average and originate
within ±30o from the solar disk center. The solar sources of MCs also
followed the butterfly diagram. The correlation between the magnetic
field strength and speed of MCs was found to be valid over a much
wider range of speeds. The number of south-north (SN) MCs was dominant
and decreased with solar cycle, while the number of north-south (NS)
MCs increased confirming the odd-cycle behavior. Two-thirds of MCs
were geoeffective; the Dst index was highly correlated with speed
and magnetic field in MCs as well as their product. Many (55%) fully
northward (FN) MCs were geoeffective solely due to their sheaths. The
non-geoeffective MCs were slower (average speed ), had a weaker
southward magnetic field (average ), and occurred mostly during the
rise phase of the solar activity cycle.
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Title: Spatial Relationship between Solar Flares and Coronal Mass
Ejections
Authors: Yashiro, S.; Michalek, G.; Akiyama, S.; Gopalswamy, N.;
Howard, R. A.
2008ApJ...673.1174Y Altcode: 2007arXiv0710.3054Y
We report on the spatial relationship between solar flares and coronal
mass ejections (CMEs) observed during 1996-2005 inclusive. We identified
496 flare-CME pairs considering limb flares (distance from central
meridian >=45°) with soft X-ray flare size >=C3 level. The CMEs
were detected by the Large Angle and Spectrometric Coronagraph (LASCO)
on board the Solar and Heliospheric Observatory (SOHO). We investigated
the flare positions with respect to the CME span for the events with
X-class, M-class, and C-class flares separately. It is found that
the most frequent flare site is at the center of the CME span for all
the three classes, but that frequency is different for the different
classes. Many X-class flares often lie at the center of the associated
CME, while C-class flares widely spread to the outside of the CME
span. The former is different from previous studies, which concluded
that no preferred flare site exists. We compared our result with the
previous studies and conclude that the long-term LASCO observation
enabled us to obtain the detailed spatial relation between flares and
CMEs. Our finding calls for a closer flare-CME relationship and supports
eruption models typified by the CSHKP magnetic reconnection model.
---------------------------------------------------------
Title: Origin of Geoeffective Coronal Mass Ejections during Solar
Cycle 23
Authors: Gopalswamy, Nat
2008cosp...37.1057G Altcode: 2008cosp.meet.1057G
The importance of coronal mass ejections (CMEs) in causing major
geomagnetic storms has been well established in the 1990s due to the
southward magnetic field contained in the sheath and ejecta portions
of the interplanetary (IP) counterparts of CMEs (or ICMEs). The nice
ordering of the internal structure of ICMEs revealed by in situ
observations (shock followed by sheath and ejecta with or without
flux rope structure) is far from clear at the Sun because the remote
sensing technique reveals only the mass content of the CME rather
than the magnetic properties. Nevertheless, there have been several
attempts to relate the internal structure of CMEs to the magnetic
properties of the source active regions on the Sun. For example,
the filament marking the polarity inversion lines have been shown
to be in the same direction as the axis of the flux rope observed
in the IP medium. Such a correspondence is supported by the close
relationship found between post eruption arcades at the Sun and the
IP magnetic clouds (i.e., flux ropes). However, not all ICMEs or flux
ropes, which may very well be an observational effect. The number of
ICMEs with flux rope structure observed near Earth varies with the
solar cycle and there are indications that the global magnetic field
of the Sun and the active region field have varying contribution in
deciding the magnetic properties of ICMEs. The sheath is most likely
related to the global field of the Sun, while the ejecta is related
to the active region magnetic field. The sheath is created by the
ejecta portion as it compresses the overlying global field. We are
still not in a position to resolve the sheath and ejecta portions
of CMEs near the Sun, especially in those heading towards Earth and
causing geomagnetic storms. Nevertheless, CME observations can help
us infer the strength and orientation of the magnetic field in ICMEs,
which are key parameters deciding the occurrence and strength of
geomagnetic storms. This paper summarizes the current developments in
the understanding of the CME-ICME relationship using the complete data
sets on CMEs, ICMEs, and geomagnetic storms over one complete solar
cycle that just ended in December 2007.
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Title: Width of Radio-Loud and Radio-Quiet CMEs
Authors: Michalek, G.; Gopalswamy, N.; Xie, H.
2007SoPh..246..409M Altcode: 2007arXiv0710.4519M
In the present paper we report on the difference in angular sizes
between radio-loud and radio-quiet CMEs. For this purpose we compiled
these two samples of events using Wind/WAVES and SOHO/LASCO observations
obtained during 1996 - 2005. We show that the radio-loud CMEs are almost
twice as wide as the radio-quiet CMEs (considering expanding parts of
CMEs). Furthermore, we show that the radio-quiet CMEs have a narrow
expanding bright part with a large extended diffusive structure. These
results were obtained by measuring the CME widths in three different
ways.
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Title: A Statistical Study of the Ejecta - Shock Standoff Distance
of Geoeffective Events
Authors: Lara, A.; Gopalswamy, N.; Yashiro, S.; Borgazzi, A. I.
2007AGUFMSH31A0236L Altcode:
e study the interplanetary transport of 57 coronal mass ejections
(CMEs), which are part of the events responsible for large geomagnetic
storms of solar cycle 23 listed in the CDAW database. The interplanetary
counterparts of these CMEs (ICMEs) were shock-driving and have caused
intense (Dst < -100) geomagnetic storms. We study the statistical
behavior of the standoff distance and time between the ICME and
the shock. We divided our events into two groups, 1) events where
there is likely a one-to-one relationship between the CMEs and ICMEs
(unique events) and 2) events where multiple CMEs may be associated
with a single ICME. We find that the standoff time of the unique events
follows a normal distribution whit a mean of 7.6 hr. and a sigma σ =
4.7 hr. The standoff distance of unique events also follows a normal
distribution with a mean of ~ 0.1 AU and a sigma of ~ 0.05 AU. We did
not found any relationship between the position of the AR,associated
to the low coronal CME activity, and the standoff distance. On the
other hand there seems to be a linear relationship between the CME
speed and the standoff distance.
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Title: Prediction of Space Weather Using an Asymmetric Cone Model
for Halo CMEs
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.
2007SoPh..246..399M Altcode: 2007arXiv0710.4372M
Halo coronal mass ejections (HCMEs) are responsible of the most
severe geomagnetic storms. A prediction of their geoeffectiveness
and travel time to Earth's vicinity is crucial to forecast space
weather. Unfortunately, coronagraphic observations are subjected
to projection effects and do not provide true characteristics of
CMEs. Recently, Michalek (Solar Phys.237, 101, 2006) developed an
asymmetric cone model to obtain the space speed, width, and source
location of HCMEs. We applied this technique to obtain the parameters
of all front-sided HCMEs observed by the SOHO/LASCO experiment during
a period from the beginning of 2001 until the end of 2002 (solar cycle
23). These parameters were applied for space weather forecasting. Our
study finds that the space speeds are strongly correlated with the
travel times of HCMEs to Earth's vicinity and with the magnitudes
related to geomagnetic disturbances.
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Title: Synoptic Solar Radio Burst Source Directions Derived by the
Ulysses URAP Investigation
Authors: MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Hess, R. A.;
Reiner, M. J.; Hoang, S.
2007AGUFMSH41A0308M Altcode:
The Unified Radio and Plasma (URAP) investigation is one of 10
instruments on the Ulysses spacecraft. Ulysses, with its highly inclined
orbit around the sun, provides URAP with a unique perspective on solar
radio bursts, which are usually emitted at low heliolatitudes as the
electron sources move outward from the sun. These radio bursts provide
positional information relating to interplanetary coronal mass ejections
(type II radio bursts), the initiation of CMEs (type III-L bursts), and
solar flares (type III bursts). In this presentation, we use the routine
radio direction-finding data from URAP to track radio bursts and locate
their sources when Ulysses is near perihelion. Plots of these data are
available on the URAP Goddard Space Flight Center web site (for example,
http://urap.gsfc.nasa.gov/cgi/giffer?date=20070726&PLOT_TYPE=
DIRFIND), as are ASCII data files. The results shown are derived
from fitting the spin-plane antenna data only; we compare the
source directions so derived to the more accurate determinations
made by fitting to both URAP antennas. The accuracy of the radio
source directions to identify flare locations, determine solar wind
densities remotely, etc., will be compared to previously published
determinations. Applications to Wind Waves and STEREO Waves data,
for which the spacecraft are in-ecliptic, will be addressed briefly.
---------------------------------------------------------
Title: A Catalog of Halo Coronal Mass Ejections from SOHO
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Xie, H.; Vourlidas,
A.; Howard, R. A.; Schmidt, J.
2007AGUFMSH51A0262G Altcode:
Halo coronal mass ejections (CMEs) have become one of the important
subsets of CMEs, thanks to the extensive data accumulated by the Solar
and Heliospheric Observatory (SOHO) mission. Halo CMEs are inherently
more energetic on the average, so they are important for producing
geomagnetic storms and solar energetic particle events (Gopalswamy et
al., 2007). One of the key aspects halo CMEs is their source location,
which decides whether the halo is symmetric or not. When the source
is closer to the solar limb, the CMEs tend to become asymmetric halos
or partial halos. Halos with their sources nearer to the limb are also
the fastest (because of projection effects), but are less geoeffective
due to the glancing blow they deliver to Earth's magnetosphere. Thus,
providing source information to all halo CMEs in a separate catalog is
useful information in selecting candidate geoeffective CMEs. The second
important quantity of CMEs is the space speed, which decides the arrival
time of CMEs at Earth. Since CMEs change their width during their early
evolution, it is not easy to correct for the projection effects from the
geometry of eruption. One way of correcting for projection effects is to
use a cone model for CMEs. There are at least 3 published cone models,
all of them seem to remove the projection effects reasonably well. The
geometric parameters of the cone are determined using different methods
in each model. Here we use the model by Xie et al. (2004), which has
generally less restrictions, and hence can be applied to more number
of halos. This paper provides a brief description of the catalog of
halo CMEs, which resides at the CDAW Data Center, NASA Goddard Space
Flight Center, Greenbelt, MD. The catalog enhances the existing data
services at the CDAW Data Center, which participates in the Virtual
Solar Observatory. Work supported by NASA's Virtual Observatories for
Solar and Space Physics Data Program. References Gopalswamy et al.,
JGR, 112, A06112, doi:10.1029/2006JA012149, 2007 Xie et al. JGR, 109,
A03109, doi: 10.1029/2003JA010226, 2004
---------------------------------------------------------
Title: Synthetic Radio Maps of CMEs up to 24 Solar Radii Heliocentric
Distance
Authors: Schmidt, J. M.; Gopalswamy, N.
2007AGUFMSH23B..01S Altcode:
We present numerical MagnetoHydroDynamic (MHD) simulations of coronal
mass ejections (CMEs) and plasma simulations of radio emission from
the CME-driven shocks. The simulations correspond to an idealized
system, where rotational symmetry around the rotation axis of the Sun
is assumed. So the CME has a flux rope structure that extends like a
torus around the symmetry axis, i.e. no geometrical effects due to a
connection of footpoints of the flux rope with the solar surface are
considered. The CME-driven shock extends to an almost spherical shape
during the temporal evolution of the CME. We find that our simulations
can reproduce the dynamic spectra of coronal radio type II bursts, where
the frequency drift rates correspond to the CME-driven shock speeds. We
find further, that the CME-driven shock is an effective radio emitter at
metric wavelengths, when the CME has reached a heliocentric distance of
about two solar radii (R\odot). Towards the center of the CME, where the
plasma emission frequency drops significantly due to an over expansion
of the core of the CME, the emission is eclipsed for a fixed frequency
radio receiver. We apply our simulation results to explain the radio
images of type II bursts obtained by radio heliographs, in particular
to the banana-shaped images of radio sources associated with fast
CMEs. The shock at the rear part of the CME can become an effective
radio emitter, where reconnection of magnetic field lines leads to
enhanced gradients of magnetic fields. Yet, this emission is usually at
lower frequencies than that at the shock front. We apply our kinetic
and analytic model of plasma radiation further to MHD simulations of
CMEs in 3D. The differences between the 3D and 2D cases are discussed.
---------------------------------------------------------
Title: Division II / Working Group International Collaboration in
Space Weather
Authors: Webb, David F.; Gopalswamy, Nat; Liu, William; Sibeck,
David G.; Schmieder, Brigitte; Wang, Jingxiu; Wang, Chi
2007IAUTB..26..107W Altcode:
The IAU Division II WG on International Collaboration in Space Weather
has as its main goal to help coordinate the many activities related to
space weather at an international level. The WG currently includes
the international activities of the International Heliospheric
Year (IHY), the International Living with a Star (ILWS) program,
the CAWSES (Climate and Weather of the Sun-Earth System) Working
Group on Sources of Geomagnetic Activity, and Space Weather Studies
in China. The coordination of IHY activities within the IAU is led
by Division II under this working group. The focus of this half-day
meeting was on the activities of the IHY program. About 20 people
were in attendance. The Chair of the WG, David F. Webb, gave a brief
introduction noting that the meeting would have two parts: first, a
session on IHY activities emphasizing IHY Regional coordination and,
second, a general discussion of the other programs of the WG involving
international Space Weather activities.
---------------------------------------------------------
Title: Correction to “Solar and interplanetary sources of major
geomagnetic storms (Dst <= -100 nT) during 1996-2005”
Authors: Zhang, J.; Richardson, I. G.; Webb, D. F.; Gopalswamy, N.;
Huttunen, E.; Kasper, J.; Nitta, N. V.; Poomvises, W.; Thompson,
B. J.; Wu, C. -C.; Yashiro, S.; Zhukov, A. N.
2007JGRA..11212103Z Altcode:
<A href="/journals/ja/ja0712/2007JA012891/">Abstract Available</A>
from <A href="http://www.agu.org">http://www.agu.org</A>
---------------------------------------------------------
Title: Solar and interplanetary sources of major geomagnetic storms
(Dst <= -100 nT) during 1996-2005
Authors: Zhang, J.; Richardson, I. G.; Webb, D. F.; Gopalswamy, N.;
Huttunen, E.; Kasper, J. C.; Nitta, N. V.; Poomvises, W.; Thompson,
B. J.; Wu, C. -C.; Yashiro, S.; Zhukov, A. N.
2007JGRA..11210102Z Altcode:
We present the results of an investigation of the sequence of
events from the Sun to the Earth that ultimately led to the 88 major
geomagnetic storms (defined by minimum Dst ≤ -100 nT) that occurred
during 1996-2005. The results are achieved through cooperative
efforts that originated at the Living with a Star (LWS) Coordinated
Data-Analysis Workshop (CDAW) held at George Mason University in
March 2005. On the basis of careful examination of the complete array
of solar and in situ solar wind observations, we have identified
and characterized, for each major geomagnetic storm, the overall
solar-interplanetary (solar-IP) source type, the time, velocity, and
angular width of the source coronal mass ejection (CME), the type and
heliographic location of the solar source region, the structure of the
transient solar wind flow with the storm-driving component specified,
the arrival time of shock/disturbance, and the start and ending times
of the corresponding IP CME (ICME). The storm-driving component,
which possesses a prolonged and enhanced southward magnetic field
(B<SUB>s</SUB>), may be an ICME, the sheath of shocked plasma (SH)
upstream of an ICME, a corotating interaction region (CIR), or a
combination of these structures. We classify the Solar-IP sources
into three broad types: (1) S-type, in which the storm is associated
with a single ICME and a single CME at the Sun; (2) M-type, in which
the storm is associated with a complex solar wind flow produced by
multiple interacting ICMEs arising from multiple halo CMEs launched
from the Sun in a short period; (3) C-type, in which the storm is
associated with a CIR formed at the leading edge of a high-speed stream
originating from a solar coronal hole (CH). For the 88 major storms,
the S-type, M-type, and C-type events number 53 (60%), 24 (27%), and 11
(13%), respectively. For the 85 events for which the surface source
regions could be investigated, 54 (63%) of the storms originated in
solar active regions, 11 (13%) in quiet Sun regions associated with
quiescent filaments or filament channels, and 11 (13%) were associated
with coronal holes. Remarkably, nine (11%) CME-driven events showed no
sign of eruptive features on the surface or in the low corona (e.g.,
no flare, no coronal dimming, and no loop arcade, etc.), even though
all the available solar observations in a suitable time period were
carefully examined. Thus while it is generally true that a major
geomagnetic storm is more likely to be driven by a frontside fast
halo CME associated with a major flare, our study indicates a broad
distribution of source properties. The implications of the results
for space weather forecasting are briefly discussed.
---------------------------------------------------------
Title: Energetic Phenomena on the Sun
Authors: Gopalswamy, Nat
2007AIPC..919..275G Altcode:
Solar flares, coronal mass ejections (CMEs), solar energetic particles
(SEPs), and fast solar wind represent the energetic phenomena on the
Sun. Flares and CMEs originate from closed magnetic field structures
on the Sun typically found in active regions and quiescent filament
regions. On the other hand, fast solar wind originates from open field
regions on the Sun, identified as coronal holes. Energetic particles
are associated with flares, CMEs, and fast solar wind, but the ones
associated with CMEs are the most intense. The energetic phenomena have
important consequences in the heliosphere and contribute significantly
to adverse space weather. This paper provides an over view of the
energetic phenomena on the Sun including their origin interplanetary
propagation and space weather consequences.
---------------------------------------------------------
Title: The Early Life Of A Coronal Mass Ejection From SECCHI And
SOHO Observations
Authors: Gopalswamy, N.; Yashiro, S.; Davila, J. M.; Howard, R. A.;
SECCHI/COR1 Team
2007AAS...210.2813G Altcode: 2007BAAS...39..324G
One of the key advantages of STEREO/SECCHI is the inner coronagraph
(COR1), which can observe CMEs in the coronal region where CMEs
attain their maximum acceleration. The first CME observed by COR1
was on 2006 December 30. The CME was also observed by the C2 and C3
coronagraphs of SOHO. We compare the morphological and height-time
histories between COR1 and SOHO/LASCO data. We find that the flux
rope structure evolves significantly between the COR1 and LASCO/C2
FOVs, although we can track features to get a continuous height-time
history of the CME. We find excellent agreement between the two sets
of data which could be combined to obtain the kinematic properties
of the CME. We also superposed a STEREO/COR1 image of the CME on a
STEREO/EUVI image and SOHO/C2 image to compare the solar origin and
morphology. The CME originated from the southwest quadrant of the Sun
and was of flux-rope type moving with an average speed of 200 km/s and
an acceleration of 6 m/s/s, with a characteristic two-ribbon structure
and an extended post-eruption arcade. In addition to the similarity in
CME features, there was excellent correspondence between the outlying
streamers in the two coronagraph images.
---------------------------------------------------------
Title: Geoeffectiveness of halo coronal mass ejections
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2007JGRA..112.6112G Altcode: 2007JGRA..11206112G
We studied the geoeffectiveness, speed, solar source, and flare
association of a set of 378 halo coronal mass ejections (CMEs) of cycle
23 (1996-2005, inclusive). We compiled the minimum Dst values occurring
within 1-5 days after the CME onset. We compared the distributions of
such Dst values for the following subsets of halo CMEs: disk halos
(within 45 deg from disk center), limb halos (beyond 45 degrees but
within 90 deg from disk center), and backside halo CMEs. Defining that a
halo CME is geoeffective if it is followed by Dst ≤ -50 nT, moderately
geoeffective if -50 nT < Dst < -100 nT, and strongly geoeffective
if Dst ≤ -100 nT, we find that the disk halos are followed by strong
storms, limb halos are followed by moderate storms, and backside halos
are not followed by significant storms. The Dst distribution for a
random sample is nearly identical to the case of backside halos. About
71% of all frontside halos are geoeffective, supporting the high rate
of geoeffectiveness of halo CMEs. A larger fraction (75%) of disk halos
are geoeffective. Intense storms are generally due to disk halos and
the few intense storms from limb halos occur only in the maximum and
declining phases. Most intense storms occur when there are successive
CMEs. The delay time between CME onset and minimum Dst value is the
smallest for limb halos, suggesting that the sheath is geoeffective
in these cases. The geoeffectiveness rate has prominent dips in 1999
and 2002 (the beginning and end years of the solar maximum phase). The
numbers of all frontside and geoeffective frontside halos show a triple
peak structure similar to the number of intense geomagnetic storms. The
difference in flare sizes among geoeffective and nongeoeffective halos
is not significant. The nongeoeffective CMEs are generally slower
and have more easterly or limbward solar sources compared to the
geoeffective ones; source location and speed are the most important
parameters for geoeffectiveness.
---------------------------------------------------------
Title: Why Some Fast and Wide Coronal Mass Ejections are Radio-quiet?
Authors: Gopalswamy, N.; Xie, H.; Aguilar-Rodriguez, E.; Akiyama,
S.; Yashiro, S.; Kaiser, M. L.; Howard, R. A.; Bougeret, J. L.
2007AAS...210.5801G Altcode: 2007BAAS...39..167G
The radio-quiet CMEs lack type II radio burst association in the
metric and decameter-hectometric (DH) wavelengths. We compiled CMEs
faster than 900 km/s and wider than 60 degrees and checked against
metric and interplanetary type II bursts and found that about
one third of them were radio-quiet. We compared the radio-quiet
CMEs with the radio-loud ones occurring over the same study period
(1996-2005). The radio-quiet and radio-loud CMEs had average speeds
of 1129 and 1524 km/s, respectively bracketing the average speed of
all FW CMEs (1303 km/s). The width distributions also showed a similar
behavior: the fraction of halo and partial halo CMEs was the largest
for the radio-loud CMEs (54%), smallest for the radio-quiet CMEs
(18%) and intermediate for all fast and wide CMEs (42%). The majority
of radio-quiet CMEs (55%) were back-sided; most of the frontsided
ones also originated close to the limb. This is in contrast to the
radio-loud CMEs which originated generally on the disk with only
a small fraction (13%) was back-sided. The average flare size was
also slightly smaller for the radio-quiet CMEs compared to that of
radio-loud CMEs. Back-sided and limb CMEs have only part of the shock
surface visible to the observer. This seems to be an important factor
deciding whether a CME is radio quiet.
---------------------------------------------------------
Title: IHY - An International Cooperative Program
Authors: Rabello-Soares, M. Cristina; Davila, J.; Gopalswamy, N.;
Thompson, B.
2007AAS...210.5701R Altcode: 2007BAAS...39..167R
The International Heliophysical Year (IHY) in 2007/2008 involves
thousands of scientists representing over 70 nations. It consists
of four distinct elements that will be described here. <P />Taking
advantage of the large amount of heliophysical data acquired routinely
by a vast number of sophisticated instruments aboard space missions and
at ground-based observatories, IHY aims to develop the basic science of
heliophysics through cross-disciplinary studies of universal processes
by means of Coordinated Investigation Programs (CIPs). <P />The second
component is in collaboration with the United Nations Basic Space
Science Initiative (UNBSSI) and consists of the deployment of arrays of
small, inexpensive instruments such as magnetometers, radio antennas,
GPS receivers, etc. around the world to provide global measurements. An
important aspect of this partnership is to foster the participation
of developing nations in heliophysics research. <P />IHY coincides
with the commemoration of 50 years of the space age that started with
launch of Sputnik on October 4, 1957 and it is on the brink of a new
age of space exploration where the Moon, Mars and the outer planets
will be the focus of the space programs in the next years. As a result,
it presents an excellent opportunity to create interest for science
among young people with the excitement of discovery of space. The
education and outreach program forms another cornerstone of IHY. <P
/>Last but not least, an important part of the IHY activities, its
forth component, is to preserve the history and memory of IGY 1957.
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Melrose, Donald B.; Klimchuk, James A.; Benz, A. O.; Craig,
I. J. D.; Gopalswamy, N.; Harrison, R. A.; Kozlovsky, B. Z.; Poletto,
G.; Schrijver, K. J.; van Driel-Gesztelyi, L.; Wang, J. -X.
2007IAUTA..26...75M Altcode:
Commission 10 aims at the study of various forms of solar activity,
including networks, plages, pores, spots, fibrils, surges, jets,
filaments/prominences, coronal loops, flares, coronal mass ejections
(CMEs), solar cycle, microflares, nanoflares, coronal heating etc.,
which are all manifestation of the interplay of magnetic fields and
solar plasma. Increasingly important is the study of solar activities
as sources of various disturbances in the interplanetary space
and near-Earth "space weather".Over the past three years a major
component of research on the active Sun has involved data from the
RHESSI spacecraft. This review starts with an update on current and
planned solar observations from spacecraft. The discussion of solar
flares gives emphasis to new results from RHESSI, along with updates on
other aspects of flares. Recent progress on two theoretical concepts,
magnetic reconnection and magnetic helicity is then summarized, followed
by discussions of coronal loops and heating, the magnetic carpet
and filaments. The final topic discussed is coronal mass ejections
and space weather.The discussions on each topic is relatively brief,
and intended as an outline to put the extensive list of references
in context.The review was prepared jointly by the members of the
Organizing Committee, and the names of the primary contributors to
the various sections are indicated in parentheses.
---------------------------------------------------------
Title: Properties of Interplanetary Coronal Mass Ejections
Authors: Gopalswamy, Nat
2007sdeh.book..145G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: International Heliophysical Year 2007: Basic space science
initiatives
Authors: Davila, Joe; Gopalswamy, Nat; Haubold, Hans J.; Thompson,
Barbara
2007SpPol..23..121D Altcode:
The UN Office for Outer Space Affairs, through the IHY Secretariat
and the United Nations Basic Space Science Initiative (UNBSSI),
assists scientists and engineers world-wide to participate in
the International Heliophysical Year (IHY) 2007. A major thrust of
IHY/UNBSSI is to deploy arrays of small, inexpensive instruments such
as magnetometers, radio telescopes, GPS receivers, all-sky cameras,
etc. around the world to allow global measurements of ionospheric and
heliospheric phenomena. The small instrument program is envisioned
as a partnership between instrument providers and instrument hosts
in developing nations, with the former providing the instruments,
the host nation the manpower, facilities and operational support,
typically at a local university. Funds are not available through
IHY/UNBSSI to build the instruments; these must be obtained through the
normal proposal channels. All instrument operational support for local
scientists, facilities, data acquisition, etc. will be provided by the
host nation. The IHY/UNBSSI can facilitate the deployment of several
of these networks and existing databases and relevant software tools
will be identified to promote space science activities in developing
nations. Extensive data on space science have been accumulated
by a number of space missions. Similarly, long-term databases are
available from ground-based observations. These data can be utilized
in ways different from those originally intended for understanding the
heliophysical processes. This report provides an overview of IHY/UNBSSI,
its achievements, future plans and outreach to the 192 member states
of the United Nations.
---------------------------------------------------------
Title: The United Nations Basic Space Science Initiative for IHY 2007
Authors: Gopalswamy, Nat; Davila, Joseph; Thompson, Barbara; Haubold,
Hans
2007IAUSS...5..295G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scientific Justification For The Low- Frequency Radio
Measurements By The Solar Orbiter Mission
Authors: Gopalswamy, N.; MacDowall, R. J.; Kaiser, M. L.; Bale, S. D.;
Maksimovic, M.; Bougeret, J. -L.
2007ESASP.641E..66G Altcode:
The importance of the radio measurements in the frequency range 1-14
MHz has been demonstrated only recently by the Radio and Plasma Wave
(WAVES) Experiment on board Wind. The shock-related radio emission
below 14 MHz originates from a heliocentric distance beyond 2 solar
radii in association with coronal mass ejections. Although several
issues on the origin of shocks and their connection to solar eruptions
have been clarified by the SOHO-Wind synergistic observations, some
of them remain mainly because of lack of radio imaging and/or in situ
observations at the shock source. The Solar Orbiter mission will be able
to address these issues by directly sampling the shock at a location
where the radio emission originates to provide measurements of physical
parameters for direct comparison with theory and modelling. We highlight
some of the science issues that can be addressed by a radio and plasma
wave analyzer on board the Solar Orbiter mission in combination with
in situ measurements close to the Sun.
---------------------------------------------------------
Title: The United Nations Basic Space Science Initiative: the
TRIPOD concept
Authors: Kitamura, Masatoshi; Wentzel, Don; Henden, Arne; Bennett,
Jeffrey; Al-Naimiy, H. M. K.; Mathai, A. M.; Gopalswamy, Nat; Davila,
Joseph; Thompson, Barbara; Webb, David; Haubold, Hans
2007IAUSS...5..277K Altcode: 2006physics..10149K
Since 1990, the United Nations is annually holding a workshop on
basic space science for the benefit of the worldwide development of
astronomy. Additional to the scientific benefits of the workshops and
the strengthening of international cooperation, the workshops lead to
the establishment of astronomical telescope facilities through the
Official Development Assistance (ODA) of Japan. Teaching material,
hands-on astrophysics material, and variable star observing programmes
had been developed for the operation of such astronomical telescope
facilities in an university environment. This approach to astronomical
telescope facility, observing programme, and teaching astronomy has
become known as the basic space science TRIPOD concept. Currently,
a similar TRIPOD concept is being developed for the International
Heliophysical Year 2007, consisting of an instrument array, data taking
and analysis, and teaching space science.
---------------------------------------------------------
Title: The CME-productivity associated with flares from two active
regions
Authors: Akiyama, S.; Yashiro, S.; Gopalswamy, N.
2007AdSpR..39.1467A Altcode:
We report on two flare-productive adjacent active regions (ARs),
with different levels of coronal mass ejection (CME) association. AR
10039 and AR 10044 produced strong X-ray flares during their disk
passages. We examined the CME association rate of X-ray flares and
found it to be different between the two ARs. AR 10039 was CME-rich
with 72% association with flares, while AR 10044 was CME-poor with an
association rate of only 14%. CMEs from the CME-rich AR were faster
and wider than the ones from the CME-poor AR. The flare activity of AR
10044 was temporally concentrated over a short interval and spatially
localized over a compact area between the major sun spots. We suggest
that different pre-eruption evolution and magnetic configuration in
the two regions might have contributed to the difference between the
two ARs.
---------------------------------------------------------
Title: Energetic Particles Related with Coronal and Interplanetary
Shocks
Authors: Gopalswamy, N.
2007LNP...725..139G Altcode:
Acceleration of electrons and ions at the Sun is discussed in the
framework of CME-driven shocks. Based on the properties of coronal
mass ejections associated with type II bursts at various wavelengths,
the possibility of a unified approach to the type II phenomena is
suggested. Two aspects of primary importance to shock accelerations are:
(1) Energy of the driving CME and (2) the conditions in the medium
that supports shock propagation. The high degree of overlap between
CMEs associated with large solar energetic particle events and type II
bursts occurring at all wavelengths underscores the importance of CME
energy in driving shocks far into the interplanetary medium. Presence
of preceding CMEs can alter the conditions in the ambient medium, which
is shown to influence the intensity of large solar energetic particle
events. Both statistical evidence and case studies are presented that
underscore the importance of the ambient medium.
---------------------------------------------------------
Title: The International Heliophysical Year
Authors: Davila, Joseph M.; Gopalswamy, Nat; Thompson, Barbara J.
2007RoAJ...17....3D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio Observatory for Lunar Sortie Science (ROLSS)
Authors: MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Demaio,
L. D.; Lazio, J.; Weiler, K. W.; Bale, S. D.; Burns, J. O.; Jones,
D. L.; Kasper, J. C.; Reiner, M. J.
2006AGUFMSM43A1476M Altcode:
It is widely recognized that the lunar surface is an ideal
base for radio astronomy observations at frequencies below the
terrestrial ionospheric cutoff frequency. The ionospheric cutoff
(10-20 MHz) prevents observations of very low frequency radio
sources outside the ionosphere from being conducted by ground-based
observatories. Spacecraft or lunar-based observatories are the only
alternative, with the lunar surface providing the real estate for
establishing radio arrays with large dimensions (tens of kilometers)
to perform high resolution imaging at the lowest frequencies (< 10
MHz). In this presentation, we describe a concept study for a pathfinder
radio observatory to be deployed during a lunar sortie. The concept
study focuses on appropriate antenna, receiver, deployment, power,
and communication systems for the observatory. These systems must be
low mass to permit the lunar sortie package to maximize science and
engineering goals. Power requirements for the receiver systems and
the downlink to Earth must also be minimized. The concept study also
addresses in detail the science goals of this observatory, which include
observations of solar radio bursts as proxies of solar and heliospheric
particle acceleration, detailed measurement of the lunar ionosphere
scale height as a function of time, integrated spectra of strong
(extragalactic) sources to probe particle acceleration processes,
and a survey of natural and man-made emissions from the Earth. These
observations will enhance our understanding of the various radio
sources and the lunar observing environment and pave the way for future
larger-scale lunar radio astronomy arrays.
---------------------------------------------------------
Title: Investigating the state of the Sun-Earth system during extreme
events: First science results of a worldwide online conference series
Authors: Kozyra, J. U.; Shibata, K.; Fox, N. J.; Basu, S.; Coster,
A. J.; Davila, J. M.; Gopalswamy, N.; Liou, K.; Lu, G.; Mann, I. R.;
Pallamraju, D.; Paxton, L. J.; Peterson, W. K.; Talaat, E. R.;
Weatherwax, A. T.; Young, C. A.; Zanetti, L. J.
2006AGUFMSA43A..01K Altcode:
This presentation reports on new science results from an online
conference entitled "Return to the Auroral Oval for the Anniversary
of the IGY" designed to bring together researchers worldwide: (1)
to investigate newly reported features in the auroral oval during
substorms that occur in the main phase of superstorms and how these
features map throughout geospace, (2) to explore implications for the
state of the geospace system, (3) to identify signatures associated
with this geospace state from equatorial to polar latitudes,
(4) to investigate the unusual aspects of the solar sources, and
(5) to understand how propagation from Sun to Earth modified the
observed solar drivers. The main focus of the first conference is on
worldwide data exchange, the construction of global data products and
assimilative global views, and identifying coupled chains of events
from sun-to-Earth. The collaborative conference data products and
enhanced understanding of the observed features of the events will
form the basis for a follow-on conference in 2007 focused primarily
on theoretical studies and collaborative simulation efforts between
modeling groups, observers and data analysts. This conference is the
first in a series of sun-Earth connection online conferences, sponsored
by CAWSES, IHY, eGY, ICESTAR, NASA/LWS, and NSF Atmospheric Science
Programs, and designed to bring interdisciplinary researchers together
with the vast developing cyber-infrastructure of large international
data sets, high performance computing and advanced visualizations to
address grand challenge science issues in a way not previously possible.
---------------------------------------------------------
Title: Relationships Among Magnetic Clouds, CMES, and Geomagnetic
Storms
Authors: Wu, C. C.; Lepping, R. P.; Gopalswamy, N.
2006SoPh..239..449W Altcode: 2006SoPh..tmp...93W
During solar cycle 23, 82 interplanetary magnetic clouds (MCs) were
identified by the Magnetic Field Investigation (MFI) team using Wind
(1995 - 2003) solar wind plasma and magnetic field data from solar
minimum through the maximum of cycle 23. The average occurrence rate is
9.5 MCs per year for the overall period. It is found that some of the
anomalies in the frequency of occurrence were during the early part
of solar cycle 23: (i) only four MCs were observed in 1999, and (ii)
an unusually large number of MCs (17 events) were observed in 1997,
just after solar minimum. We also discuss the relationship between
MCs, coronal mass ejections (CMEs), and geomagnetic storms. During the
period 1996 - 2003, almost 8000 CMEs were observed by SOHO-LASCO. The
occurrence frequency of MCs appears to be related neither to the
occurrence of CMEs as observed by SOHO LASCO nor to the sunspot
number. When we included "magnetic cloud-like structures" (MCLs,
defined by Lepping, Wu, and Berdichevsky, 2005), we found that the
occurrence of the joint set (MCs + MCLs) is correlated with both
sunspot number and the occurrence rate of CMEs. The average duration
of the MCL structures is ~40% shorter than that of the MCs. The MCs
are typically more geoeffective than the MCLs, because the average
southward field component is generally stronger and longer lasting in
MCs than in MCLs. In addition, most severe storms caused by MCs/MCLs
with Dst<SUB>min</SUB>≤ −100 nT occurred in the active solar period.
---------------------------------------------------------
Title: Consequences of Coronal Mass Ejections in the Heliosphere
Authors: Gopalswamy, N.
2006SunGe...1b...5G Altcode: 2006SunGe...1....5G
Coronal mass ejections (CMEs) are the most energetic events in the
heliosphere. They carry large amounts of coronal magnetic fields and
plasma with them and drive large-scale interplanetary shocks. The CMEs
and shock have significant consequences at various locations in the
heliosphere, including the production of intense geomagnetic storms and
large energetic particle events. CMEs form merged interaction regions
in the heliosphere, which act as magnetic barriers for the galactic
cosmic rays entering the heliosphere. After a brief summary of the
observed properties of CMEs at the Sun, I discuss the properties
of the interplanetary CMEs (ICMEs) and their connection to shocks,
radio bursts, solar energetic particles and the modulation of galactic
cosmic rays.
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Title: Radio Observations of Solar Eruptions
Authors: Gopalswamy, N.
2006spnr.conf...81G Altcode:
Coronal mass ejections (CMEs) are composed of multithermal plasmas,
which make them produce different radio signatures at different
wavelengths. The prominence core of CMEs are of the lowest temperature
and hence optically thick at microwave frequencies and hence are
readily observed. The Nobeyama Radioheliograph has exploited this fact
and observed a large number of prominence eruptions over most of solar
cycle 23 and parts of cycle 22. This paper reviews recent studies on
prominence eruptions and their contributions for understanding the
CME phenomenon. In particular, the following issues are discussed:
(i) the statistical and physical relationship between CMEs and the
radio prominence eruptions, and how this relationship manifests as a
function of the solar cycle; (ii) The asymmetry of prominence eruptions
between northern and southern hemispheres; (iii) the relationship
between prominence eruptions and CME cores; (iv) the implications of
the cessation of high-latitude PEs before the reversal of the global
solar magnetic field, and (v) the implications of the high-latitude
PEs and CMEs for the modulation of galactic cosmic rays. Finally,
the importance of the Nobeyama Radioheliograph data to future missions
such as STEREO and Solar-B are discussed.
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Title: General Discussion on Donor Programs
Authors: Gopalswamy, N.
2006ihy..workE..88G Altcode:
No abstract at ADS
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Title: Coronal Mass Ejections in the Heliosphere
Authors: Gopalswamy, N.
2006ihy..workE..46G Altcode:
Coronal mass ejections (CMEs) are the most energetic events in the
heliosphere. They carry large amounts of coronal magnetic fields and
plasma with them and driving large-scale interplanetary shocks. The
CMEs and shock have significant consequences at various locations in the
heliosphere, including the production of intense geomagnetic storms and
large energetic particle events. CMEs form merged interaction regions
in the heliosphere, which act as magnetic barriers for the galactic
cosmic rays entering the heliosphere. After a brief summary of the
observed properties of CMEs at the Sun, I discuss the properties
of the interplanetary CMEs (ICMEs) and their connection to shocks,
radio bursts, solar energetic particles and modulation of galactic
cosmic rays.
---------------------------------------------------------
Title: General Discussion on Donor Programs N. Gopalswamy
Authors: Gopalswamy, N.
2006ihy..workE..86G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IHY-CAWSES Data base
Authors: Young, C. A.; Thompson, B. J.; Davila, J.; Gopalswamy, N.
2006ihy..workE..90Y Altcode:
In partnership with the CAWSES (Climate And Weather of the Sun-Earth
System) program, IHY is sponsoring a series of Virtual Workshops
and a special IHY/CAWSES database to provide virtual access of data
collected for IHY and CAWSES campaigns. The first of the virtual
workshops occurred November 13-17, 2006, and had more than 200 online
participants. Online presentation and discussion tools are being
refined for future workshops. The IHY/CAWSES database provides a means
of entering data into the Virtual Solar Observatory (to provide the
maximum and easiest possible access to the data) while still maintaining
a close connection to the other data sets used in IHY/CAWSES activities.
---------------------------------------------------------
Title: General Discussion on Donor Programs
Authors: Gopalswamy, N.
2006ihy..workE..87G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IHY/UNBSS Program: Success Stories
Authors: Gopalswamy, N.; Davila, J.; Thompson, B. J.; Haubold, H. J.
2006ihy..workE..15G Altcode:
The United Nations Office for Outer Space Affairs, through the IHY
secretariat and the United Nations Basic Space Science Initiative
(UNBSSI) is assisting scientists and engineers from all over the world
in participating in the International Heliophysical Year (IHY) 2007. A
major thrust of the IHY/UNBSSI program is to deploy arrays of small,
inexpensive instruments such as magnetometers, radio telescopes, GPS
receivers, etc. around the world to provide global measurements of
ionospheric and heliospheric phenomena. The small instrument program
is a partnership between instrument providers, and instrument hosts in
developing countries. The lead scientist will provide the instruments
(or fabrication plans for instruments) in the array; the host country
will provide manpower, facilities, and operational support to obtain
data with the instrument typically at a local university. Existing data
bases and relevant software tools can be identified to promote space
science activities in developing countries. Extensive data on space
science have been accumulated by a number of space missions. Similarly,
long-term data bases are available from ground based observations. These
data can be utilized in ways different from originally intended for
understanding the heliophysical processes. This paper provides an
overview of the IHY/UNBSS program, its achievements and future plans.
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Title: Improved input to the empirical coronal mass ejection (CME)
driven shock arrival model from CME cone models
Authors: Xie, H.; Gopalswamy, N.; Ofman, L.; St. Cyr, O. C.; Michalek,
G.; Lara, A.; Yashiro, S.
2006SpWea...410002X Altcode:
We study the Sun-Earth travel time of interplanetary shocks driven
by coronal mass ejections (CMEs) using empirical cone models. Three
different cone models have been used to obtain the radial speeds of
the CMEs, which are then used as input to the empirical shock arrival
(ESA) model to obtain the Sun to Earth travel time of the shocks. We
compare the predicted and observed shock transit times and find that
the accuracy of the ESA model is improved by applying CME radial speeds
from the cone models. There are two ways of calculating the shock travel
time: using the ESA model or using the simplified ESA formula obtained
by an exponential fit to the ESA model. The average mean error in the
travel time with the cone model speeds is 7.8 hours compared to 14.6
hours with the sky plane speed, which amounts to an improvement of
46%. With the ESA formula, the corresponding mean errors are 9.5 and
11.7 hours, respectively, representing an improvement of 19%. The cone
models minimize projection effects and hence can be used to obtain
CME radial speeds. When input to the ESA model, the large scatter in
the shock travel time is reduced, thus improving CME-related space
weather predictions.
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Title: Solar Eruptions and Energetic Particles: An Introduction
Authors: Gopalswamy, N.; Mewaldt, R.; Torsti, J.
2006GMS...165....1G Altcode:
This introductory article highlights current issues concerning
two related phenomena involving mass emission from the Sun: solar
eruptions and solar energetic particles. A brief outline of the
chapters is provided indicating how the current issues are addressed
in the monograph. The sections in this introduction roughly group the
chapters dealing with coronal mass ejections (CMEs), solar energetic
particles (SEPs), shocks, and space weather. The concluding remarks
include a brief summary of outstanding issues that drive current and
future research on CMEs and SEPs.
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Title: Coronal Mass Ejections and Type II Radio Bursts
Authors: Gopalswamy, Nat
2006GMS...165..207G Altcode:
The simultaneous availability of white light data on CMEs from the Solar
and Heliospheric Observatory (SOHO) and radio data on shock waves from
the Radio and Plasma Wave experiment on board the Wind spacecraft over
the past decade have helped in making rapid progress in understanding
the CME-driven shocks. I review some recent developments in the type
II-CME relationship, focusing on the properties of CMEs as shock drivers
and those of the medium supporting shock propagation. I also discuss
the solar cycle variation of the type II bursts in comparison with other
eruptive phenomena such as CMEs, flares, large solar energetic particle
events, and shocks detected in situ. The hierarchical relationship found
between the CME kinetic energy and wavelength range of type II radio
bursts, non-existence of CMEless type II bursts, and the explanation
of type II burst properties in terms of shock propagation with a
realistic profile of the fast mode speed suggest that the underlying
shocks are driven by CMEs, irrespective of the wavelength domain. Such
a unified approach provides an elegant understanding of the entire type
II phenomenon (coronal and interplanetary). The blast wave scenario
remains an alternative hypothesis for type II bursts only over a small
spatial domain (within one solar radius above the solar surface) that
is not accessible to in situ observation. Therefore the existence of
blast waves cannot be directly confirmed. CMEs, on the other hand,
can be remote sensed from this domain.
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Title: Different Power-Law Indices in the Frequency Distributions
of Flares with and without Coronal Mass Ejections
Authors: Yashiro, S.; Akiyama, S.; Gopalswamy, N.; Howard, R. A.
2006ApJ...650L.143Y Altcode: 2006astro.ph..9197Y
We investigated the frequency distributions of flares with and without
coronal mass ejections (CMEs) as a function of flare parameters (peak
flux, fluence, and duration of soft X-ray flares). We used CMEs observed
by the Large Angle and Spectrometric Coronagraph (LASCO) on board the
Solar and Heliospheric Observatory (SOHO) mission and soft X-ray flares
(C3.2 and above) observed by the Geostationary Operational Environmental
Satellite (GOES) during 1996-2005. We found that the distributions
obey a power law of the form dN/dX~X<SUP>-α</SUP>, where X is a
flare parameter and dN is the number of events recorded within the
interval [X, X+dX]. For the flares with (without) CMEs, we obtained
the power-law index α=1.98+/-0.05 (α=2.52+/-0.03) for the peak flux,
α=1.79+/-0.05 (α=2.47+/-0.11) for the fluence, and α=2.49+/-0.11
(α=3.22+/-0.15) for the duration. The power-law indices for flares
without CMEs are steeper than those for flares with CMEs. The larger
power-law index for flares without CMEs supports the possibility that
nanoflares contribute to coronal heating.
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Title: Properties and geoeffectiveness of halo coronal mass ejections
Authors: Michalek, G.; Gopalswamy, N.; Lara, A.; Yashiro, S.
2006SpWea...410003M Altcode: 2007arXiv0710.4526M
Halo coronal mass ejections (HCMEs) originating from regions close to
the center of the Sun are likely to be geoeffective. Assuming that the
shape of HCMEs is a cone and that the HCMEs propagate with constant
angular widths and velocities, at least in their early phase, we have
developed a technique which allowed us to obtain the space speed, width,
and source location. We apply this technique to obtain the parameters
of all full HCMEs observed by the Solar and Heliospheric Observatory
(SOHO) mission's Large Angle and Spectrometric Coronagraph (LASCO)
experiment until the end of 2002. Using this data, we examine which
parameters determine the geoeffectiveness of HCMEs. We show that in the
considered period of time, only fast halo CMEs (with space velocities
higher than ~1000 km/s) and originating from the Western Hemisphere
close to the solar center could cause intense geomagnetic storms. We
illustrate how the HCME parameters can be used for space weather
forecast. It is also demonstrated that the strength of a geomagnetic
storm does not depend on the determined width of HCMEs. This means that
HCMEs do not have to be very large to cause major geomagnetic storms.
---------------------------------------------------------
Title: Coronal Mass Ejections of Solar Cycle 23
Authors: Gopalswamy, Nat
2006JApA...27..243G Altcode:
I summarize the statistical, physical, and morphological properties
of coronal mass ejections (CMEs) of solar cycle 23, as observed by the
Solar and Heliospheric Observatory (SOHO) mission. The SOHO data is by
far the most extensive data, which made it possible to fully establish
the properties of CMEs as a phenomenon of utmost importance to Sun-Earth
connection as well as to the heliosphere. I also discuss various subsets
of CMEs that are of primary importance for their impact on Earth.
---------------------------------------------------------
Title: On the Rates of Coronal Mass Ejections: Remote Solar and In
Situ Observations
Authors: Riley, Pete; Schatzman, C.; Cane, H. V.; Richardson, I. G.;
Gopalswamy, N.
2006ApJ...647..648R Altcode:
We compare the rates of coronal mass ejections (CMEs) as inferred from
remote solar observations and interplanetary CMEs (ICMEs) as inferred
from in situ observations at both 1 AU and Ulysses from 1996 through
2004. We also distinguish between those ICMEs that contain a magnetic
cloud (MC) and those that do not. While the rates of CMEs and ICMEs
track each other well at solar minimum, they diverge significantly
in early 1998, during the ascending phase of the solar cycle, with
the remote solar observations yielding approximately 20 times more
events than are seen at 1 AU. This divergence persists through 2004. A
similar divergence occurs between MCs and non-MC ICMEs. We argue that
these divergences are due to the birth of midlatitude active regions,
which are the sites of a distinct population of CMEs, only partially
intercepted by Earth, and we present a simple geometric argument showing
that the CME and ICME rates are consistent with one another. We also
acknowledge contributions from (1) an increased rate of high-latitude
CMEs and (2) focusing effects from the global solar field. While our
analysis, coupled with numerical modeling results, generally supports
the interpretation that whether one observes a MC within an ICME is
sensitive to the trajectory of the spacecraft through the ICME (i.e.,
an observational selection effect), one result directly contradicts
it. Specifically, we find no systematic offset between the latitudinal
origin of ICMEs that contain MCs at 1 AU in the ecliptic plane and
that of those that do not.
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Title: Solar Energetic Particles and CME-driven Shocks
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.; Bougeret, J. -L.
