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Author name code: vourlidas
ADS astronomy entries on 2022-09-14
author:"Vourlidas, Angelos"
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Title: Extracting the Heliographic Coordinates of Coronal Rays using
Images from WISPR/Parker Solar Probe
Authors: Liewer, P. C.; Qiu, J.; Ark, F.; Penteado, P.; Stenborg,
G.; Vourlidas, A.; Hall, J. R.; Riley, P.
2022arXiv220902779L Altcode:
The Wide-field Imager for Solar Probe (WISPR) onboard Parker Solar
Probe (PSP), observing in white light, has a fixed angular field
of view, extending from 13.5 degree to 108 degree from the Sun and
approximately 50 degree in the transverse direction. In January 2021,
on its seventh orbit, PSP crossed the heliospheric current sheet (HCS)
near perihelion at a distance of 20 solar radii. At this time, WISPR
observed a broad band of highly variable solar wind and multiple coronal
rays. For six days around perihelion, PSP was moving with an angular
velocity exceeding that of the Sun. During this period, WISPR was able
to image coronal rays as PSP approached and then passed under or over
them. We have developed a technique for using the multiple viewpoints
of the coronal rays to determine their location (longitude and latitude)
in a heliocentric coordinate system and used the technique to determine
the coordinates of three coronal rays. The technique was validated by
comparing the results to observations of the coronal rays from Solar
and Heliophysics Observatory (SOHO) / Large Angle and Spectrometric
COronagraph (LASCO)/C3 and Solar Terrestrial Relations Observatory
(STEREO)-A/COR2. Comparison of the rays' locations were also made with
the HCS predicted by a 3D MHD model. In the future, results from this
technique can be used to validate dynamic models of the corona.
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Title: Overview of the Remote Sensing Observations from PSP Solar
Encounter 10 with Perihelion at 13.3 R <SUB>⊙</SUB>
Authors: Howard, Russell A.; Stenborg, Guillermo; Vourlidas, Angelos;
Gallagher, Brendan M.; Linton, Mark G.; Hess, Phillip; Rich, Nathan
B.; Liewer, Paulett C.
2022ApJ...936...43H Altcode: 2022arXiv220712175H
The closest perihelion pass of Parker Solar Probe (PSP), so far,
occurred between 2021 November 16 and 26 and reached ~13.29 R
<SUB>☉</SUB> from Sun center. This pass resulted in very unique
observations of the solar corona by the Wide-field Instrument for Solar
PRobe (WISPR). WISPR observed at least 10 coronal mass ejections (CMEs),
some of which were so close that the structures appear distorted. All
of the CMEs appeared to have a magnetic flux rope (MFR) structure, and
most were oriented such that the view was along the axis orientation,
revealing very complex interiors. Two CMEs had a small MFR develop in
the interior, with a bright circular boundary surrounding a very dark
interior. Trailing the larger CMEs were substantial outflows of small
blobs and flux-rope-like structures within striated ribbons, lasting
for many hours. When the heliospheric plasma sheet was inclined,
as it was during the days around perihelion on 2021 November 21, the
outflow was over a very wide latitude range. One CME was overtaken
by a faster one, with a resultant compression of the rear of the
leading CME and an unusual expansion in the trailing CME. The small
Thomson surface creates brightness variations of structures as they
pass through the field of view. In addition to this dynamic activity,
a brightness band from excess dust along the orbit of asteroid/comet
3200 Phaethon is also seen for several days.
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Title: Defining the Middle Corona
Authors: West, Matthew J.; Seaton, Daniel B.; Wexler, David B.;
Raymond, John C.; Del Zanna, Giulio; Rivera, Yeimy J.; Kobelski,
Adam R.; DeForest, Craig; Golub, Leon; Caspi, Amir; Gilly, Chris R.;
Kooi, Jason E.; Alterman, Benjamin L.; Alzate, Nathalia; Banerjee,
Dipankar; Berghmans, David; Chen, Bin; Chitta, Lakshmi Pradeep; Downs,
Cooper; Giordano, Silvio; Higginson, Aleida; Howard, Russel A.; Mason,
Emily; Mason, James P.; Meyer, Karen A.; Nykyri, Katariina; Rachmeler,
Laurel; Reardon, Kevin P.; Reeves, Katharine K.; Savage, Sabrina;
Thompson, Barbara J.; Van Kooten, Samuel J.; Viall, Nicholeen M.;
Vourlidas, Angelos
2022arXiv220804485W Altcode:
The middle corona, the region roughly spanning heliocentric altitudes
from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential
physical transitions and processes that govern the behavior of
coronal outflow into the heliosphere. Eruptions that could disrupt
the near-Earth environment propagate through it. Importantly, it
modulates inflow from above that can drive dynamic changes at lower
heights in the inner corona. Consequently, this region is essential
for comprehensively connecting the corona to the heliosphere and for
developing corresponding global models. Nonetheless, because it is
challenging to observe, the middle corona has been poorly studied by
major solar remote sensing missions and instruments, extending back to
the Solar and Heliospheric Observatory (SoHO) era. Thanks to recent
advances in instrumentation, observational processing techniques,
and a realization of the importance of the region, interest in the
middle corona has increased. Although the region cannot be intrinsically
separated from other regions of the solar atmosphere, there has emerged
a need to define the region in terms of its location and extension
in the solar atmosphere, its composition, the physical transitions
it covers, and the underlying physics believed to be encapsulated by
the region. This paper aims to define the middle corona and give an
overview of the processes that occur there.
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Title: The Low-Corona Evolution of Coronal Mass Ejections: Solar
Truth and Implications for Stellar Coronal Mass Ejections
Authors: Patsourakos, Spiros; Vourlidas, Angelos; Balmaceda, Laura
2022cosp...44.1407P Altcode:
Once a Coronal Mass Ejection (CME) is underway, it sparks a variety
of phenomena in the low corona including dimmings, waves and
shocks. An important finding of multi-viewpoint and high-cadence
imaging observations of the initial stages of CMEs from STEREO and
SDO is that they evolve differently in the lateral compared to the
radial direction. The CME lateral expansion in the low corona is of
particular interest to solar-stellar studies because it occurs in the
region that dominates the emission in stellar observations, and triggers
wave and shock phenomena. With this presentation we will discuss: i)
basic observational aspects of the lateral expansion of CMEs in the
solar corona, and ii) how these may contribute to the hunt for stellar
CMEs. We will show how our understanding of the low lateral expansion
of CMEs in the solar corona may help into deciphering and eventually
modeling of the light-curves of dimmings presumably associated with
stellar CMEs.
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Title: 4π Heliospheric Observing System - 4π-HeliOS: Exploring
the Heliosphere from the Solar Interior to the Solar Wind
Authors: Raouafi, Nour E.; Gibson, Sarah; Ho, George; Laming,
J. Martin; Georgoulis, Manolis K.; Szabo, Adam; Vourlidas, Angelos;
Mason, Glenn M.; Hoeksema, J. Todd; Velli, Marco; Berger, Thomas;
Hassler, Donald M.; Kinnison, James; Viall, Nicholeen; Case, Anthony;
Newmark, Jeffrey; Lepri, Susan; Krishna Jagarlamudi, Vamsee; Raouafi,
Nour; Bourouaine, Sofiane; Vievering, Juliana T.; Englander, Jacob A.;
Shannon, Jackson L.; Perez, Rafael M.; Chattopadhyay, Debarati; Mason,
James P.; Leary, Meagan L.; Santo, Andy; Casti, Marta; Upton, Lisa A.
2022cosp...44.1530R Altcode:
The 4$\pi$ Heliospheric Observing System (4$\pi$-HeliOS) is an
innovative mission concept study for the next Solar and Space
Physics Decadal Survey to fill long-standing knowledge gaps in
Heliophysics. A constellation of spacecraft will provide both remote
sensing and in situ observations of the Sun and heliosphere from a
full 4$\pi$-steradian field of view. The concept implements a holistic
observational philosophy that extends from the Sun's interior, to the
photosphere, through the corona, and into the solar wind simultaneously
with multiple spacecraft at multiple vantage points optimized for
continual global coverage over much of a solar cycle. The mission
constellation includes two spacecraft in the ecliptic and two flying as
high as $\sim$70$^\circ$ solar latitude. 4$\pi$-HeliOS will provide
new insights into the fundamental processes that shape the whole
heliosphere. The overarching goals of the 4$\pi$-HeliOS concept are
to understand the global structure and dynamics of the Sun's interior,
the generation of solar magnetic fields, the origin of the solar cycle,
the causes of solar activity, and the structure and dynamics of the
corona as it creates the heliosphere. The mission design study is
underway at the Johns Hopkins Applied Physics Laboratory Concurrent
Engineering Laboratory (ACE Lab), a premier mission design center,
fostering rapid and collaborative mission design evolutions.
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Title: Parker Solar Probe Observations of Near-Sun 3He-rich Solar
Energetic Particle Events
Authors: Leske, Richard; Roelof, Edmond; Davis, Andrew; Mitchell,
Donald; Cohen, Christina; Labrador, Allan; Cummings, A. C.; McNutt,
Ralph; Stone, E. C.; Hill, Matthew; De Nolfo, Georgia; Matthaeus,
William; Christian, Eric; Macdowall, Robert; Schwadron, Nathan;
Giacalone, Joe; Bale, Stuart; Desai, Mihir; Mewaldt, Richard;
Vourlidas, Angelos; Wiedenbeck, Mark; Szalay, Jamey; McComas, David;
Pulupa, Marc; Mitchell, John Grant; Joyce, Colin; Rankin, Jamie
2022cosp...44.1443L Altcode:
On 21 January 2021, just after Parker Solar Probe's 7th solar perihelion
while at $\sim$0.18 AU, the EPI-Hi instrument in the Integrated Science
Investigation of the Sun (IS$\Theta$IS) instrument suite observed two
tiny, very anisotropic solar energetic particle (SEP) events that were
highly enriched in $^{3}$He. In both events at $\sim$1 MeV/nucleon, the
$^{3}$He intensity exceeded the proton intensity. The $^{3}$He/$^{4}$He
ratio exceeded 10, but dropped rapidly at higher energies and also was
below 1 in EPI-Lo between $\sim$0.1 and 0.4 MeV/nucleon. The spectra
of both $^{3}$He and $^{4}$He were power laws in EPI-Hi, with $^{3}$He
softer than $^{4}$He, so if this had continued down to lower energies
$^{3}$He should have greatly exceeded $^{4}$He in EPI-Lo. Instead, the
lack of a detected $^{3}$He/$^{4}$He enhancement in EPI-Lo indicates
that either the $^{3}$He spectrum or the $^{4}$He spectrum or both
changed at lower energies, perhaps suggesting that the $^{3}$He spectrum
was curved as has been reported in other $^{3}$He-rich events at 1
AU. Type III radio emission was observed by the PSP/FIELDS instrument in
association with both of these events. Since PSP was $\sim$120$^\circ$
west of the Earth-Sun line and directly behind the Sun from STEREO, the
solar source region was unseen. We present PSP observations of the H and
He time profiles, spectra, composition, and anisotropies of these events
and compare them with earlier $^{3}$He-rich events observed near 1 AU.
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Title: Deciphering the Genesis of Coronal Mass Ejections and Shock
Waves in the Low Corona
Authors: Balmaceda, Laura; Vourlidas, Angelos; Kwon, Ryun Young;
Stenborg, Guillermo
2022cosp...44.2428B Altcode:
We study the formation and 3D evolution of fast Coronal Mass
Ejections (CMEs) and their associated waves in the low corona
via a detailed multi-viewpoint analysis of extreme ultraviolet
observations. We carefully separate the erupting magnetic structure
from the surrounding wave and analyze the kinematics in the radial and
lateral directions. Our analysis reveals three stages in the early
evolution of the CME: (1) the hyper-inflation stage, when the CME
laterally expands at speeds of ~1000 km/s, (2) followed by a shorter
and slower expansion stage of a few minutes and (3) ending with a
self-similar phase that carries the CME into the middle corona. The
first two stages coincide with the impulsive phase of the accompanying
X-ray flare, the formation and separation of an EUV wave from the CME
and the start of the metric type-II radio burst. Although detected in
previous analyses, the hyper-inflation phase has received relatively
little attention. Our 3D analysis suggests that it may be a crucial
stage in the CME formation with wide-ranging implications for solar
eruption research. The hyper-inflation phase likely represents the
formation stage of the magnetic structure that is eventually ejected
into the corona, as the white light CME. It appears to be driven by
the injection of poloidal flux into the ejecting magnetic structure,
which leads to the lateral (primarily) growth of the magnetic flux
rope (MFR). The rapid growth results in the creation of EUV waves and
eventually shocks at the CME flanks. The coronal shocks are detected as
metric type-II radio bursts. In other words, the hyper-inflation stage
in the early CME evolution may be the 'missing' link between CMEs,
flares, and coronal shocks.
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Title: COSPAR Roadmap update from the ISWAT clusters H1 and 2
Authors: Temmer, Manuela; Richardson, Ian G.; Vourlidas, Angelos; Bisi,
Mario M.; Scolini, Camilla; Heinemann, Stephan; Paouris, Evangelos
2022cosp...44.3523T Altcode:
We present the COSPAR Roadmap update paper from the ISWAT clusters
H1 and 2. These two clusters are focused on interplanetary space and
its dynamic features such as stream interaction regions and coronal
mass ejections, the major drivers of space weather. The interplay
between these phenomena changes the structure of interplanetary space
on various temporal and spatial scales and effects the propagation
behavior of individual events. The limitations of observational data
and current models lead to large uncertainties in our understanding
of solar wind structures, making reliablespace weather forecasts
difficult. The solar wind also becomes more complex as solar activity
increases. We discuss the current understanding of dynamic changes in
interplanetary space, indicate the caveats related to data and models,
and provide recommendations for future studies.
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Title: High-sensitivity ultra-compact Lyman-alpha Spectrometer
Authors: Hosseini, Sona; Vourlidas, Angelos; Vievering, Juliana T.
2022cosp...44.1178H Altcode:
We present the results of developing the Compact Lyman-alpha Spatial
heterodyne Spectrometer (CLASS) based on an interferometric technology
called Spatial Heterodyne Spectrometer (SHS) to obtain ultra-high
sensitivity data from angularly extended and diffused targets such as
the solar corona. The measurement approach aims to detect deviations of
the line profile wings from its nominal Gaussian profile, as evidence
of a suprathermal proton population in the extended solar corona. The
science objectives that can be addressed by the development of this
measurement capability are Q.1) Do proton seed particles exist in
the inner corona, where CME shocks may form? Q.2) How does the seed
particle abundance vary with time? Q.3) How does the presence of seed
particles relate to SEP production? Current investigations to study
these questions are accomplished by large instruments with considerable
demands on spacecraft resources (mass, power, volume). The low-mass,
compact configuration of CLASS enables sensitive, high-resolution
spectroscopy for SmallSat missions. CLASS is configured to target the
H I Lyα line at 1216Å but in the future CLASS is configurable for a
variety of spectral lines with a very narrow bandpass anywhere from the
FUV to the visible region. For that reason, our concept is applicable
to more than one mission and is capable of meeting multiple science
objectives onboard SmallSats or larger spacecraft.
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Title: The impact of virtual mass and magnetic erosion on the
propagation of fast ICMEs
Authors: Stamkos, Sotiris; Patsourakos, Spiros; Daglis, Ioannis A.;
Vourlidas, Angelos
2022cosp...44.1406S Altcode:
In order to enhance our understanding of the dynamic interactions of
Interplanetary Coronal Mass Ejections (ICMEs) with the solar wind
and interplanetary magnetic field, we investigate the effect of
magnetic erosion on the well-known aerodynamic drag force acting on
ICMEs. In particular, we generate empirical equations for the basic
parameters of an ICME assuming a cylindrical morphology. Furthermore,
we examine the impact of the virtual mass on the equation of motion
by essentially studying a variable mass system. We quantify the
effect of the reconnection process, which erodes part of the ICME's
magnetic flux and outer-shell mass, on the drag acting on ICMEs and,
eventually, we determine its impact on the time and speed of arrival
of those transients at 1 AU.
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Title: The Solar 'Yardstick': What Can the Sun Teaches us About
Stellar Eruptions
Authors: Vourlidas, Angelos
2022cosp...44.1403V Altcode:
The Sun-Earth system holds a special place in astrophysics. As
the only known inhabited planetary system where stellar-planetary
interactions cab be studied in detail, it forms the foundation for
understanding exoplanetary environments, and by extension, assessing
their habitability. Explosive energy release in the form of solar flares
and coronal mass ejections (CMEs) comprise the two major drivers of
space weather for the inner planets. In the last 50 years, we have
learned a great deal about the nature of solar eruptions. Can we use
this knowledge to understand stellar activity or assess the habitability
of exoplanet environments? In this review, I summarize our current
knowledge of the properties of flares and CMEs and how it is used to
estimate the eruptive activity of there stars. I look into the obvious
question on whether the solar observation can be used as a reliable
yardstick, discuss the constraints and offer some ideas for discussion
on how to move forward.
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Title: On the Structure of the Zodiacal Cloud in the Inner Heliosphere
Authors: Howard, Russell; Vourlidas, Angelos; Stenborg, Guillermo
2022cosp...44.1018H Altcode:
Images from the STEREO/SECCHI/HI-1 heliospheric imager (launched in
2006) and the PSP/WISPR (launched in 2018) have been used to update and
extend the historical observations of the zodiacal light (ZL), (e.g.,
Leinert et al 1981). We will discuss the findings from a series of
recent papers giving the following results from the SECCHI and WISPR
observations: (1) Constancy of the intensity of the symmetry axis
of the ZL; (2) Extension of the exponent of the radial profile from
-2.3 to -2.31 down to ~0.1 AU; (3) Confirmation of a slight increase
in the slope approaching the Sun; (4) Observation of the dependence
of the inclination and ascending node on heliocentric distance;
(5) Center of the Zodiacal Cloud offset toward the barycenter; (6)
Determination of the shape of the ZL as a function of heliocentric
distance; (7) Discovery of dust in or near the orbit of Mercury;
(8) Discovery of dust in or near the entire orbit of Venus; (9)
Determination of a dust depletion zone beginning at 19 Rsun; (10)
Determination of the dust free zone beginning at about 5 Rsun.
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Title: On modeling ICME cross sections as static MHD columns
Authors: Bhattacharjee, Debesh; Nieves-Chinchilla, Teresa; Bothmer,
Volker; Subramanian, Prasad; Vourlidas, Angelos
2022cosp...44.1376B Altcode:
Solar coronal mass ejections (CMEs) are observed to expand during
their propagation through the solar wind. However, their cross-sections
are usually modeled as static plasma columns within the framework of
magnetohydrodynamics (MHD). In this study, we test the validity of
this approach using in-situ plasma data from 151 magnetic clouds
(MCs) observed by the WIND spacecraft and 45 observed by the
Helios spacecrafts. We find that the most probable cross-section
expansion speeds for the WIND events are only $\approx 0.06$ times
the Alfvén speed inside the MCs while the most probable cross-section
expansion speeds for the Helios MCs is $\approx 0.03$. Hence, the MC
cross-sections can be considered approximately static over an Alfvén
crossing timescale. Using estimates of electrical conductivity arising
from Coulomb collisions, we find that the Lundquist number inside MCs is
high ( $\approx 10^{13}$), suggesting that the MHD description is well
justified. The Joule heating rates using our conductivity estimates
are several orders of magnitude lower than the requirement for plasma
heating inside MCs at 1 AU. The low heating rates are consistent
with the MHD description which assumes no dissipation. However, the
discrepancy with the heating requirement suggests possible departures
from MHD and the need for a better understanding of plasma heating
inside MCs.
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Title: State-of-the-art modelling of CMEs kinematics utilizing
heliospheric imagers: Challenges and Perspectives
Authors: Paouris, Evangelos; Vourlidas, Angelos; Papaioannou,
Athanasios; Anastasiadis, Anastasios
2022cosp...44.1375P Altcode:
The interplanetary coronal mass ejections (ICMEs) are the main drivers
of the most intense geomagnetic storms. These events could also produce
space radiation storms as they can accelerate energetic particles which
are dangerous especially for astronauts in orbit. Nowadays, where the
planned manned missions to Moon are a reality, the early and accurate
forecast of the arrival and impact of ICMEs in a specific place in the
heliosphere is a necessity for the success of such missions. We present
the state-of-the-art modelling of CME kinematics utilizing heliospheric
imagers. Our approach is simple and at the same time reasonable:
(1) all the fast (slow) CMEs are decelerating (accelerating) from the
Sun up to some distance and (2) they move with a constant speed past
that distance. The core of our algorithm is based on this "two-phase
kinematics" behavior. We transform the elongation angle of CME's
front into radial distance utilizing basic stereoscopic techniques
(i.e. fixed-phi, harmonic mean, and self-similar expansion). Then we
use our algorithm to create kinematic profiles for each case to provide
two basic results: the Time-of-Arrival (ToA) and the Speed-on-Arrival
(SoA) of ICMEs. We test our methodology in a sample of 50 Earth-directed
CMEs/ICMEs with promising results as the predictions for the ToA for
almost 60% of our sample has an error ($\Delta$t) for ToA of the order
of $\pm$5 hours and for SoA of $\pm$100 km/s. In particular, 80% of
these cases has an absolute error less than 55 minutes. We further
discuss the challenges and the limitations of our methodology and
the perspectives of our work such as: a) the development of a near
real-time space weather forecasting tool for CME propagation as soon
as L5 data will be available and b) the first attempt for forecasts
at the orbit of Mars.
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Title: The Characteristics of Magnetic Flux Ropes in the Low and
Middle Corona
Authors: Vourlidas, Angelos
2022cosp...44.2430V Altcode:
The magnetic structure of Coronal Mass Ejections (CMEs) holds
vital information for understanding explosive energy release from
the Sun. Theory and simulations predict that a magnetic flux rope
structure (MFR) should be the core structure of all CMEs. Visible
light coronagraph observations have been offering tantalizing hints
that such structure exists within CMEs for decades. More recently,
MFR-like structures have been detected in EUV observations of the low
corona. Yet, such signatures are not as ubiquitous as theory seems
to suggest. Is this (apparent) discrepancy an observational effect or
does it imply a gap in our physical understanding of explosive energy
release? In this talk, I will explore this questions by reviewing the
current state of observations of MFRs in the low and middle corona
and discuss the implications for understanding CME images and how we
can now create a common picture among CMEs, flux ropes, interplanetary
CMEs and magnetic clouds.
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Title: Extracting characteristics of interplanetary CMEs from database
of synthetic white-light images based on ensemble MHD simulations
Authors: Provornikova, Elena; Gibson, Sarah; Wiltberger, Michael;
Dalmasse, Kévin; Merkin, Viacheslav; Malanushenko, Anna; Vourlidas,
Angelos; Arge, Charles
2022cosp...44.2433P Altcode:
In this work, we investigate to what extent properties of CMEs
determined from synthetic white light images represent properties of
simulated interplanetary CMEs. The propagation of an interplanetary CME
with an internal flux rope is modeled with the GAMERA global model of
the inner heliosphere (0.1- 1 AU) coupled with the Gibson-Low (G&L)
model of a self-similarly expanding CME with an internal magnetic
field. The solar wind background in the inner heliosphere is driven
by the Wang-Sheeley-Arge (WSA)-ADAPT corona solution. An ensemble of
CME simulations is created by setting different input parameters of a
CME flux rope in the G&L model (e.g., magnetic field topology and
magnetic field strength, angular width, speed, orientation, latitude,
and longitude). A set of values for each of the defining G&L
parameters are taken from statistical distributions obtained from
an analysis of white light CME imagery near the Sun. To set the CME
magnetic structure we choose four topologies allowed by the G&L
model: spheromak, tethered spheromak, flux rope, and magnetic arcade. We
run an ensemble of a few hundred MHD simulations of interplanetary CMEs
with internal flux rope. The ensemble is used to produce a database of
synthetic CME images in white-light total brightness. We use the CACTUS
package to autonomously detect CMEs in synthetic white light images and
determine CME angular width and variations of CME velocity, mass, and
trajectory during the interplanetary CME propagation. We then compare
results from CACTUS with the ground truth data extracted directly from
MHD simulation output. We analyze cases showing a disagreement between
the true and inferred properties in more detail.
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Title: The view of the corona from within the Alfven surface
Authors: Howard, Russell; Liewer, Paulett; Linton, Mark; Vourlidas,
Angelos; Hess, Phillip; Stenborg, Guillermo; Rich, Nathan; Gallagher,
Brendan
2022cosp...44.1446H Altcode:
Since its launch in August, 2018, the Parker Solar Probe (PSP) has
used five close fly-bys of Venus to gradually reduce its perihelion
distance from the initial perihelion of 35 Rsun on 5 November, 2018 to
the lowest perihelion of 13.3 Rsun achieved on 21 November 2021 in Orbit
10. This perihelion will be the same for the next seven orbits. The
Orbit 10 perihelion pass occurred from 16 to 25 November 2021 and has
enabled very unique observations of the solar corona by the Widefield
Imager for Solar PRobe (WISPR). At the perihelion of 13.3 Rsun, the
WISPR field of view is 3.1 - 25 Rsun. The detailed views of the CMEs
and outflows are revealing new features including the details of the
CME flux rope, the collision and resulting interactions between a fast
CME overtaking a slower one. In addition to this dynamic activity,
enhanced scattering from dust in the orbit of asteroid/comet Phaethon
is seen for several days.
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Title: The dust environment near the Sun: Remote observations from
0.062-0.25 AU
Authors: Stenborg, Guillermo; Vourlidas, Angelos; Howard, Russell
2022cosp...44.1445S Altcode:
Visible light observations obtained by the Wide-field Imager for Solar
PRobe (WISPR) on board the Parker Solar Probe (PSP) mission provide
a unique opportunity to shed light on the dust environment near the
Sun. Our analysis of WISPR images, obtained from PSP heliocentric
distances between 13.3 - 53.7 Rsun (0.062 - 0.25 AU) over multiple
PSP orbits, shows a gradually decreasing brightness gradient along
the symmetry axis of the F-corona in coronal heights from 19 to 9
Rsun. (The field of view of WISPR inner telescope covers coronal heights
as low as 3.5 Rsun from this observer's location range). Below 9 Rsun,
the brightness gradient reverses the trend, its slope asymptotically
approaching a constant value that matches the value found for heights
beyond 19 Rsun (which agrees with the gradients' slope obtained from
observer's distances between 0.3 and 1 AU). In addition, the brightness
of the F-corona is found to be dependent on the observer's location
for coronal heights below 15 Rsun. After considering the effects of 1)
the diffuse component of the K-corona background, and 2) the presence
of discrete dust density enhancements over the background Zodiacal
dust cloud, the aggregated brightness measurements can be explained by
forward-modeling simulations of the F-corona expected brightness from
a dust cloud assuming 1) a circumsolar region of depleted dust density
between 19 and 5 Rsun and, 2) a region free of dust below 5 Rsun (i.e.,
a dust free zone or DFZ). The DFZ, a direct consequence of the DDZ,
has been postulated for almost a century. Despite numerous attempts to
detect it from as close as 0.3 AU, the DFZ has remained elusive until
now. Here, we present the observations and analysis that led to these
groundbreaking findings.
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Title: Learning about Flares and Coronal Mass Ejections from Some
of the Largest Stellar Flaring Events
Authors: Osten, Rachel; Vourlidas, Angelos; Salander, Samuel;
Norman, Colin
2022cosp...44.2447O Altcode:
We report on a coherent analysis of a set of large stellar flaring
events in the nearby universe, captured as part of the Neil Gehrels'
Swift Observatory rapid response and multi-wavelength follow-up. The
characteristics of these stellar flares (rapid increase in signal at
hard X-ray energies, multi-wavelength signatures) make the automated
response for probing gamma-ray bursts and their afterglows complementary
to understanding energy release in these extreme magnetic reconnection
events. I will present an initial study of time-resolved spectroscopy
which has two main goals: to characterize the properties of these large
flaring events in comparison and contrast with lower intensity flaring
events, and to search in the time-spectral signal for any signature
of associated transient mass loss.
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Title: When do solar erupting hot magnetic flux ropes form?
Authors: Nindos, Alexander; Zhang, Jie; Patsourakos, Spiros; Cheng,
Xin; Vourlidas, Angelos
2022cosp...44.2419N Altcode:
We investigate the formation times of eruptive magnetic flux ropes
relative to the onset of solar eruptions, which is important for
constraining models of coronal mass ejection (CME) initiation. We
inspected uninterrupted sequences of 131 A images that spanned more than
eight hours and were obtained by the Atmospheric Imaging Assembly on
board the Solar Dynamics Observatory to identify the formation times
of hot flux ropes that erupted in CMEs from locations close to the
limb. The appearance of the flux ropes as well as their evolution toward
eruptions were determined using morphological criteria. Two-thirds
(20/30) of the flux ropes were formed well before the onset of the
eruption (from 51 min to more than eight hours), and their formation
was associated with the occurrence of a confined flare. We also found
four events with preexisting hot flux ropes whose formations occurred
a matter of minutes (from three to 39) prior to the eruptions without
any association with distinct confined flare activity. Six flux ropes
were formed once the eruptions were underway. However, in three of
them, prominence material could be seen in 131 Å images, which may
indicate the presence of preexisting flux ropes that were not hot. The
formation patterns of the last three groups of hot flux ropes did not
show significant differences. For the whole population of events, the
mean and median values of the time difference between the onset of the
eruptive flare and the appearance of the hot flux rope were 151 and 98
min, respectively. Our results provide, on average, indirect support
for CME models that involve preexisting flux ropes; on the other hand,
for a third of the events, models in which the ejected flux rope is
formed during the eruption appear more appropriate.
---------------------------------------------------------
Title: Evidence of a complex structure within the 2013 August 19
coronal mass ejection. Radial and longitudinal evolution in the
inner heliosphere
Authors: Rodríguez-García, L.; Nieves-Chinchilla, T.; Gómez-Herrero,
R.; Zouganelis, I.; Vourlidas, A.; Balmaceda, L. A.; Dumbović,
M.; Jian, L. K.; Mays, L.; Carcaboso, F.; dos Santos, L. F. G.;
Rodríguez-Pacheco, J.
2022A&A...662A..45R Altcode: 2022arXiv220302713R
Context. Late on 2013 August 19, a coronal mass ejection (CME) erupted
from an active region located near the far-side central meridian
from Earth's perspective. The event and its accompanying shock were
remotely observed by the STEREO-A, STEREO-B, and SOHO spacecraft. The
interplanetary counterpart (ICME) was intercepted by MESSENGER
near 0.3 au and by both STEREO-A and STEREO-B near 1 au, which were
separated from each other by 78° in heliolongitude. <BR /> Aims: The
main objective of this study is to follow the radial and longitudinal
evolution of the ICME throughout the inner heliosphere and to examine
possible scenarios for the different magnetic flux-rope configuration
observed on the solar disk and measured in situ at the locations of
MESSENGER and STEREO-A, separated by 15° in heliolongitude, and at
STEREO-B, which detected the ICME flank. <BR /> Methods: Solar disk
observations are used to estimate the "magnetic flux-rope type",
namely, the magnetic helicity, axis orientation, and axial magnetic
field direction of the flux rope. The graduated cylindrical shell
model is used to reconstruct the CME in the corona. The analysis of
in situ data, specifically the plasma and magnetic field, is used
to estimate the global interplanetary shock geometry and to derive
the magnetic flux-rope type at different in situ locations, which
is compared to the type estimated from solar disk observations. The
elliptical cylindrical analytical model is used for the in situ magnetic
flux-rope reconstruction. <BR /> Results: Based on the CME geometry and
on the spacecraft configuration, we find that the magnetic flux-rope
structure detected at STEREO-B belongs to the same ICME detected at
MESSENGER and STEREO-A. The opposite helicity deduced at STEREO-B
might be due to that fact that it intercepted one of the legs of the
structure far from the flux-rope axis, in contrast to STEREO-A and
MESSENGER, which were crossing through the core of the magnetic flux
rope. The different flux-rope orientations measured at MESSENGER and
STEREO-A probably arise because the two spacecraft measure a curved,
highly distorted, and rather complex magnetic flux-rope topology. The
ICME may have suffered additional distortion in its evolution in the
inner heliosphere, such as the west flank propagating faster than
the east flank when arriving near 1 au. <BR /> Conclusions: This work
illustrates how a wide, curved, highly distorted, and rather complex
CME showed different orientations as observed on the solar disk and
measured in situ at 0.3 au and near 1 au. Furthermore, the work shows
how the ambient conditions can significantly affect the expansion and
propagation of the CME and ICME, introducing additional irregularities
to the already asymmetric eruption. The study also manifests how these
complex structures cannot be directly reconstructed with the currently
available models and that multi-point analysis is of the utmost
importance in such complex events. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142966/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: PSP/WISPR Observations of Dust Density Depletion near the
Sun. II. New Insights from within the Depletion Zone
Authors: Stenborg, Guillermo; Howard, Russell A.; Vourlidas, Angelos;
Gallagher, Brendan
2022ApJ...932...75S Altcode:
Visible light observations from the Wide-field Imager for Solar
PRobe (WISPR) aboard the Parker Solar Probe (PSP) mission offer a
unique opportunity to study the dust environment near the Sun. The
existence of a dust-free zone (DFZ) around stars was postulated almost
a century ago. Despite numerous attempts to detect it from as close
as 0.3 au, observational evidence of a circumsolar DFZ has remained
elusive. Analysis of WISPR images obtained from heliocentric distances
between 13.3-53.7 R <SUB>⊙</SUB> over multiple PSP orbits shows a
gradually decreasing brightness gradient along the symmetry axis of the
F-corona for coronal heights between 19 and 9 R <SUB>⊙</SUB>. Below
9 R <SUB>⊙</SUB>, the gradient reverses its trend, approaching the
radial dependence exhibited at heights above 19 R <SUB>⊙</SUB>. After
taking into account the effects of both the electron corona background
and the nonresolved starlight, the WISPR observations down to 4 R
<SUB>⊙</SUB> are consistent with forward-modeling simulations of
the F-corona brightness within [-6, 5]% if a circumsolar region of
depleted dust density between 19 and 5 R <SUB>⊙</SUB> enclosing a
DFZ is considered. In addition, we show, for the first time, that the
F-corona brightness inward of about 15 R <SUB>⊙</SUB> depends on the
observer's location for observing distances below 35 R <SUB>⊙</SUB>.
---------------------------------------------------------
Title: VizieR Online Data Catalog: 421 Forbush Decreases with
1995/2015 EPHIN/SOHO (Belov+, 2021)
Authors: Belov, A.; Papaioannou, A.; Abunina, M.; Dumbovic, M.;
Richardson, I. G.; Heber, B.; Kuhl, P.; Herbst, K.; Anastasiadis,
A.; Vourlidas, A.; Eroshenko, E.; Abunin, A.
2022yCat..19080005B Altcode:
The rigidity dependence of all Forbush Decreases (FDs) recorded from
1995 to 2015 has been determined using neutron monitor (NM) and Solar
and Heliospheric Observatory (SOHO) (EPHIN) spacecraft data, covering
the energy (rigidity) range from ~433MeV (1GV) to 9.10GeV (10GV). We
analyzed a total of 421 events and determined the spectrum in rigidity
with an inverse power-law fit. As a result, the mean spectral index
was identified to be <γF>=0.46{+/-}0.02. The majority (~66%)
of the FDs have γF within the range 0.3-0.7. The remaining one-third
of the events (~33%) have either (very) soft or hard FD spectra, with
the latter being more common than the former. Significant variations
of γF occur within almost every FD event. During the initial FD
decay phase the spectrum becomes gradually harder, in contrast to the
recovery phase, when it becomes softer. Additionally, low energies
(rigidities) seem to be better suited for studying the fine structure
of interplanetary disturbances (primarily interplanetary coronal
mass ejections) that lead to FDs. In particular, FDs recorded by the
EPHIN instrument on SOHO better capture a two-step structure than
FDs observed by NMs. Finally, the ejecta of an ICME, especially when
identified as a magnetic cloud, often leads to abrupt changes in the
slope of γF. <P />(1 data file).
---------------------------------------------------------
Title: The Hyper-inflation Stage in the Coronal Mass Ejection
Formation: A Missing Link That Connects Flares, Coronal Mass
Ejections, and Shocks in the Low Corona
Authors: Balmaceda, Laura A.; Vourlidas, Angelos; Stenborg, Guillermo;
Kwon, Ryun-Young
2022ApJ...931..141B Altcode:
We analyze the formation and three-dimensional (3D) evolution of two
coronal mass ejections (CMEs) and their associated waves in the low
corona via a detailed multi-viewpoint analysis of extreme-ultraviolet
observations. We analyze the kinematics in the radial and lateral
directions and identify three stages in the early evolution of the CME:
(1) a hyper-inflation stage, when the CME laterally expands at speeds of
~1000 km s<SUP>-1</SUP>, followed by (2) a shorter and slower expansion
stage of a few minutes and ending with (3) a self-similar phase that
carries the CME into the middle corona. The first two stages coincide
with the impulsive phase of the accompanying flare, the formation and
separation of an EUV wave from the CME, and the start of the metric
type II radio burst. Our 3D analysis suggests that the hyper-inflation
phase may be a crucial stage in the CME formation with wide-ranging
implications for solar eruption research. It likely represents the
formation stage of the magnetic structure that is eventually ejected
into the corona, as the white-light CME. It appears to be driven by the
injection of poloidal flux into the ejecting magnetic structure, which
leads to the lateral (primarily) growth of the magnetic flux rope. The
rapid growth results in the creation of EUV waves and eventually shocks
at the CME flanks that are detected as metric type II radio bursts. In
other words, the hyper-inflation stage in the early CME evolution may
be the "missing" link between CMEs, flares, and coronal shocks.
---------------------------------------------------------
Title: On Modeling ICME Cross-Sections as Static MHD Columns
Authors: Bhattacharjee, Debesh; Subramanian, Prasad; Bothmer, Volker;
Nieves-Chinchilla, Teresa; Vourlidas, Angelos
2022SoPh..297...45B Altcode: 2022arXiv220306996B
Solar coronal mass ejections are well-known to expand as they propagate
through the heliosphere. Despite this, their cross-sections are usually
modeled as static plasma columns within the magnetohydrodynamics
(MHD) framework. We test the validity of this approach using
in-situ plasma data from 151 magnetic clouds (MCs) observed by
the WIND spacecraft and 45 observed by the Helios spacecraft. We
find that the most probable cross-section expansion speeds for the
WIND events are only ≈0.06 times the Alfvén speed inside the MCs,
while the most probable cross-section expansion speeds for the Helios
events is ≈0.03 . MC cross-sections can thus be considered to be
nearly static over an Alfvén crossing timescale. Using estimates
of electrical conductivity arising from Coulomb collisions, we find
that the Lundquist number inside MCs is high (≈10<SUP>13</SUP>),
suggesting that the MHD description is well justified. The Joule
heating rates using our conductivity estimates are several orders
of magnitude lower than the requirement for plasma heating inside
MCs near the Earth. While the (low) heating rates we compute are
consistent with the MHD description, the discrepancy with the heating
requirement points to possible departures from MHD and the need for
a better understanding of plasma heating in MCs.
---------------------------------------------------------
Title: Parker Solar Probe's Measurements of the 29 November 2020
Solar Energetic Particle Event
Authors: Cohen, C.; Christian, E. R.; Cummings, A. C.; Davis, A. J.;
Desai, M. I.; Nolfo, G. A. de.; Giacalone, J.; Hill, M. E.; Joyce,
C. J.; Labrador, A. W.; Leske, R. A.; Matthaeus, W. H.; McComas,
D. J.; Mewaldt, R. A.; Mitchell, D. G.; Mitchell, J. G.; Rankin,
J. S.; Roelof, E. C.; Schwadron, N. A.; Stone, E. C.; Szalay, J. R.;
Wiedenbeck, M. E.; Vourlidas, A.; Bale, S. D.; Pulupa, M.; MacDowall,
R. J.; McNutt, R. L., Jr.
2022icrc.confE1292C Altcode: 2022PoS...395E1292C
No abstract at ADS
---------------------------------------------------------
Title: Parker Solar Probe Imaging of the Night Side of Venus
Authors: Wood, Brian E.; Hess, Phillip; Lustig-Yaeger, Jacob;
Gallagher, Brendan; Korwan, Daniel; Rich, Nathan; Stenborg, Guillermo;
Thernisien, Arnaud; Qadri, Syed N.; Santiago, Freddie; Peralta,
Javier; Arney, Giada N.; Izenberg, Noam R.; Vourlidas, Angelos;
Linton, Mark G.; Howard, Russell A.; Raouafi, Nour E.
2022GeoRL..4996302W Altcode:
We present images of Venus from the Wide-Field Imager for Parker
Solar Probe (WISPR) telescope on board the Parker Solar Probe (PSP)
spacecraft, obtained during PSP's third and fourth flybys of Venus
on 2020 July 11 and 2021 February 20, respectively. Thermal emission
from the surface is observed on the night side, representing the
shortest wavelength observations of this emission ever, the first
detection of the Venusian surface by an optical telescope observing
below 0.8 μm. Consistent with previous observations at 1 μm, the
cooler highland areas are fainter than the surrounding lowlands. The
irradiances measured by WISPR are consistent with model predictions
assuming a surface temperature of T = 735 K. In addition to the thermal
emission, the WISPR images also show bright nightglow emission at the
limb, and we compare the WISPR intensities with previous spectroscopic
measurements of the molecular oxygen nightglow lines from Venus Express.
---------------------------------------------------------
Title: Small Satellite Mission Concepts for Space Weather Research
and as Pathfinders for Operations
Authors: Caspi, Amir; Barthelemy, M.; Bussy-Virat, C. D.; Cohen, I. J.;
DeForest, C. E.; Jackson, D. R.; Vourlidas, A.; Nieves-Chinchilla, T.
2022SpWea..2002554C Altcode: 2022arXiv220107426C
Recent advances in miniaturization and commercial availability of
critical satellite subsystems and detector technology have made
small satellites (SmallSats, including CubeSats) an attractive,
low-cost potential solution for space weather research and operational
needs. Motivated by the first International Workshop on SmallSats
for Space Weather Research and Forecasting, held in Washington,
DC on 1-4 August 2017, we discuss the need for advanced space
weather measurement capabilities, driven by analyses from the World
Meteorological Organization (WMO), and how SmallSats can efficiently
fill these measurement gaps. We present some current, recent missions
and proposed/upcoming mission concepts using SmallSats that enhance
space weather research and provide prototyping pathways for future
operational applications; how they relate to the WMO requirements;
and what challenges remain to be overcome to meet the WMO goals
and operational needs in the future. With additional investment from
cognizant funding agencies worldwide, SmallSats—including standalone
missions and constellations—could significantly enhance space weather
research and, eventually, operations, by reducing costs and enabling new
measurements not feasible from traditional, large, monolithic missions.
---------------------------------------------------------
Title: Parker Solar Probe Observations of the January 2021 3He-Rich
Solar Energetic Particle Events
Authors: Leske, Richard; Christian, Eric; Cohen, Christina; Cummings,
Alan; Davis, Andrew; Desai, Mihir; de Nolfo, Georgia; Giacalone, Joe;
Hill, Matthew; Joyce, Colin; Labrador, Allan; Matthaeus, William;
McComas, David; McNutt, Ralph; Mewaldt, Richard; Mitchell, Donald;
Mitchell, J. Grant; Rankin, Jamie; Roelof, Edmond; Schwadron, Nathan;
Stone, Edward; Szalay, Jamey; Wiedenbeck, Mark; Vourlidas, Angelos;
Bale, Stuart; Pulupa, Marc; MacDowall, Robert
2021AGUFMSH15A2029L Altcode:
On 21 January 2021, while at ~0.18 AU after its seventh solar perihelion
pass, Parker Solar Probe's Integrated Science Investigation of the Sun
(ISIS) detected a pair of small, highly anisotropic solar energetic
particle (SEP) events. In terms of their composition, these events were
distinguished by a very high helium abundance, with the elemental He
and H intensities essentially equal at 1 MeV/nucleon. These events were
by far the most 3He-rich detected by PSP to date, with a 3He/4He ratio
of ~4 at 1 MeV/nucleon, but less at both lower and higher energies,
as has sometimes been seen in earlier SEP events at 1 AU. Both events
were accompanied by clear type III radio emission observed by the PSP
FIELDS instrument, but the source region was unobserved since PSP was
~120 degrees west of Earth and directly opposite the Sun from STEREO. We
present ISIS observations of the composition, spectra, time profiles,
and anisotropies of these events and compare them with other 3He-rich
events observed much farther from the Sun.
---------------------------------------------------------
Title: Investigating Energy Release during Solar Eruptive Events
with RHESSI, STEREO, and SDO
Authors: Vievering, Juliana; Vourlidas, Angelos; Zhu, Chunming; Qiu,
Jiong; Glesener, Lindsay
2021AGUFMSH22B..05V Altcode:
Hard X-rays (HXRs) provide a key diagnostic for energy release during a
solar flare, as HXRs are emitted from flare-accelerated electrons and
strongly heated flare plasma. In the case of a solar eruptive event,
a flare is associated with the eruption of a coronal mass ejection
(CME); though it is largely understood that reconnection is important
for the eventual release of the CME, the triggering mechanism for the
eruption and its relationship to flare energy release remains under
debate. In this study, we leverage the optimal viewing geometry of
the Solar TErrestrial RElations Observatory (STEREO) relative to the
Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy
Solar Spectroscopic Imager (RHESSI) during 2010-2013 to provide
simultaneous measurements of CME evolution, magnetic reconnection,
and flare energy release for 12 solar eruptive events. We analyze
the relative timing of these phenomena, focusing on event onset and
fast-varying features, or bursts, in the time profiles to improve our
understanding of particle acceleration mechanisms and the connections
between flare and CME energization. Notably, this study has identified
two events with rarely-studied RHESSI HXR flares occurring outside
of active regions, which can provide additional insight on how the
magnetic configuration affects the evolution of eruptive events.
---------------------------------------------------------
Title: Variations in the He/H Abundance Ratio Measured in Solar
Energetic Particle Events by Parker Solar Probe
Authors: Cohen, Christina; Christian, Eric; Cummings, Alan; Davis,
Andrew; Desai, Mihir; de Nolfo, Georgia; Giacalone, Joe; Hill, Matthew;
Joyce, Colin; Labrador, Allan; Leske, Richard; Matthaeus, William;
McComas, David; McNutt, Ralph; Mewaldt, Richard; Mitchell, Donald;
Mitchell, J. Grant; Rankin, Jamie; Roelof, Edmond; Schwadron, Nathan;
Stone, Edward; Szalay, Jamey; Wiedenbeck, Mark; Vourlidas, Angelos;
Bale, Stuart; Pulupa, Marc; MacDowall, Robert
2021AGUFMSH51B..06C Altcode:
In late May, 2020 the Integrated Science Investigation of the Sun (ISIS)
on Parker Solar Probe observed a triad of solar energetic particle (SEP)
events originating from the same active region on the Sun. Although
these events were each separated in time by less than 24 hours,
their He/H abundance ratios varied by over a factor of 50, with one
event exhibiting an extremely low value of 0.33% (as compared to the
typical value of 3.5%). During the following year, ISIS detected many
additional SEP events, some similar in size to the May 2020 events, some
significantly larger (e.g., the circumsolar November 2020 event). Among
these events the He/H continued to be quite variable, including events
with He/H ratios a factor of two lower than the lowest of the May 2020
events. Here we summarize these variations and investigate the solar and
interplanetary conditions in which they occur in an effort to understand
the process(es) that dictate the observed SEP He/H abundance ratios.
---------------------------------------------------------
Title: Coronal Mass Ejection Distortion at 0.1 au Observed by WISPR
Authors: Braga, Carlos; Vourlidas, Angelos; Liewer, Paulett; Hess,
Phillip; Stenborg, Guillermo
2021AGUFMSH42A..09B Altcode:
Although many coronal mass ejections (CMEs) are modeled using
geometric models expanding self-similarly, various numerical MHD
simulations, imaging, and in situ observations suggest that CMEs
become distorted. Common distortions descriptions are "pancaking",
front flattering, and rotational skew. Many distortions are associated
with spatial and temporal changes in CME background solar wind
conditions. Other studies suggest that distortion happens because CMEs
lose coherence over their full angular extend once portions of plasma
separate exceeding the Alfven speed, which can occur between 0.1 and
0.2 au. We present evidence of one CME becoming distorted while WISPR
observed it and explore possible explanations. The inner and outer
cameras observe the CME on January 20-22, 2021, while it propagates
almost through the entire field-of-view, extending 95 degrees
radially. We derive the CME kinematics using multiple techniques,
and reconstruct it using WISPR and coronagraph observations. We find
that up to ~0.08 au, the CME follows the graduated cylindrical shell
(GCS) model well and expands approximately self-similarly. After
this period in which WISPR observes a circular-like front profile,
it becomes concave. By projecting the GCS model over WISPR images,
we are unable to reproduce the profile change observed. As projection
effects cannot explain the concave profile, our interpretation is that
the CME becomes distorted by ~0.1 au. The CME seems to expand more
at higher latitudes, where the solar wind speed is likely higher. We
also discuss CME plasma conditions necessary for loss of coherence at
~0.1 au, which occurs when the relative separation speed between CME
plasma parcels becomes higher than the Alfven speed.
---------------------------------------------------------
Title: PSP/IS⊙IS observations of the 29 November 2020 solar
energetic particle event
Authors: Cohen, C. M. S.; Christian, E. R.; Cummings, A. C.; Davis,
A. J.; Desai, M. I.; de Nolfo, G. A.; Giacalone, J.; Hill, M. E.;
Joyce, C. J.; Labrador, A. W.; Leske, R. A.; Matthaeus, W. H.;
McComas, D. J.; McNutt, R. L.; Mewaldt, R. A.; Mitchell, D. G.;
Mitchell, J. G.; Rankin, J. S.; Roelof, E. C.; Schwadron, N. A.;
Stone, E. C.; Szalay, J. R.; Wiedenbeck, M. E.; Vourlidas, A.; Bale,
S. D.; Pulupa, M.; MacDowall, R. J.
2021A&A...656A..29C Altcode:
<BR /> Aims: On 29 November 2020, at 12:34 UT, active region 12790
erupted with an M4.4 class flare and a 1700 km s<SUP>−1</SUP> coronal
mass ejection. Parker Solar Probe (PSP) was completing its seventh orbit
around the Sun and was located at 0.8 au when the Integrated Science
Investigation of the Sun (IS⊙IS) measured the ensuing mid-sized
solar energetic particle (SEP) event. Not only was this the first SEP
event with heavy ions above 10 MeV nuc<SUP>−1</SUP> to be measured
by IS⊙IS, it was also measured by several spacecraft positioned
around the Sun, making it the first circumsolar event of solar cycle
25. Here we describe an overview of the SEP event characteristics at
PSP. <BR /> Methods: Fluence spectra for electrons, H, He, O, and Fe
were calculated for the decay portion of the event. For the entire time
period of the event, it was possible to calculate fluence spectra for
electrons, O, and Fe only due to instrumental mode changes in one of
the IS⊙IS telescopes, affecting H and He during the period of peak
intensities. Using higher time resolution data, we also studied the
onset of the event and temporal variations in the particle intensities
at the shock and during the magnetic cloud passage. <BR /> Results:
During the decay, the ion spectra are consistent with power laws at low
energies with an exponential rollover at a few MeV nuc<SUP>−1</SUP>,
while the electron spectrum is consistent with a power law of index
−5.3. Based on fits to the spectra, Fe/O and He/H abundance ratios
as a function of energy are calculated and found to be nominal for
large SEP events at hundreds of keV/nuc, but decrease strongly with
increasing energy. The full-event spectra for O and Fe have similar
shapes to those of the decay, but with higher roll-over energies. The
electron spectrum for the full event is harder with an index of −3.4
and there is some evidence of higher energy components near ∼2 MeV and
above ∼4 MeV. Despite the spacecraft being tilted 45° with respect
to the nominal orientation of the spacecraft's long axis pointed
towards the Sun, there is some anisotropy apparent in MeV protons
during the onset of the event. Velocity dispersion is also evident,
consistent with a solar release time of 13:15 UT and pathlength of
1.3 au. The arrival of the related magnetic cloud resulted in the
suppression of SEP intensities, although a brief increase in particle
intensities suggests PSP moved out of the cloud for ∼30 min. This
appears to be the first medium-sized event in the rise of cycle 25
activity, with additional large events likely to occur. Additional
details of the event beyond this overview can be found in several
related papers. <P />Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140967/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Relationship Between Onsets of CME Acceleration and Magnetic
Reconnection in CME-flare Events
Authors: Zhu, Chunming; Balentine, Danny; Qiu, Jiong; Vievering,
Juliana; Vourlidas, Angelos; Hu, Qiang
2021AGUFMSH25E2141Z Altcode:
What role magnetic reconnection plays in the initiation of solar
eruptions is still not clear. In this study, we focus on the initiation
of ~10 CME-flare events by combining flare reconnection and CME
kinematics. We measure CME kinematics in the early stage from two
viewpoints of SDO (12s cadence) and STEREO (up to 75s cadence). We also
measure the reconnection flux rate by evaluating magnetic fluxes swept
by the flare foot-point brightenings on the solar disk observed from
SDO, with the cadence of 12--24s. With these measurements, we determine
the time and location of early signatures of magnetic reconnection with
respect to the CME evolution. By exploring the related magnetic field
configuration, we classify these early reconnection signatures based on
their locations and evolutions, and discuss how the early reconnection
signatures could be related to the initiation of the solar eruptions.
---------------------------------------------------------
Title: Internal Structure of the 2019 April 2 CME
Authors: Wood, Brian E.; Braga, Carlos R.; Vourlidas, Angelos
2021ApJ...922..234W Altcode: 2021arXiv211014083W
We present the first analysis of internal coronal mass ejection (CME)
structure observed very close to the Sun by the Wide-field Imager
for Solar PRobe (WISPR) instrument on board the Parker Solar Probe
(PSP). The transient studied here is a CME observed during PSP's
second perihelion passage on 2019 April 2, when PSP was only 40 R
<SUB>⊙</SUB> from the Sun. The CME was also well observed from 1 au by
the STEREO-A spacecraft, which tracks the event all the way from the Sun
to 1 au. However, PSP/WISPR observes internal structure not apparent in
the images from 1 au. In particular, two linear features are observed,
one bright and one dark. We model these features as two loops within
the CME flux rope (FR) channel. The loops can be interpreted as bundles
of field lines, with the brightness of the bright loop indicative of
lots of mass being loaded into those field lines, and with the dark
loop being devoid of such mass loading. It is possible that these
loops are actually representative of two independent FR structures
within the overall CME outline.
---------------------------------------------------------
Title: Analysis of Coronal Mass Ejections Observed by Multiple
Spacecraft, including by WISPR on Parker Solar Probe
Authors: Liewer, Paulett; Hall, Jeffrey; Braga, Carlos; Hess, Phillip;
Penteado, Paulo; Stenborg, Guillermo; Vourlidas, Angelos; Qiu, Jiong
2021AGUFMSH15A2019L Altcode:
The Wide-field Imager for Solar Probe (WISPR) has provided high
resolution images of multiple coronal mass ejections (CMEs) during
its first seven encounters with the Sun and most of these have been
observed by white-light instruments on either STEREO A or SOHO or
both. The multiple viewpoints have been important in determining the
source of the CMEs and their trajectories. Here we present results
from the analysis of the origin and trajectories of several WISPR
CMEs with some unexpected results. WISPR has a wide fixed angular
field-of-view (FOV), extending radially from 13.5° to 108° from
the Sun and approximately 50° in the transverse direction, but the
physical extent of the imaged coronal region varies directly with the
distance of the spacecraft from the Sun. We have developed tools for
determining the trajectories of solar ejecta which take into account
the rapid spacecraft motion. We have also developed tools to relate and
compare the CMEs seen in the WISPR images to simultaneous observation
from the other white light telescope (SOHO/LASCO or STEREO/SECCHI),
making uses of the World Coordinate System information in the images
FITS headers. This software allows us to project the trajectory
determined from WISPR or features seen in the WISPR images onto images
from the second white light telescope (or visa versa) to verify the
trajectory determined from the WISPR data alone or to determine a CMEs
location by triangulation. Utilizing the multiple viewpoints has led
to a better understanding of the structure and evolution of the CMEs.
---------------------------------------------------------
Title: Large ensemble simulations of CMEs in the inner heliosphere:
toward constraining distributions of CME parameters near the Sun
Authors: Provornikova, Elena; Merkin, Viacheslav; Malanushenko, Anna;
Gibson, Sarah; Vourlidas, Angelos; Arge, Charles; Dalmasse, Kevin
2021AGUFMSH32A..01P Altcode:
In this work, we take a comprehensive approach which combines
physics-based simulations, observations and statistical methods
toward understanding the evolution of coronal mass ejections in
the inner heliosphere and linking characteristics of CMEs near the
Sun and their plasma and magnetic field properties as they would be
observed at 1 AU. We simulate the propagation of ICMEs using a global
model of the inner heliosphere driven at the coronal boundary by
the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs are initiated at 21.5
solar radii using an MHD analytical Gibson-Low (G&L) model of a
self-similarly expanding magnetic bubble with defining parameters (e.g.,
latitude and longitude, magnetic field topology and strength, angular
width, speed, orientation). The ICME propagation is simulated using
the inner heliosphere version of the Grid Agnostic MHD for Extended
Research Applications (GAMERA) MHD model, which is a reinvention of the
high-heritage Lyon-Fedder-Mobarry (LFM) code. A set of values for each
of the defining G&L parameters was constrained by the statistical
representation of CME images near the Sun. Intending to span the solar
cycle, we model ICME propagation in different solar wind backgrounds
corresponding to rising, declining, and minimum solar cycle phases. A
grid of CME parameters and three solar wind backgrounds constitute
a parameter space for 50,000 ICME simulations. We describe types and
a structure of the output data from simulations and an algorithm of
automatic performance of many thousands of runs. We discuss methods to
incorporate CME data from both solar observations and in-situ at 1 AU
in a statistical study to construct posterior predictive distributions
of CME model input parameters.
---------------------------------------------------------
Title: Connecting the Low to the High Corona: A Method to Isolate
Transients in STEREO/COR1 Images
Authors: Alzate, Nathalia; Morgan, Huw; Viall, Nicholeen; Vourlidas,
Angelos
2021ApJ...919...98A Altcode: 2021arXiv210702644A
We present a method that isolates time-varying components from
coronagraph and extreme ultraviolet images, allowing substreamer
transients propagating within streamers to be tracked from the
low to the high corona. The method uses a temporal bandpass filter
with a transmission bandwidth of ~2.5-10 hr that suppresses both
high- and low-frequency variations in observations made by the
STEREO/SECCHI suite. We demonstrate that this method proves crucial
in linking features in the low corona, where the magnetic field is
highly nonradial, to their counterparts in the high corona, where the
magnetic field follows a radial path, through the COR1 instrument. We
also apply our method to observations by the COR2 and EUVI instruments
on board SECCHI and produce height-time profiles that reveal small
density enhancements, associated with helmet streamers propagating from
~1.2 R<SUB>⊙</SUB> out to beyond 5 R<SUB>⊙</SUB>. Our processing
method reveals that these features are common during the period
of solar minimum in this study. The features recur on timescales
of hours, originate very close to the Sun, and remain coherent out
into interplanetary space. We measure the speed of the features and
classify them as slow (a few to tens of kilometers per second) or fast
(~100 km s<SUP>-1</SUP>). Both types of features serve as an observable
tracer of a variable component of the slow solar wind to its source
regions. Our methodology helps overcome the difficulties in tracking
small-scale features through COR1. As a result, it proves successful
in measuring the connectivity between the low and high corona and in
measuring the velocities of small-scale features.