2006IAUJD...1E..54G Altcode:
Large solar energetic particle (SEP) events are associated with
coronal mass ejections (CMEs) of very high speed (~1500 km/s). A mass
mtion of such high speeds in the coronal and interplanetary plasma
has to drive fast mode MHD shocks. Direct evidence of such shocks
come from in situ observations of shock arriving at 1 AU immediately
followed by the driving CMEs. The energetic storm particle (ESP)
events associated with these shocks present direct evidence for shock
acceleration. Shocks near the Sun have to be remote-sensed using type
II bursts of type II. Type II bursts occurring over wide range of
wavelengths are known to be associated with very fast and wide CMEs
(Gopalswamy et al., 2005). We analyze a set of such type II bursts
observed during solar cycle 23 and the associated SEP and CME events
to explore the relationship bewteen CME-driven shocks and SEPs near the
Sun. We also study the association of the type II burst events with the
interplanetary shocks observed in situ and ESP events. The main result
is that when the CME associated with the type II bursts originate on
the disk center of the Sun, they result in shocks at 1 AU followed by
driving CMEs. We also discuss the relationship bewteen type II bursts
and ESP events. Reference: Gopalswamy, N., E. Aguilar-Rodriguez,
S. Yashiro, S. Nunes, M. L. Kaiser, and R. A. Howard, Type II radio
bursts and energetic solar eruptions, JGRA, 110, 12, 2005
---------------------------------------------------------
Title: Mission Concepts for Spacecraft and Lunar-based Radio Source
Imaging at Frequencies below the Ionospheric Cutoff
Authors: Gopalswamy, N.; MacDowall, R. J.; Kaiser, M. L.; Demaio,
L. D.; Bale, S. D.; Howard, R. E.; Jones, D. L.; Kasper, J. C.;
Kassim, N. E.; Lazio, J. W.; Weiler, K. W.; Reiner, M. J.
2006IAUJD..12E..21G Altcode:
No present or approved spacecraft mission has the capability to
provide high angular resolution imaging of solar or magnetospheric
radio bursts or of the celestial sphere at frequencies below the
ionospheric cutoff. In this presentation, we review briefly the history
of space-based radio observations by single spacecraft. Although
these missions did not produce images of discrete radio sources,
they did establish important constraints for future imaging
missions. Subsequently, we present in detail an active NASA mission
proposal to perform such imaging in the frequency range ~30 kHz to
15 MHz. The focus of this mission, the Solar Imaging Radio Array
(SIRA), is solar and NASA exploration-oriented, with emphasis on
improved understanding and space weather application of radio bursts
associated with solar energetic particle (SEP) events and on tracking
shocks and other components of coronal mass ejections (CMEs). SIRA
will also map the astrophysical sky. SIRA will require a minimum of 12
to 16 micro-satellites to establish a sufficient number of baselines
with separations on the order of a kilometer. The baseline microsat is
3-axis stabilized with body-mounted solar arrays and an articulated,
earth pointing high gain antenna. The constellation will likely
be placed in an L1 halo orbit, which is the preferred location for
full-time solar observations. We will also discuss follow-on missions
that would be lunar-based, ultimately with of order 10,000 dipole
antennas. The lunar missions would be adaptations of ground-based
interferometric arrays like LOFAR, LWA, MWA, etc. Basic research in
radio astronomy at the Naval Research Laboratory is supported by the
Office of Naval Research; part of this work is being carried out at
the Jet Propulsion Laboratory, California Institute of Technology,
under contract with the National Aeronautics and Space Administration.
---------------------------------------------------------
Title: The IHY Program and Associated IAU Activities
Authors: Webb, D.; Gopalswamy, N.
2006IAUSS...5E..43W Altcode:
The International Heliospheric Year is an international program of
scientific collaboration planned for the time period starting next
year, the 50th anniversary of the International Geophysical Year. The
physical realm of the IHY encompasses all of the solar system out
to the interstellar medium, representing a direct connection between
in-situ and remote observations. The IHY is of great interest to the
IAU because of this broad astronomical coverage as well as its emphasis
on international cooperation and developing nations. The IHY program
is promoting worldwide participation in its activities that include
dispersing networks of inexpensive instrumentation to achieve its
scientific goals. Within the IAU the IHY program is organized under
Division II, which covers the Sun and Heliosphere. Nat Gopalswamy
is the IHY International Coordinator and Chair of the IHY subgroup
within the IAU's Working Group on International Collaboration on
Space Weather. David Webb is the IAU representative for the IHY and
the outgoing President of Division II. The United Nations IHY effort
is led by Hans Haubold under the UNBSS program and will be discussed
next by Dr. Gopalswamy. Under this program the IAU is supporting the
annual IHY Workshops and is facilitating the communications between
scientists in developed and developing countries.
---------------------------------------------------------
Title: Correction to “Introduction to special section on corotating
solar wind streams and recurrent geomagnetic activity”
Authors: Tsurutani, B. T.; McPherron, R. L.; Gonzalez, W. D.; Lu,
G.; Sobral, J. H. A.; Gopalswamy, N.
2006JGRA..111.8S90T Altcode: 2006JGRA..11108S90T
No abstract at ADS
---------------------------------------------------------
Title: Anemone structure of Active Region NOAA 10798 and related
geo-effective flares/ CMEs
Authors: Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.
2006IAUJD...3E..72A Altcode:
Introduction: We report the evolution and the coronal features of an
active region NOAA 10798, and the related magnetic storms. Method:
We examined in detail the photospheric and coronal features of
the active region by using observational data in soft X-rays, in
extreme ultraviolet images, and in magnetogram obtained with GOES,
SOHO satellites. We also examined the interplanetary disturbances from
the ACE data. Results: This active region was located in the middle of
a small coronal hole, and generated 3 M-class flares. The flares are
associated with high speed CMEs up to 2000 km/s. The interplanetary
disturbances also show a structure with southward strong magnetic
field. These produced a magnetic storm on 2005 August 24. Conclusions:
The anemone structure may play a role for producing the high-speed
and geo-effective CMEs even the near limb locations.
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Title: The United Nations Basic Space Science Initiative for IHY 2007
Authors: Gopalswamy, N.; Davila, J. M.; Thompson, B. J.; Haubold, H.
2006IAUSS...5E..47G Altcode:
The United Nations, in cooperation with national and international
space-related agencies and organizations, has been organizing annual
workshops since 1990 on basic space science, particularly for the
benefit of scientists and engineers from developing nations. The United
Nations Office for Outer Space Affairs, through the IHY Secretariat and
the United Nations Basic Space Science Initiative (UNBSSI) will assist
scientists and engineers from all over the world in participating in
the International Heliophysical Year (IHY) 2007. A major thrust of the
IHY/UNBSSI program is to deploy arrays of small, inexpensive instruments
such as magnetometers, radio telescopes, GPS receivers, all-sky cameras,
etc. around the world to provide global measurements of ionospheric
and heliospheric phenomena. The small instrument program is envisioned
as a partnership between instrument providers, and instrument hosts in
developing countries. The lead scientist will provide the instruments
(or fabrication plans for instruments) in the array; the host country
will provide manpower, facilities, and operational support to obtain
data with the instrument typically at a local university. Funds
are not available through the IHY to build the instruments; these
must be obtained through the normal proposal channels. However all
instrument operational support for local scientists, facilities, data
acquisition, etc will be provided by the host nation. It is our hope
that the IHY/UNBSSI program can facilitate the deployment of several of
these networks world wide. Existing data bases and relevant software
tools that can will be identified to promote space science activities
in developing countries. Extensive data on space science have been
accumulated by a number of space missions. Similarly, long-term data
bases are available from ground based observations. These data can be
utilized in ways different from originally intended for understanding
the heliophysical processes. This paper provides an overview of the
IHY/UNBSS program, its achievements and future plans.
---------------------------------------------------------
Title: Observational Properties of CMEs from a Decade-Long
Observations by SOHO
Authors: Gopalswamy, N.; Yashiro, S.; Howard, R. A.
2006ESASP.617E.129G Altcode: 2006soho...17E.129G
No abstract at ADS
---------------------------------------------------------
Title: Introduction to special section on corotating solar wind
streams and recurrent geomagnetic activity
Authors: Tsurutani, Bruce T.; McPherron, Robert L.; Gonzalez, Walter
D.; Lu, Gang; Sobral, Jose H. A.; Gopalswamy, Nat
2006JGRA..111.7S00T Altcode: 2006JGRA..11107S00T
No abstract at ADS
---------------------------------------------------------
Title: Corotating solar wind streams and recurrent geomagnetic
activity: A review
Authors: Tsurutani, Bruce T.; Gonzalez, Walter D.; Gonzalez, Alicia
L. C.; Guarnieri, Fernando L.; Gopalswamy, Nat; Grande, Manuel;
Kamide, Yohsuke; Kasahara, Yoshiya; Lu, Gang; Mann, Ian; McPherron,
Robert; Soraas, Finn; Vasyliunas, Vytenis
2006JGRA..111.7S01T Altcode: 2006JGRA..11107S01T
Solar wind fast streams emanating from solar coronal holes cause
recurrent, moderate intensity geomagnetic activity at Earth. Intense
magnetic field regions called Corotating Interaction Regions or CIRs
are created by the interaction of fast streams with upstream slow
streams. Because of the highly oscillatory nature of the GSM magnetic
field z component within CIRs, the resultant magnetic storms are
typically only weak to moderate in intensity. CIR-generated magnetic
storm main phases of intensity Dst < -100 nT (major storms) are
rare. The elongated storm "recovery" phases which are characterized
by continuous AE activity that can last for up to 27 days (a solar
rotation) are caused by nonlinear Alfven waves within the high streams
proper. Magnetic reconnection associated with the southward (GSM)
components of the Alfvén waves is the solar wind energy transfer
mechanism. The acceleration of relativistic electrons occurs during
these magnetic storm "recovery" phases. The magnetic reconnection
associated with the Alfvén waves cause continuous, shallow injections
of plasma sheet plasma into the magnetosphere. The asymmetric plasma is
unstable to wave (chorus and other modes) growth, a feature central to
many theories of electron acceleration. It is noted that the continuous
AE activity is not a series of substorm expansion phases. Arguments
are also presented why these AE activity intervals are not convection
bays. The auroras during these continuous AE activity intervals are
less intense than substorm auroras and are global (both dayside and
nightside) in nature. Owing to the continuous nature of this activity,
it is possible that there is greater average energy input into the
magnetosphere/ionosphere system during far declining phases of the solar
cycle compared with those during solar maximum. The discontinuities
and magnetic decreases (MDs) associated with interplanetary Alfven
waves may be important for geomagnetic activity. In conclusion,
it will be shown that geomagnetic storms associated with high-speed
streams/CIRs will have the same initial, main, and "recovery" phases
as those associated with ICME-related magnetic storms but that the
interplanetary causes are considerably different.
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Title: Coronal and Interplanetary Type II Bursts
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.
2006SPD....37.2501G Altcode: 2006BAAS...38..251G
The kinetic energy of coronal mass ejections (CMEs) has been
shown to essentially decide the wavelength range over which type
II radio emission occurs. The larger the kinetic energy the wider
is the wavelength range over which emission takes place. In other
words, CMEs with larger kinetic energy drive shocks farther into the
interplanetary medium. We studied a set of about 70 type II bursts that
had emission components in the three well-known wavelength domains:
metric (m), decameter-hectometric (DH), and kilometric (km). We find
that the properties of CMEs associated with the m-to-km type II bursts
are nearly identical to those CMEs associated with solar energetic
particle events. We suggest that this correlation is evidence for
the same shock accelerating electrons and ions. Next we examined the
time delay between the onsets of metric and interplanetary type II
emission. This is an important parameter because only when a metric
type II burst has IP counterpart, it is likely to have space weather
consequences. We find that the typical delay is about 1 hour. This is
sufficiently small that one can use the DH type II bursts to identify
shocks that might impact various destinations in the inner heliosphere.
---------------------------------------------------------
Title: Comment on “Interplanetary shocks unconnected with earthbound
coronal mass ejections” by T. A. Howard and S. J. Tappin
Authors: Gopalswamy, Nat; Akiyama, Sachiko; Yashiro, Seiji; Kasper, J.
2006GeoRL..3311108G Altcode:
<A href="/journals/gl/gl0611/2005GL024983/">Abstract Available</A>
from <A href="http://www.agu.org">http://www.agu.org</A>
---------------------------------------------------------
Title: Are halo coronal mass ejections special events?
Authors: Lara, Alejandro; Gopalswamy, Nat; Xie, Hong; Mendoza-Torres,
Eduardo; PéRez-EríQuez, RomáN.; Michalek, Gregory
2006JGRA..111.6107L Altcode: 2006JGRA..11106107L
We revisited the properties of wide coronal mass ejections (CMEs)
called halo CMEs. Using the large LASCO/SOHO CMEs data set, from 1996
to 2004, we examined the statistical properties of (partial and full)
halo CMEs and compare with the same properties of "normal" width (lower
than 120°) CMEs. We found that halo CMEs have different properties than
"normal" CMEs, which cannot be explained merely by the current geometric
interpretation that they are seen as halos because they are traveling
in the Sun Earth direction. We found that the CME width distribution
is formed by, at least, three different populations: Two gaussians:
a narrow and a medium distribution centered at ∼17° and ∼38°,
respectively; the narrow population most likely corresponds to the
"true" observed widths, whereas the medium width population is the
product of projection effects. The third distribution corresponds
to wider CMEs (80° < W < 210°) which behaves as a power
law. Partial and full halo CMEs wider than these do not follow any
particular distribution. This lack of regularity may be due to the
small number of such events. In particular, we found (and test by a
statistical approach) that the number of observed full halo CMEs is
lower than expected. The CME speed follows a log-normal distribution,
except for the very low speed CME population, which follows a gaussian
distribution centered at ∼100 km/s and is probably due to projection
effects. When the CMEs are divided by width into nonhalo, partial
halo, and full halo, we found that the peaks of the distributions
are shifted toward higher speeds, ∼300, ∼400 and ∼600 km/s for
nonhalo, partial halo, and full halo CMEs, respectively. This confirms
that halo CMEs tend to be high speed CMEs. The acceleration of full
halo CMEs tends to be more negative compared with nonhalo and partial
halo CMEs. We introduce a new observational CME parameter: The final
observed distance (FOD), i.e., the highest point within the coronograph
field of view where a CME can be distinguished from the background. In
other words, the highest CME altitude measured. The FOD for nonhalo CMEs
decreases exponentially from ∼5 to ∼30 R<SUB>⊙</SUB> in the LASCO
field of view. On the other hand, the FOD of halo CMEs increase with
distance. This means that it is more likely to see halo CMEs at large
distances (from the Sun) than nonhalo CMEs. These halo CME properties
may be explained if the white light wide enhancements (or halo) seen
by coronographs correspond to a combination of an expanding (shock)
wave which disturbs and/or compresses the ambient material and the
CME material itself.
---------------------------------------------------------
Title: Preface
Authors: Gopalswamy, Nat
2006JApA...27...57G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of Interplanetary Coronal Mass Ejections
Authors: Gopalswamy, Nat
2006SSRv..124..145G Altcode: 2007SSRv..tmp...53G
Interplanetary coronal mass ejections (ICMEs) originating from closed
field regions on the Sun are the most energetic phenomenon in the
heliosphere. They cause intense geomagnetic storms and drive fast mode
shocks that accelerate charged particles. ICMEs are the interplanetary
manifestations of CMEs typically remote-sensed by coronagraphs. This
paper summarizes the observational properties of ICMEs with reference
to the ordinary solar wind and the progenitor CMEs.
---------------------------------------------------------
Title: Solar Imaging Radio Array: Space-based Radio Imaging at
Frequencies Below the Ionospheric Cutoff
Authors: MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Demaio,
L. D.; Bale, S. D.; Kasper, J. C.; Lazarus, A. J.; Howard, R. E.;
Jones, D. L.; Reiner, M. J.; Weiler, K. W.
2006AGUSMSH33A..11M Altcode:
No present or approved spacecraft mission has the capability to provide
high angular resolution imaging of solar or magnetospheric radio
bursts or of the celestial sphere at frequencies below the ionospheric
cutoff. In this presentation, we review a NASA MIDEX-class mission
to perform such imaging in the frequency range 30 kHz to 15 MHz. The
focus of the mission, the Solar Imaging Radio Array (SIRA), is solar
and exploration- oriented, with emphasis on improved understanding and
application of radio bursts associated with solar energetic particle
(SEP) events and on tracking shocks and other components of coronal
mass ejections (CMEs). The data stream will also permit high angular
resolution mapping of the celestial sphere at frequencies below 15 MHz,
permitting detection of numerous astrophysical objects and extension of
their observed spectra to much lower frequencies. SIRA will require 12
to 16 micro-satellites to establish a sufficient number of baselines
with separations on the order of kilometers. The constellation
consists of microsats located quasi-randomly on a spherical shell,
initially of radius 5 km. The baseline microsat is 3-axis stabilized
with body-mounted solar arrays and an articulated, Earth-pointing high
gain antenna. The constellation will likely be placed at L1, which
is the preferred location for full-time solar observations. Detailed
mission science and technology goals will be reviewed.
---------------------------------------------------------
Title: On the rates of coronal mass ejections: remote solar and in
situ observations
Authors: Riley, P.; Cane, H.; Richardson, I. G.; Gopalswamy, N.;
Linker, J. A.; Mikic, Z.; Lionello, R.
2006AGUSMSA21A..01R Altcode:
In this study we compare the rates of coronal mass ejections (CMEs)
as inferred from remote solar observations and interplanetary CMEs
(ICMEs) as inferred from in situ observations at both 1 AU and Ulysses
for almost an entire solar cycle (1996 through 2004). We find that,
while the rates of CMEs and ICMEs track each other well at solar
minimum, they diverge significantly in early 1998, during the ascending
phase of the solar cycle, with the remote solar observations yielding
approximately 20 times more events than are seen in situ at 1 AU. This
divergence persists through 2004. We discuss several possible causes,
including: (1) the appearance of mid-latitude active regions; (2)
the increased rate of high-latitude CMEs; and (3) the strength of the
global solar field. We conclude that the most likely interpretation
is that this divergence is due to the birth of mid-latitude active
regions, which are the sites of a distinct population of CMEs that are
only partially intercepted by Earth. This conclusion is supported by
the following points: (1) A similar divergence occurs between ICMEs in
which magnetic clouds are observed (MCs), and those that are not; and
(2) a number of pronounced enhancements in the CME rate, separated
by approximately one year, are also mirrored and in ICME rate, but
not obviously in the MC rate. We provide a simple geometric argument
that shows that the computed CME and ICME rates are consistent with
each other. The origins of the individual peaks can be traced back
to unusually strong active regions on the Sun. Taken together, these
results suggest that whether one observes a flux rope within an ICME
is sensitive to the trajectory of the spacecraft through the ICME,
i.e., an observational selection effect. This conclusion is supported
by models of CME eruption and evolution, which: (1) are incapable of
producing a CME that does not contain an embedded flux rope; and (2)
demonstrate that glancing intercepts can produce ICME-like signatures
without the magnetic structures associated with a flux rope
---------------------------------------------------------
Title: A Sun-to-Earth Campaign Joining Observations from the Great
Observatory with Worldwide Satellite and Ground-Based Resources to
Investigate System Science Frontiers
Authors: Kozyra, J. U.; Shibata, K.; Barnes, R. J.; Basu, S.; Davila,
J. M.; Fox, N. J.; Gopalswamy, N.; Kuznetsova, M. M.; Pallamraju,
D.; Paxton, L. J.; Ridley, A.; Weiss, M.; Young, C. A.; Zanetti, L. J.
2006AGUSMSM23A..03K Altcode:
An Internet-based cross-disciplinary analysis campaign that will
make heavy use of Great Observatory missions as well as international
satellite and ground-based assets is being undertaken with joint support
from the CAWSES, IHY, LWS, and ICESTAR programs planned for late
April or early May 2006. An evolving list of open science questions
that serve as sun-to-Earth focus areas for the worldwide campaign
were identified during a small interdisciplinary CAWSES workshop
at Stanford University in December 2005 as well as during a joint
CAWSES/ICESTAR session at the CEDAR meeting in Boulder the preceding
summer. The analysis campaign will take place over the Internet in the
form of virtual poster sessions with message boards and monitors that
summarize the important science issues and new results daily. Poster
authors will be asked to closely monitor their message boards during
the day of their poster session as well as the following day. Outreach
to other disciplines and international students will take the form of
tutorial talks that place campaign science issues into the context of
the current state of knowledge in each discipline area. Global models
and data sets (TEC, magnetometer maps, ULF wave maps, assimilative
models, MHD model outputs, continuous solar images) will be available
to provide context for local and regional observations. The Community
Coordinated Data Center (CCMC) is developing a small number of new data
display formats that extract data from global models and place it in
the same format as the observations either for ground-based stations
or along satellite tracks. Other ideas being explored include real
time upload of additional posters in response to issues raised during
the poster session, library of related articles, reference archive of
observations, etc. A summary of which aspects and/or tools worked and
which were less useful will be presented.
---------------------------------------------------------
Title: Radio manifestation of the interaction between ultra-fast CMEs
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2006AGUSMSH24A..03G Altcode:
Active region 720 was one of the super active regions of cycle 23
in that it produced large numbers of coronal mass ejections (CMEs)
and major flares. The average recurrence time between flares in the
region was about 2.5 h, but several flares and CMEs occurred with
much shorter recurrence time. In this paper, we are concerned with
two ultra-fast CMEs (speed > 2000 km/s) originating within 45
minutes. The CMEs merged with each other within the field of view of
SOHO coronagraphs. Both CMEs were associated with long wavelength
type II radio bursts. The type II burst associated with the first
CME was normal, while that associated with the second CME showed
irregular spectral behavior, including a characteristic broadband
enhancement. Solar energetic particles (SEPs) associated with the
two CMEs also showed some peculiarities, which are consistent with
the interaction between the two CMEs. The SEP intensity reached a
very high value around the time of interaction. We present radio and
white light observations of the CMEs and provide an interpretation
of the observed spectral features in the radio dynamic spectrum. Work
supported by NASA's LWS TR&T and SR&T programs.
---------------------------------------------------------
Title: Science Plans for the International Heliophysical Year
Authors: Davila, J. M.; Gopalswamy, N.; Harrison, R. A.; Stamper,
R.; Briand, C.; Potgieter, M. S.
2006AGUSM.U34A..04D Altcode:
On October 4, 1957, only 53 years after the beginning of flight in Kitty
Hawk, the launch of Sputnik 1 marked the beginning of the space age;
as mankind took the first steps to leaving the protected environment of
Earth's atmosphere. Discovery of the radiation belts, the solar wind,
and the structure of Earth's magnetosphere prepared the way for the
inevitable human exploration to follow. Soon, Cosmonauts and Astronauts
orbited Earth, and then in 1969, Astronauts landed on the Moon. Today
a similar story is unfolding, the spacecraft Voyager has crossed the
termination shock, and will soon leave the heliosphere. For the first
time, man will begin to explore the local interstellar medium. It is
inevitable that, during the next 50 years, exploration of the solar
system including the Moon, Mars and the outer planets will be the
focus of the space program, and like 50 years ago, unmanned probes
will lead the way, followed by human exploration. The International
Geophysical Year (IGY) of 1957, a broad-based and all-encompassing
effort to push the frontiers of geophysics, resulted in a tremendous
increase of knowledge in space physics, Sun-Earth Connection, planetary
science and the heliosphere in general. Now, 50 years later, we have
the unique opportunity to further advance our knowledge of the global
heliosphere and its interaction with the interstellar medium through
the International Heliophysical Year (IHY) in 2007, and to raise
public awareness of space physics. This presentation will focus on
global science planning efforts and campaigns for all participating
IHY nations.
---------------------------------------------------------
Title: United Nations Basic Space Science Initiative Programme for
the International Heliophysical Year 2007
Authors: Gopalswamy, Nat
2006UNPSA..17...47G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Pre-CME Sun
Authors: Gopalswamy, N.; Mikić, Z.; Maia, D.; Alexander, D.; Cremades,
H.; Kaufmann, P.; Tripathi, D.; Wang, Y. -M.
2006SSRv..123..303G Altcode: 2006SSRv..tmp...77G
The coronal mass ejection (CME) phenomenon occurs in closed magnetic
field regions on the Sun such as active regions, filament regions,
transequatorial interconnection regions, and complexes involving a
combination of these. This chapter describes the current knowledge
on these closed field structures and how they lead to CMEs. After
describing the specific magnetic structures observed in the CME source
region, we compare the substructures of CMEs to what is observed before
eruption. Evolution of the closed magnetic structures in response to
various photospheric motions over different time scales (convection,
differential rotation, meridional circulation) somehow leads to the
eruption. We describe this pre-eruption evolution and attempt to link
them to the observed features of CMEs. Small-scale energetic signatures
in the form of electron acceleration (signified by nonthermal radio
bursts at metric wavelengths) and plasma heating (observed as compact
soft X-ray brightening) may be indicative of impending CMEs. We survey
these pre-eruptive energy releases using observations taken before
and during the eruption of several CMEs. Finally, we discuss how the
observations can be converted into useful inputs to numerical models
that can describe the CME initiation.
---------------------------------------------------------
Title: Coronal Observations of CMEs. Report of Working Group A
Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.;
Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.;
Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.;
Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J.
2006SSRv..123..127S Altcode: 2006SSRv..tmp...58S
CMEs have been observed for over 30 years with a wide variety of
instruments. It is now possible to derive detailed and quantitative
information on CME morphology, velocity, acceleration and mass. Flares
associated with CMEs are observed in X-rays, and several different
radio signatures are also seen. Optical and UV spectra of CMEs both on
the disk and at the limb provide velocities along the line of sight
and diagnostics for temperature, density and composition. From the
vast quantity of data we attempt to synthesize the current state of
knowledge of the properties of CMEs, along with some specific observed
characteristics that illuminate the physical processes occurring during
CME eruption. These include the common three-part structures of CMEs,
which is generally attributed to compressed material at the leading
edge, a low-density magnetic bubble and dense prominence gas. Signatures
of shock waves are seen, but the location of these shocks relative
to the other structures and the occurrence rate at the heights where
Solar Energetic Particles are produced remains controversial. The
relationships among CMEs, Moreton waves, EIT waves, and EUV dimming
are also cloudy. The close connection between CMEs and flares suggests
that magnetic reconnection plays an important role in CME eruption
and evolution. We discuss the evidence for reconnection in current
sheets from white-light, X-ray, radio and UV observations. Finally, we
summarize the requirements for future instrumentation that might answer
the outstanding questions and the opportunities that new space-based
and ground-based observatories will provide in the future.
---------------------------------------------------------
Title: Planning the International Heliophysical Year (IHY)
Authors: Davila, Joseph M.; Thompson, Barbara J.; Gopalswamy, Nat
2006UNPSA..17...37D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Long-lived geomagnetic storms and coronal mass ejections
Authors: Xie, H.; Gopalswamy, N.; Manoharan, P. K.; Lara, A.; Yashiro,
S.; Lepri, S.
2006JGRA..111.1103X Altcode: 2006JGRA..11101103X
Coronal mass ejections (CMEs) are major solar events that are known to
cause large geomagnetic storms (Dst < -100 nT). Isolated geomagnetic
storms typically have a main phase of 3-12 hours and a recovery phase
of around 1 day. However, there are some storms with main and recovery
phases exceeding ∼3 days. We trace the origin of these long-lived
geomagnetic storms (LLGMS) to frontside halo CMEs. We studied 37 LLGMS
events with Dst < -100 nT and the associated CMEs which occurred
during 1998-2002. It is found that LLGMS events are caused by (1)
successive CMEs, accounting for ∼64.9% (24 of 37); (2) single CMEs,
accounting for ∼21.6% (8 of 37); and (3) high-speed streams (HSS) in
corotating interaction regions (CIRs) with no related CME, accounting
for ∼13.5% (5 of 37). The long duration of the LLGMS events was found
to be due to successive CMEs and HSS events; the high intensity of the
LLGMS events was related to the interaction of CMEs with other CMEs and
HSS events. We find that the duration of LLGMS is well correlated to the
number of participating CMEs (correlation coefficient r = 0.78). We also
find that the intensity of LLGMS has a good correlation with the degree
of interaction (the number of CMEs interacting with a HSS event or with
themselves) (r = 0.67). The role of preconditioning in LLGMS events,
where the Dst development occurred in multiple steps in the main and
recovery phases, has been investigated. It is found that preconditioning
does not affect the main phase of the LLGMS events, while it plays an
important role during the recovery phase of the LLGMS events.
---------------------------------------------------------
Title: Composition and magnetic structure of interplanetary coronal
mass ejections at 1 AU
Authors: Aguilar-Rodriguez, E.; Blanco-Cano, X.; Gopalswamy, N.
2006AdSpR..38..522A Altcode:
We study the magnetic structure and charge state ratio of
interplanetary coronal mass ejections (ICMEs) observed by ACE and Wind
spacecraft. Measurements of abundances and charge state ratio of heavy
ions (e.g. O<SUP>7+</SUP>/O<SUP>6+</SUP>, C<SUP>6+</SUP>/C<SUP>5+</SUP>,
and Mg<SUP>10+</SUP>/O<SUP>6+</SUP>) in the plasma as well as magnetic
field structure are important tracers for physical conditions and
processes in the source regions of ICMEs. We used ion composition
(from ACE), plasma (from Wind) and magnetic field (from Wind and ACE)
data from 1998 to 2002. Using the low proton temperature criterion,
a common plasma signature of ICMEs, we identified 154 events which
include magnetic clouds, non-cloud ejecta and complex ICMEs. The
latter one refers to compound events resulting from the overtaking
of successive ICMEs which can include both magnetic clouds and
non-cloud ejecta. We find that there is a close relationship between
the increase in the charge state ionization factor and the magnetic
structure of ICMEs. Events with magnetic cloud topology show higher
Q<SUB></SUB>andQ<SUB></SUB> charge state ratios than those with
non-magnetic cloud structure. However, both magnetic cloud and non-cloud
events show an increase in these ratios when compared with the ambient
solar wind. In contrast, perhaps due to instrumental effects, the charge
state ratio Q<SUB></SUB> for all events does not show a real enhancement
when compared with the ambient solar wind. The difference in ionization
states between non-cloud ejecta and magnetic clouds is more pronounced
in fast solar wind than when events are embedded in slow wind.
---------------------------------------------------------
Title: Associations of Coronal Mass Ejections as a function of X-ray
Flare Properties
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.; Howard, R. A.
2006cosp...36.1778Y Altcode: 2006cosp.meet.1778Y
We examined the associations between coronal mass ejections CMEs and
X-ray flares using data from the Large Angle Spectrometric Coronagraph
LASCO on board the Solar and Heliospheric Observatory SOHO The CME
association of 1540 X-ray flares M classand above detected by GOES
satellite were examined As reported in previous studies the CME
association rate clearly increased with the peak X-ray intensity the
total X-ray intensity and the decay time The CME association rate
increased from 40 flare size between M1 0 and M1 7 to 98 flare size
above X1 8 Except for an X3 6 flare on July 16 2004 all the 50 huge
flares above X1 8 definitely have associated CMEs Furthermore all
the X-ray flares with a decay time exceeding 90 min were associated
CMEs We discuss which X-ray parameters are essential in order to have
CME association
---------------------------------------------------------
Title: Solar wind speed within 20 R<SUB>S</SUB> of the Sun estimated
from limb coronal mass ejections
Authors: Nakagawa, Tomoko; Gopalswamy, Nat; Yashiro, Seiji
2006JGRA..111.1108N Altcode: 2006JGRA..11101108N
An estimation of the solar wind speed in the vicinity of the Sun
is carried out using the initial speed and acceleration of coronal
mass ejections (CMEs) that appeared close to the solar limb. A linear
relationship was found between the initial acceleration and the speed of
the limb CMEs. It appears that a dragging force is acting on the CMEs,
depending on the speed difference between the CMEs and the ambient
plasma. The ambient solar wind speed within 20 solar radii estimated
from low-latitude CMEs during 1998-2003 ranged from 100 to 700 km
s<SUP>-1</SUP>, while the solar wind speed measured at 1 AU ranged
from 300 to 700 km s<SUP>-1</SUP>. The estimated solar wind speeds
in the vicinity of the Sun sometimes agreed with the simultaneous in
situ measurements at 1 AU, but in other periods they were slower than
the speeds measured at 1 AU. It is suggested that most of the time
the low-latitude solar wind completes accelerating within 20 solar
radii, but occasionally additional acceleration is present beyond 20
solar radii.
---------------------------------------------------------
Title: Coronal mass ejections and space weather due to extreme events
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2006ilws.conf...79G Altcode:
This paper summarizes the extreme solar activity and its space
weather implications during the declining phase of the solar cycle 23:
October-November 2003 (AR 486), November 2004 (AR 696), January 2005
(AR 720), and September 2005 (AR 808). We have compiled and compared the
properties of eruptions and the underlying active regions. All these
are super active regions, but the flare and CME productivity varied
significantly. While the CMEs from all the regions kept the level of
solar energetic particles (SEPs) at storm level for several days,
their geoeffectiveness (the ability to produce geomagnetic storms)
was significantly different, probably due to the location of the
eruptions on the Sun.
---------------------------------------------------------
Title: Coronal Observations of CMEs
Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.;
Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.;
Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.;
Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J.
2006cme..book..127S Altcode:
CMEs have been observed for over 30 years with a wide variety of
instruments. It is now possible to derive detailed and quantitative
information on CME morphology, velocity, acceleration and mass. Flares
associated with CMEs are observed in X-rays, and several different
radio signatures are also seen. Optical and UV spectra of CMEs both on
the disk and at the limb provide velocities along the line of sight
and diagnostics for temperature, density and composition. From the
vast quantity of data we attempt to synthesize the current state of
knowledge of the properties of CMEs, along with some specific observed
characteristics that illuminate the physical processes occurring during
CME eruption. These include the common three-part structures of CMEs,
which is generally attributed to compressed material at the leading
edge, a low-density magnetic bubble and dense prominence gas. Signatures
of shock waves are seen, but the location of these shocks relative
to the other structures and the occurrence rate at the heights where
Solar Energetic Particles are produced remains controversial. The
relationships among CMEs, Moreton waves, EIT waves, and EUV dimming
are also cloudy. The close connection between CMEs and flares suggests
that magnetic reconnection plays an important role in CME eruption
and evolution. We discuss the evidence for reconnection in current
sheets from white-light, X-ray, radio and UV observations. Finally, we
summarize the requirements for future instrumentation that might answer
the outstanding questions and the opportunities that new space-based
and ground-based observatories will provide in the future.
---------------------------------------------------------
Title: Coronal mass ejections and space weather
Authors: Webb, D. F.; Gopalswamy, N.
2006ilws.conf...71W Altcode:
Coronal mass ejections (CMEs) are a key feature of coronal and
interplanetary (IP) dynamics. Major CMEs inject large amounts of mass
and magnetic fields into the heliosphere and, when aimed Earthward,
can cause major geomagnetic storms and drive IP shocks, a key source
of solar energetic particles. Studies over this solar cycle using the
excellent data sets from the SOHO, TRACE, Yohkoh, Wind, ACE and other
spacecraft and ground-based instruments have improved our knowledge
of the origins and early development of CMEs at the Sun and how they
affect space weather at Earth. A new heliospheric experiment, the Solar
Mass Ejection Imager, has completed 3 years in orbit and has obtained
results on the propagation of CMEs through the inner heliosphere
and their geoeffectiveness. We review key coronal properties of CMEs,
their source regions, their manifestations in the solar wind, and their
geoeffectiveness. Halo-like CMEs are of special interest for space
weather because they suggest the launch of a geoeffective disturbance
toward Earth. However, not all halo CMEs are equally geoeffective
and this relationship varies over the solar cycle. Although CMEs are
involved with the largest storms at all phases of the cycle, recurrent
features such as interaction regions and high speed wind streams can
also be geoeffective.
---------------------------------------------------------
Title: Preparing for the International Heliophysical Year (IHY) 2007
Authors: Davila, J. M.; Gopalswamy, N.; Thompson, B. J.
2006ilws.conf..231D Altcode:
The International Geophysical Year (IGY) of 1957, a broad-based and
all-encompassing effort to push the frontiers of geophysics, resulted
in a tremendous increase of knowledge in space physics, Sun-Earth
Connection, planetary science and the heliosphere in general. Now, 50
years later, we have the unique opportunity to advance our knowledge of
the global heliosphere and its interaction with planetary bodies and
the interstellar medium through the International Heliophysical Year
(IHY) in 2007. This will be an international effort, which will raise
public awareness of space physics.
---------------------------------------------------------
Title: The IHY/United Nations Distributed Observatory Development
Program
Authors: Haubold, H.; Thompson, B. J.; Al-Naimiy, H.; Davila, J. M.;
Gopalswamy, N.; Groves, K.; Scherrer, D.
2006cosp...36.3304H Altcode: 2006cosp.meet.3304H
A major thrust of the International Heliophysical Year IHY is to
deploy arrays of small inexpensive instruments such as magnetometers
radio antennas GPS receivers all-sky cameras etc around the world
to provide global measurements of ionospheric magnetospheric and
heliospheric phenomena This program is a collaboration between the IHY
and the United Nations Basic Space Science Initiative UNBSSI which has
been dedicated to the IHY through 2009 The small instrument program
consists of a partnership between instrument providers and instrument
host countries The lead scientist provides the instrumentation or
fabrication plans for instruments in the array the host country
provides manpower facilities and operational support to obtain data
with the instrument typically at a local university This program has
been active in deploying instrumentation developing plans for new
instrumentation and identifying educational opportunities for the host
nations in association with this program We will discuss the program
s status significant deployment activities and plans for 2007-2009
---------------------------------------------------------
Title: Geoeffectiveness of CMEs: A simple analysis using halo CMEs
from SOHO
Authors: Gopalswamy, N.; Yashiro, S.; Akiyama, S.
2006cosp...36.2723G Altcode: 2006cosp.meet.2723G
We considered the geoeffectiveness of a set of all halo coronal mass
Ejections CMEs detected by the Solar and Heliospheric Observatory SOHO
during 1996-2003 inclusive Since CMEs take 1-4 days to reach Earth we
chose the minimum Dst value over an interval of 1-5 days after the
onset of a halo CME Distributions of these Dst values were compared
for the following subsets of halo CMEs 1 front-side halos whose solar
sources were within 45 degrees from the central meridian 2 Asymmetric
halos or limb halos whose sources are front-sided but located beyond
45 degrees from the central meridian and 3 backside halo CMEs We find
that the average and median Dst values following the front-side halos
are at the intense storm level -100 nT those following the asymmetric
halos are at weak storm level -60 nT and those following the backside
halos are not indicative of storms Note that we did not eliminate
moderate storms caused by high speed streams from coronal holes
When we compiled the minimum Dst values during 1-5 days following
a set of random days we found that the Dst distribution is nearly
identical to the case of backside halos This simple analysis clearly
demonstrates that the front-side halos are highly geoeffective whereas
the asymmetric halos are marginally geoeffective The backside halo
CMEs are not geoeffective at all because the CME plasma is unlikely
to reach Earth from backside CMEs
---------------------------------------------------------
Title: Magnetic Storms Caused by Corotating Solar Wind Streams
Authors: Tsurutani, Bruce T.; McPherron, Robert L.; Gonzalez, Walter
D.; Lu, Gang; Gopalswamy, Nat; Guarnieri, Fernando L.
2006GMS...167....1T Altcode:
Geomagnetic activity at Earth due to corotating high speed solar wind
streams are reviewed. High density plasma regions in the vicinity
of the heliospheric current sheet in the slow solar wind impinge
upon the magnetosphere and create magnetic storm intial phases. Dst
increases can be higher than those associated with shocks in front of
interplanetary coronal mass ejections. High speed streams following
the high density interplanetary plasma interact with the upstream slow
speed streams and create magnetic field compression regions called
corotating interaction regions (CIRs). The southward components of
the typically rapid Bz fluctuations within the CIRs, through sporadic
magnetic reconnection with the Earth's magnetic fields, lead to
weak to moderate intensity magnetic storm main phases, typically Dst
>-100 nT. Some CIRs (without southward component Bz fields) cause no
perceptible Dst changes at all. The "recovery" phases of CIR-induced
magnetic storms can last for a few days up to 27 days. The cause of
these particularly long duration storm "recoveries" is near-continuous
shallow plasma injections into the magnetosphere. Magnetic reconnection
associated with the southward component of the Alfvén waves within
the high speed streams with magnetopause fields is the cause of
these injections. The auroras during these intervals are continuous
and global auroral zone features. The AE/AL maxima are not substorms
or convection bays. Relativistic electrons are accelerated/observed
during these high speed stream intervals. The electrons first appear
in the beginning of the lengthy storm "recovery" phases. Geomagnetic
quiet is due to weak interplanetary magnetic fields with a lack of
Alfvénic fluctuations. These interplanetary regions generally occur
in the decay portion of high speed streams.
---------------------------------------------------------
Title: The CME-productivity associated with flares from two ARs
Authors: Akiyama, S.; Gopalswamy, N.; Yashiro, S.
2006cosp...36..556A Altcode: 2006cosp.meet..556A
NOAA active region AR 10039 appeared at the east limb on 21 July 2002
and rotated out of the earthside on 4 August This AR was magnetically
complex consisting of a spot group with a beta-gamma delta BGD
configuration from the start It produced 3 X- and 8 M-Class X-ray
flares during its disk passage NOAA AR 10044 located just to the
southwest of AR 10039 developed gradually into a BGD configuration
on 26 July and produced 9 M-class flares We examined the coronal mass
ejection CME associations rate R of these X-ray flares using data from
the Large Angle Spectrometric Coronagraph LASCO on board the Solar
and Heliospheric Observatory SOHO We found the CME-productivity to be
different between the two ARs AR 10039 was CME-rich with 72 association
with flares while AR 10044 was CME-poor with an association rate of
only 13 We also calculated the average velocity and angular width of
CMEs from the two ARs On the average the CMEs from the CME-rich AR were
faster 1195 km s and wider 246 deg than the ones from the CME-poor AR
282 km s and 12 deg We discuss the characteristics of the ARs which
might have resulted in the observed differences
---------------------------------------------------------
Title: International coordinated efforts for IHY 2007
Authors: Gopalswamy, N.; Davila, J.; Thompson, B.
2006cosp...36.2743G Altcode: 2006cosp.meet.2743G
The International Heliophysical Year IHY in 2007 marks the enormous
progress made since the International Geophysical Year IGY in 1957
The philosophy behind IHY is similar to that of IGY in studying the
environment of our habitat except that the scope has increased to the
physical space extending to the interstellar medium This paper describes
the international organization of the IHY and planning for a successful
program in 2007 In particular we describe the national regional and
global efforts in pooling the resources to address the universal
processes that govern the solar system and its interaction with the
surrounding medium The efforts include identifying science questions of
immediate concern and the data sets needed to address these questions
The data will be acquired using a truly distributed observatory
consisting of all the ground and space-based instruments that exist
today and those to be constructed before 2007 The international planning
also involves coordinating with the United Nations which through its
Basic Space Science Initiative is facilitating the participation of the
developing nations in the IHY program An update of the current status
of the planning activities at the international level will be presented
---------------------------------------------------------
Title: Anemone structure of AR NOAA 10798 and related geo-effective
flares and CMEs
Authors: Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.
2006cosp...36.2406A Altcode: 2006cosp.meet.2406A
We report coronal features of an active region NOAA 10798 This
active region was located in the middle of a small coronal hole and
generated 3 M-class flares The flares are associated with high speed
CMEs which produced a magnetic storm on 2005 August 24 We examined
the coronal features by using observational data in soft X-rays in
extreme ultraviolets and in microwaves obtained with GOES SOHO TRACE
satellites and Nobeyama Radioheliograph
---------------------------------------------------------
Title: The Pre-CME Sun
Authors: Gopalswamy, N.; Mikić, Z.; Maia, D.; Alexander, D.; Cremades,
H.; Kaufmann, P.; Tripathi, D.; Wang, Y. -M.
2006cme..book..303G Altcode:
The coronal mass ejection (CME) phenomenon occurs in closed magnetic
field regions on the Sun such as active regions, filament regions,
transequatorial interconnection regions, and complexes involving a
combination of these. This chapter describes the current knowledge
on these closed field structures and how they lead to CMEs. After
describing the specific magnetic structures observed in the CME source
region, we compare the substructures of CMEs to what is observed before
eruption. Evolution of the closed magnetic structures in response to
various photospheric motions over different time scales (convection,
differential rotation, meridional circulation) somehow leads to the
eruption. We describe this pre-eruption evolution and attempt to link
them to the observed features of CMEs. Small-scale energetic signatures
in the form of electron acceleration (signified by nonthermal radio
bursts at metric wavelengths) and plasma heating (observed as compact
soft X-ray brightening) may be indicative of impending CMEs. We survey
these pre-eruptive energy releases using observations taken before
and during the eruption of several CMEs. Finally, we discuss how the
observations can be converted into useful inputs to numerical models
that can describe the CME initiation.
---------------------------------------------------------
Title: Preface
Authors: Tsurutani, Bruce T.; McPherron, Robert L.; Gonzalez, Walter
D.; Lu, Gang; Sobral, José Humberto A.; Gopalswamy, Nat
2006GMS...167D...1T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Influence on the Heliosphere and Earth's Environment:
Recent Progress and Prospects
Authors: Gopalswamy, N.; Bhattacharyya, A.
2006ilws.conf.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The International Heliophysical Year (IHY) 2007
Authors: Davila, J. M.; Thompson, B. J.; Gopalswamy, N.
2006AfrSk..10....4D Altcode:
The International Geophysical Year (IGY) of 1957, a broad-based
and all-encompassing effort to push the frontiers of geophysics,
resulted in a tremendous increase of knowledge in space physics,
the Sun-Earth connection, planetary science, and the heliosphere in
general. Now, fifty years later, we have the unique opportunity to
advance our knowledge of the global heliosphere and its interaction with
planetary bodies and the interstellar medium through the International
Heliophysical Year (IHY) in 2007. This will be an international effort
which will raise public awareness of space physics. Because of its
unique geographic position, Africa is well-positioned to play a
critical role.
---------------------------------------------------------
Title: Microsat and Lunar-Based Imaging of Radio Bursts
Authors: MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Demaio,
L. D.; Bale, S. D.; Hewitt, J.; Kasper, J. C.; Lazarus, A. J.; Howard,
R. E.; Jones, D. L.; Reiner, M. J.; Weiler, K. W.
2006pre6.conf..491M Altcode: 2006pre4.conf..491M
No present or approved spacecraft mission has the capability to
provide high angular resolution imaging of solar or magnetospheric
radio bursts or of the celestial sphere at frequencies below the
ionospheric cutoff. Here, we describe a spacecraft mission to perform
such imaging in the frequency range ∼30 kHz to 15 MHz. This mission,
the Solar Imaging Radio Array (SIRA), is solar and exploration-oriented,
with emphasis on improved understanding and application of radio
bursts associated with solar energetic particle (SEP) events and
on tracking shocks and other components of coronal mass ejections
(CMEs). SIRA will require 12 to 16 micro- satellites to establish
a sufficient number of baselines. The proposed microsat is 3-axis
stabilized with body-mounted solar arrays and an articulated, Earth
pointing high gain antenna. Crossed dipoles and simple radio receivers
are the detectors for the aperture synthesis imaging. The microsats
will be located quasi-randomly on a spherical shell, initially of
∼10 km diameter. This constellation will likely be placed in a halo
orbit around L1, which is the preferred location for full-time solar
observations. We also discuss briefly follow-on missions such as a
lunar-based radio interferometer with of order 10 000 dipole antennas.
---------------------------------------------------------
Title: The Solar Imaging Radio Array: Space-Based Imaging of Solar,
Heliospheric, Magnetospheric, and Astrophysical Sources at Frequencies
below the Ionospheric Cutoff
Authors: MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Bale, S. D.;
Demaio, L. D.; Hewitt, J. N.; Kasper, J. C.; Lazarus, A. J.; Howard,
R. E.; Jones, D. L.; Reiner, M. J.; Weiler, K. W.
2005ASPC..345..476M Altcode:
Solar Imaging Radio Array (SIRA) is a mission concept for space-based,
interferometric imaging of solar and interplanetary radio emission
at frequencies below the Earth's ionospheric cutoff. Observing in a
frequency range of ∼30 kHz to 15 MHz, SIRA will observe the radio
emission from shocks driven by fast coronal mass ejections (CMEs). The
radio emissions permit tracking the leading boundaries of CMEs from
∼2 R<SUB>s</SUB> to 1 AU. When a CME impacts Earth's magnetosphere,
the dynamic response will be imaged in the light of magnetospheric
radio emissions, such as auroral kilometric radiation (AKR), scattered
on magnetospheric density gradients. The near-term possibility for a
SIRA mission is based on a NASA MIDEX-class mission, consisting of a
single constellation of ∼16 microsats located quasi-randomly on a
spherical shell of ∼10 km diameter. Such a mission is the logical
next step in space-based solar radio observations, as well as offering
a unique space weather prediction capability for the NASA Exploration
Initiative. SIRA will also serve a valuable role as a pathfinder for
more complex constellation and interferometry missions.
---------------------------------------------------------
Title: Introduction to special section on Solar Coronal Mass Ejections
and Energetic Particles
Authors: Gopalswamy, Nat; Torsti, J.
2005JGRA..11012S00G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Space-based Radio Imaging at Frequencies below the Ionospheric
Cutoff with SIRA
Authors: MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Demaio,
L. D.; Bale, S. D.; Howard, R. E.; Jones, D. L.; Kasper, J. C.;
Reiner, M. J.; Weiler, K. W.
2005AAS...207.2308M Altcode: 2005BAAS...37Q1197M
No present or approved spacecraft mission has the capability to provide
high angular resolution imaging of solar or magnetospheric radio
bursts or of the celestial sphere at frequencies below the ionospheric
cutoff. In this presentation, we review a MIDEX-class mission to
perform such imaging in the frequency range 30 kHz to 15 MHz. The
focus of the mission, the Solar Imaging Radio Array (SIRA), is solar
and exploration-oriented, with emphasis on improved understanding and
application of radio bursts associated with solar energetic particle
(SEP) events and on tracking shocks and other components of coronal
mass ejections (CMEs). SIRA will require 12 to 16 micro-satellites
to establish a sufficient number of baselines with separations on the
order of kilometers. The constellation consists of microsats located
quasi-randomly on a spherical shell, initially of radius 5 km. The
baseline microsat is 3-axis stabilized with body-mounted solar arrays
and an articulated, earth pointing high gain antenna. The constellation
will likely be placed at L1, which is the preferred location for
full-time solar observations. Detailed mission science and technology
goals will be reviewed.
---------------------------------------------------------
Title: Visibility of coronal mass ejections as a function of flare
location and intensity
Authors: Yashiro, S.; Gopalswamy, N.; Akiyama, S.; Michalek, G.;
Howard, R. A.
2005JGRA..11012S05Y Altcode:
We report the visibility (detection efficiency) of coronal mass
ejections (CMEs) of the Large Angle Spectrometric Coronagraph (LASCO) on
board the Solar and Heliospheric Observatory (SOHO). We collected 1301
X-ray flare events (above C3 level) detected by the GOES satellite and
examined their CME associations using data from LASCO coronagraphs. The
CME visibility was examined using the longitudinal variation of
CME association of X-ray flares, under the assumption that all CMEs
associated with limb flares are detectable by LASCO. Our findings are
(1) the CME association rate clearly increased with X-ray flare size
from 20% for C-class flares (between C3 and C9 levels) to 100% for
huge flares (above X3 level), (2) all CMEs associated with X-class
flares were detected by the LASCO coronagraphs, while half (25-67%)
of CMEs associated with C-class flares were invisible. We examined
the statistical properties of the flare-associated CMEs and compared
them by flare size and longitude. CMEs associated with X-class flares
were significantly faster (median 1556 km/s) and wider (median 244°)
than those of CMEs associated with disk C-class flares (432 km/s,
68°). We conclude that all fast and wide CMEs are detectable by LASCO,
but slow and narrow CMEs may not be visible when the CMEs originate
from the disk center.
---------------------------------------------------------
Title: Workshop Highlights Progress in Solar-Heliospheric Physics
Authors: Gopalswamy, Nat
2005EOSTr..86..525G Altcode:
The Solar, Heliospheric, and Interplanetary Environment (SHINE) group
is an affiliation of researchers dedicated to promoting an enhanced
understanding of the processes by which magnetic fields, plasmas,
and energetic particles are produced near the Sun and propagated
through the interplanetary medium to Earth and other locations in
the heliosphere. The group conducted its annual workshop in July to
discuss recent developments in the study of solar variability and its
impact on Earth's space environment. One hundred fifty-five scientists,
including 27 students, participated in the plenary, working group,
and poster sessions. Student Day activities on 10 July consisted of
tutorials given by experienced scientists: solar flares and particle
acceleration (Robert Lin, University of California Berkeley), the
origin of coronal mass ejections (CMEs) (Spiro Antiochos, Naval
Research Laboratory, Washington, D.C.), connecting the Sun and
heliosphere (Thomas Zurbuchen, University of Michigan, Ann Arbor),
and acceleration and transport of solar energetic particles (SEPs)
(Christina Cohen, California Institute of Technology, Pasadena). The
tutorials were followed by student presentations on CMEs near the sun
and in the interplanetary medium, solar wind, and SEPs.
---------------------------------------------------------
Title: Type II radio bursts and energetic solar eruptions
Authors: Gopalswamy, N.; Aguilar-Rodriguez, E.; Yashiro, S.; Nunes,
S.; Kaiser, M. L.; Howard, R. A.
2005JGRA..11012S07G Altcode:
We report on a study of type II radio bursts from the Wind/WAVES
experiment in conjunction with white-light coronal mass ejections (CME)
from the Solar and Heliospheric Observatory (SOHO). The type II bursts
considered here have emission components in all the spectral domains:
metric, decameter-hectometric (DH) and kilometric (km), so we refer to
them as m-to-km type II bursts. CMEs associated with the m-to-km type
II bursts were more energetic than those associated with bursts in any
single wavelength regime. CMEs associated with type II bursts confined
to the metric domain were more energetic (wider and faster) than the
general population of CMEs but less energetic than CMEs associated
with DH type II bursts. Thus the CME kinetic energy seems to organize
the life time of the type II bursts. Contrary to previous results,
the starting frequency of metric type II bursts with interplanetary
counterparts seems to be no different from that of type II bursts
without interplanetary counterparts. We also verified this by showing
that the average CME height at the onset time of the type II bursts
is the same for the two metric populations. The majority (78%) of the
m-to-km type II bursts were associated with solar energetic particle
(SEP) events. The solar sources of the small fraction of m-to-km
type II bursts without SEP association were poorly connected to the
observer near Earth. Finally, we found that the m-to-km type II bursts
were associated with bigger flares compared to the purely metric type
II bursts.
---------------------------------------------------------
Title: A universal characteristic of type II radio bursts
Authors: Aguilar-Rodriguez, E.; Gopalswamy, N.; MacDowall, R.; Yashiro,
S.; Kaiser, M. L.
2005JGRA..11012S08A Altcode:
We present a study on the spectral properties of interplanetary
type II radio bursts observed by the Radio and Plasma Wave (WAVES)
experiment on board the Wind spacecraft. We investigated the relative
bandwidth of the type II radio bursts observed by WAVES from 1997 up to
2003. We obtained three sets of events, based on the frequency domain of
occurrence: 109 events in the low-frequency domain (30 KHz to 1000 kHz,
detected by the RAD1 receiver), 216 events in the high-frequency domain
(1-14 MHz, observed by the RAD2 receiver), and 73 events that spanned
both domains (RAD1 and RAD2). Statistical results show that the average
bandwidth-to-frequency ratio (BFR) was 0.28 ± 0.15, 0.26 ± 0.16,
and 0.32 ± 0.15 for RAD1, RAD2, and RAD1 + RAD2, respectively. We
compared our results with those obtained for ISEE-3 type II bursts
and found a difference in the average BFR, which seems to be due to
a selection effect. The BFR of the WAVES type II bursts is similar
to that of metric type II bursts reported in published works. This
suggests that the BFR is a universal characteristic, irrespective of
the spectral domain. Finally, we also studied the BFR evolution with
heliocentric distance using white-light observation of the associated
coronal mass ejections. We found that the BFR remains roughly constant
in the SOHO/LASCO field of view (i.e., from 2.1 to 32 solar radii),
while the bandwidth itself decreases.
---------------------------------------------------------
Title: What is Unusual About the 2005 January 20 SEP Event?
Authors: Gopalswamy, N.; Xie, H.; Yashiro, S.; Usoskin, I.
2005AGUFMSH23A0318G Altcode:
We report on the solar energetic particle (SEP) event of 2005 January
20 that had an associated ground level enhancement (GLE). The Solar
and Heliospheric Observatory (SOHO) spacecraft observed a CME, which
was among the fastest of cycle 23 CMEs. This event is consistent with
the results that the GLE-associated CMEs represent the fastest known
population of CMEs. A metric type II burst started before the proton
injection time, suggesting that a coronal shock was formed before
high-energy protons were released at the Sun. These 2005 January 20
event is consistent with the current paradigm that large SEP events
originate in CME-driven shocks. We also determined the height of
the CME at two time marks: the metric type II onset (2.1 Rs) and
the proton injection time (4.5 Rs). At a height of 4.5 Rs the CME
should have attained the maximum speed, thus driving the strongest
shocks. We discuss the estimation of the CME speed given that the
coronagraph observations were hampered by the SEPs arriving at the SOHO
spacecraft. We also discuss the arrival of the CME-associated plasma
and shock at 1 AU. Work supported by NASA/LWS and NSF/SHINE programs.
---------------------------------------------------------
Title: Distributed Instrumentation Deployment During the IHY
Authors: Davila, J. M.; Thompson, B. J.; Gopalswamy, N.
2005AGUFMSM21A0347D Altcode:
A major thrust of the International Heliophysical Year (IHY) is to
deploy arrays of small, inexpensive instruments such as magnetometers,
radio antennas, GPS receivers, all-sky cameras, etc. around the
world to provide global measurements of ionospheric and heliospheric
phenomena. This program is a collaboration between the IHY and the
United Nations Basic Space Science (UNBSS) program, which has been
dedicated to the IHY through 2009. The small instrument program is
envisioned as a partnership between instrument providers, and instrument
host countries. The lead scientist will provide the instruments (or
fabrication plans for instruments) in the array; the host country
will provide manpower, facilities, and operational support to obtain
data with the instrument typically at a local university. Instrument
operational support for local scientists, facilities, data acquisition,
etc will be provided by the host nation.
---------------------------------------------------------
Title: Introduction to violent Sun-Earth connection events of
October-November 2003
Authors: Gopalswamy, N.; Barbieri, L.; Cliver, E. W.; Lu, G.; Plunkett,
S. P.; Skoug, R. M.
2005JGRA..110.9S00G Altcode: 2005JGRA..11009S00G
The solar-terrestrial events of late October and early November 2003,
popularly referred to as the Halloween storms, represent the best
observed cases of extreme space weather activity observed to date and
have generated research covering multiple aspects of solar eruptions and
their space weather effects. In the following article, which serves as
an abstract for this collective research, we present highlights taken
from 61 of the 74 papers from the Journal of Geophysical Research,
Geophysical Research Letters, and Space Weather which are linked under
this special issue. (An overview of the 13 associated papers published
in Geophysics Research Letters is given in the work of Gopalswamy et
al. (2005a)).
---------------------------------------------------------
Title: A Study of the Drift Rate of Type II Radio Bursts at Different
Wavelengths
Authors: Aguilar-Rodriguez, E.; Gopalswamy, N.; MacDowall, R.; Yashiro,
S.; Kaiser, M. I.
2005ESASP.592..393A Altcode: 2005soho...16E..65A; 2005ESASP.592E..65A
No abstract at ADS
---------------------------------------------------------
Title: Coronal mass ejections and other extreme characteristics of
the 2003 October-November solar eruptions
Authors: Gopalswamy, N.; Yashiro, S.; Liu, Y.; Michalek, G.; Vourlidas,
A.; Kaiser, M. L.; Howard, R. A.
2005JGRA..110.9S15G Altcode: 2005JGRA..11009S15G
Fast coronal mass ejections (CMEs), X-class flares, solar energetic
particle (SEP) events, and interplanetary shocks were abundantly
observed during the episode of intense solar activity in late October
and early November 2003. Most of the 80 CMEs originated from three
active regions (NOAA ARs 484, 486, and 488). We compare the statistical
properties of these CMEs with those of the general population of CMEs
observed during cycle 23. We find that (1) the 2003 October-November
CMEs were fast and wide on the average and hence were very energetic,
(2) nearly 20 percent of the ultrafast CMEs (speed ≥2000 km
s<SUP>-1</SUP>) of cycle 23 occurred during the October-November
interval, including the fastest CME of the study period (∼2700
km s<SUP>-1</SUP> on 4 November 2003 at 1954 UT), (3) the rate of
full-halo CMEs was nearly four times the average rate during cycle 23,
(4) at least sixteen shocks were observed near the Sun, while eight of
them were intercepted by spacecraft along the Sun-Earth line, (5) the
CMEs were highly geoeffective: the resulting geomagnetic storms were
among the most intense of cycle 23, (6) the CMEs were associated with
very large SEP events, including the largest event of cycle 23. These
extreme properties were commensurate with the size and energy of the
associated active regions. This study suggests that the speed of CMEs
may not be much higher than ∼3000 km s<SUP>-1</SUP>, consistent with
the free energy available in active regions. An important practical
implication of such a speed limit is that the Sun-Earth travel times of
CME-driven shocks may not be less than ∼0.5 day. Two of the shocks
arrived at Earth in <24 hours, the first events in ∼30 years and
only the 14th and 15th documented cases of such events since 1859.
---------------------------------------------------------
Title: Flare-generated shock evolution and geomagnetic storms during
the “Halloween 2003 epoch”: 29 October to 2 November
Authors: Wu, Chin-Chun; Wu, S. T.; Dryer, M.; Fry, C. D.; Berdichevsky,
D.; Smith, Z.; Detman, T.; Gopalswamy, N.; Skoug, R.; Zurbuchen, T.;
Smith, C.
2005JGRA..110.9S17W Altcode: 2005JGRA..11009S17W
The October/November 2003 ("Halloween 2003") epoch of intense solar
flares provided an opportunity to test the results of earlier
parametric 1.5 MHD studies of interacting interplanetary shock
waves. These preliminary studies used an adaptive numerical grid that
made it possible to identify products of these interactions. During 28
October to 2 November 2003, three shocks generated by four solar flares
were observed at the L1 libration point by ACE/SWEPAM/SWICS/MAG. Two
very distinct geomagnetic storms, associated with two of these flares
(X17/4B and X10/2B), rank as two of the largest storms of solar cycle
23. The purpose of this paper is to present the use of an adaptive
grid 1.5-dimensional MHD model that is initiated at the solar surface
to study in detail the three shocks observed at L1 that were generated
by the four solar flares. Accordingly, four separate pressure pulses,
at the appropriate times and with different strengths and duration,
determined via a trial and error procedure, are introduced on the Sun
to mimic the four flares. The results show that the simulated solar
wind velocity temporal profiles successfully matched the observations
at L1. The major objective, to demonstrate the detailed nature of
interacting shocks and some of their products after origination from
closely spaced solar events, is achieved. In addition, the MHD model
is able to suggest the solar sources that are associated with specific
geomagnetic storms at Earth.
---------------------------------------------------------
Title: Coronal Mass Ejections and Galactic Cosmic-Ray Modulation
Authors: Lara, A.; Gopalswamy, N.; Caballero-López, R. A.; Yashiro,
S.; Xie, H.; Valdés-Galicia, J. F.
2005ApJ...625..441L Altcode:
We present a study of the long-term evolution of coronal mass ejections
(CMEs) observed by the Large Angle and Spectrometric Coronograph
(LASCO) on board SOHO during the ascending, maximum, and part of
the descending phases of solar cycle 23 and their relation with the
modulation of galactic cosmic-ray (GCR) intensity observed at 1 AU
by the Climax neutron monitor and IMP-8 spacecraft. We compare the
long-term GCR modulation with the CME occurrence rate at all, low,
and high latitudes, as well as the observed CME parameters (width and
speed). Twenty-seven day averages of CME occurrence rates and CME
properties from 1996 January to 2003 December are presented in the
Appendix. The general anticorrelation between GCR intensity and the
CME rate is relatively high (~-0.88). However, when we divide the CME
rate into low- and high-latitude rates and compare them with the GCR
intensity during the ascending phase of solar cycle 23, we find a lower
anticorrelation between the low-latitude the CME rate and GCR intensity
(~-0.71) and a very high anticorrelation between the high-latitude
CME rate and GCR intensity (~-0.94). This suggests that, in general,
CMEs could cause the decrease in the GCR flux in the inner heliosphere,
as stated by the global merged interaction region (GMIR) theory. In
particular, during the ascending phase of cycle 23 (qA>0), this flux
comes mainly from heliospheric polar regions. Thus, high-latitude CMEs
may play a central role in the long-term cosmic-ray modulation during
this phase of the cycle by blocking the polar entrance of GCRs to the
inner heliosphere. This study supports the scenario in which CMEs, among
other structures, are the building blocks of GMIRs, although we propose
that the spherical shells (GMIRs) are closed separately at polar and
equatorial regions by CMEs of different latitudes. Our results suggest
that all CME properties show some correlation with the GCR intensity,
although there is no specific property (width, speed, or a proxy of
energy) that definitely has a higher correlation with GCR intensity.
---------------------------------------------------------
Title: Statistical Study of Shocks and CMEs Associated With
Interplanetary Type II Bursts
Authors: Aguilar-Rodriguez, E.; Gopalswamy, N.; MacDowall, R.; Yashiro,
S.; Kaiser, M. L.
2005AGUSMSH43A..04A Altcode:
We present a study of some spectral properties associated with
interplanetary Type II radio emission. Type II radio bursts are
signatures of violent eruptions from the Sun that result in shock
waves propagating through the corona and the interplanetary medium. We
investigated the relative bandwidth of all the type II bursts observed
by the Radio and Plasma Wave Experiment (WAVES) on board the Wind
spacecraft from 1997 up to 2003. We obtained three sets of events,
based on the frequency domain of occurrence: 109 events in the low
frequency domain (30 KHz to 1000 kHz detected by the RAD1 receiver),
216 events in the high frequency domain (1-14 MHz, observed by the RAD2
receiver), and 73 events that spanned both domains (RAD1 and RAD2). We
present statistical results for the bandwidth-to-frequency ratio (BFR)
in the three subsets as well as a comparision of our results with the
Type II solar radio bursts observed by ISEE-3 radio experiment, which
is similar to WAVES/RAD1. We analyzed the bandwidth and BFR evolution
with the heliocentric distance as well as an analysis of drift rate
magnitude of type II radio bursts and its starting frequency. We also
present some properties of shocks and coronal mass ejections associated
with interplanetary type II bursts. This work is partially supported
by NSF/SHINE (ATM 0204588)
---------------------------------------------------------
Title: Sun-Earth Propagation Time of CMEs Originated at different
Helio Longitudes
Authors: Lara, A.; Gopalswamy, N.; Xie, H.; Gonzalez-Esparza, A.
2005AGUSMSH53A..10L Altcode:
We present a study of the transport of coronal mass ejections
(CMEs) in the interplanetary medium and the probability that they,
or the associated shocks, reach the Earth surroundings when they are
ejected in different Helio-longitudes. To reach this goal we choose the
CME events associated with the active region 0486 which crosses the
solar disk during October - November 2003 and produced several CMEs
during its crossing from East to West limb. We measured and analyzed
the speed profile of each event, we found that the speed profile of
halos and partial-halo CMEs are very symmetric and an elliptical model
seems to fit the profiles very well. Using a cone model we determine
the space direction of CMEs and then, the most probable speed in the
Sun-Earth direction. Using these speeds, we applied the CME travel
time empirical model to determine the near Earth arrival times of both
interplanetary CME and related shock. We found that the difference
between the predicted and observed arrival times increase with the
Helio-longitude of the CME. To help in the identification of CME -
1 AU shocks and to validate the empirical model, we use 2D numerical
simulations of the events.
---------------------------------------------------------
Title: Solar source of the largest geomagnetic storm of cycle 23
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Xie, H.; Lepping,
R. P.; Howard, R. A.
2005GeoRL..3212S09G Altcode:
The largest geomagnetic storm of solar cycle 23 occurred on 2003
November 20 with a Dst index of -472 nT, due to a coronal mass ejection
(CME) from active region 0501. The CME near the Sun had a sky-plane
speed of ~1660 km/s, but the associated magnetic cloud (MC) arrived
with a speed of only 730 km/s. The MC at 1 AU (ACE Observations) had
a high magnetic field (~56 nT) and high inclination to the ecliptic
plane. The southward component of the MC's magnetic field was made
up almost entirely of its axial field because of its east-south-west
(ESW) chirality. We suggest that the southward pointing strong axial
field of the MC reconnected with Earth's front-side magnetic field,
resulting in the largest storm of the solar cycle 23.
---------------------------------------------------------
Title: Putting the Rubber to the Road: The Whos, Whys and Hows of
the International Heliophysical Year 2007
Authors: Thompson, B. J.; Davila, J. M.; Drobnes, E.; Gopalswamy,
N.; Wesenberg, R. P.
2005AGUSM.U23A..07T Altcode:
In 1957 a program of international research, inspired by the
International Polar Years of 1882 and 1932, was organized as the
International Geophysical Year (IGY) to study global phenomena
of the Earth and geospace. Fifty years later, the world's science
community will again come together for international programs of
scientific collaboration: the International Heliophysical Year
(IHY), the electronic Geophysical Year (eGY), and the International
Polar Year (IPY) 2007. This time, research will extend out into the
heliosphere to focus on solar-terrestrial-planetary interactions. The
ambitious plans for the IHY, eGY and IPY incorporate the activities
of scientists in 191 nations, the "IGY Gold" Historical Preservation
initiative, a series of coordinated campaigns involving more than
100 instruments and models, education and public outreach programs,
a developing nations instrument development program, and opportunities
for supported research worldwide. The presentation will focus on the
efforts and operations which will make these activities possible.
---------------------------------------------------------
Title: Improved Empirical CME Arrival Time Model Via Cone Model
Authors: Xie, H.; Gopalswamy, N.; Ofman, L.; Michalek, G.; Lara, A.;
Yashiro, S.
2005AGUSMSH53A..09X Altcode:
In this study, we compare the results obtained from two cone models
and carry out the statistical study of the distribution of the actual
size and space speed of Coronal Mass Ejections (CMEs). We improved
the existing empirical CME arrival (ECA) model, based on previously
developed empirical models and provided the prediction of CME transit
time from the Sun to the Earth. The previous ECA model was in good
agreement with the observations for high-speed CMEs. However, the
agreement was not as good for low-speed events. One of possible reasons
may be due to errors caused by the significant scatter of CME projection
speeds in low projected-speed events. Using the cone models we reduced
the errors and improved the accuracy of the ECA model by applying the
cone models to halo CMEs erupted from near disk center of the Sun
(within < 30 deg.) to determine the actual speed. We found that
both cone models provide similar improved accuracy for the arrival time.
---------------------------------------------------------
Title: Photospheric sources of very fast coronal mass ejections
Authors: Yurchyshyn, V.; Yashiro, S.; Gopalswamy, N.
2005AGUSMSH51C..04Y Altcode:
We identified photospheric sources for 39 very fast (v > 1100
km/s) front-side coronal mass ejections that erupted between 1999 and
2001. For our study we used data on CMEs and their sources provided
by the CME Catalog, SOHO spacecraft (LASCO, EIT, MDI), Big Bear Solar
Observatory (Halpha, magnetograms), Mount Wilson Observatory (sunspot
drawings) and Joint USAF/NOAA active region summary. Our results are
as follows. We distinguished three different groups of active regions
which are responsible for very fast CMEs: 1) Complex delta spots (21
events). This group of active regions is characterized by the presence
of at least two large opposite polarity sunspots located close to
each other. 2) Simple delta spots (8 events). A typical configuration
of this type consists of one large twisted tadpole-shaped sunspot,
surrounded by many small satellite-sunspots. 3) Extended magnetic
regions, which consist of two adjacent decaying active regions or a
new active region emerging inside a decaying active region.
---------------------------------------------------------
Title: Estimation of Projection Effect of CMEs from the Onset Time
of the Shock-Associated Type III Radio Burst
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.
2005AcA....55..151M Altcode:
We present a new possibility to estimate the projection effects
on coronal mass ejection (CME) measurements. It is well known
that coronagraphic observations of CMEs are subject to projection
effects. Fortunately, the WIND/WAVES observations of type III radio
bursts associated with shock waves are free from projection effects. We
assume that (1) high energy electrons are produced at the shock front
ahead of the CME, and (2) the radio burst starts when the shock reaches
open field lines (approx 3 R_odot). In other words, the onset time
of the radio burst corresponds to the time when the CME leading edge
reaches 3 R_odot. The difference between the onset times of CMEs and
radio bursts should be strongly correlated with the position of CMEs
on the Sun. This correlation seems to be strongly dependent on solar
activity. Using particular linear fits on the scatter plots, we can
determine the source location of CMEs and tell how much the projection
effect can really affect CME measurements.
---------------------------------------------------------
Title: Introduction to the special section: Violent Sun-Earth
connection events of October-November 2003
Authors: Gopalswamy, N.; Barbieri, L.; Lu, G.; Plunkett, S. P.; Skoug,
R. M.
2005GeoRL..32.3S01G Altcode: 2005GeoRL..3203S01G
During 2003 October and November, a series of solar eruptions
occurred from three solar active regions. Some of these eruptions were
extreme in terms of their origin (source properties) and heliospheric
consequences. This paper summarizes the first results of the analysis
of these violent Sun-Earth connection events.
---------------------------------------------------------
Title: CMEs and Long-Lived Geomagnetic Storms: A Case Study
Authors: Xie, H.; Gopalswamy, N.; Manoharan, P. K.; Yashiro, S.;
Lara, A.; Lepri, S.
2005IAUS..226..475X Altcode:
We studied the relationship between successive coronal mass ejections
(CMEs) and a long-lived geomagnetic storm (LLGMS) by examining the 1998
May 4 event. Five successive CMEs from the same active region and four
interplanetary shocks were found to be associated with this LLGMS. We
investigated the effect of successive and interacting CMEs on the LLGMS.
---------------------------------------------------------
Title: An empirical model to predict the 1-AU arrival of
interplanetary shocks
Authors: Gopalswamy, N.; Lara, A.; Manoharan, P. K.; Howard, R. A.
2005AdSpR..36.2289G Altcode:
We extend the empirical coronal mass ejection (CME) arrival model of
Gopalswamy et al. [Gopalswamy, N. et al. Predicting the 1-AU arrival
times of coronal mass ejections, J. Geophys. Res. 106, 29207, 2001]
to predict the 1-AU arrival of interplanetary (IP) shocks. A set of
29 IP shocks and the associated magnetic clouds observed by the Wind
spacecraft are used for this study. The primary input to this empirical
shock arrival model is the initial speed of white-light CMEs obtained
using coronagraphs. We use the gas dynamic piston-shock relationship
to derive the ESA model which provides a simple means of obtaining the
1-AU speed and arrival times of interplanetary shocks using CME speeds.
---------------------------------------------------------
Title: CME Interaction and the Intensity of Solar Energetic Particle
Events
Authors: Gopalswamy, N.; Yashiro, S.; Krucker, S.; Howard, R. A.
2005IAUS..226..367G Altcode:
Large Solar Energetic Particles (SEPs) are closely associated with
coronal mass ejections (CMEs). The significant correlation observed
between SEP intensity and CME speed has been considered as the evidence
for such a close connection. The recent finding that SEP events with
preceding wide CMEs are likely to have higher intensities compared to
those without was attributed to the interaction of the CME-driven shocks
with the preceding CMEs or with their aftermath. It is also possible
that the intensity of SEPs may also be affected by the properties
of the solar source region. In this study, we found that the active
region area has no relation with the SEP intensity and CME speed,
thus supporting the importance of CME interaction. However, there is a
significant correlation between flare size and the active region area,
which probably reflects the spatial scale of the flare phenomenon as
compared to that of the CME-driven shock.
---------------------------------------------------------
Title: Statistical Distributions of Speeds of Coronal Mass Ejections
Authors: Yurchyshyn, V.; Yashiro, S.; Abramenko, V.; Wang, H.;
Gopalswamy, N.
2005ApJ...619..599Y Altcode:
We studied the distribution of plane-of-sky speeds determined for
4315 coronal mass ejections (CMEs) detected by the Large Angle and
Spectrometric Coronagraph Experiment on board the Solar and Heliospheric
Observatory (SOHO LASCO). We found that the speed distributions
for accelerating and decelerating events are nearly identical and
to a good approximation they can be fitted with a single lognormal
distribution. This finding implies that, statistically, there is no
physical distinction between the accelerating and the decelerating
events. The lognormal distribution of the CME speeds suggests that
the same driving mechanism of a nonlinear nature is acting in both
slow and fast dynamical types of CMEs.
---------------------------------------------------------
Title: Coronal Mass Ejections and Ground Level Enhancements
Authors: Gopalswamy, N.; Xie, H.; Yashiro, S.; Usoskin, I.
2005ICRC....1..169G Altcode: 2005ICRC...29a.169G
No abstract at ADS
---------------------------------------------------------
Title: Solar Imaging Radio Array (SIRA): a multispacecraft mission
Authors: MacDowall, R. J.; Bale, S. D.; Demaio, L.; Gopalswamy, N.;
Jones, D. L.; Kaiser, M. L.; Kasper, J. C.; Reiner, M. J.; Weiler,
K. W.
2005SPIE.5659..284M Altcode:
The Solar Imaging Radio Array (SIRA) is a mission to perform
aperture synthesis imaging of low frequency solar, magnetospheric,
and astrophysical radio bursts. The primary science targets are
coronal mass ejections (CMEs), which drive shock waves that may
produce radio emission. A space-based interferometer is required,
because the frequencies of observation (<15 MHz) are cutoff by the
ionosphere. SIRA will require a 12 to 16 microsatellite constellation
to establish a sufficient number of baselines with separations on the
order of kilometers. The microsats will be located quasi-randomly on
a spherical shell, initially of diameter 10 km or less. The baseline
microsat, as presented here, is 3-axis stabilized with a body-mounted,
earth-directed high gain antenna and an articulated solar array;
this design was developed by the Integrated Mission Design Center
(IMDC) at NASA Goddard Space Flight Center (GSFC). A retrograde orbit
at a distance of ~500,000 km from Earth was selected as the preferred
orbit because the 8 Mbps downlink requirement is easy to meet, while
keeping the constellation sufficiently distant from terrestrial radio
interference. Also, the retrograde orbit permits imaging of terrestrial
magnetospheric radio sources from varied perspectives. The SIRA mission
serves as a pathfinder for space-based satellite constellations and for
spacecraft interferometry at shorter wavelengths. It will be proposed
to the NASA MIDEX proposal opportunity in mid-2005.
---------------------------------------------------------
Title: The Solar Imaging Radio Array (SIRA) Mission
Authors: Jones, D. L.; MacDowall, R.; Gopalswamy, N.; Kaiser, M.;
Reiner, M.; Demaio, L.; Weiler, K.; Kasper, J.; Bale, S.; Howard, R.
2004AAS...205.1012J Altcode: 2004BAAS...36.1351J
The Solar Imaging Radio Array will be proposed to NASA as a Medium
Explorer (MIDEX) mission by a team of investigators at GSFC, JPL, NRL,
MIT, and UC Berkeley. The main science goal of the mission is imaging
and tracking of solar radio bursts, particularly those associated with
coronal mass ejections, and understanding their evolution and influence
on Earth's magnetosphere. Related goals are mapping the 3-dimensional
morphology of the interplanetary magnetic field and improving the
prediction of geomagnetic storms. A number of topics in galactic
and extragalactic astrophysics will also be addressed by SIRA. The
mission concept is a free-flying array of about 16 small, inexpensive
satellites forming an aperture synthesis interferometer in space. By
observing from above the ionosphere, and far from terrestrial radio
interference, SIRA will cover frequencies between a few tens of kHz up
to 15 MHz. This wide spectral window is essentially unexplored with
high angular resolution. <P />Part of this work is being carried out
at the Jet Propulsion Laboratory, California Institute of Technology,
under contract with the National Aeronautics and Space Administration.
---------------------------------------------------------
Title: Intensity variation of large solar energetic particle events
associated with coronal mass ejections
Authors: Gopalswamy, N.; Yashiro, S.; Krucker, S.; Stenborg, G.;
Howard, R. A.
2004JGRA..10912105G Altcode:
We studied the coronal mass ejections (CMEs) and flares associated
with large solar energetic particle (SEP) events of solar cycle 23
(1996-2002) in order to determine what property of the solar eruptions
might order the SEP intensity. The SEP events were divided into three
groups: (1) events in which the primary CME was preceded by one or more
wide CMEs from the same solar source, (2) events with no such preceding
CMEs, and (3) events in which the primary CME might have interacted
with a streamer or with a nearby halo CME. The SEP intensities are
distinct for groups 1 and 2 although the CME properties were nearly
identical. Group 3 was similar to group 1. The primary findings of this
study are as follows: (1) Higher SEP intensity results whenever a CME
is preceded by another wide CME from the same source region. (2) The
average flare size was also larger for high-intensity SEP events. (3)
The intensity of SEP events with preceding CMEs showed a tighter
correlation with CME speed. The extent of scatter in the CME speed
versus SEP intensity plots was reduced when various subgroups were
considered separately. (4) The intensities of energetic electrons were
better correlated with flare size than with CME speed. (5) The SEP
intensity showed poor correlation with the flare size, except for group
3 events. Since only a third of the events did not have preceding CMEs,
we conclude that the majority of SEP producing CMEs propagate through
the near-Sun interplanetary medium severely disturbed and distorted by
the preceding CMEs. Furthermore, the preceding CMEs are faster and wider
on the average, so they may provide seed particles for CME-driven shocks
that follow. Therefore we conclude that the differing intensities of
SEP events in the two groups may not have resulted due to the inherent
properties of the CMEs. The presence of preceding CMEs seems to be the
discriminating characteristic of the high- and low-intensity SEP events.
---------------------------------------------------------
Title: Improved Empirical CME Arrival Time Prediction Model
Authors: Xie, H.; Gopalswamy, N.; Lara, A.; Yashiro, S.
2004AGUFMSH53B0324X Altcode:
We have successfully developed an innovative analytical method
to determine the angular width and propagation orientation of Halo
Coronal Mass Ejections (Xie et al. 2003). We will apply this new method
to improve the existing empirical space weather forecasting models
(e.g., Gopalswamy et al., 2001). Gopalswamy et al. (2001) presented an
empirical model to provide the predication of CME transit time from the
Sun to the Earth. The model is in good agreement with the observations
for high-speed CMEs. However, the agreement is not good for low-speed
events. One of possible reasons may be due to errors caused by the
significant scatter of CME prjection speeds used in the model. Using
our new method can determine the actual speed of CMEs and thus reduce
the errors and improve the model.
---------------------------------------------------------
Title: Association of Coronal Mass Ejections and Type II Radio Bursts
with Impulsive Solar Energetic Particle Events
Authors: Yashiro, S.; Gopalswamy, N.; Cliver, E. W.; Reames, D. V.;
Kaiser, M. L.; Howard, R. A.
2004ASPC..325..401Y Altcode:
We report the association of impulsive solar energetic particle (SEP)
events with coronal mass ejections (CMEs) and metric type II radio
bursts. We identified 38 impulsive SEP events using the WIND/EPACT
instrument and their CME association was investigated using white
light data from SOHO/LASCO. We found that (1) at least ∼ 28--39 % of
impulsive SEP events were associated with CMEs, (2) only 8--13 % were
associated with metric type II radio bursts. The statistical properties
of the associated CMEs were investigated and compared with those of
general CMEs and CMEs associated with large gradual SEP events. The
CMEs associated with impulsive SEP events were significantly slower
(median speed of 613 kmps) and narrower (49 deg) than those of CMEs
associated with large gradual SEP events (1336 kmps, 360 deg), but
faster than the general CMEs (408 kmps).
---------------------------------------------------------
Title: Brightness Characteristics of Halo CMEs
Authors: Lara, A.; Gopalswamy, N.; Michalek, G.; Xie, H.; Yashiro, S.
2004AGUFMSH53B0316L Altcode:
It is generally accepted that halo Coronal Mass Ejections (CMEs)
are regular, low latitude, CMEs traveling towards (or away FROM)
the observer. The association between halo CMEs and solar energetic
particles events (SEPs) and Type II bursts is higher compared to regular
CMEs. Halo CMEs are observed up to large heliocentric distances as
compared to the regular CMEs. This is somewhat contradictory to the
theory of Thomson scattering because the visibility conditions for
halo CMEs are rather poor, assuming that the longitudinal widths of
halo CMEs are the similar to those of regular CMEs. In this paper, we
present some observational characteristics of halo CMEs, such as high
brightness at large distances and symmetry in the velocity space. The
CMEs were observed by the Solar and Heliospheric Observatory (SOHO)
mission's Large Angle and Spectrometric Coronagraph (LASCO). We also
present a possible model that explains the apparent contradiction
---------------------------------------------------------
Title: Radio-quiet Fast Coronal Mass Ejections
Authors: Gopalswamy, N.; Aguilar-Rodriguez, E.; Kaiser, M. L.; Howard,
R. A.
2004AGUFMSH23A..05G Altcode:
Coronal mass ejections (CMEs) drive shocks in the interplanetary
medium that produce type II radio emission. These CMEs are faster and
wider on the average, than the general population of CMEs. However,
when we start from fast (speed > 900 km/s) and wide (angular
width > 60 degrees), more than half of them are not associated
with radio bursts. In order to understand why these CMEs are radio
quiet, we collected all the fast and wide (FW) CMEs detected by the
Solar and Heliospheric Observatory (SOHO) mission's Large Angle and
Spectrometric Coronagraph (LASCO) and isolated those without associated
type II radio bursts. The radio bursts were identified in the dynamic
spectra of the Radio and Plasma Wave (WAVES) Experiment on board the
Wind spacecraft. We also checked the list against metric type II radio
bursts reported in Solar Geophysical Data and isolated those without
any radio emission. This exercise resulted in about 140 radio-quiet FW
CMEs. We identified the source regions of these CMEs using the Solar
Geophysical Data listings, cross-checked against the eruption regions
in the SOHO/EIT movies. We explored a number of possibilities for the
radio-quietness: (i) Source region being too far behind the limb, (ii)
flare size, (iii) brightness of the CME, and (iv) the density of the
ambient medium. We suggest that a combination of CME energy and the
Alfven speed profile of the ambient medium is primarily responsible
for the radio-quietness of these FW CMEs.
---------------------------------------------------------
Title: Solar Imaging Radio Array (SIRA): Imaging solar,
magnetospheric, and astrophysical sources at < 15 MHz
Authors: Howard, R.; MacDowall, R.; Gopalswamy, N.; Kaiser, M. L.;
Reiner, M. J.; Bale, S.; Jones, D.; Kasper, J.; Weiler, K.
2004DPS....36.1424H Altcode: 2004BAAS...36Q1097H
The Solar Imaging Radio Array (SIRA) is a mission to perform
aperture synthesis imaging of low frequency solar, magnetospheric, and
astrophysical radio bursts. The primary science targets are coronal mass
ejections (CMEs), which drive radio emission producing shock waves. A
space-based interferometer is required, because the frequencies of
observation (<15 MHz) do not penetrate the ionosphere. As such,
the SIRA mission serves as a lower frequency counterpart to LWA, LOFAR,
and similar ground-based radio imaging arrays. SIRA will require 12 to
16 microsatellites to establish a sufficient number of baselines with
separations on the order of kilometers. The microsat constellation
consists of microsats located quasi-randomly on a spherical shell,
initially of radius 5 km or less. The baseline microsat is 3-axis
stabilized with body-mounted solar arrays and an articulated, earth
pointing high gain antenna. A retrograde orbit at 500,000 km from Earth
was selected as the preferred orbit because it reduces the downlink
requirement while keeping the microsats sufficiently distant from
terrestrial radio interference. Also, the retrograde orbit permits
imaging of terrestrial magnetospheric radio sources from varied
perspectives. The SIRA mission serves as a pathfinder for space-based
satellite constellations and for spacecraft interferometry at shorter
wavelengths. It will be proposed to the NASA MIDEX proposal opportunity
in mid-2005.
---------------------------------------------------------
Title: Recent advances in the long-wavelength radio physics of the Sun
Authors: Gopalswamy, N.
2004P&SS...52.1399G Altcode:
Solar radio bursts at long wavelengths provide information on solar
disturbances such as coronal mass ejections (CMEs) and shocks at the
moment of their departure from the Sun. The radio bursts also provide
information on the physical properties (density, temperature and
magnetic field) of the medium that supports the propagation of the
disturbances with a valuable cross-check from direct imaging of the
quiet outer corona. The primary objective of this paper is to review
some of the past results and highlight recent results obtained from
long-wavelength observations. In particular, the discussion will
focus on radio phenomena occurring in the outer corona and beyond
in relation to those observed in white light. Radio emission from
nonthermal electrons confined to closed and open magnetic structures
and in large-scale shock fronts will be discussed with particular
emphasis on its relevance to solar eruptions. Solar cycle variation of
the occurrence rate of shock-related radio bursts will be discussed
in comparison with that of interplanetary shocks and solar proton
events. Finally, case studies describing the newly-discovered radio
signatures of interacting CMEs will be presented.
---------------------------------------------------------
Title: A Global Picture of CMEs in the Inner Heliosphere
Authors: Gopalswamy, N.
2004ASSL..317..201G Altcode: 2004shis.conf..201G
No abstract at ADS
---------------------------------------------------------
Title: Energy partition in two solar flare/CME events
Authors: Emslie, A. G.; Kucharek, H.; Dennis, B. R.; Gopalswamy, N.;
Holman, G. D.; Share, G. H.; Vourlidas, A.; Forbes, T. G.; Gallagher,
P. T.; Mason, G. M.; Metcalf, T. R.; Mewaldt, R. A.; Murphy, R. J.;
Schwartz, R. A.; Zurbuchen, T. H.
2004JGRA..10910104E Altcode:
Using coordinated observations from instruments on the Advanced
Composition Explorer (ACE), the Solar and Heliospheric Observatory
(SOHO), and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI),
we have evaluated the energetics of two well-observed flare/CME events
on 21 April 2002 and 23 July 2002. For each event, we have estimated
the energy contents (and the likely uncertainties) of (1) the coronal
mass ejection, (2) the thermal plasma at the Sun, (3) the hard X-ray
producing accelerated electrons, (4) the gamma-ray producing ions,
and (5) the solar energetic particles. The results are assimilated
and discussed relative to the probable amount of nonpotential magnetic
energy available in a large active region.
---------------------------------------------------------
Title: Interplanetary Radio Bursts
Authors: Gopalswamy, N.
2004ASSL..314..305G Altcode:
Nonthermal radio bursts in the interplanetary medium indicate
the far-reaching effect of solar eruptions that inject energetic
particles, plasmas and shock waves into the inner heliosphere. More
than half a century of ground-based observations and subsequent
space-based observations exist on this phenomena. In this paper, I
summarize the understanding we have gained on the type III and type
II radio bursts, which are indicative of electron beams and shocks,
respectively. Observations in the new radio window (1-14 MHz) from
Wind/WAVES have not only confirmed previous results, but also led to
a number of new discoveries. Availability of simultaneous white light
(SOHO) and radio (Wind) observations from the same spatial domain in
the near-Sun IP medium is largely responsible for these discoveries on
the IP propagation of CMEs, so this paper discusses radio bursts in
the context of white light observations. After exploring the origin
of normal, complex and storm type III bursts, I discuss the type II
bursts and their relation to coronal mass ejections. Finally I discuss
some of the recent developments on IP radio emission.
---------------------------------------------------------
Title: Kinematics of coronal mass ejections between 2 and 30 solar
radii. What can be learned about forces governing the eruption?
Authors: Vršnak, B.; Ruždjak, D.; Sudar, D.; Gopalswamy, N.
2004A&A...423..717V Altcode:
Kinematics of more than 5000 coronal mass ejections (CMEs)
measured in the distance range 2-30 solar radii is investigated. A
distinct anticorrelation between the acceleration, a, and the
velocity, v, is found. In the linear form, it can be represented
as a=-k<SUB>1</SUB>(v-v<SUB>0</SUB>), where v<SUB>0</SUB>=400 km
s<SUP>-1</SUP>, i.e., most of CMEs faster than 400 km s<SUP>-1</SUP>
decelerate, whereas slower ones generally accelerate. After grouping
CMEs into the width and mean-distance bins, it was found that the
slope k<SUB>1</SUB> depends on these two parameters: k<SUB>1</SUB>
is smaller for CMEs of larger width and mean-distance. Furthermore,
the obtained CME subsets show distinct quadratic-form correlations,
of the form a= -k<SUB>2</SUB> (v-v<SUB>0</SUB>)| v-v<SUB>0</SUB>|. The
value of k<SUB>2</SUB> decreases with increasing distance and width,
whereas v<SUB>0</SUB> increases with the distance and is systematically
larger than the slow solar wind speed by 100-200 km s<SUP>-1</SUP>. The
acceleration-velocity relationship is interpreted as a consequence of
the aerodynamic drag. The excess of v<SUB>0</SUB> over the solar wind
speed is explained assuming that in a certain fraction of events the
propelling force is still acting in the considered distance range. In
most events the inferred propelling force acceleration at 10 solar radii
ranges between a<SUB>L</SUB>=0 and 10 m s<SUP>-2</SUP>, being on average
smaller at larger distances. However, there are also events that show
a<SUB>L</SUB>>50 m s<SUP>-2</SUP>, as well as events indicating
a<SUB>L</SUB><0. Implications for the interplanetary motion of
CMEs are discussed, emphasizing the prediction of the 1 a.u. arrival
time. <P />Appendices A and B are only available in electronic form
at http://www.edpsciences.org
---------------------------------------------------------
Title: Arrival time of halo coronal mass ejections in the vicinity
of the Earth
Authors: Michałek, G.; Gopalswamy, N.; Lara, A.; Manoharan, P. K.
2004A&A...423..729M Altcode:
We describe an empirical model to predict the 1-AU arrival time of
halo CMEs. This model is based on the effective acceleration described
by Gopalswamy et al. (\cite{Gopalswamy00}a, Geophys. Res. Lett., 27,
145). We verify the Helios/Pioneer Venus Orbiter(PVO) estimation of the
effective acceleration profile (Gopalswamy et al. \cite{Gopalswamy01}a,
J. Geophys. Res., 106, 29207) by considering all full halo CMEs recorded
by SOHO/LASCO coronagraphs until the end of 2002. In comparison with
previous studies, the present work includes CMEs of a wider range of
initial velocities. To improve the accuracy of prediction, we propose to
introduce the effective acceleration from two groups of CMEs only, which
are expected to have no acceleration cessation at any place between
the Sun and Earth. In addition, we consider acceleration cessation
distance dependent on initial velocities of a given event CME. For a
detailed analysis of this model, we examine projected sky-plane and
space speeds (Michałek et al. \cite{Michalek03}, ApJ, 584, 472) of
CMEs. We show that a correct acceleration profile is crucial for the
estimation of 1 AU arrival time of halo CMEs. We estimate that the CME
arrival times can be predicted with an average error of 9 and 11 h for
space and sky-plane initial velocities, respectively. <P />Table 1 is
only available in electronic form at <P />http://www.edpsciences.org
---------------------------------------------------------
Title: A catalog of white light coronal mass ejections observed by
the SOHO spacecraft
Authors: Yashiro, S.; Gopalswamy, N.; Michalek, G.; St. Cyr, O. C.;
Plunkett, S. P.; Rich, N. B.; Howard, R. A.
2004JGRA..109.7105Y Altcode:
The Solar and Heliospheric Observatory (SOHO) mission's white light
coronagraphs have observed nearly 7000 coronal mass ejections (CMEs)
between 1996 and 2002. We have documented the measured properties of
all these CMEs in an online catalog. We describe this catalog and
present a summary of the statistical properties of the CMEs. The
primary measurements made on each CME are the apparent central
position angle, the angular width in the sky plane, and the height
(heliocentric distance) as a function of time. The height-time
measurements are then fitted to first- and second-order polynomials
to derive the average apparent speed and acceleration of the CMEs. The
statistical properties of CMEs are (1) the average width of normal CMEs
(20° < width ≤ 120°) increased from 47° (1996; solar minimum)
to 61° (1999; early phase of solar maximum) and then decreased to
53° (2002; late phase of solar maximum), (2) CMEs were detected
around the equatorial region during solar minimum, while during solar
maximum CMEs appear at all latitudes, (3) the average apparent speed
of CMEs increases from 300 km s<SUP>-1</SUP> (solar minimum) to 500
km s<SUP>-1</SUP> (solar maximum), (4) the average apparent speed
of halo CMEs (957 km s<SUP>-1</SUP>) is twice of that of normal CMEs
(428 km s<SUP>-1</SUP>), and (5) most of the slow CMEs (V ≤ 250 km
s<SUP>-1</SUP>) show acceleration while most of the fast CMEs (V >
900 km s<SUP>-1</SUP>) show deceleration. Solar cycle variation and
statistical properties of CMEs are revealed with greater clarity in
this study as compared with previous studies. Implications of our
findings for CME models are discussed.
---------------------------------------------------------
Title: Influence of coronal mass ejection interaction on propagation
of interplanetary shocks
Authors: Manoharan, P. K.; Gopalswamy, N.; Yashiro, S.; Lara, A.;
Michalek, G.; Howard, R. A.
2004JGRA..109.6109M Altcode:
We studied 91 interplanetary (IP) shocks associated with coronal mass
ejections (CMEs) originating within about ±30° in longitude and
latitude from the center of the Sun during 1997-2002. These CMEs cover
a wide range of initial speeds of about 120 to 2400 kms<SUP>-1</SUP>
and they also include a special population of 25 interacting CMEs. This
study provides the characteristics of propagation effects of more number
of high-speed CMEs (V<SUB>CME</SUB> > 1500 kms<SUP>-1</SUP>) than the
data used in earlier studies. It enables to extend the shock-arrival
prediction model to high-speed CMEs. The results on comparison
of IP shock speed and transit time at 1 AU suggest that the shock
transit time is not controlled by its final speed but is primarily
determined by the initial speed of the CME and effects encountered
by it during the propagation. It is found that the CME interaction
tends to slow the shock and associated CME. The deviations of shock
arrival times from the empirical model are considerably large for slow
(V<SUB>CME</SUB> < 300 kms<SUP>-1</SUP>) and fast (V<SUB>CME</SUB>
> 800 kms<SUP>-1</SUP>) CMEs. Results show that the slow and fast
CMEs experience stronger effective acceleration.
---------------------------------------------------------
Title: Coronal Mass Ejections When the Sun Went Wild
Authors: Gopalswamy, N.; Yashiro, S.; Vourlidas, A.; Lara, A.;
Stenborg, G.; Kaiser, M. L.; Howard, R. A.