---------------------------------------------------------
Title: Energetic particle evolution during coronal mass ejection
passage from 0.3 to 1 AU
Authors: Joyce, C. J.; McComas, D. J.; Schwadron, N. A.; Vourlidas,
A.; Christian, E. R.; McNutt, R. L.; Cohen, C. M. S.; Leske, R. A.;
Mewaldt, R. A.; Stone, E. C.; Mitchell, D. G.; Hill, M. E.; Roelof,
E. C.; Allen, R. C.; Szalay, J. R.; Rankin, J. S.; Desai, M. I.;
Giacalone, J.; Matthaeus, W. H.; Niehof, J. T.; de Wet, W.; Winslow,
R. M.; Bale, S. D.; Kasper, J. C.
2021A&A...651A...2J Altcode:
We provide analysis of a coronal mass ejection (CME) that passed
over Parker Solar Probe (PSP) on January 20, 2020 when the spacecraft
was at just 0.32 AU. The Integrated Science Investigation of the Sun
instrument suite measures energetic particle populations associated with
the CME before, during, and after its passage over the spacecraft. We
observe a complex evolution of energetic particles, including a brief
~2 h period where the energetic particle fluxes are enhanced and the
nominal orientation of the energetic particle streaming outward from
the Sun (from 30 to 100 keV nuc<SUP>−1</SUP>) abruptly reverses inward
toward the Sun. This transient and punctuated evolution highlights the
importance of magnetic field structures that connect the spacecraft
to different acceleration sites, one of which is likely more distant
from the Sun than PSP during the evolution of the CME. We discuss
these characteristics and what they tell us about the source of the
energetic particles. During this period, PSP was radially aligned with
the Solar Terrestrial Relations Observatory A (STEREO-A), which measured
the same CME when it passed 1 AU. The magnetic field measurements at
both spacecraft are remarkably similar, indicating that the spacecraft
are likely encountering the same portion of the magnetic structure
that has not evolved significantly in transit. The energetic particle
observations on the other hand, are quite different at STEREO-A, showing
how transport effects have acted on the energetic particle populations
and obscured the detailed properties present earlier in the development
of the CME. This event provides a unique case study in how energetic
particle populations evolve as CMEs propagate through the heliosphere.
---------------------------------------------------------
Title: Parker Solar Probe observations of He/H abundance variations
in SEP events inside 0.5 au
Authors: Cohen, C. M. S.; Christian, E. R.; Cummings, A. C.; Davis,
A. J.; Desai, M. I.; de Nolfo, G. A.; Giacalone, J.; Hill, M. E.;
Joyce, C. J.; Labrador, A. W.; Leske, R. A.; Matthaeus, W. H.;
McComas, D. J.; McNutt, R. L.; Mewaldt, R. A.; Mitchell, D. G.;
Mitchell, J. G.; Rankin, J. S.; Roelof, E. C.; Schwadron, N. A.;
Stone, E. C.; Szalay, J. R.; Wiedenbeck, M. E.; Vourlidas, A.; Bale,
S. D.; Pulupa, M.; MacDowall, R. J.
2021A&A...650A..23C Altcode:
<BR /> Aims: The Parker Solar Probe (PSP) orbit provides an opportunity
to study the inner heliosphere at distances closer to the Sun than
previously possible. Due to the solar minimum conditions, the initial
orbits of PSP yielded only a few solar energetic particle (SEP) events
for study. Recently during the fifth orbit, at distances from 0.45
to 0.3 au, the energetic particle suite on PSP, Integrated Science
Investigation of the Sun (IS⊙IS), observed a series of six SEP
events, adding to the limited number of SEP events studied inside of
0.5 au. Variations in the H and He spectra and the He/H abundance ratio
are examined and discussed in relation to the identified solar source
regions and activity. <BR /> Methods: IS⊙IS measures the energetic
particle environment from ~20 keV to >100 MeV/nuc. Six events were
selected using the ~1 MeV proton intensities, and while small, they
were sufficient to calculate proton and helium spectra from ~1 to ~10
MeV/nuc. For the three larger events, the He/H ratio as a function of
energy was determined. Using the timing of the associated radio bursts,
solar sources were identified for each event and the eruptions were
examined in extreme ultraviolet emission. <BR /> Results: The largest
of the selected events has peak ~1 MeV proton intensities of 3.75
(cm<SUP>2</SUP> sr s MeV)<SUP>−1</SUP>. Within uncertainties, the
He and H spectra have similar power law forms with indices ranging
from −2.3 to −3.3. For the three largest events, the He/H ratios
are found to be relatively energy independent; however, the ratios
differ substantially with values of 0.0033 ± 0.0013, 0.177 ± 0.047,
and 0.016 ± 0.009. An additional compositional variation is evident
in both the <SUP>3</SUP>He and electron signatures. These variations
are particularly interesting as the three larger events are likely
a result of similar eruptions from the same active region. <P
/>Movies associated to Figs. 3 and 8 are only available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039299/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: An Observational Study of a "Rosetta Stone" Solar Eruption
Authors: Mason, E. I.; Antiochos, Spiro K.; Vourlidas, Angelos
2021ApJ...914L...8M Altcode: 2021arXiv210509164M
This Letter reports observations of an event that connects all major
classes of solar eruptions: those that erupt fully into the heliosphere
versus those that fail and are confined to the Sun, and those that eject
new flux into the heliosphere, in the form of a flux rope, versus those
that eject only new plasma in the form of a jet. The event originated
in a filament channel overlying a circular polarity inversion line
and occurred on 2016 March 13 during the extended decay phase of the
active region designated NOAA 12488/12501. The event was especially
well observed by multiple spacecraft and exhibited the well-studied
null-point topology. We analyze all aspects of the eruption using Solar
Dynamics Observatory Atmospheric Imaging Assembly and Helioseismic
and Magnetic Imager, Solar-Terrestrial Relations Observatory Extreme
Ultraviolet Imager, and Solar and Heliospheric Observatory Large
Angle and Spectrometric Coronagraph (SOHO LASCO) imagery. One section
of the filament undergoes a classic failed eruption with cool plasma
subsequently draining onto the section that did not erupt, but a complex
structured coronal mass ejection/jet is clearly observed by SOHO/LASCO
C2 shortly after the failed filament eruption. We describe in detail
the slow buildup to eruption, the lack of an obvious trigger, and the
immediate reappearance of the filament after the event. The unique
mixture of major eruption properties observed during this event places
severe constraints on the structure of the filament channel field and,
consequently, on the possible eruption mechanism.
---------------------------------------------------------
Title: Coronal mass ejections observed by heliospheric imagers at
0.2 and 1 au. The events on April 1 and 2, 2019
Authors: Braga, Carlos R.; Vourlidas, Angelos
2021A&A...650A..31B Altcode: 2020arXiv201105229B
Context. We study two coronal mass ejections (CMEs) observed between
April 1 to 2, 2019 by both the inner Wide-Field Imager for Parker
Solar Probe (WISPR-I) onboard the Parker Solar Probe (PSP) spacecraft
(located between about 46 and 38 solar radii during this period) and
the inner heliospheric imager (HI-1) onboard the Solar Terrestrial
Relations Observatory Ahead (STEREO-A) spacecraft, orbiting the Sun at
about 0.96 au. This is the first study of CME observations from two
viewpoints in similar directions but at considerably different solar
distances. <BR /> Aims: Our objective is to derive CME kinematics
from WISPR-I observations and to compare them with results from
HI-1. This allows us to understand how the PSP observations affect
the CME kinematics, especially due to its proximity to the Sun. <BR
/> Methods: We estimated the CME positions, speeds, accelerations,
propagation directions, and longitudinal deflections using imaging
observations from two spacecrafts and a set of analytical expressions
that consider the CME as a point structure and take the rapid change
in spacecraft position into account. We derived the kinematics using
each viewpoint independently and both viewpoints as a constraint. <BR />
Results: We found that both CMEs are slow (<400 km s<SUP>−1</SUP>),
propagating eastward of the Sun-Earth line (westward of PSP and
STEREO-A). The second CME seems to accelerate between ~0.1 and ~0.2 au
and deflect westward with an angular speed consistent with the solar
rotation speed. We found some discrepancies in the CME solar distance
(up to 0.05 au, particularly for CME #1), latitude (up to ~10°),
and longitude (up to 24°) when comparing results from different
fit cases (different observations or set of free parameters). <BR
/> Conclusions: Discrepancies in longitude are likely due to the
feature that is tracked visually, rather than instrumental biases
or fit assumptions. For similar reasons, the CME #1 solar distance,
as derived from WISPR-I observations, is larger than the HI-1 result,
regardless of the fit parameters considered. Error estimates for CME
kinematics do not show any clear trend associated with the observing
instrument. The source region location and the lack of any clear in
situ counterparts (both at near-Earth and at PSP) support our estimate
of the propagation direction for both events.
---------------------------------------------------------
Title: Periodic Solar Wind Density Structures Observed with Parker
Solar Probe WISPR
Authors: Viall, N. M.; Vourlidas, A.; Howard, R.; Linton, M.; Kepko,
L.; Di Matteo, S.; Higginson, A. K.
2021AAS...23812305V Altcode:
Periodic trains of mesoscale structures in solar wind density have been
observed close to the Sun with in situ data from the Helios spacecraft,
as well as remotely in STEREO/COR2 and STEREO/HI1 white light imaging
data. While some periodic density structures may be a consequence of
the development of dynamics en route, many are remnants of the formation
and release of the solar wind, and thus provide important constraints on
solar wind models. The instrument suite on Parker Solar Probe offers an
unprecedented viewpoint of the ambient solar wind and structure therein,
shortly after its formation and release from the solar corona. Here,
we report on the first observations of periodic trains of mesoscale
structures in solar wind density observed by the Wide-field Imager
for Parker Solar PRobe (WISPR). We describe our open-source Fourier
analysis and robust spectral background estimation technique used to
identify the periodic density structures. The observation of periodic
density structures so near to the Sun allows us to begin disentangling
how much structure is created during solar wind formation, versus how
much is due to evolution as the solar wind advects outward.
---------------------------------------------------------
Title: Mind The Gap: Observing The Jet/CME Continuum In A Hybrid
Eruption
Authors: Mason, E.; Antiochos, S.; Vourlidas, A.
2021AAS...23821316M Altcode:
Coronal mass ejections, jets, prominence eruptions: solar eruptions are
an active field with a broad range of accepted phenomena, and an even
broader range of proposed mechanisms that cause the phenomena. This
talk reports the observations of an event that connects the major
eruption classes, and could provide a holistic explanation for all of
them. The event originated in a filament channel overlying a circular
polarity inversion line (PIL) and occurred on 2013 March 13 during the
extended decay phase of the active region designated (sequentially)
NOAA 12488/12501. This event was especially well-observed by multiple
spacecraft and was seen to have the well-studied null-point topology. We
analyze all aspects of the eruption using SDO AIA and HMI, STEREO-A,
and SOHO LASCO imagery. One section of the filament undergoes a
classic failed eruption with cool plasma subsequently draining onto
the section that did not erupt, but a complex structured CME/jet is
clearly observed by SOHO LASCO C2 shortly after the failed filament
eruption. We describe in detail the long, slow buildup to eruption;
the lack of an obvious trigger; and the immediate reappearance of
the filament after the event. The unique mixture of major eruption
properties that are observed in this event places severe constraints
on the structure of the filament channel field and, consequently,
on the possible eruption mechanism.
---------------------------------------------------------
Title: Analysis of Coronal Mass Ejections Observed by the Wide-field
Imager (WISPR) on Parker Solar Probe
Authors: Liewer, P. C.; Qiu, J.; Vourlidas, A.; Penteado, P.; Hall,
J. R.
2021AAS...23832204L Altcode:
The Wide-field Imager for Solar Probe (WISPR) has provided high
resolution images of multiple coronal mass ejections (CMEs) during
its first seven encounters with the Sun. Here we present results
of the analysis of the origin and trajectories of several of these
CMEs with some unexpected results. WISPR has a wide fixed angular
field-of-view (FOV), extending radially from 13.5° to 108° from
the Sun and approximately 50° in the transverse direction, but the
physical extent of the imaged coronal region varies directly with the
distance of the spacecraft from the Sun. We have developed tools for
determining the trajectories of solar eject which take into account
the rapid spacecraft motion. The CMEs analyzed have also been observed
by either STEREO A or LASCO or both. To relate and compare the CMEs
seen in the WISPR images to simultaneous observation from another
white light telescope, it is necessary to relate the fields-of-view
of the telescopes at any given time to a common inertial frame of
reference, e.g., the Heliocentric Inertial coordinate frame. Using
World Coordinate System information in the images' FITS headers, we
project the trajectory determined from WISPR or features seen in the
WISPR images onto images from the second white light telescope (or
visa versa) to verify the trajectory determined from the WISPR data
alone and to better understand the structure and evolution of the CMEs.
---------------------------------------------------------
Title: In-flight Calibration and Data Reduction for the WISPR
Instrument On Board the PSP Mission
Authors: Hess, Phillip; Howard, Russell A.; Stenborg, Guillermo;
Linton, Mark; Vourlidas, Angelos; Thernisien, Arnaud; Colaninno,
Robin; Rich, Nathan; Wang, Dennis; Battams, Karl; Kuroda, Natsuha
2021SoPh..296...94H Altcode:
We present the calibration status and data reduction methodology for
the Wide Field Imager for Solar Probe (WISPR) on board the Parker
Solar Probe (PSP) mission. In particular, we describe the process
for converting a raw image, measured in digital numbers (DN), to a
calibrated image, measured in mean solar brightness (MSB). We also
discuss details of the on board image processing including bias removal,
the linearity of the electronics, pointing, geometric distortion,
and photometric calibration using stellar measurements, and the
characterization of vignetting and other instrumental artifacts. The
analysis presented here is based on data from the first four WISPR
orbits. As the PSP perihelia get progressively closer to the Sun and
the WISPR concept of operation evolves to deal with the brighter scene,
the calibration will likely need to be updated. Aging of the optics
and the possibility of detector degradation may also occur. Hence,
we consider the WISPR calibration as work in progress with updates
reported as necessary.
---------------------------------------------------------
Title: Tracking solar wind flows from rapidly varying viewpoints by
the Wide-field Imager for Parker Solar Probe
Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Liewer, P. C.;
Penteado, P.; Hall, J. R.
2021A&A...650A..30N Altcode: 2020arXiv201013140N
<BR /> Aims: Our goal is to develop methodologies to seamlessly track
transient solar wind flows viewed by coronagraphs or heliospheric
imagers from rapidly varying viewpoints. <BR /> Methods: We
constructed maps of intensity versus time and elongation (J-maps)
from Parker Solar Probe (PSP) Wide-field Imager (WISPR) observations
during the fourth encounter of PSP. From the J-map, we built an
intensity on impact-radius-on-Thomson-surface map (R-map). Finally,
we constructed a latitudinal intensity versus time map (Lat-map). Our
methodology satisfactorily addresses the challenges associated with
the construction of such maps from data taken from rapidly varying
viewpoint observations. <BR /> Results: Our WISPR J-map exhibits
several tracks, corresponding to transient solar wind flows ranging
from a coronal mass ejection down to streamer blobs. The latter
occurrence rate is about 4-5 per day, which is similar to the
occurrence rate in a J-map made from ~1 AU data obtained with the
Heliospheric Imager-1 (HI-1) on board the Solar Terrestrial Relations
Observatory Ahead spacecraft (STEREO-A). STEREO-A was radially aligned
with PSP during the study period. The WISPR J-map tracks correspond
to angular speeds of 2.28 ± 0.7°/h (2.49 ± 0.95°/h), for linear
(quadratic) time-elongation fittings, and radial speeds of about
150-300 km s<SUP>−1</SUP>. The analysis of the Lat-map reveals
a bifurcating streamer, which implies that PSP was flying through
a slightly folded streamer during perihelion. <BR /> Conclusions:
We developed a framework to systematically capture and characterize
transient solar wind flows from space platforms with rapidly varying
vantage points. The methodology can be applied to PSP WISPR observations
as well as to upcoming observations from instruments on board the Solar
Orbiter mission. <P />Movie associated to Fig. 8 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039414/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Evolution of a streamer-blowout CME as observed by imagers
on Parker Solar Probe and the Solar Terrestrial Relations Observatory
Authors: Liewer, P. C.; Qiu, J.; Vourlidas, A.; Hall, J. R.;
Penteado, P.
2021A&A...650A..32L Altcode: 2020arXiv201205174L
Context. On 26-27 January 2020, the Wide-field Imager for Solar
Probe on Parker Solar Probe (PSP) observed a coronal mass ejection
(CME) from a distance of approximately 30 R<SUB>⊙</SUB> as it
passed through the instrument's 95° field-of-view, providing an
unprecedented view of the flux rope morphology of the CME's internal
structure. The same CME was seen by Solar Terrestrial Relations
Observatory-Ahead (STEREO-A), beginning on 25 January. <BR /> Aims:
Our goal is to understand the origin and determine the trajectory
of this CME. <BR /> Methods: We analyzed data from three well-placed
spacecrafts: PSP, STEREO-A, and Solar Dynamics Observatory (SDO). The
CME trajectory was determined using a tracking-and-fitting technique
and verified using simultaneous images of the CME propagation from
STEREO-A. The fortuitous alignment with STEREO-A also provided views
of coronal activity leading up to the eruption. Observations from SDO,
in conjunction with potential magnetic field models of the corona,
were used to analyze the coronal magnetic evolution for the three days
leading up to the flux rope ejection from the corona on 25 January. <BR
/> Results: We found that the 25 January CME is likely the end result
of a slow magnetic flux rope eruption that began on 23 January and was
observed by STEREO-A/Extreme Ultraviolet Imager. The analysis of these
observations suggest that the flux rope was apparently constrained
in the corona for more than a day before its final ejection on 25
January. STEREO-A/COR2 observations of swelling and brightening of the
overlying streamer for several hours prior to eruption on 25 January
led us to classify this as a streamer-blowout CME. The analysis of the
SDO data suggests that restructuring of the coronal magnetic fields
caused by an emerging active region led to the final ejection of the
flux rope. <P />Movies associated to Figs. 3, 7-9 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039641/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Solar Physics and Solar Wind
Authors: Raouafi, Nour E.; Vourlidas, Angelos
2021GMS...258.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Improving the Medium-Term Forecasting of Space Weather:
A Big Picture Review from a Solar Observer's Perspective
Authors: Vourlidas, Angelos
2021FrASS...8...68V Altcode:
Our scientific understanding of the solar drivers of Space Weather,
i.e. Coronal Mass Ejections, flares, and solar energetic particles,
has improved considerably in the last 20+ years thanks to a plethora
of space missions and modeling advances. Yet, there has been no major
breakthrough in assessing the geo-effectiveness of a given CME and
associated phenomena, largely holding back actionable medium-term
(up to 7 days) forecasting of Space Weather. Why is that? <P />To
search for answers, I first summarise the results of the last 20+
years of research on solar drivers by collecting lessons-learned and
identifying paradigm shifts in our view of solar activity, always in
relation to Space Weather concerns. Then, I review the state of the
key observational-based quantities used in forecasting, which allows me
to identify the choke points and research gaps that drive the current
medium-term forecasting performance. Finally, I outline a path forward
consisting of the measurements with the strongest potential to improve
space weather forecasting horizon and robustness.
---------------------------------------------------------
Title: The CME arrival prediction with the Effective Acceleration
Model: Further testing with heliospheric imaging observations
Authors: Paouris, Evangelos; Vourlidas, Angelos; Papaioannou,
Athanasios; Anastasiadis, Anastasios
2021EGUGA..2310254P Altcode:
The estimation of the Coronal Mass Ejection (CME) arrival is an open
issue in the field of Space Weather. Many models have been developed
to predict Time-of-Arrival (ToA). In this work, we utilize an updated
version of the Effective Acceleration Model (EAM) to calculate the
ToA. The EAM predicts the ToA of the CME-driven shock and the sheath's
average speed at 1 AU. The model assumes that the interaction between
the ambient solar wind and the interplanetary CME (ICME) results
in constant acceleration or deceleration. We recently compared EAM
against ENLIL and drag based models (DBEM) with a sample of 16 CMEs. We
confirmed the well-known fact that the deceleration of fast ICMEs in the
interplanetary medium is not captured by most models. We study further
the deceleration of fast ICMEs by introducing, for the first time,
wide-angle observations by the STEREO heliospheric imagers into the
EAM model. The speed profiles for some test cases show deceleration
in the interplanetary medium at greater distances compared with the
field-of-view of the coronagraphs.
---------------------------------------------------------
Title: High fidelity spectroscopic imaging at low radio frequencies
to estimate plasma parameters of solar coronal mass ejections at
higher coronal heights
Authors: Kansabanik, Devojyoti; Mondal, Surajit; Oberoi, Divya;
Vourlidas, Angelos
2021EGUGA..2311089K Altcode:
Coronal Mass Ejections (CMEs) are large-scale explosive eruptions
of magnetised plasma from the Sun into the Heliosphere. Measuring
the physical parameters of CMEs is crucial for understanding their
physics and for assessing their geo-effectiveness. Radio observations
offer the most direct means for estimating these plasma parameters when
gyrosynchrotron (GS) emission is detected from the CME plasma. However,
since the first detection by Bastian et al.2001, only a handful of
studies have successfully detected GS emission from CME plasma. This
is usually attributed to the challenges involved in obtaining the high
dynamic range imaging required for observing this faint gyrosynchrotron
emission in the vicinity of active solar emissions.The newly developed
imaging pipeline (Mondal et al., 2019) designed for the data from
Murchison Widefield Array (MWA) marks a significant improvement in
metrewave solar radio imaging. Our work suggests that we should now
be able to routinely detect GS emission from CME plasma. We present
an example where we have successfully detected radio emission from CME
plasma and modelled it as GS emission, leading to reliable estimates of
CME magnetic field as well as the distribution of energetic electrons
(Mondal et al. 2020). In a different example we are able to detect
the radio emission from the CME plasma out to as far as 8.3 solar
radii. We find that the observed spectra are not always consistent with
simple GS models. This highlights that more complicated physics might
be at play and points to the need for building more detailed models
for interpreting these emissions. We hope that with the availability
of polarimetric imaging capability, which we are in the process of
developing, this technique will provide a robust way to routinely
measure CME magnetic fields along with its other physical parameters. We
note that these are the weakest detections of GS emissions from CME
plasma reported yet.
---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
---------------------------------------------------------
Title: Validation of Global EUV Wave MHD Simulations and Observational
Techniques
Authors: Downs, Cooper; Warmuth, Alexander; Long, David M.; Bloomfield,
D. Shaun; Kwon, Ryun-Young; Veronig, Astrid M.; Vourlidas, Angelos;
Vršnak, Bojan
2021ApJ...911..118D Altcode:
Global EUV waves remain a controversial phenomenon more than 20 yr
after their discovery by SOHO/EIT. Although consensus is growing in the
community that they are most likely large-amplitude waves or shocks,
the wide variety of observations and techniques used to identify
and analyze them have led to disagreements regarding their physical
properties and interpretation. Here, we use a 3D magnetohydrodynamic
(MHD) model of the solar corona to simulate an EUV wave event on 2009
February 13 to enable a detailed validation of the various commonly used
detection and analysis techniques of global EUV waves. The simulated
event exhibits comparable behavior to that of a real EUV wave event,
with similar kinematic behavior and plasma parameter evolution. The
kinematics of the wave are estimated via visual identification and
profile analysis, with both approaches providing comparable results. We
find that projection effects can affect the derived kinematics of the
wave, due to the variation in fast-mode wave speed with height in the
corona. Coronal seismology techniques typically used for estimates
of the coronal magnetic field are also tested and found to estimate
fast-mode speeds comparable to those of the model. Plasma density
and temperature variations of the wave front are also derived using
a regularized inversion approach and found to be consistent with
observed wave events. These results indicate that global waves are
best interpreted as large-amplitude waves and that they can be used
to probe the coronal medium using well-defined analysis techniques.
---------------------------------------------------------
Title: Addressing Gaps in Space Weather Operations and Understanding
With Small Satellites
Authors: Verkhoglyadova, O. P.; Bussy-Virat, C. D.; Caspi, A.; Jackson,
D. R.; Kalegaev, V.; Klenzing, J.; Nieves-Chinchilla, J.; Vourlidas, A.
2021SpWea..1902566V Altcode: 2020arXiv201203343V
Gaps in space weather observations that can be addressed with small
satellites are identified. Potential improvements in solar inputs to
space weather models, space radiation control, estimations of energy
budget of the upper Earth's atmosphere, and satellite drag modeling
are briefly discussed. Key observables, instruments, and observation
strategies by small satellites are recommended. Tracking optimization
for small satellites is proposed.
---------------------------------------------------------
Title: Estimating plasma parameters of solar coronal mass ejections at
higher coronal heights using high fidelity low-frequency radio images
Authors: Kansabanik, Devojyoti; Mondal, Surajit; Oberoi, Divya;
Vourlidas, Angelos
2021csss.confE..36K Altcode:
Coronal Mass Ejection (CMEs) are large scale explosive eruptions of
magnetised plasma from Sun into Heliosphere. Measuring the physical
parameters of CMEs is crucial for understanding their physics and for
assessing their geoeffectiveness. Radio observations offer the most
direct means for estimating these plasma parameters when gyrosynchrotron
(GS) emission is detected from the CME. But only a handful of studies
have successfully managed to detect this GS emissions (Bastian et
al. 2001; Maia et al. 2007; and Demoulin et al. 2012).We will show that
it is now routinely possible to detect these GS emissions using high
dynamic range radio images produced by an automated imaging pipeline
(Mondal et al. 2019a) using the data from Murchison Widefield Array. We
have detected the radio emission from CME plasma at the largest distance
(8.3 solar radii) till date. We will show that magnetic field and
energetic electron distribution inside CME plasma can be estimated
directly at higher coronal heights by fitting a model of GS emission
to the observed spectra. On the other hand it is also observed that
radio spectra always can not be represented by simple GS spectra. This
indicates that a more complicated physics is involved for these radio
emissions.
---------------------------------------------------------
Title: On the Rigidity Spectrum of Cosmic-Ray Variations within
Propagating Interplanetary Disturbances: Neutron Monitor and
SOHO/EPHIN Observations at ∼1-10 GV
Authors: Belov, Anatoly; Papaioannou, Athanasios; Abunina, Maria;
Dumbovic, Mateja; Richardson, Ian G.; Heber, Bernd; Kuhl, Patrick;
Herbst, Konstantin; Anastasiadis, Anastasios; Vourlidas, Angelos;
Eroshenko, Eugenia; Abunin, Artem
2021ApJ...908....5B Altcode:
The rigidity dependence of all Forbush decreases (FDs) recorded
from 1995 to 2015 has been determined using neutron monitor (NM)
and Solar and Heliospheric Observatory (SOHO) (EPHIN) spacecraft
data, covering the energy (rigidity) range from ∼433 MeV (1 GV)
to 9.10 GeV (10 GV). We analyzed a total of 421 events and determined
the spectrum in rigidity with an inverse power-law fit. As a result,
the mean spectral index was identified to be ⟨γ<SUB>F</SUB>⟩ =
0.46 ± 0.02. The majority (∼66%) of the FDs have γ<SUB>F</SUB>
within the range 0.3-0.7. The remaining one-third of the events (∼33%)
have either (very) soft or hard FD spectra, with the latter being more
common than the former. Significant variations of γ<SUB>F</SUB> occur
within almost every FD event. During the initial FD decay phase the
spectrum becomes gradually harder, in contrast to the recovery phase,
when it becomes softer. Additionally, low energies (rigidities) seem
to be better suited for studying the fine structure of interplanetary
disturbances (primarily interplanetary coronal mass ejections) that
lead to FDs. In particular, FDs recorded by the EPHIN instrument on SOHO
better capture a two-step structure than FDs observed by NMs. Finally,
the ejecta of an ICME, especially when identified as a magnetic cloud,
often leads to abrupt changes in the slope of γ<SUB>F</SUB>.
---------------------------------------------------------
Title: Assessing the Projection Correction of Coronal Mass Ejection
Speeds on Time of Arrival Prediction Performance Using the Effective
Acceleration Model
Authors: Paouris, Evangelos; Vourlidas, Angelos; Papaioannou,
Athanasios; Anastasiadis, Anastasios
2021SpWea..1902617P Altcode: 2020arXiv201204703P
White light images of coronal mass ejections (CMEs) are projections
on the plane of sky (POS). As a result, CME kinematics are subject to
projection effects. The error in the true (deprojected) speed of CMEs
is one of the main causes of uncertainty to Space Weather forecasts,
since all estimates of the CME time of arrival (ToA) at a certain
location within the heliosphere require, as input, the CME speed. We
use single viewpoint observations for 1,037 flare CME events between
1996 and 2017 and propose a new approach for the correction of the CME
speed assuming radial propagation from the flare site. Our method is
uniquely capable to produce physically reasonable deprojected speeds
across the full range of source longitudes. We bound the uncertainty in
the deprojected speed estimates via limits in the true angular width
of a CME based on multiview point observations. Our corrections range
up to 1.37-2.86 for CMEs originating from the center of the disk. On
average, the deprojected speeds are 12.8% greater than their POS
speeds. For slow CMEs (V<SUB>POS</SUB> < 400 km/s) the full ice
cream cone model performs better while for fast and very fast CMEs
(V<SUB>POS</SUB> > 700 km/s) the shallow ice cream model gives
much better results. CMEs with 691-878 km/s POS speeds have a minimum
ToA mean absolute error (MAE) of 11.6 h. This method, is robust, easy
to use, and has immediate applicability to Space Weather forecasting
applications. Moreover, regarding the speed of CMEs, our work suggests
that single viewpoint observations are generally reliable.
---------------------------------------------------------
Title: Plasma heating induced by tadpole-like downflows in the
flaring solar corona
Authors: Samanta, T.; Tian, H.; Chen, B.; Reeves, K. K.; Cheung,
M. C. M.; Vourlidas, A.; Banerjee, D.
2021Innov...200083S Altcode: 2021arXiv210314257S
As one of the most spectacular energy release events in the solar
system, solar flares are generally powered by magnetic reconnection in
the solar corona. As a result of the re-arrangement of magnetic field
topology after the reconnection process, a series of new loop-like
magnetic structures are often formed and are known as flare loops. A
hot diffuse region, consisting of around 5-10 MK plasma, is also
observed above the loops and is called a supra-arcade fan. Often,
dark, tadpole-like structures are seen to descend through the bright
supra-arcade fans. It remains unclear what role these so-called
supra-arcade downflows (SADs) play in heating the flaring coronal
plasma. Here we show a unique flare observation, where many SADs collide
with the flare loops and strongly heat the loops to a temperature
of 10-20 MK. Several of these interactions generate clear signatures
of quasi-periodic enhancement in the full-Sun-integrated soft X-ray
emission, providing an alternative interpretation for quasi-periodic
pulsations that are commonly observed during solar and stellar flares.
---------------------------------------------------------
Title: Propagating Conditions and the Time of ICME Arrival:
A Comparison of the Effective Acceleration Model with ENLIL and
DBEM Models
Authors: Paouris, Evangelos; Čalogović, Jaša; Dumbović, Mateja;
Mays, M. Leila; Vourlidas, Angelos; Papaioannou, Athanasios;
Anastasiadis, Anastasios; Balasis, Georgios
2021SoPh..296...12P Altcode: 2020arXiv201205857P
The Effective Acceleration Model (EAM) predicts the Time-of-Arrival
(ToA) of the Coronal Mass Ejection (CME) driven shock and the average
speed within the sheath at 1 AU. The model is based on the assumption
that the ambient solar wind interacts with the interplanetary CME
(ICME) resulting in constant acceleration or deceleration. The
upgraded version of the model (EAMv3), presented here, incorporates
two basic improvements: (i) a new technique for the calculation of the
acceleration (or deceleration) of the ICME from the Sun to 1 AU and
(ii) a correction for the CME plane-of-sky speed. A validation of
the upgraded EAM model is performed via comparisons to predictions
from the ensemble version of the Drag-Based model (DBEM) and the
WSA-ENLIL+Cone ensemble model. A common sample of 16 CMEs/ICMEs, in
2013 - 2014, is used for the comparison. Basic performance metrics
such as the mean absolute error (MAE), mean error (ME) and root mean
squared error (RMSE) between observed and predicted values of ToA are
presented. MAE for EAM model was 8.7 ±1.6 hours while for DBEM and
ENLIL was 14.3 ±2.2 and 12.8 ±1.7 hours, respectively. ME for EAM
was −1.4 ±2.7 hours in contrast with −9.7 ±3.4 and −6.1 ±3.3
hours from DBEM and ENLIL. We also study the hypothesis of stronger
deceleration in the interplanetary (IP) space utilizing the EAMv3 and
DBEM models. In particularly, the DBEM model perform better when a
greater value of drag parameter, of order of a factor of 3, is used
in contrast to previous studies. EAMv3 model shows a deceleration of
ICMEs at greater distances, with a mean value of 0.72 AU.
---------------------------------------------------------
Title: Nonthermal electrons revealed by LOFAR
Authors: Zucca, Pietro; Pellizzoni, Alberto; Krankowski, Andrzej;
Rothkaehl, Hanna; Mann, Gottfried; Vocks, Christian; Magdalenic,
Jasmina; Marque, Christophe; Jackson, Bernard; Fallows, Richard;
Tomasik, Lukasz; Hamish; Reid, A. S.; Gallagher, Peter; Vourlidas,
Angelos; Bisi, Mario M.; Carley, Eoin; Matyjasiak, Barbara; Kozarev,
Kamen; Dabrowski, Bartosz; Morosan, Diana; Tiburzi, Caterina; Chang,
Peijin
2021cosp...43E1065Z Altcode:
During solar flares and CMEs, the corona is heated, plasma motion,
waves and shocks are ignited, and particles are accelerated. The
accelerated particles propagate through the solar corona causing a
variety of plasma instabilities that lead to enhanced non-thermal
radio emission, known as "radio bursts". By studying radio-bursts'
characteristics we can gain insight into the properties of energetic
particles and the ambient coronal plasma, and the properties of particle
acceleration mechanisms, such as magnetic reconnection and/or shocks
in the solar atmosphere. The Low Frequency aRray (LOFAR) can be used
to study the fundamental plasma physics of solar radio bursts with
unprecedented time resolution in dynamic spectra, as well as with
both interferometric imaging and tied array imaging. In this talk, an
overview of recent results obtained with the LOFAR telescope will be
given, including observations of a different variety of radio bursts
such as type II, III and IV. These observations were performed with
simultaneous beam formed and interferometric imaging, resulting in
unprecedented special resolution with baselines up to ~120 km. Finally,
we will present the plan for future observations and the remaining
challenges of solar-heliospheric low-frequency observations.
---------------------------------------------------------
Title: Gibson & Low Flux Rope Model: More Than a Spheromak!
Authors: Malanushenko, Anna; Gibson, Sarah; Provornikova, Elena;
Dalmasse, Kévin; Merkin, Viacheslav; Vourlidas, Angelos; Nychka,
Doug; Flyer, Natasha; Arge, Charles
2021cosp...43E1736M Altcode:
Modeling solar coronal mass ejections (CMEs) is very important for
both understanding coronal physics and for improving the accuracy of
space weather forecasts. While it is generally accepted that CMEs
are primarily magnetic structures, the exact properties of these
structures could differ in different models and events. A structure
often considered is a spheromak, a toroidal twisted flux rope, which
is ejected as a CME bubble. Another commonly considered structure is a
twisted magnetic flux rope, which is anchored to the solar surface while
its upper portion is ejected into interplanetary space. In this talk
we will show how a well-known analytical magnetohydrodynamic CME model
(Gibson \& Low, 1998), generally considered a spheromak-like model,
can be extended to represent both standard spheromak and twisted flux
tube configurations, as well as other topologically distinct magnetic
structures. We will begin with the general parameters of the flux rope
in this model (such as size and stretching parameters), and explore
topologically different congurations possible with their variation. We
then present several dimensionless parameters which can be varied to
achieve these different configurations and consider how they relate
to directly observable quantities. This work is particularly timely,
as the Gibson \& Low model is been increasingly used as input to
numerical models of the solar corona and the heliosphere. The ability
to generate topologically different magnetic congurations within this
analytic solution is of great value to such simulations, as well as
for the studies of the flux ropes forming in the solar corona.
---------------------------------------------------------
Title: Constraining the physical parameters of coronal mass ejections
at large coronal heights using high fidelity low radio frequency
images
Authors: Kansabanik, Devojyoti; Oberoi, Divya; Vourlidas, Angelos;
Mondal, Surajit
2021cosp...43E1009K Altcode:
Coronal Mass Ejections (CMEs) are large scale explosive eruptions
of magnetised plasma from the Sun into the Heliosphere. Measuring
the physical parameters of CMEs is crucial for understanding their
physics and for assessing their geo-effectiveness. Radio observations
offer the most direct means for estimating these plasma parameters when
gyrosynchrotron (GS) emission is detected from the CME. However, since
the first detection by Bastian et al.2001, only a handful of studies
have successfully detected GS emission from CME plasma. This is usually
attributed to the challenges involved in obtaining the high contrast
imaging required for observing this faint emission in the vicinity
of active solar emissions. Recent work using data from the Murchison
Wide field Array (MWA), a low frequency radio interferometer, and the
newly developed imaging pipeline designed for solar radio imaging
(Mondal et al., 2019) marks a significant improvement in metrewave
solar radio imaging. Our work suggests that we should now be able to
routinely detect GS emission from CME plasma. We present an example
where we have successfully detected radio emission from CME plasma
and modelled it as GS emission, leading to reliable estimates of CME
magnetic eld as well as the distribution of energetic electrons (Mondal
et al.2020). In a different example, we find that the observed spectra
are not always consistent with simple GS models. For this CME we are
able to detect the radio emission from the CME plasma out to as far as
8.3 solar radii. This highlights that more complicated physics might
be at play and points to the need for building more detailed models
for interpreting these emissions. We note that these are the weakest
detections of GS emissions from CME plasma reported yet.
---------------------------------------------------------
Title: Investigating the circumsolar wind with Parker Solar Probe
near-imaging and in-situ high cadence observations
Authors: Patsourakos, Spiros; Liewer, Paulett; Stenborg, Guillermo;
Howard, Russell; Hess, Phillip; Stevens, Michael; Vourlidas, Angelos;
Kasper, Justin; Nindos, Alexander; Penteado, Paulo; Korreck, Kelly;
Case, Anthony
2021cosp...43E.940P Altcode:
The proposition of the existence of the solar wind and its subsequent
discovery were major milestones at the dawn of the Space Age. Since
then, the solar wind has been extensively observed by in-situ
instruments at various locations in the inner and outer heliosphere
but mainly at 1 AU, and by remote sensing instruments at 1 AU. Despite
significant progress in the characterization and understanding of
the solar wind, important questions about the nature of the solar
wind remain unsettled. These questions include the nature of the
launch and acceleration of the solar wind and whether it is steady,
quasi-steady, periodic or intermittent. The recently launched Parker
Solar Probe (PSP) mission, which has been already plunged several times
in the solar corona, is ideally suited to shed more light into these
lingering questions. We present a coordinated analysis of up-close
and high-cadence imaging observations of the solar wind taken by WISPR
and of in-situ solar-wind observations taken inside the solar corona
by SWEAP during the first solar encounters of PSP. A discussion of
instrumental and orbital aspects of the WISPR observations pertinent to
our analysis is also included. Imaging data of the solar wind from ~
1 AU by COR2 on STEREO-A spacecraft is also analyzed. We submit the
time-series of the imaging and in-situ solar wind data to an array of
methods aiming to map their properties. We conclude with a discussion
of future PSP (WISPR and SWEAP) and Solar Orbiter (SoloHI) observing
and analysis strategies pertinent to our science questions.
---------------------------------------------------------
Title: Recent Advances with EUV Irradiance Inputs to the Upper
Atmosphere
Authors: Vourlidas, Angelos
2021cosp...43E.817V Altcode:
The proliferation of satellites in low Earth orbits has increased the
need for accurate tracking and orbit predictions. Those require reliable
modeling of the atmospheric drag in the upper atmosphere, which, in
turn, depends the quality of the solar forcing inputs to the atmospheric
models. In this talk, I review the status of the solar focusing inputs
with emphasis on the EUV irradiance measurements and indices. I discuss
recent developments and the issues that prevent us from improving
atmospheric drag prediction beyond a few days in the future. I finally
offer possible mitigation strategies for consideration.
---------------------------------------------------------
Title: Unraveling the Internal Magnetic Field Structure of the
Earth-directed Interplanetary Coronal Mass Ejections
Authors: Nieves-Chinchilla, Teresa; Jian, Lan; Szabo, Adam; Vourlidas,
Angelos; Balmaceda, Laura; Guedes Dos Santos, Luiz Fernando
2021cosp...43E1739N Altcode:
The magnetic field configurations associated with interplanetary
coronal mass ejections (ICMEs) are the in situ manifestations of the
entrained magnetic structure associated with coronal mass ejections
(CMEs). We present a comprehensive study of the internal magnetic
field configurations of ICMEs observed at 1 AU by the Wind mission
during 1995 - 2015. The goal is to unravel the internal magnetic
structure associated with the ICMEs and establish the signatures that
validate a flux-rope structure. We examine the expected magnetic field
signatures by simulating spacecraft trajectories within a simple flux
rope, i.e., with circular-cylindrical (CC) helical magnetic field
geometry. By comparing the synthetic configurations with the 353
ICME in situ observations, we find that only 152 events (Fr) display
the clear signatures of an expected axial-symmetric flux rope. Two
more populations exhibit possible signatures of flux rope; 58 cases
(F−) display a small rotation (<90$^{\circ}$) of the magnetic
field direction, interpreted as a large separation of the spacecraft
from the center, and, 62 cases (F+) exhibit larger rotations, possibly
arising from more complex configuration. The categories, Cx (14$%$) and
E events (9$%$), reveal signatures of complexity possibly related with
evolutionary processes. We then reconstruct the flux ropes assuming
CC geometry. We examine the orientation and geometrical properties
during the solar activity levels at the end of Solar Cycle 22 (SC22),
SC23 and part of SC24. The orientation exhibits solar cycle trends and
follow the heliospheric current sheet orientation. We confirm previous
studies that found a Hale cycle dependence of the poloidal field
reversal. By comparing our results with the occurrence of CMEs with
large angular width (AW> 60$^{\circ}$) we find a broad correlation
suggesting that such events are highly inclined CMEs. The solar cycle
distribution of bipolar vs. unipolar Bz configuration confirms that
the CMEs may remove solar cycle magnetic field and helicity.
---------------------------------------------------------
Title: On the Quasi-Three Dimensional Configuration of Magnetic Clouds
Authors: Hu, Qiang; He, Wen; Qiu, Jiong; Vourlidas, Angelos; Zhu,
Chunming
2021GeoRL..4890630H Altcode: 2020arXiv201011889H
We develop an optimization approach to model the magnetic field
configuration of magnetic clouds, based on a linear force-free
formulation in three dimensions. Such a solution, dubbed the Freidberg
solution, is kin to the axisymmetric Lundquist solution, but with more
general "helical symmetry." The merit of our approach is demonstrated
via its application to two case studies of in situ measured magnetic
clouds. Both yield results of reduced χ<SUP>2</SUP> ≈ 1. Case 1
shows a winding flux rope configuration with one major polarity. Case
2 exhibits a double-helix configuration with two flux bundles winding
around each other and rooted on regions of mixed polarities. This
study demonstrates the three-dimensional complexity of the magnetic
cloud structures.
---------------------------------------------------------
Title: Results from the LOFAR coordination with PSP
Authors: Zucca, Pietro; Pellizzoni, Alberto; Krankowski, Andrzej;
Rothkaehl, Hanna; Mann, Gottfried; Vocks, Christian; Magdalenic,
Jasmina; Marque, Christophe; Jackson, Bernard; Fallows, Richard;
Tomasik, Lukasz; Miteva, Rositsa; Hamish; Reid, A. S.; Gallagher,
Peter; Vourlidas, Angelos; Bisi, Mario M.; Carley, Eoin; Matyjasiak,
Barbara; Kozarev, Kamen; Dabrowski, Bartosz; Morosan, Diana; Tiburzi,
Caterina; Zhabngm, Peijin
2021cosp...43E.945Z Altcode:
Understanding and modelling the complex state of the Sun-solar
wind-magnetosphere-ionosphere-thermosphere system, requires a
comprehensive set of multiwavelength observations. LOFAR has unique
capabilities in the radio domain. Some examples of these include: a)
the ability to take high-resolution solar dynamic spectra and radio
images of the Sun; b) observing the scintillation (interplanetary
scintillation - IPS) of distant, compact, astronomical radio sources
to determine the density, velocity and turbulence structure of the
solar wind; and c) the use of Faraday rotation as a tool to probe
the interplanetary magnetic-field strength and direction. However, to
better understand and predict how the Sun, its atmosphere, and more
in general the Heliosphere works and impacts Earth, the combination
of in-situ spacecraft measurements and ground-based remote-sensing
observations of coronal and heliospheric plasma parameters is extremely
useful. Ground-based observations can be used to infer a global
picture of the inner heliosphere, providing the essential context into
which in-situ measurements from spacecraft can be placed. Conversely,
remote-sensing observations usually contain information from extended
lines of sight, with some deconvolution and modelling necessary to build
up a three-dimensional (3-D) picture. Precise spacecraft measurements,
when calibrated, can provide ground truth to constrain these models. The
PSP mission is observing the solar corona and near-Sun interplanetary
space. It has a highly-elliptical orbit taking the spacecraft as close
as nearly 36 solar radii from the Sun centre on its first perihelion
passage, and subsequent passages ultimately reaching as close as 9.8
solar radii. Four instruments are on the spacecraft's payload: FIELDS
measuring the radio emission, electric and magnetic fields, Poynting
flux, and plasma waves as well as the electron density and temperature;
ISOIS measuring energetic electrons, protons, and heavy ions in the
energy range 10 keV-100 MeV; SWEAP measuring the density, temperature,
and flow speed of electrons, protons, and alphas in the solar wind;
and finally, WISPR imaging coronal streamers, coronal mass ejections
(CMEs), their associated shocks, and other solar wind structures in the
corona and near-Sun interplanetary space, and provide context for the
other three in-situ instruments. In this talk, several results of the
joint LOFAR/PSP campaign will be presented, including fine structures
of radio bursts, localization and kinematics of propagating radio
sources in the heliosphere, and the challenges and plans for future
observing campaigns including PSP and Solar Orbiter.
---------------------------------------------------------
Title: On the Quasi-Three Dimensional Configuration of Magnetic Clouds
Authors: Hu, Q.; Jiong, Q.; Liewer, P. C.; Vourlidas, A.; Zhu, C.
2020AGUFMSH0440015H Altcode:
Magnetic clouds (MCs) identified in the solar wind from in-situ
spacecraft measurements represent a subset of interplanetary coronal
mass ejections (ICMEs). They possess a specific set of observational
signatures based on magnetic field and plasma parameters. In particular
a relatively smooth rotation of the magnetic field and elevated
field magnitude usually hint at a well-organized field configuration
traversing the single-point observing platform. Additional evidence
in support of such a configuration can be obtained from the solar
source regions where they originate, generally taken in the form of
a flux rope. Based on in-situ spacecraft measurements, various flux
rope models in one-dimensional and two-dimensional configurations
have been developed and applied to event studies, with the latter
represented by the Grad-Shafranov reconstruction technique. However
given the significant variability in the in-situ measurements, not all
MC events can be modeled successfully by the existing methods. We
develop a quasi-three dimensional model which is intrinsically
three-dimensional. We demonstrate, in several case studies, that a
satisfactory fitting to the in-situ spacecraft data along the path
across such a magnetic structure is obtained as judged by the proper
Chi^2 statistics, taking into account the underlying data uncertainties.
---------------------------------------------------------
Title: Constraining the Physical Parameters of Coronal Mass Ejections
at Large Coronal Heights using Low Radio Frequency Gyrosynchrotron
Emission
Authors: Kansabanik, D.; Mondal, S.; Oberoi, D.; Vourlidas, A.
2020AGUFMSH0280017K Altcode:
Coronal Mass Ejection (CMEs) are large scale explosive eruptions
of magnetised plasma from the Sun into the Heliosphere. Measuring
the physical parameters of CMEs is crucial for understanding their
physics and for assessing their geo-effectiveness. Radio observations
offer the most direct means for estimating these plasma parameters
when gyrosynchrotron (GS) emission is detected from the CME. However,
since the first detection by Bastian et al. in 2001, only a handful of
studies have successfully detected GS emission from CME plasma.This is
usually attributed to the challenges involved in obtaining the high
contrast imaging required for observing this faint emission in the
vicinity of active solar emissions.
---------------------------------------------------------
Title: Imaging the Solar Wind From Space: Where do we stand?
Authors: Vourlidas, A.
2020AGUFMSH031..04V Altcode:
Next year marks the 50th anniversary of the detection of Coronal Mass
Ejections from space. The discovery and subsequent observations of
thousands of events from a stream of coronagraph telescopes marked
a paradigm shift of our view of the corona, from a physical system
changing gradually over a solar cycle, to a system marked with
explosive transient activity on timescales from seconds to days to
months. Thanks to coronagraphs, and more recently EUV imagers, Space
Weather forecasting and research have become strong research areas
within the Heliophysics discipline. adding to that, the transients and
even the more quiescent background wind can now be imaged directly in
the inner heliosphere thanks to the advent of heliospheric imaging since
the mid-2000s. <P />The recent deployment of the Parker Solar Probe
and Solar Orbiter missions ushers a new era of coronal/heliospheric
imaging from widely varying vantage points along with future missions,
such as PUNCH, and operational mission at the L1 and L5 point. It is,
therefore, an appropriate time to take stock of the lessons learned
from the decades of imaging of the solar wind, both quiescent and
transient. In this talk, I review those lessons/learned and discuss
where to go next.
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Title: Investigation of a prominent solar wind structure observed
by PSP on June 13, 2020
Authors: Niembro Hernandez, T.; Stevens, M. L.; Korreck, K. E.;
Paulson, K. W.; Nieves-Chinchilla, T.; Szabo, A.; Balmaceda, L. A.;
Vourlidas, A.; Horbury, T. S.; Luhmann, J. G.; Case, A. W.; Kasper,
J. C.; Larson, D. E.; Livi, R.; Rahmati, A.; Huang, J.; Whittlesey,
P. L.; Bale, S. D.; Pulupa, M.; Malaspina, D.; Bonnell, J. W.; Harvey,
P.; Goetz, K.; Dudok de Wit, T.; MacDowall, R. J.; Koval, A.
2020AGUFMSH0490007N Altcode:
In the early hours of June 13, 2020, just after the end of its 5 th
solar encounter, the Faraday Cup on-board Parker Solar Probe (PSP)
registered the passage of a prominent solar wind structure embedded
in highly variable plasma and characterized by regions with distinct
plasma conditions (speed, density, magnetic field, etc) and wave
activity. From remote sensing observations, using spacecraft at
different heliospheric locations, several transients were observed
ejected from the Sun, including a coronal mass ejection (CME) oriented
away from PSP that may have also influenced the solar wind conditions
through which the structure in question has propagated. In this work,
we report the PSP-SPC observations around this structure and identify
possible solar sources relying on multi-spacecraft observations. We
also characterized the propagation and evolution of the CME observed
on June 12, 2020 and the role it played influencing the conditions of
the unusual variable ambient solar wind.
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Title: Ensemble modeling of interplanetary CMEs with data-constrained
internal magnetic flux rope
Authors: Provornikova, E.; Merkin, V. G.; Malanushenko, A. V.; Gibson,
S. E.; Vourlidas, A.; Arge, C. N.
2020AGUFMSH0030016P Altcode:
Understanding the evolution of the CME magnetic structure as it
propagates through the interplanetary space is a key aspect in the
development of forecasting of magnetic properties of a CME arriving
at Earth and thus its impact on space weather. To analyze processes
of interplanetary CME (ICME)/solar-wind interactions and the role of
CME flux rope specification and solar wind background structure, we
take a statistical approach and perform thousands of data-driven MHD
simulations of ICME propagation in the inner heliosphere. Data-driven
modeling of ICMEs in the inner heliosphere (starting beyond the critical
surface in the corona) presents an attractive and computationally
feasible approach, since it bypasses the complex problem of CME
initiation and eruption in the corona. We simulate the propagation
of ICMEs in the inner heliosphere using a global model driven at the
coronal boundary by the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs
are initiated at 21.5 solar radii using an MHD analytical Gibson-Low
(G&L) model of a self-similarly expanding magnetic flux rope
with defining parameters (e.g., location, magnetic topology, width,
magnetic field strength, speed, orientation). The ICME propagation
is simulated using the inner heliosphere version of the Grid Agnostic
MHD for Extended Research Applications (GAMERA) MHD model, which is a
reinvention of the high-heritage Lyon-Fedder-Mobarry (LFM) code. A set
of values for each of the defining G&L parameters was constrained
by statistical representation of solar CME observations. With the
aim to span the solar cycle, we model ICME propagation in different
solar wind backgrounds corresponding to rising, maximum, declining and
minimum solar cycle phases. A grid of G&L parameters and four solar
wind backgrounds constitute a parameter space for thousands of MHD
ICME runs. For each of the simulations we extract synthetic in-situ
observations of ICME as it passes Earth and synthetic white-light
images of an ICME as it propagates in the interplanetary space. We
present an analysis of produced distributions of ICME parameters and
characteristics.
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Title: Analysis of Solar Wind Ejecta Observed by the Wide-field Imager
(WISPR) on Parker Solar Probe
Authors: Liewer, P. C.; Qiu, J.; Vourlidas, A.; Hall, J. R.; Penteado,
P.; Howard, R. A.
2020AGUFMSH0490005L Altcode:
The three-to-five-month highly elliptical orbit of Parker Solar Probe
(PSP), approaching within 10 solar radii of the Sun, allows the
Wide-field Imager for Solar Probe (WISPR) to view the corona with
unprecedented spatial resolution. WISPR has a wide fixed angular
field-of-view (FOV), extending radially from 13.5° to 108° from
the Sun and approximately 50° in the transverse direction, but the
physical extent of the imaged coronal region varies directly with the
distance of the spacecraft from the Sun. We have developed tools for
determining the trajectories of solar eject which take into account
the spacecraft motion. Here, we present results of the analysis of
the trajectory of several CMEs observed by WISPR using these tools,
including CMEs observed on 2020 January 20 and 2020 January 26-27. The
CMEs were also observed in white light by either STEREO A or LASCO or
both. Observations from STEREO A, LASCO and SDO are used to study the
origin and evolution of these events. To relate and compare the ejecta
seen in the WISPR images to simultaneous observation from another
white light telescope, it is necessary to relate the fields-of-view
of the telescopes at any given time to a common frame of reference,
such as the Heliocentric Inertial coordinate frame. Using World
Coordinate System information in the images' FITS headers, we project
the trajectory determined from WISPR or features seen in the WISPR
images onto images from the second white light telescope to better
understand the structure and evolution of the CMEs.
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Title: Relating Imaged Streamer Flows to the Slow Solar Winds measured
by Solar Orbiter and Parker Solar Probe
Authors: Rouillard, A. P.; Griton, L.; Louarn, P.; Fedorov, A.;
Horbury, T. S.; Kouloumvakos, A.; Poirier, N.; Lavarra, M.; Vourlidas,
A.; Howard, R. A.; Moncuquet, M.; Lavraud, B.; Fargette, N.; Réville,
V.; Bruno, R.; Prech, L.; Livi, S. A.; Owen, C. J.; Angelini, V.; Bale,
S. D.; Evans, V.; Kasper, J. C.; O'Brien, H.; Penou, E.; Pinto, R.
2020AGUFMSH0360002R Altcode:
The physical mechanisms that produce the slow solar wind are still
highly debated. Parker Solar Probe's (PSP's) recent solar encounters
during Solar Orbiter's (SolO) cruise phase provide new opportunities
to relate in situ measurements of the nascent slow solar wind with
white-light images of the solar corona. We exploit data taken by the
Solar and Heliospheric Observatory, the Solar TErrestrial RElations
Observatory (STEREO), and the Wide Imager on Solar Probe to study the
connection between real and pseudo-streamer flows with high-density
plasma measured by the different spacecraft. We exploit these images to
classify the different types of slow winds measured by PSP and SolO and
investigate the magneto-plasma properties of these different winds. In
this presentation a particular focus will be put on the interpretation
of the high-cadence measurements taken by the Proton-Alpha Sensor on
Solar Orbiter.
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Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2020SSRv..216..131P Altcode: 2020arXiv201010186P
A clear understanding of the nature of the pre-eruptive magnetic
field configurations of Coronal Mass Ejections (CMEs) is required
for understanding and eventually predicting solar eruptions. Only
two, but seemingly disparate, magnetic configurations are considered
viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
(MFR). They can form via three physical mechanisms (flux emergence,
flux cancellation, helicity condensation). Whether the CME culprit
is an SMA or an MFR, however, has been strongly debated for thirty
years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review
the status of the field across modeling and observations, identify
the open and closed issues, compile lists of SMA and MFR observables
to be tested against observations and outline research activities
to close the gaps in our current understanding. We propose that the
combination of multi-viewpoint multi-thermal coronal observations
and multi-height vector magnetic field measurements is the optimal
approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.
---------------------------------------------------------
Title: Radio observations of coronal mass ejection initiation and
development in the low solar corona
Authors: Carley, Eoin P.; Vilmer, Nicole; Vourlidas, Angelos
2020FrASS...7...79C Altcode:
Coronal mass ejections are large eruptions of plasma and magnetic
field from the low solar corona into the heliosphere. These eruptions
are often associated with energetic electrons that produce various
kinds of radio emission. However, there is ongoing investigation into
exactly where, when and how the electron acceleration occurs during
flaring and eruption, and how the associated radio emission can be
exploited as a diagnostic of both the particle acceleration and CME
eruptive physics. Here, we review past and present developments in radio
observations of flaring and eruption, from the destabilisation of flux
ropes to development of a CME and the eventual driving of shocks in
the corona. We concentrate primarily on the progress made in CME radio
physics in the past two decades, and show how radio imaging spectroscopy
provides the ability to diagnose the locations and kinds of electron
acceleration during eruption, which provides insight into CME eruptive
models in the early stages of their evolution (<10 Rsun). We finally
discuss how new instrumentation in the radio domain will pave the way
for a deeper understanding of CME physics in the near future.
---------------------------------------------------------
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
2020A&A...642A...6A Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements. <BR /> Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together. <BR /> Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis. <BR /> Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.
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Title: When do solar erupting hot magnetic flux ropes form?
Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Cheng, X.;
Zhang, J.
2020A&A...642A.109N Altcode: 2020arXiv200804380N
<BR /> Aims: We investigate the formation times of eruptive magnetic
flux ropes relative to the onset of solar eruptions, which is
important for constraining models of coronal mass ejection (CME)
initiation. <BR /> Methods: We inspected uninterrupted sequences of
131 Å images that spanned more than eight hours and were obtained
by the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory to identify the formation times of hot flux ropes that
erupted in CMEs from locations close to the limb. The appearance
of the flux ropes as well as their evolution toward eruptions were
determined using morphological criteria. <BR /> Results: Two-thirds
(20/30) of the flux ropes were formed well before the onset of the
eruption (from 51 min to more than eight hours), and their formation
was associated with the occurrence of a confined flare. We also found
four events with preexisting hot flux ropes whose formations occurred
a matter of minutes (from three to 39) prior to the eruptions without
any association with distinct confined flare activity. Six flux ropes
were formed once the eruptions were underway. However, in three of
them, prominence material could be seen in 131 Å images, which may
indicate the presence of preexisting flux ropes that were not hot. The
formation patterns of the last three groups of hot flux ropes did not
show significant differences. For the whole population of events, the
mean and median values of the time difference between the onset of the
eruptive flare and the appearance of the hot flux rope were 151 and 98
min, respectively. <BR /> Conclusions: Our results provide, on average,
indirect support for CME models that involve preexisting flux ropes; on
the other hand, for a third of the events, models in which the ejected
flux rope is formed during the eruption appear more appropriate. <P
/>Movies attached to Figs. 2, 5, 8, and 10 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038832/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
2020A&A...642A...2R Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk. <BR /> Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies. <BR /> Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter. <BR /> Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission. <BR /> Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.
---------------------------------------------------------
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
---------------------------------------------------------
Title: Trajectory Determination for Coronal Ejecta Observed by
WISPR/Parker Solar Probe
Authors: Liewer, P. C.; Qiu, J.; Penteado, P.; Hall, J. R.; Vourlidas,
A.; Howard, R. A.
2020SoPh..295..140L Altcode: 2020arXiv200909323L
The Wide-field Imager for Solar Probe (WISPR) onboard the Parker
Solar Probe (PSP), observing in white light, has a fixed angular
field of view, extending from 13.5<SUP>∘</SUP> to 108<SUP>∘</SUP>
from the Sun and approximately 50<SUP>∘</SUP> in the transverse
direction. Because of the highly elliptical orbit of PSP, the physical
extent of the imaged coronal region varies directly as the distance
from the Sun, requiring new techniques for analysis of the motions of
observed density features. Here, we present a technique for determining
the 3D trajectory of CMEs and other coronal ejecta moving radially at a
constant velocity by first tracking the motion in a sequence of images
and then applying a curve-fitting procedure to determine the trajectory
parameters (distance vs. time, velocity, longitude, and latitude). To
validate the technique, we have determined the trajectory of two CMEs
observed by WISPR that were also observed by another white-light imager,
either the Solar and Heliophysics Observatory (SOHO) / Large Angle
and Spectrometric COronagraph (LASCO)-C3 or the Solar Terrestrial
Relations Observatory (STEREO)-A/HI1. The second viewpoint was used
to verify the trajectory results from this new technique and help
determine its uncertainty.
---------------------------------------------------------
Title: Understanding the origins of the heliosphere: integrating
observations and measurements from Parker Solar Probe, Solar Orbiter,
and other space- and ground-based observatories
Authors: Velli, M.; Harra, L. K.; Vourlidas, A.; Schwadron,
N.; Panasenco, O.; Liewer, P. C.; Müller, D.; Zouganelis, I.;
St Cyr, O. C.; Gilbert, H.; Nieves-Chinchilla, T.; Auchère, F.;
Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker,
S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli,
M.; Solanki, S. K.; Wimmer-Schweingruber, R. F.; Bale, S.; Kasper,
J.; McComas, D. J.; Raouafi, N.; Martinez-Pillet, V.; Walsh, A. P.;
De Groof, A.; Williams, D.
2020A&A...642A...4V Altcode:
Context. The launch of Parker Solar Probe (PSP) in 2018, followed
by Solar Orbiter (SO) in February 2020, has opened a new window in
the exploration of solar magnetic activity and the origin of the
heliosphere. These missions, together with other space observatories
dedicated to solar observations, such as the Solar Dynamics Observatory,
Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations
from WIND and ACE, and ground based multi-wavelength observations
including the DKIST observatory that has just seen first light,
promise to revolutionize our understanding of the solar atmosphere
and of solar activity, from the generation and emergence of the Sun's
magnetic field to the creation of the solar wind and the acceleration of
solar energetic particles. <BR /> Aims: Here we describe the scientific
objectives of the PSP and SO missions, and highlight the potential for
discovery arising from synergistic observations. Here we put particular
emphasis on how the combined remote sensing and in situ observations of
SO, that bracket the outer coronal and inner heliospheric observations
by PSP, may provide a reconstruction of the solar wind and magnetic
field expansion from the Sun out to beyond the orbit of Mercury in the
first phases of the mission. In the later, out-of-ecliptic portions of
the SO mission, the solar surface magnetic field measurements from SO
and the multi-point white-light observations from both PSP and SO will
shed light on the dynamic, intermittent solar wind escaping from helmet
streamers, pseudo-streamers, and the confined coronal plasma, and on
solar energetic particle transport. <BR /> Methods: Joint measurements
during PSP-SO alignments, and magnetic connections along the same
flux tube complemented by alignments with Earth, dual PSP-Earth,
and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will
allow a better understanding of the in situ evolution of solar-wind
plasma flows and the full three-dimensional distribution of the
solar wind from a purely observational point of view. Spectroscopic
observations of the corona, and optical and radio observations,
combined with direct in situ observations of the accelerating solar
wind will provide a new foundation for understanding the fundamental
physical processes leading to the energy transformations from solar
photospheric flows and magnetic fields into the hot coronal plasma
and magnetic fields and finally into the bulk kinetic energy of the
solar wind and solar energetic particles. <BR /> Results: We discuss
the initial PSP observations, which already provide a compelling
rationale for new measurement campaigns by SO, along with ground-
and space-based assets within the synergistic context described above.
---------------------------------------------------------
Title: The Solar Orbiter Heliospheric Imager (SoloHI)
Authors: Howard, R. A.; Vourlidas, A.; Colaninno, R. C.; Korendyke,
C. M.; Plunkett, S. P.; Carter, M. T.; Wang, D.; Rich, N.; Lynch,
S.; Thurn, A.; Socker, D. G.; Thernisien, A. F.; Chua, D.; Linton,
M. G.; Koss, S.; Tun-Beltran, S.; Dennison, H.; Stenborg, G.; McMullin,
D. R.; Hunt, T.; Baugh, R.; Clifford, G.; Keller, D.; Janesick, J. R.;
Tower, J.; Grygon, M.; Farkas, R.; Hagood, R.; Eisenhauer, K.; Uhl,
A.; Yerushalmi, S.; Smith, L.; Liewer, P. C.; Velli, M. C.; Linker,
J.; Bothmer, V.; Rochus, P.; Halain, J. -P.; Lamy, P. L.; Auchère,
F.; Harrison, R. A.; Rouillard, A.; Patsourakos, S.; St. Cyr, O. C.;
Gilbert, H.; Maldonado, H.; Mariano, C.; Cerullo, J.
2020A&A...642A..13H Altcode:
<BR /> Aims: We present the design and pre-launch performance of
the Solar Orbiter Heliospheric Imager (SoloHI) which is an instrument
prepared for inclusion in the ESA/NASA Solar Orbiter mission, currently
scheduled for launch in 2020. <BR /> Methods: The goal of this paper
is to provide details of the SoloHI instrument concept, design, and
pre-flight performance to give the potential user of the data a better
understanding of how the observations are collected and the sources
that contribute to the signal. <BR /> Results: The paper discusses
the science objectives, including the SoloHI-specific aspects, before
presenting the design concepts, which include the optics, mechanical,
thermal, electrical, and ground processing. Finally, a list of planned
data products is also presented. <BR /> Conclusions: The performance
measurements of the various instrument parameters meet or exceed the
requirements derived from the mission science objectives. SoloHI is
poised to take its place as a vital contributor to the science success
of the Solar Orbiter mission.
---------------------------------------------------------
Title: Predicting the Time of Arrival of Coronal Mass Ejections at
Earth From Heliospheric Imaging Observations
Authors: Braga, Carlos Roberto; Vourlidas, Angelos; Stenborg,
Guillermo; Dal Lago, Alisson; Mendonça, Rafael Rodrigues Souza de;
Echer, Ezequiel
2020JGRA..12527885B Altcode: 2020arXiv200809005B
The time of arrival (ToA) of coronal mass ejections (CMEs) at Earth
is a key parameter due to the space weather phenomena associated
with the CME arrival, such as intense geomagnetic storms. Despite the
incremental use of new instrumentation and the development of novel
methodologies, ToA estimated errors remain above 10 h on average. Here,
we investigate the prediction of the ToA of CMEs using observations
from heliospheric imagers, i.e., from heliocentric distances higher
than those covered by the existent coronagraphs. In order to perform
this work, we analyze 14 CMEs observed by the heliospheric imagers HI-1
onboard the twin STEREO spacecraft to determine their front location and
speed. The kinematic parameters are derived with a new technique based
on the Elliptical Conversion (ElCon) method, which uses simultaneous
observations from the two viewpoints from STEREO. Outside the field
of view of the instruments, we assume that the dynamics of the CME
evolution is controlled by aerodynamic drag, i.e., a force resulting
from the interaction with particles from the background solar wind. To
model the drag force, we use a physical model that allows us to derive
its parameters without the need to rely on drag coefficients derived
empirically. We found a CME ToA mean error of 1.6 ± 8.0 h ToA and
a mean absolute error of 6.9 ± 3.9 h for a set of 14 events. The
results suggest that observations from HI-1 lead to estimates with
similar errors to observations from coronagraphs.
---------------------------------------------------------
Title: The Coronal Mass Ejection Visibility Function of Modern
Coronagraphs
Authors: Vourlidas, Angelos; Balmaceda, L. A.; Xie, H.; St. Cyr, O. C.
2020ApJ...900..161V Altcode: 2020arXiv200803348V
We analyze the detection capability of coronal mass ejections (CMEs)
for all currently operating coronagraphs in space. We define as CMEs
events that propagate beyond 10 solar radii with morphologies broadly
consistent with a magnetic flux-rope presence. We take advantage
of multi-viewpoint observations over five month-long intervals,
corresponding to special orbital configurations of the coronagraphs
aboard the Solar Terrestrial Relations Observatory (STEREO) and Solar
and Heliospheric Observatory missions. This allows us to sort out CMEs
from other outward-propagating features (e.g., waves or outflows),
and thus to identify the total number of unique CMEs ejected during
those periods. We determine the CME visibility functions (VFs) of the
STEREO COR2-A/B and LASCO C2/C3 coronagraphs directly as the ratio of
observed to unique CMEs. The VFs range from 0.71 to 0.92 for a 95%
confidence interval. By comparing detections between coronagraphs
on the same spacecraft and from multiple spacecraft, we assess the
influence of field of view (FOV), instrument performance, and projection
effects on the CME detection ability without resorting to proxies,
such as flares or radio bursts. We find that no major CMEs are missed
by any of the coronagraphs, that a few slow halo-like events may be
missed in synoptic cadence movies, and that narrow FOV coronagraphs
have difficulties discriminating between CMEs and other ejections,
leading to "false" detection rates. We conclude that CME detection can
only be validated with multi-viewpoint imaging—two coronagraphs in
quadrature offer adequate detection capability. Finally, we apply the
VFs to observed CME rates resulting in upward corrections of 40%.
---------------------------------------------------------
Title: The Science Case for the $4{\pi}$ Perspective: A Polar/Global
View for Studying the Evolution & Propagation of the Solar Wind
and Solar Transients
Authors: Vourlidas, A.; Gibson, S.; Hassler, D.; Hoeksema, T.; Linton,
M.; Lugaz, N.; Newmark, J.
2020arXiv200904880V Altcode:
To make progress on the open questions on CME/CIR propagation, their
interactions and the role and nature of the ambient solar wind, we need
spatially resolved coverage of the inner heliosphere -- both in-situ and
(critically) imaging -- at temporal scales matching the evolutionary
timescales of these phenomena (tens of minutes to hours), and from
multiple vantage points. The polar vantage is uniquely beneficial
because of the wide coverage and unique perspective it provides. The
ultimate goal is to achieve full $4\pi$ coverage of the solar surface
and atmosphere by 2050.
---------------------------------------------------------
Title: Trigger Shy? Flare-less Active Region Circular Prominence
Eruption
Authors: Mason, E.; Antiochos, S.; Vourlidas, A.
2020SPD....5121001M Altcode:
Prominence eruptions have been studied since the days of Skylab, and
generally fall into two categories based on their locations: quiet Sun
and active regions. Quiescent prominences are generally slow to grow and
take can days to erupt, with or without any evidence of energization
prior to eruption. By contrast, active region prominences generally
erupt on time scales of hours or minutes, and are often accompanied by
powerful flares. This study reports on an observation of an unusual
circular prominence eruption located in an active region which
occurs without any evidence of flaring as a trigger. The prominence
is under the dome surface of a raining null point topology, which was
part of the extended decay phase of the active region designated NOAA
12488/12501. One half of the prominence undergoes a partial eruption,
and the cool plasma subsequently drains onto the side which did not
erupt, followed by a poorly-structured CME observed by SOHO LASCO C2
shortly after the eruption. We analyze both the failed eruption and
secondary CME using SDO AIA, STEREO-A, and SOHO LASCO imagery. The
location of the null-point topology raises critical questions about
the role of open/closed boundaries in eruptive phenomena and CME
structure. The poor structure of the outflowing CME is likely the
result of the destruction of the flux rope through reconnection as
it passes through the null-point structure, and possibly through
additional overlying closed field. The eruption does not show a
trigger, but arcades and ribbons form over the erupted half of the
prominence. Taken together, the failed eruption presents eruption
characteristics of both a CME and a jet, with potential evidence of a
low-energy reconnection mechanism driving failed eruptions in highly
decayed but still topologically compact magnetic fields.
---------------------------------------------------------
Title: Radio Observations of Coronal Mass Ejections: Space Weather
Aspects
Authors: Vourlidas, Angelos; Carley, Eoin P.; Vilmer, Nicole
2020FrASS...7...43V Altcode:
We review the current state-of-affairs in radio observations of Coronal
Mass Ejections (CMEs) from a Space Weather perspective. In particular,
we examine the role of radio observations in predicting or presaging
an eruption, in capturing the formation stages of the CME, and in
following the CME evolution in the corona and heliosphere. We then
look to the future and identify capabilities and research areas where
radio observations---particularly, spectropolarimetric imaging---offer
unique advantages for Space Weather research on CMEs. We close with
a discussion of open issues and possible strategies for enhancing the
relevance and importance of radio astronomy for Space Weather science.
---------------------------------------------------------
Title: The Solar Origin of Particle Events Measured by Parker
Solar Probe
Authors: Kouloumvakos, Athanasios; Vourlidas, Angelos; Rouillard,
Alexis P.; Roelof, Edmond C.; Leske, Rick; Pinto, Rui; Poirier, Nicolas
2020ApJ...899..107K Altcode:
During the second solar encounter phase of Parker Solar Probe (PSP),
two small solar energetic particle (SEP) events were observed by the
Integrated Science Investigation of the Sun, on 2019 April 2 and 4. At
the time, PSP was approaching its second perihelion at a distance of
∼24.8 million kilometers from the solar center, it was in near-radial
alignment with STEREO-A and in quadrature with Earth. During the two
SEP events multiple narrow ejections and a streamer-blowout coronal mass
ejection (SBO-CME) originated from a solar region situated eastward of
PSP. We analyze remote-sensing observations of the solar corona, and
model the different eruptions and how PSP was connected magnetically
to the solar atmosphere to determine the possible origin of the two
SEP events. We find that the SEP event on April 2 was associated with
the two homologous ejections from active region 12738 that included two
surges and EUV waves occurring in quick succession. The EUV waves appear
to merge and were fast enough to form a shock in the low corona. We
show that the April 4 SEP event originates in the SBO-CME. Our modeling
work suggests that formation of a weak shock is likely for this CME.
---------------------------------------------------------
Title: On the Expansion Speed of Coronal Mass Ejections: Implications
for Self-Similar Evolution
Authors: Balmaceda, L. A.; Vourlidas, A.; Stenborg, G.; St. Cyr, O. C.
2020SoPh..295..107B Altcode:
A proper characterization of the kinematics of coronal mass
ejections (CMEs) is important not only for practical purposes,
i.e. space weather forecasting, but also to improve our current
understanding of the physics behind their evolution in the middle
corona and into the heliosphere. The first and core step toward
this goal is the estimation of the three main components of the CME
speeds, namely the expansion speed relative to the center of motion
in both, the radial and lateral directions, and the propagation
speed (i.e. V<SUB>front</SUB>, V<SUB>lat</SUB>, V<SUB>bulk</SUB>,
respectively). To this aim, we exploit the observations obtained
with COR2 onboard the Solar Terrestrial Relations Observatory
(STEREO) from 2007 to 2014 to investigate the relationships among the
different components as a function of the heliocentric distance of
the CME events. Here, we analyze a sample of 475 CMEs. The selected
events exhibit clear flux rope signatures as seen either edge on
(i.e. F-CMEs: three-part structure, presence of a cavity) or face on
(i.e. L- or loop CMEs) in white light images. Our main findings are: i)
L-CMEs show almost twice as large expansion speeds compared to F-CMEs
(V<SUB>front ,L</SUB>=367 kms−<SUP>1</SUP>, V<SUB>lat ,L</SUB>=365
kms−<SUP>1</SUP> vs. V<SUB>front ,F</SUB>=215 kms−<SUP>1</SUP>,
V<SUB>lat ,F</SUB>=182 kms−<SUP>1</SUP>); ii) the relationship
between the two components of the expansion speeds is linear and does
not change with height; iii) the ratio of the propagation speed to
the lateral expansion speed is a function of the angular width that
describes the self-similarity evolution of a CME; and iv) 65% of the
CMEs exhibit a self-similar evolution at 10 solar radii, reaching 70%
at 15 solar radii.
---------------------------------------------------------
Title: How Reliable are CME speeds derived from single viewpoint
observations?
Authors: Paouris, Evangelos; Vourlidas, Angelos; Papaioannou,
Athanasios; Anastasiadis, Anastasios
2020EGUGA..22..625P Altcode:
Images of Coronal Mass Ejections (CMEs) are primarily acquired
by space-based coronagraphs. Such images capture the outward flow
of density structures from the Sun by observing Thompson-scattered
sunlight from the free electrons entrained in these structures. Because
the emission is optically thin, CMEs images are projections of their
real 3D structure on the field of view (FOV) of the coronagraph. As
a result, the CME characteristics (e.g. linear speed, angular width)
calculated from these images, suffer from projection effects and
their reliability needs to be quantified. In this work we apply a
geometrical method for the de-projection of the linear CME speeds
of 4009 CMEs from the CDAW catalog, associated with solar flares
(3225 C-class, 736 M-class and 48 X-class solar flares). Our aim is
to provide a robust quantification of the reliability of the CME
properties from L1 (SOHO/LASCO) single viewpoint measurements.In
addition, we compare the intensity and location of solar flares
with the CME kinematic characteristics. In particular, 482 M-class
solar flares associated with CMEs with an angular width 30°<
w < 120°, show a dependence of the mean CME linear speed with
the longitude of the parent solar flare, indicating that projection
effects of CMEs should be reduced near the solar limb. However, such
deprojections tend to overcorrect the CME speed for sources near the
solar meridian. They result in speeds of the order of 5000-7000 km/s,
which seem physically unreasonable. By considering the 3D extent of
the CMEs, we provide a novel geometrical correction of the deprojected
CME linear speed. The resulting speeds range from a few 100 km/s up to
almost 2600 km/s, a much more physically acceptable correction. This
study has important implications for Space Weather applications since
the reliable estimation of the CME linear speed has a direct effect
on the time of arrival of CMEs at Earth and the quantification of the
expected peak flux of solar radiation storms.Acknowledgement: This work
was funded from the State Scholarships Foundation of Greece (I.K.Y.),
in the framework of: "Funding Post-doctoral Researchers" of the b.p.:
"Human Resources Development, Education and Lifelong Learning" from ESPA
(2014-2020).
---------------------------------------------------------
Title: The forming slow solar wind imaged along streamer rays by
the wide-angle imager on Parker Solar Probe
Authors: Poirier, Nicolas; Kouloumvakos, Athanasios; Rouillard, Alexis
P.; Pinto, Rui; Vourlidas, Angelos; Stenborg, Guillermo; Valette,
Emeline; Howard, Russell A.; Hess, Phillip; Thernisien, Arnaud; Rich,
Nathan; Griton, Léa; Indurain, Mikel; Raouafi, Nour-Edine; Lavarra,
Michael; Réville, Victor
2020EGUGA..2211552P Altcode:
The Wide-field Imager for Solar PRobe (WISPR) obtained the first
high-resolution images of coronal rays at heights below 15 Rsun when
Parker Solar Probe (PSP) was located inside 0.25 AU during the first
encounter. We exploit these remarkable images to reveal the structure
of coronal rays at scales that are not easily discernible in images
taken from near 1 AU. To analyze and interpret WISPR observations
which evolve rapidly both radially and longitudinally, we construct
a latitude versus time map using full WISPR dataset from the first
encounter. From the exploitation of this map and also from sequential
WISPR images we show the presence of multiple sub-structures inside
streamers and pseudo-streamers. WISPR unveils the fine-scale structure
of the densest part of streamer rays that we identify as the solar
origin of the heliospheric plasma sheet typically measured in situ in
the solar wind. We exploit 3-D magneto-hydrodynamic (MHD) models and
we construct synthetic white-light images to study the origin of the
coronal structures observed by WISPR. Overall, including the effect of
the spacecraft relative motion towards the individual coronal structures
we can interpret several observed features by WISPR. Moreover, we
relate some coronal rays to folds in the heliospheric current sheet
that are unresolved from 1 AU. Other rays appear to form as a result
of the inherently inhomogeneous distribution of open magnetic flux
tubes. This work was funded by the European Research Council through
the project SLOW_SOURCE - DLV-819189.
---------------------------------------------------------
Title: Estimation of the Physical Parameters of a CME at High Coronal
Heights Using Low-frequency Radio Observations
Authors: Mondal, Surajit; Oberoi, Divya; Vourlidas, Angelos
2020ApJ...893...28M Altcode: 2019arXiv190912041M
Measuring the physical parameters of coronal mass ejections
(CMEs), particularly their entrained magnetic field, is crucial for
understanding their physics and for assessing their geoeffectiveness. At
the moment, only remote sensing techniques can probe these quantities
in the corona, the region where CMEs form and acquire their defining
characteristics. Radio observations offer the most direct means
for estimating the magnetic field when gyrosynchrotron emission
is detected. In this work we measure various CME plasma parameters,
including its magnetic field, by modeling the gyrosynchrotron emission
from a CME. The dense spectral coverage over a wide frequency range
provided by the Murchison Widefield Array (MWA) affords a much better
spectral sampling than possible before. The MWA images also provide
a much higher imaging dynamic range, enabling us to image these weak
emissions. Hence we are able to detect radio emission from a CME at
larger distances (∼4.73 R<SUB>⊙</SUB>) than have been reported
before. The flux densities reported here are among the lowest measured
in similar works. Our ability to make extensive measurements on a slow
and otherwise unremarkable CME suggests that with the availability of
data from the new-generation instruments like the MWA, it should now
be possible to make routine, direct detections of radio counterparts
of CMEs.
---------------------------------------------------------
Title: How Does Magnetic Reconnection Drive the Early-stage Evolution
of Coronal Mass Ejections?
Authors: Zhu, Chunming; Qiu, Jiong; Liewer, Paulett; Vourlidas,
Angelos; Spiegel, Michael; Hu, Qiang
2020ApJ...893..141Z Altcode: 2020arXiv200311134Z
Theoretically, coronal mass ejection (CME) kinematics are related
to magnetic reconnection processes in the solar corona. However, the
current quantitative understanding of this relationship is based on the
analysis of only a handful of events. Here we report a statistical study
of 60 CME-flare events from 2010 August to 2013 December. We investigate
kinematic properties of CMEs and magnetic reconnection in the low
corona during the early phase of the eruptions, by combining limb
observations from STEREO with simultaneous on-disk views from SDO. For
a subset of 42 events with reconnection rate evaluated by the magnetic
fluxes swept by the flare ribbons on the solar disk observed from SDO,
we find a strong correlation between the peak CME acceleration and
the peak reconnection rate. Also, the maximum velocities of relatively
fast CMEs (≳600 km s<SUP>-1</SUP>) are positively correlated with the
reconnection flux, but no such correlation is found for slow CMEs. A
time-lagged correlation analysis suggests that the distribution
of the time lag of CME acceleration relative to reconnection rate
exhibits three peaks, approximately 10 minutes apart, and on average,
acceleration-led events have smaller reconnection rates. We further
compare the CME total mechanical energy with the estimated energy
in the current sheet. The comparison suggests that, for small-flare
events, reconnection in the current sheet alone is insufficient to
fuel CMEs. Results from this study suggest that flare reconnection
may dominate the acceleration of fast CMEs, but for events of slow
CMEs and weak reconnection, other mechanisms may be more important.
---------------------------------------------------------
Title: Solar physics in the 2020s: DKIST, parker solar probe, and
solar orbiter as a multi-messenger constellation
Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.;
Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi,
G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.;
Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.;
Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R.
2020arXiv200408632M Altcode:
The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope
(DKIST) is about to start operations at the summit of Haleakala
(Hawaii). DKIST will join the early science phases of the NASA
and ESA Parker Solar Probe and Solar Orbiter encounter missions. By
combining in-situ measurements of the near-sun plasma environment and
detail remote observations of multiple layers of the Sun, the three
observatories form an unprecedented multi-messenger constellation to
study the magnetic connectivity inside the solar system. This white
paper outlines the synergistic science that this multi-messenger
suite enables.
---------------------------------------------------------
Title: Simulating White-Light Images of Coronal Structures for Parker
Solar Probe/WISPR: Study of the Total Brightness Profiles
Authors: Nisticò, Giuseppe; Bothmer, Volker; Vourlidas, Angelos;
Liewer, Paulett C.; Thernisien, Arnaud F.; Stenborg, Guillermo;
Howard, Russell A.
2020SoPh..295...63N Altcode: 2020arXiv200405447N
The Wide-field Imager for Parker Solar Probe (WISPR) captures
unprecedented white-light images of the solar corona and inner
heliosphere. Thanks to the uniqueness of the Parker Solar Probe's
(PSP) orbit, WISPR is able to image "locally" coronal structures at
high spatial and time resolutions. The observed plane of sky, however,
rapidly changes because of the PSP's high orbital speed. Therefore,
the interpretation of the dynamics of the coronal structures recorded
by WISPR is not straightforward. A first study, undertaken by Liewer et
al. (Solar Phys.294, 93, 2019), shows how different coronal features
(e.g., streamers, flux ropes) appear in the field-of-view of WISPR
by means of raytracing simulations. In particular, they analyze
the effects of the spatial resolution changes on both the images
and the associated height-time maps, and introduce the fundamentals
for geometric triangulation. In this follow-up paper, we focus on
the study of the total brightness of a simple, spherical, plasma
density structure, to understand how the analysis of Thomson-scattered
emission by the electrons in a coronal feature can shed light into the
determination of its kinematic properties. We investigate two cases:
(i) a density sphere at a constant distance from the Sun for different
heliographic longitudes; (ii) a density sphere moving outwardly with
constant speed. The study allows us to characterize the effects of
the varying heliocentric distance of the observer and scattering angle
on the total brightness observed, which we exploit to contribute to a
better determination of the position and speed of the coronal features
observed by WISPR.
---------------------------------------------------------
Title: Relating Streamer Flows to Density and Magnetic Structures
at the Parker Solar Probe
Authors: Rouillard, Alexis P.; Kouloumvakos, Athanasios; Vourlidas,
Angelos; Kasper, Justin; Bale, Stuart; Raouafi, Nour-Edine; Lavraud,
Benoit; Howard, Russell A.; Stenborg, Guillermo; Stevens, Michael;
Poirier, Nicolas; Davies, Jackie A.; Hess, Phillip; Higginson,
Aleida K.; Lavarra, Michael; Viall, Nicholeen M.; Korreck, Kelly;
Pinto, Rui F.; Griton, Léa; Réville, Victor; Louarn, Philippe;
Wu, Yihong; Dalmasse, Kévin; Génot, Vincent; Case, Anthony W.;
Whittlesey, Phyllis; Larson, Davin; Halekas, Jasper S.; Livi, Roberto;
Goetz, Keith; Harvey, Peter R.; MacDowall, Robert J.; Malaspina, D.;
Pulupa, M.; Bonnell, J.; de Witt, T. Dudok; Penou, Emmanuel
2020ApJS..246...37R Altcode: 2020arXiv200101993R
The physical mechanisms that produce the slow solar wind are still
highly debated. Parker Solar Probe's (PSP's) second solar encounter
provided a new opportunity to relate in situ measurements of the
nascent slow solar wind with white-light images of streamer flows. We
exploit data taken by the Solar and Heliospheric Observatory, the Solar
TErrestrial RElations Observatory (STEREO), and the Wide Imager on Solar
Probe to reveal for the first time a close link between imaged streamer
flows and the high-density plasma measured by the Solar Wind Electrons
Alphas and Protons (SWEAP) experiment. We identify different types of
slow winds measured by PSP that we relate to the spacecraft's magnetic
connectivity (or not) to streamer flows. SWEAP measured high-density and
highly variable plasma when PSP was well connected to streamers but more
tenuous wind with much weaker density variations when it exited streamer
flows. STEREO imaging of the release and propagation of small transients
from the Sun to PSP reveals that the spacecraft was continually impacted
by the southern edge of streamer transients. The impact of specific
density structures is marked by a higher occurrence of magnetic field
reversals measured by the FIELDS magnetometers. Magnetic reversals are
associated with much stronger density variations inside than outside
streamer flows. We tentatively interpret these findings in terms of
magnetic reconnection between open magnetic fields and coronal loops
with different properties, providing support for the formation of a
subset of the slow wind by magnetic reconnection.
---------------------------------------------------------
Title: Modeling the Early Evolution of a Slow Coronal Mass Ejection
Imaged by the Parker Solar Probe
Authors: Rouillard, Alexis P.; Poirier, Nicolas; Lavarra, Michael;
Bourdelle, Anthony; Dalmasse, Kévin; Kouloumvakos, Athanasios;
Vourlidas, Angelos; Kunkel, Valbona; Hess, Phillip; Howard, Russ A.;
Stenborg, Guillermo; Raouafi, Nour E.
2020ApJS..246...72R Altcode: 2020arXiv200208756R
During its first solar encounter, the Parker Solar Probe (PSP) acquired
unprecedented up-close imaging of a small coronal mass ejection (CME)
propagating in the forming slow solar wind. The CME originated as a
cavity imaged in extreme ultraviolet that moved very slowly (<50
km s<SUP>-1</SUP>) to 3-5 solar radii (R <SUB>⊙</SUB>), where it
then accelerated to supersonic speeds. We present a new model of
an erupting flux rope (FR) that computes the forces acting on its
expansion with a computation of its internal magnetic field in three
dimensions. The latter is accomplished by solving the Grad-Shafranov
equation inside two-dimensional cross sections of the FR. We use this
model to interpret the kinematic evolution and morphology of the CME
imaged by PSP. We investigate the relative role of toroidal forces,
momentum coupling, and buoyancy for different assumptions on the
initial properties of the CME. The best agreement between the dynamic
evolution of the observed and simulated FR is obtained by modeling the
two-phase eruption process as the result of two episodes of poloidal
flux injection. Each episode, possibly induced by magnetic reconnection,
boosted the toroidal forces accelerating the FR out of the corona. We
also find that the drag induced by the accelerating solar wind could
account for about half of the acceleration experienced by the FR. We
use the model to interpret the presence of a small dark cavity, clearly
imaged by PSP deep inside the CME, as a low-density region dominated
by its strong axial magnetic fields.
---------------------------------------------------------
Title: Small, Low-energy, Dispersive Solar Energetic Particle Events
Observed by Parker Solar Probe
Authors: Hill, M. E.; Mitchell, D. G.; Allen, R. C.; de Nolfo,
G. A.; Vourlidas, A.; Brown, L. E.; Jones, S. I.; McComas, D. J.;
McNutt, R. L., Jr.; Mitchell, J. G.; Szalay, J. R.; Wallace, S.; Arge,
C. N.; Christian, E. R.; Cohen, C. M. S.; Crew, A. B.; Desai, M. I.;
Giacalone, J.; Henney, C. J.; Joyce, C. J.; Krimigis, S. M.; Leske,
R. A.; Mewaldt, R. A.; Nelson, K. S.; Roelof, E. C.; Schwadron, N. A.;
Wiedenbeck, M. E.
2020ApJS..246...65H Altcode:
The Energetic Particle Instrument-Low Energy (EPI-Lo) experiment has
detected several weak, low-energy (∼30-300 keV nucleon<SUP>-1</SUP>)
solar energetic particle (SEP) events during its first two closest
approaches to the Sun, providing a unique opportunity to explore the
sources of low-energy particle acceleration. As part of the Parker
Solar Probe (PSP) Integrated Science Investigation of the Sun (IS⊙IS)
suite, EPI-Lo was designed to investigate the physics of energetic
particles; however, in the special lowest-energy "time-of-flight only"
product used in this study, it also responds to solar photons in a
subset of approximately sunward-looking apertures lacking special
light-attenuating foils. During the first three perihelia, in a frame
rotating with the Sun, PSP undergoes retrograde motion, covering a
17° heliographic longitudinal range three times during the course
of the ∼11-day perihelion passes, permitting a unique spatial
and temporal study into the location, correlation, and persistence
of previously unmeasurable SEPs. We examine the signatures of these
SEPs (during the first PSP perihelion pass only) and the connection to
possible solar sources using remote observations from the Solar Dynamics
Observatory (SDO), the Solar TErrestrial RElations Observatory (STEREO),
and the ground-based Global Oscillation Network Group (GONG). The
orientation of the Sun relative to STEREO, SDO, and GONG makes such
identifications challenging, but we do have several candidates,
including an equatorial coronal hole at a Carrington longitude of
∼335°. To analyze observations from EPI-Lo, which is a new type
of particle instrument, we examine instrumental effects and provide
a preliminary separation of the ion signal from the photon background.
---------------------------------------------------------
Title: Observations of the 2019 April 4 Solar Energetic Particle
Event at the Parker Solar Probe
Authors: Leske, R. A.; Christian, E. R.; Cohen, C. M. S.; Cummings,
A. C.; Davis, A. J.; Desai, M. I.; Giacalone, J.; Hill, M. E.; Joyce,
C. J.; Krimigis, S. M.; Labrador, A. W.; Malandraki, O.; Matthaeus,
W. H.; McComas, D. J.; McNutt, R. L., Jr.; Mewaldt, R. A.; Mitchell,
D. G.; Posner, A.; Rankin, J. S.; Roelof, E. C.; Schwadron, N. A.;
Stone, E. C.; Szalay, J. R.; Wiedenbeck, M. E.; Vourlidas, A.; Bale,
S. D.; MacDowall, R. J.; Pulupa, M.; Kasper, J. C.; Allen, R. C.;
Case, A. W.; Korreck, K. E.; Livi, R.; Stevens, M. L.; Whittlesey,
P.; Poduval, B.
2020ApJS..246...35L Altcode: 2019arXiv191203384L
A solar energetic particle event was detected by the Integrated
Science Investigation of the Sun (IS⊙IS) instrument suite on Parker
Solar Probe (PSP) on 2019 April 4 when the spacecraft was inside of
0.17 au and less than 1 day before its second perihelion, providing
an opportunity to study solar particle acceleration and transport
unprecedentedly close to the source. The event was very small, with
peak 1 MeV proton intensities of ∼0.3 particles (cm<SUP>2</SUP>
sr s MeV)<SUP>-1</SUP>, and was undetectable above background levels
at energies above 10 MeV or in particle detectors at 1 au. It was
strongly anisotropic, with intensities flowing outward from the Sun up
to 30 times greater than those flowing inward persisting throughout
the event. Temporal association between particle increases and small
brightness surges in the extreme-ultraviolet observed by the Solar
TErrestrial RElations Observatory, which were also accompanied by type
III radio emission seen by the Electromagnetic Fields Investigation
on PSP, indicates that the source of this event was an active region
nearly 80° east of the nominal PSP magnetic footpoint. This suggests
that the field lines expanded over a wide longitudinal range between
the active region in the photosphere and the corona.
---------------------------------------------------------
Title: Detailed Imaging of Coronal Rays with the Parker Solar Probe
Authors: Poirier, Nicolas; Kouloumvakos, Athanasios; Rouillard, Alexis
P.; Pinto, Rui F.; Vourlidas, Angelos; Stenborg, Guillermo; Valette,
Emeline; Howard, Russell A.; Hess, Phillip; Thernisien, Arnaud; Rich,
Nathan; Griton, Lea; Indurain, Mikel; Raouafi, Nour-Edine; Lavarra,
Michael; Réville, Victor
2020ApJS..246...60P Altcode: 2019arXiv191209345P
The Wide-field Imager for Solar PRobe (WISPR) obtained the
first high-resolution images of coronal rays at heights below 15
R<SUB>⊙</SUB> when the Parker Solar Probe (PSP) was located inside
0.25 au during the first encounter. We exploit these remarkable
images to reveal the structure of coronal rays at scales that are
not easily discernible in images taken from near 1 au. To analyze and
interpret WISPR observations, which evolve rapidly both radially and
longitudinally, we construct a latitude versus time map using the full
WISPR data set from the first encounter. From the exploitation of this
map and also from sequential WISPR images. we show the presence of
multiple substructures inside streamers and pseudostreamers. WISPR
unveils the fine-scale structure of the densest part of streamer
rays that we identify as the solar origin of the heliospheric plasma
sheet typically measured in situ in the solar wind. We exploit 3D
magnetohydrodynamic models, and we construct synthetic white-light
images to study the origin of the coronal structures observed by
WISPR. Overall, including the effect of the spacecraft relative
motion toward the individual coronal structures, we can interpret
several observed features by WISPR. Moreover, we relate some coronal
rays to folds in the heliospheric current sheet that are unresolved
from 1 au. Other rays appear to form as a result of the inherently
inhomogeneous distribution of open magnetic flux tubes.
---------------------------------------------------------
Title: Imaging the Solar Corona From Within
Authors: Hess, P.; Howard, R.; Vourlidas, A.; Bothmer, V.; Colaninno,
R.; DeForest, C.; Gallagher, B.; Hall, J. R.; Higginson, A.; Korendyke,
C.; Kouloumvakos, A.; Lamy, P.; Liewer, P.; Linker, J.; Linton, M.;
Penteado, P.; Plunkett, S.; Poirer, N.; Raouafi, N.; Rich, N.; Rochus,
P.; Rouillard, A.; Socker, D.; Stenborg, G.; Thernisien, A.; Viall, N.
2020AAS...23514907H Altcode:
Parker Solar Probe (PSP), launched, in August 2018 is humanity's
first probe of a stellar atmosphere. It will make measurements of
the near-Sun plasma from 'within' the outer corona with gradually
reduced perihelia from its first perihelia of 35 Rs in 2018-19 to 9.8
Rs in 2025. Here we report the results from the imaging observations
of the electron and dust corona, whe PSP was 35-54 Rs from the solar
surface, taken by the Wide-field Imager for Solar Probe (WISPR). The
spacecraft was near-corotating with the solar corona throughout the
observing window, which is an unprecedented situation for any type of
coronal imaging. Our initial analysis uncovers a long-hypothesized
depletion of the primordial dust orbiting near the Sun, reveals the
plasma structure of small-scale ejections, and provides a strict test
for validating model predictions of the large-scale configuration of
the coronal plasma. Thus, WISPR imaging allows the study of near-Sun
dust dynamics as the mission progresses. The high-resolution images
of small transients, largely unresolved from 1 AU orbits, unravel
the sub-structures of small magnetic flux ropes and show that the
Sun continually releases helical magnetic fields in the background
wind. Finally, WISPR's observations of the coronal streamer evolution
confirm the large-scale topology of the solar corona but they also
reveal that, as recently predicted, streamers are composed of yet
smaller sub-streamers channeling continual density fluctuations at
all visible scales.
---------------------------------------------------------
Title: A "Classic" Z-Rich Solar Energetic Particle Event Observed
by Parker Solar Probe at 0.2AU (April 2-3, 2019)
Authors: Roelof, E. C.; Allen, R. C.; Bale, S. D.; Christian, E. R.;
Cohen, C.; Cummings, A. C.; Hill, M. E.; Leske, R. A.; McComas,
D. J.; McNutt, R. L., Jr.; Mewaldt, R. A.; Mitchell, D. G.; Pulupa,
M.; Schwadron, N.; Stone, E. C.; Szalay, J. R.; Wiedenbeck, M. E.;
Vourlidas, A.
2019AGUFMSH21B..09R Altcode:
An impulsive solar energetic particle event displaying enhanced
abundances of heavy ions was observed on 02 April 2019 from 0.2 AU
by the EPI-Lo ion spectrometer of the ISOIS instrument suite on the
Parker Solar Probe (PSP). It was associated with brightenings and
south-westerly surges from the active region (2738) east of central
meridian as viewed in 193 nm images from STEREO-A (fortuitously
only10.7deg eastward of PSP). Compared to a subsequent impulsive
SEP event observed by ISOIS/EPI-Hi/EPI-Lo (only two days later on 04
April 2019), the enhancements (by species) were: 1-to-1 for ~60 keV
H; 20-fold for ~210 keV He; and >50-fold for both ~375 keV O and
~1500 keV Fe (i.e., unmeasurable above background on 04 April). The
velocity-dispersed ion onset ~1200 UT on 02 April implied that
impulsive ion injection began at about same time as a type iii burst
group (0850-1905 UT) observed by PSP/FIELDS. The ion event began with
beam-like pitch-angle anisotropies. The event was abruptly terminated by
a dramatic flux dropout ~0750 UT on 03 April, in close coincidence with
what appears to be a tangential discontinuity (or separatrix) in the
local magnetic field lines at PSP. We seem to have observed a "classic"
Z-rich ion event, as first identified during the decline of Solar Cycle
20 (Hurford et al., ApJLett, 1975; Zwickl et al., ApJ, 1978). These
were characterized by normal ion spectra, normal SW conditions,
association with small H-alpha flares, but with long-lasting (~1 day)
beam-like highly anisotropic pitch-angle distributions. Because the ion
spectra were similar to impulsive events with normal ion abundances,
Zwickl et al. argued that these events were Z-rich as a consequence of
enhanced abundances in the seed population, rather than differences in
the acceleration mechanism itself. Recently, Mason and Klecker (ApJ,
2017) have suggested a very efficient abundance enrichment process,
whereby propagation of all ions through a material thickness of ~20
micrograms/cm2 produces a selective (Z-rich) enhancement, because
of the heavies' greater affinity for electrons that mitigates the
Z^2/A energy loss rate. At low-coronal H-densities of 10^8-10^9 /cc,
this thickness would imply an ion path length of 0.2-2.0 solar radii,
which might produce a seed population consistent with the constraints
of our PSP observations.
---------------------------------------------------------
Title: Parker Solar Probe Observations of the 4 April 2019 Solar
Energetic Particle Event Near Perihelion
Authors: Leske, R. A.; Christian, E. R.; Cohen, C.; Cummings, A. C.;
Davis, A. D.; Hill, M. E.; Labrador, A. W.; McComas, D. J.; McNutt,
R. L., Jr.; Mewaldt, R. A.; Mitchell, D. G.; Roelof, E. C.; Schwadron,
N.; Stone, E. C.; Szalay, J. R.; Wiedenbeck, M. E.; Bale, S. D.;
MacDowall, R. J.; Pulupa, M.; Vourlidas, A.
2019AGUFMSH23C3357L Altcode:
A solar energetic particle (SEP) event was detected by the ISOIS
instrument suite on Parker Solar Probe (PSP) on 4 April 2019 when the
spacecraft was almost at its second perihelion of 0.17 AU, providing
an opportunity to study solar particle acceleration and transport
unprecedentedly close to the source. The event was small, with peak
1 MeV proton intensities at PSP of ~0.3 protons/(cm<SUP>2</SUP> sr s
MeV), and was not observed above background levels in either STEREO
or ACE particle detectors at 1 AU. It was strongly anisotropic, with
intensities flowing outward from the Sun ~30 times greater than those
flowing inward. Curiously, although the event was clearly observed in
the ISOIS EPI-Hi instrument at proton energies of a few MeV, it was much
less pronounced at energies of a few hundred keV in EPI-Lo. Conversely,
an event two days earlier on 2 April was observed in EPI-Lo, with
almost no detectable signature in EPI-Hi except for a significant
(though statistically limited) enhancement in heavy ions up to Fe at
energies of several MeV/nucleon. Based on STEREO/EUVI observations of
small brightness surges (several of which were also associated with type
III emission seen by both STEREO/WAVES and PSP/FIELDS), the source of
both these events appears to be an active region that was later numbered
Region 2738 when it rotated over the east limb and became visible from
Earth several days later. This region was far (nearly 90 degrees) to
the east of the nominal PSP magnetic footpoint, raising the question of
how these particles traveled to the observer. <P />We present EPI-Hi
and EPI-Lo observations of the time profiles, spectra, composition,
and anisotropy of this event, compare it with the earlier 2 April event,
and examine the associated solar activity and interplanetary environment
to assess the implications for particle acceleration and transport. <P
/>This work was supported by NASA under contract NNN06AA01C.
---------------------------------------------------------
Title: Observations of Magnetic Island Formation by the Wide Field
Imager on Parker Solar Probe (WISPR/PSP)
Authors: Linton, M.; Stenborg, G.; Howard, R. A.; Ko, Y. K.; Vourlidas,
A.; Higginson, A. K.; Tenerani, A.; Velli, M.; Liewer, P. C.
2019AGUFMSH33D3397L Altcode:
We report on observations by the Wide Field Imager on Parker Solar
Probe of possible magnetic island formation in a solar coronal streamer
current sheet. Remote sensing observations during the second perihelion
of Parker Solar Probe show the formation and ejection of an elliptical
structure in the center of the streamer current sheet. The morphology
and evolution of this candidate magnetic island is consistent with
magnetohydrodynamical simulations of island formation and ejection
in solar wind current sheets. We will review the relevant theory and
simulations as they relate to this observation, and will compare
and contrast these observations with corresponding remote sensing
observation of candidate island formation events made from 1 AU by
the SOHO and STEREO spacecraft. <P />This work was supported by the
NASA Parker Solar Probe Program Office.
---------------------------------------------------------
Title: Imaging the Solar Corona from Within: First Results from the
Parker Solar Probe Telescope
Authors: Howard, R. A.; Vourlidas, A.; Bothmer, V.; Colaninno, R. C.;
DeForest, C.; Gallagher, B.; Hall, J. R.; Hess, P.; Higginson, A. K.;
Korendyke, C.; Kouloumvakos, A.; Lamy, P.; Liewer, P. C.; Linker, J.;
Linton, M.; Penteado, P. F.; Plunkett, S. P.; Poirier, N.; Raouafi,
N.; Rich, N.; Rochus, P. L.; Rouillard, A. P.; Socker, D. G.; Stenborg,
G.; Thernisien, A.; Viall, N. M.
2019AGUFMSH11A..04H Altcode:
Parker Solar Probe (PSP) launched in August 2018 is humanity's
first probe of a stellar atmosphere. It will make measurements of
the near-Sun plasma from 'within' the outer corona with gradually
reduced perihelia from its first perihelia of 35 Rs in 2018-19 to 9.8
Rs in 2025. Here we report the results from the imaging observations
of the electron and dust corona, whe PSP was 35-54 Rs from the solar
surface, taken by the Wide-field Imager for Solar Probe (WISPR). The
spacecraft was near-corotating with the solar corona throughout the
observing window, which is an unprecedented situation for any type of
coronal imaging. Our initial analysis uncovers a long-hypothesized
depletion of the primordial dust orbiting near the Sun, reveals the
plasma structure of small-scale ejections, and provides a strict test
for validating model predictions of the large-scale configuration of
the coronal plasma. Thus, WISPR imaging allows the study of near-Sun
dust dynamics as the mission progresses. The high-resolution images
of small transients, largely unresolved from 1 AU orbits, unravel
the sub-structures of small magnetic flux ropes and show that the
Sun continually releases helical magnetic fields in the background
wind. Finally, WISPR's observations of the coronal streamer evolution
confirm the large-scale topology of the solar corona but they also
reveal that, as recently predicted, streamers are composed of yet
smaller sub-streamers channeling continual density fluctuations at
all visible scales.
---------------------------------------------------------
Title: Evolution of the geoeffective April 5, 2010 CME in the inner
heliosphere: A global MHD model with a data-constrained magnetic
flux rope specification.
Authors: Provornikova, E.; Merkin, V. G.; Gibson, S. E.; Malanushenko,
A. V.; Arge, C. N.; Vourlidas, A.
2019AGUFMSH42A..03P Altcode:
Modeling the evolution of internal magnetic structure of interplanetary
coronal mass ejections (ICMEs) is important both for space weather
prediction and for basic understanding of magnetized space plasma
interactions. Data-driven modeling of ICMEs in the inner heliosphere
(starting beyond the critical surface in the corona) presents
an attractive and computationally feasible approach, since it
bypasses the complex problem of CME initiation and eruption in the
corona. Using this approach, we simulate the propagation of ICMEs
through the inner heliosphere using a global model driven at the
coronal boundary by the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs
are initiated at 20 solar radii (Rs) using a magnetohydrodynamic
(MHD) analytical Gibson-Low (GL) model of a self-similarly expanding
magnetic flux rope with parameters (e.g., location, geometry, speed,
orientation) constrained by white-light coronograph observations. The
ICME propagation is simulated using the Grid Agnostic MHD for Extended
Research Applications (GAMERA) MHD model, which is a recent reinvention
of the high-heritage Lyon-Fedder-Mobarry (LFM) code. We apply this
approach to the study of a geoeffective ICME which arrived at Earth
on April 5, 2010. This ICME appeared bright in SOHO/LASCO and STEREO
coronagraphs allowing derivation of its parameters near the Sun thus
constraining its properties in our model. However, the orientation of
the flux rope was not determined uniquely from the observations. It was
also not clear which part of the ICME hit Earth and caused the severe
geomagnetic storm. By comparing synthetic white-light images derived
from our MHD modeling with images from SOHO/LASCO and STEREO/HI1 and
HI2, we shed light on the ICME initial orientation and it evolution due
to the interaction with the background solar wind. We further compare
the modeling results with ACE observations at 1 AU and discuss which
part of the CME was probed by the spacecraft.
---------------------------------------------------------
Title: Estimating the Visibility Function of Modern Coronagraphs
Authors: Balmaceda, L. A.; Xie, H.; Vourlidas, A.; St Cyr, O. C.
2019AGUFMSH41F3331B Altcode:
Estimates of the coronal mass ejection (CME) rate have been
well-documented and are quasi-continuous since the mid-1970s based on
coronagraph observations operating from ground and space. However,
because coronagraphs detect CMEs via the scattering of photospheric
emission from the electrons in the CME plasma, the visibility of a
given CME depends strongly on its direction of propagation. Moreover,
the detection of a CME by a given coronagraph depends both on the
event-observer geometry and on the instrumental sensitivity and
stray-light level of the detecting instrument. This dependence is
called the CME Visibility Function (VF), and is specific to a given
instrument. Here we determine and compare the visibility functions
for SOHO LASCO and STEREO COR1/COR2 coronagrpahs. Our goal is to
provide a thorough analysis of CME detectability for all currently
operating coronagraphs, over different phases of the solar cycle,
and to interpret the VF results both in terms of instrument design,
performance, and effects of projection. Taking advantage of the
multi-viewpoint observations available since the launch of STEREO we
are able to obtain new estimates of the global CME rate. We provide
the results based on specific periods of interest.
---------------------------------------------------------
Title: Gibson & Low Flux Rope Model: More Than a Spheromak!
Authors: Malanushenko, A. V.; Gibson, S. E.; Provornikova, E.;
Merkin, V. G.; Vourlidas, A.; Arge, C. N.; Dalmasse, K.; Nychka,
D. W.; Flyer, N.
2019AGUFMSH11C3397M Altcode:
Modeling solar coronal mass ejections (CMEs) is very important for
both understanding coronal physics and for improving the accuracy of
space weather forecasts. While it is generally accepted that CMEs
are primarily magnetic structures, the exact properties of these
structures could differ in different models and events. A structure
often considered is a spheromak, a toroidal twisted flux rope, which
is ejected as a CME bubble. Another commonly considered structure is a
twisted magnetic flux rope, which is anchored to the solar surface while
its upper portion is ejected into interplanetary space. In this talk
we will show how a well-known analytical magnetohydrodynamic CME model
(Gibson&Low, 1998), generally considered a spheromak-like model,
can be extended to represent both standard spheromak and twisted flux
tube configurations, as well as other topologically distinct magnetic
structures. We will begin with the general parameters of the flux rope
in this model (such as size and stretching parameters), and explore
topologically different configurations possible with their variation. We
then present several dimensionless parameters which can be varied to
achieve these different configurations and consider how they relate
to directly observable quantities. This work is particularly timely,
as the Gibson&Low model is been increasingly used as input to
numerical models of the solar corona and the heliosphere. The ability
to generate topologically different magnetic configurations within
this analytic solution is of great value to such simulations, as well
as for the studies of the flux ropes forming in the solar corona.
---------------------------------------------------------
Title: Combining Remote and in situ Parker Solar Probe and STEREO
Data to Understand Solar Wind Density Structures
Authors: Viall, N. M.; Howard, R. A.; Vourlidas, A.; DeForest, C.;
Kasper, J. C.; Korreck, K. E.; Case, A. W.; Stevens, M. L.; Whittlesey,
P. L.; Larson, D. E.; Livi, R.; Szabo, A.; Kepko, L.; Lavraud, B.;
Rouillard, A. P.; Velli, M.
2019AGUFMSH13C3432V Altcode:
The instrument suite on Parker Solar Probe offers an unprecedented
viewpoint of the ambient solar wind and structure therein, shortly after
its formation and release from the solar corona. We take advantage of
the synergistic observations of the first Parker Solar Probe encounters
and the STEREO COR2 deep field campaigns covering the same time periods
to study mesoscale solar wind density structures. They often occur
in a quasi-periodic train, especially near the heliospheric current
sheet. Some may be a consequence of the development of dynamics en
route; many are remnants of the formation and release of the solar
wind, and provide important constraints on solar wind models. The
opportunity to combine the different observing angles and fields of
view of the white light WISPR observations and white light STEREO COR2
observations with in situ density and plasma measurements from SWEAP
allows better understanding of the characteristics and properties of
mesoscale density structures. The in situ data measure precise size
scales, plasma boundaries, and relationships between density and
other parameters. They help in the interpretation of the structures
seen in white light images and in unraveling projection effects. The
white light images enhance the in situ data by providing global
heliospheric context, as well as the occurrence rate and 2-D size
scales of structures as a function of latitude and distance from the
Sun. Together, these observations provide crucial constraints on the
formation of structures in the solar wind.
---------------------------------------------------------
Title: The Solar Orbiter Heliospheric Imager (SoloHI) for the Solar
Orbiter Mission: Science and Instrument Status
Authors: Vourlidas, A.; Howard, R. A.; Colaninno, R. C.; Korendyke,
C.; Thernisien, A.; Linton, M.; Tun Beltran, S.; Liewer, P. C.; Velli,
M.; Linker, J.; Bothmer, V.; Rochus, P. L.; Lamy, P. L.
2019AGUFMSH24A..08V Altcode:
The SoloHI instrument has completed its development effort and has been
integrated onto the Solar Orbiter spacecraft. The mission, scheduled
for launch in February 2020, will undergo gravity assist maneuvers
around Venus to change both the perihelion distance as well as the
plane of the orbit to ultimately achieve a minimum perihelion of 0.28
AU and an orbital inclination of about 35° relative to the ecliptic
plane. The remote sensing instruments will operate for three 10-day
periods out of the nominal 6-month orbit. SoloHI detects sunlight
scattered by free electrons in the corona and solar wind from 5° to
45° elongation in visible wavelengths, providing linkage between solar
and solar wind observations. The science investigation focuses mainly on
the solar wind, including streamers, small-scale intensity and density
fluctuations, jets, and Coronal Mass Ejections (CMEs). SoloHI is very
similar to the HI-1 instrument on STEREO/SECCHI but with double the FOV
of HI-1. In this paper, we present our preparations for the mission
including the instrument status, our science planning strategy, our
observing plans for cruise phase, calibrations, early science and our
low-latency and science data products <P />This work has been supported
by NASA.
---------------------------------------------------------
Title: Challenges in the Analysis of Images from the Wide-field Imager
(WISPR) on Parker Solar Probe
Authors: Liewer, P. C.; Hall, J. R.; Penteado, P.; Vourlidas, A.;
Thernisien, A.; Howard, R. A.; Qiu, J.; Nistico, G.; Bothmer, V.
2019AGUFMSH23A..09L Altcode:
The three-to-five-month highly elliptical orbit of Parker Solar Probe
(PSP), approaching within 10 solar radii of the Sun, will allow the
Wide-field Imager for Solar Probe (WISPR) to view the corona with
unprecedented spatial resolution from multiple viewpoints. WISPR,
located on the ram side of PSP, will image and fly through structures
sample by the in situ instruments. WISPR has a wide fixed angular
field-of-view (FOV), extending radially from 13.5° to 108° from
the Sun and approximately 50° in the transverse direction, but the
physical extent of the imaged coronal region varies directly with the
distance of the spacecraft from the Sun. Challenges to interpreting
the motion of density features seen in the WISPR images come from the
wide and changing field-of-view and the unknown extent of the region
of the coronal that co-rotates with the Sun. To relate and compare
features seen in the images to observation by other instruments and
spacecraft with other locations and viewpoints, it is necessary to
relate the field-of-view of the WISPR telescopes at any given time
to other frames of reference, such as the various Heliographic and
Heliocentric coordinate systems. Here we discuss re-projections of
WISPR images into several frames, made utilizing the World Coordinate
System, which relies on information in the images' FITS headers
(see W. T. Thompson, 2006, DOI: 10.1051/0004 6361:20054262). We will
present methods for creating elongation vs. time images (J-maps)
for WISPR images and also a technique for tracking observed density
features to determine their 3D trajectories. These methods will be
illustrated using data from WISPR's first encounters with the Sun.