2004AAS...204.4709G Altcode: 2004BAAS...36..738G
The Large Angle and Spectrometric Coronagraph (LASCO) on board SOHO
detected more than five dozen CMEs from three active regions (NOAA ARs
0484, 0486, and 0488) during the October-November 2003 super storms. The
CMEs were accompanied by X-class flares, solar energetic particles,
and interplanetary shocks. We compare the statistical properties of
these super-storm CMEs with those of the general population of CMEs
observed during cycle 23. We find that (i) the super-storm CMEs are
faster and wider than average, and hence possess enormous energy,
(ii) nearly 20 percent of the ultra-fast CMEs (speed > 2000 km/s)
occurred during the October-November interval, including the fastest
CME of cycle 23 (2700 km/s), and (iii) the rate of full-halo CMEs was
nearly four times the average rate during cycle 23. As expected, many
of these CMEs were driving shocks near the Sun as inferred from the
Wind/WAVES radio data and at least eight of them impacted Earth. These
strong shocks accelerated solar energetic particles, which remained at
hazardous levels for many days. We discuss the implications of these
extreme properties of CMEs for the solar energy source.
---------------------------------------------------------
Title: Shock Evolution During 29 - 06 November 2003 period of
Solar-Flare-CME-Shock-Geomagnetic Storms
Authors: Wu, C.; Wu, S.; Dryer, M.; Fry, C.; Berdichevsky, D.; Smith,
Z.; Gopalswamy, N.; Zurbuchen, T.; Smith, C.; Detman, T.
2004AGUSMSH51A..14W Altcode:
During the period 29 October - 6 November four shocks were observed
at Earth by ACE/SWEPAM/MAG and ACE/SWICS on 29 October, 30 October,
4 November, and 6 November. Two distinct and very intense geomagnetic
storms, associated with the X17.2 and X10/2B flares, rank as the
largest storms of Solar Cycle 23. For example, the X17.2 flare (28
October, S16E08 in AR0486), via its associated halo CME and shock wave,
was responsible for the Dst = -347 nT index on 30 October 2003. We
will present the use of an adaptive grid 2D MHD model to study these
four shocks in detail. Accordingly, four separate pressure pulses,
at the appropriate times and with different strengths and duration are
introduced at the Sun to mimic the four flares. The results show that
the simulated solar wind velocity time series successfully match the
observations at L1.
---------------------------------------------------------
Title: Sun-Earth Propagation Time of the October - November 2003
Shocks
Authors: Lara, A.; Gopalswamy, N.; Yashiro, S.
2004AGUSMSH51A..06L Altcode:
We computed the radial and expansion speed profiles of the CMEs that
resulted in shocks detected at 1 AU, in order to evaluate the empirical
shock arrival (ESA) model. The CMEs were observed by the Large Angle
and Spectrometric Coronagraph (LASCO) on board SOHO during October -
November 2003 period. The shocks were detected by CELIAS/MTOF Proton
Monitor on board SOHO and ACE spacecraft. The basic input to the ESA
model is the CME speed. For limb events, we assume axial symmetry
in order to obtain the most probable CME speed in the Sun-Earth
direction. We apply the ESA model to obtain the travel times of shocks
driven by Earth-directed and limb CMEs which had in situ observations at
1AU. For most cases the difference between the predicted and observed
shock arrival times is negligible. We discuss these differences and
their possible causes. Work supported by NASA/LWS and NSF/SHINE programs
---------------------------------------------------------
Title: Characteristic Periodicities in the Coronal Mass Ejection
Production
Authors: Lara, A.; Gopalswamy, N.; Yashiro, S.
2004AAS...204.3806L Altcode: 2004BAAS...36..713L
The solar activity is cyclic by nature, some periods of activity are
obvious and well known and some are hidden, but all of them should
be related to fundamental processes in the solar interior like
the dynamo. The search for hidden periodicities, which can give us
information about the solar activity causes, has been done for many
years with different degrees of success. Almost all measurable solar
parameters have been subject to a power spectral analysis and now
there are some well known periodicities related to such parameters. On
the other hand there are some events like Coronal Mass Ejections
(CMEs) which, until recently, were difficult to observe routinely
and then, we did not have a reliable database to perform a power
spectrum analysis. Using the LASCO/SOHO CME list, which contains the
information of the CME characteristics observed from 1996 to 2003, we
have now a reliable time series of the CME production during 8 years
covering the minimum, maximum and part of the declining phases of solar
activity cycle 23, in this work we present preliminary results of the
power spectral analysis of the CME activity. <P />This work work was
supported by NASA/LWS and NSF/SHINE (ATM 0204588) programs
---------------------------------------------------------
Title: Plasma and magnetic field of the solar wind
Authors: Gopalswamy, N.
2004cosp...35.2396G Altcode: 2004cosp.meet.2396G
Earth is always embedded in one of the three types of flows related to
coronal mass ejections (CMEs), slow solar wind or fast solar wind. The
topology of the magnetic field is different in the CME-related
flows compared to the other two. I discuss the solar sources of the
three types of flows. In particular, the relationship between CMEs
in the solar wind and their solar counterparts will be explored to
understand the possible reasons for the different number and speed
distributions. Earth-directed CMEs constitute a special population
of CMEs because they directly impact Earth. Earth-directed halo
CMEs also seem to have properties different from the ordinary CMEs:
their average speed is twice that of the general population. Finally,
the solar cycle variation of the number of instances of CME-related
flows at Earth will be compared with the occurrence rates of CMEs,
solar energetic particle events, and interplanetary type II radio
bursts produced by CME-driven shocks.
---------------------------------------------------------
Title: Variability of solar eruptions during cycle 23
Authors: Gopalswamy, N.; Nunes, S.; Yashiro, S.; Howard, R. A.
2004AdSpR..34..391G Altcode:
We report on the solar cycle variation of the rate of coronal mass
ejections (CMEs), their mean and median speeds, and the rate of type II
radio bursts. We found that both CME rate and speed (mean and median)
increased from solar minimum to maximum by factors of 10 and 2,
respectively. The CME rate during solar maximum is nearly twice the
rates quoted previously. Large spikes in the speed variation were
due to active regions that were highly active. The poor correlation
between metric and DH type II bursts is confirmed, and the difference
is attributed to the different Alfven speeds in the respective source
regions.
---------------------------------------------------------
Title: Prominence eruptions and coronal mass ejection: a statistical
study using microwave observations
Authors: Gopalswamy, N.; Lu, W.; Yashiro, S.; Shimojo, M.; Shibasaki,
K.
2004naoj.book...18G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On coronal streamer changes
Authors: Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki,
K.; Howard, R. A.
2004AdSpR..33..676G Altcode:
Coronal streamer represents one of the pre-eruption configurations
of coronal mass ejections (CMEs), because they overlie prominences
and often possess all the substructures of CMEs. In this paper,
we report on a study of streamer changes associated with prominence
eruptions. The prominence eruptions and streamer changes were observed
by the Nobeyama radioheliograph and Solar and Heliospheric Observatory
(SOHO), respectively. Multiwavelength data showed that at least one of
the streamer events involved heating and small-scale material ejection
that subsequently stalled. After presenting illustrative examples,
we compare the properties of the streamer-related events with those of
general population of prominence events. We find that the properties
of streamer-related prominence events are closer to those of prominence
eruptions with transverse trajectories.
---------------------------------------------------------
Title: Composition and magnetic structure of interplanetary coronal
mass ejections at 1 AU
Authors: Aguilar-Rodriguez, E.; Blanco-Cano, X.; Gopalswamy, N.
2004cosp...35.2411A Altcode: 2004cosp.meet.2411A
We present a combined study of magnetic structure and charge state
ratio of interplanetary coronal mass ejections (ICMEs) observed in
interplanetary space by ACE and Wind spacecrafts. Measurements
of abundances and charge state ratio of heavy ions
(e.g. O<SUP>+7</SUP>/O<SUP>+6</SUP>, C<SUP>+5</SUP>/C<SUP>+6</SUP>,
and Mg/O) in the solar wind as well as magnetic field structure are
important tracers for physical conditions and processes in the source
regions of the solar wind. We used ion composition (ACE), plasma (Wind)
and magnetic field (Wind and ACE) data over a period of time from 1998
to 2002. Using the low proton temperature criterion, a common plasma
signature of ICMEs, we identified 154 events which were classified as
magnetic cloud, non-cloud and complex ICMEs. The later one is refered
to the overtaking of succesive ICMEs which can include both magnetic
clouds and non-cloud ejecta. We discuss the differences and similarities
of our results with those of previous studies. Supported by NSF/SHINE,
NASA/LWS, and CONACyT.
---------------------------------------------------------
Title: Coronal Mass Ejections and Galactic Cosmic Ray Modulation
Authors: Lara, A.; Gopalswamy, N.; Caballero, R.; Yashiro, S.
2004cosp...35.2926L Altcode: 2004cosp.meet.2926L
We present a study of the long term evolution of Coronal Mass Ejections
(CME) observed by LASCO/SOHO during the ascending, maximum and part
of the descending phase of cycle 23 and its relation with the galactic
cosmic ray (GCR) intensity modulation observed at one astronomical unit
by Climax Neutron Monitor and IMP-8 spacecraft. We compare the long
term GCR modulation with the CME production at low and high latitudes
and CME parameters (width and speed). We found a very high (∼ 0.94)
correlation between the number of high latitude CMEs and GCR during
the ascending phase of solar cycle 23.
---------------------------------------------------------
Title: Coronal Mass Ejections and Solar Particle Events in Solar
Cycle 23
Authors: Gopalswamy, N.
2004cosp...35.2358G Altcode: 2004cosp.meet.2358G
I provide an overview of the coronal mass ejection (CME) phenomenon
as recorded primarily by the Solar and Heliospheric Observatory
(SOHO) mission during the current solar activity cycle (23). After
summarizing the statistical properties of CMEs and their solar-cycle
variation, a discussion on the CME-associated activities will be
presented. Particular emphasis will be placed on solar energetic
particles (SEPs), which are related to CMEs that are faster and wider on
average. Even though it is generally accepted that large SEP events are
due to CME-driven shocks, the correlation between the two phenomena is
less than perfect. Reasons for this poor correlation will be explored,
including the influence of preceding CMEs. Fast and wide CMEs also
produce long-wavelength radio bursts, so the connection between SEP
events and radio bursts will be explored. Finally, I will discuss the
implications of CMEs to the evolution of the global solar magnetic
field and to the 22-year cosmic ray modulation cycle.
---------------------------------------------------------
Title: Estimation of solar wind speed within 20Rs of the Sun by
using limb CMEs
Authors: Nakagawa, T.; Gopalswamy, N.; Yashiro, S.; Matsuoka, A.;
Nozomi/Mgf Team
2004cosp...35.1632N Altcode: 2004cosp.meet.1632N
The speeds of propagation of CMEs in interplanetary space are less
distributed than their initial speeds measured on their departure
from the limb of the Sun. Gopalswamy et al.(2000, 2001) presented a
linear relationship between initial speeds of limb CMEs and their
average acceleration during their travel time in interplanetary
space. The linear relationship suggests that some dragging force
is acting on CMEs, depending on difference in speed between the
CME and their ambient plasmas. The ambient speed obtained from the
coeficcients of the linear relationship was 406 km/s, which is nearly
the same as the real solar wind speed. If similar relationship holds
within 20 solar radii from the Sun, it would give information on
the initial speed of 'ambient' solar wind in the vicinity of the
Sun. The relationship between the initial acceleration and the
initial speeds of limb CMEs was examined by using SOHO/LASCO CME
Catalogue (http://cdaw.gsfc.nasa.gov/CME_list/). Coefficients of
correlation between the initial acceleration and the initial speeds
of low-latitude CMEs were calculated by sliding 27-day windows in
1999. Although there were many cases where linear relationship was not
clear, we found significant number of periods for which correlation
coefficient was fairly good (from -0.6 to -1). For such cases, the
'ambient' solar wind speed within 20 solar radii was estimated to be
150 - 570 km/s. It is somewhat slower than but close to the speeds
of real solar wind measured in interplanetary space. It suggests
that low-latitude solar wind plasma was accelerated within a short
distance. It may also indicate that coronal holes are not the only
source of the solar wind. The 'ambient' speeds thus obtained did not
always agreed with simultaneous, in-situ measurements by NOZOMI and
ACE. Estimation of 'ambient' speed was also carried out by using CMEs
that appeared in higher latitude, but no latitudinal dependence was
found. Acknowledgments:This CME catalog is generated and maintained
by NASA and The Catholic University of America in cooperation with
the Naval Research Laboratory. SOHO is a project of international
cooperation between ESA and NASA. Reference: Gopalswamy et al., GRL,
27, p145, 2000. Gopalswamy et al., JGR, 106, p29207, 2001.
---------------------------------------------------------
Title: Type II Radio Bursts and Energetic Solar Eruptions
Authors: Gopalswamy, N.; Nunes, S.; Yashiro, S.; Howard, R. A.;
Kaiser, M. L.
2003AGUFMSH42C0556G Altcode:
Type II radio bursts at decameter-hectometric (DH) and kilometric
wavelengths are indicative of CME-driven shocks in the interplanetary
medium. Only a subset of these type II bursts continue from the DH
to the km regimes. We report on a study of these long-lasting type II
bursts using data from the Wind/WAVES experiment in conjunction with
white-light coronal mass ejection (CME) data from SOHO. We find the
majority of these events (80 percent) are also associated with metric
Type II bursts. We also studied the properties of the associated CMEs
and found them to be the most energetic when compared to CMEs associated
with bursts in any single wavelength regime.
---------------------------------------------------------
Title: Merged interaction regions at 1 AU
Authors: Burlaga, L.; Berdichevsky, D.; Gopalswamy, N.; Lepping, R.;
Zurbuchen, T.
2003JGRA..108.1425B Altcode:
We discuss the existence of large, complex merged interaction regions
(MIRs) in the solar wind near Earth. MIRs can have configurations that
cause more prolonged geomagnetic effects than a single flow structure. A
MIR or successive MIRs can produce relatively long lasting Forbush
decreases at 1 AU. We illustrate MIRs at 1 AU with two examples (MIR-1
and MIR-2) seen by WIND and ACE in the interval from 18 March through
29 March 2002. We determined the probable structure and origin of
each in terms of interacting flows and shocks using in situ and solar
observations, but we emphasize that there are uncertainties that cannot
be resolved with these data alone. The MIRs were relatively large
structures with radial extent ~2/3 and 3/4 AU, respectively. MIR-1
was formed by interactions related to at least two complex ejecta,
a magnetic cloud, and two shocks. MIR-2 was related to a corotating
stream, the heliospheric plasma sheet (HPS), two complex ejecta, a
magnetic cloud and at least two shocks. A MIR can evolve significantly
while it moves to 1 AU, and memory of the conditions near the Sun
is lost in the process. Thus one cannot unambiguously determine the
structure of a MIR and the manner in which it formed using observations
from a single spacecraft at 1 AU. The magnetic field strength profiles
in MIRs are not correlated with the speed and density profiles so
that one cannot infer the magnetic field strength in MIRs from remote
sensing observation that give density and speed information. It will be
possible to better understand the dynamical processes leading to the
formation of MIRs with remote sensing observations, but they cannot
measure the magnetic fields in MIRs.
---------------------------------------------------------
Title: Radio Coverage from Chromosphere to Earth: FASR-LOFAR-SIRA
Synergy
Authors: Gary, D. E.; Kassim, N.; Gopalswamy, N.; Aschwanden, M. J.
2003AGUFMSH42E..02G Altcode:
Radio emission is uniquely sensitive to a number of key plasma
parameters (magnetic field, temperature, density, high-energy
electrons, and various plasma waves) over heights ranging without
gaps from the chromosphere, throughout the corona and heliosphere, to
the Earth. Two ground-based radio arrays, the Frequency Agile Solar
Radiotelescope (FASR) and the Low Frequency Array (LOFAR), together
with the space-based Solar Imaging Radio Array (SIRA) are planned
that will for the first time provide direct imaging of disturbances
over this vast height range through interferometric imaging over their
equally impressive frequency range of 24 GHz to 30 kHz. We describe the
science goals of these instruments, focusing especially on the science
addressed jointly by all three instruments. Among the examples are
(1) simultaneous imaging of CMEs, flaring loops, and shock-associated
(type II) emission and (2) imaging the propagation of electrons on
open field lines (type III), from their acceleration point through
the corona and heliosphere to the point where they are measured in
situ by near-Earth spacecraft. In addition to spatially relating the
different phenomena, the spectral information is rich in quantitative
diagnostics. We give some examples of the revolutionary results we
can expect from the combined instruments.
---------------------------------------------------------
Title: Comment on “Coronal mass ejections, interplanetary ejecta
and geomagnetic storms” by H. V. Cane, I. G. Richardson, and
O. C. St. Cyr
Authors: Gopalswamy, N.; Manoharan, P. K.; Yashiro, S.
2003GeoRL..30.2232G Altcode: 2003GeoRL..30xSSC1G
<A href="/journals/gl/gl0324/2003GL017562/index.html">Abstract
Available</A> from <A href="http://www.agu.org">AGU</A>
---------------------------------------------------------
Title: Key Issues Related to Solar Sources and Interplanetary
Propagation of the April 2002 Events
Authors: Gopalswamy, N.
2003AGUFMSM41A..02G Altcode:
A summary of the solar events such as coronal mass ejections (CMEs)
and flares associated with the April 2002 storms will be provided. In
particular events from the primary active region, AR9906 and the
underlying magnetic configuration will be discussed. The connection
of these CMEs to the interplanetary shocks and the solar energetic
particles events will be explored. Based on the arrival times of the
interplanetary CMEs and shocks, the evolution of these disturbances as
they propagated between the Sun and Earth will be described. Finally,
a comparison of the April 2002 events with other geoeffective events
will be made.
---------------------------------------------------------
Title: Probing Solar Energetic Particles with SIRA
Authors: Aschwanden, M. J.; Nitta, N.; Lemaster, E.; Byler, E.; Gary,
D.; Kassim, N.; Gopalswamy, N.
2003AGUFMSH42C0555A Altcode:
The space-based SIRA (Solar Imaging Radio Array) will provide a powerful
capability to track high energy particles from solar flare and CME sites
through interplanetary/heliospheric space all the way to Earth. Together
with two other overlapping planned radio interferometers, i.e., FASR
(Frequency-Agile Solar Radiotelescope) and LOFAR (Low-Frequency Array)
the entire plasma frequency range from 30 GHz all the way down to
the plasma frequency cutoff of 30 kHz at 1 AU will be covered. These
instruments will track the magnetic trajectory of high energy particles,
beam-driven radio emission, and localize the acceleration sites in
the corona or interplanetary shocks. We simulate some CME and type III
events, as they will be mapped with these instruments, using realistic
scattering functions of radio waves on coronal and heliospheric density
inhomogeneities.
---------------------------------------------------------
Title: Coronal Mass Ejections, Flares and Type II Radio Bursts
Authors: Rosas, A. M.; Gopalswamy, N.; Kaiser, M. L.; Yahsiro, S.;
Nunes, S.
2003AGUFMSH42C0559R Altcode:
An investigation of 210 interplanetary type II radio bursts and the
associated white-light coronal mass ejections (CMEs) is presented. The
radio bursts were detected by the Wind/WAVES experiment in the 1-14
MHz (decameter-hectometric, DH) range, while the CMEs were observed
by the Solar and Heliospheric Observatory (SOHO). The study period,
1997-2002, encompasses the current solar cycle (23) between minimum and
beyond maximum. We could only find 108 solar flares associated with
DH type IIs. We obtained the difference onset times (solar flare -
DH type II) and found that DH type IIs start at the same time as the
flares. On the other hand the difference between CME and DH type II
onset times is indicates that the type II bursts occur well after the
CME onset. The present study suggests that the CMEs are more likely
to be the source of the shocks responsible for the type II bursts. We
extend the study to metric type II bursts and obtained similar results.
---------------------------------------------------------
Title: Coronal Mass Ejections and Solar Polarity Reversal
Authors: Gopalswamy, N.; Lara, A.; Yashiro, S.; Howard, R. A.
2003ApJ...598L..63G Altcode:
We report on a close relationship between the solar polarity reversal
and the cessation of high-latitude coronal mass ejections (CMEs). This
result holds good for individual poles of the Sun for cycles 21 and
23, for which CME data are available. The high-latitude CMEs provide a
natural explanation for the disappearance of the polar crown filaments
(PCFs) that rush the poles. The PCFs, which are closed field structures,
need to be removed before the poles could acquire open field structure
of the opposite polarity. Inclusion of CMEs along with the photospheric
and subphotospheric processes completes the full set of phenomena to
be explained by any solar dynamo theory.
---------------------------------------------------------
Title: Dynamics of coronal mass ejections in the near-Sun
interplanetary space
Authors: Vrsnak, B.; Ruzdajak, D.; Sudar, D.; Gopalswamy, N.
2003ESASP.535..517V Altcode: 2003iscs.symp..517V
Kinematics of more than 5000 coronal mass ejections (CMEs) measured
between 2 and 30 solar radii is investigated. A distinct relationship
between the late-phase acceleration of CMEs and their velocities is
found. It can be represented in the form a<SUB>[m s<SUP>-2</SUP>]</SUB>
= -0.02(v-400)<SUB>[km s<SUP>-1</SUP>]</SUB>. The relationship is
interpreted in terms of coupling of the CME motion and the solar wind,
i.e., by the action of the aerodynamic drag. The results indicate that
in the considered radial distance range the Lorentz force acceleration
becomes weak, in the majority of the events spanning between 0 and 10
m s<SUP>-2</SUP>. Implications for the interplanetary motion of CMEs
are discussed, emphasising the prediction of the 1 a.u. arrival time.
---------------------------------------------------------
Title: Variations of magnetic clouds and CMEs with solar activity
cycle
Authors: Wu, Chin-Chun; Lepping, R. P.; Gopalswamy, N.
2003ESASP.535..429W Altcode: 2003iscs.symp..429W
Sixty-eight magnetic clouds were observed by Wind during November 1994 -
May 2002. The average occurrence rate is ~9 magnetic clouds per year for
the overall period (68 events/7.6 years). It is found that some of the
frequency of occurrence anomalies were during the early part of solar
cycle 23: (I) only 4 clouds were observed in 1999, (II) an unusually
large number of clouds (16 events) were observed in 1997 in which the
Sun was starting to leave solar minimum. During the period of 1996-2001,
the results also show: (1) the occurrence frequency of magnetic cloud
appears to be related neither to the occurrence of solar coronal mass
ejections (CMEs) as observed by SOHO nor to solar activity cycle,
(2) the intensity of geomagnetic storms related to magnetic clouds is
affected by both solar activity and the occurrence frequency of CMEs,
and (3) ~91% of magnetic clouds induced geomagnetic storms.
---------------------------------------------------------
Title: Effect of CME Interactions on the Production of Solar
Energetic Particles
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Kaiser, M. L.;
Howard, R. A.; Leske, R.; von Rosenvinge, T.; Reames, D. V.
2003AIPC..679..608G Altcode:
We analyzed a set of 52 fast and wide, frontside western hemispheric
(FWFW) CMEs in conjunction with solar energetic particle (SEP) and
radio burst data and found that 42 of these CMEs were associated
with SEPs. All but two of the 42 SEP-associated FWFW CMEs (95%)
were interacting with preceding CMEs or dense streamers. Most of
the remaining 10 SEP-poor FWFW CMEs had either insignificant or no
interaction with preceding CMEs or streamers, and were ejected into
a tenuous corona. There is also a close association between type II
radio bursts in the near-Sun interplanetary medium and SEP-associated
FWFW CMEs suggesting that electron accelerators are also good proton
accelerators.
---------------------------------------------------------
Title: A Numerical Study on the Evolution of CMEs and Shocks in the
Interplanetary Medium
Authors: González-Esparza, J. A.; Lara, A.; Santillán, A.;
Gopalswamy, N.
2003AIPC..679..206G Altcode:
We studied the evolution in the solar wind of four CMEs detected by
SOHO-LASCO which were associated with ICMEs and interplanetary (IP)
shocks detected afterward by Wind at 1 AU. The study is based on a
1-D hydrodynamic single fluid model using the ZEUS code. These simple
numerical simulations of CME like pulses illuminate several aspects of
the heliocentric evolution of the ICME front and its associated IP shock
and we were able to reproduce some characteristics of the IP shocks
and ICMEs inferred from the two-point measurements from spacecraft. The
simulation shows that ICMEs and IP shocks follow different evolutions
in the interplanetary medium both having phases of about constant speed
propagation followed by an exponential deceleration with heliocentric
distance. IP shocks always propagate faster than their associated
ICME drivers and the former began to decelerate well before the IP
shock. The results indicate that, in general, although an IP shock is
driven by its ICME in the inner heliosphere in most of the cases this
is not true any more when they approach to 1 AU.
---------------------------------------------------------
Title: Coronal mass ejection activity during solar cycle 23
Authors: Gopalswamy, Nat; Lara, Alejandro; Yashiro, Seiji; Nunes,
Steven; Howard, Russell A.
2003ESASP.535..403G Altcode: 2003iscs.symp..403G
We studied the solar cycle varition of various properties of coronal
mass ejections (CMEs), such as daily CME rate, mean and median speeds,
and the latitude of solar sources for cycle 23 (1996-2002). We find
that (1) there is an order of magnitude increase in CME rate from the
solar minimum (0.5/day) to maximum (6/day), (2) the maximum rate is
significantly higher than previous estimates, (3) the mean and median
speeds of CMEs also increase from minimum to maximum by a factor of 2,
(4) the number of metric type II bursts (summed over CR) tracks CME
rate, but the CME speed seems to be only of secondary importance,
(5) for type II bursts originating farther from the Sun the CME
speed is important, (6) the latitude distribution of CMEs separate the
prominence-associated (high-latitude) and active-region associated CMEs,
and (7) the rate of high-latitude CMEs shows north-south asymmetry and
the cessation eruptions in the north and south roughly mark the polarity
reversals. We compared the rates of the fast-and-wide CMEs, major solar
flares, interplanetary (IP) shocks, long-wavelength type II bursts and
large SEP events. This comparison revealed that the number of major
flares is generally too large compared to all the other numbers. In
other words, fast-and-wide CMEs, long-wavelength type II bursts,
large SEP events, and IP shocks have a close physical relationship.
---------------------------------------------------------
Title: Coronal and Interplanetary Environment of Large Solar Energetic
Particle Events
Authors: Gopalswamy, Nat; Yashiro, S.; Stenborg, G.; Howard, R. A.
2003ICRC....6.3549G Altcode: 2003ICRC...28.3549G
We studied the properties of coronal mass ejections (CMEs) associated
with large solar energetic particle (SEP) events during 1997-2002
and compared them with those of preceding CMEs from the same source
region. The primary findings of this study are (1) High-intensity
(> 50 protons cm-2 s-1 sr-1 ) events are more likely to be preceded
by other wide CMEs. (2) The preceding CMEs are faster and wider
than average CMEs. (3) The primary CMEs often propagate through the
near-Sun interplanetary medium severely disturb ed and distorted by
the preceding CMEs.
---------------------------------------------------------
Title: Large solar energetic particle events of cycle 23: A global
view
Authors: Gopalswamy, N.; Yashiro, S.; Lara, A.; Kaiser, M. L.;
Thompson, B. J.; Gallagher, P. T.; Howard, R. A.
2003GeoRL..30.8015G Altcode: 2003GeoRL..30lSEP3G
We report on a study of all the large solar energetic particle
(SEP) events that occurred during the minimum to maximum interval
of solar cycle 23. The main results are: 1. The occurrence rate of
the SEP events, long-wavelength type II bursts and the fast and wide
frontside western hemispheric CMEs is quite similar, consistent with the
scenario that CME-driven shocks accelerate both protons and electrons;
major flares have a much higher rate. 2. The SEP intensity is better
correlated with the CME speed than with the X-ray flare class. 3. CMEs
associated with high-intensity SEPs are about 4 times more likely to
be preceded by wide CMEs from the same solar source region, suggesting
the importance of the preconditioning of the eruption region. We use
a specific event to demonstrate that preceding eruption from a nearby
source can significantly affect the properties of SEPs and type II
radio bursts.
---------------------------------------------------------
Title: Solar and geospace connections of energetic particle events
Authors: Gopalswamy, N.
2003GeoRL..30.8013G Altcode: 2003GeoRL..30lSEP1G
A Coordinated Data Analysis Workshop (CDAW) was conducted recently
to study the solar and geospace connections of large solar energetic
particle (SEP) events of solar cycle 23 (up to the end of 2001). This
paper summarizes the properties these events, the scientific issues
discussed, and some of the results obtained during the workshop.
---------------------------------------------------------
Title: A statistical study of CMEs associated with metric type
II bursts
Authors: Lara, A.; Gopalswamy, N.; Nunes, S.; Muñoz, G.; Yashiro, S.
2003GeoRL..30.8016L Altcode: 2003GeoRL..30lSEP4L
We present a statistical study of the characteristics of CMEs which
show temporal association with type II bursts in the metric domain but
not in the decameter/hectometric (DH) domain. This study is based on
a set of 80 metric (m) type II bursts associated with surface events
in the solar western hemisphere. It was found that in general, the
distribution of the widths and speeds of the CMEs associated with metric
(but not DH) type II bursts are shifted towards higher values compared
to those of all CMEs observed by LASCO in the 1996-2001 period. We
also found that these distributions have lower values than the same
distributions of the CMEs associated with DH type II bursts. In terms
of energy, this means that the CMEs associated only with metric type
II bursts are more energetic (wider and faster) than regular CMEs but
less energetic than the CMEs associated with DH type II bursts.
---------------------------------------------------------
Title: Solar Imaging Radio Array (SIRA): Radio Aperture Synthesis
from Space
Authors: MacDowall, R.; Kaiser, M.; Gopalswamy, N.
2003SPD....34.2022M Altcode: 2003BAAS...35Q.848M
SIRA, the Solar Imaging Radio Array, will be a constellation of about
16 microsats designed to image radio sources in the solar corona and
heliosphere using aperture synthesis techniques. These images will
permit the mapping and tracking of CME-driven shocks (type II radio
bursts) and solar flare electrons (type III radio bursts) as a function
of time from near the sun to 1 AU. Two dimensional imaging of the
CME-driven shock front is important for determination of space weather
effects of CMEs, whereas imaging of the ubiquitous type III bursts will
permit the derivation of density maps in the outer corona and solar
wind. This will be the first mission to image the heliosphere (and the
celestial sphere) with good angular resolution at frequencies below
the ionospheric cutoff ( 10 MHz). The radio images are intrinsically
complementary to white-light coronograph data, such as those of SDO,
and can play a valuable role in the NASA Living with a Star program.
---------------------------------------------------------
Title: Analysis of Onset Times between CMEs and Associated DH Type
II Bursts
Authors: Rosas, A. M.; Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.;
Howard, R. L.
2003SPD....34.0506R Altcode: 2003BAAS...35..815R
An investigation of 210 interplanetary type II radio bursts and the
associated white-light coronal mass ejections (CMEs) is presented.The
radio bursts were detected by the Wind/WAVES experiment in the 1-14 MHz
(decameter-hectometric,DH) range, while the CMEs were observed by the
Solar and Heliospheric Observatory (SOHO).The study period, 1997-2002,
encompasses the current solar cycle (23) between minimum and beyond
maximum. We find that 91% of CMEs have speeds greater than 450 km/s
and 94% have angular widths greater than 60 degrees obtained from
SOHO/LASCO C2 and C3 CME measurements.We made a linear and quadratic
fit using CME height time measurements to extrapolate CME onset times
to 2 and 1 solar radius. We find that the quadratic onset times (QOTs)
illustrates less scatter in the difference times (CME onset time - DH
onset time) than the linear onset times (LOTs). Both the QOT and LOT
for 1 solar radius shows that ∼ 80% DH type II bursts occurred within
1 hour of CME onset time and for 2 solar radius extrapolation shows
∼ 87%. Correlation coefficients were found to be very weak between
difference times and CME longitude, speed, angular width, and DH type
II starting frequency. We are continuing to investigate the outlier (DH
type II bursts occurring more than 2 hours after CMEs) events.(1) The
onset times and starting frequency of DH type IIs with respect to CME
onset times provides insight into the coronal density distribution.(2)
The relationship between CME onset time and the occurrence of the DH
type II will be discussed in terms of the radial distribution of the
Alfven speed near the Sun. <P />This work is supported by NASA living
with a Star and NSF/SHINE (ATM 0204588) and AFOSR Programs.
---------------------------------------------------------
Title: Towards Automatic Tracking of Coronal Mass Ejections
Authors: Stenborg, G. A.; Cobelli, P. J.; Gopalswamy, N.; Yashiro, S.
2003SPD....34.0306S Altcode: 2003BAAS...35..809S
Tracing identifiable features of dynamical phenomena such as coronal
mass ejections (CMEs), as they propagate through the corona, is a real
challenge. In particular, different features from a single event usually
display different velocities. Moreover, the lack of sharpness of the
structures involved on top of the subjective nature of the measuring
process makes it difficult to track the event unambiguously. To overcome
the lack of sharpness, we developed a multiresolution image processing
technique applicable to any 2D data set to enhance both boundaries and
internal details of originally faint and diffuse structures. The method
implemented employs a multi-level decomposition scheme (splitting
algorithm of a wavelet packet on non-orthogonal wavelets) via the
`a trous' wavelet transform, local noise reduction and interactive
weighted recomposition. This approach represents a major advance
towards unambiguous image interpretation and provides a means for the
quantification of stationary and dynamic coronal structures required
for conducting morphological studies. Moreover, it proved to be a
necessary step in the development of a non-subjective technique for
automatic tracking of CMEs. Examples based on LASCO-C1, -C2, -C3, and
EIT data sets are shown. Different reconstruction strategies are also
discussed. <P />This work is supported by NASA living with a Star and
NSF/SHINE (ATM 0204588) Programs.
---------------------------------------------------------
Title: Long Lasting Type II Radio Bursts
Authors: Nunes, S.; Gopalswamy, N.; Yashiro, S.; Howard, R.
2003SPD....34.0607N Altcode: 2003BAAS...35..818N
Plasma frequencies starting in the decameter-hectametric (DH) regime and
continuing into the kilometric (km) regime correspond to approximately
to the entire Sun-Earth distance. Accordingly, we consider Type II radio
bursts observed by the WAVES experiment on the WIND spacecraft that
are observed from the DH to the km regimes and their association with
white-light coronal mass ejections (CMEs). We find that approximately
80% of these events are associated with metric Type II bursts observed
on Earth. We also consider correlations of DH/km Type II's with
sunspot numbers and other cyclical measures of solar activity, and
properties of CMEs associated with DH/km Type II bursts. <P />This
work is supported by the Air Force Office of Scientific Research,
the National Science Foundation's SHINE Program, and NASA.
---------------------------------------------------------
Title: Why was there no Solar Energetic Particle Event Associated
with the Gamma-ray-line Flare of 2002 July 23?
Authors: Gopalswamy, N.; Dennis, B. R.; Kaiser, M. L.; Krucker, S.;
Lin, R. P.; Vourlidas, A.
2003SPD....34.2202G Altcode: 2003BAAS...35..850G
We investigated the coronal and interplanetary (IP) events associated
with two X-class flares on 2002 July 20 and 23. Both flares were
associated with ultra-fast (>2000 km s<SUP>-1</SUP>) coronal mass
ejections (CMEs) and IP shocks. We use white-light, EUV, hard X-ray and
radio observations to trace the origin of the CMEs to active region
0039 located close to the east limb. The July 20 flare was partly
occulted by the east limb, yet it resulted in a major solar energetic
particle event with intensity ∼ 20 pfu in the >10 MeV channel
(1 pfu = 1 particle per (cm<SUP>2</SUP> s sr MeV)). The July 23 event
was the first gamma-ray-line flare detected by RHESSI, but it did
not show any enhancement in SEPs above the elevated background from
the July 20 event. We identified two distinguishing factors between
the July 2 and July 23 CMEs: (1) The July 20 CME had a higher kinetic
energy, and (2) The July 20 CME was interacting with another fast CME
(1350 km s<SUP>-1</SUP>) that preceded by less than an hour from the
same region; there were also two other CMEs on July 19 from the same
region. Thus the coronal and IP environment of the July 20 event was
highly disturbed due to preceding CMEs (as compared to the July 23
event). We suggest that the different coronal/IP environments may be
responsible for the lack of SEP event associated with the July 23 event.
---------------------------------------------------------
Title: Influence of CME interaction on the Propagation of
Interplanetary Shocks
Authors: Manoharan, P. K.; Gopalswamy, N.; Yashiro, S.; Howard, R. A.
2003SPD....34.0610M Altcode: 2003BAAS...35Q.819M
We studied a large number of coronal mass ejections (CMEs) and their
associated interplanetary (IP) shocks for the period 1996-2002, using
white-light images from the Large Angle and Spectrometric Coronagraph
(LASCO) on the Solar Heliospheric Observatory (SOHO) spacecraft and
solar wind measurements from the Mass Time-of-Flight spectrometer
(MTOF on SOHO) and Solar Wind Experiment (SWE on the WIND satellite)
instrument. The 1-AU arrival times of the CME and its shock are
obtained from the initial CME speed. We studied the influence of
preceding CMEs on the propagation of the IP shocks. We note that the
propagation characteristics of some of the fast CMEs and their shocks
are modified by the interaction with the preceding CMEs. We also
find that the arrival times of IP shocks show deviation from that of
non-interacting cases. We use an empirical model to explain the change
in the travel time of shocks. We also discuss other consequences in the
solar wind caused by the CME interactions. <P />This work is supported
by NASA living with a Star, NSF/SHINE (ATM 0204588), and AFOSR Programs.
---------------------------------------------------------
Title: Recent advances in long-wavelength radio physics of the Sun
Authors: Gopalswamy, N.
2003EAEJA.....4473G Altcode:
Low frequency imaging of the solar radio bursts provides the best means
of studying the solar disturbances such as coronal mass ejections and
shocks at the moment of their departure from the Sun. The radio bursts
also provide information on the physical properties of the medium
such as the density, temperature and magnetic field. Direct imaging of
the quiet Sun also provides information on the outer corona. I review
some of the results obtained from recent long-wavelength observations
and summarize the relevance of these results to LOFAR. In addition,
I discuss the significance of LOFAR to future low frequency imaging
observations from space such as the Solar Imaging Radio Array (SIRA).
---------------------------------------------------------
Title: The Solar Radio Imaging Array (SIRA) microsatellite mission
Authors: MacDowall, R.; Gopalswamy, N.; Kaiser, M.
2003EAEJA....12917M Altcode:
SIRA, the Solar Imaging Radio Array, will be a constellation of about
16 microsats designed to image radio sources in the solar corona
and heliosphere using aperture synthesis techniques. These images
will permit the mapping and tracking of CME-driven shocks (type II
radio bursts) and solar flare electrons (type III radio bursts) as a
function of time from near the sun to 1 AU. Two dimensional imaging
of the CME-driven shock front is important for determination of space
weather effects of CMEs, whereas imaging of the ubiquitous type III
bursts will permit the derivation of density maps in the outer corona
and solar wind. This will be the first mission to image the heliosphere
(and the celestial sphere) with good angular resolution at frequencies
below the ionospheric cutoff (~10 MHz). In this presentation, we
highlight the ways in which SIRA is complementary to LOFAR and FASR.
---------------------------------------------------------
Title: Coronal mass ejections as a source of space Weather
Authors: Gopalswamy, N.
2003EAEJA.....4456G Altcode:
White-light and radio observations of solar eruptions obtained by SOHO
and Wind, respectively have helped us understand the space weather
aspect of coronal mass ejections (CMEs). From space weather point of
CMEs are important in two respects: (1) CMEs departing from close to
the disk center are important for producing geomagnetic storms, so it
is important to understand how they evolve and when they arrive at the
earth, (2) Fast and wide CMEs drive shocks and hence accelerate solar
energetic particles detected in situ or via the long wavelength type
II radio bursts. The SEP-associated CMEs can depart from the Sun from
any longitude, but western events are more geoeffective. Recent results
show that only 1-2 percent of all CMEs are important for space weather
purposes. In this paper, we review the recent results obtained on
these two populations of CMEs in comparison with the general population.
---------------------------------------------------------
Title: Low frequency radio astronomy from space: the Solar Radio
Imaging Array
Authors: MacDowall, R.; Gopalswamy, N.; Kaiser, M.
2003EAEJA....12863M Altcode:
SIRA, the Solar Imaging Radio Array, will be a constellation of
about 16 microsats designed to image radio sources in the solar
corona and heliosphere using aperture synthesis techniques. Using
crossed dipoles and high dynamic range radio receivers, SIRA will
observe solar radio emissions in the frequency range from ~15 MHz to
~30 kHz. These frequencies correspond to distances of 2 R_sun to 1
AU. Frequency spacing and time resolution will be optimized for solar
burst analysis. The quasi-spherical constellation (diameter 25-50
km) will provide appropriate baselines for angular resolution of ~10
arcsec at 15 MHz . Several orbit possibilities are currently under
consideration. Rapid data processing for space weather prediction
of CME arrival at 1 AU is a major goal. It is anticipated that this
mission will be proposed for the next NASA MIDEX opportunity.
---------------------------------------------------------
Title: Prominence Eruptions and Coronal Mass Ejection: A Statistical
Study Using Microwave Observations
Authors: Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki,
K.; Howard, R. A.
2003ApJ...586..562G Altcode:
We present the results of a statistical study of a large
number of solar prominence events (PEs) observed by the Nobeyama
Radioheliograph. We studied the association rate, relative timing,
and spatial correspondence between PEs and coronal mass ejections
(CMEs). We classified the PEs as radial and transverse, depending on
whether the prominence moved predominantly in the radial or horizontal
direction. The radial events were faster and attained a larger height
above the solar surface than the transverse events. Out of the 186
events studied, 152 (82%) were radial events, while only 34 (18%)
were transverse events. Comparison with white-light CME data revealed
that 134 (72%) PEs were clearly associated with CMEs. We compare our
results with those of other studies involving PEs and white-light CMEs
in order to address the controversy in the rate of association between
CMEs and prominence eruptions. We also studied the temporal and spatial
relationship between prominence and CME events. The CMEs and PEs seem
to start roughly at the same time. There was no solar cycle dependence
of the temporal relationship. The spatial relationship was, however,
solar cycle dependent. During the solar minimum, the central position
angle of the CMEs had a tendency to be offset closer to the equator
as compared to that of the PE, while no such effect was seen during
solar maximum.
---------------------------------------------------------
Title: A New Method for Estimating Widths, Velocities, and Source
Location of Halo Coronal Mass Ejections
Authors: Michałek, G.; Gopalswamy, N.; Yashiro, S.
2003ApJ...584..472M Altcode: 2007arXiv0710.4524M
It is well known that coronagraphic observations of halo coronal mass
ejections (CMEs) are subject to projection effects. Viewing in the plane
of the sky does not allow us to determine the crucial parameters that
define the geoeffectiveness of CMEs, such as the space speed, width,
or source location. Assuming that halo CMEs have constant velocities,
are symmetric, and propagate with constant angular widths, at least
in their early phase, we have developed a technique that allows us to
obtain the required parameters. This technique requires measurements
of sky-plane speeds and the moments of the first appearance of the
halo CMEs above opposite limbs. We apply this technique to obtain the
parameters of all the halo CMEs observed by the Solar and Heliospheric
Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph
experiment until the end of 2000. We also present a statistical summary
of these derived parameters of the halo CMEs.
---------------------------------------------------------
Title: Coronal mass ejection interaction and particle acceleration
during the 2001 April 14 15 events
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.; Howard, R. A.
2003AdSpR..32.2613G Altcode:
Two successive solar energetic particle (SEP) events associated with
fast and wide coronal mass ejections (CMEs) on 2001 April 14 and 15
are compared. The weak SEP event of April 14 associated with an 830
km/s CME and an M1.0 flare was the largest impulsive event of cycle
23. The April 15 event, the largest ground level event of cycle 23, was
three orders of magnitude more intense than the April 14 <SUP>th</SUP>
event and was associated with a faster CME (1200 km/s) and an X14.4
flare. We compiled and compared all the activities (flares, CMEs,
interplanetary conditions and radio bursts) associated with the two SEP
events to understand the intensity difference between them. Different
coronal and interplanetary environments of the two events (presence
of preceding CME and seed particles ahead of the April 15 event)
may explain the intensity difference.
---------------------------------------------------------
Title: Properties of narrow coronal mass ejections observed with LASCO
Authors: Yashiro, S.; Gopalswamy, N.; Michalek, G.; Howard, R. A.
2003AdSpR..32.2631Y Altcode:
We report the statistical properties of narrow coronal mass ejections
(CMEs, angular width < 20°) withparticular emphasis on comparison
with normal CMEs. We investigated 806 narrow CMEs from an online
LASCO/CME catalog and found that (1) the fraction of narrow CMEs
increases from 12% to 22% towards solar maximum, (2) during the solar
maximum, the narrow CMEs are generally faster than normal ones, (3)
the maximum speed of narrow CMEs (1141 km s <SUP>-1</SUP>) is much
smaller than that of the normal CMEs (2604 km s <SUP>-1</SUP>). These
results imply that narrow CMEs do not form a subset of normal CMEs
and have a different acceleration mechanism from normal CMEs.
---------------------------------------------------------
Title: A numerical study on the acceleration and transit time of
coronal mass ejections in the interplanetary medium
Authors: GonzáLez-Esparza, J. AméRico; Lara, Alejandro;
PéRez-Tijerina, Eduardo; SantilláN, Alfredo; Gopalswamy, Nat
2003JGRA..108.1039G Altcode:
Recently, an empirical model of the acceleration/deceleration of
coronal mass ejections (CMEs) as they propagate through the solar wind
was developed using near-Sun (coronagraphic) and near-Earth (in situ)
observations [, 2000, 2001a]. This model states and quantifies the
fact that slow CMEs are accelerated and fast CMEs are decelerated
toward the ambient solar wind speed (∼400 km/s). In this work we
study the propagation of CMEs from near the Sun (0.083 AU) to 1 AU
using numerical simulations and compare the results with those of the
empirical model. This is a parametric study of CME-like disturbances
in the solar wind using a one-dimensional, hydrodynamic single-fluid
model. Simulated CMEs are propagated through a variable ambient
solar wind and their 1 AU characteristics are derived to compare
with observations and the empirical CME arrival model. We were able
to reproduce the general characteristics of the prediction model
and to obtain reasonable agreement with two-point measurements from
spacecraft. Our results also show that the dynamical evolution of
fast CMEs has three phases: (1) an abrupt and strong deceleration
just after their injection against the ambient wind, which ceases
before 0.1 AU, followed by (2) a constant speed propagation until
about 0.45 AU, and, finally, (3) a gradual and small deceleration
that continues beyond 1 AU. The results show that it is somewhat
difficult to predict the arrival time of slow CMEs (V<SUB>cme</SUB>
< 400 km/s) probably because the travel time depends not only on
the CME initial speed but also on the characteristics of the ambient
solar wind and CMEs. However, the simulations show that the arrival
time of very fast CMEs (V<SUB>cme</SUB> > 1000 km/s) has a smaller
dispersion so the prediction can be more accurate.
---------------------------------------------------------
Title: Coronal mass ejections: Initiation and detection
Authors: Gopalswamy, N.
2003AdSpR..31..869G Altcode:
Coronal mass ejections (CMEs) are large-scale magnetic structures
expelled from the Sun due to MHD processes involving interaction
between plasma and magnetic field in closed field regions. I provide
a summary of the observational signatures and current models on CME
initiation. I also discuss the multiwavelength signatures of CMEs,
which have helped us obtain a global picture of the CME phenomenon in
the inner heliosphere.
---------------------------------------------------------
Title: Arrival time of coronal mass ejections
Authors: Michalek, G.; Gopalswamy, N.; Chane, E.
2002ESASP.506..177M Altcode: 2002svco.conf..177M; 2002ESPM...10..177M
Halo coronal mass ejections (CMEs), originating near the disk
center, cause the severest geomagnetic storms. Thus, estimation
of the arrival of magnetic clouds in the Earth vicinity is very
important in space weather investigation. We describe an empirical
model to predict the 1 AU arrival time of CMEs. This model is
based on the effective acceleration described by Gopalswamy et. al
(2000). It was improved by considering halo CMEs for which the space
velocities are determined. This allowed us to receive the more accurate
estimations. The new model reduces the average prediction error from
≍10 to ≍5 hours.
---------------------------------------------------------
Title: Solar, Interplanetary, and Geospace Disturbances Associated
with the April 2002 Coronal Mass Ejections
Authors: Gopalswamy, N.; Yashiro, S.; St. Cyr, O.; Lawrence, G.;
Kaiser, M. L.; Gurman, J. B.; Howard, R. A.
2002AGUFMSA12A..02G Altcode:
The Solar and Heliospheric Observatory (SOHO) detected a large number of
coronal mass ejections (CMEs) during the April 14-24, 2002 period. We
describe the properties of these CMEs and contrast them with those of
the general population of CMEs. We explore the connection of these
CMEs to the interplanetary shocks and the solar energetic particles
events using Wind and GOES data, respectively. We assess the extent of
preconditioning of the corona by repeated flaring and mass ejections
from the active regions involved. Based on the arrival times of the
interplanetary CMEs and shocks, we discuss the evolution of these
disturbances as they propagated between the Sun and Earth. We compare
the extended nature of the main phase of the complex geomagnetic storm
to other other similar extended storm periods
---------------------------------------------------------
Title: A Statistical Study of Two Classes of Coronal Mass Ejections
Authors: Moon, Y. -J.; Choe, G. S.; Wang, Haimin; Park, Y. D.;
Gopalswamy, N.; Yang, Guo; Yashiro, S.