---------------------------------------------------------
Title: Near-Sun observations of an F-corona decrease and K-corona
fine structure
Authors: Howard, R. A.; Vourlidas, A.; Bothmer, V.; Colaninno, R. C.;
DeForest, C. E.; Gallagher, B.; Hall, J. R.; Hess, P.; Higginson,
A. K.; Korendyke, C. M.; Kouloumvakos, A.; Lamy, P. L.; Liewer, P. C.;
Linker, J.; Linton, M.; Penteado, P.; Plunkett, S. P.; Poirier, N.;
Raouafi, N. E.; Rich, N.; Rochus, P.; Rouillard, A. P.; Socker, D. G.;
Stenborg, G.; Thernisien, A. F.; Viall, N. M.
2019Natur.576..232H Altcode:
Remote observations of the solar photospheric light scattered by
electrons (the K-corona) and dust (the F-corona or zodiacal light)
have been made from the ground during eclipses<SUP>1</SUP> and from
space at distances as small as 0.3 astronomical units<SUP>2-5</SUP> to
the Sun. Previous observations<SUP>6-8</SUP> of dust scattering have
not confirmed the existence of the theoretically predicted dust-free
zone near the Sun<SUP>9-11</SUP>. The transient nature of the corona
has been well characterized for large events, but questions still
remain (for example, about the initiation of the corona<SUP>12</SUP>
and the production of solar energetic particles<SUP>13</SUP>) and
for small events even its structure is uncertain<SUP>14</SUP>. Here
we report imaging of the solar corona<SUP>15</SUP> during the first
two perihelion passes (0.16-0.25 astronomical units) of the Parker
Solar Probe spacecraft<SUP>13</SUP>, each lasting ten days. The view
from these distances is qualitatively similar to the historical views
from ground and space, but there are some notable differences. At
short elongations, we observe a decrease in the intensity of the
F-coronal intensity, which is suggestive of the long-sought dust
free zone<SUP>9-11</SUP>. We also resolve the fine-scale plasma
structure of very small eruptions, which are frequently ejected from
the Sun. These take two forms: the frequently observed magnetic flux
ropes<SUP>12,16</SUP> and the predicted, but not yet observed, magnetic
islands<SUP>17,18</SUP> arising from the tearing-mode instability in
the current sheet. Our observations of the coronal streamer evolution
confirm the large-scale topology of the solar corona, but also reveal
that, as recently predicted<SUP>19</SUP>, streamers are composed of
yet smaller substreamers channelling continual density fluctuations
at all visible scales.
---------------------------------------------------------
Title: Unraveling the Internal Magnetic Field Structure of the
Earth-directed Interplanetary Coronal Mass Ejections During 1995
- 2015
Authors: Gilbert, H. R.; Nieves-Chinchilla, T.; Jian, L.; Balmaceda,
L.; Vourlidas, A.; Szabo, A.; St Cyr, O. C.; Guedes dos Santos, L. F.
2019AGUFMSH43C3377G Altcode:
The magnetic field configurations associated with interplanetary
coronal mass ejections (ICMEs) are the in situ manifestations of the
entrained magnetic structure associated with coronal mass ejections
(CMEs). We present a comprehensive study of the internal magnetic
field configurations of ICMEs observed at 1 AU by the Wind mission
during 1995 - 2015. The goal is to unravel the internal magnetic
structure associated with the ICMEs and establish the signatures that
validate a flux-rope structure. We examine the expected magnetic field
signatures by simulating spacecraft trajectories within a simple flux
rope, i.e., with circular-cylindrical (CC) helical magnetic field
geometry. By comparing the synthetic configurations with the 353 ICME
in situ observations, we find that only 152 events (Fr) display the
clear signatures of an expected axial-symmetric flux rope. Two more
populations exhibit possible signatures of flux rope; 58 cases (F-)
display a small rotation (<90◦) of the magnetic field direction,
interpreted as a large separation of the spacecraft from the center,
and, 62 cases (F+) exhibit larger rotations, possibly arising from
more complex configuration. <P />The categories, Cx (14%) and E
events (9%), reveal signatures of complexity possibly related with
evolutionary processes. We then reconstruct the flux ropes assuming
CC geometry. We examine the orientation and geometrical properties
during the solar activity levels at the end of Solar Cycle 22 (SC22),
SC23 and part of SC24. The orientation exhibits solar cycle trends
and follow the heliospheric current sheet orientation. We confirm
previous studies that found a Hale cycle dependence of the poloidal
field reversal. By comparing our results with the occurrence of CMEs
with large angular width (AW> 60◦) we find a broad correlation
suggesting that such events are highly inclined CMEs. The solar cycle
distribution of bipolar vs. unipolar Bz configuration confirms that
the CMEs may remove solar cycle magnetic field and helicity.
---------------------------------------------------------
Title: Impacts of small coronal transients at Parker Solar Probe at
times of density increases and burst of magnetic switchbacks
Authors: Rouillard, A. P.; Kouloumvakos, A.; Vourlidas, A.; Raouafi,
N. E.; Lavraud, B.; Stenborg, G.; Kasper, J. C.; Bale, S.; Poirier,
N.; Howard, R. A.; Viall, N. M.; Lavarra, M.; Stevens, M. L.; Korreck,
K. E.; Case, A. W.; Whittlesey, P. L.; Larson, D. E.; Halekas, J. S.;
Livi, R.; Goetz, K.; Harvey, P.; MacDowall, R. J.; Malaspina, D.;
Pulupa, M.; Bonnell, J. W.; Dudok de Wit, T.
2019AGUFMSH12A..04R Altcode:
A subset at least of the slow solar wind is released in the form
of transients ejected continually along streamer rays. The physical
mechanisms responsible for these transient releases of dense material
are not yet fully understood. We exploit a period when the NASA
Solar-TErrestrial RElations Observatory-A (STEREO-A) was in orbital
quadrature with Parker Solar Probe (PSP) to track the release and
propagation of dense material from the corona to PSP. At the time
PSP had passed its second perihelion and was located near the Thomson
sphere of the inner Heliospheric Imager (HI-1) onboard STEREO-A. This
provided optimal observing conditions to track dense and therefore
bright structures from the corona to the Sun-approaching spacecraft. We
show that the streamers were continually ejecting bursts of dense
structures (so-called 'blobs') many of which exhibiting V-shapes that
are reminiscent of either magnetic kinks and/or the well-known back
ends of small magnetic flux ropes. The wide-angle imager on Parker
Solar Probe imaged similar structures at other locations of the
streamers during this second encounter suggesting a global nature
of this transient activity. We find evidence in STEREO ultraviolet
images for slow reconfigurations of the corona near the estimated source
regions of these structures but no one-to-one association is yet clearly
established between the lower and upper corona. The exploitation of
height-time maps ('J-maps') built from COR-2 and HI-1 images of the
solar wind allow us to track the dense features all the way to PSP. We
show that the spacecraft was repeatedly impacted by the southern edge
of these structures. The passage of the bright coronal material at
PSP is associated with clear density increases measured by the plasma
instrument as expected. We also find evidence that the impact of the
specific dense structures are correlated with a higher occurrence of
magnetic field reversals. Part of this work was funded by the European
Research Council through the project SLOW_SOURCE - DLV-819189
---------------------------------------------------------
Title: A Comparative Study of 2017 July and 2012 July Complex
Eruptions: Are Solar Superstorms "Perfect Storms" in Nature?
Authors: Liu, Y. D.; Zhao, X.; Hu, H.; Vourlidas, A.; Zhu, B.
2019AGUFMSH32A..02L Altcode:
It is paramount from both scientific and societal perspectives to
understand the generation of extreme space weather. We discuss the
formation of solar superstorms based on a comparative study of the 2012
July 23 and 2017 July 23 eruptions. The first one is Carrington-class,
and the second could rival the 1989 March event that caused the
most intense geomagnetic storm of the space age. Observations of
these events in the historically weak solar cycle 24 indicate that
a solar superstorm can occur in any solar cycle and at any phase of
the cycle. Recurrent patterns are identified in both cases, including
the long-lived eruptive nature of the active region, a complex event
composed of successive eruptions from the same active region, and
in-transit interaction between the successive eruptions resulting in
exceptionally strong ejecta magnetic fields at 1 AU. Each case also
shows unique characteristics. Preconditioning of the upstream solar
wind leading to unusually high solar wind speeds at 1 AU is observed
in the first case whereas not in the latter. This may suggest that
the concept of "preconditioning" appears to be necessary for making a
Carrington-class storm. We find a considerable deflection by nearby
coronal holes in the second case but not in the first. On the basis
of these results, we propose a hypothesis for further investigation
that superstorms are "perfect storms" in nature, i.e., a combination of
circumstances that results in an event of unusual magnitude. Historical
records of some extreme events seem to support our hypothesis.
---------------------------------------------------------
Title: Tracking Outward Propagating Small-Scale Structures from EUVI
through COR1 and COR2
Authors: Viall, N. M.; Alzate, N.; Morgan, H.; Vourlidas, A.
2019AGUFMSH13A..07V Altcode:
The challenge of connecting slow solar wind variability to its source
at the Sun is primarily due to the limitations on observational
data of the low corona. Instrumental light scattering is higher in
coronagraph observations very close to the solar surface, resulting
in poor signal-to-noise ratios. Additionally, the non-radial nature
of the coronal structures in this region hampers the tracking of
small-scale structures in observations, since they produce weaker
signals. Our work focuses on developing and applying advanced image
processing techniques to solar imaging data in an effort to connect
the low corona to the high corona with a focus on the identification
of the sources of small-scale structures in the slow solar wind. The
inner coronagraph, COR1, onboard the STEREO spacecraft, observes the low
corona from ~1.1 to 4 R<SUB>s</SUB>, imaging the important connection
between the solar wind, its source, and the formation of the solar
wind structures. We have developed an approach for processing COR1
that allows the tracking of small-scale structures. The core process
is a bandpass filter of the data over time, where the signal from high
frequency noise is suppressed, as well as slowly evolving structures. We
applied this method to a 10-day period of observations during solar
minimum and compared them to observations from the imager EUVI and outer
coronagraph COR2. Height-time profiles reveal structures propagating
through the different fields of view, establishing a connection between
the low and high corona. Further analysis will allow us to characterize
these structures and determine occurrence frequencies, size scales,
formation height and mechanism. Our method for processing COR1 opens
the door to ~13 years of STEREO/COR1 data for studies in general of
the connection between the low and high corona, and specifically of
small-scale coronal structures.
---------------------------------------------------------
Title: The Forming Slow Solar Wind Imaged along Streamer Rays by
the Wide-Angle Imager on Parker Solar Probe
Authors: Poirier, N.; Rouillard, A. P.; Kouloumvakos, A.; Vourlidas,
A.; Stenborg, G.; Pinto, R.; Réville, V.; Valette, E.; Howard,
R. A.; Hess, P.; Thernisien, A.; Rich, N.; Raouafi, N. E.; Lavarra,
M.; Liewer, P. C.; Qiu, J.; Indurain, M.
2019AGUFMSH12A..08P Altcode:
The Wide-field Imager for Solar PRobe (WISPR) recorded the first
detailed imaging of streamer rays when Parker Solar Probe was in
quasi-corotation with the corona. We exploit these new images to reveal
the time and space variability in these streamers at scales that are
not easily discernible in images taken from near 1AU, this provides new
insights on the forming slow solar wind. WISPR images are projected into
Carrington like maps to reveal the multiple white-light structures
of a streamer observed during the first perihelion passage. We
exploit 3-D magneto-hydrodynamic models to study the origin of these
sub-structures and interpret them as small corrugation in the streamers
and heliospheric current sheets. High-resolution simulations explain
a number of observational features observed by WISPR including the
effect of the spacecraft moving at high speed towards the individual
streamer rays that make up a streamer. Finally we highlight the level
of temporal variability in the streamers induced by propagating density
structures likely induced by time-dependent processes occurring in the
corona. This work was funded by the European Research Council through
the project SLOW_SOURCE - DLV-819189.
---------------------------------------------------------
Title: LOCKYER: Large Optimized Coronagraphs for KeY Emission line
Research
Authors: Laming, J. M.; Vourlidas, A.
2019AGUFMSH31B..15L Altcode:
LOCKYER will investigate the birth region of the Solar Wind, CMEs, SEPs,
and Space Weather. The mission will explore this critical coronal region
by acquiring spectroscopic and imaging observations of the off-limb
corona, from 1.2 to 12 Rs, across the EUV-UV-Visible spectrum. The
science investigation addresses two key long-standing science questions
<P />1. What powers the Solar Wind? <P />2. How do CMEs form and acquire
their defining characteristics? <P />The sun-pointed payload consists of
three telescopes mounted on a LEOstar spacecraft in a 650 km Sun-Sync
orbit. Observations are taken continuously, except during the brief
eclipses, and downlinked through a Ka-band link once daily. LOCKYER
observes over the western solar limb, synoptically, with either a
single or dual slit system. Visible and EUV images are obtained at a
1-5 minute cadence, depending on the objective. The spacecraft rotates
to the east limb every 30 min to acquire a full image of the equatorial
corona for Space Weather purposes. LOCKYER comprises three telescopes:
<P />1. A spectroscopic coronagraph in the EUV-UV range (70 - 170 nm)
<P />2. A visible coronagraph with a FOV of 1.5-12 Rs with polarization
and emission line filter capabilities <P />3. A broadband EUV (17-20
nm) coronagraph with FOV of 1.5 to 5 Rs. <P />All three instruments
use the same occulter mounted on an 8.5m boom. We will describe how
this instrument suite will be used to measure waves and dynamics,
coronal element abundances, and solar wind acceleration as three coupled
sets of phenomena, and used to investigate the various regimes of the
background solar wind, coronal mass ejections, and their associated
shock waves. <P />LOCKYER is a collaborative project between JHU APL,
NRL, SAO, Univ. of New Hampshire, Univ. of Colorado, Univ. of Montana,
SWRI, IAS, and IRAP.
---------------------------------------------------------
Title: Multi-species modelling of the forming solar wind from the
upper chromosphere to Parker Solar Probe
Authors: Lavarra, M.; Rouillard, A. P.; Blelly, P. L.; Pinto, R.;
Poirier, N.; Indurain, M.; Réville, V.; Stevens, M. L.; Kasper, J. C.;
Korreck, K. E.; Case, A. W.; Whittlesey, P. L.; Larson, D. E.; Bale,
S.; Halekas, J. S.; Livi, R.; Raouafi, N. E.; Goetz, K.; Harvey,
P.; MacDowall, R. J.; Malaspina, D.; Pulupa, M.; Bonnell, J. W.;
Dudok de Wit, T.; Lavraud, B.; Vourlidas, A.; Howard, R. A.
2019AGUFMSH11C3401L Altcode:
The effects of coronal heating on the properties of the escaping solar
wind are still debated. We investigate the development of temperature
anisotropies in the middle corona measured by past coronal spectrometers
by using a 1-D multi-species model of the forming solar wind. The model
assumes a bi-Maxwellian distribution function for all species, couples
neutral (hydrogen, helium) and charged particles (electrons, protons,
charged helium) and includes a self-consistent treatment of ionisation
processes in the upper chromosphere and low corona. Our simulations
extend to 70 solar radii and we compare our first results with the
bulk properties and anisotropies of the ions and electrons measured in
situ by Helios and Parker Solar Probe. We study the effects of ion and
electron heating separately as well as wave transport and dissipation
on the resulting solar wind properties for different coronal topologies
including streamers, pseudo-streamers and interplume regions. A first
multi-tube implementation of this kinetic-fluid code allows us to
compare our results with past spectroscopic measurements by the Solar
and Heliospheric Observatory and the future Solar Orbiter mission. Part
of this work was funded by the European Research Council through the
project SLOW_SOURCE - DLV-819189
---------------------------------------------------------
Title: Lyα science from the LST aboard the ASO-S mission
Authors: Vourlidas, Angelos
2019RAA....19..168V Altcode:
We review the status of solar Lyα science in anticipation of the
upcoming Advanced Space-based Solar Observatory (ASO-S) mission,
planned for a late 2021 (or 2022) launch. The mission carries a pair
of the Lyα Solar Telescopes (LST) capable of high resolution disk
and off-limb imaging, which will provide the first synoptic Lyα
imaging observations of the solar atmosphere. We discuss the history
of Lyα imaging and latest results, and outline the open questions
that ASO-S could address. ASO-S will launch at an optimal time for
Lyα science. Several other Lyα telescopes will be in operation. We
identify the synergies between ASO-S and other missions as well as
serendipitous non-solar science opportunities. We conclude that ASO-S
has the potential for breakthrough observations and discoveries in
the chromosphere-corona interface where the Lyα emission is the
major player.
---------------------------------------------------------
Title: Comparing extrapolations of the coronal magnetic field
structure at 2.5 R<SUB>⊙</SUB> with multi-viewpoint coronagraphic
observations
Authors: Sasso, C.; Pinto, R. F.; Andretta, V.; Howard, R. A.;
Vourlidas, A.; Bemporad, A.; Dolei, S.; Spadaro, D.; Susino, R.;
Antonucci, E.; Abbo, L.; Da Deppo, V.; Fineschi, S.; Frassetto, F.;
Landini, F.; Naletto, G.; Nicolini, G.; Nicolosi, P.; Pancrazzi, M.;
Romoli, M.; Telloni, D.; Ventura, R.
2019A&A...627A...9S Altcode: 2019arXiv190509005S
The magnetic field shapes the structure of the solar corona, but we
still know little about the interrelationships between the coronal
magnetic field configurations and the resulting quasi-stationary
structures observed in coronagraphic images (such as streamers,
plumes, and coronal holes). One way to obtain information on the
large-scale structure of the coronal magnetic field is to extrapolate
it from photospheric data and compare the results with coronagraphic
images. Our aim is to verify whether this comparison can be a fast
method to systematically determine the reliability of the many methods
that are available for modeling the coronal magnetic field. Coronal
fields are usually extrapolated from photospheric measurements that
are typically obtained in a region close to the central meridian on
the solar disk and are then compared with coronagraphic images at the
limbs, acquired at least seven days before or after to account for solar
rotation. This implicitly assumes that no significant changes occurred
in the corona during that period. In this work, we combine images from
three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) that
observe the Sun from different viewing angles to build Carrington maps
that cover the entire corona to reduce the effect of temporal evolution
to about five days. We then compare the position of the observed
streamers in these Carrington maps with that of the neutral lines
obtained from four different magnetic field extrapolations to evaluate
the performances of the latter in the solar corona. Our results show
that the location of coronal streamers can provide important indications
to distinguish between different magnetic field extrapolations.
---------------------------------------------------------
Title: Predicting the geoeffective properties of coronal mass
ejections: current status, open issues and path forward
Authors: Vourlidas, A.; Patsourakos, S.; Savani, N. P.
2019RSPTA.37780096V Altcode:
Much progress has been made in the study of coronal mass ejections
(CMEs), the main drivers of terrestrial space weather thanks to the
deployment of several missions in the last decade. The flow of energy
required to power solar eruptions is beginning to be understood. The
initiation of CMEs is routinely observed with cadences of tens
of seconds with arc-second resolution. Their inner heliospheric
evolution can now be imaged and followed routinely. Yet relatively
little progress has been made in predicting the geoeffectiveness of a
particular CME. Why is that? What are the issues holding back progress
in medium-term forecasting of space weather? To answer these questions,
we review, here, the measurements, status and open issues on the main
CME geoeffective parameters; namely, their entrained magnetic field
strength and configuration, their Earth arrival time and speed, and
their mass (momentum). We offer strategies for improving the accuracy
of the measurements and their forecasting in the near and mid-term
future. To spark further discussion, we incorporate our suggestions
into a top-level draft action plan that includes suggestions for sensor
deployment, technology development and modelling/theory improvements. <P
/>This article is part of the theme issue `Solar eruptions and their
space weather impact'.
---------------------------------------------------------
Title: Unraveling the Internal Magnetic Field Structure of the
Earth-directed Interplanetary Coronal Mass Ejections During 1995
- 2015
Authors: Nieves-Chinchilla, Teresa; Jian, Lan K.; Balmaceda, Laura;
Vourlidas, Angelos; dos Santos, Luiz F. G.; Szabo, Adam
2019SoPh..294...89N Altcode:
The magnetic field configurations associated with interplanetary
coronal mass ejections (ICMEs) are the in situ manifestations of the
entrained magnetic structure associated with coronal mass ejections
(CMEs). We present a comprehensive study of the internal magnetic field
configurations of ICMEs observed at 1 AU by the Wind mission during
1995 - 2015. The goal is to unravel the internal magnetic structure
associated with the ICMEs and establish the signatures that validate a
flux-rope structure. We examine the expected magnetic field signatures
by simulating spacecraft trajectories within a simple flux rope, i.e.,
with circular-cylindrical (CC) helical magnetic field geometry. By
comparing the synthetic configurations with the 353 ICME in situ
observations, we find that only 152 events (F<SUB>r</SUB>) display
the clear signatures of an expected axial-symmetric flux rope. Two
more populations exhibit possible signatures of flux rope; 58 cases
(F<SUP>−</SUP>) display a small rotation (<90<SUP>∘</SUP>)
of the magnetic field direction, interpreted as a large separation of
the spacecraft from the center, and, 62 cases (F<SUP>+</SUP>) exhibit
larger rotations, possibly arising from more complex configuration. The
categories, C<SUB>x</SUB> (14%) and E events (9%), reveal signatures
of complexity possibly related with evolutionary processes. We
then reconstruct the flux ropes assuming CC geometry. We examine
the orientation and geometrical properties during the solar activity
levels at the end of Solar Cycle 22 (SC22), SC23 and part of SC24. The
orientation exhibits solar cycle trends and follow the heliospheric
current sheet orientation. We confirm previous studies that found a
Hale cycle dependence of the poloidal field reversal. By comparing
our results with the occurrence of CMEs with large angular width
(AW>60<SUP>∘</SUP>) we find a broad correlation suggesting that
such events are highly inclined CMEs. The solar cycle distribution
of bipolar vs. unipolar B<SUB>z</SUB> configuration confirms that the
CMEs may remove solar cycle magnetic field and helicity.
---------------------------------------------------------
Title: Element Abundances: A New Diagnostic for the Solar Wind
Authors: Laming, J. Martin; Vourlidas, Angelos; Korendyke, Clarence;
Chua, Damien; Cranmer, Steven R.; Ko, Yuan-Kuen; Kuroda, Natsuha;
Provornikova, Elena; Raymond, John C.; Raouafi, Nour-Eddine; Strachan,
Leonard; Tun-Beltran, Samuel; Weberg, Micah; Wood, Brian E.
2019ApJ...879..124L Altcode: 2019arXiv190509319L
We examine the different element abundances exhibited by the closed
loop solar corona and the slow speed solar wind. Both are subject
to the first ionization potential (FIP) effect, the enhancement in
coronal abundance of elements with FIP below 10 eV (e.g., Mg, Si,
Fe) with respect to high-FIP elements (e.g., O, Ne, Ar), but with
subtle differences. Intermediate elements, S, P, and C, with FIP
just above 10 eV, behave as high-FIP elements in closed loops, but
are fractionated more like low-FIP elements in the solar wind. On
the basis of FIP fractionation by the ponderomotive force in the
chromosphere, we discuss fractionation scenarios where this difference
might originate. Fractionation low in the chromosphere where hydrogen
is neutral enhances the S, P, and C abundances. This arises with
nonresonant waves, which are ubiquitous in open field regions, and is
also stronger with torsional Alfvén waves, as opposed to shear (i.e.,
planar) waves. We discuss the bearing these findings have on models
of interchange reconnection as the source of the slow speed solar
wind. The outflowing solar wind must ultimately be a mixture of the
plasma in the originally open and closed fields, and the proportions
and degree of mixing should depend on details of the reconnection
process. We also describe novel diagnostics in ultraviolet and extreme
ultraviolet spectroscopy now available with these new insights, with
the prospect of investigating slow speed solar wind origins and the
contribution of interchange reconnection by remote sensing.
---------------------------------------------------------
Title: Simulating White Light Images of Coronal Structures for WISPR/
Parker Solar Probe: Effects of the Near-Sun Elliptical Orbit
Authors: Liewer, P.; Vourlidas, A.; Thernisien, A.; Qiu, J.; Penteado,
P.; Nisticò, G.; Howard, R.; Bothmer, V.
2019SoPh..294...93L Altcode:
The three-to-five-month elliptical orbit of Parker Solar Probe
(PSP), approaching within 10 solar radii of the Sun, will allow the
Wide-field Imager for Solar Probe (WISPR) to view the corona with
unprecedented spatial resolution from multiple viewpoints. WISPR has
a wide fixed angular field of view, extending from 13.5<SUP>∘</SUP>
to 108<SUP>∘</SUP> from the Sun and approximately 50<SUP>∘</SUP>
in the transverse direction, but the physical extent of the imaged
coronal region varies directly with the distance of the spacecraft from
the Sun. In a solar encounter period of approximately 10 days around
perihelion, PSP covers over 100 - 200° of heliographic longitude and
the distance from the Sun varies by a factor of two to five. In this
paper, we use synthetic white-light images to study the effects of the
rapid elliptical orbit on the images that can be anticipated for WISPR's
observations. We find that sequences of images can help identify coronal
density features that will be sampled by in-situ instruments. We also
find that the multiple viewpoints, provided by the rapid motion near
perihelion, can be used to obtain three-dimensional information on
the coronal density features.
---------------------------------------------------------
Title: Solar energetic particles in the inner heliosphere: status
and open questions
Authors: Anastasiadis, Anastasios; Lario, David; Papaioannou,
Athanasios; Kouloumvakos, Athanasios; Vourlidas, Angelos
2019RSPTA.37780100A Altcode:
Solar energetic particle (SEP) events are related to both solar flares
and coronal mass ejections (CMEs) and they present energy spectra that
span from a few keV up to several GeV. A wealth of observations from
widely distributed spacecraft have revealed that SEPs fill very broad
regions of the heliosphere, often all around the Sun. High-energy SEPs
can sometimes be energetic enough to penetrate all the way down to the
surface of the Earth and thus be recorded on the ground as ground level
enhancements (GLEs). The conditions of the radiation environment are
currently unpredictable due to an as-yet incomplete understanding of
solar eruptions and their corresponding relation to SEP events. This
is because the complex nature and the interplay of the injection,
acceleration and transport processes undergone by the SEPs in the solar
corona and the interplanetary space prevent us from establishing an
accurate understanding (based on observations and modelling). In this
work, we review the current status of knowledge on SEPs, focusing
on GLEs and multi-spacecraft events. We extensively discuss the
forecasting and nowcasting efforts of SEPs, dividing these into three
categories. Finally, we report on the current open questions and the
possible direction of future research efforts. <P />This article is part
of the theme issue `Solar eruptions and their space weather impact'.
---------------------------------------------------------
Title: Tomography of the Solar Corona with the Wide-Field Imager
for the Parker Solar Probe
Authors: Vásquez, Alberto M.; Frazin, Richard A.; Vourlidas, Angelos;
Manchester, Ward B.; van der Holst, Bart; Howard, Russell A.; Lamy,
Philippe
2019SoPh..294...81V Altcode:
The Wide-field Imager for the Parker Solar Probe (PSP/WISPR) comprises
two telescopes that record white-light total brightness [B ] images of
the solar corona. Their fields of view cover a widely changing range
of heliocentric heights over the 24 highly eccentric orbits planned for
the mission. In this work, the capability of PSP/WISPR data to carry out
tomographic reconstructions of the three-dimensional (3D) distribution
of the coronal electron density is investigated. Based on the precise
orbital information of the mission, B -images for Orbits 1, 12, and 24
are synthesized from a 3D magnetohydrodynamic model of the corona. For
each orbit, the time series of synthetic images is used to carry out a
tomographic reconstruction of the coronal electron density and results
are compared with the model. As the PSP perihelion decreases, the range
of heights that can be tomographically reconstructed progressively
shifts to lower values, and the period required to gather the data
decreases. For Orbit 1 tomographic reconstruction is not possible. For
Orbit 12, tomographic reconstruction is possible in the heliocentric
height range ≈5 -15 R<SUB>⊙</SUB>, over a region spanning up to
≈160<SUP>∘</SUP> in Carrington longitude, with data gathered over
a ≈3.4 day-long period. For Orbit 24, tomographic reconstruction is
possible in the heliocentric height range ≈3 -10 R<SUB>⊙</SUB>, over
a region spanning up to ≈170<SUP>∘</SUP> in Carrington longitude,
with data gathered over a ≈2.8 day-long period.
---------------------------------------------------------
Title: Radio Propagation Diagnostics of the Inner Heliosphere in
the Era of the Parker Solar Probe
Authors: Kobelski, Adam; Bastian, Timothy S.; Vourlidas, Angelos
2019AAS...23410706K Altcode:
The solar wind offers and extraordinary laboratory for studying
turbulence, turbulent dissipation, and heating. The Parker Solar Probe
(PSP) was launched in August 2018 to study these and other important
processes in the inner heliosphere. One type of observation that will
complement those of PSP are radio propagation measurements of solar
wind turbulence in the outer corona and the inner heliosphere. This
type of observation can provide measurements of the angular broadening
of distant spatially coherent background sources that transilluminate
the foreground solar wind plasma. This well-known technique can be used
to measure the spatial spectrum of electron density inhomogeneities in
the solar wind on scales of 100s of meters to 10s of kilometers inside
of 10-15 solar radii over a wide range of position angles. <P />Here
we report the results of a pilot study of background sources using the
Jansky Very Large Array (JVLA) in summer 2015. Unlike previous studies
of this kind, the JVLA's much greater sensitivity allows fainter
and more numerous sources to be used as probes of the foreground
medium. We observed 11 background sources in 16 sessions at apparent
radial distances of 2-7 solar radii. We confirm previous findings:
that the spectrum is flatter than Kolmogorov and that is highly
anisotropic. Unlike previous studies we find breaks into steeper spectra
for some sources on short spatial scales, suggestive of a transition to
dissipation. <P />Looking forward, we describe observations planned in
August 2019 in support of the third PSP perihelion passage (35.7 solar
radii). The VLA will be used to observe the corona and inner heliosphere
along 70 pierce points <10 solar radii. These observations will not
only provide global context about the state of the inner heliosphere
at time of perihelion passage, they will also baseline key solar wind
parameters that can be compared directly with PSP measurements. These
include turbulence level, spectral index, degree of anisotropy, and
the orientation of the magnetic field. The PSP measurements will, in
turn, provide measurements that will validate key assumptions made in
interpreting the radio data.
---------------------------------------------------------
Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2019shin.confE.194P Altcode:
Our thinking about the pre-eruptive magnetic configuration of Coronal
Mass Ejections has been effectively dichotomized into two opposing
and often fiercely contested views: namely, sheared magnetic arcades
and magnetic flux ropes. Finding a solution to this issue will have
important implications for our understanding of CME initiation. We
first discuss the very value of embarking into the arcade vs. flux rope
dilemma and illustrate the corresponding challenges and difficulties to
address it. Next, we are compiling several observational diagnostics of
pre-eruptive sheared magnetic arcades stemming from theory/modeling,
discuss their merits, and highlight potential ambiguities that could
arise in their interpretation. We finally conclude with a discussion
of possible new observables, in the frame of upcoming or proposed
instrumentation, that could help to circumvent the issues we are
currently facing.
---------------------------------------------------------
Title: MHD modeling of evolving ICME magnetic structure in the
inner heliosphere
Authors: Provornikova, Elena; Merkin, Vyacheslav; Malanushenko, Anna;
Gibson, Sarah; Arge, Nick; Vourlidas, Angelos
2019shin.confE.230P Altcode:
As CME propagates through the inner heliosphere, evolution of its
structure is influenced by the interaction with the solar wind
streams. I will present our recent simulations with GAMERA code
of propagating flux rope-CME from 0.1 to 1 AU in the background
solar wind. We evaluate self-similarly an erupting CME at 0.1 AU
based on the Gibson-Low model and insert it into our global inner
heliosphere model driven by the Wang-Sheeley-Arge (WSA) model of the
corona, while WSA, in turn, is driven by ADAPT global photospheric
magnetic field maps. To simulate the ICME propagation in the inner
heliosphere, we use the GAMERA (Grid Agnostic MHD for Extended Research
Applications) magnetohydrodynamic (MHD) code which is a reinvention of
the high-heritage Lyon-Fedder-Mobarry (LFM) code. We present modeling
results and focus on the evolution of the large-scale structure of
the CME from the outer solar corona to Earth. In particular I will
present a simulation of the April 3, 2010 CME event.
---------------------------------------------------------
Title: Deriving the Near-Sun Magnetic Field of Coronal Mass Ejections
from Magnetic Helicity Conservation
Authors: Patsourakos, Spiros; Georgoulis, M. K.; Petroulea, G.;
Vourlidas, A.; Nieves-Chinchilla, T.
2019shin.confE.222P Altcode:
The near-Sun magnetic field of Coronal Mass Ejections represents
a key parameter for assessing their energetics and structuring, and
additionally, it is a major element of methods/applications/simulations
aiming to predict the magnetic field of Earth-directed CMEs upon
impact at geospace. Diagnostics of CME magnetic fields in the corona
can be achieved via observations in the radio domain, which however,
are currently not available on a regular basis. Therefore, several
methods to infer the CME magnetic field in the corona have recently
emerged. We developed one such method which is based on the magnetic
helicity conservation principle applied to flux rope CMEs. Its
input parameters could be readily retrieved from the analysis of
HMI magnetograms and SOHO/STEREO WL coronagraph images. We present
parametric and case-study applications of this method, and discuss how
it be could be used to predict the CME magnetic field magnitude at 1 AU.
---------------------------------------------------------
Title: Unraveling the internal magnetic field structure of the
Earth-directed interplanetary coronal mass ejections during
1995-2015.?
Authors: Nieves-Chinchilla, Teresa; Jian, Lan K.; Balmaceda, Laura;
Vourlidas, Angelos; dos Santos, Luiz F. G.; Szabo, Adam
2019shin.confE..19N Altcode:
The magnetic field configurations associated with interplanetary
coronal mass ejections (ICMEs) are the in-situ manifestations of
the entrained magnetic structure associated with the coronal mass
ejections (CMEs). The prediction of such configurations is essential
to Space Weather in order to forecast any resulting geomagnetic
disturbances. The main hypothesis in such predictions is to assume
that such structure is a flux rope. We present a comprehensive study
of the internal magnetic field configurations of ICMEs observed at 1
AU in the period 1995-2015 in order to unravel the internal magnetic
structure associated with the CMEs and establish under what signatures
a flux rope model is valid. In the first part of the presentation,
we examine the expected magnetic field configurations by simulating
various spacecraft trajectories within an ICME. This simulation is based
on the assumption of a flux rope with the simplest flux rope geometry,
i.e. circular-cylindrical helical magnetic field configuration. In the
second part of the paper, we reconstruct the flux ropes by using the
technique described on Nieves-Chinchilla et al. 2016. We examine the
orientation and geometrical properties during the solar activity levels
at the end of solar cycle 22, solar cycle 23 and part of solar cycle 24.
---------------------------------------------------------
Title: COHERENT: Studying the corona as a holistic environment
Authors: Caspi, Amir; Seaton, Daniel B.; Case, Traci; Cheung, Mark;
Cranmer, Steven; DeForest, Craig E.; de Toma, Giuliana; Downs, Cooper;
Elliott, Heather; Gold, Anne U.; Longcope, Dana; Savage, Sabrina L.;
Sullivan, Susan; Viall, Nicholeen; Vourlidas, Angelos; West, Matthew J.
2019shin.confE.241C Altcode:
The solar corona and the heliosphere must be part of a single
physical system, but because the dominant physical processes change
dramatically from the magnetically-dominated low corona, through the
sparsely-observed middle corona, and into the plasma flow-dominated
outer corona and heliospheric interface, unified frameworks to study
the corona as a whole are essentially nonexistent. Understanding how
physical processes shape and drive the dynamics of the corona as a
global system, on all spatiotemporal scales, is critical for solving
many fundamental problems in solar and heliospheric physics. However,
the lack of unifying observations and models has led to a fragmentation
of the community into distinct regimes of plasma parameter space,
largely clustering around regions where existing instrumentation has
made observations widely available and where models can be sufficiently
self-contained to be tractable. We describe COHERENT, the 'Corona as a
Holistic Environment' Research Network, a focused effort to facilitate
interdisciplinary collaborative research to develop frameworks for
unifying existing and upcoming observations, theory, models, and
analytical tools to study the corona as a holistic system.
---------------------------------------------------------
Title: Coronal Mass Ejections from Sun to Earth: Recent Advances in
Modeling and Statistical Approaches
Authors: Malanushenko, Anna; Gibson, S.; Dalmasse, K.; Merkin, V.;
Provornikova, E.; Vourlidas, A.; Arge, C.; Nychka, D.; Wiltberger,
M.; Flyer, N.
2019shin.confE.206M Altcode:
Solar coronal mass ejections (CMEs) are violent eruptive phenomena
which originate on the Sun; their heliospheric extensions, called
interplanetary CMEs, are known for their potential to impact the
whole heliosphere and, in particular, the Earth. While not all CMEs
are launched in such a way as to hit the Earth, those that do can
have big impacts on Earth's magnetosphere. The magnitude of such
impact depends upon many factors such as the CME launch location and
velocity, its positioning within the background solar wind, its mass,
and its magnetic properties such as the orientation of its front with
respect to the Earth's magnetic field. <P />Case studies of how iCMEs
propagate through the heliosphere are complicated by many factors,
including often incomplete input for models. We present and discuss
a different approach. Rather than focusing on modeling a particular
event, we intend to carry out a large statistical study in the event
parameter space. Further, Bayesian statistics will be used along with
large statistical databases of near-Sun and near-Earth observables,
to infer statistical distributions of relevant CME input parameters,
which are capable of yielding given distributions of observables,
for a given stage of the the solar cycle. <P />We use a analytical
flux rope model (Gibson&Low model) and a background solar wind
boundary (Wang-Sheeley-Arge model) as inputs for a new MHD heliospheric
simulation code (Gamera). We give an overview and update of the project
and show first modeling results.
---------------------------------------------------------
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: Radio Observational Constraints on Turbulent Astrophysical
Plasmas
Authors: Bastian, Tim; Cordes, James; Kasper, Justin; Kobelski,
Adam; Korreck, Kelly; Howes, Gregory; Salem, Chadi; Spangler, Steve;
Vourlidas, Angelos
2019astro2020T.307B Altcode: 2019arXiv190405807B
Using radio observations of background sources, scattering phenomena
may be used to characterize the properties of foreground turbulent
plasma. We discuss the potential of such techniques to explore
turbulence in the solar wind and interstellar medium. The Next
Generation VLA will be an ideal instrument to exploit these techniques.
---------------------------------------------------------
Title: Challenges in the Analysis of Images from the Wide-field Imager
(WISPR) on Parker Solar Probe
Authors: Liewer, Paulett; Penteado, Paulo; Hall, Jeff; Vourlidas,
Angelos; Qiu, Jiong; Howard, Russ
2019shin.confE.133L Altcode:
The three-to-five-month elliptical orbit of Parker Solar Probe (PSP),
approaching within 10 solar radii of the Sun, will allow the Wide-field
Imager for Solar Probe (WISPR) to view the corona with unprecedented
spatial resolution from multiple viewpoints. WISPR, located on the ram
side of PSP, will image and fly through structures sample by the in
situ instruments. WISPR has a wide fixed angular field-of-view (FOV),
extending radially from 13.5? to 108? from the Sun and approximately
50? in the transverse direction, but the physical extent of the imaged
coronal region varies directly with the distance of the spacecraft
from the Sun. To relate and compare features seen in the images to
observation by other instruments and spacecraft with other locations
and viewpoints, it is first necessary to relate the field-of-view of
the WISPR telescopes at any given time to other frames of reference,
such as the various Heliographic and Heliocentric coordinate
systems. Here we present projections of WISPR images in several
frames, made utilizing the World Coordinate System which relies
on information in the images’ FITS headers (see W. T. Thompson,
2006, DOI: 10.1051/0004-6361:20054262). Specifically, the projection
software uses the SolarSoft Sunpice package ($SSW/sunspice), developed
by W. Thompson to obtain the proper SPICE information on spacecraft
location, orientation, and the pointing of the WISPR telescopes relative
to the spacecraft pointing. The changing size of the FOV relative to
the Sun must be considered when analyzing tracks of density features
in a sequence of images. We discuss how to create elongation (angle
from the Sun as seen by the observer) vs. time images from WISPR and
show J-maps created from data on WISPR’s first encounter.
---------------------------------------------------------
Title: Connecting the Low Corona to the High Corona: Outward
Propagating Small-Scale Transients Tracked from EUVI Through COR1
and COR2
Authors: Alzate, Nathalia; Viall, Nicholeen; Morgan, Huw; Vourlidas,
Angelos
2019shin.confE..59A Altcode:
Identification of the source of the slow solar wind has been hampered
by the complexity of plasma structures in the very low corona and data
limitations in terms of noise reduction. Application of state-of-the-art
image processing techniques has revealed very faint structures in
the low corona that have an impact on the structure of the extended
corona. These techniques, which overcome faint signals and noise in
the data, allow us to identify and characterize the sources of the slow
solar wind as we explore the variability of coronal density structures
over a distance range starting from the solar surface out to tens
of radii and beyond using data from the STEREO spacecraft. Having
successfully conquered the noise issues in the COR1 instrument, as
a proof of concept we revisited a 10-day period in January 2008 in
which density enhancements were previously identified as sources of the
slow solar wind in in situ, HI2 and COR2 data. Our preliminary results
show transients present in the EUVI, COR1 and COR2 FOVs, with several
transients propagating through at least two FOVs. Further analysis
will enable us to properly determine the exact formation heights of
ambient solar wind structures, formation mechanisms, and the features
in the low corona they connect to. We will include data from other
instruments to study different coronal configurations in order to
characterize solar wind structures low in the corona as a function
of coronal magnetic complexity, which will be an essential test for
theories of solar wind formation. Our method for processing COR1 data
opens the door to 12 years of data for studies of small-scale coronal
structures and their geoeffectiveness. This work is part of the broad
effort in Heliospheric physics to understand the different types of
transient structures created in the solar wind as it is formed.
---------------------------------------------------------
Title: A Statistical Study of CME Kinematics and its Relationship
to the Magnetic Reconnection Flux
Authors: Zhu, Chunming; Qiu, Jiong; Spiegel, Michael; Liewer, Paulett;
Vourlidas, Angelos; Hu, Qiang
2019shin.confE..84Z Altcode:
It is well known that CME kinematics are strongly related to
the magnetic reconnection process in the solar corona. However,
a quantitative understanding of this relationship still remains
elusive. To determine the role of reconnection in CME initiation and
acceleration, we carry out a statistical study of the CME kinematics
relative to the onset and progress of magnetic reconnection, using
56 eruptions. The CMEs are measured utilizing the EUV and white light
observations at the solar limb viewed from STEREO, while the magnetic
reconnection processes are evaluated by the magnetic fluxes which are
swept by the flare ribbons on the solar disk observed from SDO. With
these measurements, we explore the duration and magnitude of the CME
accelerations and the correlation to those of the magnetic reconnection
flux. The distributions of the heights at which the CMEs are initiated
and which the peak acceleration is reached are addressed. Based on
these observational results, the triggering mechanisms for the CMEs
are discussed.
---------------------------------------------------------
Title: Connecting the Properties of Coronal Shock Waves with Those
of Solar Energetic Particles
Authors: Kouloumvakos, Athanasios; Rouillard, Alexis P.; Wu, Yihong;
Vainio, Rami; Vourlidas, Angelos; Plotnikov, Illya; Afanasiev,
Alexandr; Önel, Hakan
2019ApJ...876...80K Altcode:
We develop and exploit a new catalog of coronal pressure waves modeled
in 3D to study the potential role of these waves in accelerating solar
energetic particles (SEPs) measured in situ. Our sample comprises
modeled shocks and SEP events detected during solar cycle 24 observed
over a broad range of longitudes. From the 3D reconstruction of shock
waves using coronagraphic observations we derived the 3D velocity along
the entire front as a function of time. Combining new reconstruction
techniques with global models of the solar corona, we derive the 3D
distribution of basic shock parameters such as Mach numbers, compression
ratios, and shock geometry. We then model in a time-dependent manner
how the shock wave connects magnetically with spacecraft making in
situ measurements of SEPs. This allows us to compare modeled shock
parameters deduced at the magnetically well-connected regions, with
different key parameters of SEPs such as their maximum intensity. This
approach accounts for projection effects associated with remote-sensing
observations and constitutes the most extensive study to date of
shock waves in the corona and their relation to SEPs. We find a high
correlation between the maximum flux of SEPs and the strength of coronal
shock waves quantified, for instance, by the Mach number. We discuss
the implications of that work for understanding particle acceleration
in the corona.
---------------------------------------------------------
Title: TRAcking interplanetary Coronal mass Ejections with foRbush
decreases (TRACER)
Authors: Papaioannou, Athanasios; Belov, Anatoly; Vourlidas, Angelos;
Anastasiadis, Anastasios
2019EGUGA..2117133P Altcode:
During their travel from Sun to Earth, coronal mass ejections (CMEs)
interact with Galactic cosmic rays (GCRs) that fill the interplanetary
(IP) space. The leading shock wave when present and the following
CME structure modulate GCRs, which results in a reduction of the
cosmic ray (CR) intensity, known as Forbush decrease (FD). CMEs
are regularly observed via both remote sensing (coronagraph and
heliospheric imaging instruments) and in-situ measurements of plasma
and magnetic field. However, this two way approach can be augmented
with the identification of FDs in the measurements of GCRs; one may
detect interplanetary CMEs passing by the observational site. Thereby,
the recordings of FDs at different points within the heliosphere could
be used as tracers of the IP evolution of CMEs. In this work, we present
FD events that have been recorded at Earth by neutron monitors and in
the inner heliosphere by the Helios 1 and 2 spacecraft. Using these
FDs as a tracer of the agent CMEs, we identify their kinematics from
0.3 to 1 AU and quantify the effect of the CME physical parameters to
the recorded intensity decrease during the FDs.
---------------------------------------------------------
Title: A Comparative Study of 2017 July and 2012 July Complex
Eruptions: Are Solar Superstorms “Perfect Storms” in Nature?
Authors: Liu, Ying D.; Zhao, Xiaowei; Hu, Huidong; Vourlidas, Angelos;
Zhu, Bei
2019ApJS..241...15L Altcode: 2019arXiv190203416L
It is paramount from both scientific and societal perspectives to
understand the generation of extreme space weather. We discuss the
formation of solar superstorms based on a comparative study of the 2012
July 23 and 2017 July 23 eruptions. The first one is Carrington-class,
and the second could rival the 1989 March event that caused the
most intense geomagnetic storm of the space age. Observations of
these events in the historically weak solar cycle 24 indicate that
a solar superstorm can occur in any solar cycle and at any phase of
the cycle. Recurrent patterns are identified in both cases, including
the long-lived eruptive nature of the active region, a complex event
composed of successive eruptions from the same active region, and
in-transit interaction between the successive eruptions resulting
in exceptionally strong ejecta magnetic fields at 1 au. Each case
also shows unique characteristics. Preconditioning of the upstream
solar wind leading to unusually high solar wind speeds at 1 au is
observed in the first case, but not in the latter. This may suggest
that the concept of “preconditioning” appears to be necessary for
making a Carrington-class storm. We find a considerable deflection
by nearby coronal holes in the second case, but not in the first. On
the basis of these results, we propose a hypothesis for further
investigation that superstorms are “perfect storms” in nature,
i.e., a combination of circumstances that results in an event of an
unusual magnitude. Historical records of some extreme events seem to
support our hypothesis.
---------------------------------------------------------
Title: The Parker Solar Probe WISPR Instrument: Status and
Observations
Authors: Howard, Russell; Vourlidas, Angelos; Colaninno, Robin;
Stenborg, Guillermo; Hess, Phillip; Liewer, Paulett; Rich, Nathan;
Dennison, Hillary
2019EGUGA..2110704H Altcode:
The PSP mission was launched Aug 12, 2018 into orbit about the Sun. In
Oct/Nov it performed its first perihelion pass at 0.16 AU (36 solar
radii). We present the plans and first observations of the corona for
the WISPR instrument on the PSP mission. Observing the corona/solar
wind from 0.25 AU to the ultimate perihelion distance of 0.04 AU is
absolutely unique, but presents new challenges due to the rapidly
changing heliocentric distance. WISPR, a heliospheric imager type of
instrument, consists of two telescopes, which together observe in the
spacecraft ram direction along the ecliptic plane from 13.5 - 108 deg
from the Sun. This range of elongations encompasses the Thomson circle
(the locus of points of maximum Thomson scattering efficiency) thereby
transitioning from remote observations of structures close to the Sun
to local observations of structures close to the spacecraft. Three
different types of observations are envisioned: synoptic full field,
partial field high cadence shock studies and partial field turbulence
studies. The last one is a sequence of images at a 10-second cadence
for which a power spectrum of intensity or electron density will be
generated at selected heights in the corona, to see where wave energy is
being deposited. In these preliminary images we anticipate that the view
will be quite different as PSP plunges into the corona than the view
from 1 AU. The spatial resolution will be greatly increased as we fly
through the coronal structures and will reveal fine-scale details such
as fluctuations in the plasma sheet, perhaps indicating individual flux
tubes or magnetic islands or maybe something totally unexpected. The
vantage points will remove a large fraction of the circumsolar dust
contributing to the F-corona, perhaps also revealing the first dust to
sublimate. To prepare for the mission, techniques have been developed
to determine the background, track features that are moving through
the field of view, among others. Due to the relative positions of PSP,
Earth and the Sun, only a small fraction of the data has been received
on ground, but WISPR has worked well through the first perihelion. We
gratefully acknowledge support from the NASA Parker Solar Probe Project.
---------------------------------------------------------
Title: Raytracing simulations of Parker Solar Probe/WISPR images
Authors: Nisticò, Giuseppe; Liewer, Paulett; Vourlidas, Angelos;
Thernisien, Arnaud; Howard, Russell; Bothmer, Volker
2019EGUGA..2114202N Altcode:
The Wide-field Imager for Parker Solar Probe (WISPR) provides
unprecedented white-light images of the solar corona and inner
heliosphere from unconventional viewpoints thanks to the close
perihelion transits of Parker Solar Probe. WISPR images coronal
structures at high spatial and time resolutions, but the data
analysis needs to consider the continuous change of the observation's
plane-of-sky and hence of the projection due to PSP's fast orbital
speed and high orbital eccentricity. Therefore, it is important to
understand how these factors affect the images. Here, we present an
analysis of simulated WISPR images and discuss how WISPR data can
be analyzed to study the physical conditions of the corona and the
near-Sun environment.
---------------------------------------------------------
Title: Combined geometrical modelling and white-light mass
determination of coronal mass ejections
Authors: Pluta, Adam; Mrotzek, Niclas; Vourlidas, Angelos; Bothmer,
Volker; Savani, Neel
2019A&A...623A.139P Altcode:
Context. We use forward modelling on multi-viewpoint coronagraph
observations to estimate the 3-dimensional morphology, initial speed
and deprojected masses of Coronal Mass Ejections (CMEs). The CME
structure is described via the Graduated Cylindrical Shell (GCS) model,
which enables the measurement of CME parameters in a consistent and
comparable manner. <BR /> Aims: This is the first large-scale use of the
GCS model to estimate CME masses, so we discuss inherent peculiarities
and implications for the mass determination with a special focus on CME
events emerging from close to the observer's central meridian. Further,
we analyse the CME characteristics best suited to estimate the CME mass
in a timely manner to make it available to CME arrival predictions. <BR
/> Methods: We apply the method to a set of 122 bright events observed
simultaneously from two vantage points with the COR2 coronagraphs
onboard of the twin NASA STEREO spacecraft. The events occurred between
January 2007 and December 2013 and are compiled in an online catalogue
within the EU FP7 project HELCATS. We statistically analyse the derived
CME parameters, their mutual connection and their relation to the solar
cycle. <BR /> Results: We show that the derived morphology of intense
disk events is still systematically overestimated by up to a factor of
2 with stereoscopic modelling, which is the same order of magnitude as
for observations from only one vantage point. The overestimation is very
likely a combination of projection effects as well as the increased
complexity of separating CME shocks and streamers from CME fronts
for such events. We further show that CME mass determination of disk
events can lead to overestimation of the mass by about a factor of 10
or more, in case of overlapping bright structures. <BR /> Conclusions:
We conclude that for stereoscopic measurements of disk events, the
measurement of the initial CME speed is the most reliable one. We
further suggest that our presented CME speed-mass correlation is most
suited to estimate the CME mass early from coronagraph observations.
---------------------------------------------------------
Title: Solar Physics from Unconventional Viewpoints
Authors: Gibson, Sarah E.; Vourlidas, Angelos; Hassler, Donald M.;
Rachmeler, Laurel A.; Thompson, Michael J.; Newmark, Jeffrey; Velli,
Marco; Title, Alan; McIntosh, Scott W.
2018FrASS...5...32G Altcode: 2018arXiv180509452G
We explore new opportunities for solar physics that could be realized
by future missions providing sustained observations from vantage
points away from the Sun-Earth line. These include observations from
the far side of the Sun, at high latitudes including over the solar
poles, or from near-quadrature angles relative to the Earth (e.g.,
the Sun-Earth L4 and L5 Lagrangian points). Such observations fill
known holes in our scientific understanding of the three-dimensional,
time-evolving Sun and heliosphere, and have the potential to open new
frontiers through discoveries enabled by novel viewpoints.
---------------------------------------------------------
Title: How Reliable Are the Properties of Coronal Mass Ejections
Measured from a Single Viewpoint?
Authors: Balmaceda, Laura A.; Vourlidas, Angelos; Stenborg, Guillermo;
Dal Lago, Alisson
2018ApJ...863...57B Altcode:
We present an analysis of widths and kinematic properties of
coronal mass ejections (CMEs) obtained via a supervised image
segmentation algorithm, the CORonal SEgmentation Technique (CORSET),
on simultaneous observations from the two COR2 telescopes on the Solar
Terrestrial Relations Observatory (STEREO) mission, from 2007 May
to 2014 September. The sample of 460 events with measurements from
two vantage points offers the opportunity to test the accuracy and
constraints of single-viewpoint properties that underlie the bulk of
CME research to date. In addition, we examine the dependence of the
properties on the morphology of the events. The main findings are as
follows. (1) The radial speeds derived from different perspectives
are in good agreement with a relatively low intrinsic uncertainty
of 39%. (2) Projection effects are more important for determination
of CME width rather than for speed. (3) The expansion speeds depend
on CME morphology, with loop-type CMEs expanding twice as fast as
flux-rope CMEs, possibly underpinning the more explosive nature. (4)
Triangulations of CME speed and propagation direction are optimal from
viewpoints separated by 60°-90° e.g., between the Lagrangian points
L<SUB>1</SUB> and L<SUB>5</SUB> (or L<SUB>4</SUB>). (5) The projected
speeds are underestimated, on average, by at least 20% when compared
to their deprojected (triangulated) values. We also discuss in detail
the lessons learned from the application of the CORSET algorithm to
event tracking. Our findings should hopefully be a useful guide in
the use of (semi)automated algorithms for extraction of CME physical
parameters and in the interpretation of single-viewpoint observations
(likely to be the norm after the end of the STEREO mission).
---------------------------------------------------------
Title: Streamer-blowout Coronal Mass Ejections: Their Properties
and Relation to the Coronal Magnetic Field Structure
Authors: Vourlidas, Angelos; Webb, David F.
2018ApJ...861..103V Altcode: 2018arXiv180600644V
We present a comprehensive analysis of a particular class of coronal
mass ejection (CME) event called streamer-blowout CMEs (SBOs). The
events are characterized by a gradual swelling of the overlying
streamer, lasting hours to days, followed by a slow, wide CME,
generally exhibiting a three-part structure, which leaves the streamer
significantly depleted in its wake. We identify 909 SBO events in the
LASCO/C2 observations between 1996 and 2015. The average blowout lasts
for 40.5 hr, but the evacuation can take days for some events. The SBO
CMEs are wider and more massive than the average CME. Their properties
generally vary during and between solar cycles. Their minimum (maximum)
monthly occurrence rate of one (six) events in cycle 23 has doubled
in cycle 24—a probable manifestation of the weaker global fields
in the current cycle. The locations of SBOs follow the tilt of the
global dipole (but not from 2014 onward), do not correlate with sunspot
numbers, and exhibit flux rope morphology at a much higher rate (61%)
than regular CMEs (40%). We propose that these characteristics are
consistent with SBOs arising from extended polarity inversion lines
outside active regions (e.g., quiet Sun and polar crown filaments)
through the release via reconnection of magnetic energy, likely
accumulated via differential rotation.
---------------------------------------------------------
Title: Connecting Shock Waves Properties in the Solar Corona with
the Characteristics of Solar Energetic Particle Events
Authors: Kouloumvakos, Athanasios; Rouillard, A. P.; Vainio, R.;
Vourlidas, A.; Plotnikov, I.; Wu, Y.; Afanasiev, A.
2018shin.confE.114K Altcode:
We exploit a new catalog of coronal pressure waves modeled in 3-D
to study the potential role of shock waves as accelerators of Solar
Energetic Particle events (SEPs) measured in situ. Our samples of
modeled shocks and SEPs are related to events detected during solar
cycle 24 that were observed over a broad range of longitudes. From the
3D-reconstruction of shock waves using multi-viewpoint coronagraphic
observations we estimated the 3-D velocity of the entire front as a
function of time. We then used the method presented in Rouillard et
al. (2016) for the derivation of the 3D-distribution of Alfvenic Mach
number and other key shock properties including the density compression
ratio. We present for the first time a comparison of modeled shock
parameters such as the shock speed, the Alfvenic Mach number and
the compression ratio deduced at the magnetically well-connected
regions, with different key parameters of SEPs such as their maximum
intensity, spectral index, and element abundance and for a large
number of events. We discuss the implications of our results for our
understanding of particle acceleration at shocks waves.
---------------------------------------------------------
Title: Alfvenic critical point inferred from coronal shock and
wave properties
Authors: Kwon, Ryun Young; Vourlidas, Angelos
2018shin.confE.137K Altcode:
We compare an empirical solar wind speed profile from Sheeley et
al. (1997) with Alfven speed profiles derived from coronal shock and
wave properties to infer the possible height of the Alfvenic critical
point. We derive the Alfven speed profiles with three different
techniques. (1) We estimate the shock density compression ratios at
different heights using fits of a sheath electron density model to
shock fronts observed in coronagraphic images (Kwon et al. 2018). The
three-dimensional geometry is considered to examine the electron
density jump along the shock normal. The Rankine-Hugoniot (jump)
relation is used to estimate the Alfvenic Mach number, i.e., the ratio
between the shock speeds and local Alfven speeds, from the density
compression ratios. Since the 3D kinematics of the shocks is known
at the points where we determined the density compression ratios, the
Alfvenic Mach numbers are also derived. (2) We assume that the lower
part (lateral flank) of a spherical shock front degenerates into a
linear fast-mode wave (or weak shock wave) and fit the time-dependent
geometric solution of a linear fast-mode wave given in Uchida (1970)
to the lateral flanks. We select the Alfven speed profile associated
with the best fits. (3) We use a measure of Alfvenic Mach numbers
obtained from the standoff distances (Gopalswamy & Yashiro 2011;
Poomvises et al. 2012). In general, we assume that an empirical model
gives the upstream electron density, the adiabatic index is 5/3,
and the Alfven speed at 1 AU is 50 km/s. The height of the Alfvenic
critical point is found to be around 15 - 25 Rs [solar radii], whereas
the peak of the Alfven speed profile is located at 2 - 3 Rs.
---------------------------------------------------------
Title: Preparing for Parker Solar Probe: Tracking Moving Solar Wind
Features in Images from the Wide-field Imager for Parker Solar Probe
(WISPR)
Authors: Liewer, Paulett C.; Qiu, Jiong; Nisticò, Giuseppe;
Vourlidas, Angelos; Penteado, Paulo; Thernisien, Arnaud; Howard,
Russell; Bothmer, Volker
2018shin.confE..43L Altcode:
The Parker Solar Probe (PSP) trajectory, approaching within 10 solar
radii, will allow the white light imager, WISPR, to view the inner
corona with unprecedented spatial resolution. WISPR, with a field of
view extending from 13.5° to 108° elongation angle from the Sun,
will image the fine-scale coronal structure with arcminute resolution
at high cadence ( 5 - 60 min). The dependency of Thomson scattering on
the distance between the observer and the Sun dictates that WISPR will
be a “local" heliospheric imager, and thus can provide a crucial link
between the visible corona and PSP's in-situ measurements. To prepare
for this unprecedented viewing of the structures in the inner corona,
we are creating synthetic white light images and animations, viewed from
the PSP trajectory, using the white-light ray-tracing package developed
at NRL (available through SolarSoft). We will present results for small
flux ropes moving outward through the corona as well as fly-throughs
of finely structured coronal streamers. We also investigated whether
the 3-D trajectory (direction and velocity) of a density enhancement
(flux rope or
---------------------------------------------------------
Title: Understanding the initiation and early evolution of the 2012
July 12 CME
Authors: Nikou, Eleni; Kwon, Ryun-Young; Vourlidas, Angelos; Zhang, Jie
2018shin.confE.141N Altcode:
The early evolution of Coronal Mass Ejections (CMEs), particularly
the fast, highly
---------------------------------------------------------
Title: Simulations of PSP/WISPR observations of the corona/inner
heliosphere with raytracing software
Authors: Nisticò, Giuseppe; Liewer, Paulett; Qiu, Jiong; Vourlidas,
Angelos; Bothmer, Volker; Thernisien, Arnaud
2018shin.confE..40N Altcode:
The Wide-Field Imager for Parker Solar Probe (WISPR) will observe the
Thomson scattered emission of the corona/inner heliosphere, covering
a range of elongation angles from 13.5 to 108 deg, at high temporal
(0.05-60 min) and spatial resolution (plate scale of 1.2-1.7 arcmin
per pixel). Such images will be taken from unprecedented points of
observation thanks to the highly-eccentric orbits of Parker Solar Probe
(PSP), which will reach the minimum perihelion distance below 10 solar
radii from the Sun's centre.
---------------------------------------------------------
Title: Probing the Properties and Effects of Coronal Shocks Using
Modeling, Simulations and Observations
Authors: Rouillard, Alexis; Kouloumvakos, A.; Kwon, R. -K. .;
Vourlidas, A.; Vainio, R.; Wu, Y.; Afanasiev, A.; Önel, H.; Mann,
G.; Warmuth, A.; Vilmer, N.; Share, G.
2018shin.confE.140R Altcode:
We start with the 3D reconstruction of evolving shock waves based on
remote-sensing observations that provide the shock's outermost extent,
3-D expansion speeds, geometry, Mach and a new technique to derive
compression ratio. We compare the results of these reconstructions
with other techniques. We then carried out case studies and surveys to
study the link between these shock waves and electromagnetic emissions
at radio, X-ray and gamma-ray frequencies. We focus on the onsets of
radio type II bursts and exploit a new modeling framework that includes
particle acceleration and transport effects to study the onset of a
number of hard X-ray and gamma-ray events.
---------------------------------------------------------
Title: Preparing for Parker Solar Probe: Synthetic White-light
Imagery and Analysis for the Wide-field Imager (WISPR)
Authors: Liewer, Paulett; Nisticó, Giuseppe; Howard, Russell; Bothmer,
Volker; Thernisien, Arnaud; Vourlidas, Angelos; Penteado, Paulo
2018cosp...42E2010L Altcode:
The Parker Solar Probe (PSP) trajectory, approaching within 10 solar
radii, will allow the white light imager, WISPR, to view the inner
corona with unprecedented spatial resolution. WISPR, with a field of
view extending from 13.5° to 108° elongation angle from the Sun, will
image the fine-scale coronal structure with arcminute resolution. The
dependency of the Thomson scattering on the imaging geometry (distance
and angle from the Sun) dictates that WISPR will be very sensitive to
the emission from plasma close to the spacecraft, in contrast to the
situation for imaging from 1 AU. Thus, WISPR will be the first 'local'
imager providing a crucial link between the large-scale corona and
PSP's in-situ measurements. To prepare for this unprecedented viewing
of the structures in the inner corona, we are creating synthetic
white light images and animations, viewed from the PSP trajectory,
using the white-light ray-tracing package developed at NRL (available
through SolarSoft). We will present results for small flux ropes moving
outward through the corona as well as fly-throughs of finely structured
coronal streamers. Using the synthetic images, analysis techniques
similar to traditional white light "jmaps" are used to find the "track"
of a flux rope's elongation versus time. The "track" is compared with
predictions using simple geometric expressions to gain information on
the 3D trajectory of the flux rope. Additional analysis techniques,
such as re-projections of the images, will also be discussed.
---------------------------------------------------------
Title: The Highly Structured Outer Solar Corona
Authors: DeForest, C. E.; Howard, R. A.; Velli, M.; Viall, N.;
Vourlidas, A.
2018ApJ...862...18D Altcode:
We report on the observation of fine-scale structure in the outer
corona at solar maximum, using deep-exposure campaign data from the
Solar Terrestrial Relations Observatory-A (STEREO-A)/COR2 coronagraph
coupled with postprocessing to further reduce noise and thereby improve
effective spatial resolution. The processed images reveal radial
structure with high density contrast at all observable scales down to
the optical limit of the instrument, giving the corona a “woodgrain”
appearance. Inferred density varies by an order of magnitude on spatial
scales of 50 Mm and follows an f <SUP>-1</SUP> spatial spectrum. The
variations belie the notion of a smooth outer corona. They are
inconsistent with a well-defined “Alfvén surface,” indicating
instead a more nuanced “Alfvén zone”—a broad trans-Alfvénic
region rather than a simple boundary. Intermittent compact structures
are also present at all observable scales, forming a size spectrum
with the familiar “Sheeley blobs” at the large-scale end. We use
these structures to track overall flow and acceleration, finding that
it is highly inhomogeneous and accelerates gradually out to the limit
of the COR2 field of view. Lagged autocorrelation of the corona has
an enigmatic dip around 10 R <SUB>⊙</SUB>, perhaps pointing to new
phenomena near this altitude. These results point toward a highly
complex outer corona with far more structure and local dynamics than
has been apparent. We discuss the impact of these results on solar
and solar-wind physics and what future studies and measurements are
necessary to build upon them.
---------------------------------------------------------
Title: Connecting Shock Waves Properties in the Solar Corona with
the Characteristics of Solar Energetic Particle Events
Authors: Kouloumvakos, Athanasios; Rouillard, A. P.; Vainio, R.;
Vourlidas, A.; Plotnikov, I.; Wu, T.; Afanasiev, A.
2018shin.confE.113K Altcode:
We exploit a new catalog of coronal pressure waves modeled in 3-D
to study the potential role of shock waves as accelerators of Solar
Energetic Particle events (SEPs) measured in situ. Our samples of
modeled shocks and SEPs are related to events detected during solar
cycle 24 that were observed over a broad range of longitudes. From the
3D-reconstruction of shock waves using multi-viewpoint coronagraphic
observations we estimated the 3-D velocity of the entire front as a
function of time. We then used the method presented in Rouillard et
al. (2016) for the derivation of the 3D-distribution of Alfvenic Mach
number and other key shock properties including the density compression
ratio. We present for the first time a comparison of modeled shock
parameters such as the shock speed, the Alfvenic Mach number and
the compression ratio deduced at the magnetically well-connected
regions, with different key parameters of SEPs such as their maximum
intensity, spectral index, and element abundance and for a large
number of events. We discuss the implications of our results for our
understanding of particle acceleration at shocks waves.
---------------------------------------------------------
Title: Assessing the Geo-effectiveness of CMEs: Where do we stand
at the end of Solar Cycle 24
Authors: Vourlidas, Angelos
2018cosp...42E3563V Altcode:
As the minimum of Cycle 24 nears, the database of CME observations
from the LASCO coronagraphs will encompass two full solar cycles. This
unprecedented coverage of the eruptive sun is complemented by 10+ years
of stereoscopic observations from STEREO, sub-minute imaging of the EUV
corona from SDO/AIA, and a plethora of high-resolution spectroscopic
observations in many atmospheric layers from Hinode and IRIS. So, what
have we learned from these missions about the geo-effective potential
of CMEs and their sources? In this talk, I will discuss that current
status, identify some of the gaps and offer strategies for improving
our understanding of geo-effective CMEs in the future.
---------------------------------------------------------
Title: Elliptic-cylindrical Analytical Flux Rope Model for Magnetic
Clouds
Authors: Nieves-Chinchilla, T.; Linton, M. G.; Hidalgo, M. A.;
Vourlidas, A.
2018ApJ...861..139N Altcode:
In this paper, we present the elliptic-cylindrical analytical
flux rope model, which constitutes the first level of complexity
above that of a circular-cylindrical geometry. The framework of this
series of models was established by Nieves-Chinchilla et al. with the
circular-cylindrical analytical flux rope model. The model describes the
magnetic flux rope topology with distorted cross section as a possible
consequence of the flux rope interaction with the solar wind. In this
model, for the first time, a flux rope is completely described by a
nonorthogonal geometry. The Maxwell equations can be consistently
solved using tensorial analysis, and relevant physical quantities
can be derived, such as magnetic fluxes, number of turns, or Lorentz
force distribution. The model is generalized in terms of the radial
dependence of the poloidal and axial current density components. The
circular-cylindrical reconstruction technique has been adapted to the
new geometry for a specific case of the model and tested against an
interplanetary coronal mass ejection observed by the Wind spacecraft
on 2005 June 12. In this specific case, from the comparative analysis
between the circular-cylindrical and elliptic-cylindrical models,
the inclusion of the cross-section distortion in the 3D reconstruction
results in significant changes in the derived axis orientation, size,
central magnetic field, magnetic fluxes, and force-freeness. The
case studied in this paper exemplifies the use of the model and
reconstruction technique developed. Furthermore, the novel mathematical
formulation to model flux ropes in heliophysics paves the way to the
inclusion of more complex magnetic field configurations.
---------------------------------------------------------
Title: Solar Observations Away from the Sun-Earth Line
Authors: Gibson, Sarah E.; McIntosh, Scott William; Rachmeler,
Laurel; Thompson, Michael J.; Title, Alan M.; Velli, Marco C. M.;
Vourlidas, Angelos
2018tess.conf40340G Altcode:
Observations from satellite missions have transformed the field of solar
physics. High-resolution observations with near-continuous temporal
coverage have greatly extended our capability for studying long-term
and transient phenomena, and the opening of new regions of the solar
spectrum has made detailed investigation of the solar atmosphere
possible. <P />However, to date most solar space-based missions
have been restricted to an observational vantage in the vicinity of
the Sun-Earth line, either in orbit around the Earth or from the L1
Lagrangian point. As a result, observations from these satellites
represent the same geometrical view of the Sun that is accessible
from the Earth. <P />Understanding the deep interior structure of the
Sun and the full development of solar activity would really benefit
from fully three-dimensional monitoring of the solar atmosphere and
heliosphere. On the one hand, simultaneous spacecraft observations
from multiple vantage points would allow studies of the deep interior
structure of the sun via stereoscopic helioseismology; on the other,
distributed observations would allow the understanding of the complete
evolution of activity complexes and enhance space weather predictions
dramatically. <P />Presently, observations of the Sun away from Earth
are obtained by the STEREO pair of satellites, which have provided
an unprecedented global view by orbiting around to the far side of
the Sun, and the Ulysses mission, which achieved a high-inclination
(80˚) near-polar orbit (but which, however, did not include any solar
imaging instruments). The forthcoming Solar Orbiter mission, which
will orbit the sun and reach a maximum inclination of 34˚ out of the
ecliptic should provide the first detailed mapping of the sun's polar
fields. In addition, Solar Probe Plus will explore the outer corona
and inner Heliosphere with very rapid solar encounters at a minimum
perihelion 9.86 solar radii from the center of the Sun. <P />We explore
some of the new opportunities for solar physics that can be realized
by future missions that provide sustained observations from vantage
points away from the Sun-Earth line (and in some cases the ecliptic
plane): observations from the far side of the Sun, over its poles,
or from the L5 Lagrangian point.
---------------------------------------------------------
Title: Information theoretical approach to discovering causalities
in solar cycle
Authors: Wing, Simon; Johnson, Jay; Vourlidas, Angelos
2018tess.conf22407W Altcode:
The causal parameters and response lag times of the solar cycle
dynamics are investigated with transfer entropy, which can determine
the amount of information transfer from one variable to another. The
causal dependency of the solar cycle parameters is bidirectional. The
transfer of information from the solar polar field to the sunspot number
(SSN) peaks at lag time (t) ~ 30-40 months, but thereafter it remains
at a persistent low level for at least 400 months (~ 3 solar cycles)
for the period 1906-2014. The latter may indicate the persistency of
the polar fields from cycle to cycle. It may lend support to the idea
that the polar fields from the last 3 or more solar cycles can affect
the production of SSN of the subsequent cycle. There is also a similarly
long term information transfer from the SSN to the polar field. Both the
meridional flow speed and flux emergence (proxied by the SSN) transfer
information to the polar field, but one transfers more information
than the other, depending on the lag times. The meridional flow speed
transfers more information to the polar field than SSN at t ~28-30
months and at t ~90-110 months, which may be consistent with some flux
transfer dynamo models and some surface flux transport models. However,
the flux emergence transfers more information to the polar field than
the meridional flow at t ~60-80 months, which may be consistent with
a recently developed surface flux transport model. The transfer of
information from the meridional flow to SSN peaks at t ~110-120 months
(~1 solar cycle), suggesting that the meridional flow can be used to
predict SSN one cycle ahead.
---------------------------------------------------------
Title: Solar Polar Diamond Explorer (SPDEx): Understanding the
Origins of Solar Activity Using a New Perspective
Authors: Vourlidas, A.; Liewer, P. C.; Velli, M.; Webb, D.
2018arXiv180504172V Altcode:
Our knowledge of the Sun, its atmosphere, long term activity and
space weather potential is severely limited by the lack of good
observations of the polar and far-side regions. Observations from
a polar vantage point would revolutionize our understanding of the
mechanism of solar activity cycles, polar magnetic field reversals,
the internal structure and dynamics of the Sun and its atmosphere. Only
with extended (many day) observations of the polar regions can the
polar flows be determined down to the tachocline where the dynamo is
thought to originate. Rapid short period polar orbits, using in situ
and remote sensing instrumentation, distributed over a small number of
spacecraft, will provide continuous 360o coverage of the solar surface
and atmosphere in both longitude and latitude for years on end. This
unprecedented full coverage will enable breakthrough studies of the
physical connection between the solar interior, the solar atmosphere,
the solar wind, solar energetic particles and the inner heliosphere at
large. A potential implementation, the Solar Polar Diamond Explorer
(SPDEx) built upon the Solar Polar Imager mission design, involves
up to four small spacecraft in a 0.48-AU orbit with an inclination
of 75o. The orbit is achieved using solar sails or ion engines, both
technologies already demonstrated in space.
---------------------------------------------------------
Title: Turtles All The Way Down: The finely structured outer corona,
and its implications for PSP
Authors: DeForest, Craig E.; Howard, Russell A.; Velli, Marco C. M.;
Viall, Nicholeen M.; Vourlidas, Angelos
2018tess.conf30928D Altcode:
Based on optical resolution of the starfield with SOHO/LASCO,
STEREO/COR, and other coronagraphs, there is widespread intuition that
the solar corona becomes more smooth with altitude. This is an optical
illusion, caused by the interplay between signal-to-noise ratio (SNR)
and feature size in typical coronal images. Processed, low-noise,
deep-field COR2 images of the outer corona reveal rich structure at
all observable scales, with surprising time variability and very short
spatial correlation scales under 50 Mm, at altitudes near 10 Rs. This
has deep implications not only for the solar wind and outer coronal
physics, but also for the types of structure that Parker Solar Probe
will encounter. We will present and discuss the fundamental result,
and explore its implications for in-situ science and required context
imaging from PSP. We will also make specific predictions about the
environment PSP will encounter at solar altitudes of 10-15 Rs.
---------------------------------------------------------
Title: Using Solar Wind Structures as a Rosetta Stone for
Understanding Solar Wind Formation
Authors: Viall, Nicholeen M.; Kepko, Larry; Antiochos, Spiro K.;
Higginson, Aleida Katherine; Vourlidas, Angelos; Lepri, Susan T.
2018tess.conf31702V Altcode:
In the inner heliosphere, the slow solar wind is often comprised of
mesoscale structures: structures with timescales of hours and length
scales of hundreds of mega meters. White light coronagraph data suggest
that these mesoscale structures are formed and embedded in the solar
wind within the first several solar radii above the solar surface,
which is still below even the closest approach of Parker Solar Probe at
nine solar radii. We argue that these mesoscale structures represent a
'Rosetta Stone' for using the embedded solar wind plasma signatures
to understand the fundamental release and acceleration of solar wind
plasma. We study events identified in data from current missions
to demonstrate how mesoscale structures can link dynamics observed
remotely in the lower corona with in situ observations. We discuss the
observations that Parker Solar Probe will make and how to capitalize
on this remote-to-in situ data connection.
---------------------------------------------------------
Title: Opportunities for Space Weather Research from Parker Solar
Probe and Solar Orbiter Imaging
Authors: Vourlidas, Angelos
2018tess.conf41101V Altcode:
<span class="s1" <p class="p2" <span class="s1" One of the most
exciting NASA missions is scheduled to be launch in summer 2018. The
Parker Solar Probe (PSP) will be the first spacecraft to enter the
atmosphere of a star, reaching within 6 million km from the solar
surface. It will be followed by another inner heliospheric probe,
ESA's Solar Orbiter (SO), which will imagef the solar atmosphere from
above the ecliptic for the first time.The two probes will revolutionize
our understanding of the origins and structure of the quiescent and
transient solar wind (CMEs, CIRs, etc) thanks to their comprehensive
package of remote sensing and in-situ instrumentation, <p class="p2"
<span class="s1" Both are encounter missions and hence unsuited
for Space Weather monitoring, Their Space Weather research potential,
on the other hand, is extremely high. In this talk, I'll discuss how
PSP and SO can address current gaps in our understanding of the source
of Space Weather and guide the development of future Space Weather
systems and models.
---------------------------------------------------------
Title: Distributed Mission Concepts to Achieve Comprehensive Coverage
of Solar Activity
Authors: Vourlidas, Angelos
2018tess.conf41205V Altcode:
<span class="s1" Accurate terrestrial weather forecasting relies on
comprehensive coverage of the terrestrial system provided by a huge
number of distributed surface, air and space sensors. Space weather
is no different. We need to research and monitor solar disturbances
throughout the inner heliosphere. Unfortunately, achieving coverage
at the same level as in the terrestrial system is unfeasible for the
Sun-Earth system due to its scale. We need is a clear strategy and
'outside the box' thinking for the deployment of our sensors to
optimize coverage within a reasonable timetable and budget.<p
class="p1" <span class="s1" In this talk, I discuss multi-point
and multi-viewpoint "string-of-pearls" concepts for achieving nearly
complete coverage of solar activity. The concepts are driven by the
needs of SpW research and operations and take advantage of uncommon
orbits and mission designs. Their implementation is not straightforward
and I outline the challenges that lay ahead for moving forward with
such ideas.
---------------------------------------------------------
Title: Understanding the Internal Magnetic Field Configurations of
ICMEs using more than 20 years of Wind Observations
Authors: Nieves-Chinchilla, Teresa; Vourlidas, Angelos; Raymond,
John C.; Linton, Mark; Al-Haddad, Nada A.; Savani, Neel; Szabo, A.;
Hidalgo, Miguel A. UAH
2018tess.conf10415N Altcode:
The magnetic topology, structure, and geometry of the magnetic
obstacles embedded within interplanetary coronal mass ejections (ICMEs)
are not yet fully and consistently described by in situ models and
reconstruction techniques. The main goal of this work is to understand
better the status of the internal magnetic field of ICMEs and to
explore in situ signatures to identify clues to develop a more accurate
and reliable in situ analytical model. We take advantage of more
than 20 years of Wind observations of transients at 1~AU to compile a
comprehensive database of ICMEs through three solar cycles, from 1995 to
2015. The catalog is publicly available at wind.gsfc.nasa.gov and fully
described in this article. We identify and collect the properties of 337
ICMEs of which 298 show organized magnetic field signatures. To allow
for departures from idealized magnetic configurations, we introduce
the term of 'magnetic obstacle' (MO) to signify the possibility of
more complex configurations.To quantify the asymmetry of the magnetic
field strength profile within these events, we introduce the distortion
parameter (DiP) and calculate the expansion velocity within the magnetic
obstacle. Circular-cylindrical geometry is assumed when the magnetic
field strength displays a symmetric profile. We perform a statistical
study of these two parameters, to find that: (1) Only 35% of the events
show symmetric magnetic profiles and a small enough expansion velocity
to be compatible with the assumption of an idealized cylindrical
static flux rope. (2) 41% of the events do not show the expected
relationship between expansion and magnetic field compression in the
front, with the maximum magnetic field closer to the first encounter
of the spacecraft with the magnetic obstacle; 18% show contractions
(i.e. apparent negative expansion velocity) and 30% show magnetic field
compression in the back. <P />In summary, our main results demonstrate
that the assumed correlation between expanding structure and asymmetric
magnetic field is not always valid. Although 59% of the cases could be
described by circular-cylindrical geometry, with or without expansion,
the remaining cases show significant in situ signatures of departures
from circular-cylindrical geometry. These results will aid in the
development of more accurate in situ models to reconcile image.
---------------------------------------------------------
Title: Coronal properties inferred from the measure of shock Mach
numbers from the coronal base to the Alfvenic critical point
Authors: Kwon, RyunYoung; Vourlidas, Angelos
2018tess.conf30927K Altcode:
We estimate the radial profiles of coronal parameters, such as
local Alfvén (fast-mode) speed, magnetic field, electron density,
temperature, plasma beta, polytropic index, and magnetic/gas pressure,
from the coronal shock Mach numbers (density compression ratios). We
employ five methodologies to determine the Mach numbers; (1) fits
of a sheath electron density model to coronagraphic images (Kwon
et al. 2018), (2) fits of a linear fast magnetosonic wave model to
observed shock wave fronts in the corona (Kwon et al. 2017), (3)
measures of standoff distance at the shock noses (Gopalswamy &
Yashiro 2011), (4) comparisons of 3D shock properties with MHD models
(Rouillard et al. 2016), and (5) comparisons of 3D shock kinematics
with empirical coronal magnetic field and electron density models. The
3D geometry and kinematics of coronal shock waves are determined with
the ellipsoid model using successive multi-perspective observations. We
discuss its physical implications for the characteristics of solar wind
and solar energetic particle acceleration in the sub-Alfvénic region.
---------------------------------------------------------
Title: Simulating observations of the corona/inner heliosphere with
the Wide-Field Imager for Parker Solar Probe by raytracing software
Authors: Nisticò, Giuseppe; Liewer, Paulett; Bothmer, Volker;
Vourlidas, Angelos
2018EGUGA..2018677N Altcode:
The Wide-Field Imager for Parker Solar PRobe (WISPR) will provide us
with white-light images of the corona/inner heliosphere offset from the
Sun, covering a range of elongation angles from 13.5 to 108 deg, with
a high temporal (0.05-60 min) and spatial resolution (plate scale of
1.2-1.7 arcmin per pixel). Such images will be taken from unprecedented
points of observation thanks to the highly-eccentric orbits of
Parker Solar Probe (PSP), which will reach the minimum perihelion
distance below 10 solar radii from the Sun's centre. Therefore,
it is important to understand how WISPR images will look during the
perihelion phases and when PSP will eventually fly throughout various
coronal structures, e.g. streamers, expanding flux ropes, and jets. In
this talk we will provide a collection of synthetic WISPR images for
different coronal structures by using the raytracing tools available
with the SolarSoftWare package. We will discuss the effects due to the
varying radial distance and the high orbital speed ( 200 km/s) of PSP
on the WISPR images, including the possibility of 3D reconstruction
and the determination of the correct kinematics for expanding flux
ropes and jets.
---------------------------------------------------------
Title: Evolution of CME Mass in the Corona
Authors: Howard, Russell A.; Vourlidas, Angelos
2018SoPh..293...55H Altcode:
The idea that coronal mass ejections (CMEs) pile up mass in
their transport through the corona and heliosphere is widely
accepted. However, it has not been shown that this is the case. We
perform an initial study of the volume electron density of the fronts of
13 three-part CMEs with well-defined frontal boundaries observed with
the Solar and Heliospheric Observatory/Large Angle and Spectrometric
COronagraph (SOHO/LASCO) white-light coronagraphs. We find that, in all
cases, the volume electron density decreases as the CMEs travel through
the LASCO-C2 and -C3 fields of view, from 2.6 -30 <SUB>R⊙</SUB>. The
density decrease follows closely a power law with an exponent of −3,
which is consistent with a simple radial expansion. This indicates
that in this height regime there is no observed pile-up.
---------------------------------------------------------
Title: Evolution of CME Mass in The Corona
Authors: Howard, Russell A.; Vourlidas, Angelos
2018EGUGA..2018390H Altcode:
The idea that Coronal Mass Ejections (CMEs) pile up mass in
their transport through the corona and heliosphere is widely
accepted. However, it has not been shown that this is the case. We
perform an initial study of the volume electron density of the fronts of
thirteen 3-part CMEs with well defined frontal boundaries observed with
the SOHO/LASCO white light coronagraphs. We find that, in all cases,
the volume electron density decreases as the CMEs travel through the
LASCO/C2 & C3 fields of view, from 2.6 - 30 Rs. The density decrease
follows closely a power law with an exponent of -3, which is consistent
with a simple radial expansion. This indicates that in this height
regime there is no observed pileup. This work was supported by NASA.
---------------------------------------------------------
Title: Bridging the Gap: Capturing the Lyα Counterpart of a Type-II
Spicule and Its Heating Evolution with VAULT2.0 and IRIS Observations
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Pereira, Tiago M. D.; Vourlidas, Angelos; Tun Beltran, Samuel
2018ApJ...857...73C Altcode: 2018arXiv180303405C
We present results from an observing campaign in support of the
VAULT2.0 sounding rocket launch on 2014 September 30. VAULT2.0 is a Lyα
(1216 Å) spectroheliograph capable of providing spectroheliograms at
high cadence. Lyα observations are highly complementary to the IRIS
observations of the upper chromosphere and the low transition region
(TR) but have previously been unavailable. The VAULT2.0 data provide new
constraints on upper-chromospheric conditions for numerical models. The
observing campaign was closely coordinated with the IRIS mission. Taking
advantage of this simultaneous multi-wavelength coverage of target
AR 12172 and by using state-of-the-art radiative-MHD simulations of
spicules, we investigate in detail a type-II spicule associated with
a fast (300 km s<SUP>-1</SUP>) network jet recorded in the campaign
observations. Our analysis suggests that spicular material exists
suspended high in the atmosphere but at lower temperatures (seen in
Lyα) until it is heated and becomes visible in TR temperatures as a
network jet. The heating begins lower in the spicule and propagates
upwards as a rapidly propagating thermal front. The front is then
observed as fast, plane-of-the-sky motion typical of a network jet,
but contained inside the pre-existing spicule. This work supports
the idea that the high speeds reported in network jets should not be
taken as real mass upflows but only as apparent speeds of a rapidly
propagating heating front along the pre-existing spicule.
---------------------------------------------------------
Title: Information Theoretic Approach to Discovering Causalities in
the Solar Cycle
Authors: Wing, Simon; Johnson, Jay R.; Vourlidas, Angelos
2018ApJ...854...85W Altcode:
The causal parameters and response lag times of the solar cycle dynamics
are investigated with transfer entropy, which can determine the amount
of information transfer from one variable to another. The causal
dependency of the solar cycle parameters is bidirectional. The transfer
of information from the solar polar field to the sunspot number (SSN)
peaks at lag time (τ) ∼ 30-40 months, but thereafter it remains at
a persistently low level for at least 400 months (∼3 solar cycles)
for the period 1906-2014. The latter may lend support to the idea that
the polar fields from the last three or more solar cycles can affect
the production of the SSN of the subsequent cycle. There is also a
similarly long-term information transfer from the SSN to the polar
field. Both the meridional flow speed and flux emergence (proxied by
the SSN) transfer information to the polar field, but one transfers
more information than the other, depending on the lag times. The
meridional flow speed transfers more information than the SSN to
the polar field at τ ∼ 28-30 months and at τ ∼ 90-110 months,
which may be consistent with some flux transfer dynamo models and some
surface flux transport models. However, the flux emergence transfers
more information than the meridional flow to the polar field at τ ∼
60-80 months, which may be consistent with a recently developed surface
flux transport model. The transfer of information from the meridional
flow to the SSN peaks at τ ∼ 110-120 months (∼1 solar cycle).
---------------------------------------------------------
Title: The density compression ratio of shock fronts associated with
coronal mass ejections
Authors: Kwon, Ryun-Young; Vourlidas, Angelos
2018JSWSC...8A...8K Altcode: 2018JSWSC...8A..08K; 2018arXiv180104355K
We present a new method to extract the three-dimensional electron
density profile and density compression ratio of shock fronts associated
with coronal mass ejections (CMEs) observed in white light coronagraph
images. We demonstrate the method with two examples of fast halo CMEs
(∼2000 km s<SUP>-1</SUP>) observed on 2011 March 7 and 2014 February
25. Our method uses the ellipsoid model to derive the three-dimensional
geometry and kinematics of the fronts. The density profiles of the
sheaths are modeled with double-Gaussian functions with four free
parameters, and the electrons are distributed within thin shells behind
the front. The modeled densities are integrated along the lines of
sight to be compared with the observed brightness in COR2-A, and a
χ<SUP>2</SUP> approach is used to obtain the optimal parameters for
the Gaussian profiles. The upstream densities are obtained from both
the inversion of the brightness in a pre-event image and an empirical
model. Then the density ratio and Alfvénic Mach number are derived. We
find that the density compression peaks around the CME nose, and
decreases at larger position angles. The behavior is consistent with
a driven shock at the nose and a freely propagating shock wave at
the CME flanks. Interestingly, we find that the supercritical region
extends over a large area of the shock and lasts longer (several tens
of minutes) than past reports. It follows that CME shocks are capable
of accelerating energetic particles in the corona over extended spatial
and temporal scales and are likely responsible for the wide longitudinal
distribution of these particles in the inner heliosphere. Our results
also demonstrate the power of multi-viewpoint coronagraphic observations
and forward modeling in remotely deriving key shock properties in an
otherwise inaccessible regime.
---------------------------------------------------------
Title: Using the Deep Space Gateway to Build the Next Generation
Heliophysics Research Grid
Authors: Vourlidas, A.; Ho, G. C.; Cohen, I. J.; Korendyke, C. M.;
Tun-Beltran, S.; Plunkett, S. P.; Newmark, J.; St Cyr, O. C.;
Hoeksema, T.
2018LPICo2063.3055V Altcode:
The Heliophysics Research Grid (HRG) consists of in situ and imaging
sensors, distributed in key locations in the heliosphere for research
and to support space exploration needs. The Deep Space Gateway enables
the HRG as a storage and staging hub for HRG launches.
---------------------------------------------------------
Title: Understanding the Internal Magnetic Field Configurations of
ICMEs Using More than 20 Years of Wind Observations
Authors: Nieves-Chinchilla, T.; Vourlidas, A.; Raymond, J. C.; Linton,
M. G.; Al-haddad, N.; Savani, N. P.; Szabo, A.; Hidalgo, M. A.
2018SoPh..293...25N Altcode:
The magnetic topology, structure, and geometry of the magnetic
obstacles embedded within interplanetary coronal mass ejections (ICMEs)
are not yet fully and consistently described by in situ models and
reconstruction techniques. The main goal of this work is to better
understand the status of the internal magnetic field of ICMEs and to
explore in situ signatures to identify clues to develop a more accurate
and reliable in situ analytical models. We take advantage of more
than 20 years of Wind observations of transients at 1 AU to compile
a comprehensive database of ICMEs through three solar cycles, from
1995 to 2015. The catalog is publicly available at wind.gsfc.nasa.gov
and is fully described in this article. We identify and collect
the properties of 337 ICMEs, of which 298 show organized magnetic
field signatures. To allow for departures from idealized magnetic
configurations, we introduce the term "magnetic obstacle" (MO) to
signify the possibility of more complex configurations. To quantify the
asymmetry of the magnetic field strength profile within these events,
we introduce the distortion parameter (DiP) and calculate the expansion
velocity within the magnetic obstacle. Circular-cylindrical geometry
is assumed when the magnetic field strength displays a symmetric
profile. We perform a statistical study of these two parameters and
find that only 35% of the events show symmetric magnetic profiles and a
low enough expansion velocity to be compatible with the assumption of
an idealized cylindrical static flux rope, and that 41% of the events
do not show the expected relationship between expansion and magnetic
field compression in the front, with the maximum magnetic field closer
to the first encounter of the spacecraft with the magnetic obstacle;
18% show contractions (i.e. apparent negative expansion velocity),
and 30% show magnetic field compression in the back. We derive an
empirical relation between DiP and expansion velocity that is the first
step toward improving reconstructions with possible applications to
space weather studies. In summary, our main results demonstrate that
the assumed correlation between expanding structure and asymmetric
magnetic field is not always valid. Although 59% of the cases could be
described by circular-cylindrical geometry, with or without expansion,
the remaining cases show significant in situ signatures of departures
from circular-cylindrical geometry. These results will aid in the
development of more accurate in situ models to reconcile image.
---------------------------------------------------------
Title: The Deep Space Gateway Opportunity for Next Generation Space
Weather Measurements
Authors: Ho, G. C.; Vourlidas, A.; Westlake, J. H.; Cohen, I. J.
2018LPICo2063.3046H Altcode:
The near-Earth vicinity of the Deep Space Gateway could represent the
first step in formulation of a new space weather system, potentially
providing a broad range of infrastructure to enable a paradigm-shifting
approach to how measurements are made.
---------------------------------------------------------
Title: EUV Irradiance Inputs to Thermospheric Density Models: Open
Issues and Path Forward
Authors: Vourlidas, A.; Bruinsma, S.
2018SpWea..16....5V Altcode: 2018arXiv180106092V
One of the objectives of the NASA Living With a Star Institute on
"Nowcasting of Atmospheric Drag for low Earth orbit (LEO) Spacecraft"
was to investigate whether and how to increase the accuracy of
atmospheric drag models by improving the quality of the solar forcing
inputs, namely, extreme ultraviolet (EUV) irradiance information. In
this focused review, we examine the status of and issues with EUV
measurements and proxies, discuss recent promising developments, and
suggest a number of ways to improve the reliability, availability,
and forecast accuracy of EUV measurements in the next solar cycle.
---------------------------------------------------------
Title: The Solar Orbiter Heliospheric Imager (SoloHI) for the Solar
Orbiter Mission
Authors: Howard, R.; Colaninno, R. C.; Plunkett, S. P.; Thernisien,
A. F.; Wang, D.; Rich, N.; Korendyke, C.; Socker, D. G.; Linton, M.;
McMullin, D. R.; Vourlidas, A.; Liewer, P. C.; De Jong, E.; Velli,
M.; Mikic, Z.; Bothmer, V.; Philippe, L.; Carter, M. T.
2017AGUFMSH23D2681H Altcode:
The SoloHI instrument has completed its development effort and has been
integrated onto the Solar Orbiter (SolO) spacecraft. The SolO mission,
scheduled for launch in February 2019, will undergo gravity assist
maneuvers around Venus to change both the perihelion distance as well
as the plane of the orbit to ultimately achieve a minimum perihelion
of 0.28 AU and an orbital inclination of about 35° relative to the
ecliptic plane. The remote sensing instruments will operate for three
10-day periods out of the nominal 6-month orbit. SoloHI will observe
sunlight scattered by free electrons in the corona/solar wind from 5°
to 45° elongation in visible wavelengths and will provide a coupling
between remote sensing and in situ observations. It is very similar
to the HI-1 instrument on STEREO/SECCHI except that the FOV is twice
the size at 40o. We present our efforts to prepare for the mission
including our observing plans, quick-look plans and some results of
the calibration activities. We gratefully acknowledge the support of
the NASA Solar Orbiter Collaboration project.
---------------------------------------------------------
Title: The Wide-Field Imager for the Parker Solar Probe Mission
(WISPR)
Authors: Plunkett, S. P.; Howard, R.; Chua, D. H.; Crump, N. A.;
Dennison, H.; Korendyke, C.; Linton, M.; Rich, N.; Socker, D. G.;
Thernisien, A. F.; Wang, D.; Vourlidas, A.; Baugh, R.; Van Duyne,
J. P.; Liewer, P. C.; De Jong, E.; Boies, M. T.; Mikic, Z.; Bothmer,
V.; Rochus, P.; Halain, J. P.
2017AGUFMSH23D2693P Altcode:
The Parker Solar Probe (PSP) mission will be humanity's first visit
to the atmosphere of our nearest star, the Sun, when it is launched
in July 2018. PSP will complete 24 orbits between the Sun and Venus
with diminishing perihelia reaching as close as 7 million km (9.86
solar radii) from Sun center. In addition to a suite of in-situ probes
for the magnetic field, plasma, and energetic particles, the payload
includes the Wide Field Imager for Solar Probe (WISPR) that will
record unprecedented visible light images of the solar corona and the
inner heliosphere. WISPR is the smallest heliospheric imager to date,
and comprises two nested wide-field telescopes with large-format (2K
x 2K) APS CMOS detectors to optimize the performance over a combined
95º radial by 58º transverse field of view and to minimize the risk
of dust damage, which may be considerable close to the Sun. WISPR will
discover - in this never-before explored region of the heliosphere - the
fundamental nature of coronal structures and the source regions of the
solar wind as the PSP flies through them, and will determine whether a
dust-free zone exists near the Sun. WISPR has completed its development
effort and has been integrated onto the PSP spacecraft. In this paper,
we will present our efforts to prepare for the mission including our
observing plans and some results of the calibration activities.
---------------------------------------------------------
Title: Combining Remote and In Situ Observations with MHD models to
Understand the Formation of the Slow Solar Wind
Authors: Viall, N. M.; Kepko, L.; Antiochos, S. K.; Lepri, S. T.;
Vourlidas, A.; Linker, J.
2017AGUFMSH21C..05V Altcode:
Connecting the structure and variability in the solar corona to the
Heliosphere and solar wind is one of the main goals of Heliophysics
and space weather research. The instrumentation and viewpoints of
the Parker Solar Probe and Solar Orbiter missions will provide an
unprecedented opportunity to combine remote sensing with in situ data
to determine how the corona drives the Heliosphere, especially as it
relates to the origin of the slow solar wind. We present analysis of
STEREO coronagraph and heliospheric imager observations and of in
situ ACE and Wind measurements that reveal an important connection
between the dynamics of the corona and of the solar wind. We show
observations of quasi-periodic release of plasma into the slow solar
wind occurring throughout the corona - including regions away from the
helmet streamer and heliospheric current sheet - and demonstrate that
these observations place severe constraints on the origin of the slow
solar wind. We build a comprehensive picture of the dynamic evolution
by combining remote imaging data, in situ composition and magnetic
connectivity information, and MHD models of the solar wind. Our results
have critical implications for the magnetic topology involved in slow
solar wind formation and magnetic reconnection dynamics. Crucially,
this analysis pushes the limits of current instrument resolution and
sensitivity, showing the enormous potential science to be accomplished
with the Parker Solar Probe and Solar Orbiter missions.
---------------------------------------------------------
Title: Investigating the ability of solar coronal shocks to accelerate
solar energetic particles
Authors: Kwon, R. Y.; Vourlidas, A.
2017AGUFMSH31B2734K Altcode:
We estimate the density compression ratio of shocks associated
with coronal mass ejections (CMEs) and investigate whether they can
accelerate solar energetic particles (SEPs). Using remote-sensing,
multi-viewpoint coronagraphic observations, we have developed a
method to extract the sheath electron density profiles along the
shock normal and estimate the density compression ratio. Our method
uses the ellipsoid model to derive the 3D geometry of the sheaths,
including the line-of-sight (LOS) depth. The sheath density profiles
along the shock normal are modeled with double-Gaussian functions, and
the modeled densities are integrated along the LOSs to be compared with
the observed brightness in STEREO COR2-Ahead. The upstream densities are
derived from either the pB-inversion of the brightness in a pre-event
image or an empirical model. We analyze two fast halo CMEs observed
on 2011 March 7 and 2014 February 25 that are associated with SEP
events detected by multiple spacecraft located over a broad range of
heliolongitudes. We find that the density compression peaks around
the CME nose and decreases at larger position angles. Interestingly,
we find that the supercritical region extends over a large area of the
shock and lasts longer (several tens of minutes) than past reports. This
finding implies that CME shocks may be capable of accelerating energetic
particles in the corona over extended spatial and temporal scales and
may, therefore, be responsible for the wide longitudinal distribution
of these particles in the inner heliosphere.
---------------------------------------------------------
Title: A model for heliospheric flux-ropes
Authors: Nieves-Chinchilla, T.; Linton, M.; Vourlidas, A.; Hidalgo,
M. A. U.
2017AGUFMSH12B..08N Altcode:
This work is presents an analytical flux-rope model, which explores
different levels of complexity starting from a circular-cylindrical
geometry. The framework of this series of models was established by
Nieves-Chinchilla et al. 2016 with the circular-cylindrical analytical
flux rope model. The model attempts to describe the magnetic flux rope
topology with distorted cross-section as a possible consequence of
the interaction with the solar wind. In this model, the flux rope is
completely described in a non-orthogonal geometry. The Maxwell equations
are solved using tensor calculus consistent with the geometry chosen,
invariance along the axial direction, and with the assumption of no
radial current density. The model is generalized in terms of the radial
and azimuthal dependence of the poloidal current density component
and axial current density component. The misalignment between current
density and magnetic field is studied in detail for several example
profiles of the axial and poloidal current density components. This
theoretical analysis provides a map of the force distribution inside of
the flux-rope. For reconstruction of the heliospheric flux-ropes, the
circular-cylindrical reconstruction technique has been adapted to the
new geometry and applied to in situ ICMEs with a flux-rope entrained and
tested with cases with clear in situ signatures of distortion. The model
adds a piece in the puzzle of the physical-analytical representation of
these magnetic structures that should be evaluated with the ultimate
goal of reconciling in-situ reconstructions with imaging 3D remote
sensing CME reconstructions. Other effects such as axial curvature
and/or expansion could be incorporated in the future to fully understand
the magnetic structure.
---------------------------------------------------------
Title: Bridging the Gap: Capturing the Lyα Counterpart of a Type-II
Spicule and its Heating Evolution with VAULT2.0 and IRIS Campaign
Observations
Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.; Mendes
Domingos Pereira, T.; Vourlidas, A.; Tun Beltran, S.
2017AGUFMSH43A2794C Altcode:
We present the analysis of data from the observing campaign in support
to the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0
is a Lyα (1216 Å) spectroheliograph capable of providing fast
cadence spectroheliograms of high-spectral purity. High resolution
Lyα observations are highly complementary with the IRIS observations
of the upper chromosphere and the low transition region but have
previously been unavailable. The VAULT2.0 data provide critical, new
upper-chromospheric constraints for numerical models. The observing
campaign was closely coordinated with the IRIS mission. Taking
advantage of this simultaneous multi-wavelength coverage of target
AR 12172 and by using state-of-the-art radiative-MHD simulations of
spicules, we are able to perform a detailed investigation of a type-II
spicule associated with a fast apparent network jet recorded in the
campaign observations during the VAULT2.0 flight. Our unique analysis
suggests that spicular material exists suspended in lower temperatures
until it rapidly gets heated and becomes visible in transition-region
temperatures as an apparent network jet.
---------------------------------------------------------
Title: Mapping The Territory: What Current Remote Sensing Tells Us
To Expect For PSP
Authors: DeForest, C. E.; McComas, D. J.; Vourlidas, A.; Howard, R.
2017AGUFMSH21C..06D Altcode:
Remote sensing with current coronagraphs affords the best current
estimate of plasma conditions PSP will encounter. Over the past few
years, analyses of the synoptic data sets from the STEREO/COR2 and
STEREO/HI1 imagers have yielded rough locations for critical loci such
as the Alfvén and β=1 surfaces. We now present new results from
the deepest-field coronagraph sequence made to date: the STEREO-A
deep-field campaign. Recently-developed noise reduction techniques
and the unique deep-exposure data set reveal small scale motions and
fluctuations throughout the visible corona and give new insight into
the structure of the outer corona.
---------------------------------------------------------
Title: Turbulent Density Fluctuations and Proton Heating Rate in
the Solar Wind from 9-20 R <SUB>⊙</SUB>
Authors: Sasikumar Raja, K.; Subramanian, Prasad; Ramesh, R.;
Vourlidas, Angelos; Ingale, Madhusudan
2017ApJ...850..129S Altcode: 2017arXiv171006295S
We obtain scatter-broadened images of the Crab Nebula at 80 MHz as
it transits through the inner solar wind in 2017 and 2016 June. These
images are anisotropic, with the major axis oriented perpendicular to
the radially outward coronal magnetic field. Using these data, we deduce
that the density modulation index (δ {N}<SUB>e</SUB>/{N}<SUB>e</SUB>)
caused by turbulent density fluctuations in the solar wind ranges
from 1.9× {10}<SUP>-3</SUP> to 7.7× {10}<SUP>-3</SUP> between 9 and
20 R <SUB>⊙</SUB>. We also find that the heating rate of solar wind
protons at these distances ranges from 2.2× {10}<SUP>-13</SUP> to 1.0×
{10}<SUP>-11</SUP> {erg} {{cm}}<SUP>-3</SUP> {{{s}}}<SUP>-1</SUP>. On
two occasions, the line of sight intercepted a coronal streamer. We
find that the presence of the streamer approximately doubles the
thickness of the scattering screen.
---------------------------------------------------------
Title: Is There a CME Rate Floor? CME and Magnetic Flux Values for
the Last Four Solar Cycle Minima
Authors: Webb, D. F.; Howard, R. A.; St. Cyr, O. C.; Vourlidas, A.
2017ApJ...851..142W Altcode:
The recent prolonged activity minimum has led to the question of
whether there is a base level of the solar magnetic field evolution
that yields a “floor” in activity levels and also in the solar
wind magnetic field strength. Recently, a flux transport model
coupled with magneto-frictional simulations has been used to simulate
the continuous magnetic field evolution in the global solar corona
for over 15 years, from 1996 to 2012. Flux rope eruptions in the
simulations are estimated (Yeates), and the results are in remarkable
agreement with the shape of the SOlar Heliospheric Observatory/Large
Angle and Spectrometric Coronagraph Experiment coronal mass ejection
(CME) rate distribution. The eruption rates at the two recent minima
approximate the observed-corrected CME rates, supporting the idea of
a base level of solar magnetic activity. In this paper, we address
this issue by comparing annual averages of the CME occurrence rates
during the last four solar cycle minima with several tracers of the
global solar magnetic field. We conclude that CME activity never ceases
during a cycle, but maintains a base level of 1 CME every 1.5 to ∼3
days during minima. We discuss the sources of these CMEs.
---------------------------------------------------------
Title: CME Dynamics Using STEREO and LASCO Observations: The Relative
Importance of Lorentz Forces and Solar Wind Drag
Authors: Sachdeva, Nishtha; Subramanian, Prasad; Vourlidas, Angelos;
Bothmer, Volker
2017SoPh..292..118S Altcode: 2017arXiv170504871S
We seek to quantify the relative contributions of Lorentz forces and
aerodynamic drag on the propagation of solar coronal mass ejections
(CMEs). We use Graduated Cylindrical Shell (GCS) model fits to a
representative set of 38 CMEs observed with the Solar and Heliospheric
Observatory (SOHO) and the Solar and Terrestrial Relations Observatory
(STEREO) spacecraft. We find that the Lorentz forces generally peak
between 1.65 and 2.45 R<SUB>⊙</SUB> for all CMEs. For fast CMEs,
Lorentz forces become negligible in comparison to aerodynamic drag as
early as 3.5 - 4 R<SUB>⊙</SUB>. For slow CMEs, however, they become
negligible only by 12 - 50 R<SUB>⊙</SUB>. For these slow events,
our results suggest that some of the magnetic flux might be expended in
CME expansion or heating. In other words, not all of it contributes to
the propagation. Our results are expected to be important in building
a physical model for understanding the Sun-Earth dynamics of CMEs.
---------------------------------------------------------
Title: Three-dimensional characteristics of solar coronal shocks
determined from observations; Geometry, Kinematics, and Compression
ratio
Authors: Kwon, Ryun Young; Vourlidas, Angelos
2017SPD....4820102K Altcode:
We investigate the three-dimensional (3D) characteristics of coronal
shocks associated with Coronal Mass Ejections (CMEs), in terms of
geometry, kinematics, and density compression ratio, employing a new
method we have developed. The method uses multi-viewpoint observations
from the STEREO-A, -B and SOHO coronagraphs. The 3D structure and
kinematics of coronal shock waves and the driving CMEs are derived
separately using a forward modeling method. We analyze two CMEs that
are observed as halos by the three spacecraft, and the peak speeds
are over 2000 km s<SUP>-1</SUP>. From the 3D modeling, we find (1) the
coronal shock waves are spherical apparently enclosing the Sun, in which
the angular widths are much wider than those of CMEs (92° and 252°
versus 58° and 91°), indicating shock waves are propagating away from
the CMEs in the azimuthal directions, and (2) the speeds of the shock
waves around the CME noses are comparable to those of the CME noses,
but the speeds at the lateral flanks seem to be limited to the local
fast magnetosonic speed. Applying our new method, we determine electron
densities in the shock sheaths, the downstream-upstream density ratios,
and the Mach numbers. We find (1) the sheath electron densities decrease
with height in general but have the maximum near the CME noses, (2)
the density ratios and Mach numbers also seem to depend on the position
angle from the CME nose to the far-flank but are more or less constant
in time, while the sheath electron densities and speeds decrease with
time, because of the reduced local Alfven speed with height, and (3)
the shocks could be supercritical in a wider spatial range, and it
lasts longer, than those of what have been reported in the past. We
conclude that the shock wave associated with an energetic CME is a
phenomenon that is becoming a non-driven (blast-type), nearly freely
propagating wave at the flank from a driven (bow- and/or piston-type)
wave near the CME nose.
---------------------------------------------------------
Title: Observation of an Extremely Large-Density Heliospheric Plasma
Sheet Compressed by an Interplanetary Shock at 1 AU
Authors: Wu, Chin-Chun; Liou, Kan; Lepping, R. P.; Vourlidas, Angelos;
Plunkett, Simon; Socker, Dennis; Wu, S. T.
2017SoPh..292..109W Altcode:
At 11:46 UT on 9 September 2011, the Wind spacecraft encountered an
interplanetary (IP) fast-forward shock. The shock was followed almost
immediately by a short-duration (∼ 35 minutes) extremely dense pulse
(with a peak ∼ 94 cm<SUP>−3</SUP>). The pulse induced an extremely
large positive impulse (SYM-H = 74 nT and Dst = 48 nT) on the ground. A
close examination of other in situ parameters from Wind shows that
the density pulse was associated with i) a spike in the plasma β
(ratio of thermal to magnetic pressure), ii) multiple sign changes in
the azimuthal component of the magnetic field (B<SUB>ϕ</SUB>), iii) a
depressed magnetic field magnitude, iv) a small radial component of the
magnetic field, and v) a large (> 90°) change in the suprathermal
(∼ 255 eV) electron pitch angle across the density pulse. We
conclude that the density pulse is associated with the heliospheric
plasma sheet (HPS). The thickness of the HPS is estimated to be ∼8.2
×10<SUP>5</SUP>km. The HPS density peak is about five times the value
of a medium-sized density peak inside the HPS (∼ 18 cm<SUP>−3</SUP>)
at 1 AU. Our global three-dimensional magnetohydrodynamic simulation
results (Wu et al. in J. Geophys. Res. 212, 1839, 2016) suggest that
the extremely large density pulse may be the result of the compression
of the HPS by an IP shock crossing or an interaction between an
interplanetary shock and a corotating interaction region.
---------------------------------------------------------
Title: Magnetic flux-rope configurations embedded in the Coronal
Mass Ejections
Authors: Nieves-Chinchilla, Teresa; Vourlidas, A.; Raymond, J.;
Linton, M.; Savani, P. N.; Al-haddad, N.; Szabo, A.
2017shin.confE..37N Altcode:
Interplanetary coronal mass ejections (ICMEs) are manifestations of
magnetized plasma moving from the Sun throughout the heliosphere. The
understanding of the magnetic field topology, structure, global
morphology and the effect of the evolution from the first stages of
the heliospheric journey of the CMEs are still a challenge. Today the
reconciliation between local and global ICMEs reconstruction are far
to converge systematically in a unique scenario and vision. Also the
lack of consensus between in-situ models, lead to the need to revisit
the heliospheric definition of the magnetic obstacle embedded in the
ICMEs. In this work we approach this discussion from the point of view
of in-situ observations of the ICMEs using the catalogues of ICMEs
provided by Heliospheric observatories. We address three questions:
1) Can we find any relationship between the in-situ observed magnetic
field strength compression and the apparent Vexp?, 2) Can we quantify
the flux-rope distortion, curvatures or deformations at any heliospheric
distance?, and finally, 3) can we quantify the forces that govern the
internal evolution of the ICMEs in the inner heliosphere?.
---------------------------------------------------------
Title: Magnetic Flux Rope Shredding By a Hyperbolic Flux Tube:
The Detrimental Effects of Magnetic Topology on Solar Eruptions
Authors: Chintzoglou, Georgios; Vourlidas, Angelos; Savcheva, Antonia;
Tassev, Svetlin; Tun Beltran, Samuel; Stenborg, Guillermo
2017ApJ...843...93C Altcode: 2017arXiv170600057C
We present the analysis of an unusual failed eruption captured in high
cadence and in many wavelengths during the observing campaign in support
of the Very high Angular resolution Ultraviolet Telescope (VAULT2.0)
sounding rocket launch. The refurbished VAULT2.0 is a Lyα (λ 1216 Å)
spectroheliograph launched on 2014 September 30. The campaign targeted
active region NOAA AR 12172 and was closely coordinated with the Hinode
and IRIS missions and several ground-based observatories (NSO/IBIS,
SOLIS, and BBSO). A filament eruption accompanied by a low-level
flaring event (at the GOES C-class level) occurred around the VAULT2.0
launch. No coronal mass ejection was observed. The eruption and its
source region, however, were recorded by the campaign instruments in
many atmospheric heights ranging from the photosphere to the corona
in high cadence and spatial resolution. This is a rare occasion
that enabled us to perform a comprehensive investigation on a failed
eruption. We find that a rising Magnetic Flux Rope (MFR)-like structure
was destroyed during its interaction with the ambient magnetic field,
creating downflows of cool plasma and diffuse hot coronal structures
reminiscent of “cusps.” We employ magnetofrictional simulations to
show that the magnetic topology of the ambient field is responsible for
the destruction of the MFR. Our unique observations suggest that the
magnetic topology of the corona is a key ingredient for a successful
eruption.
---------------------------------------------------------
Title: The Density Structure of Shock Sheaths Associated with Coronal
Mass Ejections
Authors: Kwon, Ryun Young; Vourlidas, Angelos
2017shin.confE..23K Altcode:
We present the three-dimensional (3D) geometry and property of coronal
mass ejections (CMEs) focusing on the density structure of the shock
sheaths. We have developed a new method utilizing remote-sensing,
multi-viewpoint coronagraphic observations, to extract the 3D electron
density profiles and thus the density compression ratio of shock sheaths
associated with CMEs close to the Sun. <P />We analyze two fast halo
CMEs observed on 2011 March 7 and 2014 February 25. Our method uses
the ellipsoid model to derive the 3D geometry of the sheaths, including
the line-of-sight (LOS) depth. The density profiles of the sheaths are
modeled with double-Gaussian functions, with four free parameters. The
modeled densities are integrated along the 3D LOSs and compared with
the observed brightness in COR2-A, using a chi-squares approach to
obtain the optimal parameters for the Gaussian profiles. The upstream
densities are derived from both the inversion of the brightness in
a pre-event image and an empirical model. Then the density ratio and
Alfvenic Mach number are calculated across the shock front. <P />We find
that the density compression peaks around the CME nose and decreases
at larger position angles. It is consistent with a driven shock at
the nose and a free-propagating wave at the CME flanks. Interestingly,
we find that the compression ratio and hence the supercritical region
extend over a large area of the shock and last longer (several tens
of minutes) than past reports. Our results demonstrate the power of
multi-viewpoint coronagraphic observations and forward modeling in
remotely deriving key shock properties in an otherwise inaccessible
regime. They also show that CME shocks are capable of accelerating
energetic particles in the corona over extended spatial and temporal
scales and may, therefore, be responsible for the wide longitudinal
distribution of these particles in the inner heliosphere.
---------------------------------------------------------
Title: The 'baby' steps of CMEs: What can we learn about their future
journey to the heliosphere?
Authors: Guedes dos Santos, Luiz Fernando; Nieves-Chinchilla, Teresa;
Vourlidas, Angelos; Uritsky, Vadim M.
2017shin.confE..24G Altcode:
Coronal mass ejections (CMEs) are large-scale explosions of magnetic
field and plasma from the Sun's corona and the primary drivers of
terrestrial space weather. The fastest CMEs can reach Earth in 1-5
days expanding in size as they travel due to their strong entrained
magnetic fields.