2002ApJ...581..694M Altcode:
A comprehensive statistical study is performed to address the question
of whether two classes of coronal mass ejections (CMEs) exist. A
total of 3217 CME events observed by SOHO/LASCO in 1996-2000 have
been analyzed. We have examined the distributions of CMEs according to
speed and acceleration, respectively, and investigated the correlation
between speed and acceleration of CMEs. This statistical analysis is
conducted for two subsets containing those CMEs that show a temporal and
spatial association either with GOES X-ray solar flares or with eruptive
filaments. We have found that CMEs associated with flares have a higher
median speed than those associated with eruptive filaments and that the
median speed of CMEs associated with strong flares is higher than that
of weak-flare-associated CMEs. The distribution of CME acceleration
shows a conspicuous peak near zero, not only for the whole data set,
but also for the two subsets associated either with solar flares or
with eruptive filaments. However, we have confirmed that the CMEs
associated with major flares tend to be more decelerated than the CMEs
related to eruptive filaments. The fraction of flare-associated CMEs
has a tendency to increase with the CME speed, whereas the fraction
of eruptive-filament-associated CMEs tends to decrease with the CME
speed. This result supports the concept of two CME classes. We have
found a possibility of two components in the CME speed distribution
for both the CME data associated with flares larger than M1 class and
the CME data related with limb flares. Our results suggest that the
apparent single-peak distribution of CME speed can be attributed to
the projection effect and possibly to abundance of small flares too. We
also note that there is a possible correlation between the speed of CMEs
and the time-integrated X-ray flux of the CME-associated limb flares.
---------------------------------------------------------
Title: The International Heliophysical Year (IHY)
Authors: Davila, J. M.; Harrison, R.; Poland, A.; Thompson, B.;
Gopalswamy, N.
2002AGUFMSH21A0518D Altcode:
In 1957 a program of international research, inspired by the
International Polar Years of 1882-83 and 1932-33, was organized as
the International Geophysical Year (IGY) to study global phenomena of
the Earth and geospace. The IGY involved about 60,000 scientists from
66 nations, working at thousands of stations, from pole to pole to
obtain simultaneous, global observations on Earth and in space. There
had never been anything like it before. The fiftieth anniversary of
the International Geophysical Year will occur in 2007. We propose to
organize an international program of scientific collaboration for this
time period called the International Heliophysical Year (IHY). Like
it predecessors, the IHY will focus on fundamental global questions
of Earth science.
---------------------------------------------------------
Title: MHD modelling of CME and CME interactions in a bi-modal
solar wind: a preliminary analysis of the 20 January 2001 two CMEs
interaction event
Authors: Wu, S. T.; Wang, A. H.; Gopalswamy, N.
2002ESASP.505..227W Altcode: 2002solm.conf..227W; 2002IAUCo.188..227W
Observations from SOHO and WIND reveal that coronal mass ejections
(CMEs) cannibalize and deflect one another. CMEs also are accelerated
and decelerated due to their interactions with the solar wind. These
CME interactions with CME and with the solar wind result in producing
significant differences in solar wind signatures as compared to
isolated CME events. To understand these dynamical evolutionary
processes, we have constructed a magnetohydrodynamic (MHD)
simulation model based on a flux-rope and streamer model including
bi-modal solar wind to investigate the physical processes of CME
interactions. Specifically, the January 20, 2001 CME-CME interaction
event recorded by SOHO/LASCO/C2/C3 are used to guide this simulation
study. The results showed that CME cannibalism is caused by magnetic
reconnection. The CME's acceleration and deceleration are caused by
solar wind and the CME's deflection of one another.
---------------------------------------------------------
Title: Measurements of Three-dimensional Coronal Magnetic Fields
from Coordinated Extreme-Ultraviolet and Radio Observations of a
Solar Active Region Sunspot
Authors: Brosius, Jeffrey W.; Landi, Enrico; Cook, John W.; Newmark,
Jeffrey S.; Gopalswamy, N.; Lara, Alejandro
2002ApJ...574..453B Altcode:
We observed NOAA Active Region 8108 around 1940 UT on 1997 November 18
with the Very Large Array and with three instruments aboard the NASA/ESA
Solar and Heliospheric Observatory satellite, including the Coronal
Diagnostic Spectrometer, the EUV Imaging Telescope, and the Michelson
Doppler Imager. We used the right-hand and left-hand circularly
polarized components of the radio observing frequencies, along with
the coordinated EUV observations, to derive the three-dimensional
coronal magnetic field above the region's sunspot and its immediate
surroundings. This was done by placing the largest possible harmonic
(which corresponds to the smallest possible magnetic field strength)
for each component of each radio frequency into appropriate atmospheric
temperature intervals such that the calculated radio brightness
temperatures at each spatial location match the corresponding
observed values. The temperature dependence of the derived coronal
magnetic field, B(x,y,T), is insensitive to uncertainties on the
observed parameters and yields field strengths in excess of 580 G
at 2×10<SUP>6</SUP> K and in excess of 1500 G at 1×10<SUP>6</SUP>
K. The height dependence of the derived coronal magnetic field,
B(x,y,h), varies significantly with our choice of magnetic scale height
L<SUB>B</SUB>. Based on L<SUB>B</SUB>=3.8×10<SUP>9</SUP> cm derived
from the relative displacements of the observed radio centroids, we
find magnetic field strengths in excess of 1500 G at heights of 15,000
km and as great as 1000 G at 25,000 km. By observing a given target
region on several successive days, we would obtain observations at a
variety of projection angles, thus enabling a better determination of
L<SUB>B</SUB> and, ultimately, B(x,y,h). We compare coronal magnetic
fields derived from our method with those derived from a potential
extrapolation and find that the magnitudes of the potential field
strengths are factors of 2 or more smaller than those derived from our
method. This indicates that the sunspot field is not potential and that
currents must be present in the corona. Alfvén speeds between 25,000
and 57,000 km s<SUP>-1</SUP> are derived for the 1×10<SUP>6</SUP>
K plasma at the centroids of the radio observing frequencies. Filling
factors between 0.003 and 0.1 are derived for the 1×10<SUP>6</SUP>
K plasma at the centroids of the radio observing frequencies.
---------------------------------------------------------
Title: Estimation of projection effect of CMEs from the onset time
of shock-associated type III radio burst
Authors: Michalek, G.; Gopalswamy, N.; Reiner, M.; Yashiro, S.;
Kaiser, M. L.; Howard, R. A.
2002ESASP.508..449M Altcode: 2002soho...11..449M
We present a new possibility to estimate the projection effects on CME
measurements. We assume that (1) high energy electrons are produced at
the shock front ahead of the CME, and (2) the radio burst starts when
the shock reaches open field lines (~3 R<SUB>solar</SUB>). In other
words, the onset time of the radio burst corresponds to the time when
the CME leading edge reaches 3 R<SUB>solar</SUB>. It is well known
that coronagraphic observations of halo CMEs are subject to projection
effects. Fortunately, the Wind/WAVES observations of type III radio
bursts associated with shock waves are free from projection effects. The
difference between the onset times of CMEs and radio bursts should be
strongly correlated with the position of CMEs on the Sun. We found
this correlation and showed that it strongly depends on a period of
solar activity and source location on the Sun. Particular linear fits
to the considered scattered plots can be used to further determination
of source location and projection of CMEs on the plane of sky.
---------------------------------------------------------
Title: A new possibility to estimate the width, source location and
velocity of halo CMEs
Authors: Michalek, G.; Gopalswamy, N.; Yashiro, S.
2002ESASP.508..453M Altcode: 2002soho...11..453M
It is well known that the coronagraphic observations of halo CMEs are
subject to projection effects. Viewing in the plane of the sky does not
allow us to determine the crucial parameters defining geoeffectivness
of CMEs, such as the velocity, width or source location. We assume
that halo CMEs at the beginning phase of propagation have constant
velocities, are symmetric and propagate with constant angular
widths. Using these approximations and determining projected velocities
and difference between times when CME appears on the opposite sides
of the occultation disk we are able to get necessary parameters. We
present consideration for the whole halo CMEs from SOHO/LASCO catalog
until the end of 2000.
---------------------------------------------------------
Title: Interacting Coronal Mass Ejections and Solar Energetic
Particles
Authors: Gopalswamy, N.; Yashiro, S.; Michałek, G.; Kaiser, M. L.;
Howard, R. A.; Reames, D. V.; Leske, R.; von Rosenvinge, T.
2002ApJ...572L.103G Altcode:
We studied the association between solar energetic particle (SEP) events
and coronal mass ejections (CMEs) and found that CME interaction is
an important aspect of SEP production. Each SEP event was associated
with a primary CME that is faster and wider than average CMEs and
originated from west of E45°. For most of the SEP events, the primary
CME overtakes one or more slower CMEs within a heliocentric distance of
~20 R<SUB>solar</SUB>. In an inverse study, we found that for all the
fast (speed greater than 900 km s<SUP>-1</SUP>) and wide (width greater
than 60°) western hemispheric frontside CMEs during the study period,
the SEP-associated CMEs were ~4 times more likely to be preceded by
CME interaction than the SEP-poor CMEs; i.e., CME interaction is a
good discriminator between SEP-poor and SEP-associated CMEs. We infer
that the efficiency of the CME-driven shocks is enhanced as they
propagate through the preceding CMEs and that they accelerate SEPs
from the material of the preceding CMEs rather than from the quiet
solar wind. We also found a high degree of association between major
SEP events and interplanetary type II radio bursts, suggesting that
proton accelerators are also good electron accelerators.
---------------------------------------------------------
Title: Prominence Eruptions and CMEs: A Statistical Study
Authors: Gopalswamy, N.; Shimojo, M.; Yashiro, S.; Shibasaki, K.
2002AAS...200.3705G Altcode: 2002BAAS...34..695G
Prominence eruptions are thought to be an integral part of coronal mass
ejections. However, recent statistical studies obtained conflicting
conclusions regarding this relationship: a nearly one-to-one
correspondence to a poor association. We revisited this problem using
all the eruptive prominences detected automatically from the daily
images obtained by the Nobeyama Radioheliograph. The images were
made with a 10 min cadence so only slower eruptions could be detected
from these images. During January 1996 to December 2001, there were
226 prominence eruptions detected this way and 182 of them had white
light observations from the Solar and Heliospheric Observatory (SOHO)
mission. When we compared the radio and white light data, we found
that 76 CMEs, while only 16 remaining 8 suggesting partial eruption. We
conclude that there is good association between CMEs when the prominence
eruptions have a radial component of the velocity is dominant.
---------------------------------------------------------
Title: Properties of coronal mass ejections and relationship with
solar flares
Authors: Yashiro, S.; Gopalswamy, N.; Michalek, G.; Howard, R. A.
2002AAS...200.3704Y Altcode: 2002BAAS...34..695Y
Coronal mass ejections (CMEs) associated with flares are thought to
be faster than those associated with filament eruptions. However,
Hundhausen (1997) examined that the relationship between CME kinetic
energy and X-ray flare peak intensity, and found that there is only
a weak correlation. We have measured the speed, size, location,
and acceleration of more than 4000 CMEs observed by the SOHO LASCO
Coronagraph from January 1996 through December 2001, providing a good
opportunity to revisit the relationship between CMEs and flares. We
identified flare-CME pairs as follows: Since the field of view of the
LASCO C2 coronagraph limited to heliocentric distances over 2 solar
radii (Ro), we cannot obtain the CME start time accurately. So, we
assume that the CMEs start from 1 Ro, and estimate the start time from
their height-time trajectories. Then, we looked for CMEs that occurred
within flare impulsive phase. This way, we found 239 flare-CME pairs. We
found a weak correlation between the CME speed and flare X-ray peak
flux (correlation coefficient = 0.52). When we isolated the limb events
(based on the solar source of the CMEs), we found the correlation to
be poorer (0.44). We compare our results with those of Hundhausen.
---------------------------------------------------------
Title: Interplanetary Radio Bursts
Authors: Gopalswamy, N.
2002AAS...200.4908G Altcode: 2002BAAS...34..722G
Radio bursts in the interplanetary (IP) medium are indicative of solar
eruptions that expel shock-driving coronal material or energetic
electron beams. Type II radio bursts originate from fast-mode MHD
shocks driven by coronal mass ejections (CMEs). Type III bursts are
produced by energetic electrons escaping along open magnetic field
lines. Occasionally, type IV bursts are also observed in the near-Sun
IP medium. Radio and Plasma Waves (WAVES) experiment on board the
Wind spacecraft routinely observes these radio bursts at frequencies
below 14 MHz since 1994. This new radio window in the 1-14 MHz band
has helped us confirm several of the well known solar-terrestrial
processes and discover new processes such as the nonthermal radio
emission due to colliding CMEs. The IP type II bursts are indicative
of faster and wider CMEs, which are important from a space weather
point of view. There is also a high degree of association between
solar energetic particles and type II radio bursts implying that the
same shocks accelerate protons and electrons. I provide a summary of
the recent results obtained using radio and white light data.
---------------------------------------------------------
Title: Relationship Between DH Type II Radio Bursts and Energetic
Particle Events
Authors: Rosas, A. M.; Gopalswamy, N.; Kaiser, M. L.
2002AAS...200.3703R Altcode: 2002BAAS...34Q.695R
A comparison of 134 interplanetary type II bursts detected by the
WIND/WAVES experiment in the 1-14 MHz range is made with the solar
energetic particle (SEP) events. The study period is from 1996 to 2001,
which is between minimum and slightly above maximum of the current solar
cycle (23). We find that approximately 74% of the IP type II bursts are
related to an energetic particle event. We are continuing to investigate
the reasons why some interplanetary type II radio bursts do not have
energetic particle events. A longitudinal distribution of the solar
sources of these events will be used to discriminate between the SEP
and non-SEP type II bursts. The study will be able to tell us whether
electron accelerators are also proton accelerators. This research was
supported by NASA. Travel to this meeting is partly supported by the
SPD Studentship Award.
---------------------------------------------------------
Title: Influence of CME Interaction on Solar Proton Events During
Cycle 23
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Kaiser, M. L.;
Howard, R. A.; Reames, D. V.; Leske, R. A.; Von Rosenvinge, T.
2002AGUSMSH41A..06G Altcode:
We studied the association between solar proton events and white-light
coronal mass ejections (CMEs) that occurred during the solar cycle
23 until November 2001. Each of the SEP events was associated with
a large-scale primary CME, that were faster and wider than average
CMEs. For most of the proton events, the primary CME overtakes one or
more slower CMEs. In order to confirm this result, we examined the
association and CME interaction and energetic proton events for all
the fast (speed > 900 km~s<SUP>-1</SUP>) and wide (width > 60
deg) western hemispheric and halo CMEs during the study period. CMEs
with energetic protons are 3 times more likely to be preceded by CME
interaction than those without. We conclude that CME interaction is an
important aspect of SEP acceleration. We infer that CME-driven shocks
accelerate SEPs from the material of the preceding CMEs rather than
from the quiet solar wind.
---------------------------------------------------------
Title: New Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; White, S. M.; Landi, E.; Cook, J. W.; Newmark,
J. S.; Gopalswamy, N.; Lara, A.
2002AAS...200.0307B Altcode: 2002BAAS...34..642B
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of NOAA
regions 8108 (N21E18 on 1997 November 18) and 8539 (N20W12 on 1999 May
13). The EUV spectra and images, obtained with the Coronal Diagnostic
Spectrometer (CDS) and the Extreme-ultraviolet Imaging Telescope (EIT)
aboard the Solar and Heliospheric Observatory (SOHO) satellite, were
used to derive the differential emission measure (DEM) and the plasma
electron density for each spatial pixel (along each line of sight)
within both regions. These were subsequently used to calculate maps
of the expected thermal bremsstrahlung brightness temperature at the
Very Large Array (VLA) radio observing frequencies of 1.4, 4.9, 8.4,
and 15 GHz. The thermal bremsstrahlung maps reproduce neither the
structure nor the intensity of the observed maps, and indicate that
thermal gyroemission must dominate the observed radio emission. The
radio observations were used to constrain the magnetic scale height and
the gross temperature structure of the atmosphere. These, along with
the DEM, electron density, and observed radio brightness temperature
maps, were used to derive the temperature distribution of the coronal
magnetic field strength B(T) that reproduced simultaneously the observed
right-hand and left-hand circularly polarized emission at the radio
observing frequencies for each spatial pixel in the images. Magnetic
field strengths corresponding to 3rd harmonic gyroemission at 4.9 GHz
(580 Gauss) are found in coronal plasmas at temperatures as high as
3.2 MK, while magnetic field strengths corresponding to 3rd harmonic
gyroemission at 15 GHz (1800 Gauss) are found in coronal plasmas at
temperatures as high as 1.6 MK. B(T) was ultimately converted to B(h)
and compared with extrapolations from photospheric magnetograms.
---------------------------------------------------------
Title: Evidence from Coronal Observations of Magnetic Field Structure
in CMEs
Authors: Gopalswamy, N.
2002AAS...200.6509G Altcode: 2002BAAS...34..752G
The magnetic nature of coronal mass ejections has been inferred from
the fact that they originate from closed magnetic field regions on
the Sun such as active regions and filament regions. Although we have
no direct measurement of the magnetic fields of CMEs, we can obtain
useful information on the magnetic structure of CMEs from coronal
observations at various wavelengths. The CME is a multithermal structure
with temperatures ranging from a few kilokelvin to several megakelvin,
so we need multi-wavelength observations to get a global picture of
CMEs. A wide range of ground and space based instruments routinely
observe CMEs. We present several examples of CMEs observed in X-ray,
white light, EUV and radio wavelengths that help us understand the
magnetic structure of CMEs.
---------------------------------------------------------
Title: Properties of coronal mass ejections observed by SOHO
Authors: Yashiro, S.; Gopalswamy, N.; Michalek, G.; St. Cyr, O. C.;
Plunkett, S. P.; Howard, R. A.
2002AGUSMSH32A..03Y Altcode:
We report the characteristics of more than 4000 coronal mass ejections
(CMEs) observed by the SOHO LASCO Coronagraph from January 1996
through December 2001. We have measured the speed, size, location, and
acceleration of each CME, and examined the annual variation of their
distributions. All of CME measurements are shown in the online catalog
(http://cdaw.gsfc.nasa.gov/). Using this CME catalog, we found that
(1) almost of CMEs occurred around equator during the solar minimum,
while CME appeared at all latitudes during the solar maximum. (2) the
average speed increases toward solar maximum from 306 km/s to 500 km/s,
and slightly decreases to 482 km/s in 2001. (3) The width distribution
become wider toward solar maximum. These results are consistent with
those of Solwind and Skylab.
---------------------------------------------------------
Title: Motion of an Eruptive Prominence in the Solar Corona
Authors: Filippov, B. P.; Gopalswamy, N.; Lozhechkin, A. V.
2002ARep...46..417F Altcode:
A model for the nonradial motion of an eruptive prominence in the solar
corona is proposed. Such motions, which can sometimes be inaccessible
to observation, result in an apparent break in the causal link between
eruptive prominences and coronal mass ejections. The global magnetic
field of the Sun governs coronal plasma motions. The complex structure
of this field can form prominence trajectories that differ considerably
from a simple vertical rise (i.e., radial motion). A solar filament is
modeled as a current-carrying ring or twisted toroidal magnetic rope
in equilibrium with the coronal magnetic field. The global field is
described using two spherical harmonics. A catastrophic violation of the
filament equilibrium followed by its rapid acceleration—eruption—is
possible in this nonlinear system. The numerical solution of the
equations of motion corresponds well to the eruption pattern observed
on December 14, 1997.
---------------------------------------------------------
Title: Interplanetary radio emission due to interaction between two
coronal mass ejections
Authors: Gopalswamy, Nat; Yashiro, Seiji; Kaiser, Michael L.; Howard,
Russell A.; Bougeret, J. -L.
2002GeoRL..29.1265G Altcode: 2002GeoRL..29h.106G
We report on the detection of a new class of nonthermal radio
emission due to the interaction between two coronal mass ejections
(CMEs). The radio emission was detected by the Radio and Plasma Wave
Experiment (WAVES) on board the Wind satellite, while the CMEs were
observed by the white-light coronagraphs of the Solar and Heliospheric
Observatory (SOHO) mission. There was no type II radio burst (metric or
interplanetary) preceding the nonthermal emission. The radio emission
occurred at a distance beyond 10 R<SUB>s</SUB> from the Sun, where the
two CMEs came in contact. Using H-alpha and EUV images, we found that
the two CMEs were ejected roughly along the same path. We argue that
the nonthermal electrons responsible for the new type of radio emission
were accelerated due to reconnection between the two CMEs and/or due
to the formation of a new shock at the time of the collision between
the two CMEs.
---------------------------------------------------------
Title: Influence of the aerodynamic drag on the motion of
interplanetary ejecta
Authors: Vršnak, Bojan; Gopalswamy, Nat
2002JGRA..107.1019V Altcode:
A simple semi-empirical model for the motion of interplanetary ejecta is
proposed to advance the prediction of their arrival times at Earth. It
is considered that the driving force and the gravity are much smaller
than the aerodynamic drag force. The interaction with the ambient solar
wind is modeled using a simple expression for the acceleration $[\dot
\upsilon \]$ = -γ(υ-w), where w = w(R) is the distance-dependent
solar wind speed. It is assumed that the coefficient γ decreases
with the heliocentric distance as γ = αR<SUP>-β</SUP>, where α
and β are constants. The equation of motion is integrated numerically
to relate the Earth transit time and the associated in situ velocity
with the velocity of coronal mass ejection. The results reproduce well
the observations in the whole velocity range of interest. The model
values are compared with some other models in which the interplanetary
acceleration is not velocity dependent, as well as with the model where
the drag acceleration is quadratic in velocity $\[\dot \upsilon \]$
= -γ<SUB>2</SUB>(υ - w)|υ - w|.
---------------------------------------------------------
Title: Colliding coronal mass ejections and particle acceleration
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M.; Reames, D.;
Howard, R.
2002cosp...34E1253G Altcode: 2002cosp.meetE1253G
Colliding Coronal Mass Ejections (CMEs) have important implications to
a number of physical processes in the near-Sun interplanetary medium:
Shock propagation, particle acceleration and solar wind composition. We
present statistical results on large solar energetic particle events,
associated CMEs and CME interaction during solar cycle 23. We show
that most of the large SEP events are preceded by CME interaction. As
an inverse study, we identified all the fast and wide front side CMEs
from the western hemisphere and examined the SEP association and
CME interaction. We found that fast and wide CMEs interacting with
preceding CMEs are more likely to be associated with SEPs. We discuss
the implications of the statistical results to the understanding of
particle acceleration by CME-driven shocks.
---------------------------------------------------------
Title: Propagation of coronal mass ejections from Sun to 1 AU
Authors: Manoharan, P.; Gopalswamy, N.; Yashiro, S.; Howard, R.
2002cosp...34E2699M Altcode: 2002cosp.meetE2699M
We report on the study of propagation characteristics of a large number
of CMEs over the entire range of Sun-Earth distance. Using white-light
(LASCO) and interplanetary scintillation (IPS) observations, we
investigate the radial variation of the speed of CMEs. In the case
of fast CMEs (initial speed 800 kms-1 ), speed declines slowly with
distance (VcmeR-a where a0.05-0.1) within about 100 Rsun . Beyond this
distance, the speed declines as VcmeR-b where b0.5 - 1. The evolution
of size of CMEs with distance, LcmeR, suggests a pressure balance
maintained between the CME and ambient solar wind at distances greater
than 50 Rsun . We also report the detection of interaction between
fast and slow CMEs outside the LASCO field of view. The interaction
signature is seen as an unusual enhancement in the density turbulence.
---------------------------------------------------------
Title: Space Weather Study Using Combined Coronagraphic and in
Situ Observations
Authors: Gopalswamy, N.
2002swsm.conf...39G Altcode:
Coronal mass ejections (CMEs) play an important role in space
weather studies because of their ability to cause severe geoeffects,
such as magnetic storms. Shocks driven by CMEs may also accelerate
solar energetic particles. Prediction of the arrival of these CMEs is
therefore of crucial importance for space weather applications. After
a brief review of the prediction models currently available, a
description of an empirical model to predict the 1 AU arrival CMEs
is provided. This model was developed using two-point measurements:
(i) the initial speeds and onset times of Earth-directed CMEs obtained
by white-light coronagraphs, and (ii) the corresponding interplanetary
CME speeds and onset times at 1 AU obtained in situ. The measurements
yield an empirical relationship between the interplanetary acceleration
faced by the CMEs and their initial speeds, which forms the basis
of the model. Use of archival data from spacecraft in quadrature is
shown to refine the acceleration versus initial speed relationship,
and hence the prediction model. A brief discussion on obtaining the
1-AU speed of CMEs from their initial speeds is provided. Possible
improvements to the prediction model are also suggested.
---------------------------------------------------------
Title: Relation Between Coronal Mass Ejections and their
Interplanetary Counterparts
Authors: Gopalswamy, N.
2002stma.conf..157G Altcode:
Our current knowledge on coronal mass ejections (CMEs) comes from
two spatial domains: the near-Sun (up to 30 solar radii) region
remote-sensed by coronagraphs and the geospace and beyond where in situ
observations are made by spacecraft. Comparing observations from these
two domains has helped us understand the propagation and evolution of
CMEs through the interplanetary (IP) medium and develop an empirical
model to predict the 1-AU arrival of CMEs. In this paper, we review
the available information on the relation between CMEs and their IP
counterparts. In particular, we concentrate on issues related to the
prediction of the arrival of ICMEs in the geospace. We discuss the
solar sources of the three largest geomagnetic storms of year 2000 and
compare the predicted and observed arrival times of the associated CMEs.
---------------------------------------------------------
Title: CMEs: observations of all kinds
Authors: Gopalswamy, Nat
2002ocnd.confE..13G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of Narrow Coronal Mass Ejections Observed with LASCO
Authors: Yashiro, S.; Gopalswamy, N.; Howard, R.
2002cosp...34E2602Y Altcode: 2002cosp.meetE2602Y
More than 4500 coronal mass ejections (CMEs) have been observed
with SOHO LASCO coronagraph from January 1996 to December 2001. We
have measured properties of all these CMEs and published them in an
online catalog. In this paper, we describe the properties of narrow
CMEs (width < 20 deg.). We investigated 675 narrow CMEs from the
catalog and found that (1) the fraction of narrow CMEs increases from
5% to 15% towards solar maximum, (2) the average speed of the narrow
CMEs is higher than that of the wide ones, (3) the maximum speed of
narrow CMEs (1141 km/s) is much smaller than that of the wide CMEs
(2604 km/s). We also found that the wide CMEs are likely to have the
well known three-part structure, but narrow ones do not. Wide CMEs
can be explained as due to the expansion of flux tubes, but the narrow
CMEs seem to be mass flows in vertical flux tubes (streamers).
---------------------------------------------------------
Title: Statistical Properties of Radio-Rich Coronal Mass Ejections
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Kaiser, M. L.;
Howard, R. A.; Bougeret, J. -L.
2002stma.conf..169G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Origin of coronal streamer distention
Authors: Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki,
K.; Howard, R.
2002cosp...34E1257G Altcode: 2002cosp.meetE1257G
Distention of coronal streamers is considered to be one of the
pre-eruption evolution of coronal mass ejections (CMEs), although how
mass is added to the streamers is poorly understood. During our study
of eruptive prominences and their relation to CMEs, we observed a large
number of prominences associated with significant changes in the helmet
streamers overlying the prominences. We used the white light images of
the corona obtained by the Solar and Heliospheric Mission's Large Angle
and Spectrometric Coronagraph images and the microwave images from the
Nobeyama radioheliograph in Japan. We found that the streamer distention
is associated with prominence eruption with mostly horizontal motion
(parallel to the solar limb) or with eruptive prominences with most of
the mass falling back to the solar surface. We suggest that the physical
process which activates the prominences also add mass to the streamers.
---------------------------------------------------------
Title: Variability of solar eruptions during cycle 23
Authors: Gopalswamy, N.; Nunes, S.; Yashiro, S.; Howard, R.
2002cosp...34E1260G Altcode: 2002cosp.meetE1260G
Nearly 5000 coronal mass ejections (CMEs) were observed by the Solar
and Heliospheric Observatory from the minimum to maximum of the current
solar cycle (19962001). We have measured and cataloged the properties
of all these CMEs. We have studied the variation of mean and median
speeds and the rate of CMEs (averaged over Carrington rotations)
as a function time. We compare the CME rate with those of other
energetic solar events such as interplanetary type II bursts, solar
energetic particle (SEP) events and metric type II bursts. This study
is useful in identifying the phases of the solar cycle which show rapid
variability. CMEs associated with radio bursts and SEPs belong to a
separate group characterized by high speed and large width. We discuss
the solar cycle variability of this energetic group in comparison with
the general population of CMEs.
---------------------------------------------------------
Title: An empirical model to predict the 1-AU arrival of
interplanetary shocks
Authors: Gopalswamy, N.; Lara, A.; Manoharan, P.; Howard, R.
2002cosp...34E1256G Altcode: 2002cosp.meetE1256G
We describe an empirical model to predict the 1-AU arrival of
interplanetary shocks of solar origin. This model is an extension of
Gopalswamy et al.'s [2001] empirical CME arrival model based on an
effective acceleration acting on the CMEs as they propagate through the
interplanetary medium. We measured the properties of a large number
IP shocks, their solar sources and associated CMEs. Using in situ
observations from Wind and ACE, we obtained the physical conditions
upstream and down stream of the shock. Combining the shock data with the
known piston-shock relation, we estimate the shock arrival times. We
compare the estimated and actual arrival times of shocks to determine
the error in our shock-arrival estimates. Reference: Gopalswamy, N.,
A. Lara, S. Yashiro, M. L. Kaiser, and R. A. Howard, Predicting the
1-AU Arrival Times of Coronal Mass Ejections, J. Geophys. Res., 106,
29,207, 2001
---------------------------------------------------------
Title: Phenomena Associated with EIT Waves
Authors: Thompson, B.; Biesecker, D.; Gopalswamy, N.
2002cosp...34E2672T Altcode: 2002cosp.meetE2672T
We discuss phenomena associated with "EIT Wave" transients. "EIT
Waves" are propagating disturbances first observed in SOHO/EIT EUV
images. However, a number of studies have been conducted to determine
their relationship to other observations, using data from a variety
of instruments. These phenomena include coronal mass ejections,
flares, EUV/SXR dimmings,chromospheric waves, Moreton waves, solar
energetic particle events, energetic electron events, and radio
signatures. Although the occurrence of many phenomena correlate with the
appearance of EIT waves, it is difficult to infer which associations are
causal. The presentation will include a discussion of the correlation
statistics of these phenomena.
---------------------------------------------------------
Title: Solar eruptions and long wavelength radio bursts: The 1997
May 12 event
Authors: Gopalswamy, N.; Kaiser, M. L.
2002AdSpR..29..307G Altcode:
We report on the cause of the 1997 May 12 type II bursts observed by
ground based and space-based radio instruments. We estimate the fast
mode speed in the corona as a function of heliocentric distance to
identify the regions where fast mode shocks can be driven by CMEs. We
find that both the coronal and the interplanetary type II bursts can
be explained by shocks driven by the same CME at two different spatial
domains. The fast mode speed in the corona has a peak at a heliocentric
distance of ∼ 3 R<SUB>⊙</SUB> which does not allow the coronal shock
wave to propagate beyond this distance. When the CME continues to travel
beyond the fast mode peak, another shock forms in the interplanetary
medium where the fast mode speed falls sufficiently. From the radio
observations we can infer that the plane of the sky speed of the CME
is smaller than the space speed by at least a factor of 2, consistent
with the location of the eruption at N21 W08. The inferred CME speed
is also consistent with previous deprojected speed estimates.
---------------------------------------------------------
Title: A Statistical Study for Two Classes of CMEs
Authors: Moon, Y.; Choe, G.; Park, Y.; Yang, G.; Wang, H.; Goode,
P.; Yashiro, S.; Gopalswamy, N.
2001AGUFMSH12B0747M Altcode:
MacQueen and Fisher (1983) noted the existence of two classes of CMEs;
flare-associated CMEs show the highest speeds with little acceleration,
wheras eruption-associated ones exhibit large accelerations. A
statistical study has been performed to examine the bimodality of CMEs
using the CME catalogue based on SOHO/LASCO observations from 1996 to
2000 by Yashiro and Michalek (2001). In the catalogue, we have used the
speed and acceleration data obtained from height-time plots with 2nd
order fits. We present the histogram of CME speed, the histogram of
CME acceleration, and their speed-acceleration diagram. We have also
conducted the same analysis for two different sets of data which have
both time and spatial association with GOES solar flares and filaments
activities (e.g., disappearing filaments), respectively. The filament
data were collected from the NGDC and Big Bear Solar Observatory. Major
results from this study are as follows. (1) The speed histogram for
all the CMEs has a major peaks near 300km/s but does not show any
double peaks. (2) Their acceleration histogram has a strong peak near
zero, even for the two data sets associated with solar flares and
filaments. (3) The number of CMEs with deceleration is comparable to
that of CMEs with acceleration. (4) Their acceleration distribution
has a maximum near zero regardless of their speed. (5) The ratio
of flare-associated ones to all the CMEs increases with CME speed,
wheras the ratio of filament-associated ones decreases. Finally we
compare our results with previous ones and discuss their implications
on the bimodality of CMEs.
---------------------------------------------------------
Title: Interplanetary Acceleration of Coronal Mass Ejections:
Comparison between numerical simulations and observations
Authors: Lara, A.; Gonzalez-Esparza, A.; Perez-Tijerina, E.; Santillan,
A.; Gopalswamy, N.
2001AGUFMSH11D..10L Altcode:
For a set of 50 Coronal Mass Ejections (CMEs) observed with the Large
Angle and Spectrometric COrongraph (LASCO) on board of the SOlar and
Heliospheric Observatory (SOHO) mission, we estimate the density and
measure the sky-plane speed at 18 solar radii (R<SUB>sun</SUB>). We
feed these parameters to a one dimensional, single fluid, hydrodynamic
model to simulate the CME propagation from 18 R<SUB>sun</SUB> to one
AU, and iteratively adjust the initial temperature and ambient solar
wind speed using in situ measurements by the Wind mission prior to
and during the ICMEs that pair with the white-light CMEs. Following
the evolution of the nose of the ejecta we are able to construct an
acceleration model for the simulated ICMEs. We compare and discuss the
simulated acceleration profile with the observed mean acceleration in
order to obtain a general ICME acceleration model.
---------------------------------------------------------
Title: CME Interactions Near the Sun
Authors: Gopalswamy, N.
2001AGUFMSH11D..01G Altcode:
The phenomenon of interaction between coronal mass ejections in the
near-Sun interplanetary medium is surveyed using data from SOHO and
Wind missions. Long wavelength radio data (1-14 MHz) reveal CME-CME
and CME-shock interactions. CME interactions may result in change of
CME trajectories or merger ("cannibalism"). Typically, slower CMEs
are overtaken by faster CMEs. Occasionally, multiple interactions
are observed. Solar cycle variation of the CME interaction rate will
be presented based on a careful examination of all the available CME
data from SOHO. Finally, consequences of the CME interaction in the
interplanetary medium will be discussed briefly. Research supported
by NASA, AFOSR and NSF.
---------------------------------------------------------
Title: Interacting CMEs and Solar Energetic Particles
Authors: Gopalswamy, N.; Yashiro, S.; von Rosenvinge, T. T.; Leske, R.
2001AGUFMSH12A0735G Altcode:
We examined the solar sources of a set of large solar energetic
particle (SEP) events with mixed (impulsive + gradual) abundance
signatures. The SEP events were detected by the Solar Isotope
Spectrometer (SIS) on board the Advanced Composition Explorer (ACE)
spacecraft. For each of the SEP events, we identified a "primary"
coronal mass ejection (CME), detected by the Solar and Heliospheric
observatory (SOHO). Then we examined a set of CMEs preceding the
primary CME, potentially interacting with the primary CME in the
near-Sun interplanetary medium. Twenty events from a list of 27
recently compiled von Rosenvinge et al. (Proc. ICRC 2001, p. 3136)
overlapped with SOHO observations. Preliminary results indicate that
a large majority of the primary CMEs were preceded by slower CMEs,
suggesting that CME interaction may result in abundance enhancements
in the source material. Research supported by NASA and AFOSR.
---------------------------------------------------------
Title: Characteristics of coronal mass ejections associated with
long-wavelength type II radio bursts
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.; Howard, R. A.;
Bougeret, J. -L.
2001JGR...10629219G Altcode:
We investigated the characteristics of coronal mass ejections (CMEs)
associated with long-wavelength type II radio bursts in the near-Sun
interplanetary medium. Type II radio bursts in the decameter-hectometric
(DH) wavelengths indicate powerful MHD shocks leaving the inner
solar corona and entering the interplanetary medium. Almost all of
these bursts are associated with wider and faster than average CMEs. A
large fraction of these radio-rich CMEs were found to decelerate in the
coronagraph field of view, in contrast to the prevailing view that most
CMEs display either constant acceleration or constant speed. We found a
similar deceleration for the fast CMEs (speed>900kms<SUP>-1</SUP>)
in general. We suggest that the coronal drag could be responsible
for the deceleration, based on the result that the deceleration has a
quadratic dependence on the CME speed. About 60% of the fast CMEs were
not associated with DH type II bursts, suggesting that some additional
condition needs to be satisfied to be radio-rich. The average width
(66°) of the ratio-poor, fast CMEs is much smaller than that (102°) of
the radio-rich CMEs, suggesting that the CME width plays an important
role. The special characteristics of the radio-rich CMEs suggest
that the detection of DH radio bursts may provide a useful tool in
identifying the population of geoeffective CMEs.
---------------------------------------------------------
Title: Predicting the 1-AU arrival times of coronal mass ejections
Authors: Gopalswamy, Nat; Lara, Alejandro; Yashiro, Seiji; Kaiser,
Mike L.; Howard, Russell A.
2001JGR...10629207G Altcode:
We describe an empirical model to predict the 1-AU arrival of
coronal mass ejections (CMEs). This model is based on an effective
interplanetary (IP) acceleration described by Gopalswamy et al. [2000b]
that the CMEs are subject to, as they propagate from the Sun to
1 AU. We have improved this model (1) by minimizing the projection
effects (using data from spacecraft in quadrature) in determining the
initial speed of CMEs, and (2) by allowing for the cessation of the
interplanetary acceleration before 1 AU. The resulting effective IP
acceleration was higher in magnitude than what was obtained from CME
measurements from spacecraft along the Sun-Earth line. We evaluated the
predictive capability of the CME arrival model using recent two-point
measurements from the Solar and Heliospheric Observatory (SOHO), Wind,
and ACE spacecraft. We found that an acceleration cessation distance
of 0.76 AU is in reasonable agreement with the observations. The
new prediction model reduces the average prediction error from 15.4
to 10.7 hours. The model is in good agreement with the observations
for high-speed CMEs. For slow CMEs the model as well as observations
show a flat arrival time of ~4.3 days. Use of quadrature observations
minimized the projection effects naturally without the need to assume
the width of the CMEs. However, there is no simple way of estimating the
projection effects based on the surface location of the Earth-directed
CMEs observed by a spacecraft (such as SOHO) located along the Sun-Earth
line because it is impossible to measure the width of these CMEs. The
standard assumption that the CME is a rigid cone may not be correct. In
fact, the predicted arrival times have a better agreement with the
observed arrival times when no projection correction is applied to the
SOHO CME measurements. The results presented in this work suggest that
CMEs expand and accelerate near the Sun (inside 0.7 AU) more than our
model supposes; these aspects will have to be included in future models.
---------------------------------------------------------
Title: Momentum Coupling Between Coronal Mass Ejections and the
Solar Wind
Authors: Chen, J.; Gopalswamy, N.; Yashiro, S.
2001AGUFMSH12A0740C Altcode:
The interaction of coronal mass ejections (CMEs) and the ambient
solar wind plays a critically important role in determining the CME
acceleration near the Sun and the subsequent evolution through the
interplanetary medium. In particular, the speed and the magnetic
field of associated magnetic clouds at 1 AU are dependent on the
momentum transfer from the CME to the solar wind (SW) during the
transit. Theoretically, because of the high magnetic Reynold's number,
turbulent drag has been used to model the integrated drag (retarding
or accelerating depending on the velocity differential) force on
CMEs exerted by the SW (Chen 1996). The drag coefficient has been
previously estimated to be of order unity using a 2-D MHD simulation
of flux-rope interactions with an ambient magnetizid plasma consistent
with SW conditions near 1 AU (Cargill et al. 1996). Such treatments
posit that the momentum coupling between a flux rope and the ambient
plasma is proportional to (V-V<SUB>sw</SUB>)<SUP>2</SUP>, where V
is the speed of the flux rope and V<SUB>sw</SUB> is the ambient SW
speed. Recently, Gopalswamy et al. (2001) found that the observationally
inferred drag force is approximately quadratic in CME speed, based on
61 decelerating CME events. In this paper, we examine specific events
using LASCO data and determine the drag coefficient: for each event,
we measure the speed-height profile and the minor radius at the leading
edge; then using a model of the coronal density and SW outflow speed,
estimate the drag coefficient. Work supported by ONR and NASA. Chen,
J., JGR, 101, 27499, 1996 Cargill, P. J., J. Chen, D. S. Spicer,
and S. T. Zalesak, JGR, 101, 4855, 1996. Gopalswamy, N., S. Yashiro,
M. L. kaiser, R. A. Howard, and J.-L. Bougeret, in press, JGR, 2001.
---------------------------------------------------------
Title: Limb Flares, CMEs & Metric Type II Radio Bursts: A New
Statistical Study
Authors: Hammer, D.; Gopalswamy, N.; Yashiro, S.; Nunes, S.;
Michalek, G.
2001AGUFMSH42A0767H Altcode:
Past studies of the relationship between flares, coronal mass
ejections(CMEs), and metric typeII radio bursts have been accomplished
without the significantly larger and more detailed CME database that
is available today through SOHO/LASCO observations. This abundance
of CME data allows us to more accurately study the flare-CME-typeII
relationship thereby permitting better substantiated conclusions. Our
study examines the relationship between solar flares and their
correlated CMEs and metric typeII bursts by sampling all (approximately
900) X-ray/H-alpha limb flares occurring between January 1996 and June
2001. Flare events are collected from Solar Geophysical Data (SGD)
and flare location is confirmed with SOHO EIT, Yokhoh SXT, and Nobeyama
Radioheliograph movies. All correlated CMEs are confirmed in LASCO/EIT
movies and their parameters are obtained from the CSPSW/NRL maintained,
SOHO/LASCO CME catalog. Metric typeII burst data are also obtained from
SGD and from the websites of several individual observatories (Potsdam,
Hiraiso, Learmonth, Izmiran, and Nancay). We will present statistical
analysis on the occurrences between all three solar phenomena and how
these relationships change when flare, CME, and typeII parameters
change. Additionally, we will analyze how the data relates to past
results (e.g. CME Speed vs. Flare Intensity, CME Speed vs. TypeII
Occurrence, TypeII Onset - Flare Start vs. Starting Frequency, etc.). We
will also present relationships between CME-flare-typeII onset times
in addition to solar cycle effects.
---------------------------------------------------------
Title: Numerical Study on the Acceleration of Coronal Mass Ejections
in the Interplanetary Medium
Authors: Gonzalez-Esparza, A.; Lara, A.; Perez-Tijerina, E.; Santillan,
A.; Gopalswamy, N.
2001AGUFMSH11D..09G Altcode:
Recently Gopalswamy et al. [2000] studied observations of ICMEs by
WIND spacecraft and correlated these observations with CMEs detected
previously by SOHO coronographs. They found that the Sun-Earth mean
acceleration of these events was approximately proportional to their
initial speeds, and they suggest that this result could be used for
space weather forecasting. In this work we perform a parametric study
of several CME like disturbances propagating in two different ambient
winds using a one dimensional, single fluid, hydrodynamic model, to
study the kinematics of the CME fronts near the Sun to 1 AU. These
1-D simulations of interplanetary disturbances have shown to be very
useful to understand the basic physical aspects of the injection and
heliospheric evolution of these phenomena. In this work we explore how
the CME acceleration and transit time from near the Sun to 1 AU varies
depending on the CME initial conditions and the ambient solar wind.
---------------------------------------------------------
Title: Statistical analysis of coronal shock dynamics implied by
radio and white-light observations
Authors: Reiner, M. J.; Kaiser, M. L.; Gopalswamy, N.; Aurass, H.;
Mann, G.; Vourlidas, A.; Maksimovic, M.
2001JGR...10625279R Altcode:
For 19 solar eruptive events we present a statistical comparison of the
shock dynamics derived from the measured frequency drift rates of metric
and decametric-hectometric (D-H) type II radio bursts with the dynamics
of the associated coronal mass ejection (CME). We find that the shock
speed parameters derived from the D-H type II radio emissions generated
in the high corona (~2-4R<SUB>solar</SUB>R<SUB>solar</SUB>=696,000km)
are well correlated with the corresponding CME plane-of-the-sky
speeds (correlation coefficient=0.71). On the other hand, we find
no obvious correlation between the shock speed parameters derived
from the metric type II radio bursts, generated in the middle
corona (1.4-2R<SUB>solar</SUB>), and the corresponding CME speeds
(correlation coefficient=-0.07). In general, we also find no clear
correlation between the shock speed parameters derived from the
metric type II bursts and the D-H radio emissions (correlation
coefficient=0.3). However, the metric type II radio bursts sometimes
include a second component that is possibly related to the D-H radio
emissions. These statistical comparisons of the shock dynamics, implied
by the observed metric and D-H type II frequency drift rates, provide
further evidence for two distinct coronal shocks. Our statistical
analyses are proceeded by two specific examples that illustrate the
methodology used in this study.
---------------------------------------------------------
Title: A multi-wavelength study of solar coronal-hole regions showing
radio enhancements
Authors: Moran, T.; Gopalswamy, N.; Dammasch, I. E.; Wilhelm, K.
2001A&A...378.1037M Altcode:
We observed 17 GHz microwave-enhanced regions in equatorial coronal
holes (ECH) together with extreme-ultraviolet (EUV), far-ultraviolet
(FUV) and visible emissions in a search for temperature increases which
might explain the bright spots in radio wavelengths. The ultraviolet
(UV) observations span a wide range of formation temperatures (8000 K
to 630 000 K). Increased UV emission was observed at the approximate
location of the radio enhancements, but unlike the radio brightening,
the UV emission did not exceed the mean quiet sun level. However,
there were two observations showing increased Hα brightness in radio
enhancements above mean quiet sun levels. No Hα bright spots were
detected in ECHs outside of radio enhancement regions. The ECH Hα
bright spots were caused by bright fibrils, bright points and a lack
of dark fibrils. Since the 17 GHz and Hα enhancements are co-spatial,
have equal integrated normalized enhanced emission and brightness
temperatures, the observations suggest that the radio enhancements
are caused by increased fibril radio emission. In addition, increased
Fe XII EUV emission was recorded at the location of some well-defined
radio enhancements, which were the bases of coronal plumes. Since the
radio brightness temperature is much lower than the Fe xii formation
temperature, the radio and EUV enhancements are likely both related
to the presence of concentrated magnetic flux, but do not arise from
the same physical layer.
---------------------------------------------------------
Title: Near-Sun and near-Earth manifestations of solar eruptions
Authors: Gopalswamy, N.; Lara, A.; Kaiser, M. L.; Bougeret, J. -L.
2001JGR...10625261G Altcode:
We compare the near-Sun and near-Earth manifestations of solar
eruptions that occurred during November 1994 to June 1998. We
compared white-light coronal mass ejections, metric type II radio
bursts, and extreme ultraviolet wave transients (near the Sun) with
interplanetary (IP) signatures such as decameter-hectometric type II
bursts, kilometric type II bursts, IP ejecta, and IP shocks. We did a
two-way correlation study to (1) look for counterparts of metric type
II bursts that occurred close to the central meridian and (2) look for
solar counterparts of IP shocks and IP ejecta. We used data from Wind
and Solar and Heliospheric Observatory missions along with metric radio
burst data from ground-based solar observatories. Analysis shows that
(1) most (93%) of the metric type II bursts did not have IP signatures,
(2) most (80%) of the IP events (IP ejecta and shocks) did not have
metric counterparts, and (3) a significant fraction (26%) of IP shocks
were detected in situ without drivers. In all these cases the drivers
(the coronal mass ejections) were ejected transverse to the Sun-Earth
line, suggesting that the shocks have a much larger extent than the
drivers. Shocks originating from both limbs of the Sun arrived at Earth,
contradicting earlier claims that shocks from the west limb do not reach
Earth. These shocks also had good type II radio burst association. We
provide an explanation for the observed relation between metric,
decameter-hectometric, and kilometric type II bursts based on the fast
mode magnetosonic speed profile in the solar atmosphere.
---------------------------------------------------------
Title: Introduction to special section: Global picture of solar
eruptive events
Authors: Gopalswamy, Nat
2001JGR...10625135G Altcode:
This introduction highlights some of the scientific results reported
in this special section on solar eruptive events and provides a brief
description of issues related to the new results. Most of these papers
grew out of the coordinated data analysis workshop held at the Goddard
Space Flight Center during April 27-30, 1999, and the subsequent
International Conference on Solar Eruptive Events held at the Catholic
University of America, Washington, D. C. during March 6-9, 2000.
---------------------------------------------------------
Title: X-ray Ejecta, White-Light CMEs and a Coronal Shock Wave
Authors: Gopalswamy, N.; Cyr, O. C. St.; Kaiser, M. L.; Yashiro, S.
2001SoPh..203..149G Altcode:
We report on a coronal shock wave inferred from the metric type II
burst of 13 January 1996. To identify the shock driver, we examined
mass motions in the form of X-ray ejecta and white-light coronal mass
ejections (CMEs). None of the ejections could be considered fast (>
400 km s<SUP>−1</SUP>) events. In white light, two CMEs occurred in
quick succession, with the first one associated with X-ray ejecta near
the solar surface. The second CME started at an unusually large height
in the corona and carried a dark void in it. The first CME decelerated
and stalled while the second one accelerated, both in the coronagraph
field of view. We identify the X-ray ejecta to be the driver of the
coronal shock inferred from metric type II burst. The shock speed
reported in the Solar Geophysical Data (1000-2000 km s<SUP>−1</SUP>)
seems to be extremely large compared to the speeds inferred from
X-ray and white-light observations. We suggest that the MHD fast-mode
speed in the inner corona could be low enough that the X-ray ejecta
is supermagnetosonic and hence can drive a shock to produce the type
II burst.