---------------------------------------------------------
Title: SOLARIS: Solar Sail Investigation of the Sun
Authors: Appourchaux, Thierry; Auchère, Frédéric; Antonucci, Ester;
Gizon, Laurent; MacDonald, Malcolm; Hara, Hirohisa; Sekii, Takashi;
Moses, Daniel; Vourlidas, Angelos
2017arXiv170708193A Altcode:
In this paper, we detail the scientific objectives and outline
a strawman payload of the SOLAR sail Investigation of the Sun
(SOLARIS). The science objectives are to study the 3D structure
of the solar magnetic and velocity field, the variation of total
solar irradiance with latitude, and the structure of the corona. We
show how we can meet these science objective using solar-sail
technologies currently under development. We provide a tentative
mission profile considering several trade-off approaches. We also
provide a tentative mass budget breakdown and a perspective for a
programmatic implementation.
---------------------------------------------------------
Title: Multi-viewpoint Coronal Mass Ejection Catalog Based on STEREO
COR2 Observations
Authors: Vourlidas, Angelos; Balmaceda, Laura A.; Stenborg, Guillermo;
Dal Lago, Alisson
2017ApJ...838..141V Altcode:
We present the first multi-viewpoint coronal mass ejection (CME)
catalog. The events are identified visually in simultaneous total
brightness observations from the twin SECCHI/COR2 coronagraphs on board
the Solar Terrestrial Relations Observatory mission. The Multi-View
CME Catalog differs from past catalogs in three key aspects: (1) all
events between the two viewpoints are cross-linked, (2) each event
is assigned a physics-motivated morphological classification (e.g.,
jet, wave, and flux rope), and (3) kinematic and geometric information
is extracted semi-automatically via a supervised image segmentation
algorithm. The database extends from the beginning of the COR2 synoptic
program (2007 March) to the end of dual-viewpoint observations (2014
September). It contains 4473 unique events with 3358 events identified
in both COR2s. Kinematic properties exist currently for 1747 events (26%
of COR2-A events and 17% of COR2-B events). We examine several issues,
made possible by this cross-linked CME database, including the role of
projection on the perceived morphology of events, the missing CME rate,
the existence of cool material in CMEs, the solar cycle dependence
on CME rate, speeds and width, and the existence of flux rope within
CMEs. We discuss the implications for past single-viewpoint studies
and for Space Weather research. The database is publicly available
on the web including all available measurements. We hope that it will
become a useful resource for the community.
---------------------------------------------------------
Title: Investigating the Wave Nature of the Outer Envelope of Halo
Coronal Mass Ejections
Authors: Kwon, Ryun-Young; Vourlidas, Angelos
2017ApJ...836..246K Altcode:
We investigate the nature of the outer envelope of halo coronal mass
ejections (H-CMEs) using multi-viewpoint observations from the Solar
Terrestrial Relations Observatory-A, -B, and SOlar and Heliospheric
Observatory coronagraphs. The 3D structure and kinematics of the halo
envelopes and the driving CMEs are derived separately using a forward
modeling method. We analyze three H-CMEs with peak speeds from 1355
to 2157 km s<SUP>-1</SUP> sufficiently fast to drive shocks in the
corona. We find that the angular widths of the halos range from 192° to
252°, while those of the flux ropes range between only 58° and 91°,
indicating that the halos are waves propagating away from the CMEs. The
halo widths are in agreement with widths of Extreme Ultraviolet (EUV)
waves in the low corona further demonstrating the common origin of
these structures. To further investigate the wave nature of the halos,
we model their 3D kinematic properties with a linear fast magnetosonic
wave model. The model is able to reproduce the position of the halo
flanks with realistic coronal medium assumptions but fails closer to
the CME nose. The CME halo envelope seems to arise from a driven wave
(or shock) close to the CME nose, but it is gradually becoming a freely
propagating fast magnetosonic wave at the flanks. This interpretation
provides a simple unifying picture for CME halos, EUV waves, and the
large longitudinal spread of solar energetic particles.
---------------------------------------------------------
Title: Structure, Propagation, and Expansion of a CME-driven Shock
in the Heliosphere: A Revisit of the 2012 July 23 Extreme Storm
Authors: Liu, Ying D.; Hu, Huidong; Zhu, Bei; Luhmann, Janet G.;
Vourlidas, Angelos
2017ApJ...834..158L Altcode: 2016arXiv161104239L
We examine the structure, propagation, and expansion of the
shock associated with the 2012 July 23 extreme coronal mass
ejection. Characteristics of the shock determined from multi-point
imaging observations are compared to in situ measurements at
different locations and a complex radio type II burst, which
according to our definition has multiple branches that may not all be
fundamental-harmonic related. The white-light shock signature can be
modeled reasonably well by a spherical structure and was expanding
backward even on the opposite side of the Sun. The expansion of the
shock, which was roughly self-similar after the first ∼1.5 hr from
launch, largely dominated over the translation of the shock center
for the time period of interest. Our study also suggests a bow-shock
morphology around the nose at later times due to the outward motion
in combination with the expansion of the ejecta. The shock decayed
and failed to reach Mercury in the backward direction and the Solar
Terrestrial Relations Observatory B (STEREO B) and Venus in the lateral
directions, as indicated by the imaging and in situ observations. The
shock in the nose direction, however, may have persisted to the far
outer heliosphere, with predicted impact on Dawn around 06:00 UT on July
25 and on Jupiter around 23:30 UT on July 27 by a magnetohydrodynamic
model. The type II burst shows properties generally consistent with
the spatial/temporal variations of the shock deduced from imaging and
in situ observations. In particular, the low-frequency bands agree
well with the in situ measurements of a very low density ahead of the
shock at STEREO A.
---------------------------------------------------------
Title: Understanding the Physical Nature of Coronal "EIT Waves"
Authors: Long, D. M.; Bloomfield, D. S.; Chen, P. F.; Downs, C.;
Gallagher, P. T.; Kwon, R. -Y.; Vanninathan, K.; Veronig, A. M.;
Vourlidas, A.; Vršnak, B.; Warmuth, A.; Žic, T.
2017SoPh..292....7L Altcode: 2016arXiv161105505L
For almost 20 years the physical nature of globally propagating waves in
the solar corona (commonly called "EIT waves") has been controversial
and subject to debate. Additional theories have been proposed over the
years to explain observations that did not agree with the originally
proposed fast-mode wave interpretation. However, the incompatibility
of observations made using the Extreme-ultraviolet Imaging Telescope
(EIT) onboard the Solar and Heliospheric Observatory with the fast-mode
wave interpretation was challenged by differing viewpoints from the twin
Solar Terrestrial Relations Observatory spacecraft and data with higher
spatial and temporal resolution from the Solar Dynamics Observatory. In
this article, we reexamine the theories proposed to explain EIT waves
to identify measurable properties and behaviours that can be compared
to current and future observations. Most of us conclude that the
so-called EIT waves are best described as fast-mode large-amplitude
waves or shocks that are initially driven by the impulsive expansion
of an erupting coronal mass ejection in the low corona.
---------------------------------------------------------
Title: Chromosphere to 1 AU Simulation of the 2011 March 7th Event:
A Comprehensive Study of Coronal Mass Ejection Propagation
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Sokolov, I.;
Tóth, G.; Vourlidas, A.; de Koning, C. A.; Gombosi, T. I.
2017ApJ...834..172J Altcode: 2016arXiv161108897J
We perform and analyze the results of a global magnetohydrodynamic
simulation of the fast coronal mass ejection (CME) that occurred
on 2011 March 7. The simulation is made using the newly developed
Alfvén Wave Solar Model (AWSoM), which describes the background
solar wind starting from the upper chromosphere and extends to
24 R<SUB>⊙</SUB>. Coupling AWSoM to an inner heliosphere model
with the Space Weather Modeling Framework extends the total domain
beyond the orbit of Earth. Physical processes included in the model
are multi-species thermodynamics, electron heat conduction (both
collisional and collisionless formulations), optically thin radiative
cooling, and Alfvén-wave turbulence that accelerates and heats the
solar wind. The Alfvén-wave description is physically self-consistent,
including non-Wentzel-Kramers-Brillouin reflection and physics-based
apportioning of turbulent dissipative heating to both electrons and
protons. Within this model, we initiate the CME by using the Gibson-Low
analytical flux rope model and follow its evolution for days, in which
time it propagates beyond STEREO A. A detailed comparison study is
performed using remote as well as in situ observations. Although the
flux rope structure is not compared directly due to lack of relevant
ejecta observation at 1 au in this event, our results show that the
new model can reproduce many of the observed features near the Sun
(e.g., CME-driven extreme ultraviolet [EUV] waves, deflection of the
flux rope from the coronal hole, “double-front” in the white light
images) and in the heliosphere (e.g., shock propagation direction,
shock properties at STEREO A).
---------------------------------------------------------
Title: Why are Solar Energetic Particle Intensities so Much Lower
in Solar Cycle 24, Especially at High Energies?
Authors: Mewaldt, R. A.; Li, G.; Cohen, C.; Mason, G. M.; von
Rosenvinge, T. T.; Smith, C. W.; Vourlidas, A.
2016AGUFMSH41D..01M Altcode:
Measurements by ACE, STEREO, and GOES show that the number of large
Solar Energetic Particle (SEP) events in the first 7 years of solar
cycle 24 is reduced by a factor of 2 compared to this point of solar
cycle 23, while the fluences of >10 MeV/nucleon ions from H to Fe are
reduced by factors ranging from 5 to >10. Compared to solar cycles
22 and 23, the fluence of >100 MeV protons is reduced by factors of
7 to 10 in the current cycle. A common aspect of these observations is
that the energy spectra of accelerated ions in cycle-24 have suddenly
steepen at "breaks" that are 2 to 4 times lower in energy/nucleon than
in cycle 23. We investigate the origin of these cycle-to-cycle intensity
and spectral differences by evaluating possible factors that control
the acceleration efficiency and maximum energy of CME-shock-accelerated
particles in the last two cycles, including seed-particle densities
of suprathermal ions, the interplanetary magnetic field strength and
turbulence level, and properties of coronal mass ejections (CMEs)
and their associated shocks. The effects of these conditions will
be evaluated with a state-of-the-art SEP acceleration model and by
comparing SEP data with earlier analytic evaluations of the maximum
kinetic energy to which CME shocks can accelerate solar energetic ions
from H to Fe.
---------------------------------------------------------
Title: Elliptic-cylindrical analytical flux-rope model for ICMEs
Authors: Nieves-Chinchilla, T.; Linton, M.; Hidalgo, M. A. U.;
Vourlidas, A.
2016AGUFMSH51F2648N Altcode:
We present an analytical flux-rope model for realistic magnetic
structures embedded in Interplanetary Coronal Mass Ejections. The
framework of this model was established by Nieves-Chinchilla
et al. (2016) with the circular-cylindrical analytical
flux rope model and under the concept developed by Hidalgo et
al. (2002). Elliptic-cylindrical geometry establishes the first-grade
of complexity of a series of models. The model attempts to describe the
magnetic flux rope topology with distorted cross-section as a possible
consequence of the interaction with the solar wind. In this model, the
flux rope is completely described in the non-euclidean geometry. The
Maxwell equations are solved using tensor calculus consistently
with the geometry chosen, invariance along the axial component, and
with the only assumption of no radial current density. The model
is generalized in terms of the radial dependence of the poloidal
current density component and axial current density component. The
misalignment between current density and magnetic field is studied
in detail for the individual cases of different pairs of indexes for
the axial and poloidal current density components. This theoretical
analysis provides a map of the force distribution inside of the
flux-rope. The reconstruction technique has been adapted to the model
and compared with in situ ICME set of events with different in situ
signatures. The successful result is limited to some cases with clear
in-situ signatures of distortion. However, the model adds a piece in
the puzzle of the physical-analytical representation of these magnetic
structures. Other effects such as axial curvature, expansion and/or
interaction could be incorporated in the future to fully understand the
magnetic structure. Finally, the mathematical formulation of this model
opens the door to the next model: toroidal flux rope analytical model.
---------------------------------------------------------
Title: LOCKYER (Large Optimized Coronagraph for KeY Emission line
Research): A SMEX Mission to Provide Crucial Measurements of the
Genesis of the Solar Wind and CMEs
Authors: Ko, Y. K.; Vourlidas, A.; Korendyke, C.; Laming, J. M.
2016AGUFMSH43B2569K Altcode:
The LOCKYER mission is designed to uncover the physical processes of
acceleration and heating of the quiescent and transient solar wind. It
builds on the success of the Ultraviolet Coronagraph Spectrometer
(UVCS) on SOHO with a massive increase in effective area at Lyman-alpha
(200x larger than UVCS), thanks to a modern optical design and the
use of a 4m boom. The larger effective area enables spectral line
observations from many ions, including He II (at 1640 Å), allowing us
to access the region where the coronal plasma transitions from fluid
to kinetic behavior. In addition, a visible light channel provides
simultaneous high-resolution coronagraphic images for the global
coronal structure and dynamics creating a greatly-expanded UVCS-LASCO
`hybrid' instrument within the tight constraints of a SMEX mission. The
LOCKYER mission aims to answer the following questions: 1) What are
the physical processes responsible for the heating and acceleration
of the primary (proton, electron, helium) and secondary (minor ion)
plasma components of the fast and slow solar wind? 2) How are CMEs
heated and accelerated? LOCKYER would greatly advance our knowledge
of how and where the solar wind is formed, and how the variations in
coronal microphysics impact the solar wind and heliosphere. The LOCKYER
measurements are highly complementary to the Solar Probe Plus and Solar
Orbiter measurements and provide detailed empirical descriptions of
the coronal plasma at heights where the primary energy and momentum
addition occur.
---------------------------------------------------------
Title: LASCO White-Light Observations of Eruptive Current Sheets
Trailing CMEs
Authors: Webb, David F.; Vourlidas, Angelos
2016SoPh..291.3725W Altcode: 2016SoPh..tmp..178W
Many models of eruptive flares or coronal mass ejections (CMEs) involve
formation of a current sheet connecting the ejecting CME flux rope with
a magnetic loop arcade. However, there is very limited observational
information on the properties and evolution of these structures,
hindering progress in understanding eruptive activity from the Sun. In
white-light images, narrow coaxial rays trailing the outward-moving CME
have been interpreted as current sheets. Here, we undertake the most
comprehensive statistical study of CME-rays to date. We use SOHO/LASCO
data, which have a higher cadence, larger field of view, and better
sensitivity than any previous coronagraph. We compare our results to
a previous study of Solar Maximum Mission (SMM) CMEs, in 1984 - 1989,
having candidate magnetic disconnection features at the CME base,
about half of which were followed by coaxial bright rays. We examine
all LASCO CMEs during two periods of minimum and maximum activity
in Solar Cycle 23, resulting in many more events, ∼130 CME-rays,
than during SMM. Important results include: The occurrence rate of
the rays is ∼11 % of all CMEs during solar minimum, but decreases
to ∼7 % at solar maximum; this is most likely related to the more
complex coronal background. The rays appear on average 3 - 4 hours
after the CME core, and are typically visible for three-fourths of
a day. The mean observed current sheet length over the ray lifetime
is ∼12 R<SUB>⊙</SUB>, with the longest current sheet of 18.5
R<SUB>⊙</SUB>. The mean CS growth rates are 188 kms<SUP>−1</SUP>
at minimum and 324 kms<SUP>−1</SUP> at maximum. Outward-moving blobs
within several rays, which are indicative of reconnection outflows, have
average velocities of ∼350 kms<SUP>−1</SUP> with small positive
accelerations. A pre-existing streamer is blown out in most of the
CME-ray events, but half of these are observed to reform within ∼1
day. The long lifetime and long lengths of the CME-rays challenge our
current understanding of the evolution of the magnetic field in the
aftermath of CMEs.
---------------------------------------------------------
Title: Spherically-shaped coronal shock waves associated with Coronal
Mass Ejections
Authors: Kwon, R. Y.; Vourlidas, A.
2016AGUFMSH43B2563K Altcode:
Knowing the three-dimensional (3D) geometry of Coronal mass ejections
(CMEs) and associated shock waves is crucial for interpretations of
in-situ measurements close to the Sun that will be carried out by Solar
Probe Plus and Solar Orbiter. Here, we obtain the 3D geometries of three
CMEs and associated shock waves using multiple perspective observations
from STEREO-Ahead, -Behind, SDO, and SOHO. These CMEs appeared as halo
CMEs in all three viewing perspectives and were accompanied by solar
energetic particle (SEP) events. The 3D structures and kinematics
of the halo fronts were determined by applying a forward modeling
method. We find that the angular widths of the halos are at least
192 degrees while those of the CMEs are at most 100 degrees, implying
the presence of a spherically-shaped wave, extending out much further
than the CME. The peak speeds of the CMEs are in the range of 1355-
2157 km/s, but the speeds of the halo flanks seem to reach the local
fast-mode speed of the coronal medium 500 km/s. To further investigate
the physical nature of the halo flanks, we compare the 3D properties of
the halos with a fast-mode wave model given in Uchida (1970). The model
reproduced the halo flanks with the local fast-mode speed profiles
of the coronal medium. The modeled waves refract toward the lower
altitudes as propagating through the inhomogeneous medium, and these
fast-mode waves lead to the spherically-shaped fronts. In addition,
the azimuthal extents of the halos are consistent with the SEP injection
sites far away from the flare sites, supporting that the halo fronts are
truly the signatures of the fast-mode wave. Our results suggest that
the halo-shaped fronts are likely spherically-shaped fast-mode waves,
extending out much further than the CMEs. The unprecedented in-situ
measurements of Solar Probe Plus and Solar Orbiter will probe into
the detailed physical properties of such large-scale disturbances in
the corona.
---------------------------------------------------------
Title: A Heliospheric Plasma Sheet Crossing at 1 AU that Contains
an Unusually High Density Just Downstream of Shock Wave
Authors: Liou, K.; Wu, C. C.; Lepping, R. P.; Vourlidas, A.; Plunkett,
S. P.; Socker, D. G.; Wu, S. T.
2016AGUFMSH51A2574L Altcode:
On the 9th of September 2011 the Wind spacecraft encountered an
interplanetary (IP) fast forward shock at 11:46 UT. The shock was
followed almost immediately ( 5 minutes) by a short ( 35 minutes)
duration, extremely large density pulse with a density peak of 94
cm-3. The density pulse induced an extremely large positive impulse
(SYM-H = 74 nT and Dst = 48 nT) on the ground. A close examination of
other in situ parameters from Wind, we find that the density pulse was
associated with (1) a spike in the plasma beta (β, ratio of thermal to
magnetic pressure), (2) multiple sign changes in the azimuthal angle
of magnetic field, Bϕ, (3) a depressed magnetic field magnitude,
(4) a small radial component of magnetic field, and (5) a large (
> 90º) pitch angle change in suprathermal electrons (> 200
eV) across the density pulse. We conclude that the density pulse is
associated with the heliospheric plasma sheet (HPS). The thickness of
the HPS is estimated to be 8.2x105 km. The HPS density peak is about
five times the value of the median size density peak inside the HPS (
18 cm-3). Our global three-dimensional magnetohydrodynamic simulation
suggests that the unusually large density pulse was a result of the
compression by the IP shock from behind. During this time Geotail was
in the dawn sheath region and did not see the density pulse, suggesting
the transient and localized nature of the density pulse. (Work of CCW
is supported by the Chief of Naval Research.)
---------------------------------------------------------
Title: Investigation of Streamer Blowout Events Observed by LASCO
Authors: Webb, D. F.; Vourlidas, A.
2016AGUFMSH33A..04W Altcode:
We investigate the properties of the class of large-scale coronal
eruption in which a pre-existing streamer brightens and swells for
hours or days before being removed or disrupted during a coronal
mass ejection (CME). Such events are important as a stage in the
evolution of streamers, which are associated with the heliospheric
current sheet and the separatrix (S)-web. Streamer blowouts (SBOs)
represent large-scale ejections of mass and magnetic field into the
heliosphere and are likely important for restructuring of the global
solar fields over a solar cycle. Some questions we address are: What
are the general properties of SBOs, e.g., speeds, durations, spans,
masses and energies? Do SBOs depend on their formative structures,
e.g., pseudostreamer/ quadrupolar arcades, active regions, polar
crown filaments? How are SBOs related to magnetic flux transport to
the solar poles? What roles do SBO/CMEs play in the Sun's shedding
of its magnetic flux and helicity built up over the solar cycle, and
in balancing the magnetic flux in the heliosphere? We summarize the
properties of these events as observed by the SOHO/LASCO white light
coronagraphs over solar cycle 23 from 1996-2011.
---------------------------------------------------------
Title: Deriving the Properties of Coronal Pressure Fronts in 3D:
Application to the 2012 May 17 Ground Level Enhancement
Authors: Rouillard, A. P.; Plotnikov, I.; Pinto, R. F.; Tirole, M.;
Lavarra, M.; Zucca, P.; Vainio, R.; Tylka, A. J.; Vourlidas, A.;
De Rosa, M. L.; Linker, J.; Warmuth, A.; Mann, G.; Cohen, C. M. S.;
Mewaldt, R. A.
2016ApJ...833...45R Altcode: 2016arXiv160505208R
We study the link between an expanding coronal shock and the energetic
particles measured near Earth during the ground level enhancement of
2012 May 17. We developed a new technique based on multipoint imaging to
triangulate the three-dimensional (3D) expansion of the shock forming
in the corona. It uses images from three vantage points by mapping
the outermost extent of the coronal region perturbed by the pressure
front. We derive for the first time the 3D velocity vector and the
distribution of Mach numbers, M <SUB>FM</SUB>, of the entire front as
a function of time. Our approach uses magnetic field reconstructions
of the coronal field, full magnetohydrodynamic simulations and imaging
inversion techniques. We find that the highest M <SUB>FM</SUB> values
appear near the coronal neutral line within a few minutes of the
coronal mass ejection onset; this neutral line is usually associated
with the source of the heliospheric current and plasma sheet. We
illustrate the variability of the shock speed, shock geometry, and
Mach number along different modeled magnetic field lines. Despite the
level of uncertainty in deriving the shock Mach numbers, all employed
reconstruction techniques show that the release time of GeV particles
occurs when the coronal shock becomes super-critical (M <SUB>FM</SUB>
> 3). Combining in situ measurements with heliospheric imagery,
we also demonstrate that magnetic connectivity between the accelerator
(the coronal shock of 2012 May 17) and the near-Earth environment is
established via a magnetic cloud that erupted from the same active
region roughly five days earlier.
---------------------------------------------------------
Title: Are non-driven fast-mode shocks responsible for the wide
longitudinal spread of SEP events?
Authors: Kwon, R. Y.; Vourlidas, A.
2016AGUFMSH32A..02K Altcode:
Fast-mode shock waves are believed to be the primary agent in the
acceleration of solar energetic particles (SEPs) over a wide range
of energies across the solar corona and heliosphere. In this regard,
the spatial distribution of the initial SEP injections from the solar
corona should depend on the three-dimensional (3D) geometry of coronal
shock waves. Using remote-sensing observations by STEREO-Ahead, -Behind,
SDO, and SOHO, we determine the 3D structure and properties of the
shock waves initially driven by coronal mass ejections (CMEs). As the
shock wave expands, we distinguish two types of shock waves: One is
the driven shock wave that is observed in white light observations
as propagating ahead of the CME leading edge from the low corona into
the interplanetary space. The other is the non-driven shock wave that
is observed as a nearly-circular propagating disturbance seen in EUV
observations of the low corona (i.e., the so-called EUV wave) and also
observed as a halo-shaped disturbance in white light observations far
from the eruption site. While the super-Alfvenic CME drivers constantly
energize the driven shock waves, and the angular widths are limited to
those of the drivers, the non-driven shock waves propagate in a very
broad spatial range with deceleration. The magnetic connection of the
spacecraft with the different proportions of the shock determines the
properties of the observed SEP events. Spacecraft magnetically connected
to the non-driven shock will see SEP events with intensities peaking at
the prompt component and falling off rapidly. By contrast, spacecraft
continuously connecting to driven shock waves will observe SEP events
that increase in intensity with time and that may peak at the arrival
of the shock. We suggest that the non-driven shock waves propagating
far from the eruption site contribute to the broad longitudinal spread
of SEPs. Illustrative examples of SEP events observed by STEREO and
near-Earth spacecraft and how each spacecraft establishes magnetic
connection with the different portions of the shock will be shown.
---------------------------------------------------------
Title: The Wide-Field Imager for Solar Probe Plus (WISPR)
Authors: Vourlidas, Angelos; Howard, Russell A.; Plunkett, Simon P.;
Korendyke, Clarence M.; Thernisien, Arnaud F. R.; Wang, Dennis; Rich,
Nathan; Carter, Michael T.; Chua, Damien H.; Socker, Dennis G.; Linton,
Mark G.; Morrill, Jeff S.; Lynch, Sean; Thurn, Adam; Van Duyne, Peter;
Hagood, Robert; Clifford, Greg; Grey, Phares J.; Velli, Marco; Liewer,
Paulett C.; Hall, Jeffrey R.; DeJong, Eric M.; Mikic, Zoran; Rochus,
Pierre; Mazy, Emanuel; Bothmer, Volker; Rodmann, Jens
2016SSRv..204...83V Altcode: 2015SSRv..tmp....8V; 2015SSRv..tmp...66B
The Wide-field Imager for Solar PRobe Plus (WISPR) is the sole imager
aboard the Solar Probe Plus (SPP) mission scheduled for launch in
2018. SPP will be a unique mission designed to orbit as close as
7 million km (9.86 solar radii) from Sun center. WISPR employs a
95<SUP>∘</SUP> radial by 58<SUP>∘</SUP> transverse field of view
to image the fine-scale structure of the solar corona, derive the 3D
structure of the large-scale corona, and determine whether a dust-free
zone exists near the Sun. WISPR is the smallest heliospheric imager to
date yet it comprises two nested wide-field telescopes with large-format
(2 K × 2 K) APS CMOS detectors to optimize the performance for their
respective fields of view and to minimize the risk of dust damage,
which may be considerable close to the Sun. The WISPR electronics are
very flexible allowing the collection of individual images at cadences
up to 1 second at perihelion or the summing of multiple images to
increase the signal-to-noise when the spacecraft is further from the
Sun. The dependency of the Thomson scattering emission of the corona
on the imaging geometry dictates that WISPR will be very sensitive
to the emission from plasma close to the spacecraft in contrast to
the situation for imaging from Earth orbit. WISPR will be the first
`local' imager providing a crucial link between the large-scale corona
and the in-situ measurements.
---------------------------------------------------------
Title: Scientific challenges in thermosphere-ionosphere forecasting -
conclusions from the October 2014 NASA JPL community workshop
Authors: Mannucci, Anthony J.; Hagan, Maura E.; Vourlidas, Angelos;
Huang, Cheryl Y.; Verkhoglyadova, Olga P.; Deng, Yue
2016JSWSC...6E..01M Altcode:
Interest in forecasting space weather in the thermosphere and
ionosphere (T-I) led to a community workshop held at NASA's Jet
Propulsion Laboratory in October, 2014. The workshop focus was
"Scientific Challenges in Thermosphere-Ionosphere Forecasting" to
emphasize that forecasting presumes a sufficiently advanced state of
scientific knowledge, yet one that is still evolving. The purpose of
the workshop, and this topical issue that arose from the workshop,
was to discuss research frontiers that will lead to improved space
weather forecasts. Three areas are discussed in some detail in this
paper: (1) the role of lower atmosphere forcing in the response of
the T-I to geomagnetic disturbances; (2) the significant deposition
of energy at polar latitudes during geomagnetic disturbances; and
(3) recent developments in understanding the propagation of coronal
mass ejections through the heliosphere and prospects for forecasting
the north-south component of the interplanetary magnetic field (IMF)
using observations at the Lagrangian L<SUB>5</SUB> point. We describe
other research presented at the workshop that appears in the topical
issue. The possibility of establishing a "positive feedback loop" where
improved scientific knowledge leads to improved forecasts is described
(Siscoe 2006, Space Weather, 4, S01003; Mannucci 2012, Space Weather,
10, S07003).
---------------------------------------------------------
Title: Relationship of EUV Irradiance Coronal Dimming Slope and
Depth to Coronal Mass Ejection Speed and Mass
Authors: Mason, James Paul; Woods, Thomas N.; Webb, David F.; Thompson,
Barbara J.; Colaninno, Robin C.; Vourlidas, Angelos
2016ApJ...830...20M Altcode: 2016arXiv160705284M
Extreme ultraviolet (EUV) coronal dimmings are often observed in
response to solar eruptive events. These phenomena can be generated
via several different physical processes. For space weather, the most
important of these is the temporary void left behind by a coronal mass
ejection (CME). Massive, fast CMEs tend to leave behind a darker void
that also usually corresponds to minimum irradiance for the cooler
coronal emissions. If the dimming is associated with a solar flare,
as is often the case, the flare component of the irradiance light
curve in the cooler coronal emission can be isolated and removed
using simultaneous measurements of warmer coronal lines. We apply
this technique to 37 dimming events identified during two separate
two-week periods in 2011 plus an event on 2010 August 7, analyzed in a
previous paper to parameterize dimming in terms of depth and slope. We
provide statistics on which combination of wavelengths worked best
for the flare-removal method, describe the fitting methods applied
to the dimming light curves, and compare the dimming parameters
with corresponding CME parameters of mass and speed. The best linear
relationships found are v CME km s ≈ 2.36 × 10 6 km % × s dim % s
m CME [ g ] ≈ 2.59 × 10 15 g % × d dim [ % ] . These relationships
could be used for space weather operations of estimating CME mass and
speed using near-real-time irradiance dimming measurements.
---------------------------------------------------------
Title: Understanding the Physical Nature of Coronal "EIT Waves"
Authors: Long, D. M.; Bloomfield, D. S.; Chen, P. -F.; Downs,
C.; Gallagher, P. T.; Kwon, R. -Y.; Vanninathan, K.; Veronig, A.;
Vourlidas, A.; Vrsnak, B.; Warmuth, A.; Zic, T.
2016usc..confE..24L Altcode:
For almost 20 years the physical nature of globally-propagating waves
in the solar corona (commonly called "EIT waves") has been controversial
and subject to debate. Additional theories have been proposed throughout
the years to explain observations that did not fit with the originally
proposed fast-mode wave interpretation. However, the incompatibility
of observations made using the Extreme-ultraviolet Imaging Telescope
(EIT) on the Solar and Heliospheric Observatory with the fast-mode
wave interpretation have been challenged by differing viewpoints
from the Solar Terrestrial Relations Observatory spacecraft and higher
spatial/temporal resolution data from the Solar Dynamics Observatory. In
this paper, we reexamine the theories proposed to explain "EIT waves"
to identify measurable properties and behaviours that can be compared
to current and future observations. Most of us conclude that "EIT
waves" are best described as fast-mode large-amplitude waves/shocks,
which are initially driven by the impulsive expansion of an erupting
coronal mass ejection in the low corona.
---------------------------------------------------------
Title: Using ForeCAT Deflections and Rotations to Constrain the
Early Evolution of CMEs
Authors: Kay, C.; Opher, M.; Colaninno, R. C.; Vourlidas, A.
2016ApJ...827...70K Altcode: 2016arXiv160603460K
To accurately predict the space weather effects of the impacts of
coronal mass ejection (CME) at Earth one must know if and when a CME
will impact Earth and the CME parameters upon impact. In 2015 Kay et
al. presented Forecasting a CME’s Altered Trajectory (ForeCAT),
a model for CME deflections based on the magnetic forces from the
background solar magnetic field. Knowing the deflection and rotation of
a CME enables prediction of Earth impacts and the orientation of the
CME upon impact. We first reconstruct the positions of the 2010 April
8 and the 2012 July 12 CMEs from the observations. The first of these
CMEs exhibits significant deflection and rotation (34° deflection
and 58° rotation), while the second shows almost no deflection or
rotation (<3° each). Using ForeCAT, we explore a range of initial
parameters, such as the CME’s location and size, and find parameters
that can successfully reproduce the behavior for each CME. Additionally,
since the deflection depends strongly on the behavior of a CME in the
low corona, we are able to constrain the expansion and propagation of
these CMEs in the low corona.
---------------------------------------------------------
Title: Real time tests for long lead-time forecasting of the magnetic
field vectors within CMEs
Authors: Savani, Neel; Vourlidas, Angelos; Pulkkinen, Antti; Wold,
Alexandra M.
2016cosp...41E1724S Altcode:
The direction of magnetic vectors within coronal mass ejections,
CMEs, has significant importance for forecasting terrestrial
behavior. We have developed a technique to estimate the time-varying
magnetic field at Earth for periods within CMEs (Savani et al 2015,
2016). This technique reduces the complex dynamics in order to create
a reliable prediction methodology to operate everyday under robust
conditions. In this presentation, we focus on the results and skill
scores of the forecasting technique calculated from 40 historical
CME events from the pre-STEREO mission. Since these results provided
substantial improvements in the long lead-time Kp index forecasts,
we have now begun testing under real-time conditions. We will also
show the preliminary results of our methodology under these real-time
conditions within the CCMC hosted at NASA Goddard Space Flight Center.
---------------------------------------------------------
Title: Lessons Learned from Flux-ropes Observed by Wind spacecraft
1995-2015
Authors: Nieves-Chinchilla, Teresa; Vourlidas, A.; Raymond, J.;
Al-Haddad, N.; Linton, M.; Savani, N. P.; Szabo, A.
2016shin.confE..59N Altcode:
It is well known that the geoeffectiveness of interplanetary coronal
mass ejections (ICMEs) depends on their magnetic field topology and
global geometry. The observed in-situ magnetic signatures are more
complex than a simple flux-rope magnetic topology. Sometimes these
events are called Ejectas or Magnetic flux-rope like. On the other
hand, imaging observations of CMEs close to the Sun suggest that the
entrained flux-rope undergo significant evolutionary changes, such as
deformation or distortion, during their heliospheric propagation. <P
/>The goal of this paper is to explore the magnetic field and plasma
parameter observations in order to get information about the magnetic
field configuration, structure and geometry of the magnetic obstacles
embedded in the ICMEs. This goal can be also spread on questions as: Can
we quantify the Flux-Rope distortion at any heliospheric distance? Can
we predict axial curvature or deformations? How is the expansion
affecting to the compression in the magnetic obstacle front? Can we
find any relationship between the magnetic field strength compression
and the expansion velocity?. The answers to these questions will aid
to address the final question: can we quantify the forces that govern
the ICME evolution? <P />To accomplish this study, we have selected
Earth-directed CMEs observed by in-situ instruments onboard on Wind
spacecraft (wind.nasa.gov) in the period 1995-2015.
---------------------------------------------------------
Title: Magnetic Flux Rope Shredding by Quasi-Separatrix Layers:
The Detrimental Effects of Magnetic Topology on Solar Eruptions
Authors: Chintzoglou, Georgios; Stenborg, Guillermo; Savcheva, Antonia;
Vourlidas, Angelos; Tassev, Svetlin; Tun Beltran, Samuel
2016cosp...41E.348C Altcode:
We present the analysis of an unusual failed eruption event observed in
high cadence and in many wavelengths during the campaign in support of
the VAULT2.0 sounding rocket launch. The refurbished Very high Angular
resolution Ultraviolet Telescope (VAULT2.0) is a Lyalpha (1216AA)
spectroheliograph launched on September 30, 2014. The objective of the
VAULT2.0 project is the study of the chromosphere-corona interface. The
observing campaign targeted active region AR 12172 and was closely
coordinated with the textsl{Hinode/} and textsl{IRIS/} missions and
several ground-based observatories (NSO/IBIS an SOLIS, and BBSO)
). A filament eruption accompanied by small level heating (at the
GOES C-class level) occurred around the VAULT2.0 launch. No CME was
observed. The eruption and its source region, however, was recorded by
the campaign instruments in all atmospheric heights ranging from the
photosphere to the corona in high cadence and spatial resolution. This
is a rare occasion which enables us to perform a comprehensive
investigation on a failed eruption. We find that a rising Magnetic
Flux Rope-like (MFR) structure was destroyed during its interaction
with the overlying magnetic field creating downflows of cool plasma and
diffuse hot coronal structures reminiscent of 'spines'. We employ MHD
simulations to show that the magnetic topology of the overlying field
is responsible for the destruction of the MFR. Our unique observations
suggest that the magnetic topology of the corona is a key ingredient
for a successful eruption.
---------------------------------------------------------
Title: Three-dimensional Geometry of a Current Sheet in the High
Solar Corona: Evidence for Reconnection in the Late Stage of the
Coronal Mass Ejections
Authors: Kwon, Ryun-Young; Vourlidas, Angelos; Webb, David
2016ApJ...826...94K Altcode:
Motivated by the standard flare model, ray-like structures in the wake
of coronal mass ejections (CMEs) have been often interpreted as proxies
of the reconnecting current sheet connecting the CME with the postflare
arcade. We present the three-dimensional properties of a post-CME ray
derived from white light images taken from three different viewing
perspectives on 2013 September 21. By using a forward modeling method,
the direction, cross section, and electron density are determined within
the heliocentric distance range of 5-9 R <SUB>⊙</SUB>. The width and
depth of the ray are 0.42 ± 0.08 R <SUB>⊙</SUB> and 1.24 ± 0.35 R
<SUB>⊙</SUB>, respectively, and the electron density is (2.0 ± 0.5)
× 10<SUP>4</SUP> cm<SUP>-3</SUP>, which seems to be constant with
height. Successive blobs moving outward along the ray are observed
around 13 hr after the parent CME onset. We model the three-dimensional
geometry of the parent CME with the Gradual Cylindrical Shell model
and find that the CME and ray are coaxial. We suggest that coaxial
post-CME rays, seen in coronagraph images, with successive formation
of blobs could be associated with current sheets undergoing magnetic
reconnection in the late stage of CMEs.
---------------------------------------------------------
Title: Three-Dimensional Geometry of a Current Sheet in the High
Solar Corona: Evidence for Reconnection in the Late Stage of Coronal
Mass Ejections
Authors: Kwon, Ryun Young; Vourlidas, Angelos; Webb, David
2016shin.confE.108K Altcode:
Motivated by the standard flare model, ray-like structures in the wake
of coronal mass ejections (CMEs) have been often interpreted as proxies
of the reconnecting current sheet connecting the CME with the post
flare arcade. We present the three-dimensional properties of a post-CME
ray derived from white light images taken from three different viewing
perspectives on 2013 September 21. By using a forward modeling method,
the direction, cross section, and electron density are determined
within the heliocentric distance range of 5-9 Rs. The width and depth
of the ray are 0.42 +/- 0.08 Rs and 1.24 +/- 0.35 Rs, respectively,
and the electron density is (2.0 +/- 0.5) x 10^4 cm^-3, which seems to
be constant with height. Successive blobs moving outward along the ray
are observed around 13 hours after the parent CME onset. We model the
3D geometry of the parent CME with the Gradual Cylindrical Shell model,
and find that the CME and ray are coaxial. We suggest that coaxial
post-CME rays, seen in coronagraph images, with successive formation
of blobs could be associated with current sheets undergoing magnetic
reconnection in the late stage of CMEs.
---------------------------------------------------------
Title: The acceleration sites of solar energetic particles inferred
from the three-dimensional geometry of shock waves associated with
coronal mass ejections
Authors: Kwon, Ryun Young; Vourlidas, Angelos; Lario, David
2016shin.confE..19K Altcode:
The observation of solar energetic particle (SEP) events by spacecraft
widely separated in longitude results from processes associated with
the acceleration, release and transport of SEPs on the Sun and in the
inner heliosphere. We analyze the possibility that the distribution
of SEPs in the inner heliosphere results from their injection by
shocks associated with coronal mass ejections (CMEs). We pay especial
attention to a very widespread SEP event observed on 2014 February 25
that originated from a single flare-CME event. The SEPs were detected
by near-Earth spacecraft (SOHO and ACE) located at 82° west of the
flare site and STEREO-Ahead and -Behind, located at 1 AU from the Sun,
and 125° east and 78° east of the flare site, respectively. The
3D geometric modeling of the shock wave associated with the parent
CME reveals that the shock wave propagated laterally over 45° in
longitude and intercepted the field lines nominally connecting the
Sun with STEREO-Ahead and -Behind, below 4 solar radii (Rs) with an
angle between the magnetic field and the shock normal ranging between
24°-79°, at the times estimated for the initial release of the
SEPs. In contrast, the in-situ measurements indicate that the spacecraft
located on the west of the flare established magnetic connection with
the shock driven when its leading edge was already in the high corona
(> 14 Rs). The shock properties measured at the spacecraft and the
electron peak intensities of the SEPs were well correlated with the
longitudinal separations of the spacecraft with respect to the flare
site. We conclude that the shock wave propagating around the solar
surface was responsible for the initial injection of SEPs in the low
corona (< 4 Rs), whereas the CME-driven shock in the interplanetary
space played a major role in the observed SEP intensity-time profiles.
---------------------------------------------------------
Title: 3D reconstruction and particle acceleration properties of
Coronal Shock Waves During Powerful Solar Particle Events
Authors: Plotnikov, Illya; Vourlidas, Angelos; Tylka, Allan J.; Pinto,
Rui; Rouillard, Alexis; Tirole, Margot
2016cosp...41E1570P Altcode:
Identifying the physical mechanisms that produce the most energetic
particles is a long-standing observational and theoretical challenge
in astrophysics. Strong pressure waves have been proposed as efficient
accelerators both in the solar and astrophysical contexts via various
mechanisms such as diffusive-shock/shock-drift acceleration and betatron
effects. In diffusive-shock acceleration, the efficacy of the process
relies on shock waves being super-critical or moving several times
faster than the characteristic speed of the medium they propagate
through (a high Alfven Mach number) and on the orientation of the
magnetic field upstream of the shock front. High-cadence, multipoint
imaging using the NASA STEREO, SOHO and SDO spacecrafts now permits
the 3-D reconstruction of pressure waves formed during the eruption
of coronal mass ejections. Using these unprecedented capabilities,
some recent studies have provided new insights on the timing and
longitudinal extent of solar energetic particles, including the first
derivations of the time-dependent 3-dimensional distribution of the
expansion speed and Mach numbers of coronal shock waves. We will
review these recent developments by focusing on particle events that
occurred between 2011 and 2015. These new techniques also provide the
opportunity to investigate the enigmatic long-duration gamma ray events.
---------------------------------------------------------
Title: Circular-cylindrical flux-rope analytical model for Magnetic
Clouds
Authors: Nieves-Chinchilla, Teresa; Linton, Mark; Hidalgo, Miguel A.;
Vourlidas, Angelos; Savani, Neel P.; Szabo, Adam; Farrugia, Charlie;
Yu, Wenyuan
2016SPD....4710203N Altcode:
We present an analytical model to describe magnetic flux-rope
topologies. When these structures are observed embedded in
Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton
temperature, they are called Magnetic Clouds ( MCs). The model extends
the circular-cylindrical concept of Hidalgo et al. (2000) by introducing
a general form for the radial dependence of the current density. This
generalization provides information on the force distribution inside
the flux rope in addition to the usual parameters of MC geometrical
information and orientation.The generalized model provides flexibility
for implementation in 3D MHD simulations. Here, we evaluate its
performance in the reconstruction of MCs in in-situ observations. Four
Earth directed ICME events, observed by the Wind spacecraft, are used
to validate the technique. The events are selected from the ICME Wind
list with the magnetic obstacle boundaries chosen consistently with
the magnetic fi eld and plasma in situ observations and with a new
parameter (EPP, Electron Pitch angle distribution Parameter) which
quantifies the bidirectionally of theplasma electrons. The goodness
of the fit is evaluated with a single correlation parameter to enable
comparative analysis of the events. In general, at first glance, the
model fits the selected events very well. However, a detailed analysis
of events with signatures of significant compression indicates the
need to explore geometries other than the circular-cylindrical.
---------------------------------------------------------
Title: A Circular-cylindrical Flux-rope Analytical Model for
Magnetic Clouds
Authors: Nieves-Chinchilla, T.; Linton, M. G.; Hidalgo, M. A.;
Vourlidas, A.; Savani, N. P.; Szabo, A.; Farrugia, C.; Yu, W.
2016ApJ...823...27N Altcode:
We present an analytical model to describe magnetic flux-rope
topologies. When these structures are observed embedded in
Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton
temperature, they are called Magnetic Clouds (MCs). Our model extends
the circular-cylindrical concept of Hidalgo et al. by introducing a
general form for the radial dependence of the current density. This
generalization provides information on the force distribution inside
the flux rope in addition to the usual parameters of MC geometrical
information and orientation. The generalized model provides flexibility
for implementation in 3D MHD simulations. Here, we evaluate its
performance in the reconstruction of MCs in in situ observations. Four
Earth-directed ICME events, observed by the Wind spacecraft, are used
to validate the technique. The events are selected from the ICME Wind
list with the magnetic obstacle boundaries chosen consistently with the
magnetic field and plasma in situ observations and with a new parameter
(EPP, the Electron Pitch angle distribution Parameter) which quantifies
the bidirectionally of the plasma electrons. The goodness of the fit
is evaluated with a single correlation parameter to enable comparative
analysis of the events. In general, at first glance, the model fits the
selected events very well. However, a detailed analysis of events with
signatures of significant compression indicates the need to explore
geometries other than the circular-cylindrical. An extension of our
current modeling framework to account for such non-circular CMEs will
be presented in a forthcoming publication.
---------------------------------------------------------
Title: An Analysis of Interplanetary Solar Radio Emissions Associated
with a Coronal Mass Ejection
Authors: Krupar, V.; Eastwood, J. P.; Kruparova, O.; Santolik, O.;
Soucek, J.; Magdalenić, J.; Vourlidas, A.; Maksimovic, M.; Bonnin,
X.; Bothmer, V.; Mrotzek, N.; Pluta, A.; Barnes, D.; Davies, J. A.;
Martínez Oliveros, J. C.; Bale, S. D.
2016ApJ...823L...5K Altcode: 2016arXiv160604301K
Coronal mass ejections (CMEs) are large-scale eruptions of magnetized
plasma that may cause severe geomagnetic storms if Earth directed. Here,
we report a rare instance with comprehensive in situ and remote
sensing observations of a CME combining white-light, radio, and plasma
measurements from four different vantage points. For the first time,
we have successfully applied a radio direction-finding technique
to an interplanetary type II burst detected by two identical widely
separated radio receivers. The derived locations of the type II and
type III bursts are in general agreement with the white-light CME
reconstruction. We find that the radio emission arises from the flanks
of the CME and are most likely associated with the CME-driven shock. Our
work demonstrates the complementarity between radio triangulation and
3D reconstruction techniques for space weather applications.
---------------------------------------------------------
Title: Multi-viewpoint Observations of a Widely distributed Solar
Energetic Particle Event: The Role of EUV Waves and White-light
Shock Signatures
Authors: Kouloumvakos, A.; Patsourakos, S.; Nindos, A.; Vourlidas,
A.; Anastasiadis, A.; Hillaris, A.; Sandberg, I.
2016ApJ...821...31K Altcode:
On 2012 March 7, two large eruptive events occurred in the same active
region within 1 hr from each other. Each consisted of an X-class flare,
a coronal mass ejection (CME), an extreme-ultraviolet (EUV) wave,
and a shock wave. The eruptions gave rise to a major solar energetic
particle (SEP) event observed at widely separated (∼120°) points
in the heliosphere. From multi-viewpoint energetic proton recordings
we determine the proton release times at STEREO B and A (STB, STA)
and the first Lagrange point (L1) of the Sun-Earth system. Using EUV
and white-light data, we determine the evolution of the EUV waves in
the low corona and reconstruct the global structure and kinematics of
the first CME’s shock, respectively. We compare the energetic proton
release time at each spacecraft with the EUV waves’ arrival times
at the magnetically connected regions and the timing and location
of the CME shock. We find that the first flare/CME is responsible
for the SEP event at all three locations. The proton release at STB
is consistent with arrival of the EUV wave and CME shock at the STB
footpoint. The proton release time at L1 was significantly delayed
compared to STB. Three-dimensional modeling of the CME shock shows
that the particle release at L1 is consistent with the timing and
location of the shock’s western flank. This indicates that at L1
the proton release did not occur in low corona but farther away from
the Sun. However, the extent of the CME shock fails to explain the
SEP event observed at STA. A transport process or a significantly
distorted interplanetary magnetic field may be responsible.
---------------------------------------------------------
Title: Longitudinal Properties of a Widespread Solar Energetic
Particle Event on 2014 February 25: Evolution of the Associated
CME Shock
Authors: Lario, D.; Kwon, R. -Y.; Vourlidas, A.; Raouafi, N. E.;
Haggerty, D. K.; Ho, G. C.; Anderson, B. J.; Papaioannou, A.;
Gómez-Herrero, R.; Dresing, N.; Riley, P.
2016ApJ...819...72L Altcode:
We investigate the solar phenomena associated with the origin of the
solar energetic particle (SEP) event observed on 2014 February 25 by a
number of spacecraft distributed in the inner heliosphere over a broad
range of heliolongitudes. These include spacecraft located near Earth;
the twin Solar TErrestrial RElations Observatory spacecraft, STEREO-A
and STEREO-B, located at ∼1 au from the Sun 153° west and 160°
east of Earth, respectively; the MErcury Surface Space ENvironment
GEochemistry and Ranging mission (at 0.40 au and 31° west of Earth);
and the Juno spacecraft (at 2.11 au and 48° east of Earth). Although
the footpoints of the field lines nominally connecting the Sun with
STEREO-A, STEREO-B and near-Earth spacecraft were quite distant from
each other, an intense high-energy SEP event with Fe-rich prompt
components was observed at these three locations. The extent of the
extreme-ultraviolet wave associated with the solar eruption generating
the SEP event was very limited in longitude. However, the white-light
shock accompanying the associated coronal mass ejection extended over a
broad range of longitudes. As the shock propagated into interplanetary
space it extended over at least ∼190° in longitude. The release
of the SEPs observed at different longitudes occurred when the
portion of the shock magnetically connected to each spacecraft was
already at relatively high altitudes (≳2 R<SUB>⊙</SUB> above the
solar surface). The expansion of the shock in the extended corona,
as opposite to near the solar surface, determined the SEP injection
and SEP intensity-time profiles at different longitudes.
---------------------------------------------------------
Title: Numerical simulation of multiple CME-driven shocks in the
month of 2011 September
Authors: Wu, Chin-Chun; Liou, Kan; Vourlidas, Angelos; Plunkett,
Simon; Dryer, Murray; Wu, S. T.; Socker, Dennis; Wood, Brian E.;
Hutting, Lynn; Howard, Russell A.
2016JGRA..121.1839W Altcode:
A global, three-dimensional (3-D) numerical simulation model has
been employed to study the Sun-to-Earth propagation of multiple
(12) coronal mass ejections (CMEs) and their associated shocks in
September 2011. The inputs to the simulation are based on actual
solar observations, which include the CME speeds, source locations,
and photospheric magnetic fields. The simulation result is fine tuned
with in situ solar wind data observations at 1 AU by matching the
arrival time of CME-driven shocks. During this period three CME-driven
interplanetary (IP) shocks induced three sizable geomagnetic storms
on 9, 17, and 26 September, with Dst values reaching -69, -70, and
-101 nT, respectively. These storm events signify the commencement
of geomagnetic activity in the solar cycle 24. The CME propagation
speed near the Sun (e.g., < 30 R<SUB>S</SUB>) has been widely
used to estimate the interplanetary CME (ICME)/Shock arrival time at
1 AU. Our simulation indicates that the background solar wind speed,
as expected, is an important controlling parameter in the propagation
of IP shocks and CMEs. Prediction of the ICME/shock arrival time at 1
AU can be more problematic for slow (e.g., < 500 km s<SUP>-1</SUP>)
than fast CMEs (>1000 km s<SUP>-1</SUP>). This is because the effect
of the background solar wind is more pronounced for slow CMEs. Here
we demonstrate this difficulty with a slow (400 km s<SUP>-1</SUP>) CME
event that arrived at the Earth in 3 days instead of the predicted 4.3
days. Our results also demonstrate that a long period (a month in this
case) of simulation may be necessary to make meaningful solar source
geomagnetic storm associations.
---------------------------------------------------------
Title: Investigation of the Chromosphere-Corona Interface with the
Upgraded Very High Angular Resolution Ultraviolet Telescope (VAULT2.0)
Authors: Vourlidas, Angelos; Beltran, Samuel Tun; Chintzoglou,
Georgios; Eisenhower, Kevin; Korendyke, Clarence; Feldman, Ronen;
Moser, John; Shea, John; Johnson-Rambert, Mary; McMullin, Don;
Stenborg, Guillermo; Shepler, Ed; Roberts, David
2016JAI.....540003V Altcode:
Very high angular resolution ultraviolet telescope (VAULT2.0) is a
Lyman-alpha (Lyα; 1216Å) spectroheliograph designed to observe
the upper chromospheric region of the solar atmosphere with high
spatial (<0.5‧‧) and temporal (8s) resolution. Besides being
the brightest line in the solar spectrum, Lyα emission arises at
the temperature interface between coronal and chromospheric plasmas
and may, hence, hold important clues about the transfer of mass and
energy to the solar corona. VAULT2.0 is an upgrade of the previously
flown VAULT rocket and was launched successfully on September 30, 2014
from White Sands Missile Range (WSMR). The target was AR12172 midway
toward the southwestern limb. We obtained 33 images at 8s cadence at
arc second resolution due to hardware problems. The science campaign
was a resounding success, with all space and ground-based instruments
obtaining high-resolution data at the same location within the AR. We
discuss the science rationale, instrument upgrades, and performance
during the first flight and present some preliminary science results.
---------------------------------------------------------
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Ko, Yuan-Kuen; Moses, John; Laming, John; Strachan, Leonard;
Tun Beltran, Samuel; Tomczyk, Steven; Gibson, Sarah; Auchere, Frederic;
Casini, Roberto; Fineschi, Silvano; Knoelker, Michael; Korendyke,
Clarence; McIntosh, Scott; Romoli, Marco; Rybak, Jan; Socker, Dennis;
Vourlidas, Angelos; Wu, Qian
2016FrASS...3....1K Altcode:
Comprehensive measurements of magnetic fields in the solar corona have
a long history as an important scientific goal. Besides being crucial
to understanding coronal structures and the Sun’s generation of space
weather, direct measurements of their strength and direction are also
crucial steps in understanding observed wave motions. In this regard,
the remote sensing instrumentation used to make coronal magnetic field
measurements is well suited to measuring the Doppler signature of waves
in the solar structures. In this paper, we describe the design and
scientific values of the Waves and Magnetism in the Solar Atmosphere
(WAMIS) investigation. WAMIS, taking advantage of greatly improved
infrared filters and detectors, forward models, advanced diagnostic
tools and inversion codes, is a long-duration high-altitude balloon
payload designed to obtain a breakthrough in the measurement of
coronal magnetic fields and in advancing the understanding of the
interaction of these fields with space plasmas. It consists of a 20 cm
aperture coronagraph with a visible-IR spectro-polarimeter focal plane
assembly. The balloon altitude would provide minimum sky background and
atmospheric scattering at the wavelengths in which these observations
are made. It would also enable continuous measurements of the strength
and direction of coronal magnetic fields without interruptions from
the day-night cycle and weather. These measurements will be made
over a large field-of-view allowing one to distinguish the magnetic
signatures of different coronal structures, and at the spatial and
temporal resolutions required to address outstanding problems in
coronal physics. Additionally, WAMIS could obtain near simultaneous
observations of the electron scattered K-corona for context and to
obtain the electron density. These comprehensive observations are not
provided by any current single ground-based or space observatory. The
fundamental advancements achieved by the near-space observations of
WAMIS on coronal field would point the way for future ground based
and orbital instrumentation.
---------------------------------------------------------
Title: Global magnetohydrodynamic simulation of the 15 March 2013
coronal mass ejection event—Interpretation of the 30-80 MeV
proton flux
Authors: Wu, Chin-Chun; Liou, Kan; Vourlidas, Angelos; Plunkett,
Simon; Dryer, Murray; Wu, S. T.; Mewaldt, Richard A.
2016JGRA..121...56W Altcode:
The coronal mass ejection (CME) event on 15 March 2013 is one of the few
solar events in Cycle 24 that produced a large solar energetic particle
(SEP) event and severe geomagnetic activity. Observations of SEP from
the ACE spacecraft show a complex time-intensity SEP profile that is
not easily understood with current empirical SEP models. In this study,
we employ a global three-dimensional (3-D) magnetohydrodynamic (MHD)
simulation to help interpret the observations. The simulation is based
on the H3DMHD code and incorporates extrapolations of photospheric
magnetic field as the inner boundary condition at a solar radial
distance (r) of 2.5 solar radii. A Gaussian-shaped velocity pulse
is imposed at the inner boundary as a proxy for the complex physical
conditions that initiated the CME. It is found that the time-intensity
profile of the high-energy (>10 MeV) SEPs can be explained by
the evolution of the CME-driven shock and its interaction with
the heliospheric current sheet and the nonuniform solar wind. We
also demonstrate in more detail that the simulated fast-mode shock
Mach number at the magnetically connected shock location is well
correlated (r<SUB>cc</SUB> ≥ 0.7) with the concurrent 30-80 MeV
proton flux. A better correlation occurs when the 30-80 MeV proton flux
is scaled by r<SUP>-1.4</SUP>(r<SUB>cc</SUB> = 0.87). When scaled by
r<SUP>-2.8</SUP>, the correlation for 10-30 MeV proton flux improves
significantly from r<SUB>cc</SUB> = 0.12 to r<SUB>cc</SUB> = 0.73, with
1 h delay. The present study suggests that (1) sector boundary can act
as an obstacle to the propagation of SEPs; (2) the background solar
wind is an important factor in the variation of IP shock strength
and thus plays an important role in manipulation of SEP flux; (3)
at least 50% of the variance in SEP flux can be explained by the
fast-mode shock Mach number. This study demonstrates that global MHD
simulation, despite the limitation implied by its physics-based ideal
fluid continuum assumption, can be a viable tool for SEP data analysis.
---------------------------------------------------------
Title: The Major Geoeffective Solar Eruptions of 2012 March 7:
Comprehensive Sun-to-Earth Analysis
Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos,
A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou,
G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.;
Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.;
Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou,
K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.;
Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.;
Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris,
E.; Tsinganos, K.; Vlahos, L.
2016ApJ...817...14P Altcode:
During the interval 2012 March 7-11 the geospace experienced a
barrage of intense space weather phenomena including the second
largest geomagnetic storm of solar cycle 24 so far. Significant
ultra-low-frequency wave enhancements and relativistic-electron dropouts
in the radiation belts, as well as strong energetic-electron injection
events in the magnetosphere were observed. These phenomena were
ultimately associated with two ultra-fast (>2000 km s<SUP>-1</SUP>)
coronal mass ejections (CMEs), linked to two X-class flares launched
on early 2012 March 7. Given that both powerful events originated from
solar active region NOAA 11429 and their onsets were separated by less
than an hour, the analysis of the two events and the determination
of solar causes and geospace effects are rather challenging. Using
satellite data from a flotilla of solar, heliospheric and magnetospheric
missions a synergistic Sun-to-Earth study of diverse observational
solar, interplanetary and magnetospheric data sets was performed. It was
found that only the second CME was Earth-directed. Using a novel method,
we estimated its near-Sun magnetic field at 13 R<SUB>⊙</SUB> to be
in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun
CME magnetic field are required to match the magnetic fields of the
corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream
solar-wind conditions, as resulting from the shock associated with the
Earth-directed CME, offer a decent description of its kinematics. The
magnetospheric compression caused by the arrival at 1 AU of the shock
associated with the ICME was a key factor for radiation-belt dynamics.
---------------------------------------------------------
Title: Modeling AWSoM CMEs with EEGGL: A New Approach for Space
Weather Forecasting
Authors: Jin, M.; Manchester, W.; van der Holst, B.; Sokolov, I.;
Toth, G.; Vourlidas, A.; de Koning, C. A.; Gombosi, T. I.
2015AGUFMSH43C..02J Altcode:
The major source of destructive space weather is coronal mass ejections
(CMEs). However, our understanding of CMEs and their propagation in the
heliosphere is limited by the insufficient observations. Therefore,
the development of first-principals numerical models plays a vital
role in both theoretical investigation and providing space weather
forecasts. Here, we present results of the simulation of CME propagation
from the Sun to 1AU by combining the analytical Gibson & Low (GL)
flux rope model with the state-of-art solar wind model AWSoM. We also
provide an approach for transferring this research model to a space
weather forecasting tool by demonstrating how the free parameters of
the GL flux rope can be prescribed based on remote observations via
the new Eruptive Event Generator by Gibson-Low (EEGGL) toolkit. This
capability allows us to predict the long-term evolution of the CME
in interplanetary space. We perform proof-of-concept case studies to
show the capability of the model to capture physical processes that
determine CME evolution while also reproducing many observed features
both in the corona and at 1 AU. We discuss the potential and limitations
of this model as a future space weather forecasting tool.
---------------------------------------------------------
Title: Synthetic White-light Imagery for the Wide-field Imager for
Solar Probe Plus (WISPR)
Authors: Liewer, P. C.; Thernisien, A. F.; Vourlidas, A.; Howard,
R.; DeForest, C. E.; DeJong, E.; Desai, A.
2015AGUFMSH31C2426L Altcode:
The Solar Probe Plus trajectory, approaching within 10 solar radii, will
enable the white light imager, WISPR, to fly through corona features
now only imaged remotely. The dependency of the Thomson scattering
on the imaging geometry (distance and angle from the Sun) dictates
that the outer WISPR telescope will be sensitive to the emission
from plasma close to the spacecraft, in contrast to the situation
for imaging from Earth orbit. Thus WISPR will be the first 'local'
imager providing a crucial link between the large-scale corona and
SPP's in-situ measurements. The high speed at perihelion will provide
tomographic-like views of coronal structures at ≤1° resolution. As
SPP approaches perihelion, WISPR, with a 95° radial by 58° transverse
field of view, will resolve the fine-scale structure with high spatial
resolution. To prepare for this unprecedented viewing of the structure
of the inner corona, we are creating synthetic white light images and
animations from the WISPR viewpoint using the white-light ray-tracing
package developed at NRL (available through SolarSoft). We will present
simulated observations of multi-strand models of coronal streamers and
flux ropes of various size and make comparisons with views from Earth,
Solar Orbiter and SPP. Analysis techniques for WISPR images will also
be discussed.
---------------------------------------------------------
Title: Using Multiple-viewpoint Observations to Determine the
Interaction of Three Coronal Mass Ejections Observed on 2012 March 5
Authors: Colaninno, Robin C.; Vourlidas, Angelos
2015ApJ...815...70C Altcode:
We examine the interaction of three coronal mass ejections (CMEs) that
took place on 2012 March 5 at heights less than 20 R <SUB>⊙</SUB>
in the corona. We used a forward fitting model to reconstruct the
three-dimensional trajectories and kinematics of the CMEs and determine
their interaction in the observations from three viewpoints: Solar and
Heliospheric Observatory (SOHO), STEREO-A, and STEREO-B. The first
CME (CME-1), a slow-rising eruption near disk center, is already
in progress at 02:45 UT when the second CME (CME-2) erupts from AR
11429 on the east limb. These two CMEs are present in the corona not
interacting when a third CME (CME-3) erupts from AR 11429 at 03:34
UT. CME-3 has a constant velocity of 1456[±31] km s<SUP>-1</SUP> and
drives a shock that is observed as a halo from all viewpoints. We find
that the shock driven by CME-3 passed through CME-1 with no observable
change in the geometry, trajectory, or velocity of CME-1. However,
the elevated temperatures detected in situ when CME-1 reached Earth
indicate that the plasma inside CME-1 may have been heated by the
passage of the shock. CME-2 is accelerated by CME-3 to more than twice
its initial velocity and remains a separate structure ahead of the
CME-3 front. CME-2 is deflected 24° northward by CME-3 for a total
deflection of 40° from its source region. These results suggest that
the collision of CME-2 and CME-3 is superelastic. This work demonstrates
the capability and utility of fitting forward models to complex and
interacting CMEs observed in the corona from multiple viewpoints.
---------------------------------------------------------
Title: A STEREO/SECCHI COR2 Catalog of CME Properties Built via a
'Hybrid' (manual-automatic) Event Detection and Measurement Technique
Authors: Balmaceda, L. A.; Vourlidas, A.; Stenborg, G.; Dal Lago, A.
2015AGUFMSH21B2409B Altcode:
Catalogs of Coronal Mass Ejection (CME) properties are an efficient
and popular way to research the CME phenomenon. Up to now, all CME
catalogs were based on observations from a single viewpoint and
hence subject to the same projection effects. However, simultaneous
CME observations from the two vantage points of the STEREO/SECCHI
coronagraphs raises several issues: Is a CME always visible in both
telescopes? Does it look the same, etc? To answer these questions,
we compiled a cross-linked STEREO COR2 A/B catalog. First, we built,
by visual inspection, a preliminary list of CME events observed by
each of the two COR2 instruments, starting in 2007. The CME detection
and tracking is carried out by a state-of-the-art supervised image
segmentation technique named CORSET. Using a supervised technique,
we seek to overcome the intrinsic caveats that both fully automated
and fully manual methodologies exhibit, in particular when dealing
with a bi-segmentation problem where the features of interest show
different intensity levels, morphologies, and texture embedded in
an ever-changing noisy background. We have successfully applied
CORSET to about 30% of the total number of events in our list. The
catalog contains a comprehensive list of the temporal evolution of the
relevant morphological, kinematical, and dynamical properties of the
CMEs uniquely identified and cross-referenced in both datasets. Here,
we briefly review the technique, and present the first results on the
analysis of the main characteristics of this set of CMEs throughout
the whole period of the mission.
---------------------------------------------------------
Title: Observational Evidence for High-Mach Number Regime of Coronal
Shock Waves During Powerful Solar Particle Events
Authors: Rouillard, A. P.; Illya, P.; Zucca, P.; Tylka, A. J.; Vainio,
R. O.; Vourlidas, A.
2015AGUFMSH32B..03R Altcode:
Identifying the physical mechanisms that produce the most energetic
particles is a long-standing observational and theoretical challenge
in astrophysics. Strong shock waves have been proposed as efficient
accelerators both in the solar physics and astrophysical contexts
via various acceleration mechanisms. The proposed processes rely on
shock waves being super-critical or moving several times faster than
the characteristic speed of the medium they propagate through (a high
MA). Using recent imaging of the NASA STEREO, SOHO and SDO spacecraft,
we provide the first observations of the time-dependent 3-dimensional
distribution of the expansion speed and MA of a coronal shock
wave. These observations show that the high-energy particles measured
near Earth are produced at the time of the sharp rise in the shock
Mach number (>10) magnetically connected to Earth. These findings
provide direct evidence to energetic particles being accelerated during
the formation of a strong coronal shock. Using our new technique,
we study the longitudinal spread and timing of a number of other
energetic particle events during cycle 24.
---------------------------------------------------------
Title: Radio Triangulation of Type II Bursts Associated with a CME -
CME Interaction
Authors: Krupar, V.; Bothmer, V.; Davies, J. A.; Eastwood, J. P.;
Forsyth, R. J.; Kruparova, O.; Magdalenic, J.; Maksimovic, M.;
Santolik, O.; Soucek, J.; Vourlidas, A.
2015AGUFMSH53B2498K Altcode:
Coronal Mass Ejections (CMEs) are large-scale magnetized plasma
disturbances propagating through the corona and the interplanetary
(IP) medium. Along their path, some CMEs can drive shock waves, which
accelerate ions and electrons. These fast electrons can generate
type II radio bursts at the local plasma frequency and/or its first
harmonic. In this study we use data from the two STEREO spacecraft
which carry both imaging and radio instruments with direction-finding
capabilities allowing us to track energetic electrons responsible
for radio bursts. We present an analysis of type II bursts observed
on the November 29 - 30, 2013. The shock wave signatures were
possibly generated by an interaction of two consecutive CMEs. We have
investigated three time-frequency intervals when received radio waves
were sufficiently intense for direction-finding analysis. The obtained
positions of triangulated radio sources suggest that the CMEs propagate
towards the STEREO-A. The IP shock associated with this event has been
also observed in situ by the MESSENGER and STEREO-A spacecraft.
---------------------------------------------------------
Title: Modeling Magnetic Flux-Ropes Structures
Authors: Nieves-Chinchilla, T.; Linton, M.; Hidalgo, M. A. U.;
Vourlidas, A.; Savani, N.; Szabo, A.; Farrugia, C. J.; Yu, W.
2015AGUFMSH11B2388N Altcode:
Flux-ropes are usually associated with magnetic structures
embedded in the interplanetary Coronal Mass Ejections (ICMEs) with a
depressed proton temperature (called Magnetic Clouds, MCs). However,
small-scale flux-ropes in the solar wind are also identified with
different formation, evolution, and dynamic involved. We present
an analytical model to describe magnetic flux-rope topologies. The
model is generalized to different grades of complexity. It extends the
circular-cylindrical concept of Hidalgo et al. (2002) by introducing
a general form for the radial dependence of the current density. This
generalization provides information on the force distribution inside the
flux rope in addition to the usual parameters of flux-rope geometrical
information and orientation. The generalized model provides flexibility
for implementation in 3-D MHD simulations.
---------------------------------------------------------
Title: Why is the Sun No Longer Accelerating Particles to High Energy
in Solar Cycle 24?
Authors: Mewaldt, R. A.; Cohen, C. M.; Li, G.; Mason, G. M.; Smith,
C. W.; von Rosenvinge, T. T.; Vourlidas, A.
2015AGUFMSH33D..03M Altcode:
Why is the Sun No Longer Accelerating Particles to High Energy in Solar
Cycle 24?Measurements by ACE, STEREO, and GOES show that the number
of large Solar Energetic Particle (SEP) events in solar cycle 24 is
reduced by a factor of ~2 compared to this point of solar cycle 23,
while the fluences of >10 MeV/nuc ions from H to Fe are reduced by
factors ranging from ~4 to ~10. Compared to solar Cycle 22 and 23,
the fluence of >100 MeV protons is reduced by factors of ~7 to
~10 in the current cycle. A common element of these observations is
that the observed Cycle-24 energy spectra have "breaks" that suddenly
steepen 2 to 4 times lower in energy/nucleon than in Cycle 23. We
investigate the origin of these cycle-to-cycle spectral differences
by evaluating possible factors that control the maximum energy
of CME-shock-accelerated particles in the two cycles, including
seed-particle densities of suprathermal ions, the interplanetary
magnetic field strength and turbulence level, and properties of the
associated CMEs. The effect of these conditions will be evaluated in
the context of existing SEP acceleration models by comparing SEP data
with simulations and with analytic evaluations of the maximum kinetic
energy to which CME shocks can accelerate solar energetic ions from H
to Fe. Understanding the properties that control the maximum kinetic
energy of CME-shock accelerated particles has important implications
for predicting future solar activity.
---------------------------------------------------------
Title: Longitudinal Properties of a Widespread Solar Energetic
Particle Event on 2014 February 25: Evolution of the Parent CME and
Associated Shock
Authors: Lario, D.; Kwon, R. Y.; Papaioannou, A.; Dresing, N.; Raouafi,
N. E.; Gomez-Herrero, R.; Ho, G. C.; Vourlidas, A.; Riley, P.
2015AGUFMSH33B2464L Altcode:
We investigate the solar phenomena associated with the origin of the
solar energetic particle (SEP) event observed on 2014 February 25 by
a number of spacecraft distributed in the inner heliosphere over a
broad range of heliolongitudes. These include a number of near-Earth
spacecraft, the twin Solar TErrestrial RElations Observatory spacecraft,
STEREO-A and STEREO-B, located at ~1 AU from the Sun 153 deg ahead
and 160 deg behind Earth, respectively; the MErcury Surface Space
ENvironment GEochemistry and Ranging (MESSENGER) mission (at 0.40 AU and
31 deg west of Earth), and the Juno spacecraft (at 2.11 AU and 48 deg
east of Earth). Although the footpoints of the field lines nominally
connecting the Sun with STEREO-A, STEREO-B and near-Earth spacecraft
were quite distant one from each other, an intense Fe-rich SEP event
with fast rising intensities was observed at all three locations. The
extent of the Extreme UltraViolet (EUV) wave associated with the solar
eruption generating the SEP event was very limited in longitude, but
the white-light shock accompanying the associated coronal mass ejection
(CME) extended over a broad range of longitudes. As the shock propagated
into interplanetary space it extended over at least 190 deg in longitude
when it arrived at ~1 AU. The release of the SEPs observed at different
longitudes occurred when the shock associated with the CME was already
high in the corona (>~2 solar radii above the solar surface). We
argue that the expanding shock in the extended corona played a
fundamental role in the injection of SEPs at different longitudes.
---------------------------------------------------------
Title: Open issues in connecting magnetospheric dynamics to their
solar drivers
Authors: Vourlidas, A.
2015AGUFMSH43C..01V Altcode:
The inner heliospheric evolution of CMEs, the main drivers of Space
Weather, is no longer a mystery, thanks to the STEREO observations. The
initiation of these events can now be observed with cadence of tens
of seconds with arc second resolution, thanks to SDO. The flow of
energy required to power solar eruptions is beginning to be understood,
thanks to Hinode and IRIS. Yet, there is relatively little progress in
predicting the geoeffectiveness of a particular CME. Why is that? What
are the issues that holding back progress in medium-term forecasting
of Space Weather? I discuss some of the issues (e.g., Bz, drag) and
possible mitigation strategies in this talk.
---------------------------------------------------------
Title: Heliospheric Imaging from SO and SPP: Linking the solar wind
to its solar origins
Authors: Vourlidas, A.
2015AGUFMSH24A..04V Altcode:
Deciphering the complexities of the solar wind structure has been
hampered by the 'disconnected' nature of the observations; imaging of
the near-Sun corona, in-situ sampling at 1 AU. The STEREO observations
closed this gap and contributed significantly in understanding the
evolution of large scale transients. However, the solar wind origin and
evolution, especially at small spatial scales, remains a mystery. Two
upcoming missions, Solar Orbiter and Solar Probe Plus, are designed
to address this problem head-on with comprehensive suites of remote
sensing and in-situ instruments. Coronal and heliospheric imaging plays
a crucial role in connecting the activity in the solar corona with
the in-situ measurements. The SO and SPP telescopes image the large
scale structures measured subsequently by their in-situ suites. Never
before available, this tight coupling of white light imaging and
in-situ instrumentation may be the key for understanding the solar
wind. In this talk, I review the current ideas for linking hemispheric
structures to their solar origin and discuss the opportunities for
new science from the upcoming So and SPP missions.
---------------------------------------------------------
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: Observations and Analysis of the Non-Radial Propagation of
Coronal Mass Ejections Near the Sun
Authors: Liewer, Paulett; Panasenco, Olga; Vourlidas, Angelos;
Colaninno, Robin
2015SoPh..290.3343L Altcode: 2015SoPh..tmp..177L
The trajectories of coronal mass ejection (CME) are often observed
to deviate from radial propagation from the source while within the
coronagraph field of view (R<15 -30 Rsu<SUB>n</SUB>). To better
understand nonradial propagation within the corona, we first analyze the
trajectories of five CMEs for which both the source and 3D trajectory
(latitude, longitude, and velocity) can be well determined from solar
imaging observations, primarily using observations from the twin
Solar TErrestrial RElations Observatory (STEREO) spacecraft. Next we
analyze the cause of any nonradial propagation using a potential field
source surface (PFSS) model to determine the direction of the magnetic
pressure forces exerted on the CME at various heights in the corona. In
two cases, we find that the CME deviation from radial propagation
primarily occurs before it reaches the coronagraph field of view
(below 1.5 solar radii). Based on the observations and the magnetic
pressure forces calculated from the PFSS model, we conclude that for
these cases the deviation is the result of strong active-region fields
causing an initial asymmetric expansion of the CME that gives rise
to the apparent rapid deflection and nonradial propagation from the
source. Within the limitations of the PFSS model, the magnetic fields
for all five cases appear to guide the CMEs out of the corona through
the weak-field region around the heliospheric current sheet even when
the current sheet is inclined and warped.
---------------------------------------------------------
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Strachan, L.; Ko, Y. -K.; Moses, J. D.; Laming, J. M.;
Auchere, F.; Casini, R.; Fineschi, S.; Gibson, S.; Knoelker, M.;
Korendyke, C.; Mcintosh, S.; Romoli, M.; Rybak, J.; Socker, D.;
Tomczyk, S.; Vourlidas, A.; Wu, Q.
2015IAUS..305..121S Altcode:
Magnetic fields in the solar atmosphere provide the energy for most
varieties of solar activity, including high-energy electromagnetic
radiation, solar energetic particles, flares, and coronal mass
ejections, as well as powering the solar wind. Despite the fundamental
role of magnetic fields in solar and heliospheric physics, there
exist only very limited measurements of the field above the base of
the corona. What is needed are direct measurements of not only the
strength and orientation of the magnetic field but also the signatures
of wave motions in order to better understand coronal structure, solar
activity, and the role of MHD waves in heating and accelerating the
solar wind. Fortunately, the remote sensing instrumentation used to make
magnetic field measurements is also well suited to measure the Doppler
signature of waves in the solar structures. We present here a mission
concept for the Waves And Magnetism In the Solar Atmosphere (WAMIS)
experiment which is proposed for a NASA long-duration balloon flight.
---------------------------------------------------------
Title: CME Propagation: Where does Aerodynamic Drag 'Take Over'?
Authors: Sachdeva, Nishtha; Subramanian, Prasad; Colaninno, Robin;
Vourlidas, Angelos
2015ApJ...809..158S Altcode: 2015arXiv150705199S
We investigate the Sun-Earth dynamics of a set of eight well observed
solar coronal mass ejections (CMEs) using data from the Solar
Terrestrial Relations Observatory spacecraft. We seek to quantify the
extent to which momentum coupling between these CMEs and the ambient
solar wind (i.e., the aerodynamic drag) influences their dynamics. To
this end, we use results from a 3D flux rope model fit to the CME
data. We find that solar wind aerodynamic drag adequately accounts
for the dynamics of the fastest CME in our sample. For the relatively
slower CMEs, we find that drag-based models initiated below heliocentric
distances ranging from 15 to 50 {R}<SUB>⊙ </SUB> cannot account for
the observed CME trajectories. This is at variance with the general
perception that the dynamics of slow CMEs are influenced primarily by
solar wind drag from a few {R}<SUB>⊙ </SUB> onwards. Several slow
CMEs propagate at roughly constant speeds above 15-50 {R}<SUB>⊙
</SUB>. Drag-based models initiated above these heights therefore
require negligible aerodynamic drag to explain their observed
trajectories.
---------------------------------------------------------
Title: Formation of Magnetic Flux Ropes during a Confined Flaring
Well before the Onset of a Pair of Major Coronal Mass Ejections
Authors: Chintzoglou, Georgios; Patsourakos, Spiros; Vourlidas, Angelos
2015ApJ...809...34C Altcode: 2015arXiv150701165C
NOAA active region (AR) 11429 was the source of twin super-fast
coronal mass ejections (CMEs). The CMEs took place within an hour
from each other, with the onset of the first taking place in the
beginning of 2012 March 7. This AR fulfills all the requirements for
a “super active region” namely, Hale's law incompatibility and a
δ-spot magnetic configuration. One of the biggest storms of Solar
Cycle 24 to date ({D}<SUB>{st</SUB>}=-143 nT) was associated with
one of these events. Magnetic flux ropes (MFRs) are twisted magnetic
structures in the corona, best seen in ∼10 MK hot plasma emission
and are often considered the core of erupting structures. However,
their “dormant” existence in the solar atmosphere (i.e., prior to
eruptions), is an open question. Aided by multi-wavelength observations
by the Solar Dynamics Observatory (SDO) and by the Solar Terrestrial
Relations Observatory (STEREO) and a nonlinear force-free model for the
coronal magnetic field, our work uncovers two separate, weakly twisted
magnetic flux systems which suggest the existence of pre-eruption MFRs
that eventually became the seeds of the two CMEs. The MFRs could have
been formed during confined (i.e., not leading to major CMEs) flaring
and sub-flaring events which took place the day before the two CMEs
in the host AR 11429.
---------------------------------------------------------
Title: How Common Are Hot Magnetic Flux Ropes in the Low Solar
Corona? A Statistical Study of EUV Observations
Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Tagikas, C.
2015ApJ...808..117N Altcode: 2015arXiv150703766N
We use data at 131, 171, and 304 Å from the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory to search for hot
flux ropes in 141 M-class and X-class solar flares that occurred at
solar longitudes equal to or larger than 50°. Half of the flares were
associated with coronal mass ejections. The goal of our survey is to
assess the frequency of hot flux ropes in large flares irrespective
of their formation time relative to the onset of eruptions. The flux
ropes were identified in 131 Å images using morphological criteria and
their high temperatures were confirmed by their absence in the cooler
171 and 304 Å passbands. We found hot flux ropes in 45 of our events
(32% of the flares); 11 of them were associated with confined flares
while the remaining 34 were associated with eruptive flares. Therefore
almost half (49%) of the eruptive events involved a hot flux rope
configuration. The use of supplementary Hinode X-Ray Telescope data
indicates that these percentages should be considered as lower limits
of the actual rates of occurrence of hot flux ropes in large flares.
---------------------------------------------------------
Title: An Investigation of the Causes of Solar-Cycle Variations in
SEP Fluences and Composition
Authors: Mewaldt, R.; Cohen, C.; Mason, G.; von Rosenvinge, T.; Li,
G.; Smith, C. W.; Vourlidas, A.
2015ICRC...34...30M Altcode: 2015PoS...236...30M
No abstract at ADS
---------------------------------------------------------
Title: Periodic Density Structures and the Origin of the Slow
Solar Wind
Authors: Viall, Nicholeen M.; Vourlidas, Angelos
2015ApJ...807..176V Altcode:
The source of the slow solar wind has challenged scientists for
years. Periodic density structures (PDSs), observed regularly in the
solar wind at 1 AU, can be used to address this challenge. These
structures have length scales of hundreds to several thousands of
megameters and frequencies of tens to hundreds of minutes. Two lines
of evidence indicate that PDSs are formed in the solar corona as part
of the slow solar wind release and/or acceleration processes. The first
is corresponding changes in compositional data in situ, and the second
is PDSs observed in the inner Heliospheric Imaging data on board the
Solar Terrestrial Relations Observatory (STEREO)/Sun Earth Connection
Coronal and Heliospheric Investigation (SECCHI) suite. The periodic
nature of these density structures is both a useful identifier as well
as an important physical constraint on their origin. In this paper,
we present the results of tracking periodic structures identified
in the inner Heliospheric Imager in SECCHI back in time through the
corresponding outer coronagraph (COR2) images. We demonstrate that
the PDSs are formed around or below 2.5 solar radii—the inner edge
of the COR2 field of view. We compute the occurrence rates of PDSs
in 10 days of COR2 images both as a function of their periodicity
and location in the solar corona, and we find that this set of PDSs
occurs preferentially with a periodicity of ∼90 minutes and occurs
near streamers. Lastly, we show that their acceleration and expansion
through COR2 is self-similar, thus their frequency is constant at
distances beyond 2.5 solar radii.
---------------------------------------------------------
Title: The Interaction of Three Coronal Mass Ejections Observed on
2012 March 5 from Multiple Viewpoints
Authors: Colaninno, Robin C.; Vourlidas, Angelos
2015shin.confE.162C Altcode:
We examined three CMEs that were observed together on 2012 March 5
in the corona at heights less than 20 Rsun. We analyzed observations
from three viewpoints: Earth, STEREO-A and STEREO-B to reconstruct
their three-dimensional (3D) geometry and kinematics and determine
their interaction. The observations combined with our analysis show
an initial slow raising CME (CME-1) that originated from a prominence
eruption near the center of the solar disk as viewed from Earth. A
second CME (CME-2) then erupts from an active region (AR) near the NE
limb. These two CMEs are present in the corona not interacting when a
third CME (CME-3) erupts from the same AR as CME-2. CME-3 is extremely
impulsive and drives a shock that is observed as a halo from the all
viewpoints. We find that the shock driven by CME-3 passed through CME-1
with no observable change in the geometry, trajectory, or velocity of
CME-1. A possible signature of CME-1 in situ indicates that the plasma
inside the flux rope was heated by the passage of the shock. CME-2 is
accelerated by CME-3 to more than twice its initial velocity yet remains
a separate structure ahead of the CME-3 front. CME-2 is deflect by CME-3
24 deg northward for a total deflection of 40 deg north of its SR. CME-3
interacts with both CME-1 and CME-2 with very different results due to
the locations of their magnetic structures. CME-CME interactions such
as these could have profound effects on the Earth-impact of such CMEs.
---------------------------------------------------------
Title: Predicting the magnetic vectors within coronal mass ejections
arriving at Earth: 1. Initial architecture
Authors: Savani, N. P.; Vourlidas, A.; Szabo, A.; Mays, M. L.;
Richardson, I. G.; Thompson, B. J.; Pulkkinen, A.; Evans, R.;
Nieves-Chinchilla, T.
2015SpWea..13..374S Altcode: 2015arXiv150202067S
The process by which the Sun affects the terrestrial environment
on short timescales is predominately driven by the amount
of magnetic reconnection between the solar wind and Earth's
magnetosphere. Reconnection occurs most efficiently when the solar
wind magnetic field has a southward component. The most severe impacts
are during the arrival of a coronal mass ejection (CME) when the
magnetosphere is both compressed and magnetically connected to the
heliospheric environment. Unfortunately, forecasting magnetic vectors
within coronal mass ejections remain elusive. Here we report how,
by combining a statistically robust helicity rule for a CME's solar
origin with a simplified flux rope topology, the magnetic vectors
within the Earth-directed segment of a CME can be predicted. In
order to test the validity of this proof-of-concept architecture for
estimating the magnetic vectors within CMEs, a total of eight CME
events (between 2010 and 2014) have been investigated. With a focus
on the large false alarm of January 2014, this work highlights the
importance of including the early evolutionary effects of a CME for
forecasting purposes. The angular rotation in the predicted magnetic
field closely follows the broad rotational structure seen within the
in situ data. This time-varying field estimate is implemented into
a process to quantitatively predict a time-varying Kp index that is
described in detail in paper II. Future statistical work, quantifying
the uncertainties in this process, may improve the more heuristic
approach used by early forecasting systems.
---------------------------------------------------------
Title: Investigating the Causes of Solar-Cycle Variations in Solar
Energetic Particle Fluences and Composition
Authors: Mewaldt, Richard; Cohen, Christina; Mason, Glenn M.; von
Rosenvinge, Tycho; Li, Gang; Smith, Charles; Vourlidas, Angelos
2015TESS....140106M Altcode:
Measurements with ACE, STEREO, and GOES show that the number of large
Solar Energetic Particle (SEP) events in solar cycle 24 is reduced by
a factor of ~2 compared to this point of cycle 23, while the fluences
of >10 MeV/nuc ions from H to Fe are reduced by factors ranging
from ~4 to ~10. We investigate the origin of these cycle-to-cycle
differences by evaluating possible factors that include properties of
the associated CMEs, seed particle densities, and the interplanetary
magnetic field strength and turbulence levels. These properties will
be evaluated in the context of existing SEP acceleration models.
---------------------------------------------------------
Title: Observations and Analysis of the Non-Radial Propagation of
Coronal Mass Ejections Near the Sun
Authors: Liewer, Paulett C.; Colaninno, Robin; Panasenco, Olga;
Vourlidas, Angelos
2015TESS....111405L Altcode:
Coronal Mass Ejection (CME) trajectories are often observed to deviate
from radial propagation from the source while within the coronagraph
fields-of-view (R < 15-30 R<SUB>sun</SUB>). To better understand
non-radial propagation within the corona, we analyze the trajectories
of five CMEs for which both the source and 3-D trajectory can be
well determined from solar imaging observations, primarily using
observations from the twin Solar TErrestrial RElations Observatory
(STEREO) spacecraft. A potential field source surface model is used
to determine the direction of the magnetic pressure force exerted
on the CMEs at various heights in the corona. One case shows the
familiar gradual deflection of a polar crown filament CME towards
the heliospheric current sheet and streamer belt by the large-scale
coronal magnetic fields. In two cases, we find that strong active
region fields cause an initial asymmetric expansion of the CME that
gives rise to apparent rapid deflection and non-radial propagation from
the source. For all five cases, within the limitations of the potential
field source surface model, the coronal magnetic fields appear to guide
the CMEs out through the weak field region around the heliospheric
current sheet even when the current sheet is highly inclined and warped.
---------------------------------------------------------
Title: Are Halo-Like Solar Coronal Mass Ejections Merely a Matter
of Geometric Projection Effect?
Authors: Kwon, Ryun Young; Vourlidas, Angelos; Zhang, Jie
2015TESS....111406K Altcode:
We investigated the physical nature of halo coronal mass ejections
(CMEs) based on the stereoscopic observations from two STEREO Ahead
and Behind (hereafter A and B) and SOHO spacecraft. There occurred
62 halo CMEs as observed by SOHO LASCO C2 for the three-year period
from 2010 to 2012 during which the separation angles between SOHO
and STEREOs were nearly 90 degrees. In such quadrature configuration,
the coronagraphs of STEREOs, COR2-A and -B, showed the side view of
those halo CMEs seen by C2. It has been widely believed that the halo
appearance of a CME is caused by the geometric projection effect,
i.e., a CME moves along the Sun-observer line. In other words, it
would appear as a non-halo CME if viewed from the side. However, to
our surprise, we found that 41 out of 62 events (66%) were observed
as halo CMEs by all coronagraphs. This result suggests that a halo
CME is not only a matter of the propagating direction. In addition,
we show that a CME propagating normal to the line of sight can be
observed as a halo CME due to the associated fast magnetosonic wave or
shock front. We conclude that the apparent width of CMEs, especially
halos or partial halos is driven by the existence, and the extent,
of the associated waves or shocks and does not represent an accurate
measure of the CME ejecta size. This effect needs to be taken into
careful consideration in Space Weather predictions and modeling efforts.
---------------------------------------------------------
Title: Current STEREO Status on the Far Side of the Sun
Authors: Thompson, William T.; Gurman, Joseph; Ossing, Daniel; Luhmann,
Janet; Curtis, David; Schroeder, Peter; Mewaldt, Richard; Davis,
Andrew; Wortman, Kristin; Russell, Christopher; Galvin, Antoinette;
Kistler, Lynn; Ellis, Lorna; Howard, Russell; Vourlidas, Angelos; Rich,
Nathan; Hutting, Lynn; Maksimovic, Milan; Bale, Stuart D.; Goetz, Keith
2015TESS....140205T Altcode:
The current positions of the two STEREO spacecraft on the opposite side
of the Sun from Earth (superior solar conjunction) has forced some
significant changes in the spacecraft and instrument operations. No
communications are possible when the spacecraft is within 2 degrees
of the Sun, requiring that the spacecraft be put into safe mode until
communications can be restored. Unfortunately, communications were lost
with the STEREO Behind spacecraft on October 1, 2014, during testing
for superior solar conjunction operations. We will discuss what is
known about the causes of loss of contact, the steps being taken
to try to recover the Behind spacecraft, and what has been done to
prevent a similar occurrence on STEREO Ahead.We will also discuss the
effect of being on the far side of the Sun on the science operations
of STEREO Ahead. Starting on August 20, 2014, the telemetry rate from
the STEREO Ahead spacecraft has been tremendously reduced due to the
need to keep the temperature of the feed horn on the high gain antenna
below acceptable limits. However, the amount of telemetry that can be
brought down has been highly reduced. Even so, significant science is
still possible from STEREO's unique position on the solar far side. We
will discuss the science and space weather products that are, or will
be, available from each STEREO instrument, when those products will be
available, and how they will be used. Some data, including the regular
space weather beacon products, are brought down for an average of a
few hours each day during the daily real-time passes, while the in
situ and radio beacon data are being stored on the onboard recorder
to provide a continuous 24-hour coverage for eventual downlink once
the spacecraft is back to normal operations.
---------------------------------------------------------
Title: Earth-directed ICME magnetic field configurations
Authors: Nieves-Chinchilla, Teresa; Vourlidas, Angelos; Szabo, Adam;
Savani, Neel; Mays, M. Leila; Hidalgo, Miguel Angel; Wenyuan, Yu
2015TESS....121004N Altcode:
It is known that the geoeffectiveness of interplanetary
coronal mass ejections (ICMEs) depends on their magnetic field
configuration. However, it remains unclear how the ICME interactions
with the solar wind or other solar transient structures affect their
magnetic configuration through, say, distortion of their cross-section,
or deformation of their front. Obviously, precise space weather
forecasting is depended on precise understanding of the evolution
of the ICME internal magnetic topology.The goal of this study is to
identify the ambient solar wind parameters that affect the flux-rope
geometry and magnetic field configuration.
---------------------------------------------------------
Title: Investigation of a failed Filament Eruption During the VAULT2.0
Campaign Observations
Authors: Chintzoglou, Georgios; Vourlidas, Angelos; Tun-Beltran,
Samuel; Stenborg, Guillermo
2015TESS....130217C Altcode:
We report the first results from an observing campaign in support of
the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0 is
a Lya (1216Å) spectroheliograph capable of 0.4” (~300 km) spatial
resolution. The objective of the VAULT2.0 project is the study of the
chromosphere-corona interface. VAULT2.0 observations probe temperatures
between 10000 and 50000 K, a regime not accessible by Hinode or
SDO. Lyα observations are, therefore, ideal, for filling in this
gap. The observing campaign was closely coordinated with the Hinode
and IRIS missions. Several ground-based observatories also provided
important observations (IBIS, BBSO, SOLIS). Taking advantage of this
simultaneous multi-wavelength coverage of target AR 12172 we are able
to perform a detailed investigation on a failed eruption of a Magnetic
Flux Rope-like structure that was recorded in the joint observations,
starting before VAULT2.0's flight.
---------------------------------------------------------
Title: Are Halo-like Solar Coronal Mass Ejections Merely a Matter
of Geometric Projection Effects?
Authors: Kwon, Ryun-Young; Zhang, Jie; Vourlidas, Angelos
2015ApJ...799L..29K Altcode:
We investigated the physical nature of halo coronal mass ejections
(CMEs) based on the stereoscopic observations from the two STEREO
spacecraft, Ahead and Behind (hereafter A and B), and the SOHO
spacecraft. Sixty-two halo CMEs occurred as observed by SOHO LASCO C2
for the three-year period from 2010 to 2012 during which the separation
angles between SOHO and STEREO were nearly 90°. In such quadrature
configuration, the coronagraphs of STEREO, COR2-A and -B, showed the
side view of those halo CMEs seen by C2. It has been widely believed
that the halo appearance of a CME is caused by the geometric projection
effect, i.e., a CME moves along the Sun-observer line. In other words,
it would appear as a non-halo CME if viewed from the side. However,
to our surprise, we found that 41 out of 62 events (66%) were observed
as halo CMEs by all coronagraphs. This result suggests that a halo
CME is not just a matter of the propagating direction. In addition,
we show that a CME propagating normal to the line of sight can be
observed as a halo CME due to the associated fast magnetosonic wave or
shock front. We conclude that the apparent width of CMEs, especially
halos or partial halos is driven by the existence and the extent of
the associated waves or shocks and does not represent an accurate
measure of the CME ejecta size. This effect needs to be taken into
careful consideration in space weather predictions and modeling efforts.
---------------------------------------------------------
Title: The VAULT2.0 Observing Campaign: A Comprehensive Investigation
of the Chromosphere-Corona Interface at Sub-arcsecond scales
Authors: Vourlidas, A.; Korendyke, C.; Tun-Beltran, S. D.; Ugarte-Urra,
I.; Morrill, J. S.; Warren, H. P.; Young, P.; De Pontieu, B.; Gauzzi,
G.; Reardon, K.
2014AGUFMSH41C4155V Altcode:
We report the first results from an observing campaign in support of
the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0
is a Lya (1216Å) spectroheliograph capable of 0.3" (~250 km) spatial
resolution. The objective of the VAULT2.0 project is the study of
the chromosphere-corona interface. This interface has acquired renewed
emphasis over the last few years, thanks to high-resolution observations
from Hinode/SOT and EIS instruments and the Lya imaging from the two
VAULT flights. The observations have shown that the upper chromosphere
may play a more important role in heating the corona and in affecting
EUV observations that previously thought: (1) by supplying the mass
via Type-II spicules and, (2) by absorbing coronal emission. Many of
the required clues for further progress are located in sub-arcsecond
structures with temperatures between 10000 and 50000 K, a regime not
accessible by Hinode or SDO. Lyman-alpha observations are, therefore,
ideal, for filling in this gap. The observing campaign in support of
the VAULT2.0 is closely coordinated with the Hinode and IRIS missions
to study the mass/energy flow from the chromosphere to the corona with
joint observations of type-II spicules, and the magnetic connectivity
of coronal loops using the full imaging and spectral capabilities of
IRIS, Hinode and SDO. Several ground-based observatories also provide
important observations (IBIS, BBSO, SOLIS). The VAULT2.0 project is
funded by the NASA LCAS program.
---------------------------------------------------------
Title: Synthetic White-light Imagery for the Wide-field Imager for
Solar Probe Plus (WISPR)
Authors: Liewer, P. C.; Su, Y.; Vourlidas, A.; Thernisien, A. F.;
Howard, R.; Hall, J. R.; DeJong, E.
2014AGUFMSH21B4101L Altcode:
The Solar Probe Plus trajectory, approaching within 10 solar radii,
will allow the white light imager, WISPR, to view the inner corona with
unprecedented spatial resolution. WISPR, with a 95° radial by 58°
transverse field of view, will image the fine-scale structure with
arcminute-scale resolution. The dependency of the Thomson scattering
on the imaging geometry (distance and angle from the Sun) dictates
that WISPR will be very sensitive to the emission from plasma close
to the spacecraft, in contrast to the situation for imaging from Earth
orbit. Thus WISPR will be the first 'local' imager providing a crucial
link between the large-scale corona and SPP's in-situ measurements. The
high speed at perihelion will provide tomographic-like views of
coronal structures. To prepare for this unprecedented viewing of the
structure of the inner corona, we are creating synthetic white light
images and animations from the WISPR viewpoint using the white-light
ray-tracing package developed at NRL (available through SolarSoft). We
will present results from multi-strand models of coronal streamers
and currents sheets as well as images of coronal mass ejections as
seen simultaneously from Earth, Solar Orbiter and SPP.
---------------------------------------------------------
Title: When the Sun Gets in the Way: Stereo Science Observations on
the Far Side of the Sun
Authors: Vourlidas, A.; Thompson, W. T.; Gurman, J. B.; Luhmann,
J. G.; Curtis, D. W.; Schroeder, P. C.; Mewaldt, R. A.; Davis, A. J.;
Wortman, K.; Russell, C. T.; Galvin, A. B.; Popecki, M.; Kistler,
L. M.; Ellis, L.; Howard, R.; Rich, N.; Hutting, L.; Maksimovic, M.;
Bale, S. D.; Goetz, K.
2014AGUFMSH53A4202V Altcode:
With the two STEREO spacecraft on the opposite side of the Sun from
Earth, pointing the high gain antenna at Earth means that it's also
pointed very close to the Sun. This has resulted in unexpectedly
high temperatures in the antenna feed horns on both spacecraft, and
is forcing the mission operations team to take corrective action,
starting in August 2014 for STEREO Ahead, and December 2014 for STEREO
Behind. By off-pointing the antennas to use one of the lower power side
lobes instead of the main lobe, the feed horn temperatures can be kept
at a safe level while still allowing reliable communication with the
spacecraft. However, the amount of telemetry that can be brought down
will be highly reduced. Even so, significant science will still be
possible from STEREO's unique position on the solar far side. We will
discuss the science and space weather products that will be available
from each STEREO instrument, when those products will be available,
and how they will be used. Some data, including the regular space
weather beacon products, will be brought down for an average of a
few hours each day during the daily real-time passes, while the in
situ and radio beacon data will be stored on the onboard recorder to
provide a continuous 24-hour coverage for eventual downlink once the
spacecraft is back to normal operations.
---------------------------------------------------------
Title: Evolution of Three Geoeffective Shock-CME pairs in September
2011
Authors: Wu, S. T.; Liou, K.; Wu, C. C.; Vourlidas, A.; Plunkett,
S. P.; Dryer, Ph D., M.; Socker, D. G.; Wood, B. E.
2014AGUFMSH43A4179W Altcode:
Three sizable geomagnetic storms were recorded in September 2011. The
intensity of geomagnetic storms (Dstmin: minimum Dst) are -69, -70,
-101 nT and the storms' onset time are September 9, 17, and 26,
respectively. A sequence of coronal mass ejections (CMEs) correspond
causing these three geomagnetic storms. The severe geomagnetic storm
(Dstmin < -100 nT) on 26 September was caused by a couple of CMEs
erupted on 24 September. Wind spacecraft detected an interplanetary (IP)
shock at ~11:18 UT on 26 September but no magnetic cloud was recorded
behind the IP shock. A severe geomagnetic storm was recorded ~6 hours
after the IP shock passed through the Wind spacecraft. Geomagnetic
index (Dst) dropped to -101 nT which was due to the z-component of
interplanetary magnetic field (Bz) dropped to ~ -20 nT. Both September
9th and 17th IP shocks have followed by a magnetic hole with a very
sharp change in both magnetic field and density. Inside the magnetic
holes, both solar wind velocity and temperature are almost constant, and
the peak of density and dip of magnetic field occurred near the centre
of the magnetic field hole. Peak densities were close to ~94, ~60 cm-3
near the centre of the hole on Sept. 09, 17, respectively. A global,
three-dimensional (3-D) magnetohydrodynamic (MHD) numerical model with
inputs based on actual solar observations (e.g., velocity of the CME)
is used to simulate the responses of the 3-D heliosphere. These velocity
pulses are deduced from STEREO-A which are used to minic the initiation
of the observed 15 CMEs at lower boundary (2.5 Rs) to investigate
the CME evolution from the Sun to the Earth during September 03-30,
2011.Simulated background solar wind parameters (velocity, density,
magnetic field, and temperature) are matched well with 1 AU in-situ
measurement from Wind spacecraft. In summary, we have successfully
simulated these CMEs' evolution and the IP shocks arrival time at 1
AU by comparison with Wind measurement.It is found that background
solar wind is an important factor on the propagation of IP shocks and
CMEs. The simulation results are also useful for explaining "How were
the magnetic holes formed behind the IP shocks?" *Work of CCW was
supported by ONR 6.1 program
---------------------------------------------------------
Title: Cycle-to-Cycle Variations in the Properties of Solar Energetic
Particle Events
Authors: Mewaldt, R. A.; Cohen, C. M.; Mason, G. M.; von Rosenvinge,
T. T.; Vourlidas, A.
2014AGUFMSH41D..09M Altcode:
We report on a cycle-to-cycle survey of Solar Energetic Particle (SEP)
events using data from ACE, STEREO, GOES, SOHO, and other near-Earth
spacecraft. We have compared the characteristics of solar proton events
during cycles 21 - 24, including peak-intensity, fluence, spectral
and compositional signatures. As of July 2014, a total of 72 cycle-24
events have met the NOAA criterion >10 protons/cm2-sr-s for >10
MeV proton intensities at either GOES, STEREO-A, or STEREO-B, including
33 at GOES. Most were observed at multiple longitudes. Compared to the
first 5.7 years of cycles 22 and 23 the number of near-Earth GOES-class
SEP events in cycle 24 is reduced by ~40%, and the total fluence of
>10 MeV protons is a factor of ~4 lower. At >100 MeV the cycle 23
fluence is lower by a factor of >7. The two STEREOs make it possible
to test whether Earth was simply in an anomalous location. There are
also significant compositional differences between cycles 23 and 24 in
abundance ratios such as Fe/O and Fe/H. We discuss factors that may
have affected the intensity, spectra, and composition of SEPs during
cycle 23, including the interplanetary magnetic field and solar wind
properties, CME and shock properties, and seed particle abundances.
---------------------------------------------------------
Title: Observations of Near-Sun Turbulent Density Fluctuations with
the Wide Field Imager for Solar Probe Plus (WISPR)
Authors: Plunkett, S. P.; Howard, R.; Vourlidas, A.; Korendyke, C.;
Rich, N.; Thernisien, A. F.; Wang, D.; Liewer, P. C.
2014AGUFMSH32A..05P Altcode:
The trajectory of Solar Probe Plus (SPP) as it transits through
the solar corona with a perihelion of < 10 Rs will allow much
higher contrast observations of small-scale density fluctuations
with higher cadence than is possible from 1 AU. The WISPR instrument
will implement a high-cadence mode (up to 1 second) in which it will
obtain images of the corona and inner heliosphere with high spatial
resolution over a restricted field of view around specified regions of
interest. Two-dimensional power spectra of the density fluctuations
can then be constructed with variable cadences for direct comparison
to similar spectra obtained by in-situ instruments on SPP and Solar
Orbiter (SO). WISPR will provide density power spectra at or below
the spectral break between inertial and injection scales, even at the
closest perihelion approach, for different coronal structures. When
combined with tomographic information from synoptic images, the
WISPR turbulence program will be a major enhancement to the turbulence
measurements from the SPP and SO in-situ instruments resulting in a much
more robust understanding of the near-Sun turbulence. We will present
details of the planned observations and will discuss the coordinated
science objectives that can be addressed using these observations.
---------------------------------------------------------
Title: Open Issues on CME Propagation in the Inner Heliosphere
Authors: Vourlidas, A.
2014AGUFMSH42A..07V Altcode:
Over the last few years, the SECCHI imagers aboard the STEREO mission
have revealed the inner heliosphere in unprecedented detail. We
can image and track CMEs from their birth in the solar corona to
their impact on Earth and beyond. We can routinely compare imaging
observations with in-situ measurements of the same event and at the same
time. It is tempting to think that the understanding the evolution of
CMEs in the inner heliosphere should be straighforward. This is not the
case. Although the prediction of the time of arrival of CMEs at Earth
has improved somewhat, there are many outliers. Predicting the speed of
the transient at Earth remain hit-or-miss. Clearly, the details of the
propagation of CMEs in the inner heliosphere still elude us, preventing
progress in Space Weather forecasting amongh other things. In this talk,
I review the open issues, as revealed by joint imaging and in-situ
analyses, and discuss strategies for making progress on the subject.
---------------------------------------------------------
Title: Global MHD Simulation of the Coronal Mass Ejection on 2011
March 7: from Chromosphere to 1 AU
Authors: Jin, M.; Manchester, W.; van der Holst, B.; Sokolov, I.;
Toth, G.; Vourlidas, A.; de Koning, C. A.; Gombosi, T. I.
2014AGUFMSH43A4176J Altcode:
Performing realistic simulations of solar eruptions and validating
those simulations with observations are important goals in order
to achieve accurate space weather forecasts. Here, we perform and
analyze results of a global magnetohydrodyanmic (MHD) simulation of the
fast coronal mass ejection (CME) that occurred on 2011 March 7. The
simulation is made using the newly developed Alfven Wave Solar Model
(AWSoM), which describes the background solar wind starting from the
upper chromosphere and expands to 24 Rs. Coupling of AWSoM to an inner
heliosphere (IH) model with the Space Weather Modeling Framework (SWMF)
extends the total domain beyond the orbit of Earth. Physical processes
included in the model are multi-species thermodynamics, electron heat
conduction (both collisional and collisionless formulations), optically
thin radiative cooling, and Alfven-wave pressure that accelerates
the solar wind. The Alfven-wave description is physically consistent,
including non-WKB reflection and physics-based apportioning of turbulent
dissipative heating to both electrons and protons. Within this model,
we initiate the CME by using the Gibson-Low (GL) analytical flux rope
model and follow its evolution for days, in which time it propagates
beyond 1 AU. A comprehensive validation study is performed using
remote as well as in-situ observations from SDO, SOHO, STEREOA/B,
and OMNI. Our results show that the new model can reproduce many
of the observed features near the Sun (e.g., CME-driven EUV waves,
deflection of the flux rope from the coronal hole, "double-front"
in the white light images) and in the heliosphere (e.g., CME-CIR
interaction, shock properties at 1 AU). The CME-driven shock arrival
time is within 1 hour of the observed arrival time, and nearly all the
in-situ parameters are correctly simulated, which suggests the global
MHD model as a powerful tool for the space weather forecasting.
---------------------------------------------------------
Title: Coronal shocks properties and their associations with energetic
particle events measured near 1AU.
Authors: Rouillard, A. P.; Vourlidas, A.; Tylka, A. J.; Ng, C. K.;
Cohen, C. M.
2014AGUFMSH43A4170R Altcode:
We combine ultraviolet and white-light images obtained by the Solar
Dynamics Observatory (SDO) and the Solar-Terrestrial Relations
Observatory (STEREO) to track, in the lower corona, the spatial and
temporal evolution of pressure waves and shocks associated with the
onset of Coronal Mass Ejections (CMEs). We use ideal geometrical 3-D
surfaces to follow with time the location of the global disturbance
observed in EUV and white-light images. This fitting technique provides
a tracking of the evolution of shocks from the Sun to 20 solar
radii. We combine potential field source surface calculations with
simple models of the distribution of interplanetary magnetic field lines
in the interplanetary medium to determine the magnetic connectivity of
the shock with spacecraft located near 1AU. We extract the 3-D shock
velocity vector, the shock geometry and, by using empirical functions
of temperature and density variations in the corona, the local Alfven
speed at the point of magnetic connectivity with STEREO-A, STEREO-B
and L1 spacecraft. The properties of the tracked coronal shocks are
compared with the properties of SEPs measured in situ. We concentrate
on the proton-rich events detected by the near-Earth spacecraft as
well as the STEREO spacecraft from 2011 to 2014. We use the onset of
solar energetic particle events (SEPs) to determine their release time
near the Sun. We show that the shock speed at the point of magnetic
connectivity is a determining factor for the intensity of the SEP
measured in situ with a steep relation between coronal shock speed
and SEP maximum intensity. This analysis naturally removes projection
effects associated with single viewpoint analysis presented in previous
studies. We discuss how the interplay between the radial dependence
of the Alfven speed and the complex topology of magnetic field lines
in the corona is likely to control the onset time of SEPs at 1AU. We
discuss the successes and challenges faced when interpreting SEP events
in terms of the speed and geometry of coronal shocks.
---------------------------------------------------------
Title: Earth-Directed ICME Magnetic Field Configurations
Authors: Nieves-Chinchilla, T.; Szabo, A.; Vourlidas, A.; Savani,
N.; Hidalgo, M. A. U.; Yu, W.
2014AGUFMSH23D..08N Altcode:
It is known that the geoeffectiveness of interplanetary
coronal mass ejections (ICMEs) depends on their magnetic field
configuration. However, it remains unclear how the ICME interactions
with the solar wind or other solar transient structures affect their
magnetic configuration through, say, distortion of their cross-section,
or deformation of their front. Obviously, precise space weather
forecasting is depended on precise understanding of the evolution
of the ICME internal magnetic topology. The goal of this study is to
identify the ambient solar wind parameters that affect the flux-rope
geometry and magnetic field configuration
---------------------------------------------------------
Title: An Unusual Heliospheric Plasma Sheet Crossing at 1 AU
Authors: Wu, C. C.; Liou, K.; Vourlidas, A.; Lepping, R. P.; Wang,
Y. M.; Plunkett, S. P.; Socker, D. G.; Wu, S. T.
2014AGUFMSH43A4166W Altcode:
At 11:46UT on September 9, 2011, the Wind spacecraft encountered
an interplanetary (IP) fast forward shock. The shock was followed
almost immediately (~5 minutes) by a short duration (~35 minutes),
extremely large density pulse with a density peak of ~100 cm-3. While
a sharp increase in the solar wind density is typical of an IP shock
downstream, the unusual large density increase prompts a further
investigation. After a close examination of other in situ data from
Wind, we find the density pulse was associated with (1) a spike in
the plasma beta (ratio of thermal to magnetic pressure), (2) multiple
sign changes in the azimuthal angle of magnetic field, (3) depressed
magnetic field, (4) a small radial component of magnetic field, and (5)
a large (>90 degrees) pitch-angle change in suprathermal electrons
(>200 eV) across the density pulse. We conclude that the density
pulse is the heliospheric plasma sheet and the estimated thickness is
~820,000km. The unusually large density pulse is likely to be a result
of the shock compression from behind. This view is supported by our 3D
magnetohydrodynamic simulation. The detailed result and implications
will be discussed. *This work is supported partially by ONR 6.1 program
---------------------------------------------------------
Title: The CME event on 07 January 2014: Why was it a geomagnetic dud?
Authors: Raouafi, N. E.; Colaninno, R. C.; Vourlidas, A.; Stenborg,
G.; Lario, D.; Merkin, V. G.
2014AGUFMSH51E..05R Altcode:
The X-class flare-associated CME event on 07 January 2014 originated
from a large sunspot group near disk center and reached > 2000 km s-1
at its initial phases. In-situ measurements at 1 AU show a strong solar
proton event. The CME was expected to cause a significant geomagnetic
response. However, arriving at 1 AU the CME was significantly slower
than expected (~500 km s-1) and was a complete dud in terms of
geomagnetic activity. We present a comprehensive analysis of the CME
using EUV and white light observations as well as in-situ measurements
to understand why it was not geo-effective. We particularly study CME
deflection caused by coronal holes and eventual interaction with other
pre-existing and slower CMEs.
---------------------------------------------------------
Title: Forecasting the magnetic vectors within a CME at L1 by using
solar observations.
Authors: Savani, N.; Vourlidas, A.; Szabo, A.; Mays, M. L.; Evans,
R. M.; Thompson, B. J.; Richardson, I. G.; Pulkkinen, A. A.;
Nieves-Chinchilla, T.
2014AGUFMSH43B4213S Altcode:
The direction of magnetic vectors within coronal mass ejections has
important consequences to forecasting terrestrial behaviour, however
forecasting these vectors remains predominately elusive. Here,
we report that a simplified system is capable of replicating the
broad field rotations seen within flux rope CMEs at L1 monitors. The
predictions are performed under three main themes: 1) The majority of
the field rotations can be simplified to the constant-alpha force-free
(CAFF) flux model first implemented circa 1990. 2) The helicity will
follow the Bothmer & Schwenn system that relies on a reliable
helicity prediction of active regions during solar cycle. Which has
been recently confirmed by Wang [2013 ApJ]. 3) The majority of the
distortions, deflections and rotations will have already occurred
within coronagraphic field of view, thereby allowing the creation
of a projected "volume-of-influence" on the Sun, from which Earth's
position relative to the CME can be estimated. This presentation will
compare predicted results to the observations from 7 CME events and then
estimate the sources of uncertainty. As an example, the difference in
robust statistics from 2 solar cycles of CAFF model fittings for the
field magnitude will be compared to estimates generated from simulated
CME-sheaths within forecasting Enlil runs. The figure displays an
example field vector forecast from the techniques employed above.
---------------------------------------------------------
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Ko, Y. K.; Auchere, F.; Casini, R.; Fineschi, S.; Gibson,
S. E.; Knoelker, M.; Korendyke, C.; Laming, J. M.; Mcintosh, S. W.;
Moses, J. D.; Romoli, M.; Rybak, J.; Socker, D. G.; Strachan, L.;
Tomczyk, S.; Vourlidas, A.; Wu, Q.
2014AGUFMSH53B4221K Altcode:
Magnetic fields in the solar atmosphere provide the energy for most
varieties of solar activity, including high-energy electromagnetic
radiation, solar energetic particles, flares, and coronal mass
ejections, as well as powering the solar wind. Despite the fundamental
role of magnetic fields in solar and heliospheric physics, there
exists only very limited measurements of the field above the base of
the corona. What is needed are direct measurements of not only the
strength and orientation of the magnetic field but also the signatures
of wave motions in order to better understand coronal structure,
solar activity and the role of MHD waves in heating and accelerating
the solar wind. Fortunately, the remote sensing instrumentation used
to make magnetic field measurements is also well suited for measuring
the Doppler signature of waves in the solar structures. With this
in mind, we are proposing the WAMIS (Waves and Magnetism in the
Solar Atmosphere) investigation. WAMIS will take advantage of greatly
improved infrared (IR) detectors, forward models, advanced diagnostic
tools and inversion codes to obtain a breakthrough in the measurement
of coronal magnetic fields and in the understanding of the interaction
of these fields with space plasmas. This will be achieved with a high
altitude balloon borne payload consisting of a coronagraph with an IR
spectro-polarimeter focal plane assembly. The balloon platform provides
minimum atmospheric absorption and scattering at the IR wavelengths in
which these observations are made. Additionally, a NASA long duration
balloon flight mission from the Antarctic can achieve continuous
observations over most of a solar rotation, covering all of the key
time scales for the evolution of coronal magnetic fields. With these
improvements in key technologies along with experience gained from
current ground-based instrumentation, WAMIS will provide a low-cost
mission with a high technology readiness leve.
---------------------------------------------------------
Title: Periodic Density Structures and the Origin of the Slow
Solar Wind
Authors: Viall, N. M.; Vourlidas, A.
2014AGUFMSH21B4114V Altcode:
Periodic density structures with length-scales of hundreds to several
thousands of Mm and frequencies of tens to hundreds of minutes are
observed regularly in the solar wind at 1 AU. These structures coexist
with, but are not due to, fluctuations in the plasma resulting from the
turbulent cascade. Two lines of evidence - one identifying corresponding
changes in compositional data in situ, and another identifying periodic
density structures in the inner Heliospheric Imaging data onboard the
Solar Terrestrial Relations Observatory (STEREO)/ Sun Earth Connection
Coronal and Heliospheric Investigation (SECCHI) suite - indicate that
periodic density structures are formed in the solar corona as part
of the slow solar wind release and/or acceleration processes. The
periodic nature of these density structures is an important physical
constraint on their origin. In this presentation, we present the results
of tracking periodic structures identified in the SECCHI/HI1 images
down through the corresponding SECCHI/COR2 images. We demonstrate that
the periodic density structures are formed around or below 2.5 solar
radii - the inner edge of the COR2 field of view. Further, we compute
the occurrence rate of periodic density structures in 10 days of COR2
images as a function of location in the solar corona. We find that this
set of periodic density structures occurs preferentially in relation
to coronal streamers. Periodic density structures are tracers of solar
wind origin and/or acceleration; this study is a pilot for the kinds
of investigations that we can carry out with the better temporal and
spatial resolution of the heliospheric imagers on Solar Orbiter and
Solar Probe Plus.