---------------------------------------------------------
Title: Non-radial motion of eruptive filaments
Authors: Filippov, B. P.; Gopalswamy, N.; Lozhechkin, A. V.
2001SoPh..203..119F Altcode:
We develop a simple model to explain the non-radial motion of eruptive
solar filaments under solar minimum conditions. The global magnetic
field is derived from the first and third components of the spherical
harmonic expansion of a magnetic scalar potential. The filament is
modeled as a toroidal current located above the mid-latitude polarity
inversion line. We investigate the stability of the filament against
changes in the filament current and attempt to explain the non-radial
motion and acceleration of the eruptive filament. We also discuss the
limitations of this model.
---------------------------------------------------------
Title: Band-splitting of coronal and interplanetary type II
bursts. I. Basic properties
Authors: Vršnak, B.; Aurass, H.; Magdalenić, J.; Gopalswamy, N.
2001A&A...377..321V Altcode:
Patterns analogous to the band-splitting of metric type II bursts are
found in a number of type II bursts observed in the dekameter-kilometer
wavelength range. A similarity of morphological and frequency-time
characteristics of two emission components are indicative of a
common source. Relative frequency splits span in the range Delta
f/f=0.05-0.6. At radial distances between 2 and 4 R<SUB>sun</SUB> only
small splits around 0.1 can be found. In the interplanetary space the
relative split on average increases with the radial distance, whereas
the inferred shock velocity decreases. In three events extrapolations
of the split components point to the base and the peak of the jump
in the local plasma frequency caused by the associated shock passage
at 1 AU. This is suggestive of the plasma radiation from the regions
upstream and downstream of the shock. Adopting this interpretation, one
finds that the drop of Delta f/f at 2-4 R<SUB>sun</SUB> is congruent
with the Alfvén velocity maximum expected there. The split increase
and the velocity decrease at larger distances can be explained as a
consequence of declining Alfvén speed in the interplanetary space.
---------------------------------------------------------
Title: Estimation of projection effect of CMEs from onset time of
type III radio bursts.
Authors: Michalek, G.; Gopalswamy, N.; Reiner, M.; Yashiro, S.
2001AGUSM..SH22A05M Altcode:
We present a new possibility to estimate the projection effect on CME
measurements. We assume that (1) high energy electrons are produced
at the shock front ahead of the CME, and (2) the radio burst starts
when the shock reaches open field lines ( ~ 3 R). In other words,
the onset time of the radio burst corresponds to the time when the
CME leading edge reaches 3 R. It is well known that white light
observations of halo CMEs with the LASCO coronagraph are subject
projection effects. Fortunately, the Wind/WAVES experiment observations
of type III radio burst associated with shock waves are free from
this problems. The difference between onset times of CMEs and radio
bursts should be strongly correlated with the position of CMEs on the
Sun. We try to determine this correlation and use it to estimate the
real starting position of CMEs.
---------------------------------------------------------
Title: Development of SOHO/LASCO CME Catalog and Study of CME
Trajectories
Authors: Yashiro, S.; Gopalswamy, N.; St. Cyr, O. C.; Lawrence, G.;
Michalek, G.; Young, C. A.; Plunkett, S. P.; Howard, R. A.
2001AGUSM..SH31C10Y Altcode:
We present a catalog of coronal mass ejections (CMEs) based on
SOHO/LASCO observations. This catalog covers the period from
1998 October to the present time. For each of the observed CMEs,
the catalog contains the following information: LASCO C2 appearance
time, Central Position Angle, Angular Width, height-time plots with
Linear (constant speed) and 2nd order (constant acceleration) fits and
corresponding speeds, and acceleration. The catalog will be open to the
public via World Wide Web after proper validation. Using a preliminary
version of this data set, we investigated the CME trajectories based
on linear and quadratic fits to the data points. We estimated the
error in the computed trajectories as follows: Generally speaking,
the error in each height measurement depends on the quality of the
CME feature that is tracked. So we grouped the observations into 5
classes based on the quality of the features on a 1-5 scale: Poor,
Fair, Typical, Good, and Excellent. For a CME with a clear leading
edge (excellent quality), the error in the measured height is small
(5% of the measured height). On the other hand, for a CME with a
ragged leading edge (poor quality), the error becomes larger (20% of
the measured height). Based on this scheme, we assigned errorbars to
the measured heights and then performed a weighted least-squares fit
to the height-time trajectories. We found that for 90% of the CMEs,
the linear (constant speed) fit is preferable. For the remaining 10%,
quadratic fit (constant acceleration) is better than the linear fit.
---------------------------------------------------------
Title: Lasco CME Speeds and Metric Type II Radio Bursts
Authors: Hammer, D.; Gopalswamy, N.; Yashiro, S.
2001AGUSM..SH22C01H Altcode:
We are using images obtained with LASCO to study correlations between
CME parameters and the occurrence of metric Type II radio bursts. In
particular, contemporary theories, based on SMM data, suggest a strict
causal relationship between CME speeds and the production of metric
Type II's. We will analyze how this relationship unfolds for Type II
events occurring since the beginning of the LASCO mission in 1996,
and look for solar cycle effects. We will also examine the speed of
metric Type II's in comparison to LASCO derived CME speeds.
---------------------------------------------------------
Title: Origin and Early Evolution of Coronal Mass Ejections
Authors: Gopalswamy, N.
2001AGUSM..SH61A01G Altcode:
Simultaneous observations at multiple wavelengths over a large field
of view have dramatically improved our understanding of coronal
mass ejections. Extreme ultraviolet and soft X-ray observations
reveal the source regions of Earth-directed CMEs. Microwave and
H-alpha observations provide information on the cool components of the
CMEs. Radio observations at long decametric and hectometric wavelengths
trace CME-driven shock waves that just enter into the interplanetary
medium. This paper summarizes recent findings on CMEs using SOHO, Yohkoh
and Wind observations and discusses how near-Sun CME observations are
useful in interpreting transient events in the inner heliosphere.
---------------------------------------------------------
Title: Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; Landi, E.; Cook, J. W.; Newmark, J.;
Gopalswamy, N.; Lara, A.
2001AGUSM..SH32C02B Altcode:
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of
NOAA region 8108 (N21 E18) on 1997 November 18. The EUV spectra
and images, obtained with the Coronal Diagnostic Spectrometer (CDS)
and the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar
and Heliospheric Observatory (SOHO) satellite, were used to derive
differential emission measure (DEM) distributions for each spatial
pixel (i.e., along each line of sight) of the region's images. These
were subsequently used to calculate maps of the expected thermal
bremsstrahlung brightness temperature at the Very Large Array
(VLA) radio observing frequencies of 4.9 and 8.4 GHz. The thermal
bremsstrahlung maps reproduce neither the structure nor the intensity
of the observed maps, and indicate that thermal gyroemission must
also contribute to the observed radio emission. Under the assumptions
of a monotonic increase in temperature and a monotonic decrease in
magnetic field strength with height above the sunspot, we derived
the temperature distribution of the coronal magnetic field strength
that reproduced simultaneously the observed right-hand and left-hand
circularly polarized radio emission at 4.9 and 8.4 GHz for each
spatial pixel in the sunspot maps. This was done by placing harmonics
of the radio observing frequencies in appropriate plasma temperature
intervals, integrating along the line of sight, and iterating until
a solution was obtained. Magnetic field strengths corresponding to
3rd harmonic gyroemission at 4.9 GHz (580 Gauss) are found in coronal
plasmas at temperatures as high as 2.2*E<SUP>6</SUP> K, while magnetic
field strengths corresponding to 2nd harmonic gyroemission at 8.4 GHz
(1500 Gauss) are found in coronal plasmas at temperatures as high as
1.1*E<SUP>6</SUP> K.
---------------------------------------------------------
Title: An Observational Study of Solar Coronal-hole Regions Showing
Radio Enhancements
Authors: Moran, T. G.; Gopalswamy, N.; Dammash, I.; Wilhelm, K.
2001AGUSM..SH41A13M Altcode:
We observed 17~GHz microwave-enhanced regions in equatorial coronal
holes (ECH) together with extreme-ultraviolet (EUV), far-ultraviolet
(FUV) and visible emissions in a search for temperature increases which
might explain the bright spots in radio wavelengths. The ultraviolet
(UV) observations span a wide range of formation temperatures (8000~K
to 630 000~K). Increased UV emission was observed at the approximate
location of the radio enhancements, but unlike the radio brightening,
the UV emission did not exceed the mean quiet sun level. However,
there were two observations showing increased Hα brightness in radio
enhancements above mean quiet sun levels. No Hα bright spots were
detected in ECHs outside of radio enhancement regions. The ECH Hα
bright spots were caused by bright fibrils, bright points and a lack
of dark fibrils. Since the 17~GHz and Hα enhancements are co-spatial,
have equal integrated normalized enhanced emission and brightness
temperatures, the observations suggest that the radio enhancements
are caused by increased fibril radio emission. In addition, increased
Fe xii EUV emission was recorded at the location of some well-defined
radio enhancements, which were the bases of coronal plumes. Since the
radio brightness temperature is much lower than the Fe xii formation
temperature, the radio and EUV enhancements are likely both related
to the presence of concentrated magnetic flux, but do not arise from
the same physical layer.
---------------------------------------------------------
Title: Acceleration and Deceleration of CMEs Associated with Long
Wavelength Radio Bursts
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.; Howard, R.
2001AGUSM..SH31C07G Altcode:
Type II radio bursts in the Decameter-Hectometric (DH) wavelengths
indicate powerful MHD shocks leaving the inner corona. Almost all
of these bursts are associated with massive and faster-than-average
coronal mass ejections (CMEs). A particularly interesting characteristic
of these DH CMEs is that they are predominantly decelerating in the
coronagraph field of view. In the past, it was thought that there are
mainly constant speed and accelerating CMEs. We discuss the possible
explanations for the CME deceleration in the near-Sun interplanetary
medium. Research supported by NASA, NSF and Air Force Office of
Scientific Research
---------------------------------------------------------
Title: Testing the Empirical CME Arrival Model Using Earth Directed
Events
Authors: Lara, A.; Gopalswamy, N.; Dasso, S.; Yashiro, S.
2001AGUSM..SH61A05L Altcode:
An empirical model to predict the arrival of coronal mass ejections at
1 AU was developed recently (Gopalswamy et al. 2000), based on SOHO
and Wind observations. The model was further improved by correcting
for the intrinsic projection effects on CME initial speed. This
correction was performed using archival data from Helios-1, Pioneer
Venus Orbiter and P78-1 (Solwind) spacecraft which were in quadrature
so that the projection effects were minimal. In this work we use the
corrected CME arrival model to predict the travel time of a large
set of Earth directed halo CMEs observed by SOHO/LASCO from January
1997 to December 2000. We search for interplanetary signatures around
the predicted arrival times. In particular, one of the most commonly
observed characteristics of interplanetary CMEs (ICME) is their low
temperature with respect to the ambient (fast and slow) solar wind. We
search for low temperature regions from in situ data obtained by
Wind, ACE, and IMP8 spacecraft, as a proxy to the ICMEs. Finally, we
compare the predicted CME arrival times with the detected ICME times
and perform a statistical analysis of the errors in the predicted time.
---------------------------------------------------------
Title: Radio Signatures of Coronal Mass Ejection Interaction:
Coronal Mass Ejection Cannibalism?
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.; Howard, R. A.;
Bougeret, J. -L.
2001ApJ...548L..91G Altcode:
We report the first detection at long radio wavelengths of interaction
between coronal mass ejections (CMEs) in the interplanetary medium. The
radio signature is in the form of intense continuum-like radio emission
following an interplanetary type II burst. At the time of the radio
enhancement, coronagraphic images show a fast CME overtaking a slow
CME. We interpret the radio enhancement as a consequence of shock
strengthening when the shock ahead of the fast CME plows through the
core of the preceding slow CME. The duration of the radio enhancement
is consistent with the transit time of the CME-driven shock through the
core of the slow CME. As a consequence of the interaction, the core of
the slow CME changed its trajectory significantly. Based on the emission
characteristics of the radio enhancement, we estimate the density of
the core of the slow CME to be ~4×10<SUP>4</SUP> cm<SUP>-3</SUP>. The
CME interaction has important implications for space weather prediction
based on halo CMEs: some of the false alarms could be accounted for
by CME interactions. The observed CME interaction could also explain
some of the complex ejecta at 1 AU, which have unusual composition.
---------------------------------------------------------
Title: Early life of coronal mass ejections
Authors: Gopalswamy, N.; Thompson, B. J.
2000JASTP..62.1457G Altcode: 2000JATP...62.1457G
Coronal mass ejections (CMEs) are large-scale magnetized plasma
structures ejected from closed magnetic field regions of the Sun. White
light coronagraphic observations from ground and space have provided
extensive information on CMEs in the outer corona. However, our
understanding of the solar origin and early life of CMEs is still in
an elementary stage because of lack of adequate observations. Recent
space missions such as Yohkoh and Solar and Heliospheric Observatory
(SOHO) and ground-based radioheliographs at Nobeyama and Nancay have
accumulated a wealth of information on the manifestations of CMEs
near the solar surface. We review some of these observations in
an attempt to relate them to what we already know about CMEs. Our
discussion relies heavily on non-coronagraphic data combined with
coronagraphic data. Specifically, we discuss the following aspects of
CMEs: (i) coronal dimming and global disk signatures, (ii) non-radial
propagation during the early phase, (iii) Photospheric magnetic field
changes during CMEs, and (iv) acceleration of fast CMEs. The relative
positions and evolution of coronal dimming, arcade formation, prominence
eruption will be discussed using specific events. The magnitude and
spatial extent of CME acceleration may be an important parameter that
distinguishes fast and slow CMEs.
---------------------------------------------------------
Title: Soft X-Ray and Gyroresonance Emission above Sunspots
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Shibasaki, K.;
Gopalswamy, N.
2000ApJS..130..485N Altcode:
Using Yohkoh SXT and Nobeyama 17 GHz data, we have studied the soft
X-ray and microwave emission above several stable, large sunspots
near central meridian passage. Our study confirms the well-known fact
that soft X-ray emission is depressed above sunspots. It also shows
that the distribution of their soft X-ray intensity is not uniform;
usually the darkest pixels are associated with the umbra or the far
edges of the leading part of the penumbra while the following part
of the penumbra may contain higher intensity pixels associated with
brighter loops. For the first time, we present a systematic survey
of the temperatures and emission measures of the soft X-ray material
above sunspots. Sunspots always contain the lowest temperatures and
emission measures in the active regions. The mean umbral temperature
is 1.8×10<SUP>6</SUP> K, and the mean penumbral temperature is
2.4×10<SUP>6</SUP> K. The mean umbral and penumbral emission measures
are logEM=26.60 cm<SUP>-5</SUP> and logEM=27.00 cm<SUP>-5</SUP>,
respectively. The differences between the umbral and penumbral plasma
temperatures are physically significant. The higher penumbral values
imply that the loops associated with the penumbrae are generally hotter
and denser than the loops associated with the umbrae. The highest
sunspot temperatures and emission measures are still lower than the
average active region parameters but higher than the quiet-Sun plasma
parameters. The coronal radiative energy loss rate above the umbrae
is 15% higher than the radiative loss rate of the quiet-Sun plasma
but a factor of 8.3 lower than the typical active region radiative
loss rate. The radio emission comes from the gyroresonance mechanism,
and, as expected, it is sensitive to the magnetic field rather than
the soft X-ray-emitting plasma.
---------------------------------------------------------
Title: Correction to “Change in photospheric magnetic flux during
coronal mass ejections”
Authors: Lara, Alejandro; Gopalswamy, Nat; DeForest, Craig
2000GeoRL..27.1863L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microwave Enhancement in Coronal Holes: Statistical Propeties
Authors: Gopalswamy, N.; Shibasaki, K.; Salem, M.
2000JApA...21..413G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SOHO and radio observations of a CME shock wave
Authors: Raymond, John C.; Thompson, Barbara J.; St. Cyr, O. C.;
Gopalswamy, Nat; Kahler, S.; Kaiser, M.; Lara, A.; Ciaravella, A.;
Romoli, M.; O'Neal, R.
2000GeoRL..27.1439R Altcode:
A 1200 km s<SUP>-1</SUP> Coronal Mass Ejection was observed with the
SOHO instruments EIT, LASCO and UVCS on June 11, 1998. Simultaneously,
Type II radio bursts were observed with the WAVES experiment aboard
the Wind spacecraft at 4 MHz and by ground-based instruments at metric
wavelengths. The density in the shock wave implied by the higher
frequency is close to that inferred from the SOHO/UVCS experiment. The
drift rates of the Type II radio bursts suggest shock speeds lower than
the speed derived from SOHO observations. The SOHO/UVCS spectrum shows
enhanced emission in lines of O<SUP>5+</SUP> and Si<SUP>11+</SUP>,
consistent with modest compression in an MHD shock.
---------------------------------------------------------
Title: Radio-rich solar eruptive events
Authors: Gopalswamy, N.; Kaiser, M. L.; Thompson, B. J.; Burlaga,
L. F.; Szabo, A.; Lara, A.; Vourlidas, A.; Yashiro, S.; Bougeret,
J. -L.
2000GeoRL..27.1427G Altcode:
We report on the analysis of a large number of solar eruptive events
that produced radio emission in the dekameter-hectometric (DH) radio
window (1-14 MHz), newly opened by the Wind/WAVES experiment. The
distinguishing characteristics of coronal mass ejections (CMEs)
associated with the DH type II radio bursts are larger-than-average
width and speed. Flares of all sizes (X-ray importance B to X) occurring
at all longitudes were associated with the DH type II bursts and
CMEs. We found a global enhancement in EUV over an area much larger than
the flaring active region in the beginning many events. A comparison
between the ‘Shock Associated’ events and microwave bursts shows
that at least half of the events do not have temporal relation. A
majority of the DH type II bursts were associated with IP shocks
and kilometric type II bursts. In particular, we found a very close
relationship between the kilometric type II bursts and the IP shocks.
---------------------------------------------------------
Title: Change in photospheric magnetic flux during coronal mass
ejections
Authors: Lara, Alejandro; Gopalswamy, Nat; DeForest, Craig
2000GeoRL..27.1435L Altcode:
We report on the variations of photospheric magnetic flux during
coronal mass ejections (CMEs). Using magneograms from the SOHO/MDI
instrument, we have computed the magnetic flux of 7 active regions and
one disappearing filament region associated with CMEs. When we plotted
the flux versus time over a period of few days before, during and after
the CME event, we found changes in the mean magnetic flux per pixel
(∼4 arcsec²), ranging from ∼0.4 to ∼3.1 × 10<SUP>17</SUP> Mx,
in structures of size smaller than the active region. Flare onsets
and the filament disappearance clearly occurred during periods of
significant variations in the measured magnetic flux.
---------------------------------------------------------
Title: An Empirical Model to Predict the Arrival of CMEs at 1 AU
Authors: Gopalswamy, N.; Lara, A.; Kaiser, M. L.
2000SPD....31.0283G Altcode: 2000BAAS...32..825G
We describe an empirical model to predict the arrival of coronal mass
ejections (CMEs) at 1 AU based on the initial speed of CMEs obtained
from coronagraphs. The only input needed in this model is the measured
initial speed of CMEs. This model is based on an effective acceleration
that CMEs are subject to, as they propagate from the Sun to 1 AU. We
developed this model based on the two-point measurements made from
SOHO and Wind spacecraft. We validate our model based on older data
obtained by Helios-1, P78-1, Pioneer Venus Orbiter and Solar Maximum
Mission spacecraft. We discuss the merits and limitations of this
model. Research supported by the National Research Council, NSF,
and NASA.
---------------------------------------------------------
Title: Magnetic Evolution and Eruptive Events Associated to Active
Region 8210
Authors: Lara, A.; Gopalswamy, N.
2000SPD....31.1403L Altcode: 2000BAAS...32..846L
We present a study of one active region with high flare and CME
activity. From April 27 to May 5, 1998, AR8210 was crossing the south
solar hemisphere and produced many flares, and at least five CMEs
were related to activity in this region, some of them were homologous
events. We use magnetograms from the Michelson Doppler Imager (MDI)
experiment on board of the Solar Heliospheric Observatory (SOHO) to
construct the time series of the photospheric magnetic elements. We
compute the line of sight magnetic flux over the entire active region,
and over localized areas inside the active region in which activity
was detected in EUV (198 Angstroms) maps from the Extreme ultraviolet
Imaging Telescope (EIT) on board of SOHO. We found considerable
differences between the positive and negative fluxes computed
over the entire region, the mean negative flux per pixel was 50 to
100 % greater than the positive flux. Using microwave polarization
measures from Nobeyama Radio Heliograph, we were able to confirm such
differences. The magnetic flux computed over AR8210 also showed a
considerable increasing phase when the flare and CME activity of the
region was increasing. On the other hand, we found that in general,
flares occur during a maximum phase in the magnetic flux computed over
localized subregions and that the major changes on this magnetic flux
seems to be related to CMEs. Finally we discuss the flare and CME
production, with special emphasis in the homologous events.
---------------------------------------------------------
Title: Observations of the 24 September 1997 Coronal Flare Waves
Authors: Thompson, B. J.; Reynolds, B.; Aurass, H.; Gopalswamy, N.;
Gurman, J. B.; Hudson, H. S.; Martin, S. F.; St. Cyr, O. C.
2000SoPh..193..161T Altcode:
We report coincident observations of coronal and chromospheric `flare
wave' transients in association with a flare, large-scale coronal
dimming, metric radio activity and a coronal mass ejection. The two
separate eruptions occurring on 24 September 1997 originate in the
same active region and display similar morphological features. The
first wave transient was observed in EUV and Hα data, corresponding
to a wave disturbance in both the chromosphere and the solar corona,
ranging from 250 to approaching 1000 km s<SUP>−1</SUP> at different
times and locations along the wavefront. The sharp wavefront had a
similar extent and location in both the EUV and Hα data. The data did
not show clear evidence of a driver, however. Both events display a
coronal EUV dimming which is typically used as an indicator of a coronal
mass ejection in the inner corona. White-light coronagraph observations
indicate that the first event was accompanied by an observable coronal
mass ejection while the second event did not have clear evidence of a
CME. Both eruptions were accompanied by metric type II radio bursts
propagating at speeds in the range of 500-750 km s<SUP>−1</SUP>,
and neither had accompanying interplanetary type II activity. The
timing and location of the flare waves appear to indicate an origin
with the flaring region, but several signatures associated with coronal
mass ejections indicate that the development of the CME may occur in
concert with the development of the flare wave.
---------------------------------------------------------
Title: Space VLBI at Low Frequencies
Authors: Jones, D. L.; Allen, R.; Basart, J.; Bastian, T.; Blume, W.;
Bougeret, J. -L.; Dennison, B.; Desch, M.; Dwarakanath, K.; Erickson,
W.; Farrell, W.; Finley, D.; Gopalswamy, N.; Howard, R.; Kaiser,
M.; Kassim, N.; Kuiper, T.; MacDowall, R.; Mahoney, M.; Perley, R.;
Preston, R.; Reiner, M.; Rodriguez, P.; Stone, R.; Unwin, S.; Weiler,
K.; Woan, G.; Woo, R.
2000aprs.conf..265J Altcode: 2000astro.ph..3120J
At sufficiently low frequencies, no ground-based radio array will
be able to produce high resolution images while looking through
the ionosphere. A space-based array will be needed to explore the
objects and processes which dominate the sky at the lowest radio
frequencies. An imaging radio interferometer based on a large number
of small, inexpensive satellites would be able to track solar radio
bursts associated with coronal mass ejections out to the distance
of Earth, determine the frequency and duration of early epochs of
nonthermal activity in galaxies, and provide unique information about
the interstellar medium. This would be a “space-space" VLBI mission,
as only baselines between satellites would be used. Angular resolution
would be limited only by interstellar and interplanetary scattering.
---------------------------------------------------------
Title: Structure of a Large low-Latitude Coronal Hole
Authors: Bromage, B. J. J.; Alexander, D.; Breen, A.; Clegg, J. R.;
Del Zanna, G.; DeForest, C.; Dobrzycka, D.; Gopalswamy, N.; Thompson,
B.; Browning, P. K.
2000SoPh..193..181B Altcode:
Coronal holes on the Sun are the source of high-speed solar wind
streams that produce magnetic disturbances at the Earth. A series
of multi-wavelength, multi-instrument observations obtained during
the 1996 `Whole Sun Month' campaign examined a large coronal hole in
greater detail than ever before. It appeared on the Sun in August, and
extended from the north pole to a large active region in the southern
hemisphere. Its physical and magnetic structure and subsequent evolution
are described.
---------------------------------------------------------
Title: Radial Evolution and Turbulence Characteristics of a Coronal
Mass Ejection
Authors: Manoharan, P. K.; Kojima, M.; Gopalswamy, N.; Kondo, T.;
Smith, Z.
2000ApJ...530.1061M Altcode:
We investigate a coronal mass ejection (CME) associated with an
X3.9 solar flare that occurred on 1992 June 25. This long-duration
event showed a system of large postflare loops at the activity site
throughout the period of the enhanced X-ray emission. The drift rate of
the metric type IV radio burst observed near the X-ray maximum suggests
the speed of the ejecta to be ~350 km s<SUP>-1</SUP> at heights <=2
solar radii. The solar proton intensities, in the energy range 1-100
MeV observed in the interplanetary medium, show gradual-decay profiles
lasting for more than two days and suggest CME-driven acceleration near
the Sun. The inference on the spatial and kinematical characteristics
of the propagating CME in the inner heliosphere (0.2-1 AU) is primarily
based on the interplanetary scintillation observations at 327 MHz,
obtained from the Ooty Radio Telescope and the Solar-Terrestrial
Environment Laboratory. The scintillation data show the deceleration
of propagating disturbance speed, V<SUB>CME</SUB>~R<SUP>-0.8</SUP>,
in the interplanetary medium. The speeds obtained from the radio and
scintillation measurements also suggest that the coronal shock may not
be directly related to the interplanetary shock. The size of the CME in
the interplanetary medium seems to follow a simple scaling with distance
from the Sun, indicating the pressure balance maintained between the
ejecta and the ambient solar wind. The density turbulence spectrum of
the plasma carried by the propagating disturbance seems to be flat,
Φ<SUB>N<SUB>e</SUB>(IPD)</SUB>~κ<SUP>-2.8</SUP>, also having a small
dissipative scale length, S<SUB>i(IPD)</SUB><=5 km. The spectrum is
significantly different from that of high-speed flow from coronal holes
and low-speed wind originating above closed-field coronal streamers.
---------------------------------------------------------
Title: The ALFA Medium Explorer Mission
Authors: Jones, D. L.; Allen, R. J.; Basart, J. P.; Bastian, T.;
Blume, W. H.; Bougeret, J. -L.; Dennison, B. K.; Desch, M. D.;
Dwarakanath, K. S.; Erickson, W. C.; Farrell, W.; Finley, D. G.;
Gopalswamy, N.; Howard, R. E.; Kaiser, M. L.; Kassim, N. E.; Kuiper,
T. B. H.; MacDowall, R. J.; Mahoney, M. J.; Perley, R. A.; Preston,
R. A.; Reiner, M. J.; Rodriguez, P.; Stone, R. G.; Unwin, S. C.;
Weiler, K. W.; Woan, G.; Woo, R.
2000AdSpR..26..743J Altcode:
The frequency range below a few tens of MHz is unexplored with high
angular resolution due to the opacity of Earth's ionosphere. An
interferometer array in space providing arcminute angular resolution
images at frequencies of a few MHz would allow a wide range of
problems in solar, planetary, galactic, and extragalactic astronomy
to be attacked. These include the evolution of solar radio emissions
associated with shocks driven by coronal mass ejections and searches
for coherent radio emission from supernova remnants and relativistic
jets. In addition, it is likely that unexpected objects or emission
processes will be discovered by such an instrument, as has always
happened when high resolution astronomical observations first
become possible in a new region of the electromagnetic spectrum. The
Astronomical Low Frequency Array (ALFA) mission will consist of 16
identical small satellites forming an aperture synthesis array. The
satellites will cover the surface of a spherical region. ~100 km
in diameter, thus providing good aperture plane coverage in all
directions simultaneously. The array will operate in two modes: 1)
“snapshot” imaging of strong, rapidly changing sources such as
solar radio bursts and 2) long-term aperture synthesis observations
for maximum sensitivity, high dynamic range imaging. In both cases a
large number of array elements is needed
---------------------------------------------------------
Title: Time Evolution of Microwave and Hard X-ray Spectral Indexes
Authors: Lara, A.; Gopalswamy, N.
2000ASPC..206..355L Altcode: 2000hesp.conf..355L
No abstract at ADS
---------------------------------------------------------
Title: The Catholic University of America, Institute for Astrophysics
and Computational Sciences, Department of Physics, Washington,
District of Columbia 20064. Report for the period Sep 1998 - Sep 1999.
Authors: Gopalswamy, N.
2000BAAS...32...32G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Astronomical Low Frequency Array: A Proposed Explorer
Mission for Radio Astronomy
Authors: Jones, D.; Allen, R.; Basart, J.; Bastian, T.; Blume, W.;
Bougeret, J. -L.; Dennison, B.; Desch, M.; Dwarakanath, K.; Erickson,
W.; Finley, D.; Gopalswamy, N.; Howard, R.; Kaiser, M.; Kassim, N.;
Kuiper, T.; MacDowall, R.; Mahoney, M.; Perley, R.; Preston, R.;
Reiner, M.; Rodriguez, P.; Stone, R.; Unwin, S.; Weiler, K.; Woan,
G.; Woo, R.
2000GMS...119..339J Altcode: 2000ralw.conf..339J
A radio interferometer array in space providing high dynamic range
images with unprecedented angular resolution over the broad frequency
range from 0.03 - 30 MHz will open new vistas in solar, terrestrial,
galactic, and extragalactic astrophysics. The ALFA interferometer
will image and track transient disturbances in the solar corona
and interplanetary medium - a new capability which is crucial
for understanding many aspects of solar-terrestrial interaction
and space weather. ALFA will also produce the first sensitive,
high-angular-resolution radio surveys of the entire sky at low
frequencies. The radio sky will look entirely different below about
30 MHz. As a result, ALFA will provide a fundamentally new view of
the universe and an extraordinarily large and varied science return.
---------------------------------------------------------
Title: Commission 10: Solar Activity: (Activite Solaire)
Authors: Ai, G.; Benz, A.; Dere, K. P.; Engvold, O.; Gopalswamy, N.;
Hammer, R.; Hood, A.; Jackson, B. V.; Kim, I.; Marten, P. C.; Poletto,
G.; Rozelot, J. P.; Sanchez, A. J.; Shibata, K.; van Driel-Geztelyi, L.
2000IAUTA..24...67A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Type II Solar Radio Bursts
Authors: Gopalswamy, N.
2000GMS...119..123G Altcode: 2000ralw.conf..123G
Solar radio bursts of type II are thought to be caused by MHD shock
waves propagating through the corona and interplanetary medium. They
are identified as slowly drifting features in the dynamic spectra
recorded by ground based and spaceborne radio instruments. The
radio emission itself occurs as a final step in a series of physical
processes: initiation of the shock, particle acceleration, generation
of plasma waves and finally, conversion of the plasma waves into
electromagnetic waves. Type II bursts play an important role in
understanding the Sun-Earth connection, because of their association
with flares and coronal mass ejections (CMEs). Images of type II
bursts made by radioheliographs are crucial to understand the physical
relationship between shocks, CMEs and solar flares. Observations of
a new type of coronal waves by the EIT instrument on board the SOHO
mission and long-decametric and hectometric type II bursts by the
WIND/WAVES experiment have added new dimensions to the study of type
II radio bursts. In this review, I summarize the basic properties and
associated solar activities of type II bursts and discuss some of the
current issues.
---------------------------------------------------------
Title: Shock Wave and EUV Transient During a Flare
Authors: Gopalswamy, N.; Kaiser, M. L.; Sato, J.; Pick, Monique
2000ASPC..206..351G Altcode: 2000STIN...0032759G
A metric type II burst and a 'brow' type enhancement in EUV were
observed during the hard X-ray flare of 1997 April 15 from a newly
emerging region, AR 8032. The position of the type II burst obtained
from the Nancay radioheliograph coincided with the EUV transient. The
type II burst and the EUV transient were in the equatorial streamer
region to the north of the flaring region. This observation suggests
that the EUV transient may be the manifestation of the MHD shock
responsible for the type II burst.
---------------------------------------------------------
Title: Structure and Dynamics of the Corona Surrounding an Eruptive
Prominence
Authors: Gopalswamy, N.; Hanaoka, Y.; Hudson, H. S.
2000AdSpR..25.1851G Altcode:
We report on the 1997 December 14 prominence eruption event that was
accompanied by eruptive signatures in X-rays, EUV and white light:
coronal dimming, X-ray arcade formation , X-ray brightenings, EUV
eruption, and a white light CME. The data used were obtained by
the Nobeyama Radioheliograph, Yohkoh Soft X-ray Telescope (SXT) and
SOHO/LASCO and EIT. We identified various substructures of the eruption
and their inter-relationships. We found that the pre-disruption swelling
of the equatorial streamer was caused by the outward displacement of
the coronal material around the prominence location. The dynamical
behaviors of the CME and the accompanying eruptive prominence seem to
be very different
---------------------------------------------------------
Title: Interplanetary acceleration of coronal mass ejections
Authors: Gopalswamy, N.; Lara, A.; Lepping, R. P.; Kaiser, M. L.;
Berdichevsky, D.; St. Cyr, O. C.
2000GeoRL..27..145G Altcode:
Using an observed relation between speeds of CMEs near the Sun
and in the solar wind, we determine an “effective” acceleration
acting on the CMEs. We found a linear relation between this effective
acceleration and the initial speed of the CMEs. The acceleration is
similar to that of the slow solar wind in magnitude. The average solar
wind speed naturally divides CMEs into fast and slow ones. Based on
the relation between the acceleration and initial speed, we derive an
empirical model to predict the arrival of CMEs at 1 AU.
---------------------------------------------------------
Title: Multi-wavelength Signatures of Coronal Mass Ejection
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M. L.; Thompson, B. J.;
Plunkett, S.
1999spro.proc..207G Altcode:
We report on the near-surface and outer coronal manifestations of the
1998 January 25 coronal mass ejection (CME) using white light, EUV,
X-ray and hectometric radio data which reveal the three dimensional
structure and long term evolution of the CME. We find that (i) the
substructures of the CME (prominence core, cavity, frontal structure
and the arcade formation) are clearly observed in X-ray and EUV
wavelengths. (ii) The filament heats up early on and is observed as
a backbone in X-rays. (iii) The filament also expands considerably
as it erupts. (iv) The CME is observed through direct leading edge
signature as well as through dimming process in X-rays and in EUV.
---------------------------------------------------------
Title: 17 GHz Mode Coupling in the Solar Corona
Authors: Lara, A.; Gopalswamy, N.; Pérez-Enríquez, R.; Shibasaki, K.
1999spro.proc...83L Altcode:
We studied the development of microwave polarization of a group
of active regions for a period of 10 days during April, 1993 using
data obtained by the Nobeyama radioheliograph. The observed sense
of polarization at 17 GHz changed with the active region position on
the solar disk. This change of polarization can be explained by the
mode coupling theory according to which a weak coupling between the
ordinary and extraordinary electromagnetic modes takes place when the
radiation crosses a region of transverse magnetic field and results in
a polarization reversal. Since the strength of the mode coupling depends
on the physical parameters (and their gradients) of the quasi-transverse
region, observations of polarization changes can be used to obtain key
values of the magnetic field and field gradient in the active region
corona. Using the intensity and polarization images of active regions,
we found that the coupling constant is typically > 10<SUP>3</SUP>
corresponding to a weak coupling regime. We determined the mean
value of the transition frequency to be ~ 5.3 × 10<SUP>11</SUP>
Hz, below which the weak coupling effect is important. For all the
active regions studied in this paper, there seems to be a similarity
in the position on the solar disk where the mode coupling effects
become important. The polarization reversal always occurred when the
active regions were farther than the 500 arc sec mark from the disk
center. Using this fact and extrapolated photospheric magnetic field
we are able to estimate heights of both the quasi-transverse layer
and the source region. Assuming a value of ~ 70 G, we obtain a value
of 2.2 × 10<SUP>4</SUP> km for the Q-T layer height.
---------------------------------------------------------
Title: Solar Physics with Radio Observations
Authors: Bastian, T. S.; Gopalswamy, N.; Shibasaki, K.
1999spro.proc.....B Altcode:
Radio observations contribute a unique perspective on the many physical
phenomena, which occur on the Sun. From thermal bremsstrahlung emission
in the quiet solar atmosphere and filaments, to thermal gyroresonance
emission in strongly magnetized solar active regions, to the nonthermal
emission from MeV electrons accelerated in flares, observations of radio
emission provide a powerful probe of physical conditions on the Sun and
provide an additional means of understanding the myriad phenomena which
occur there. Moreover, radio observing techniques have led the way in
developing and exploiting Fourier synthesis imaging techniques. The
Nobeyama Radioheliograph, commissioned in June, 1992, soon after the
launch of Yohkoh satellite in August, 1991, is the most powerful,
solar-dedicated Fourier synthesis in the world, now capable of imaging
the full disk of the Sun simultaneously at frequencies of 17 and 34
GHz, with an angular resolution as much as 10" and 5", respectively,
and with a time resolution as fine as 100 msec. Between 27-30 October,
1998, the Nobeyama Radio Observatory and the National Astronomical
Observatory of Japan hosted the Nobeyama Symposium on Solar Physics
with Radio Observations, an international meeting bringing more than
sixty participants together at the Seisenryo Hotel in Kiyosato, for a
meeting devoted to reviewing recent progress in outstanding problems
in solar physics. Emphasis was placed on radio observations and,
in particular, radio observations from the very successful Nobeyama
Radioheliograph. These results were compared and contrasted with those
that have emerged from the Yohkoh mission. In addition, looking forward
to the next solar maximum, new instruments, upgrades, and collaborative
efforts were discussed. The result is the more than seventy invited
and contributed papers that appear in this volume.
---------------------------------------------------------
Title: The Astronomical Low Frequency Array (ALFA): Imaging from Space
Authors: Gopalswamy, N.; Kaiser, M. L.; Jones, D. L.; Alfa Team
1999spro.proc..447G Altcode:
The ALFA mission is a proposed astronomical observatory in space to
make high resolution radio images at frequencies below the ionospheric
cutoff (~ 20 MHz). This multi-satellite interferometric array will
image solar as well as non-solar phenomena in the frequency range 0.03
- 30 MHz. In this paper, we provide an overview of the ALFA mission,
with particular emphasis on solar studies to be undertaken.
---------------------------------------------------------
Title: X-ray and Microwave Signatures of Coronal Mass Ejections
Authors: Gopalswamy, N.
1999spro.proc..141G Altcode:
X-ray and microwave imaging of structures associated with coronal mass
ejections (CMEs) have provided a wealth of new information towards a
better understanding of solar eruptions. I review the recent research
based on microwave imaging from the Nobeyama Radioheliograph and X-ray
imaging from the Yohkoh Soft X-ray Telescope. I shall discuss the
advances made towards understanding the near surface manifestations
of CMEs best observed in X-rays and microwaves. In particular,
I discuss (i) observability of CMEs in X-rays and microwaves,
(ii) coronal dimming, (iii) relation between CME substructures,
(iv) heating and expansion of eruptive prominences, (v) timing of
flare, CME and prominence eruptions, and (vi) CME mass estimates from
non-optical observations.
---------------------------------------------------------
Title: Microwave Enhancement in Coronal Holes: Structure, Variability
and Magnetic Nature
Authors: Gopalswamy, N.; Shibasaki, K.
1999STIN...0011601G Altcode:
The microwave enhancement in coronal holes in comparison with the
quiet Sun is a distinct and easily observed signature related to the
magnetic activity. This has proven to be a new tool to study the
solar atmospheric layer where the fast solar wind originates. We
have developed a catalog of a large number of coronal holes using
images obtained by SOHO's Extreme-ultraviolet Imaging Telescope in
EUV and by the Nobeyama radioheliograph in microwaves. We also have
high resolution longitudinal magnetograms obtained by SOHO's Michelson
Doppler Imager. We present the statistical properties of the microwave
enhancements and discuss the small-scale dynamics as revealed by the
magnetograms and radioheliograms. We also discuss the geoeffectiveness
of these coronal holes.
---------------------------------------------------------
Title: "Driverless" Shocks in the Interplanetary Medium
Authors: Gopalswamy, N.; Kaiser, M. L.; Lara, A.
1999STIN...0011206G Altcode:
Many interplanetary shocks have been detected without an obvious driver
behind them. These shocks have been thought to be either blast waves
from solar flares or shocks due to sudden increase in solar wind speed
caused by interactions between large scale open and closed field lines
of the Sun. We investigated this problem using a set of interplanetary
shock detected in situ by the Wind space craft and tracing their solar
origins using low frequency radio data obtained by the Wind/WAVES
experiment. For each of these "driverless shocks" we could find
a unique coronal mass ejections (CME) event observed by the SOHO
(Solar and Heliospheric Observatory) coronagraphs. We also found that
these CMEs were ejected at large angles from the Sun-Earth line. It
appears that the "driverless shocks" are actually driver shocks, but
the drivers were not intercepted by the spacecraft. We conclude that
the interplanetary shocks are much more extended than the driving CMEs.
---------------------------------------------------------
Title: X-ray and radio manifestations of a solar eruptive event
Authors: Gopalswamy, N.; Nitta, N.; Manoharan, P. K.; Raoult, A.;
Pick, M.
1999A&A...347..684G Altcode:
We report on a study of the changes in the vicinity of a disappearing
solar filament (DSF) that occurred on 1993 April 30. The DSF was
associated with a long duration X-ray event (LDE) observed by the
GOES and Yohkoh spacecraft. A detailed analysis of the X-ray images
obtained by the Yohkoh Soft X-ray Telescope revealed that X-ray
manifestations of the eruption were wide-spread: (i) X-ray enhancement
over a coronal volume several times larger than that of the eruption
region, probably the X-ray counterpart of a coronal mass ejection (CME),
(ii) X-ray ejecta accelerating to 670 km s(-1) into the corona, and
(iii) quasi-stationary X-ray loops as in long decay events (LDEs) were
observed. One of the important findings of this study is the large-scale
X-ray enhancement which we identify with the frontal structure of a
CME, apart from the well-known X-ray ejecta and post-eruption arcade
formation. There is evidence for triggering of a sympathetic flare in
an adjoining active region due to the X-ray ejecta from the eruption
region. Stationary metric radio continuum observed by the Nançay
Radioheliograph was found to be associated with the brightest X-ray
loops that formed following the filament eruption. The unpolarized
continuum radio emission was found to be bremsstrahlung radiation
from the hot plasma observed in X-rays. The event was also associated
with a low frequency metric type II radio burst due to a coronal shock
wave from the eruption region. The onset time of the type II emission
precludes the possibility of a CME-driven shock causing it. Although
we do not have positional information for the type II burst, we found
that the X-ray ejecta was fast enough to drive the coronal shock. We
confirmed this by comparing the speed of the X-ray ejecta with the
shock speed obtained from the radio data which agreed within 10%.
---------------------------------------------------------
Title: Is the chromosphere hotter in coronal holes?
Authors: Gopalswamy, N.; Shibasaki, K.; Thompson, B. J.; Gurman,
J. B.; Deforest, C. E.
1999AIPC..471..277G Altcode: 1999sowi.conf..277G
Coronal holes are brighter than the quiet Sun in microwaves. Microwave
emission from the quiet Sun is optically thick thermal bremsstrahlung
from the upper chromosphere. Therefore, the optically thick layer in the
coronal hole chromosphere must be hotter than the corresponding layer
in the quiet chromosphere. We present microwave and SOHO observations
in support of this idea. Because of the availability of simultaneous
EUV and microwave images it is now possible to obtain more details
of this enigmatic phenomenon. In this paper, we highlight the primary
properties of the microwave enhancement in coronal holes and point out
some related phenomena. Finally, we summarize the possible explanations
of the radio enhancement.
---------------------------------------------------------
Title: Dynamical phenomena associated with a coronal mass ejection
Authors: Gopalswamy, N.; Kaiser, M. L.; MacDowall, R. J.; Reiner,
M. J.; Thompson, B. J.; Cyr, O. C. St.
1999AIPC..471..641G Altcode: 1999sowi.conf..641G
The flare-CME-shock relationship has been controversial for more than
two decades. This issue was traditionally addressed using white light
coronagraphic data on CMEs, H-alpha or GOES data on flares and radio
spectrographic data on shocks (inferred from metric type II radio
bursts). A wealth of new information has become available after the
advent of Yohkoh, SOHO and WIND missions that can be used to address
the dynamical phenomena associated with CMEs. We present multiwavelength
observations of the 1998 April 27 CME associated with coronal dimming,
an X-class flare and type II radio bursts. We find that the coronal
dimming observed in X-rays and EUV is indeed a CME signature and that
the CME clearly precedes the accompanying flare.
---------------------------------------------------------
Title: The Long Wavelength Array: Imaging Solar Bursts and CMEs
Authors: Gopalswamy, N.; Lazio, T. J. W.; Kassim, N. E.; Erickson,
W. C.
1999AAS...19410308G Altcode: 1999BAAS...31.1002G
Almost all of the transient disturbances in the Sun-Earth connected
space are amenable to probing by metric and decametric radio wavelengths
(150 MHz down to ionospheric cut-off at 15 MHz). The long wavelength
radio imaging with polarization capability is virtually the only way of
measuring magnetic fields in the outer corona and hence an important
tool in the study of long-term evolution of the Sun as it sheds its
magnetic field through coronal mass ejections (CMEs). Shocks generated
during the CMEs are detected as type II radio bursts; some of the
energetic electrons are detected as type III bursts; ejected plasmoids
are observed as type IV bursts. Ionospheric effects used to pose a
major problem for long wavelength imaging. We now know that most of the
shortcomings due to ionospheric effects can be virtually eliminated,
thanks to the development in image restoration such as self-calibration
(Kassim and Erickson, 1998). Low frequency technologies are relatively
cheap and well proven. A synergistic combination of a ground based
Long Wavelength Array (LWA) and the space-borne coronagraphs such as on
board the STEREO mission could prove to be an extremely powerful tool to
understand the interplanetary propagation of solar disturbances. Passive
imaging of solar emissions can also be combined with radar imaging
to increase the scientific return of the LWA (see poster by Lazio
et al). The low frequency regime has also the advantage of combining
solar physics with non-solar radio astronomy: Sun in the day time and
the rest of the universe at night (see poster by Kassim et al). NG is
an NAS/NRC Senior Research Associate at NASA/GSFC on leave from the
Catholic University. Basic research in radio astronomy at the Naval
Research Laboratory is supported by the Office of Naval Research.
---------------------------------------------------------
Title: Microwave enhancement and variability in the elephant's trunk
coronal hole: Comparison with SOHO observations
Authors: Gopalswamy, N.; Shibasaki, K.; Thompson, B. J.; Gurman, J.;
DeForest, C.
1999JGR...104.9767G Altcode:
We report on an investigation of the microwave enhancement and its
variability in the elephant's trunk coronal hole observed during the
Whole Sun Month campaign (August 10 to September 9, 1996). The microwave
images from the Nobeyama radioheliograph were compared with magnetograms
and EUV images obtained simultaneously by the Michelson Doppler imager
and the extreme ultraviolet imaging telescope (EIT) on board the SOHO
spacecraft. The combined data set allowed us to understand the detailed
structure of the microwave enhancement in the spatial and temporal
domains. We find that the radio enhancement is closely associated
with the enhanced unipolar magnetic regions underlying the coronal
hole. The radio enhancement consists of a smooth component originating
from network cell interiors and a compact component associated with
network magnetic elements. When a minority polarity is present near
a majority polarity element, within the coronal hole, the resulting
mixed polarity region is associated with a bright-point-like emission
in coronal EUV lines such as the Fe XII 195 Å. These coronal bright
points are also observed distinctly in the EIT 304 Å band, but not
in microwaves. On the other hand, the lower-temperature line emission
(304 Å) and the microwave enhancement are associated with the unipolar
magnetic flux elements in the network. We found strong time variability
of the radio enhancement over multiple timescales, consistent with the
initial results obtained by SOHO instruments. The microwave enhancement
is most probably due to temperature enhancement in the chromosphere
and may be related to the origin of solar wind.
---------------------------------------------------------
Title: Synoptic Sun during the first Whole Sun Month Campaign:
August 10 to September 8, 1996
Authors: Biesecker, D. A.; Thompson, B. J.; Gibson, S. E.; Alexander,
D.; Fludra, A.; Gopalswamy, N.; Hoeksema, J. T.; Lecinski, A.;
Strachan, L.
1999JGR...104.9679B Altcode:
A large number of synoptic maps from a variety of instruments are used
to show the general morphology of the Sun at the time of the First
Whole Sun Month Campaign. The campaign was conducted from August 10 to
September 8, 1996. The synoptic maps cover the period from Carrington
rotation 1912/253° to Carrington rotation 1913/45°. The synoptic maps
encompass both on-disk data and limb data from several heights in the
solar atmosphere. The maps are used to illustrate which wavelengths and
data sets show particular features, such as active regions and coronal
holes. Of particular interest is the equatorial coronal hole known as
the “elephant's trunk,” which is clearly evident in the synoptic
maps of on-disk data. The elephant's trunk is similar in appearance
to the Skylab-era, “Boot of Italy,” equatorial coronal hole. The
general appearance of the limb maps is explained as well. The limb
maps also show evidence for equatorial coronal holes.
---------------------------------------------------------
Title: Radio Imaging of the Sun from Space
Authors: Rodriguez, P.; Kassim, N. E.; Weiler, K. W.; Kaiser, M. L.;
Reiner, M. J.; MacDowall, R. A.; Jones, D. L.; Unwin, S. C.; Kuiper,
T. B.; Gopalswamy, N.
1999AAS...194.7604R Altcode: 1999BAAS...31R.956R
Since the 1960s, ground-based radio astronomers have had the
capability to image solar radio emissions using aperture synthesis
techniques. These images show the two-dimensional time history of
CME-driven shock fronts, for example. However, ground-based observations
are limited by the terrestrial ionosphere to frequencies above about 15
MHz, which corresponds to a maximum solar altitude of about one solar
radius. To probe the altitude range from one solar radius to one AU
requires space-based radio telescopes. Many space-based low-frequency
radio telescopes have flown over the past three decades, but they
all suffered from lack of angular resolution because they consisted
of single spacecraft carrying simple dipole antennas. Even with this
limitation, much progress has been made by utilizing spacecraft spin to
deduce source location and size, thereby permitting tracking of solar
radio sources between the sun and Earth. However, no structural detail
is available from this technique, only source centroids and approximate
angular size. To provide a greater level of structural detail,
we need to take the next logical step in low-frequency solar radio
astronomy: aperture synthesis from space. We believe this can be done
with currently-available hardware as a medium-class Explorer (MIDEX)
mission. This mission would consist of approximately 16 identical
and quite simple micro-spacecraft in a spherical array approximately
100 km in diameter. The array should be situated relatively far from
Earth (to lessen terrestrial interference), such as at the distant
retrograde class of orbits at about one million kilometers from
Earth. This array will be capable of imaging not only solar transient
events to unprecedented altitudes, but also the quiet sun, the entire
terrestrial magnetosphere via scattering in the magnetosheath, and the
low-frequency cosmic background, the latter being a totally unexplored
radio window. This work is supported in part by ONR and NASA.
---------------------------------------------------------
Title: The Long Wavelength Array: A Ground-Based Coronal Mass
Ejection Detector
Authors: Lazio, T. J. W.; Kassim, N. E.; Rodriguez, P.; Gopalswamy,
N.; Erickson, W. C.
1999AAS...194.7605L Altcode: 1999BAAS...31..956L
We describe the Long Wavelength Array (LWA), a ground-based radio
interferometer capable of serving as a coronal mass ejection (CME)
detector. Previous low-frequency (nu < 50 MHz) coronal sounding
experiments have shown that CMEs exhibit large radar cross sections. The
LWA will serve as the imaging receiver for a bi-static radar observatory
that will open an entirely new field of CME research. Because the LWA
will be a synthesis interferometer, it will be capable of imaging the
return echo as well as measuring its Doppler shift. The combination
of Doppler shift, to provide the radial velocity, and the imaging,
to provide the transverse velocity, means that the LWA will determine
the total space velocity of the CME, crucial for inferring arrival
times of Earthward-bound events for geomagnetic storm predictions. A
ground-based system operating with low cost HF/VHF technology, the LWA
will be considerably less expensive and more reliable than planned
stereoscopic space-based CME detection schemes. In addition to the
practical importance to spacecraft, communication, and electrical power
systems, the reliable detection and monitoring of CMEs will allow the
study of the angular distribution, ranges, and line-of-sight velocities
of CMEs. Additional papers at this meeting describe possibilities of the
LWA for astrophysical applications (Kassim et al.) and passive solar
observations (Gopalswamy et al.). Basic research in radio astronomy
at the Naval Research Laboratory is supported by the Office of Naval
Research.
---------------------------------------------------------
Title: Reply
Authors: Gopalswamy, N.; Kaiser, M. L.; Lepping, R. P.; Berdichevsky,
D.; Ogilvie, K.; Kahler, S. W.; Kondo, T.; Isobe, T.; Akioka, M.
1999JGR...104.4749G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Catholic University of America Institute for Astrophysics
and Computational Sciences, Department of Physics, Washington,
District of Columbia 20064. Report for the period Sep 1997 - Sep 1998.
Authors: Gopalswamy, N.
1999BAAS...31...13G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Study of the dynamics of the solar RA(7794) during october
29 1994 with VLA at 2 and 20 cm.
Authors: Torres Papaqui, J. P.; Gopalswamy, N.; Mendoza-Torres, J. E.
1998larm.confE..16T Altcode:
We report VLA observation made at 2 and 20 cm of a solar active region
(AR) where flares, were observed in October 29, 1994. The aim of the
work is to study the variations in intensity and polarization, during
this day, of different zones in the AR. The zones under study are:
1) Those where the flares took place, 2) the zones of the AR where
the maximum intensities, during the day, were observed and 3) the
zones of higher polarization. The zones where the flares occurred were
selected to follow the time variati ons before and after the flares. The
other zones were selected to look for possible variables that could
be related to the flares. An IDL programm that allows systematically
analyse temporal variations of different zones was made. The program
was applied to images made for time intervals of 10 sec. The whole
interval of observations was of about 6 hours. The results of this
analysis are presented in this work.
---------------------------------------------------------
Title: On the relationship between coronal mass ejections and
magnetic clouds
Authors: Gopalswamy, N.; Hanaoka, Y.; Kosugi, T.; Lepping, R. P.;
Steinberg, J. T.; Plunkett, S.; Howard, R. A.; Thompson, B. J.;
Gurman, J.; Ho, G.; Nitta, N.; Hudson, H. S.
1998GeoRL..25.2485G Altcode:
We compare the substructures of the 1997 February 07 coronal mass
ejection (CME) observed near the Sun with a corresponding event in
the interplanetary medium to determine the origin of magnetic clouds
(MCs). We find that the eruptive prominence core of the CME observed
near the Sun may not directly become a magnetic cloud as suggested by
some authors and that it might instead become the ”pressure pulse”
following the magnetic cloud. We substantiate our conclusions using time
of arrival, size and composition estimates of the CME-MC substructures
obtained from ground based, SOHO and WIND observations.
---------------------------------------------------------
Title: Type II radio emissions in the frequency range from 1-14 MHz
associated with the April 7, 1997 solar event
Authors: Kaiser, M. L.; Reiner, M. J.; Gopalswamy, N.; Howard, R. A.;
St. Cyr, O. C.; Thompson, B. J.; Bougeret, J. -L.
1998GeoRL..25.2501K Altcode:
We present an analysis of radio emissions associated with the April
7, 1997 solar eruptive event. The event consisted of a filament
disappearance, a complex two-phase coronal mass ejection (CME),
and a C6.9, 2N flare. At the same time, intermittent type II radio
emissions in the frequency range 1-10 MHz, corresponding to an altitude
range of 2-15 R<SUB>o</SUB>, were observed by the Wind/WAVES radio
receiver. Using the onset times and inferred heights and speeds
of the radio bursts, we considered both a CME-driven shock and a
flare-associated blast wave shock as possible causes of the type II
radio emissions. We conclude that some of the radio emissions in the
WAVES data are associated with each shock. The type II radio emissions
associated with the blast wave shock were farther from the sun than
any emission of this type that has been reported previously.
---------------------------------------------------------
Title: The solar origin of the January 1997 coronal mass ejection,
magnetic cloud and geomagnetic storm
Authors: Webb, D. F.; Cliver, E. W.; Gopalswamy, N.; Hudson, H. S.;
St. Cyr, O. C.
1998GeoRL..25.2469W Altcode:
The magnetic cloud and geomagnetic storm on January 10-11, 1997 were
associated with a halo-type Coronal Mass Ejection (CME) observed by
the SOHO/LASCO coronagraphs near the sun on January 6. We summarize
the solar activity related to this CME and the subsequent storm at
Earth. This solar activity was remarkably weak and unimpressive. If
the wide CME had not been observed, the storm would not have been
forecast. Thus this case represents an extreme example of so-called
“problem” magnetic storms that lack obvious surface signatures of
eruptive solar activity. It supports the view that CMEs involve the
destabilization of large-scale coronal structures which may or may
not have associated surface activity, and that CMEs, not the surface
activity, are the key causal link between solar eruptions and space
weather at Earth.
---------------------------------------------------------
Title: Spatial Structure of Solar Coronal Magnetic Loops Revealed
by Transient Microwave Brightenings
Authors: Zhang, J.; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
1998SoPh..180..285Z Altcode:
We present the measurement of magnetic field gradient in magnetic
loops in the solar corona, based on the multi-wavelength Very Large
Array observations of two transient microwave brightenings (TMBs)
in the solar active region 7135. The events were observed at 2 cm
(spatial resolution ∼ 2=) and 3.6 cm (spatial resolution ∼ 3=)
with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray
data (spatial resolution ∼ 2.5=) were available from the Soft X-ray
Telescope on board the Yohkoh satellite. The three-dimensional structure
of simple magnetic loops, where the transient brightenings occurred,
were traced out by these observations. The 2-cm and 3.6-cm sources
were very compact, located near the footpoint of the magnetic loops
seen in the X-ray images. For the two events reported in this paper,
the projected angular separation between the centroids of 2 and 3.6-cm
sources is about 2.3= and 3.1=, respectively. We interpret that the 2
and 3.6-cm sources come from thermal gyro-resonance emission. The 2-cm
emission is at the 3rd harmonic originating from the gyro-resonance
layer where the magnetic field is 1800 G. The 3.6-cm emission is at
the 2nd harmonic, originating from the gyro-resonance layer with a
magnetic field of 1500 G. The estimated magnetic field gradient near
the footpoint of the magnetic loop is about 0.09 G km=<SUP>1</SUP> and
0.12 G km=<SUP>1</SUP> for the two events. These values are smaller
than those observed in the photosphere and chromosphere by at least
a factor of 2.
---------------------------------------------------------
Title: Coronal Dimming Associated with a Giant Prominence Eruption
Authors: Gopalswamy, N.; Hanaoka, Y.
1998ApJ...498L.179G Altcode:
We report the results of our investigation of a giant eruptive
prominence (initial mass ~6×10<SUP>16</SUP> g) using microwave,
X-ray, and white-light observations. The prominence erupted from
the northwest limb of the Sun on 1994 April 5. The speed of the
prominence was only ~70 km s<SUP>-1</SUP> when it reached a height
of ~0.5 R<SUB>solar</SUB> above the solar surface. In X-rays, a large
region with reduced X-ray emission was observed enveloping the initial
location of the prominence and extending to much larger heights. At
the bottom of this depletion and beneath the eruptive prominence,
an X-ray arcade formed, progressively spreading from south to north
along the limb. This is the first time a direct detailed comparison is
made between coronal dimming and a prominence eruption. We were able to
confirm that the coronal dimming is indeed a near-surface manifestation
of the coronal mass ejection (CME). The orientation of the structures
involved did not allow the observations of the coronal cavity, but
all the other substructures of the CME could be identified. The mass
expelled from the Sun in the form of the eruptive prominence and the
coronal dimming are comparable. The estimated total mass is somewhat
larger than that reported in other X-ray-dimming events.
---------------------------------------------------------
Title: Microwave and Soft X-ray Study of Solar Active Region Evolution
Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.; Pérez-Enríquez,
R.; Koshiishi, H.; Enome, S.
1998SoPh..178..353L Altcode:
We have studied the properties and evolution of several active
regions observed at multiple wavelengths over a period of about 10
days. We have used simultaneous microwave (1.5 and 17 GHz) and soft
X-ray measurements made with the Very Large Array (VLA), the Nobeyama
Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board
the Yohkoh spacecraft, as well as photospheric magnetograms from
KPNO. This is the first detailed comparison between observations at
radio wavelengths differing by one order of magnitude. We have performed
morphological and quantitative studies of active region properties by
making inter-comparison between observations at different wavelengths
and tracking the day-to-day variations. We have found good general
agreement between the 1.5 and 17 GHz radio maps and the soft X-rays
images. The 17 GHz emission is consistent with thermal bremsstrahlung
(free-free) emission from electrons at coronal temperatures plus a small
component coming from plasma at lower temperatures. We did not find
any systematic limb darkening of the microwave emission from active
regions. We discuss the difference between the observed microwave
brightness temperature and the one expected from X-ray data and in
terms of emission of a low temperature plasma at the transition region
level. We found a coronal optical thickness of ∼ 10<SUP>-3</SUP>
and ∼ 1 for radiation at 17 and 1.5 GHz, respectively. We have
also estimated the typical coronal values of emission measure (∼
5 × 10<SUP>28</SUP> cm<SUP>-5</SUP>), electron temperature (∼
4.5 × 10<SUP>6</SUP>6 K) and density (∼ 1.2 × 10<SUP>9</SUP>
cm<SUB>3</SUB>). Assuming that the emission mechanism at 17 GHz is
due to thermal free-free emission, we calculated the magnetic field
in the source region using the observed degree of polarization. From
the degree of polarization, we infer that the 17 GHz radiation is
confined to the low-lying inner loop system of the active region. We
also extrapolated the photospheric magnetic field distribution to the
coronal level and found it to be in good agreement with the coronal
magnetic field distribution obtained from microwave observations.
---------------------------------------------------------
Title: Multiwavelength Observations of a Coronal Hole
Authors: Gopalswamy, N.; Shibasaki, K.; Deforest, C. E.; Bromage,
B. J. I.; Del Zanna, G.
1998ASPC..140..363G Altcode: 1998ssp..conf..363G
No abstract at ADS
---------------------------------------------------------
Title: Comparison of Microwave and SOHO Synoptic Maps of the Sun
During the Whole Sun Month, 1996
Authors: Gopalswamy, N.; Thompson, B. J.; Shibasaki, K.
1998ASPC..140..401G Altcode: 1998ssp..conf..401G
No abstract at ADS
---------------------------------------------------------
Title: The Catholic University of America, Institute for Astrophysics
and Computational Sciences, Department of Physics, Washington,
DC 20064. Report for the period Sep 1996 - Sep 1997.
Authors: Gopalswamy, N.
1998BAAS...30...32G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio and X-ray Investigations of Erupting Prominences (Review)
Authors: Gopalswamy, N.; Hanoka, Y.; Lemen, J. R.
1998ASPC..150..358G Altcode: 1998IAUCo.167..358G; 1998npsp.conf..358G
No abstract at ADS
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Title: Birth Place of the 1998 January 21 CME
Authors: Gopalswamy, N.; Hanaoka, Y.; Kaiser, M.; Gurman, J.; Hudson,
H.; Howard, R. A.
1998cee..workE..40G Altcode:
The 1998 January 21 halo coronal mass ejection was launched
from high southern latitudes in association with a filament
disappearance observed by the Nobeyama Radioheliograph. Signatures
of the initial destabilization of the filament were observed by
the Extreme-ultraviolaet Imaging Telescope (EIT) on board the SOHO
spacecraft and by the Soft X-ray Telescope (SXT) on board Yohkoh. The
Wind/WAVES experiment observed a type II burst in the 600-300 kHz
range. The data coverage for this event is unusually high and we make
use of it to understand the origin and evolution of the eruption. We
address several issues based on these data: (i) relation between
filament eruption and arcade formation beneath the filament, (ii)
comparison between the hot arcade formation in X-rays and EUV, (iii)
relation between the filament eruption and the white light CME, (iv)
relation between the CME and the interplanetary shock inferred from the
WAVES data. A summary of near-surface activities associated with the
eruption can be seen in the Figure 1. Figure 1. SOHO/MDI longitudinal
magnetogram, with radio filament (white contours) and X-ray emission
(enclosed by dark lines) are overlaid. The thick white line from E to
W is the neutral line over which the eruption took place. North is to
the top and east is to the left. F is the location where the filament
split at the time of eruption.
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Title: Microwave Imaging in Support of the SERTS'97 Flight
Authors: Gopalswamy, N.; Hanaoka, Y.
1998AAS...191.7317G Altcode: 1998BAAS...30..758G
The Solar Extreme-ultraviolet Rocket Telescope and Spectrograph flown
successfully on 1997 November 18 at 19:35 UT and an observing campaign
was conducted to support the flight. Coordinated observations were
obtained by SOHO and YOHKOH and many ground based instruments. Radio
observations were obtained by the Very Large Array (VLA) and the
Nobeyama Radioheliograph in microwaves. The SERTS target was the
trailing portion of a large active region (NOAA AR 8108) close to
the disk center (N19E17 at 19:40 UT on 1997 November 18). The VLA
obtained microwave images at 20, 6 and 3.6 cm wavelengths with a
spatial resolution of about 40", 12" and 7" respectively. The Nobeyama
images (spatial resolution 10") were obtained a few hours later at 1.7
cm. The microwave images (in total intensity and circular polarization)
provide information on the physical conditions (temperature, density and
magnetic field) in the active region corona and in sunspots at various
heights above the solar surface. The AR was relatively quiet during the
SERTS flight, so we can determine its quiescent properties. We present
preliminary radio images of AR 8108 and the physical conditions derived
from them. We thank T. Bastian for help in obtaining VLA observing
time. This research was supported by NASA grant NAG-5-6139.
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Title: Origin of coronal and interplanetary shocks: A new look with
WIND spacecraft data
Authors: Gopalswamy, N.; Kaiser, M. L.; Lepping, R. P.; Kahler, S. W.;
Ogilvie, K.; Berdichevsky, D.; Kondo, T.; Isobe, T.; Akioka, M.
1998JGR...103..307G Altcode:
We have investigated type II radio bursts in the solar corona using
data from ground-based radio telescopes (>18MHz) and from the
Radio and Plasma Wave experiment (WAVES) on board the WIND spacecraft
(<14MHz). The wavelength range of the WAVES experiment includes the
2- to 14-MHz band, previously unobserved from space. We found that all
34 coronal type II bursts observed over a period of 18 months (November
1, 1994, to April 30, 1996), decayed within a few solar radii and did
not propagate into the interplanetary medium. On the other hand, most
of the accompanying type III radio bursts observed by the ground-based
instruments were observed to continue into the interplanetary medium
as the electron beams propagated freely along open magnetic field
lines. Over the same period of time, other instruments on board the
WIND spacecraft detected about 18 interplanetary shock candidates,
which seem to be unrelated to the coronal type II bursts. This result
confirms the idea that the coronal and interplanetary shocks are two
different populations and are of independent origin. We reexamine the
data and conclusions of Gosling et al. [1976], Munro et al. [1979],
and Sheeley et al. [1984] and find that their data are consistent
with our result that the coronal type II bursts are due to flares. We
also briefly discuss the implications of our result to the modeling
studies of interplanetary shocks based on input from coronal type II
radio bursts.
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Title: Fast Time Structure during Transient Microwave Brightenings:
Evidence for Nonthermal Processes
Authors: Gopalswamy, N.; Zhang, J.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
1997ApJ...491L.115G Altcode: 1997astro.ph.10200G
Transient microwave brightenings (TMBs) are small-scale energy releases
from the periphery of sunspot umbrae with a flux density 2 orders
of magnitude smaller than that from a typical flare. Gopalswamy et
al. first reported the detection of the TMBs, and it was pointed out
that the radio emission implied a region of very high magnetic field
so that the emission mechanism has to be gyroresonance or nonthermal
gyrosynchrotron, but not free-free emission. It was not possible to
decide between gyroresonance and gyrosynchrotron processes because
of the low time resolution (30 s) used in the data analysis. We have
since performed a detailed analysis of the Very Large Array data with
full time resolution (3.3 s) at two wavelengths (2 and 3.6 cm), and we
can now adequately address the question of the emission mechanism of
the TMBs. We find that nonthermal processes indeed take place during
the TMBs. We present evidence for nonthermal emission in the form of
temporal and spatial structure of the TMBs. The fast time structure
cannot be explained by a thermodynamic cooling time and therefore
requires a nonthermal process. Using the physical parameters obtained
from X-ray and radio observations, we determine the magnetic field
parameters of the loop and estimate the energy released during the
TMBs. The impulsive components of TMBs imply an energy release rate
of ~1.3×10<SUP>22</SUP> ergs s<SUP>-1</SUP>, so the thermal energy
content of the TMBs could be less than ~10<SUP>24</SUP> ergs.
---------------------------------------------------------
Title: X-Ray and Radio Studies of a Coronal Eruption: Shock Wave,
Plasmoid, and Coronal Mass Ejection
Authors: Gopalswamy, N.; Kundu, M. R.; Manoharan, P. K.; Raoult, A.;
Nitta, N.; Zarka, P.
1997ApJ...486.1036G Altcode:
On 1994 July 31, a fast (900 km s<SUP>-1</SUP>) eruptive structure
was observed in X-rays, followed by a slower plasmoid (180 km
s<SUP>-1</SUP>). They were associated with a coronal mass ejection,
prominence eruption, and a host of metric radio bursts. The X-ray
structure seems to be a part of a white light coronal mass ejections
(CME), as inferred from the white light images of July 30 and 31. A type
II burst was observed at the leading edge of the X-ray eruption, while a
type IV burst was spatially associated with the detached plasmoid. The
type III radio bursts occurred on thin overdense structures associated
with the eruption. We detected the rise of plasma levels because
of mass addition to the type III burst sources as a result of the
eruption. This event further clarifies the manifestation of a CME in
X-rays. We identify the X-ray eruption as the driver of the coronal
shock wave. This provides answer to the long-standing question regarding
the origin of coronal and interplanetary shock waves. We have also found
evidence to support the idea that herringbone bursts are produced when
the coronal shock wave crosses open magnetic field lines.
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Title: Signatures of Coronal Currents in Microwave Images
Authors: Lee, Jeongwoo; White, Stephen M.; Gopalswamy, N.; Kundu, M. R.
1997SoPh..174..175L Altcode:
Microwave emission from solar active regions at frequencies above 4
GHz is dominated by gyroresonance opacity in strong coronal magnetic
fields, which allows us to use radio observations to measure coronal
magnetic field strengths. In this paper we demonstrate one powerful
consequence of this fact: the ability to identify coronal currents
from their signatures in microwave images. Specifically, we compare
potential-field (i.e., current-free) extrapolations of photospheric
magnetic fields with microwave images and are able to identify regions
where the potential extrapolation fails to predict the magnetic field
strength required to explain the microwave images. Comparison with
photospheric vector magnetic field observations indicates that the
location inferred for coronal currents agrees with that implied by the
presence of vertical currents in the photosphere. The location, over
a neutral line exhibiting strong shear, is also apparently associated
with strong heating.
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Title: Tracking a CME from Cradle to Grave: A Multi-wavelength
Analysis of the February 6-7, 1997 Event
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Kosugi, T.; Hudson,
H.; Nitta, N.; Thompson, B.; Gurman, J.; Plunkett, S.; Howard, R.;
Burkepile, J.
1997SPD....28.0501G Altcode: 1997BAAS...29..908G
The partially earth-directed coronal mass ejection (CME) event of 1997
February 6-7 originated from the southwest quadrant of the sun. The
CME accelerated from 170 km/s to about 830 km/s when it reached a
distance of 25 solar radii. The CME was an arcade eruption followed
by bright prominence core structures. The prominence core was tracked
continuously from the solar surface to the interplanetary medium by
combining data from the Nobeyama radioheliograph (microwaves), Mauna Loa
Solar Observatory (He 10830 { Angstroms}), SOHO/EIT (EUV) and SOHO/LASCO
(white light). The CME was accompanied by an arcade formation, fully
observed by the YOHKOH/SXT (soft X-rays) and SOHO/EIT (EUV). The X-ray
and EUV observations suggest that the reconnection proceeded from
the northwest end to the southeast end of a filament channel. In the
SOHO/EIT images, the the feet of the soft X-ray arcade were observed
as EUV ribbons. The CME event also caused a medium sized geomagnetic
storm: The hourly equatorial Dst values attained storm level during
18:00-19:00 UT on February 09. This means the disturbance took about
2.25 days to reach the Earth. The first signatures of an IP shock was
a pressure jump in the WIND data around 13:00 UT on Feb 09, 1997 which
lasted for about 14 hours, followed by flux rope signatures. This CME
event confirms a number of ideas about CMEs: The three part structure
(frontal bright arcade, dark cavity and prominence core), disappearing
filament, elongated arcade formation, and terrestrial effects. We make
use of the excellent data coverage from the solar surface to the Earth
to address a number of issues regarding the origin and propagation of
the geoeffective solar disturbances. We benefited from discussions at
the first SOHO-Yohkoh Coordinated Data Analysis Workshop, held March
3-7, 1997, at Goddard Space Flight Center.
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Title: The Solar Source of the January 1997 CME/Magnetic Cloud;
Recurrent Activity on a Polar Crown Filament Channel
Authors: Webb, David; Cliver, E.; McIntosh, P.; Gopalswamy, N.;
Hudson, H.
1997SPD....28.1501W Altcode: 1997BAAS...29..918W
The magnetic cloud and geomagnetic storm on 10-11 January 1997 was
associated with a halo-type CME observed by LASCO near the sun on 6
January. As part of the ISTP and SHINE collaboration on this event we
are studying the solar source region of the CME and its propagation
through the interplanetary medium to Earth. We summarize the rather
weak solar activity that apparently was associated with this CME, and
contrast it with the strong surface and coronal activity associated
with the 9-11 February 1997 magnetic cloud/storm. We present evidence
that the solar sources of both of these events occurred over an area
where the southern polar crown filament channel diverted sharply to
the north and in the decaying remnants of the first large-scale active
region to form during the new solar cycle. Our results also suggest
that this region was the site of earlier CMEs; i.e., it was a key site
of recurrent activity during 1996-97 which, when aimed toward Earth,
produced recurrent magnetic clouds and storms.
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Title: Multi-wavelength Observations of Transient Microwave
Brightenings in a Solar Active Region
Authors: Zhang, Jie; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
1997SPD....28.0163Z Altcode: 1997BAAS...29..891Z
We present multi-wavelength Very Large Array observations of two
transient microwave brightenings (TMBs) in the solar active region
7135. The events were observed at 2 cm (spatial resolution ~ 2”) and
3.6 cm (spatial resolution ~ 3”) with a temporal resolution of 3.3 s
in a time-sharing mode. Soft X-ray data (about 5” spatial resolution)
were available from the Soft X-ray Telescope on board the YOHKOH
satellite. The 2 cm and 3.6 cm emission sources were very compact,
located near the footpoint of the magnetic loops seen in the X-ray
images. The TMBs traced out the three dimensional structure of the
magnetic loops where the transient brightenings occurred. For the
two events reported in this paper, the projected angular separation
between the centroids of 2 and 3.6 cm source is about 2.3” and 3.1”,
respectively. We interpret the spatial and temporal distributions
as implying that the 2 and 3.6 cm flux is mainly due to thermal
gyro-resonance emmision. The 2 cm emission seems to be at the 3rd
gyro-harmonic coming from the 1800 G gyro-resonance layer. The 3.6 cm
emission seems to be at both the 2nd and 3rd harmonics, originating
from gyro-resonance layers with a magnetic field of 1500 G and 1000
G, respectively. However, the two gyro-resonance layers for 3.6 cm
emission are not resolved with the current spatial resolution. The
estimated magnetic field gradient near the footpoint of the magnetic
loop is about 0.17 G km(-1) and 0.22 G km(-1) for the two events.
---------------------------------------------------------
Title: Source Parameters for Impulsive Bursts Observed in the Range
18-23 GHz
Authors: Sawant, H. S.; Rosa, R. R.; Cecatto, J. R.; Gopalswamy, N.
1997SoPh..171..155S Altcode:
Here, we report on impulsive solar radio bursts observed for the
first time with high time/spectral resolution in the range 18
to 23 GHz. Using observational parameters and assuming nonthermal
gyrosynchrotron emission from energetic electrons in a loop structure,
we have estimated the density of nonthermal electrons, magnetic field,
and dimension of the source along the line of sight.
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Title: A Multi-Wavelength Analysis of the February 6/7, 1997 Coronal
Mass Ejection
Authors: Plunkett, S. P.; Gopalswamy, N.; Kundu, M. R.; Howard, R. A.;
Thompson, B. J.; Gurman, J. B.; Lepping, R. P.; Hudson, H. S.; Nitta,
N.; Hansoka, Y.; Kosugi, T.; Burkepile, J. T.
1997ESASP.404..615P Altcode: 1997cswn.conf..615P
No abstract at ADS
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Title: Radio and X-Ray Studies of a Coronal Mass Ejection Associated
with a Very Slow Prominence Eruption
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Enome, S.; Lemen,
J. R.; Akioka, M.; Lara, A.
1997ApJ...475..348G Altcode:
We report on the observations of an X-ray coronal mass ejection
(CME) with its three part structure: frontal loop, coronal cavity,
and the eruptive prominence core. The prominence core was observed in
microwaves, and the frontal loop was observed in X-rays. A coronal
volume much larger than that occupied by the prominence seems to be
affected by the eruption. Formation of an arcade structure was also
observed beneath the erupting prominence. X-ray enhancement at the
arcade persisted for several hours similar to long decay events. At
the apex of the arcade there was a bright knot, which we interpret
as the reconnection region from which the filament gets detached. We
determined the trajectories of the frontal loop and the prominence core
and found them to have very different characteristics. The CME showed an
extremely small acceleration, while the prominence had a linear motion
in the beginning followed by an exponential rise. However, during the
several hours of simultaneous observation, the prominence did not catch
up with the frontal loop. We determined the evolution of the CME mass,
which increased by a factor of 4 during our observations. We discuss
the implications of the observations in the general context of coronal
mass ejections.
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Title: A Giant Prominence Eruption Observed by Nobeyama
Radioheliograph and YOHKOH Spacecraft
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Shibasaki, K.;
Koshiishi, H.; Enome, S.; Lemen, J. R.
1997IAUJD..19E...4G Altcode:
The results of an investigation of a giant prominence which erupted from
the northwest limb of the Sun on 1994 April 05, will be reported. The
event could be traced back to a large prominence of March 19, 1994
above the east limb. The filament was located in the north-south
direction when it appeared on the disk. At about 23:00 UT on April 05,
the filament started slowly rising and then accelerated. The speed of
the prominence was was only 75 km s^{-1} when it reached a height of
about 0.5 R_ odot above the surface. Preliminary examination shows that
the eruption caused a geomagnetic storm on April 07 at 20:00 UT. We
study the dynamical and physical properties of the erupting prominence
and obtain physical parameters of the prominence plasma. In X-rays, the
region of eruption was relatively faint. After the eruption, however,
there was a large void at the previous location of the prominence and
an arcade formed progressively spreading from south to north along
the limb. Based on the X-ray and radio observations, we determine the
characteristics of the pre- and post-eruption structures.
---------------------------------------------------------
Title: Yohkoh/SXT observations of a coronal mass ejection near the
solar surface
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.; Akioka, M.
1996NewA....1..207G Altcode:
We report the observations of a coronal mass ejection (CME) using
the Soft X-ray Telescope on board the Yohkoh Mission. The CME had
the familiar three part structure (frontal loop, prominence core
and a cavity). The erupting prominence was observed by the Nobeyama
radioheliograph. We were able to determine the mass of the CME (2.6
× 10<SUP>14</SUP> g) from X-ray observations which seems to be at
the lower end of the range of CME masses reported before from white
light observations. This is the first time the mass of a CME has been
determined from X-ray observations. The height of onset of the CME
was 0.3R<SUB>⊙</SUB>. The CME moved much faster than the erupting
prominence while its acceleration was smaller than that of the erupting
prominence. J. Leonard Culhane
---------------------------------------------------------
Title: Radio and X-ray manifestations of a bright point flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
1996AIPC..374..408G Altcode: 1996hesp.conf..408G
We have found remarkably different manifestations of a bright point
flare in X-ray and radio (microwave) wavelengths, unlike previous
observations. In X-rays, the BP flare was relatively simple while
in radio, the bright point flare had a large scale component and
a transient moving component. The large scale structure may be the
radio counterpart of large scale structures sometimes seen during
X-ray BP flares. The transient component was also compact and moved
away from the location of the X-ray BP flare with a speed of ∼60
km s<SUP>-1</SUP>. The compact source also showed fast time structure
which suggests nonthermal emission mechanism for the transient sources.
---------------------------------------------------------
Title: Tracking Type III and Type II Solar Radio Bursts from Metric
to Hectometric Wavelengths using Ground-based and Space-borne
Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Kaiser, M. L.; Kahler, S. W.;
Kondo, T.; Isobe, T.; Akioka, M.
1996AAS...188.1908G Altcode: 1996BAAS...28..851G
There exists a controversy regarding the origin of coronal and
interplanetary (IP) shocks. Present observations shows that coronal
shocks are associated with flares while the IP shocks are associated
with coronal mass ejections (CMEs). An important question in this
connection is whether the IP shocks are extensions of the coronal
shocks or they are independently driven by CMEs. The coronal shocks
have traditionally been inferred from metric type II radio bursts. The
ionospheric cut-off around 20 MHz had been a hurdle in arriving at
a firm conclusion regarding the continuation of type II bursts to
frequencies lower than the ionospheric cut off. The WAVES experiment on
board the WIND spacecraft has essentially removed this hurdle so that
we are able to track metric radio bursts to hectometric wavelengths. We
have identified about two dozen type II bursts observed by the Hiraiso
Radio Spectrograph (HiRAS) after the launch of the WIND satellite. Most
of these type II bursts were accompanied by type III bursts. We
have positively identified the solar flares associated with all the
events. When we examined the WIND Radio and Plasma waves (WAVES) data,
we found the following: (i) Most of the metric (Hiraiso) type III bursts
have counterparts in the WAVES data; (ii) None of the metric type II
bursts have counterparts in the WAVES data. This result suggest that
coronal shocks responsible for metric type II bursts are blast waves
which decay rapidly within the inner corona while the electron beams
producing type III bursts continue to propagate to the IP medium.
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Title: Polarization of Microwaves Emitted From A Bipolar Active Region
Authors: Lee, Jeongwoo; White, Stephen; Gopalswamy, N.; Kundu, M. R.
1996AAS...188.3603L Altcode: 1996BAAS...28R.873L
High resolution microwave maps of a complex bipolar active region,
AR6615, were obtained using the VLA on 1991 May 7 at three frequencies,
4.9 GHz, 8.4 GHz, and 15 GHz. Comparison of this microwave observation
with Big Bear magnetogram suggests that inversion and depolarization of
microwave emission must have occurred at different sites of the active
region depending on frequency. For quantitative interpretation of the
polarization data, we constructed the coronal magnetic fields above
the active region using the potential field extrapolation. In the
model, we identified the quasi-transverse (QT) surface across which
change of the polarization may occur. It is found that the required
topology of the QT surface to explain the observed polarization
is correctly predicted by the potential field model, although the
locations of the 15 GHz gyroresonance sources required a nonlinear
force-free field extrapolation in part. With the calculation of the mode
coupling coefficient along the QT surface, we were able to locate the
region of depolarization above a strong sunspot, consistent with the
observation. We also discuss the appropriate theoretical gyroresonant
opacity for waves propagating perpendicular to the magnetic fields,
as needed to understand the observed polarization across the magnetic
neutral line. Applicability of the present results to study of the
coronal magnetic structure above complex bipolar regions, in general,
is briefly discussed.
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Title: A Multi Wavelength Study of Active Region Development
Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.; Perez-Enriquez, R.;
Koshiishi, H.; Enome, S.
1996AAS...188.3601L Altcode: 1996BAAS...28Q.873L
We report on a study of the evolution of several active regions during
1993 April 17-28 using data obtained at multiple wavelengths that
probe various heights of the active region corona. We use simultaneous
microwave (1.5 and 17 GHz) and Soft X-ray images obtained by the
Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the
Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft. We also
use photospheric magnetograms from Kitt Peak National Observatory
to study the development of Solar Active Regions. We have followed
the development of various observed parameters such as brightness
temperature and polarization using radio images. The X-ray data were
used to track the development of density and temperature of active
regions. Using the fact that the quiet active region radiation is
thermal and adopting proper emission mechanism at each frequency
domain, we construct a consistent picture for the three dimensional
structure of the active regions. Particular attention has been paid to
the mode coupling observed at 17 GHz while the active regions crossed
the solar disk.
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Title: Coronal Disconnection Events and Metric Radio Emisison
Authors: Gopalswamy, N.
1996Ap&SS.243..129G Altcode: 1996IAUCo.154..129G
We review the existing literature on the coronal disconnection events
(CDEs) and discuss the importance of these events in understanding
coronal structures. We discuss the possible radio signatures of the
CDEs and how they may be observed by radio instruments.
---------------------------------------------------------
Title: Detection of Large-Scale Radio Structure and Plasma Flow
during a Solar Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
1996ApJ...457L.117G Altcode:
We report on the detection of a large-scale radio structure and
plasma flow associated with a bright point flare observed on 1993
July 11. The bright point (BP) flare was simultaneously imaged by the
Nobeyama radioheliograph at 17 GHz and the Soft X-Ray Telescope on board
the Yohkoh mission. The microwave emission consists of a large-scale
structure and a compact moving source. The large-scale component seems
to be the radio counterpart of large-scale loop structures sometimes
observed in association with BP flares in X-rays. The compact source
moved from the location of the X-ray BP flare with a speed of about 60
km s-1, which suggests a plasma flow. Spatial comparison between X-ray
and radio data shows that the BP flare had different manifestations in
the two wavelength domains. The emission peaks in the two wavelength
domains did not coincide, which suggests cool plasma flow along the
large-scale radio structure. We were able to determine the temperature
and emission measure of the BP flare plasma from the X-ray data,
and thus we computed the expected radio flux from the X-ray--emitting
plasma. We found that the computed radio flux was much smaller than
the total observed radio flux.
---------------------------------------------------------
Title: VLA Observations of a Solar Active Region at 6.2 and 3.5 CM
Wavelength Compared with Model Calculations
Authors: Hildebrandt, J.; Kruger, A.; Gopalswamy, N.; Raulin, J. -P.;
Kundu, M. R.
1996ASPC...93..369H Altcode: 1996ress.conf..369H
No abstract at ADS
---------------------------------------------------------
Title: Three Part Structure of a CME Revealed by X-Ray and Microwave
Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Lara, A.; Hanaoka, Y.; Enome,
S.; Lemen, J. R.; Akioka, M.
1996ASPC..111..393G Altcode: 1997ASPC..111..393G
The authors present X-ray (Yohkoh/SXT) and microwave (17 GHz Nobeyama)
observations of the 1993 July 10 - 11 CME. During this event, all the
substructures of a classical CME are revealed: frontal loop in X-rays,
prominence core in microwaves, dark cavity between prominence and
frontal loop in X-rays, and arcade structure beneath the prominence
in X-rays.
---------------------------------------------------------
Title: A Study of Active Region Magnetic Field Structure Using
VLA-Radio YOHKOH X-Ray and Mess-Optical Observations
Authors: Gopalswamy, N.
1995JApAS..16..381G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VLA and YOHKOH Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Raulin, J. -P.; Kundu, M. R.; Nitta, N.;
Lemen, J. R.; Herrmann, R.; Zarro, D.; Kosugi, T.
1995ApJ...455..715G Altcode:
A major solar flare (X-ray importance M1.5 and optical importance SB)
was fully observed by the Very Large Array and the Yohkoh mission on
1993 April 22. Both thermal and nonthermal emissions were observed
in radio. In soft X-rays, the flare was confined to a compact region
in an arcade. In hard X-rays, there were two prominent footpoints,
coincident in projection with the soft X-ray footpoints and located
on either side of the magnetic neutral line inferred from photospheric
magnetograms The Yohkoh Bent Crystal Spectrometer (B CS) data provided
important context information which was helpful in cross-checking the
quantitative agreement between the radio and X-ray data. The microwave
spectrum peaked around 10 GHz and showed Razin suppression in the
beginning. Later on, the low-frequency spectral index dropped to a
value of 2, suggesting thermal emission. The VLA images of the flare at
1.5 GHz show that the flare emission started as a single source above
one footpoint; later on, the emission centroid moved toward the soft
X-ray structure to finally become cospatial with the latter. The two
locations of the 20 cm source corresponded to nonthermal (footpoint
source) and thermal (source cospatial with the soft X-ray structure)
emissions. We performed temperature and emission measure analysis of
the X-ray data (SXT, BCS, and HXT) and used them as input to determine
the expected radio emission. While there is morphological agreement
between the radio and soft X-ray structures in the thermal phase,
the 20 cm brightness temperature shows quantitative agreement with
temperature derived from the BCS data. We were able to identify
three emission mechanisms contributing to the 20 cm radio emission
at different times without any ad hoc assumption regarding emission
mechanisms. Razin-suppressed nonthermal gyroresonance emission,
plasma emission, and thermal free-free emission seem to be operating
and are found to be consistent with the plasma parameters derived
from the X-ray data. The magnetic field structure in the flaring
region showed differences before and after the flare as traced b soft
X-ray structures in the flaring region and confirmed by 20 cm radio
images. The superhot component with a temperature of 32 MK was observed
in hard X-ray images and in light curves during the impulsive phase of
the flare with possible radio signatures at 20 cm wavelength. We derived
the physical parameters of the flaring plasma, the magnetic field,
and the characteristics of nonthermal particles in the flaring region.
---------------------------------------------------------
Title: Radio Counterpart of an X-ray Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
1995SPD....26.1317G Altcode: 1995BAAS...27Q.991G
No abstract at ADS
---------------------------------------------------------
Title: Surprises in the Radio Signatures of CMEs
Authors: Gopalswamy, N.; Kundu, M. R.
1995LNP...444..223G Altcode: 1995cmer.conf..223G
We discuss several results regarding the relationship between coronal
mass ejections (CMEs) and metric radio emissions which have changed our
understanding of these phenomena considerably. Imaging observations
of metric radio emissions along with coronagraph observations have
been used to obtain these results. We consider the following: (i) Why
slow CMEs are associated with metric type IV radio emission contrary
to the earlier belief, (ii) Why shocks piston driven by the CMEs are
not seen in the solar corona, (iii) Thermal radio emission from the
CMEs and their implications to CME-flare relationship and (iv) Radio
signatures of coronas disconnection events.
---------------------------------------------------------
Title: Polarization Features of Solar Radio Emission and Possible
Existence of Current Sheets in Active Regions
Authors: Gopalswamy, N.; Zheleznyakov, V. V.; White, S. M.; Kundu,
M. R.
1994SoPh..155..339G Altcode:
We show that it is possible to account for the polarization features
of solar radio emission provided the linear mode coupling theory is
properly applied and the presence of current sheets in the corona
is taken into account. We present a schematic model, including a
current sheet that can explain the polarization features of both the
low frequency slowly varying component and the bipolar noise storm
radiation; the two radiations face similar propagation conditions
through a current sheet and hence display similar polarization
behavior. We discuss the applications of the linear mode coupling
theory to the following types of solar radio emission: the slowly
varying component, the microwave radio bursts, metric type U bursts,
and bipolar noise storms.
---------------------------------------------------------
Title: Transient Microwave Brightenings in Solar Active Regions:
Comparison between VLA and YOHKOH Observations
Authors: Gopalswamy, N.; Payne, T. E. W.; Schmahl, E. J.; Kundu, M. R.;
Lemen, J. R.; Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
1994ApJ...437..522G Altcode:
We report observations of transient microwave (2 cm) brightenings
and their relationship with brightenings in soft X-rays. The peak
flux of the microwave brightenings observed by the Very Large Array
(VLA) is smaller than the previously reported fluxes by two orders
of magnitude. The microwave sources were highly polarized (up to
100%) and were situated on the periphery of a sunspot umbra. Among
the many transients observed in X-rays by Yohkoh, two were observed
simultaneously in microwaves. The microwave sources were found to
be closer to the umbra of the sunspot than were the X-ray loops. It
seems that the microwave sources are located at the footpoints of
the looplike X-ray transients. Using the combined VLA, Yohkoh, and
Mees data set, we determine the physical parameters of the loop in
which the brightenings occur. We find that an increase in emission
measure accompanied by small-scale heating can account for the X-ray
brightening. The microwave emission can be interpreted as thermal
gyroresonance or nonthermal gyrosynchrotron processes during the X-ray
brightening. The magnetic field in the microwave-source region is
found to be 1200-1800 G. The observations also provide evidence for
temperature gradient in the coronal loops.
---------------------------------------------------------
Title: Study of Active Region Magnetic Field Structures Using VLA
Radio, YOHKOH X-ray and MEES Optical Observations
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
1994kofu.symp..347G Altcode:
We report on the observation of compact magnetic flux tubes from the
boundary between the umbra and penumbra of a large sunspot in AR 7135
on April 24, 1992. The structure and geometry of one such flux tube
was determined using the coordinated observations obtained by the
Very Large Array, the Yohkoh Soft X-ray Telescope and the Mees Solar
Observatory. From radio observations we infer that the magnetic field
of the flux tube at the spot-side footpoint is ~ 1300-1800 G.
---------------------------------------------------------
Title: Nonthermal Radio Emission Associated with a Coronal
Disconnection Event
Authors: Gopalswamy, N.; Kundu, M. R.; St. Cyr, O. C.
1994ApJ...424L.135G Altcode:
We have found possible radio signatures of a coronal disconnection event
observed by the Solar Maximum Mission Coronagraph/Polarimeter. The
radio emission seems to be produced by charged particles accelerated
during the same reconnection process which is responsible for the
disconnection event. We discuss the implications of the radio emission
characteristics to the reconnection process.
---------------------------------------------------------
Title: Three dimensional coronal structures using clark lake
observations
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
1994AdSpR..14d..65S Altcode: 1994AdSpR..14...65S
Throughout the quiet-Sun years 1982-1987, the Clark Lake Radioheliograph
mapped the solar corona on a daily basis at frequencies from 30 to
100 MHz. The Clark Lake maps show a variety of features which we have
analyzed quantitatively. Among the features are coronal streamers,
which appear to cross the solar disk during a solar rotation. We have
modeled the streamers with various geometrics and density profiles,
and computed ray-tracing images for comparison with the CLRO maps. These
models produced estimates of density and spatial scales in 3 dimensions
for the streamers. We discuss the significance of these estimates and
compare them with inferences made from optical observations. One of
the possible conclusions we draw from these comparisons is that there
are unresolved structures in stremers, not observable optically in
the limb data.
---------------------------------------------------------
Title: Three Dimensional Coronal Structures Using Clark-Lake
Observations
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
1994SoPh..150..325S Altcode:
We have undertaken a study of coronal features observed at
meter-decameter wavelengths using the Clark Lake radioheliograph. Among
the coronal structures we have studied are the radio manifestations of
coronal streamers on the solar disk and above the solar limb. We have
analyzed the radio data quantitatively, using ray-tracing models for
comparison with the maps. Our study provides information about the
streamers' three-dimensional shapes, scales, and density profiles,
for comparison with related observations using white-light coronagraphs.
---------------------------------------------------------
Title: Non-radial magnetic field structures in the solar corona
Authors: Gopalswamy, N.; Kundu, M. R.; Raoult, A.; Pick, M.
1994SoPh..150..317G Altcode:
We report on the structure and geometry of coronal magnetic fields
inferred from the observations of meter-decimeter type III and moving
type IV radio bursts, associated with a Hα flare. This is the first
report of type III radio bursts from the Nançay radioheliograph after
it acquired the two-dimensional multifrequency capability. Dispersion of
the radio source positions with frequency suggests that open and closed
field lines are considerably inclined to the radial direction which is
consistent with the connectivity observed in the magnetogram. We suggest
that multiple arch systems are involved in the type IV emission. From
the polarization and dispersion characteristics of the type IV source,
we infer that the emission is due to fundamental plasma emission.
---------------------------------------------------------
Title: Solar Simple Bursts Observed with High Spectral Resolution
in the 18--23 GHz Range
Authors: Sawant, H. S.; Rosa, R. R.; Cecatto, J. R.; Gopalswamy, N.
1994ApJS...90..693S Altcode: 1994IAUCo.142..693S
For the first time, solar bursts in the frequency range of
(18-23) GHz have been observed with high-time (0.6-1.2 s) and
high-frequency resolution (1 GHz), by using the Itapetinga 13.7 m
diameter antenna. Here, we investigate the microwave type 'simple
low level (less than 10 SFU) bursts' associated with the impulsive
phase of solar flares. Observed properties of these simple bursts are:
rise time t<SUB>r</SUB> approximately 3 s, decay time t<SUB>d</SUB>
approximately 5 s and spectral index ranging between -1 and -4. These
bursts were found to be associated with SF or SN flares as seen in
H(alpha). The above properties suggest that they are likely to be a
microwave counterpart of elementary flare bursts. In the majority of
the cases the spectral evolution is soft-hard-soft. This suggests a
nonthermal gyrosynchrotron mechanism for generating these elementary
flare bursts. Estimated parameters of these simple burst sources are
height (h approximately 2400 km), electron density (N<SUB>epsilon</SUB>
is less than 8.8 x 10<SUP>9</SUP>/cu cm.), and magnetic field (B
approximately 300 G).
---------------------------------------------------------
Title: Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations
of Energetic Electron Populations in Solar Flares
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1994ApJS...90..599K Altcode: 1994IAUCo.142..599K
We present comparisons of multiwavelength data for a number of solar
flares observed during the major campaign of 1991 June. The different
wavelengths are diagnostics of energetic electrons in different energy
ranges: soft X-rays are produced by electrons with energies typically
below 10 keV, hard X-rays by electrons with energies in the range
10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and
millimeter-wavelength emission by electrons with energies of 0.5 MeV
and above. The flares in the 1991 June active period were remarkable in
two ways: all have very high turnover frequencies in their microwave
spectra, and very soft hard X-ray spectra. The sensitivity of the
microwave and millimeter data permit us to study the more energetic
(greater than 0.3 MeV) electrons even in small flares, where their
high-energy bremsstrahlung is too weak for present detectors. The
millimeter data show delays in the onset of emission with respect to
the emissions associated with lower energy electrons and differences in
time profiles, energy spectral indices incompatible with those implied
by the hard X-ray data, and a range of variability of the peak flux in
the impulsive phase when compared with the peak hard X-ray flux which
is two orders of magnitude larger than the corresponding variability
in the peak microwave flux. All these results suggest that the hard
X-ray-emitting electrons and those at higher energies which produce
millimeter emission must be regarded as separate populations. This has
implications for the well-known 'number problem' found previously when
comparing the numbers of non thermal electrons required to produce
the hard X-ray and radio emissions.
---------------------------------------------------------
Title: A Study of Active Region Magnetic Fields Using Radio, X-ray
and Optical Observations
Authors: Gopalswamy, N.
1994ASPC...68..395G Altcode: 1994sare.conf..395G
No abstract at ADS
---------------------------------------------------------
Title: Interferometry of Solar Flares at 3-mm Wavelength
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1994IAUS..154..131K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VLA Observations of a High Coronal Flare
Authors: Raulin, J. P.; Gopalswamy, N.; Kundu, M. R.; Nitta, N.
1993AAS...183.0706R Altcode: 1993BAAS...25.1300R
We present radio observations of a coronal flare which occurrred on 1993
April 22, in a weak magnetic field region to the west of AR 7477. The
observations were made by the Very Large Array (VLA) at 20 and 90
cm. The event consists of bright (brightness temperature of 10(10) K)
unpolarized bursts, followed by a longlasting unpolarized continuum with
moderately high brightness temperature (2-3 10(9) K) in the high corona
(90 cm observations). The low coronal counterpart of this flare is a
weak and moderatly polarized 20 cm radio emission. Full disk Yohkoh
images show that the corresponding radio emission is located in or
above magnetic loops connecting AR 7477 and its neighborhood. The
presence of permanent and non-varying noise storm associated with
AR 7477 seems to indicate that the overall magnetic field structure
of the active region is unaffected by the flare. The coronal radio
source which is indicative of acceleration of electrons to nonthermal
energies, is not associated with major Hα emissio n nor with bright
X ray emission. The absence of any detectable circular polarization,
as well as the high brightness temperature, seems to indicate that
the 90 cm emission is second harmonic plasma emission.
---------------------------------------------------------
Title: Variability in Sunspot Associated Microwave Emission: Umbral
Oscillations?
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.
1993AAS...183.6808G Altcode: 1993BAAS...25.1396G
We report on microwave observations of sunspot associated emission
that shows variability over a time scale of minutes. To our knowledge,
this is the first time such rapid variability has been observed in
microwave radiation from a sunspot. These observations were obtained
by the Very Large Array (VLA) on April 24, 1992 at 2cm. The radio
emission from the sunspot umbra was in the form of several compact
sources with a size less than 4 arcsec. The time evolution of the peak
flux of these sources showed significant time variations which were
sometimes periodic. The period of these ocillations was approximately
3 min, similar to that of intensity and Doppler shift oscillations
observed in optically thin, transition region lines such as C IV
(1548.19 Angstroms) in sunspot umbrae. There were also morphological
changes in the extended sunspot emission over which the compact sources
were superposed. We also observed the appearance of new compact sources
within the umbra where there was reduced emission before. The brightness
temperatures of these compact sources were in the range (1-5)times 10(5)
K. We explore possible interpretations of the time variability.
---------------------------------------------------------
Title: Structure of a fast coronal mass ejection from radio
observations.
Authors: Gopalswamy, N.; Kundu, M. R.
1993AdSpR..13i..75G Altcode: 1993AdSpR..13R..75G
The authors investigate the thermal structure of a coronal mass ejection
(CME) in meter-dekameter wavelengths and compare it with the optical
evidence. The multifrequency observations enable us to infer the three
dimensional structure of the CME. The authors estimated the mass of
the CME and found to be in reasonable agreement with the range of
values obtained from white light observations.
---------------------------------------------------------
Title: Interferometric observations of solar flares at 3 mm wavelength
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1993AdSpR..13i.289K Altcode: 1993AdSpR..13..289K
We report on the observations of a number of flares at a wavelength of
3.5 mm during the 1991 June solar campaign. Many flares, including
small ones, show an impulsive phase at milllimeter wavelengths
which indicates the presence of MeV electrons, and the millimeter
observations are far more sensitive to such electrons than are current
γ-ray detectors. However, these energetic electrons do not always show
a good correlation with the lower-energy electrons which produce hard
X-rays below 100 keV. The production efficiency of MeV electrons seems
to vary considerably from flare to flare. An extended phase similar to
the soft X-ray behaviour is also seen at millimeter wavelengths, which
we attribute to dense hot material radiating thermal bremsstrahlung. In
the impulsive onset the millimeter emission seems to be consistently
delayed with respect to the hard X-rays.
---------------------------------------------------------
Title: Simultaneous Observations of Solar Plage with the Solar
Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS),
the VLA, and the Kitt Peak Magnetograph
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thompson, William T.;
Thomas, Roger J.; Holman, Gordon D.; Gopalswamy, N.; White, Stephen
M.; Kundu, Mukul R.; Jones, Harrison P.
1993ApJ...411..410B Altcode:
We obtained simultaneous images of solar plage on 1991, May 7
with SERTS, the VLA,4 and the NASA/National Solar Observatory
spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. Using
intensity ratios of Fe XVI to Fe XV emission lines, we find that the
coronal plasma temperature is (2.3-2.9) x 10 exp 6 K throughout the
region. The column emission measure ranges from 2.5 x 10 exp 27 to
l.3 x 10 exp 28 cm exp -5. The calculated structure and intensity
of the 20 cm wavelength thermal bremsstrahlung emission from the hot
plasma observed by SERTS is quite similar to the observed structure and
intensity of the 20 cm microwave emission observed by the VLA. Using
the Meyer (1991, 1992) revised coronal iron abundance, we find no
evidence either for cool absorbing plasma or for contributions from
thermal gyroemission. Using the observed microwave polarization and the
SERTS plasma parameters, we calculate a map of the coronal longitudinal
magnetic field. The resulting values, about 30-60 G, are comparable
to extrapolated values of the potential field at heights of 5000 and
10,000 km.
---------------------------------------------------------
Title: A Study of the Solar Active Regions Using Simultaneous VLA
and Yohkoh Soft X-ray Imaging: CoMStOC `92
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Schmelz, J. T.
1993BAAS...25R1213G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hard X-ray and Radio Spectra for Solar Flares from AR 6659
Authors: White, S. M.; Murphy, R.; Schwartz, R. A.; Kundu, M. R.;
Gopalswamy, N.; Lim, J.
1993BAAS...25Q1222W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VLA and Yohkoh Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Lemen, J. R.; Nitta, N.;
Strong, K. T.
1993BAAS...25.1186G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VLA, OVRO, Yohkoh and Optical Observations During CoMStOC
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.; Lemen, J.;
Strong, K. T.; de La Beaujardiere, J.
1993BAAS...25.1213S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Coronal Plasma and Magnetic Field Diagnostics Using
SERTS and Coordinated VLA Observations
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Thomas, R. J.;
Holman, G. D.; Gopalswamy, N.; White, S. M.; Kundu, M. R.; Jones, H. P.
1993BAAS...25.1224B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Multiwavelength Portrait of a Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1993BAAS...25.1183W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Thermal and nonthermal emissions during a coronal mass ejection
Authors: Gopalswamy, N.; Kundu, M. R.
1993SoPh..143..327G Altcode:
We report on the thermal and nonthermal radio emissions from a coronal
mass ejection (CME) observed at meter-decameter wavelengths using the
Clark Lake multifrequency radioheliograph. From white-light observations
of the Solar Maximum Mission Coronagraph/Polarimeter instrument the CME
was found to have a speed of ∼ 450 km s<SUP>−1</SUP>. Since there
was no nonthermal radio emission in the beginning of the event and the
one which occurred later was quite weak, we were able to observe the
thermal structure of the CME in radio. Type III bursts and a nonthermal
continuum started several minutes after the CME onset. We use the radio
and optical observations to show that the CME was not driven by the
flare. We investigate the thermal structure and geometry of the mass
ejection in radio and compare it with the optical evidence. Finally
we develop a schematic model of the event and point out that particle
acceleration high in the corona is possible.
---------------------------------------------------------
Title: A new investigation of microbursts at meter-decameter
wavelengths
Authors: Subramanian, K. R.; Gopalswamy, N.; Sastry, Ch. V.
1993SoPh..143..301S Altcode:
We report on a new investigation of microbursts at meter-decameter
wavelengths observed using the Broad Band Array at Gauribidanur
Radio Observatory. This is an independent set of observations of
microbursts: previous observations had been obtained only by the Clark
Lake multifrequency radioheliograph. We confirm several properties
of microbursts reported earlier. In addition, we have studied some
new properties of microbursts such as time profile characteristics,
flux density and energy spectra for comparison with the corresponding
properties of normal type III bursts. The present study supports
the idea that the microbursts and the normal type III bursts are
generated by electron beams of similar characteristics. We interpret
the low brightness temperature of microbursts as follows: plasma waves
generated by the electron beams through beam-plasma instability are
quickly isotropized as they scatter on the density fluctuations in
the corona. The resulting low levels of plasma waves are converted
into transverse radiation of low brightness temperature. One important
consequence of the isotropization is that the second harmonic plasma
emission dominates the fundamental and hence the microbursts are
expected to be predominantly a harmonic plasma emission.
---------------------------------------------------------
Title: Analysis of EUV, Microwave and Magnetic Field Observations
of Solar Plage
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.;
Thomas, R. J.; Holman, G. D.; White, S. W.; Gopalswamy, N.; Kundu,
M. R.
1993ASPC...46..291B Altcode: 1993mvfs.conf..291B; 1993IAUCo.141..291B
No abstract at ADS
---------------------------------------------------------
Title: Plasma Emission from Isotropic Langmuir Turbulence: Are Radio
Microbursts Structureless?
Authors: Gopalswamy, N.
1993ApJ...402..326G Altcode:
The brightness temperature of radio emission through the fundamental and
second harmonic plasma processes is determined for isotropic Langmuir
waves of low-energy density in order to account for the microbursts
at meter-dekameter wavelengths. The probable cause for low levels of
Langmuir turbulence is the presence of isotropic density fluctuations
in the corona which isotropize the beam-generated Langmuir waves. We
determined the energy density of Langmuir waves attainable from
the beam-plasma instability in the presence of isotropic density
fluctuations. Since the electron density fluctuations isotropize
the beam-generated plasma waves, the head-on collision of plasma
waves becomes efficient to produce the second harmonic plasma
emission. For reasonable beam parameters, the brightness temmperature
of the fundamental never exceeds 10 exp 6 K, while the second harmonic
covers the observed range of microburst brightness temperatures. Thus,
the microbursts are predominantly at second harmonic. This leads to an
important conclusion that the microbursts are structureless, similar
to a population of normal type III bursts of low polarization with no
fundamental-harmonic structure.
---------------------------------------------------------
Title: Are coronal type II shocks piston driven?
Authors: Gopalswamy, N.; Kundu, M. R.
1992AIPC..264..257G Altcode: 1992pacp.work..257G
Flare blast waves and shocks piston driven by coronal mass ejections
(CMEs) have been proposed to be responsible for generating type II
radio bursts in the solar corona. The idea for piston-driven shocks
came primarily from temporal association of shocks and CMEs. Our
compilation of CME events with simultaneous radio observations with
positional information supports idea of flare blast waves.
---------------------------------------------------------
Title: Analysis of EUV, Microwave, and Magnetic Field Observations
of a Solar Active Region
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.;
White, S. M.; Gopalswamy, N.; Kundu, M. R.
1992AAS...180.4002B Altcode: 1992BAAS...24R.792B
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous Hard X-ray, Soft X-ray, Millimeter and Microwave
Observations of a Solar Flare
Authors: White, S. M.; Kundu, M. R.; Lim, J.; Gopalswamy, N.
1992AAS...180.4504W Altcode: 1992BAAS...24..802W
We present non-imaging data across a wide range of wavelengths for a
solar flare which occurred on 1991 June 13. This flare is of interest
because it shows a spike in hard X-rays at the beginning of the event
which had a relatively hard X-ray spectrum, and was followed by a much
softer impulsive phase. We present the BATSE and OSSE observations
(from the Gamma Ray Observatory): the former have good time resolution,
while the latter provide well-resolved spectral information. These are
contrasted with the GOES soft-X-ray data on the hot thermal component in
the corona, and radio observations up to 86 GHz which are sensitive to
both the nonthermal and thermal components of the flare. The 86 GHz data
from the BIMA millimeter interferometer show a spike in the impulsive
phase coincident with the hard X-ray spike above 100 keV, as well as
a long-duration thermal phase which appears to be consistent with an
origin in the same material seen by GOES. We discuss the implications
of the observations for particle acceleration in this flare.
---------------------------------------------------------
Title: Estimation of the Mass of a Coronal Mass Ejection from Radio
Observations
Authors: Gopalswamy, N.; Kundu, M. R.
1992ApJ...390L..37G Altcode:
The mass of a coronal mass ejection (CME) is estimated using
meter-decametric observations obtained with the Clark Lake
multifrequency radioheliograph. Mass estimates in the past were made
using coronagraph and white-light photometer observations. Since
the radiation at radio and optical wavelength regimes has different
physical origins, the radio method can provide an independent check
on the mass estimates. The estimate of the 1986 February 16 CME using
the radio method is close to the average value of CME masses reported
in the literature.
---------------------------------------------------------
Title: Are Microbursts Structureless?
Authors: Gopalswamy, N.
1992AAS...180.5601G Altcode: 1992BAAS...24Q.820G
Microbursts are of lowest brightness temperature of all the radio bursts
in the meter-decameter wavelength regime. Since the low brightness
temperature is a consequence of low level of Langmuir turbulence, it
was thought that a nonlinear process such as the second harmonic plasma
emission would be unimportant. The probable cause for low levels of
Langmuir turbulence is the presence of isotropic density fluctuations
in the corona which isotropize the beam-generated Langmuir waves. The
isotropy of the Langmuir turbulence favors the head-on collision of
plasma waves needed to satisfy the kinematic conditions of harmonic
plasma emission. For reasonable beam parameters, we find that the
second harmonic plasma emission always dominates; the fundamental
brightness temperature never exceeds 10(6) K. Thus we conclude that
the microbursts may be structureless. We also find that the microburst
electron beams are no different from the normal type III electron beams.
---------------------------------------------------------
Title: High Dynamic Range Multifrequency Radio Observations of a
Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1992ApJS...78..599W Altcode:
High-dynamic-range multifrequency radio observations of a solar active
region are presented. The evolution of the region is followed at 5
GHz as it rotates from the limb to disk center, and when it is at
disk center, observations at 0.33, 1.5, 5, 8.4, and 15 GHz are used
to analyze the distribution of density and magnetic field within
the active region. A dynamic range of up to 1500 (at 8.4 GHz) was
achieved because these data were well suited to the self-calibration
technique. The signatures of both optically thick gyroresonance emission
are unambiguously identified, and magnetic fields and optically thin
thermal free-free emission are outlined. Images are compared at 5
and 8.4 GHz in order to identify regions in the trailing part of
the active region where optically thin four-harmonic gyroresonance
emission is contributing to the observed brightness temperatures at
5 GHz, indicating the presence of 450 G fields.
---------------------------------------------------------
Title: Millimeter and hard X-ray/γ-ray observations of solar flares
during the June 91 GRO campaign.
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1992NASCP3137..502K Altcode: 1992como.work..502K
We have carried out high-spatial-resolution millimeter observations
of solar flares using the Berkeley-Illinois-Maryland Array (BIMA). At
the present time, BIMA consists of only three elements, which is
not adequate for mapping highly variable solar phenomena, but is
excellent for studies of the temporal structure of flares at millimeter
wavelengths at several different spatial scales. We present BIMA
observations made during the Gamma Ray Observatories (GRO)/Solar Max
1991 campaign in Jun. 1991 when solar activity was unusually high. Our
observations covered the period 8-9 Jun. 1991; this period overlapped
the period 4-15 Jun. when the Compton Telescope made the Sun a target
of opportunity because of the high level of solar activity.
---------------------------------------------------------
Title: Meter-decameter radio emission associated with a coronal
mass ejection
Authors: Kundu, M. R.; Gopalswamy, N.
1992LNP...399..268K Altcode: 1992esf..coll..268K; 1992LNP...399..268G; 1992IAUCo.133..268K
A study of meter-dekameter radio emission associated with the 1986
Feb 10 coronal Mass ejection event is presented here. The event
was accompanied by a major flare (optical importance 1B and X-ray
importance C9.6), preceded by a filament disappearance. Changes in
the intensity of a pre-existing noise storm was observed during the
onset of the flare. A flare continuum, a moving type IV, and a type
II occurred during the event. The event was also associated with a
strong hard X-ray burst. The speeds of moving type IV burst and CME
were of the same order of 1600 kms -1, while the type II shock speed
was 1900 kms -1. The positional data indicate that the moving type IV
burst and the inferred type II shock had different trajectories. The
moving type IV burst was confined to one leg of the CME while the
type II shock was far ahead of the CME leading edge. We discuss the
inferred relation among different entities such as the CME, type II
shock, type IV plasmoid and the erupting filament.
---------------------------------------------------------
Title: Largescale Structures Associated with Eruptive Flares and
Radio Waves
Authors: Gopalswamy, N.; Kundu, M. R.
1992LNP...399..207G Altcode: 1992esf..coll..207G; 1992IAUCo.133..207G
We review some recent results obtained from 2-dimensional imaging
observations of the Sun using the Clark Lake multifrequency
radioheliograph. The radioheliograph produced images of the Sun's
corona on a daily basis at several frequencies within the range
20-125 MHz during the period 1982-87. Using these images both large
scale structures as well as transient phenomena such as bursts have
been studied. In this paper we discuss the nature of radio emission
associated with eruptive filaments and CMEs. It is possible to
trace the structure of magnetic fields in the corona based on the
multifrequency observations of moving type IV bursts at meter and
decameter wavelengths. We illustrate this by discussing specific
events. We discuss a rare case of the detection of thermal radio
emission in association with a fast CME. We estimate the CME mass
using spatially resolved radio data.
---------------------------------------------------------
Title: Large-Scale Features of the Sun at 20 Centimeter Wavelength
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
1991ApJ...379..366G Altcode:
Results are reported from an experimental study of the characteristics
of large-scale coronal structures such as active regions, plages,
filaments, and coronal holes using data obtained with the VLA
at 1.5 GHz during the period September 11-17, 1988. The radio
data were supplemented with He 10830- A, H-alpha, and Calcium-K
spectroheliograms. A statistical analysis of some of the characteristics
of the active regions is performed. Most of the active region sources
were found to be about 100 arcsec in size, with bridges between regions
common; lower brightness temperature regions showed a higher degree of
polarization in general. The maximum polarization was found at the edge
of active regions but well within the associated plages. The degree of
polarization from bright active regions was small (not more than 20
percent), in agreement with previous results. Evidence was found for
compression of preexisting flux by the emerging flux from a new region,
which took place in the apparent absence of magnetic reconnection.
---------------------------------------------------------
Title: Simultaneous EUV, Microwave, and Magnetic Field Observations
of Solar Active Regions
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Gopalswamy,
N.; White, S. M.; Jones, H. P.; Metcalf, T. R.
1991BAAS...23.1388B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Magnetic Structures Observing Campaign. I. Simultaneous
Microwave and Soft X-Ray Observations of Active Regions at the
Solar Limb
Authors: Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman,
G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
1991ApJ...374..374N Altcode:
Using simultaneous microwave and soft X-ray measurements made with
the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator
(XRP) aboard the Solar Maximum Mission (SMM), we have studied two
active regions near the solar limb. These observations were taken as
part of the Coronal Magnetic Structures Observing Campaign (CoMStOC),
a collaboration designed to study the magnetic field in the solar
corona. The images in soft X-rays and at 20 cm wavelength are similar:
both show peaks above the active regions and extended bridge of
emission 200,000 km long connecting the two regions. The brightness
temperature of the 20 cm emission is lower than that predicted from the
X-ray emitting material, however; it can be attributed to free-free
emission in cooler (<10<SUP>6</SUP> K) plasma not visible to XRP,
with an optical depth ∼1. The 6 cm emission is concentrated at lower
altitudes and in a ∼160,000 km long bundle of loops in the northern
active region. Comparison of the 6 cm map with the potential magnetic
field lines computed from photospheric magnetic fields (measured 2 days
earlier) indicates that the 6 cm emission is associated with fields
of less than ∼200 G. Such fields would be too weak to attribute the
observed 6 cm emission to gyroresonance radiation. Analysis of the
6 cm loop bundle indicates that it is strongly asymmetric, with the
magnetic field in the northern leg ∼2 times stronger than in the
southern leg; the 6 cm emission most likely arises from a combination
of hot ( ≥ 2 × 10<SUP>6</SUP> K) and cool plasmas, while the 20 cm
emission becomes optically thick in the cooler (∼9 × 10<SUP>3</SUP>
K) plasma. We estimate an Alfvén speed ∼7000 km s<SUP>-1</SUP>
and ratio of electron gyrofrequency to plasma frequency ∼1.0 in the
northern leg of the 6 cm loop.
---------------------------------------------------------
Title: Global Streamer Evolution
Authors: Thejappa, G.; Kundu, M. R.; Gopalswamy, N.
1991BAAS...23.1045T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VLA Observations of Radio Filaments
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
1991BAAS...23.1045G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Strong Magnetic Fields and Inhomogeneity in the Solar Corona
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1991ApJ...366L..43W Altcode:
It is shown that fields of 1800 G can exist in the corona based
on observations of gyroresonance emission at 15 GHz at coronal
temperatures. The strong fields occur in a small source radiating
in the extraordinary (x) mode over the penumbra of a large symmetric
sunspot. The optically-thin ordinary mode emission from the region shows
a nearby peak at only 36,000 K which may be due to a sunspot plume,
and a hole over the umbra consistent with the expected low-density
material there. The x-mode source is highly asymmetric, despite the
apparent symmetry of the sunspot, and its appearance and location
imply that the strongest magnetic fields in the corona are localized
in a compact flux tube.
---------------------------------------------------------
Title: VLA Observations of Active Region 5555 During the 1st Max'91
Campaign
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
1991max..conf...23S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Association of a Type IV Burst with a Slow CME
Authors: Gopalswamy, N.; Kundu, M. R.
1991max..conf..139G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Observation of an Unusually Fast Type IV Plasmoid
Authors: Gopalswamy, N.; Kundu, M. R.
1990ApJ...365L..31G Altcode:
A moving type IV burst of the 'isolated source' type has been detected
whose out-of-plane speed, at 1600 km/sec, becomes about 2800 km/sec
upon assumption of radial motion; this is twice as high as previously
reported speeds for bursts of this type. While shock waves are known
to have such high speeds, and a shock wave is likely to form ahead
of a high-speed plasmoid, no radio signature has been observed for
such a shock. This lack of shock detection may, however, be primarily
due to poor observing conditions. Energetic electrons, trapped in an
about 1.4 G magnetic field of the plasmoid, can adequately account
for the emission.
---------------------------------------------------------
Title: Filament Eruption and Storm Radiation at Meter / Decameter
Wavelengths
Authors: Kundu, M. R.; Gopalswamy, N.
1990SoPh..129..133K Altcode:
We report the study of a weak noise storm observed by the Clark Lake
multifrequency radioheliograph at four frequencies. The noise storm
onset was associated with a filament eruption and a gradual rise and
fall in soft X-rays. We compare the noise storm emission with related
emissions in other wavelengths to develop a composite scenario of
the event. Using the properties of the quiet corona inferred from the
simultaneously observed quiet-Sun radiation, we estimate the brightness
temperature of the storm continuum, which seems to be consistent with
the observations reported in Solar Geophysical Data. Superthermal
particles with a temperature that is ten times the coronal electron
temperature and a density of ∼ 10<SUP>−3</SUP> times the coronal
density are adequate to explain the observed radiation. Since the noise
storm observations were made at four frequencies, we were able to obtain
a brightness temperature spectrum of the storm radiation. If the storm
radiation is affected in the same way as the quiet-Sun emission by
inhomogeneities, the observed spectrum can be interpreted as due to
propagation effects. Since the Clark Lake instrument can observe both
quiet Sun and weak bursts simultaneously, we were able to estimate
the propagation effects from the quiet-Sun observations and use it to
correct the brightness temperature of storm radiation.
---------------------------------------------------------
Title: Multiple Moving Magnetic Structures in the Solar Corona
Authors: Gopalswamy, N.; Kundu, M. R.
1990SoPh..128..377G Altcode: 1990IAUCo.121P.377G
We report the study of moving magnetic structures inferred from the
observations of a moving type IV event with multiple sources. The
ejection contains at least two moving radio emitting loops with
different relative inclinations. The radio loops are located above
multiple Hα flare loops in an active region near the limb. We
investigate the relationship between the two systems of loops. The
spatial, temporal and geometrical associations between the radio
emission and near surface activities suggest a scenario similar to
coronal mass ejection (CME) events, although no CME observations exist
for the present event. From the observed characteristics, we find that
the radio emission can be interpreted as Razin suppressed optically thin
gyrosynchrotron emission from nonthermal particles of energy ∼ 100,
keV and density ∼ 10<SUP>2</SUP>-10<SUP>5</SUP> cm<SUP>−3</SUP>
in a magnetic field ≤ 2 G.
---------------------------------------------------------
Title: First High Spatial Resolution Interferometric Observations
of Solar Flares at Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.;
Hurford, G. J.
1990ApJ...358L..69K Altcode:
The first high spatial resolution interferometric observations
of solar flares at millimeter wavelengths, carried out with the
Berkeley-Illinois-Maryland Array are presented. The observations were
made at 3.3 mm wavelength during the very active periods of March 1989,
using one or three baselines with fringe spacings of 2-5 arcsec. The
observations represent an improvement of an order of magnitude in
both sensitivity and spatial resolution compared with previous solar
observations at these wavelengths. It appears that millimeter burst
sources are not much smaller than microwave sources. The most intense
bursts imply brightness temperatures of over 10 to the 6th K and are due
to nonthermal gyrosynchrotron emission or possibly thermal free-free
emission. If the emission in the flash phase is predominantly due to
gyrosynchrotron emission, thermal gyrosynchrotron models can be ruled
out for the radio emission because the flux at millimeter wavelengths
is too high.
---------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1990SoPh..127..165T Altcode:
We study the characteristics of microbursts using a large data base
obtained with the multifrequency radioheliograph of the Clark Lake Radio
Observatory. Most of the new observations were made during July 29,
1985 to August 2, 1985; we also include for statistical studies the
microburst data used in our earlier studies. We perform a statistical
analysis of many characteristics such as frequency drift, source size
and brightness temperature and compare them with the properties of
normal type III bursts. We investigate the coronal structures and
surface activities associated with some of the events. We find that
(i) the brightness temperature is in the range 6 × 10<SUP>5</SUP>
K to 6 × 10<SUP>7</SUP> K; (ii) the drift rate of the microbursts is
slightly smaller than that of normal type III bursts, implying electron
beams with speeds ∼0.2c.
---------------------------------------------------------
Title: A Note on the Emission Mechanism of Storm Radiation
Authors: Gopalswamy, N.
1990SoPh..126..367G Altcode:
A new mechanism has been proposed for the continuum and burst components
of solar storm radiation by Genkin, Erukhimov, and Levin (1989a,
b). In this paper, we point out that while bursts can be explained by
the proposed mechanism of scattering on plasma turbulence generated
density fluctuations, the continuum cannot be explained by sattering
on thermal ion density fluctuations. The reason is, under the same
coronal conditions, second harmonic emissions will dominate over
the fundamental emission due to scattering on thermal ion density
fluctuations in contradiction to observations. We also note that the
range of plasma wave densities needed for this mechanism may not be
realistic for the case of plasma wave generation due to loss cone
instability. It is further argued that coalescence of plasma waves
with low-frequency waves still seems to be the plausible mechanism.
---------------------------------------------------------
Title: CoMStOCI: Physical Properties of an Active Region Loop Observed
at the Solar Limb
Authors: Holman, G. D.; Brosius, J. W.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
1990BAAS...22..899H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evolution of Active Regions at 20 cm
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
1990BAAS...22..795G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-Dynamic-Range Multifrequency Radio Observations of a
Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1990BAAS...22R.794W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Millimeter-Interferometer Observations of Solar Flares
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.;
Hurford, G. J.
1990BAAS...22..823K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New Observations of Storm Radiation at Decameter Wavelengths
and Their Interpretation
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1990BAAS...22..794T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some Problems in Low Frequency Solar Radio Physics
Authors: Gopalswamy, N.; Kundu, M. R.
1990LNP...362...97G Altcode: 1990lfas.work...97G
Several important problems in solar radio physics can be attacked using
the high spatial resolution observations from a low frequency space
array, as the problem of ionospheric refraction does not exist. Noise
storms are believed to occur in closed magnetic loops due to trapped
superthermal particles. Recent radioheliograph observations suggest such
a magnetic field topology up to altitudes of about 40 MHz emission. The
problem of relative locations and sources of the storm continuum and
bursts can be effectively studied by imaging them with higher spatial
resolution. Interplanetary type II bursts are observed from heights
above ~ 10 R while coronal type II bursts are observed from heights less
than ~ 3 R. Observations filling this gap have important implications
for the understanding of solar-terrestrial relations through shocks
and mass ejections.
---------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1990IAUS..142..521T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Clark-Lake Radio Observations of Coronal Mass Ejections
Authors: Gopalswamy, N.
1990IAUS..142..495G Altcode:
Some recent studies of mass ejections from the sun are reviewed
using 2D imaging observations of the Clark Lake multifrequency
radioheliograph. Radio signatures of both fast and slow coronal mass
ejections (CMEs) have been observed. Using temporal and positional
analysis of moving type-IV and type-II bursts, and white light CMEs
it is found that the type II bursts and CMEs need not have a direct
cause and effect relationship. Instead, the type II burst seems to
be generated by a 'decoupled shock', probably due to an associated
flare. The moving type IV burst requires nonthermal particles trapped
in magnetic structures associated with the CME. Since nonthermal
particles can be generated independent of the speed of CMEs, moving
type IV bursts need not be associated only with fast CMEs. Specific
examples are presented to support these views.
---------------------------------------------------------
Title: The Sun at the Vla's Metric and Decimetric Wavelengths
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.; Schmahl, E. J.
1990IAUS..142..523W Altcode:
Preliminary results of solar observations at 0.333 and 1.5 GHz
made with the VLA during the September 11-17, 1988 period are
presented. Generally, there are few structural changes in the active
region sources from one day to the next, suggesting that structural
evolution is relatively slow. Contour maps at 1.5 GHz are presented
for each of the four days. Two noise storms were present at 0.33 GHz
all week and were highly polarized.
---------------------------------------------------------
Title: The Radio Signatures of a Slow Coronal Mass Ejection: Electron
Acceleration at Slow-Mode Shocks?
Authors: Kundu, M.; Gopalswamy, N.; White, S.; Cargill, P.; Schmahl,
E. J.; Hildner, E.
1989ApJ...347..505K Altcode:
The evolution of a coronal mass ejection (CME) event observed on
February 17, 1985 is studied using two-dimensional radio imaging
observations along with simultaneously obtained coronagraph
observations. This event shows that a slow CME can be associated
with type II and type IV radio bursts. The implications of the spatial
association of the radio bursts with the CME are discussed. It is argued
that the CME is due to an instability of the large-scale magnetic
field in a helmet streamer and that the radio bursts are some of the
responses to this instability. The new feature of this event is the
clear association of the moving type IV burst with a CME traveling
slower than the coronal Alfven speed. The structure of slow shocks
driven by such a CME is discussed, and it is shown that shock drift
and diffusive acceleration are ineffective. An acceleration mechanism
involving current-driven lower hybrid waves is proposed.
---------------------------------------------------------
Title: Evidence for Noise Storm Emission by Superthermal Particles
During a Filament Eruption
Authors: Gopalswamy, N.; Kundu, M. R.
1989BAAS...21.1146G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio Observations of Coronal Changes
Authors: Kundu, M. R.; Gopalswamy, N.
1989BAAS...21.1145K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1989BAAS...21.1145T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The First Interferometric Observations with Arc-Second
Resolution of Solar Radio Bursts at Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.
1989BAAS...21..861K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Meter Wave Radio Signatures of Slow CME's and Coronal Streamer
Evolution
Authors: Kundu, M. R.; Gopalswamy, N.
1989BAAS...21R.857K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radioheliograph and White-Light Coronagraph Studies of a
Coronal Mass Ejection Event
Authors: Gopalswamy, N.; Kundu, M. R.
1989SoPh..122..145G Altcode:
We analyze the radioheliograph and SMM-C/P observations of 1986 November
3 mass ejection event. The metric radio emissions are the only detected
activity associated with the mass ejection, but are adequate to study
the evolution of the event. The start time of the ejection seems to
precede a possible flare behind the limb indicated by the early type
III bursts. We discuss the physical relation between various types of
bursts and the CME. We interpret moving type IV bursts as a plasma
emission process. It is also shown using white-light coronagraph
data that the density in the source region of the moving type IV is
sufficient to support second harmonic plasma emission at the observed
frequency of 50 MHz.
---------------------------------------------------------
Title: Interpretation of Multiwavelength Observations of Solar Active
Regions Obtained During CoMStOC
Authors: Brosius, J. W.; Holman, G. D.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. R. L.; Willson, R.
1989BAAS...21..838B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio and Optical Observations of Moving Magnetic Structures
in the Solar Corona
Authors: Gopalswamy, N.; Kundu, M. R.
1989BAAS...21..857G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous Microwave and Soft X-ray Observations of Active
Regions at the Solar Limb
Authors: Nitta, N.; White, S.; Kundu, M.; Gopalswamy, N.; Holman,
G.; Brosius, J.; Schmelz, J.; Saba, J.; Strong, K.
1989BAAS...21..828N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Sun at the VLA's Meter and Decimeter Wavelengths
Authors: White, S. M.; Gopalswamy, N.; Kundu, M. R.
1989BAAS...21..861W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Slowly Moving Plasmoid Associated with a Filament Eruption
Authors: Gopalswamy, N.; Kundu, M. R.
1989SoPh..122...91G Altcode:
We report the imaging observations of a slowly moving type IV burst
associated with a filament eruption. This event was preceded by weak
type III burst activity and was accompanied by a quasi-stationary
continuum that persisted for several hours. The starting times and
speeds of moving type IV burst and the erupting filament are nearly
the same, implying a close physical relation between the two. The
moving type IV burst is interpreted as gyrosynchrotron emission from
a plasmoid containing a magnetic field of ∼1-2 G and nonthermal
electrons of density ∼10<SUP>5</SUP>-10<SUP>6</SUP> cm<SUP>−3</SUP>
with a relatively low average energy of ∼50 keV.
---------------------------------------------------------
Title: Recent results of meter-decameter wave observations of
solar flares.
Authors: Gopalswamy, N.; Kundu, M. R.
1989sasf.confP.185G Altcode: 1989IAUCo.104P.185G; 1988sasf.conf..185G
The authors present recent results from meter-decameter imaging of
several classes of solar radio bursts: preflare activity in the form
of type III bursts, correlated type IIIs from distant sources, and
type II and moving type IV bursts associated with flares and CMEs.
---------------------------------------------------------
Title: Three dimensional structures of coronal streamers, holes and
CME plasmoids from multifrequency imaging observations
Authors: Kundu, M. R.; Schmahl, E. J.; Gopalswamy, N.; White, S. M.
1989AdSpR...9d..41K Altcode: 1989AdSpR...9R..41K
Throughout the quiet Sun years 1982-1987, the Clark Lake Radioheliograph
routinely mapped the solar corona on a daily basis at frequencies from
30 to 100 MHz. The Clark Lake maps show a variety of features which
we have analyzed quantitatively, providing information about the three
dimensional nature of large scale structures of the solar corona.
---------------------------------------------------------
Title: First interferometric observations with arc-sec. resolution
of solar radio bursts at millimeter wavelengths
Authors: Kundu, Mukul R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.
1989dots.work..119K Altcode:
The Berkeley-Maryland-Illinois Array (BIMA) is briefly described in
the context of solar observations. Specific areas of research that
could be performed using BIMA during the Solar Maximum Mission (SMM)
in 1991 are outlined. Some preliminary results of flare observations
during March 1989 are presented.
---------------------------------------------------------
Title: Millimeter wavelength observations of solar flares for Max 1991
Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.; Schmahl, E. J.;
White, S. M.; Welch, W. J.
1988fnsm.work..107K Altcode:
The Hat Creek millimeter-wave interferometer (to be known as the
Berkeley-Illinois-Maryland Array, BIMA) is being upgraded. The improved
array will become available during the coming solar maximum, and will
have guaranteed time for solar observing. The Hat Creek millimeter-wave
interferometer is described along with the improvements. The scientific
objectives are briefly discussed.
---------------------------------------------------------
Title: Millimeter Wavelength Observations of Solar Flares for Max'91
Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.; Schmahl, E. J.;
White, S. M.
1988BAAS...20..746K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Moving Radio Loop Structure During a Fast CME
Authors: Gopalswamy, N.; Kundu, M. R.; Hundhausen, A.
1988BAAS...20Q.682G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Slowly-Varying Observed with the Clark Lake Radioheliograph
Authors: Schmahl, E. J.; Kundu, M. R.; Gopalswamy, N.; Jackson, P. D.
1988BAAS...20..712S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Imaging observations of the evolution of meter-decameter
burst emission during a major flare.
Authors: Gopalswamy, N.; Kundu, M. R.
1987SoPh..111..347G Altcode:
We present the results of a study of the evolution of 3 February,
1986 flare at meter-decameter wavelengths using the two dimensional
imaging observations made with the Clark Lake multifrequency
radioheliograph. The flare was complex and produced various types
of meter-decameter bursts. The preflare activity was observed in the
form of type III bursts some tens of minutes prior to the impulsive
onset. From the positional analysis of the preflare and impulsive
phase type III bursts and other measured characteristics we discuss
the characteristics of energy release and possible magnetic field
configurations in the vicinity of energy release region. From positional
and temporal studies of the flare continuum and type II burst in
relation to the microwave and hard X-ray emissions, we discuss the
possible magnetic field structures in which the accelerated particles
are confined or along which they propagate. We develop a schematic
model of the flaring region based upon our study.
---------------------------------------------------------
Title: A Study of Solar Preflare Activity Using Two-Dimensional
Radio and Smm/xrp Observations
Authors: Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.; Schmelz,
J. T. S.; Strong, K. T.
1987SoPh..114..273K Altcode:
We present a study of type III activity at meter- decameter wavelengths
in the preflare phase of the 1986 February 3 flare using data obtained
with the Clark Lake Multifrequency Radioheliograph. We compare this
activity with similar type III burst activity during the impulsive
phase and find that there is a displacement of burst sources between the
onset and end times of the activity. A comparison of this displacement
at three frequencies suggests that the type III emitting electrons gain
access progressively to diverging and different field lines relative
to the initial field lines. The energetics of the type III emitting
electrons are inferred from observations and compared with those of
the associated hard X-ray emitting electrons. The soft X-ray data from
SMM-XRP shows enhanced emission measure, density and temperature in
the region associated with the preflare type III activity.
---------------------------------------------------------
Title: Fine Structures in Solar Microwave Flares
Authors: Gopalswamy, N.
1987SoPh..110..327G Altcode:
The pulsed electron acceleration and release from the energy release
volume in solar flares implies that there is a possibility of
interaction between a group of electrons reflected from the foot
of a bipolar flux tube with a newly injected beam. It is shown
that interaction can lead to the stoppage of the synchrotron maser
instability caused by the loss cone distribution and hence can produce
further millisecond fine structures in the solar microwave bursts.
---------------------------------------------------------
Title: Simultaneous radio and white light observations of the 1984
June 27 coronal mass ejection event
Authors: Gopalswamy, N.; Kundu, M. R.
1987SoPh..114..347G Altcode:
We present the two-dimensional imaging observations of radio bursts in
the frequency range 25-50 MHz made with the Clark Lake multifrequency
radioheliograph during a coronal mass ejection event (CME) observed
on 1984, June 27 by the SMM Coronagraph/Polarimeter and Mauna Loa
K-coronameter. The event was spatially and temporally associated
with precursors in the form of meter-decameter type III bursts, soft
X-ray emission and a Hα flare spray. The observed type IV emission
in association with the CME (and the Hα spray) could be interpreted
as gyrosynchrotron emission from a plasmoid containing a magnetic
field of ∼2.5 G and nonthermal electrons with a number density of
∼ 10<SUP>5</SUP> cm<SUP>−3</SUP> and energy ≳350 keV.
---------------------------------------------------------
Title: Two dimensional imaging observations of meter-decameter bursts
associated with the February 1986 flare activity
Authors: Gopalswamy, N.; Kundu, M. R.
1987sici.symp...16G Altcode:
An analysis is presented of the two dimensional imaging observations
of a flare observed on 3 Feb. l986 using the Clark Lake Multifrequency
Radioheliograph. The flare produced almost all types of Meter-decimeter
radio emission: enhanced storm radiation, type III/V bursts, II and
IV and flare continuum. The flare continuum had early (FCE) and late
(FC II) components and the type II occurred during the period between
these two components. Comparing the source positions of type III/V and
FCE it was found that these bursts must have occurred along adjacent
open and closed field lines, respectively. The positional analysis of
type II and FC II implies that the nonthermal electrons responsible for
FC II need not be accelerated by type II shock and this conclusion is
further supported by the close association of FC II with a microwave
peak. Using the positional and temporal analysis of all these bursts
and the associated hard X-ray and microwave emissions, a schematic
model is developed for the magnetic field configuration in the flaring
region in which the nonthermal particles responsible for these bursts
are confined or along which they propagate.
---------------------------------------------------------
Title: Propagation of Electrons Emitting Weak Type-Iii Bursts in
Coronal Streamers
Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A.
1987SoPh..108..333G Altcode:
We report the observations of weak type III bursts at 73.8, 57.5, 50.0,
and 38.5 MHz from Clark Lake Radio Observatory on four days and discuss
their characteristics. In addition to Clark Lake data, the magnetogram
and sunspot/active region data and the coronal streamer data obtained
by HAO's Coronagraph/Polarimeter aboard SMM satellite are used to
study the location of the burst sources with respect to the coronal
streamers emanating from active regions. It is shown that the bursts
occur within or close to the edge of dense coronal streamers implying
that the coronal streamers contain open magnetic field lines along
which the electrons generating the bursts propagate. The positional
analysis of the bursts is used to estimate the variation of coronal
electron density with radial distance.
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Title: Correlated Type-Iii Burst Emission from Distant Sources on
the Sun
Authors: Kundu, M. R.; Gopalswamy, N.
1987SoPh..112..133K Altcode:
We report the observation and interpretation of a correlated type III
burst emitted from distant sources on the Sun. The angular separation
between the distant sources is as large as 26' or ∼ 10<SUP>6</SUP>
km. There was an active region ∼ 30° behind the limb, and it is
believed that the type III burst emission originated from activity
in this region. The implications of the locations of the correlated
sources with regard to the geometry of the magnetic structures involved
in the flare process are discussed.
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Title: Propagation of Weak Type III Burst Electrons in Dense Coronal
Streamers
Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A.
1986BAAS...18R.900G Altcode:
No abstract at ADS
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Title: Some interesting features in the drift pair phenomena of
solar decametric radiation
Authors: Thejappa, G.; Gopalswamy, N.; Sastry, C. N.; Aubier, M. G.
1986ESASP.251..121T Altcode: 1986plas.work..121T
Observational results on drift pair (DP) chains and vertical DP bursts
in the decametric solar corona are reported. As the magnetic field in
this region is predominantly open, a free energy source propagating
sunward most of the time cannot explain the predominant reverse drift
pair chains. The appearance of the vertical chains and DPs rules out
the possibility of an agency moving in the corona causing the observed
drift. Observations support the idea that the resonance layer in which
the radiation is generated is different at different instants of time
so that one gets a slope in the frequency-time plane. If considerable
fluctuations in macroscopic parameters are assumed, it is possible
to have drifts of all directions as the drift rate depends upon the
medium in which the fluctuations occur. It is shown that the magnetic
field decreases steeply if the density of the medium is not affected
by the DP activity when the frequency drift is very high.
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Title: A Theory of Jovian Shadow Bursts
Authors: Gopalswamy, N.
1986EM&P...35...93G Altcode:
The shadow events in the dynamic spectra of Jovian decametric emission
are explained as the result of interaction between electron bunches
responsible for S and L emissions. The relevant dispersion relation
is derived for the fast extraordinary mode in the cold magnetospheric
plasma in the presence of S and L electron bunches. The growth rate
of the synchrotron maser instability is studied in the presence
and absence of S-electrons. It is shown that the synchrotron maser
instability responsible for L-emission can be temporarily quenched
by the invasion of S-electrons, thereby stopping the L-emission. The
theory accounts for various observed features of the shadow events.
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Title: Estimation of Coronal Magnetic Fields Using Type-I Emission
Authors: Gopalswamy, N.; Thejappa, G.; Sastry, Ch. V.; Tlamicha, A.
1986BAICz..37..115G Altcode:
The radial dependence of the coronal magnetic field above active
regions is calculated using Type-I chain data existing in the
literature. Assuming that Type-I emission is due to shock waves, the
upstream shock velocity and the density jump across the shock are
obtained respectively from the drift rate and the bandwidth of the
Type-I chains. Making use of the shock velocity and the density jump
in the Rankine-Hugoniot relation, the Alfvén velocity and hence the
magnetic field in the corona is calculated. The results are compared
with existing estimates.
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Title: Notes and News
Authors: Gopalswamy, N.; Krishan, V.; Tarter, Jill C.
1986BASI...14...56G Altcode:
No abstract at ADS
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Title: Type-I solar radio bursts.
Authors: Gopalswamy, N.
1986KodOB...6...77G Altcode:
A brief review of the recent work done on Type-I radio emission in the
Indian Institute of Astrophysics is presented. The most plausible low
frequency turbulence needed to generate the Type-I bursts is shown to
be ion-sound turbulence. A method is presented to evaluate the coronal
magnetic field using Type-I radio emission data.
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Title: Estimation of coronal magnetic fields using solar type I
radio emission.
Authors: Gopalswamy, N.; Thejappa, G.; Sastry, C. V.
1985BASI...13...81G Altcode:
No abstract at ADS
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Title: Ion-sound turbulence due to shock gradients in collisionless
plasmas.
Authors: Gopalswamy, N.; Thejappa, G.
1985Prama..25..575G Altcode:
No abstract at ADS
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Title: Second Indo-US workshop on solar-terrestrial physics.
Authors: Gopalswamy, N.
1984BASI...12..324G Altcode:
Report on the second Indo-US workshop on solar-terrestrial physics, held
1984 January 30 - February 3 at National Physical Laboratory, New Delhi.
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Title: Notes and News
Authors: Padmanabhan, T.; Kembhavi, A.; Bhaysar, S. P.; Bhattacharya,
D.; Gopalswamy, N.
1984BASI...12..319P Altcode:
Report on the IAGRG XII meeting held at the University of Poona,
1983 November 9 - 12.
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Title: Narrow-band, short duration radio bursts at decameter
wavelengths andtheir interpretation.
Authors: Gopalswamy, N.; Thejappa, G.; Subramanian, K. R.; Sastry,
C. V.
1984BASI...12...75G Altcode:
No abstract at ADS
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Title: An interpretation of decametric absorption bursts
Authors: Gopalswamy, N.; Thejappa, G.; Sastry, Ch. V.
1984stp..conf..197G Altcode:
No abstract at ADS
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Title: Observations on the Fine Structures in Solar Decametric
Radio Emission
Authors: Gopalswamy, N.; Thejappa, G.; Sastry, C. V.
1984KodOB...4...47G Altcode:
The solar decametric radio emission consists of a variety of fine
structures. This reflects the complexity of the corona at this
level. Two observations viz. absorption bursts and short duration
narrow band bursts are presented. An interpretation of each of these
observations is provided.
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Title: Fine structure in solar decametric radiation
Authors: Thejappa, G.; Sastry, Ch. V.; Gopalswamy, N.
1984ntpp.proc..547T Altcode:
Observations and interpretations of some of the fine structure in
decametric solar radio emission - such as (1) the time structure of
type III bursts, (2) absorption bursts, and (3) slowly drifting spikes
- are presented. Physical parameters such as the electron temperature,
the characteristics of collisionless shocks, and the coronal magnetic
field - are estimated.
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Title: Observations and interpretation of solar decametric absorption
bursts.
Authors: Gopalswamy, N.; Thejappa, G.; Sastry, Ch. V.
1983JApA....4..215G Altcode:
The observations of intensity reductions or absorption bursts in
the solar decametric radio-continuum are reported. The reductions
are interpreted as the absorption of continuum radiation by a
shock-generated ion sound turbulence present in the layer above the
continuum level. The duration of the absorption is attributed to the
life-time of the ion-sound turbulence while the depth of absorption
is determined by the level of Langmuir waves generated as a result
of absorption.
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Title: Absorption of intense electromagnetic beams in a magnetoplasma.
Authors: Gopalswamy, N.; Krishan, V.
1980Ap&SS..73..179G Altcode:
The multiphoton inverse bremsstrahlung absorption of two intense
electromagnetic beams passing through a magnetized plasma is
studied. The rate of absorption of electromagnetic energy by
the electrons is calculated by deriving a kinetic equation for
the electrons. It is found that the absorption enhances when the
frequency of one electromagnetic beam is more, and that of the other
electromagnetic beam is less, than the electron-cyclotron frequency. A
possible application to extragalactic radio sources is discussed.