---------------------------------------------------------
Title: Solar Sources of Interplanetary Coronal Mass Ejections During
the Solar Cycle 23/24 Minimum
Authors: Kilpua, E. K. J.; Mierla, M.; Zhukov, A. N.; Rodriguez, L.;
Vourlidas, A.; Wood, B.
2014SoPh..289.3773K Altcode: 2014SoPh..tmp...92K
We examine solar sources for 20 interplanetary coronal mass ejections
(ICMEs) observed in 2009 in the near-Earth solar wind. We performed
a detailed analysis of coronagraph and extreme ultraviolet (EUV)
observations from the Solar Terrestrial Relations Observatory (STEREO)
and Solar and Heliospheric Observatory (SOHO). Our study shows that
the coronagraph observations from viewpoints away from the Sun-Earth
line are paramount to locate the solar sources of Earth-bound ICMEs
during solar minimum. SOHO/LASCO detected only six CMEs in our sample,
and only one of these CMEs was wider than 120<SUP>∘</SUP>. This
demonstrates that observing a full or partial halo CME is not necessary
to observe the ICME arrival. Although the two STEREO spacecraft had the
best possible configuration for observing Earth-bound CMEs in 2009, we
failed to find the associated CME for four ICMEs, and identifying the
correct CME was not straightforward even for some clear ICMEs. Ten out
of 16 (63 %) of the associated CMEs in our study were "stealth" CMEs,
i.e. no obvious EUV on-disk activity was associated with them. Most
of our stealth CMEs also lacked on-limb EUV signatures. We found that
stealth CMEs generally lack the leading bright front in coronagraph
images. This is in accordance with previous studies that argued that
stealth CMEs form more slowly and at higher coronal altitudes than
non-stealth CMEs. We suggest that at solar minimum the slow-rising
CMEs do not draw enough coronal plasma around them. These CMEs are
hence difficult to discern in the coronagraphic data, even when viewed
close to the plane of the sky. The weak ICMEs in our study were related
to both intrinsically narrow CMEs and the non-central encounters of
larger CMEs. We also demonstrate that narrow CMEs (angular widths ≤
20<SUP>∘</SUP>) can arrive at Earth and that an unstructured CME
may result in a flux rope-type ICME.
---------------------------------------------------------
Title: Self-similar Expansion of Solar Coronal Mass Ejections:
Implications for Lorentz Self-force Driving
Authors: Subramanian, Prasad; Arunbabu, K. P.; Vourlidas, Angelos;
Mauriya, Adwiteey
2014ApJ...790..125S Altcode: 2014arXiv1406.0286S
We examine the propagation of several coronal mass ejections (CMEs)
with well-observed flux rope signatures in the field of view of the
SECCHI coronagraphs on board the STEREO satellites using the graduated
cylindrical shell fitting method of Thernisien et al. We find that
the manner in which they propagate is approximately self-similar;
i.e., the ratio (κ) of the flux rope minor radius to its major radius
remains approximately constant with time. We use this observation of
self-similarity to draw conclusions regarding the local pitch angle
(γ) of the flux rope magnetic field and the misalignment angle (χ)
between the current density J and the magnetic field B. Our results
suggest that the magnetic field and current configurations inside
flux ropes deviate substantially from a force-free state in typical
coronagraph fields of view, validating the idea of CMEs being driven
by Lorentz self-forces.
---------------------------------------------------------
Title: Solar Energetic Particle Events in Different Types of
Solar Wind
Authors: Kahler, S. W.; Vourlidas, A.
2014ApJ...791....4K Altcode:
We examine statistically some properties of 96 20 MeV gradual solar
energetic proton (SEP) events as a function of three different types
of solar wind (SW) as classified by Richardson and Cane. Gradual SEP
(E > 10 MeV) events are produced in shocks driven by fast (V >~
900 km s<SUP>-1</SUP>) and wide (W > 60°) coronal mass ejections
(CMEs). We find no differences among the transient, fast, and slow
SW streams for SEP 20 MeV proton event timescales. It has recently
been found that the peak intensities Ip of these SEP events scale
with the ~2 MeV proton background intensities, which may be a proxy
for the near-Sun shock seed particles. Both the intensities Ip and
their 2 MeV backgrounds are significantly enhanced in transient SW
compared to those of fast and slow SW streams, and the values of Ip
normalized to the 2 MeV backgrounds only weakly correlate with CME
V for all SW types. This result implies that forecasts of SEP events
could be improved by monitoring both the Sun and the local SW stream
properties and that the well known power-law size distributions of Ip
may differ between transient and long-lived SW streams. We interpret
an observed correlation between CME V and the 2 MeV background for SEP
events in transient SW as a manifestation of enhanced solar activity.
---------------------------------------------------------
Title: Predicting the magnetic vectors within coronal mass ejections
arriving at Earth
Authors: Savani, Neel P.; Vourlidas, Angelos; Szabo, Adam; Mays,
M. Leila; Thompson, Barbara; Richardson, Ian; Evans, Rebekah;
Pulkkinen, Antti; Nieves-Chinchilla, Teresa
2014shin.confE.164S Altcode:
The process by which the Sun affects the terrestrial environment
on short timescales is predominately driven by the amount
of magnetic reconnection between the solar wind and Earth's
magnetosphere. Reconnection occurs most efficiently when the solar
wind magnetic field has a southward component. The most severe impacts
are during the arrival of a coronal mass ejection (CME) when the
magnetosphere is both compressed and magnetically connected to the
heliospheric environment, leading to disruptions to, for example, power
grids and satellite navigation. Unfortunately, forecasting magnetic
vectors within coronal mass ejections remains elusive. Here we report
how, by combining a statistically robust helicity rule for a CME's solar
origin with a simplified flux rope topology the magnetic vectors within
the Earth-directed segment of a CME can be predicted. These magnetic
vectors can be incorporated into forecasting procedures to predict the
global response measured by the Kp index more reliably. In particular,
false predictions of strong geomagnetic events made without magnetic
field information are considerably reduced. As an example, the forecast
strength of a geomagnetic storm following a CME on 7 January 2014, is
reduced from G3 (strong) to G1 (minor) on the NOAA scale when magnetic
vectors are taken into account.
---------------------------------------------------------
Title: Global Magnetohydrodynamics Simulation of the Coronal Mass
Ejection on 2011 March 7: from Chromosphere to 1 AU
Authors: Jin, Meng; Manchester, W. B.; van der Holst, B.; Sokolov,
I.; Toth, G.; Vourlidas, A.; de Koning, C.; Gombosi, T. I.
2014shin.confE..10J Altcode:
Performing realistic simulations of solar eruptions and validating
those simulations with observations are important goals in order to
achieve accurate space weather forecasts. Here, we analyze results
of a global magnetohydrodyanmic (MHD) simulation of the fast coronal
mass ejection (CME) that occurred on 2011 March 7. The simulation is
made using the newly developed Alfven Wave Solar Model (AWSoM), which
describes the background solar wind starting from the upper chromosphere
and expends to 24 Rs. Coupling of AWSoM to an inner heliosphere (IH)
model with the Space Weather Modeling Framework extends the total domain
beyond the orbit of Earth. Physical processes included in the model are
multi-species thermodynamics, electron heat conduction (both collisional
and collisionless formulation), optically thin radiative cooling and
Alfven-wave pressure that accelerates the solar wind. The Alfven-wave
description is physically self-consistent, including non-WKB reflection
and physics-based apportioning of turbulent dissipative heating to both
electrons and protons. Within this model, we initiate the CME by using
the Gibson-Low (GL) analytical flux rope model and follow its evolution
for days, in which time it propagates beyond 1 AU. A comprehensive
validation study is performed using remote as well as the in situ
observations from SDO, SOHO, STEREOA/B, and OMNI. Our results show
that the new model can reproduce many of the observed features near
the Sun (e.g., CME-driven EUV waves, deflection of the flux rope from
the coronal hole, double-front in the white light images) and in the
heliosphere (e.g., CME-CIR interaction, shock properties at 1 AU). By
fitting the CME speeds near the Sun with observations, the CME-driven
shock arrival time is within 1 hour of the observed arrival time and
all the in situ parameters are correctly simulated, which suggests the
global MHD model as a powerful tool for the space weather forecasting.
---------------------------------------------------------
Title: CME Expansion as the Driver of Metric Type II Shock Emission
as Revealed by Self-consistent Analysis of High-Cadence EUV Images
and Radio Spectrograms
Authors: Kouloumvakos, A.; Patsourakos, S.; Hillaris, A.; Vourlidas,
A.; Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.;
Kontogeorgos, A.
2014SoPh..289.2123K Altcode: 2013arXiv1311.5159K
On 13 June 2010, an eruptive event occurred near the solar limb. It
included a small filament eruption and the onset of a relatively narrow
coronal mass ejection (CME) surrounded by an extreme ultraviolet
(EUV) wave front recorded by the Solar Dynamics Observatory's (SDO)
Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was
accompanied by a GOES M1.0 soft X-ray flare and a Type-II radio burst;
high-resolution dynamic spectra of the latter were obtained by the
Appareil de Routine pour le Traitement et l'Enregistrement Magnetique
de l'Information Spectral (ARTEMIS IV) radio spectrograph. The combined
observations enabled a study of the evolution of the ejecta and the
EUV wave front and its relationship with the coronal shock manifesting
itself as metric Type-II burst. By introducing a novel technique,
which deduces a proxy of the EUV compression ratio from AIA imaging
data and compares it with the compression ratio deduced from the
band-split of the Type-II metric radio burst, we are able to infer
the potential source locations of the radio emission of the shock on
that AIA images. Our results indicate that the expansion of the CME
ejecta is the source for both EUV and radio shock emissions. Early in
the CME expansion phase, the Type-II burst seems to originate in the
sheath region between the EUV bubble and the EUV shock front in both
radial and lateral directions. This suggests that both the nose and
the flanks of the expanding bubble could have driven the shock.
---------------------------------------------------------
Title: Rapid CME Cavity Formation and Expansion
Authors: Kliem, Bernhard; Forbes, Terry G.; Patsourakos, Spiros;
Vourlidas, Angelos
2014AAS...22421206K Altcode:
A cavity is supposed to be a general feature of well-developed CMEs at
the stage they can be imaged by white-light coronagraphs (in the outer
corona and solar wind). The cavity is interpreted as the cross section
of the CME flux rope in the plane of sky. Preexisting cavities are
observed around some quiescent erupting prominences, but usually not in
active regions. Observations of CME cavities in the inner corona, where
most of them appear to form, have become possible only with the STEREO
and SDO missions. These reveal a very rapid formation and expansion of
"EUV cavities" in fast and impulsively commencing eruptions early in the
phase of main CME acceleration and impulsive flare rise. Different from
the white-light observations, the EUV cavity initially appears to be
larger than the CME flux rope. However, it evolves into the white-light
cavity subsequently. MHD simulations of flux rope eruptions conform to
this picture of initially larger cavity but subsequently approaching
cavity and flux rope size. The initial expansion of ambient flux can
be understood as a "reverse pinch effect", driven by decreasing flux
rope current as the rope rises.
---------------------------------------------------------
Title: Solar Energetic Particle Events in Different Types of
Solar Wind
Authors: Kahler, Stephen W.; Vourlidas, Angelos
2014AAS...22432358K Altcode:
We examine statistically some properties of 96 20 MeV gradual solar
energetic proton (SEP) events as a function of three different types of
solar winds (SWs) as classified by Richardson and Cane (2012). Gradual
SEP (E > 10 MeV) events are produced in shocks driven by fast
(V > 900 km/s) and wide (W > 60 deg) coronal mass ejections
(CMEs). We find no differences between transient and fast or slow SW
streams for SEP 20-MeV event timescales. It has recently been found
that the peak intensities Ip of these SEP events scale with the ~
2 MeV proton background intensities, which may be a proxy for the
near-Sun shock seed particles. Both the intensities Ip and their 2
MeV backgrounds are significantly enhanced in transient SW compared
to those of fast and slow SW streams, and the values of Ip normalized
to the 2 MeV backgrounds only weakly correlate with CME V for all
SW types. This result implies that forecasts of SEP events could be
improved by monitoring both the Sun and the local SW stream properties
and that the well known power-law size distributions of Ip may differ
between transient and long-lived SW streams. We interpret an observed
correlation between CME V and the 2 MeV background for SEP events in
transient SW as a manifestation of enhanced solar activity.
---------------------------------------------------------
Title: Periodic Density Structures and the Source of the Slow
Solar Wind
Authors: Viall, Nicholeen; Vourlidas, Angelos
2014AAS...22440202V Altcode:
Periodic density structures with length-scales of hundreds to several
thousands of megameters, and frequencies of tens to hundreds of minutes,
are observed regularly in the solar wind at 1 AU. These structures
coexist with, but are not due to, fluctuations in the plasma resulting
from the turbulent cascade. Two lines of evidence suggest that periodic
density structures are formed in the solar corona as part of the slow
solar wind release and/or acceleration processes. The first is the
identification of corresponding changes in compositional data in situ,
and the other is the identification of periodic density structures in
the inner Heliospheric Imaging data onboard the STEREO/SECCHI suite. In
this presentation, we show the results of tracking periodic structures
identified in the SECCHI/Hi1 images down through the corresponding
SECCHI/Cor2 images. We demonstrate that the periodic density structures
are formed around or below 2.5 Rs - the inner edge of the Cor2 field
of view. Further, we compute the occurrence rate of periodic density
structures in 10 days of Cor2 images as a function of location in the
solar corona. We find that periodic density structures do not occur
throughout the entire space-filling volume of the solar wind; rather,
there are particular places where they occur preferentially, suggesting
source locations for periodic density structures in the slow solar wind.
---------------------------------------------------------
Title: A plasma β transition within a propagating flux rope
Authors: Savani, Neel; Vourlidas, Angelos; Shiota, Daikou; Linton,
Mark; Kusano, Kanya; Lugaz, Noe; Rouillard, Alexis
2014AAS...22421205S Altcode:
We present a 2.5D MHD simulation of a magnetic flux rope (FR)
propagating in the heliosphere and investigate the cause of the observed
sharp plasma β transition. Specifically, we consider a strong internal
magnetic field and an explosive fast start, such that the plasma β is
significantly lower in the FR than the sheath region that is formed
ahead. This leads to an unusual FR morphology in the first stage of
propagation, while the more traditional view (e.g. from space weather
simulations like Enlil) of a `pancake' shaped FR is observed as it
approaches 1AU. We investigate how an equipartition line, defined by a
magnetic Weber number, surrounding a core region of a propagating FR
can demarcate a boundary layer where there is a sharp transition in
the plasma β. The substructure affects the distribution of toroidal
flux, with the majority of the flux remaining in a small core region
which maintains a quasi-cylindrical structure. Quantitatively, we
investigate a locus of points where the kinetic energy density of the
relative inflow field is equal to the energy density of the transverse
magnetic field (i.e. effective tension force). The simulation provides
compelling evidence that at all heliocentric distances the distribution
of toroidal magnetic flux away from the FR axis is not linear; with
80% of the toroidal flux occurring within 40% of the distance from
the FR axis. Thus our simulation displays evidence that the competing
ideas of a pancaking structure observed remotely can coexist with a
quasi-cylindrical magnetic structure seen in situ
---------------------------------------------------------
Title: Earth-directed ICME magnetic field configuration
Authors: Nieves-Chinchilla, Teresa; Vourlidas, A.; Szabo, A.; Savani,
N.; Hidalgo, A. M.
2014shin.confE...8N Altcode:
It is well known that the geoeffectiveness of interplanetary
coronal mass ejections (ICMEs) depends on their magnetic field
configuration. However, it remains unclear how the ICME interactions
with the solar wind or other solar transient structures affect their
magnetic configuration through, say, distortion of their cross-section,
or deformation of their front. Obviously, precise space weather
forecasting is depended on precise understanding of the evolution of
the ICME internal magnetic topology.
---------------------------------------------------------
Title: Independent CMEs from a Single Solar Active Region - The Case
of the Super-Eruptive NOAA AR11429
Authors: Chintzoglou, Georgios; Patsourakos, Spiros; Vourlidas, Angelos
2014AAS...22432328C Altcode:
In this investigation we study AR 11429, the origin of the twin
super-fast CME eruptions of 07-Mar-2012. This AR fulfills all the
requirements for the 'perfect storm'; namely, Hale's law incompatibility
and a delta-magnetic configuration. In fact, during its limb-to-limb
transit, AR 11429 spawned several eruptions which caused geomagnetic
storms, including the biggest in Cycle 24 so far. Magnetic Flux Ropes
(MFRs) are twisted magnetic structures in the corona, best seen in
~10MK hot plasma emission and are often considered as the culprit
causing such super-eruptions. However, their 'dormant' existence in
the solar atmosphere (i.e. prior to eruptions), is a matter of strong
debate. Aided by multi-wavelength and multi-spacecraft observations
(SDO/HMI & AIA, HINODE/SOT/SP, STEREO B/EUVI) and by using a
Non-Linear Force-Free (NLFFF) model for the coronal magnetic field,
our work shows two separate, weakly-twisted magnetic flux systems
which suggest the existence of possible pre-eruption MFRs.
---------------------------------------------------------
Title: Three-Dimensional Evolution of Flux-Rope CMEs and Its Relation
to the Local Orientation of the Heliospheric Current Sheet
Authors: Isavnin, A.; Vourlidas, A.; Kilpua, E. K. J.
2014SoPh..289.2141I Altcode: 2013arXiv1312.0458I; 2014SoPh..tmp...16I
Flux ropes ejected from the Sun may change their geometrical
orientation during their evolution, which directly affects their
geoeffectiveness. Therefore, it is crucial to understand how solar
flux ropes evolve in the heliosphere to improve our space-weather
forecasting tools. We present a follow-up study of the concepts
described by Isavnin, Vourlidas, and Kilpua (Solar Phys.284, 203,
2013). We analyze 14 coronal mass ejections (CMEs), with clear
flux-rope signatures, observed during the decay of Solar Cycle 23 and
rise of Solar Cycle 24. First, we estimate initial orientations of
the flux ropes at the origin using extreme-ultraviolet observations of
post-eruption arcades and/or eruptive prominences. Then we reconstruct
multi-viewpoint coronagraph observations of the CMEs from ≈ 2 to
30 R<SUB>⊙</SUB> with a three-dimensional geometric representation
of a flux rope to determine their geometrical parameters. Finally, we
propagate the flux ropes from ≈ 30 R<SUB>⊙</SUB> to 1 AU through
MHD-simulated background solar wind while using in-situ measurements
at 1 AU of the associated magnetic cloud as a constraint for the
propagation technique. This methodology allows us to estimate the
flux-rope orientation all the way from the Sun to 1 AU. We find
that while the flux-ropes' deflection occurs predominantly below
30 R<SUB>⊙</SUB>, a significant amount of deflection and rotation
happens between 30 R<SUB>⊙</SUB> and 1 AU. We compare the flux-rope
orientation to the local orientation of the heliospheric current sheet
(HCS). We find that slow flux ropes tend to align with the streams
of slow solar wind in the inner heliosphere. During the solar-cycle
minimum the slow solar-wind channel as well as the HCS usually occupy
the area in the vicinity of the solar equatorial plane, which in the
past led researchers to the hypothesis that flux ropes align with the
HCS. Our results show that exceptions from this rule are explained
by interaction with the Parker-spiraled background magnetic field,
which dominates over the magnetic interaction with the HCS in the
inner heliosphere at least during solar-minimum conditions.
---------------------------------------------------------
Title: Do Interacting Coronal Mass Ejections Play a Role in Solar
Energetic Particle Events?
Authors: Kahler, S. W.; Vourlidas, A.
2014ApJ...784...47K Altcode:
Gradual solar energetic (E > 10 MeV) particle (SEP) events are
produced in shocks driven by fast and wide coronal mass ejections
(CMEs). With a set of western hemisphere 20 MeV SEP events, we
test the possibility that SEP peak intensities, Ip, are enhanced by
interactions of their associated CMEs with preceding CMEs (preCMEs)
launched during the previous 12 hr. Among SEP events with no, 1, or 2
or more (2+) preCMEs, we find enhanced Ip for the groups with preCMEs,
but no differences in TO+TR, the time from CME launch to SEP onset
and the time from onset to SEP half-peak Ip. Neither the timings of
the preCMEs relative to their associated CMEs nor the preCME widths W
<SUB>pre</SUB>, speeds V <SUB>pre</SUB>, or numbers correlate with the
SEP Ip values. The 20 MeV Ip of all the preCME groups correlate with
the 2 MeV proton background intensities, consistent with a general
correlation with possible seed particle populations. Furthermore, the
fraction of CMEs with preCMEs also increases with the 2 MeV proton
background intensities. This implies that the higher SEP Ip values
with preCMEs may not be due primarily to CME interactions, such as the
"twin-CME" scenario, but are explained by a general increase of both
background seed particles and more frequent CMEs during times of higher
solar activity. This explanation is not supported by our analysis of
2 MeV proton backgrounds in two earlier preCME studies of SEP events,
so the relevance of CME interactions for larger SEP event intensities
remains unclear.
---------------------------------------------------------
Title: Tracking the Evolution of a Coherent Magnetic Flux Rope
Continuously from the Inner to the Outer Corona
Authors: Cheng, X.; Ding, M. D.; Guo, Y.; Zhang, J.; Vourlidas, A.;
Liu, Y. D.; Olmedo, O.; Sun, J. Q.; Li, C.
2014ApJ...780...28C Altcode: 2013arXiv1310.6782C
The magnetic flux rope (MFR) is believed to be the underlying
magnetic structure of coronal mass ejections (CMEs). However, it
remains unclear how an MFR evolves into and forms the multi-component
structure of a CME. In this paper, we perform a comprehensive study of
an extreme-ultraviolet (EUV) MFR eruption on 2013 May 22 by tracking
its morphological evolution, studying its kinematics, and quantifying
its thermal property. As EUV brightenings begin, the MFR starts to rise
slowly and shows helical threads winding around an axis. Meanwhile, cool
filamentary materials descend spirally down to the chromosphere. These
features provide direct observational evidence of intrinsically helical
structure of the MFR. Through detailed kinematical analysis, we find
that the MFR evolution has two distinct phases: a slow rise phase and
an impulsive acceleration phase. We attribute the first phase to the
magnetic reconnection within the quasi-separatrix layers surrounding
the MFR, and the much more energetic second phase to the fast magnetic
reconnection underneath the MFR. We suggest that the transition
between these two phases is caused by the torus instability. Moreover,
we identify that the MFR evolves smoothly into the outer corona and
appears as a coherent structure within the white-light CME volume. The
MFR in the outer corona was enveloped by bright fronts that originated
from plasma pile-up in front of the expanding MFR. The fronts are also
associated with the preceding sheath region followed by the outmost
MFR-driven shock.
---------------------------------------------------------
Title: Coordinated science with the Solar Orbiter, Solar Probe Plus,
Interhelioprobe and SPORT missions
Authors: Maksimovic, Milan; Vourlidas, Angelos; Zimovets, Ivan; Velli,
Marco; Zhukov, Andrei; Kuznetsov, Vladimir; Liu, Ying; Bale, Stuart;
Ming, Xiong
2014cosp...40E1956M Altcode:
The concurrent science operations of the ESA Solar Orbiter (SO), NASA
Solar Probe Plus (SPP), Russian Interhelioprobe (IHP) and Chinese SPORT
missions will offer a truly unique epoch in heliospheric science. While
each mission will achieve its own important science objectives, taken
together the four missions will be capable of doing the multi-point
measurements required to address many problems in Heliophysics such
as the coronal origin of the solar wind plasma and magnetic field or
the way the Solar transients drive the heliospheric variability. In
this presentation, we discuss the capabilities of the four missions
and the Science synergy that will be realized by concurrent operations
---------------------------------------------------------
Title: The STEREO Encounter with the Tail of Comet Elenin and
Expectations for ISON
Authors: Galvin, A. B.; Kucharek, H.; Klecker, B.; Simunac, K.;
Farrugia, C. J.; Wimmer-Schweingruber, R. F.; Berger, L.; Drews, C.;
Vourlidas, A.
2013AGUFM.P31A1789G Altcode:
The longest encounter to date of a space probe with a comet occurred
in late July through mid August 2011 when the STEREO B (STB)
observatory was immersed in the plasma environment of comet C/2010
X1 (Elenin). Closest approach was reached on July 31 at a distance
of 7.4 million kilometers, with the nominal radial tail alignment
occurring on August 12. Continuous observations of cometary ions are
available for over three weeks. These ions were created over a broad
range of solar wind conditions, including slow and fast solar wind,
stream interaction regions, and an interplanetary coronal mass
ejection. In the mass-per-charge range of water-group ions, the
STB/PLASTIC instrument found that the major ion constituent was O+,
with significant contributions from O+2 and C+. In the mass-per-charge
range 23-36 amu/e there was a clear contribution by molecular ions. The
composition is tracked on a daily basis and shows variations. There
are also temporal variations in the speed distribution profiles. An
abrupt decrease in the water-group ion intensity coincided with the
passage of an interplanetary coronal mass ejection (ICME). STB/SECCHI
imaged this same ICME as it interacted with the comet, observing a
comet tail disconnection event. An opportunity for another comet tail
passage by STEREO will occur with comet ISON in late November 2013. This
comet's orbital plane is not near the ecliptic, hence this encounter,
if it occurs, will be a shorter duration. Using the tools developed
for the Elenin encounter, we will search for the ISON signatures in
the in-situ data set and present any preliminary results available.
---------------------------------------------------------
Title: Inner Heliospheric Evolution of a "Stealth" CME Derived from
Multi-view Imaging and Multipoint in Situ observations. I. Propagation
to 1 AU
Authors: Nieves-Chinchilla, T.; Vourlidas, A.; Stenborg, G.; Savani,
N. P.; Koval, A.; Szabo, A.; Jian, L. K.
2013ApJ...779...55N Altcode: 2013arXiv1311.6895N
Coronal mass ejections (CMEs) are the main driver of space
weather. Therefore, a precise forecasting of their likely
geo-effectiveness relies on an accurate tracking of their morphological
and kinematical evolution throughout the interplanetary medium. However,
single viewpoint observations require many assumptions to model
the development of the features of CMEs. The most common hypotheses
were those of radial propagation and self-similar expansion. The use
of different viewpoints shows that, at least for some cases, those
assumptions are no longer valid. From radial propagation, typical
attributes that can now be confirmed to exist are over-expansion and/or
rotation along the propagation axis. Understanding the 3D development
and evolution of the CME features will help to establish the connection
between remote and in situ observations, and hence help forecast space
weather. We present an analysis of the morphological and kinematical
evolution of a STEREO-B-directed CME on 2009 August 25-27. By means of
a comprehensive analysis of remote imaging observations provided by the
SOHO, STEREO, and SDO missions, and in situ measurements recorded by
Wind, ACE, and MESSENGER, we prove in this paper that the event exhibits
signatures of deflection, which are usually associated with changes in
the direction of propagation and/or also with rotation. The interaction
with other magnetic obstacles could act as a catalyst of deflection or
rotation effects. We also propose a method to investigate the change of
the CME tilt from the analysis of height-time direct measurements. If
this method is validated in further work, it may have important
implications for space weather studies because it will allow for
inference of the interplanetary counterpart of the CME's orientation.
---------------------------------------------------------
Title: A Plasma β Transition within a Propagating Flux Rope
Authors: Savani, N. P.; Vourlidas, A.; Shiota, D.; Linton, M. G.;
Kusano, K.; Lugaz, N.; Rouillard, A. P.
2013ApJ...779..142S Altcode: 2013arXiv1310.4747S
We present a 2.5 dimensional magnetohydrodynamic simulation of a
magnetic flux rope (FR) propagating in the heliosphere and investigate
the cause of the observed sharp plasma β transition. Specifically,
we consider a strong internal magnetic field and an explosive fast
start, such that the plasma β is significantly lower in the FR
than in the sheath region that is formed ahead. This leads to an
unusual FR morphology in the first stage of propagation, while the
more traditional view (e.g., from space weather simulations like
Enlil) of a pancake-shaped FR is observed as it approaches 1 AU. We
investigate how an equipartition line, defined by a magnetic Weber
number, surrounding a core region of a propagating FR, can demarcate a
boundary layer where there is a sharp transition in the plasma β. The
substructure affects the distribution of toroidal flux, with the
majority of the flux remaining in a small core region that maintains
a quasi-cylindrical structure. We quantitatively investigate a locus
of points where the kinetic energy density of the relative inflow
field is equal to the energy density of the transverse magnetic field
(i.e., effective tension force). The simulation provides compelling
evidence that at all heliocentric distances the distribution of
toroidal magnetic flux away from the FR axis is not linear, with 80%
of the toroidal flux occurring within 40% of the distance from the
FR axis. Thus, our simulation displays evidence that the competing
ideas of a pancaking structure observed remotely can coexist with a
quasi-cylindrical magnetic structure seen in situ.
---------------------------------------------------------
Title: Quantitative comparison of methods for predicting the arrival
of coronal mass ejections at Earth based on multiview imaging
Authors: Colaninno, R. C.; Vourlidas, A.; Wu, C. C.
2013JGRA..118.6866C Altcode: 2013arXiv1310.6680C
We investigate the performance of six methods for predicting the
coronal mass ejection (CME) time of arrival (ToA) and velocity at
Earth using a sample of nine Earth-impacting CMEs between March 2010
and June 2011. The CMEs were tracked continuously from the Sun to near
Earth in multiviewpoint imaging data from STEREO Sun-Earth Connection
Coronal and Heliospheric Investigation (SECCHI) and SOHO Large Angle
and Spectroscopic Coronagraph (LASCO). We use the Graduate Cylindrical
Shell model to estimate the three-dimensional direction and height
of the CMEs in every image out to ∼200R<SUB>⊙</SUB>. We fit the
derived three-dimensional (deprojected) height and time (HT) data
with six different methods to extrapolate the CME ToA and velocity at
Earth. We compare the fitting results with the in situ data from the
Wind spacecraft. We find that a simple linear fit above a height of
50R<SUB>⊙</SUB> gives the ToA with an error ±6h for seven (78%)
of the CMEs. For the full sample, we are able to predict the ToA to
within ±13h. These results are a half day improvement over past CME
arrival time methods that only used SOHO LASCO data. We conclude that
heliographic height-time measurements of the CME front made away from
the Sun-Earth line and beyond the coronagraphic field of view are
sufficient for reasonably accurate predictions of their ToA.
---------------------------------------------------------
Title: Solar Eruptive Events (SEE) 2020 Mission Concept
Authors: Lin, R. P.; Caspi, A.; Krucker, S.; Hudson, H.; Hurford,
G.; Bandler, S.; Christe, S.; Davila, J.; Dennis, B.; Holman, G.;
Milligan, R.; Shih, A. Y.; Kahler, S.; Kontar, E.; Wiedenbeck, M.;
Cirtain, J.; Doschek, G.; Share, G. H.; Vourlidas, A.; Raymond, J.;
Smith, D. M.; McConnell, M.; Emslie, G.
2013arXiv1311.5243L Altcode:
Major solar eruptive events (SEEs), consisting of both a large flare and
a near simultaneous large fast coronal mass ejection (CME), are the most
powerful explosions and also the most powerful and energetic particle
accelerators in the solar system, producing solar energetic particles
(SEPs) up to tens of GeV for ions and hundreds of MeV for electrons. The
intense fluxes of escaping SEPs are a major hazard for humans in space
and for spacecraft. Furthermore, the solar plasma ejected at high speed
in the fast CME completely restructures the interplanetary medium
(IPM) - major SEEs therefore produce the most extreme space weather
in geospace, the interplanetary medium, and at other planets. Thus,
understanding the flare/CME energy release process(es) and the related
particle acceleration processes are major goals in Heliophysics. To
make the next major breakthroughs, we propose a new mission concept,
SEE 2020, a single spacecraft with a complement of advanced new
instruments that focus directly on the coronal energy release and
particle acceleration sites, and provide the detailed diagnostics of
the magnetic fields, plasmas, mass motions, and energetic particles
required to understand the fundamental physical processes involved.
---------------------------------------------------------
Title: Origins of Rolling, Twisting, and Non-radial Propagation of
Eruptive Solar Events
Authors: Panasenco, Olga; Martin, Sara F.; Velli, Marco; Vourlidas,
Angelos
2013SoPh..287..391P Altcode: 2012arXiv1211.1376P; 2012SoPh..tmp..321P
We demonstrate that major asymmetries in erupting filaments and CMEs,
namely major twists and non-radial motions are typically related to
the larger-scale ambient environment around eruptive events. Our
analysis of prominence eruptions observed by the STEREO, SDO, and
SOHO spacecraft shows that prominence spines retain, during the
initial phases, the thin ribbon-like topology they had prior to
the eruption. This topology allows bending, rolling, and twisting
during the early phase of the eruption, but not before. The combined
ascent and initial bending of the filament ribbon is non-radial
in the same general direction as for the enveloping CME. However,
the non-radial motion of the filament is greater than that of the
CME. In considering the global magnetic environment around CMEs,
as approximated by the Potential Field Source Surface (PFSS) model,
we find that the non-radial propagation of both erupting filaments and
associated CMEs is correlated with the presence of nearby coronal holes,
which deflect the erupting plasma and embedded fields. In addition,
CME and filament motions, respectively, are guided towards weaker
field regions, namely null points existing at different heights in
the overlying configuration. Due to the presence of the coronal hole,
the large-scale forces acting on the CME may be asymmetric. We find
that the CME propagates usually non-radially in the direction of least
resistance, which is always away from the coronal hole. We demonstrate
these results using both low- and high-latitude examples.
---------------------------------------------------------
Title: Study of a Coronal Mass Ejection with SOHO/UVCS and STEREO data
Authors: Susino, Roberto; Bemporad, Alessandro; Dolei, Sergio;
Vourlidas, Angelos
2013AdSpR..52..957S Altcode:
We study the 3-D kinematics of a Coronal Mass Ejection (CME) using
data acquired by the LASCO C2 and UVCS instruments on board SOHO, and
the COR1 coronagraphs and EUVI telescopes on board STEREO. The event,
which occurred on May 20, 2007, was a partial-halo CME associated
with a prominence eruption. This is the first CME studied with UVCS
data that occurred in the STEREO era. The longitudinal angle between
the STEREO spacecrafts was ∼7.7° at that time, and this allowed us
to reconstruct via triangulation technique the 3-D trajectory of the
erupting prominence observed by STEREO/EUVI. Information on the 3-D
expansion of the CME provided by STEREO/COR1 data have been combined
with spectroscopic observations by SOHO/UVCS. First results presented
here show that line-of-sight velocities derived from spectroscopic
data are not fully in agreement with those previously derived via
triangulation technique, thus pointing out possible limitations of
this technique.
---------------------------------------------------------
Title: Shock formation characteristics in the low corona from type
II radio bursts
Authors: Kouloumvakos, A.; Preka-Papadema, P.; Vourlidas, A.; Moussas,
X.; Hillaris, A.; Tsitsipis, P.; Kontogeorgos, A.
2013hell.confS..19K Altcode:
In this analysis we have identified the formation of coronal shock
waves from 2007 to 2011, using as proxies the type II radio bursts
from radio spectrograph ARTEMIS-IV and RSTN. For the 42 events we have
identified, we combined data from STEREO, SOHO/LASCO και SDO with
the characteristics of the composite radio spectra to investigate
the properties of the type II formation with the associated flares
and CMEs. From the timings between the flare, the CME onset, the HXR
peak and the type II start, we grouped the type IIs into separate
categories. We found that in most of the cases the type II radio burst
starts at the flare maximum phase and particularly in 60% of the cases
at the HXR maximum. All the characteristics of the type IIs obtained
from their spectrum (duration, df, df/dt). We compared the computed
velocities of the type IIs, using deferent density models, with the
observed speeds of the CMEs from STEREO and SOHO/LASCO. Finally,
from the composite radio spectra we associated the type II with the
occurrence of other transient radio emissions such as, radio bursts
type III or IV.
---------------------------------------------------------
Title: 'Hurricane Season' in the Inner Heliosphere: Observations of
Coronal Mass
Authors: Vourlidas, A.
2013hell.conf....2V Altcode:
The current solar cycle, albeit low in sunspot numbers, is not lacking
in coronal explosive activity. The solar corona has produced several
spectacular Coronal Mass Ejections (CMEs) directed at Earth and other
planets. In addition, this is the first time in human history that we
are able to image continuously the full 360 degree corona and the full
inner heliosphere from the Sun to Earth, and beyond. In addition, a
host of inner heliospheric spacecraft can directly probe the quiescent
and transient solar wind at several locations around Mercury, Venus,
Earth, and Mars. These unprecedented observational capabilities offer
us a unique opportunity to study the solar maximum activity and in
particular CMEs and their impact on Earth and the other planets. The
new field of Interplanetary Space Weather is being born. In this talk,
I review our progress (sometimes) and befuddlement (more often) towards
understanding the evolution of CMEs in the inner heliosphere. I discuss
how this knowledge is shaping Space Weather efforts around the world,
including a comprehensive approach from a large group of Greek solar
and space physicists under the THALIS aegis. I will also present ideas
for future missions and instrumentation to improve our Space Weather
predictive capabilities.
---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption
within the Framework of the
Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou,
K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.;
Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema,
P.; Sarris, M.; Sarris, T.
2013hell.conf...10P Altcode:
Transient expulsions of gigantic clouds of solar coronal plasma into
the interplanetary space in the form of Coronal Mass Ejections (CMEs)
and sudden, intense flashes of electromagnetic radiation, solar flares,
are well-established drivers of the variable Space Weather. Given the
innate, intricate links and connections between the solar drivers and
their geomagnetic effects, synergistic efforts assembling all pieces
of the puzzle along the Sun-Earth line are required to advance our
understanding of the physics of Space Weather. This is precisely the
focal point of the Hellenic National Space Weather Research Network
(HNSWRN) under the THALIS Programme. Within the HNSWRN framework,
we present here the first results from a coordinated multi-instrument
case study of a major solar eruption (X5.4 and X1.3 flares associated
with two ultra-fast (>2000 km/s) CMEs) which were launched early
on 7 March 2012 and triggered an intense geomagnetic storm (min Dst
=-147 nT) approximately two days afterwards. Several elements of
the associated phenomena, such as the flare and CME, EUV wave, WL
shock, proton and electron event, interplanetary type II radio burst,
ICME and magnetic cloud and their spatiotemporal relationships and
connections are studied all way from Sun to Earth. To this end, we
make use of satellite data from a flotilla of solar, heliospheric and
magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE,
Herschel, Planck and INTEGRAL). We also present our first steps toward
formulating a cohesive physical scenario to explain the string of the
observables and to assess the various physical mechanisms than enabled
and gave rise to the significant geoeffectiveness of the eruption.
---------------------------------------------------------
Title: Analysis of the Deflection of CMEs by Coronal Magnetic Fields
Authors: Liewer, Paulett C.; Panasenco, O.; Vourlidas, A.
2013SPD....4410103L Altcode:
Understanding coronal influences on the direction of propagation
of CMEs is important for space weather prediction. It is well known
that CMEs often propagate non-radially, e.g., they do not move out
radially from the location of the solar source (see, e.g., Cremades
and Bothmer, A&A, 2004; Panasenco et al., Sol. Phys. 2013). There
is evidence that most CMEs exit the corona in the minimum field
region surrounding the coronal/heliospheric current sheet (HCS). If
this is the case, then the degree of deflection should reflect the
distance of the source region from the current sheet region. Here
we study the observed deflection in latitude of four CMEs using
STEREO/SECCHI’s EUV and white light observations to trace the
deflection. A potential-field source surface (PFSS) model (Schrijver
& DeRosa, Sol. Phys. 2003) is used to give information on the
magnetic forces acting on the CME at different heights in the lower
corona. This model, as well as the PFSS model results at the GONG
website (http://gong.nso.edu/data/magmap/archive.html) and the
coronal observations from STEREO, are used to try to determine the
location of the HCS. For the events studied, we find cases when the
deflection is gradual (occurring between the surface at several solar
radii) and cases where the deflection is immediate (within ~1.5 solar
radii). There are many cases in the literature where CMEs originating
at high latitude are deflected towards the ecliptic and eventually
impact Earth. Several of the CMEs we analyzed were later detected in
situ at ~1 AU and we compare the near-Sun trajectory information to
the trajectory information determine from the in situ information.
---------------------------------------------------------
Title: A Fractionated Space Weather Base at L5 using CubeSats and
Solar Sails
Authors: Liewer, Paulett C.; Klesh, A.; Lo, M.; Murphy, N.; Staehle,
R. L.; Vourlidas, A.; Cutler, J. W.; Lightsey, G.
2013SPD....44..151L Altcode:
The Sun-Earth L5 Lagrange point is an ideal location for an operational
space weather mission to provide early warning of Earth-directed
solar storms (CMEs, shocks and associated solar energetic particles)
so the effects on power grids, spacecraft and communications systems
can be mitigated. Such missions have been proposed using conventional
spacecraft and chemical propulsion at costs of hundreds of millions
of dollars. Here we describe a mission that can accomplish the
goals at a much lower cost by dividing the payload among a cluster
of interplanetary CubeSats that reach orbits around L5 using solar
sails. The ascendancy of CubeSats has brought renewed interest in solar
sail propulsion because sail area scales directly with spacecraft
mass. The concept presented here draws heavily on a NIAC study
(Staehle et al., AIAA, 2012) that developed a 6U CubeSat architecture
for interplanetary missions. This study allocated 2U for a solar sail;
the sail system was based on the Planetary Society’s LightSail-1TM
architecture. At a recent workshop on small satellites, hosted by
the Keck Institute for Space Studies, a concept was developed for a
fractionated Space Weather Base (SWB) at L5. In this concept, a loose
formation of CubeSats, each ~6U in size and each carrying a portion of
the science payload, can accomplish, at a much reduced cost, many of
the goals of a conventional single-spacecraft L5 mission, as described
in the 2013 NRC Solar and Space Physics Decadal report. Each of the
small ~6U interplanetary CubeSats reaches an orbit around L5 using its
own solar sail of approximately 64 m2 which fits in ~2U. Key to the
mission is that only one of the CubeSats carries a high-gain antenna
and other hardware necessary for sending high-rate science data to
Earth. The other CubeSats, in addition to carrying one or two science
instruments, carry a much smaller communication system to send the
science data to the communication hub and low-rate engineering data
to Earth. The SWB-L5 mission can later be expanded incrementally to
add new instruments and new objectives by sending additional small
spacecraft to the L5 base. The mission described below represents a
potential beginning for a permanent space warning system at L5.
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Title: SDO Observations of Solar Jets
Authors: Moschou, S. P.; Tsinganos, K.; Vourlidas, A.; Archontis, V.
2013SoPh..284..427M Altcode: 2012SoPh..tmp..310M
We present an analysis of high cadence observations of solar jets
observed in the Extreme Ultraviolet (EUV), at 304 Å, with the
Atmospheric Imaging Assembly instrument aboard the Solar Dynamics
Observatory (SDO). The jets in our sample lie very close to the solar
limb to minimize projection effects. Two of the events show clear
helical patterns during ejection. We also find that some of the jets
are recurrent and that most of them cannot overcome solar gravity.
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Title: Solar energetic particles and their variability from the sun
and beyond
Authors: Mewaldt, R. A.; Cohen, C. M. S.; Mason, G. M.; von Rosenvinge,
T. T.; Leske, R. A.; Luhmann, J. G.; Odstrcil, D.; Vourlidas, A.
2013AIPC.1539..116M Altcode:
With the onset of solar cycle 24 activity STEREO and near-Earth
spacecraft are now measuring many multi-spacecraft solar particle
events. We present examples of time-intensity distributions, energy
spectra, fits to longitude distributions, a combined imaging/in-situ
study, and MHD modeling of one event. Implications of these new results
are discussed.
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Title: A plasma beta transition within a propagating CME leading to
a magnetic substructure
Authors: Savani, Neel P.; Vourlidas, A.; Shiota, D.; Linton, M.;
Kusano, K.; Lugaz, N.; Rouillard, A. P.
2013shin.confE.149S Altcode:
We present a study of how a sharp transition in the plasma beta within
a simulated flux rope (FR) affects the distribution of toriodal flux
within the obstacle. Specifically, we consider a 2.5D MHD simulation of
a magnetic FR with a strong internal magnetic field and an explosive
fast start. Qualitatively the overall effects show that the sharp
boundary of the low-to-high plasma beta within the outer segment of
a flux rope leads to layers of magnetic flux 'peeling' off the main
body. This leads to an unusual flux rope morphology in the first stage
of propagation, while the more traditional view of a 'pancake' shaped
FR is observed as it approaches 1AU. However the simulation provides
compelling evidence that at all heliocentric distances the distribution
of magnetic flux away from the FR axis is not linear; with 80% of the
flux occurring within 40% of the distance from the FR axis. Thus our
simulation shows that the competing ideas of a pancaking structure
observed remotely can coexist with a quasi-cylindrical magnetic
structure seen in situ.
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Title: A Comparison of the Intensities and Energies of Gradual Solar
Energetic Particle Events with the Dynamical Properties of Associated
Coronal Mass Ejections
Authors: Kahler, S. W.; Vourlidas, A.
2013ApJ...769..143K Altcode:
Gradual solar energetic particle (SEP) events observed at
1 AU are produced by shocks driven by coronal mass ejections
(CMEs). Characterizations of the remotely imaged CMEs and of their
associated SEP events observed in situ can be used to increase our
ability to forecast SEP events and to understand better the physical
connections between the two phenomena. We carry out a statistical
comparison of the peak intensities Ip20, of 120 western-hemisphere 20
MeV SEP events with those of their associated CMEs observed by the Solar
and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph
over the past solar cycle. For a subset of 96 events observed with
the EPACT instrument on the Wind spacecraft we also compare the SEP
2 MeV peak intensities Ip2, power-law energy spectral exponents γ,
total SEP energies Esep, and 2 MeV nuc<SUP>-1</SUP> H/He ratios with
CME properties. New analyses of white-light CME images enable us to
improve calculations of the CME masses and potential energies and then
to determine two values of their kinetic energies based on frontal V
(fr) and center-of-mass V (cm) speeds. Despite considerable scatter
in the SEP and CME data, the large dynamical ranges of both the SEP
and CME parameters allow us to determine statistical trends in the
comparisons of the logs of the parameters. Ip2, Ip20, and Esep are
significantly correlated with CME kinetic energies, masses, and speeds,
while γ trends lower (harder). Those correlations are higher with V
(fr) than with V (cm) parameters, indicating a less significant role for
the body of the CME than for the CME front in SEP production. The high
ratios (>=10%) of Esep to CME energies found by Mewaldt et al. are
confirmed, and the fits are consistent with a linear relationship
between the two energies. The 2 MeV nuc<SUP>-1</SUP> H/He ratios
decrease with increasing CME speeds, which may be an effect of shock
geometry. We discuss several factors that limit the estimates of both
the SEP and CME energies.
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Title: The arrival of coronal mass ejections at Earth
Authors: Colaninno, Robin C.; Vourlidas, A.; Wu, C. C.
2013shin.confE.148C Altcode:
We analyze nine Earth-impacting CMEs which we track continuously
from the the Sun to near Earth in imaging data. We use the Graduate
Cylindrical Shell (GCS) model to find the three-dimensional position
of the CMEs in all the imaging data. We fit the height and time data
derived from the GCS model with six different method to extrapolate
the CME arrival time and velocity at Earth. We compare the results of
our fit methods with the in situ data from the WIND spacecraft. We find
that assuming a constant velocity after a height of 50 Rsun gives the
best predict the arrival times with an error +-13 hours. For seven
of the CMEs, we are able to predict the arrival time to within +-6
hours. This is a significant improvement over using only LASCO images
to predict CME arrival times. However, we are still unable to reliably
predict the velocity of the CME when it arrives at Earth. Modeling
the kinematics of a CME is important for exploring the forces on the
CME and interaction with the solar wind.
---------------------------------------------------------
Title: Simulation of the Coronal Mass Ejection on 2011 March 7:
from Chromosphere to 1 AU
Authors: Jin, Meng; Manchester, Ward; van der Holst, Bart; Oran, Rona;
Sokolov, Igor; Toth, Gabor; Gombosi, Tamas I.; Vourlidas, Angelos;
Liu, Yang; Sun, Xudong
2013shin.confE...4J Altcode:
On 2011 March 7, a fast CME (> 2000 km/s) occurred in NOAA
11164. This event is also associated with a Solar Energetic Particle
(SEP) event. In this study, we present the magnetohydrodynamics
simulation results of this event by using the newly developed Alfven
Wave SOlar Model (AWSOM) in Space Weather Modeling Framework (SWMF). The
background solar wind starts from chromosphere with heat conduction
and radiative cooling. The solar wind is driven by Alfven-wave pressure
and heated by Alfven-wave dissipation. The magnetic field of the inner
boundary is specified with a synoptic magnetogram from SDO/HMI. We
initiate the CME by using the Gibson-Low flux rope model. In order to
produce physically correct CME structures and CME-driven shocks, the
electron and proton temperatures are separated so that the electron
heat conduction is explicitly treated in conjunction with proton
shock heating. We simulate the CME propagation to 1 AU. Comprehensive
validation work is done by using the remote as well as the in-situ
observation from SOHO, SDO, STEREOA/B, ACE, and WIND. Our results show
that the new model can reproduce most of the observed features near the
Sun and in the heliosphere. The CME-driven shock is well reproduced,
which is important for modeling the SEP event with diffusive shock
acceleration. We also try to compare the differences and similarities
between this event and previous simulated extreme events (e.g., the
2003 Halloween CMEs).
---------------------------------------------------------
Title: The Height Evolution of the "True" Coronal Mass Ejection Mass
derived from STEREO COR1 and COR2 Observations
Authors: Bein, B. M.; Temmer, M.; Vourlidas, A.; Veronig, A. M.;
Utz, D.
2013ApJ...768...31B Altcode: 2013arXiv1303.3372B
Using combined STEREO-A and STEREO-B EUVI, COR1, and COR2 data, we
derive deprojected coronal mass ejection (CME) kinematics and CME "true"
mass evolutions for a sample of 25 events that occurred during 2007
December to 2011 April. We develop a fitting function to describe the
CME mass evolution with height. The function considers both the effect
of the coronagraph occulter, at the beginning of the CME evolution,
and an actual mass increase. The latter becomes important at about
10-15 R <SUB>⊙</SUB> and is assumed to mostly contribute up to
20 R <SUB>⊙</SUB>. The mass increase ranges from 2% to 6% per R
<SUB>⊙</SUB> and is positively correlated to the total CME mass. Due
to the combination of COR1 and COR2 mass measurements, we are able to
estimate the "true" mass value for very low coronal heights (<3 R
<SUB>⊙</SUB>). Based on the deprojected CME kinematics and initial
ejected masses, we derive the kinetic energies and propelling forces
acting on the CME in the low corona (<3 R <SUB>⊙</SUB>). The
derived CME kinetic energies range between 1.0-66 × 10<SUP>23</SUP>
J, and the forces range between 2.2-510 × 10<SUP>14</SUP> N.
---------------------------------------------------------
Title: Tracking the momentum flux of a CME and quantifying its
influence on geomagnetically induced currents at Earth
Authors: Savani, N. P.; Vourlidas, A.; Pulkkinen, A.;
Nieves-Chinchilla, T.; Lavraud, B.; Owens, M. J.
2013SpWea..11..245S Altcode: 2013arXiv1303.2574S
We investigate a coronal mass ejection (CME) propagating toward
Earth on 29 March 2011. This event is specifically chosen for its
predominately northward directed magnetic field, so that the influence
from the momentum flux onto Earth can be isolated. We focus our study
on understanding how a small Earth-directed segment propagates. Mass
images are created from the white-light cameras onboard STEREO which
are also converted into mass height-time maps (mass J-maps). The mass
tracks on these J-maps correspond to the sheath region between the CME
and its associated shock front as detected by in situ measurements at
L1. A time series of mass measurements from the STEREO COR-2A instrument
is made along the Earth propagation direction. Qualitatively, this
mass time series shows a remarkable resemblance to the L1 in situ
density series. The in situ measurements are used as inputs into a
three-dimensional (3-D) magnetospheric space weather simulation from
the Community Coordinated Modeling Center. These simulations display
a sudden compression of the magnetosphere from the large momentum
flux at the leading edge of the CME, and predictions are made for
the time derivative of the magnetic field (dB/dt) on the ground. The
predicted dB/dt values were then compared with the observations from
specific equatorially located ground stations and showed notable
similarity. This study of the momentum of a CME from the Sun down to
its influence on magnetic ground stations on Earth is presented as a
preliminary proof of concept, such that future attempts may try to use
remote sensing to create density and velocity time series as inputs
to magnetospheric simulations.
---------------------------------------------------------
Title: Three-Dimensional Evolution of Erupted Flux Ropes from the Sun
(2 - 20 R <SUB>⊙</SUB>) to 1 AU
Authors: Isavnin, A.; Vourlidas, A.; Kilpua, E. K. J.
2013SoPh..284..203I Altcode: 2012arXiv1211.2108I
Studying the evolution of magnetic clouds entrained in coronal mass
ejections using in-situ data is a difficult task, since only a limited
number of observational points is available at large heliocentric
distances. Remote sensing observations can, however, provide important
information for events close to the Sun. In this work we estimate the
flux rope orientation first in the close vicinity of the Sun (2 - 20
R<SUB>⊙</SUB>) using forward modeling of STEREO/SECCHI and SOHO/LASCO
coronagraph images of coronal mass ejections and then in situ using
Grad-Shafranov reconstruction of the magnetic cloud. Thus, we are able
to measure changes in the orientation of the erupted flux ropes as they
propagate from the Sun to 1 AU. We present both techniques and use them
to study 15 magnetic clouds observed during the minimum following Solar
Cycle 23 and the rise of Solar Cycle 24. This is the first multievent
study to compare the three-dimensional parameters of CMEs from imaging
and in-situ reconstructions. The results of our analysis confirm earlier
studies showing that the flux ropes tend to deflect towards the solar
equatorial plane. We also find evidence of rotation on their travel
from the Sun to 1 AU. In contrast to past studies, our method allows
one to deduce the evolution of the three-dimensional orientation of
individual flux ropes rather than on a statistical basis.
---------------------------------------------------------
Title: Tracking the momentum flux of a CME and quantifying its
influence on geomagnetically induced currents at Earth
Authors: Savani, N. P.; Vourlidas, A.; Pulkkinen, A.;
Nieves-Chinchilla, T.; Lavraud, B.; Owens, M. J.
2013AGUSMSH21B..01S Altcode:
We investigate a CME propagating towards Earth on 29 March 2011. This
event is specifically chosen for its predominately northward directed
magnetic field, so that the influence from the momentum flux onto
Earth can be isolated. We focus our study on understanding how a
small Earth-directed segment propagates. Mass images are created from
the white-light cameras onboard STEREO which are also converted into
mass height-time maps (mass J-maps). The mass tracks on these J-maps
correspond to the sheath region between the CME and its associated shock
front as detected by in situ measurements at L1. A time-series of mass
measurements from the STEREO COR-2A instrument are made along the Earth
propagation direction. Qualitatively, this mass time-series shows a
remarkable resemblance to the L1 in situ density series. The in situ
measurements are used as inputs into a 3D magnetospheric space weather
simulation from CCMC. These simulations display a sudden compression
of the magnetosphere from the large momentum flux at the leading edge
of the CME and predictions are made for the time-derivative of the
magnetic field (dB/dt) on the ground. The predicted dB/dt were then
compared with observations from specific equatorially-located ground
stations and show notable similarity. This study of the momentum of a
CME from the Sun down to its influence on magnetic ground stations on
Earth is presented as preliminary proof of concept, such that future
attempts may try to use remote sensing to create density and velocity
time-series as inputs to magnetospheric simulations.
---------------------------------------------------------
Title: Observational Study of the Tridimensional Trajectory of Small
White-Light Transients in the Inner Solar Corona
Authors: Lopez-Portela, C.; Blanco-Cano, X.; Stenborg, G.; Vourlidas,
A.
2013AGUSMSH23A..02L Altcode:
The physical mechanisms responsible for the low corona origin
and subsequent interplanetary development of the small scale
white-light transients, known as blobs, is relevant to the formation
and acceleration mechanisms of the slow solar wind (Sheeley et al.,
1997). Since they are considered to be reliable tracers of the slow
solar wind, a statistical kinematical characterization of these
faint features should provide to the understanding of its origins
and acceleration. The vantage observing points provided by the SECCHI
and LASCO imagers aboard the STEREO and SOHO missions, respectively,
allows us to get a good estimation of their trajectory in the 3D space
and hence perform a detailed analysis of their unprojected kinematical
parameters. To address this issue, we have surveyed the SOHO/LASCO C2
and C3, and the STEREO/SECCHI COR 1 and COR 2 databases for the year
2007 through 2010 (i.e., a period comprising the declining phase of
the extended past solar minimum and the ascending phase of cycle 24)
and selected about 100 blob-like features. The selection of events
was facilitated by the scarce presence of coronal mass ejection
events during this period, and it was limited to ±30° from the
Sun's equator. The restricted latitudinal range is inspired by the
work of Wang et al. (1998), who proposed that blobs are liberated from
the cusp of helmet steamers. Two methods have been considered for the
determination of the 3D kinematical parameters: (1) the tie-pointing and
triangulation technique (Thompson W.T., 2008) and (2) the Height-Time
analysis as developed by Mierla et al. (2008). In this work, we report
on the set of transients studied by both techniques, discuss the
limitations encountered on the determination of the 3D trajectories,
and explore their significance on understanding the physical mechanisms
behind the generation/propagation of the slow solar wind.
---------------------------------------------------------
Title: CME - Solar Wind interaction using remote and in-situ
observations
Authors: Nieves-Chinchilla, T.; Stenborg, G.; Vourlidas, A.; Savani,
N. P.; Hidalgo, M. A.; Vena, L.; Szabo, A.; Colaninno, R. C.
2013AGUSMSH23B..05N Altcode:
Coronal mass ejections (CMEs) are the main drivers of Space
Weather. Accurate forecasting of their likely geo-effectiveness requires
accurate tracking of their morphological and kinematical evolution
throughout the interplanetary medium. However, single view-point
observations depend on strong assumptions to model the development of
the CME; the most common hypotheses are those of radial propagation and
self-similar expansion. The use of different view-points show that, at
least for some cases, those assumptions may not be valid. Analyses of
remote sensing and in-situ data show signatures of strong deflection,
over-expansion and/or large deformation. These behaviors could hide
effects as rotation, deviation from radial propagation, or interaction
with other magnetic obstacles. Understanding the 3D development and
evolution of CME features is therefore of utmost importance to help
establish the connection between remote and in-situ observations,
and hence improve forecasting of Space Weather. In this work, we
present the analysis of a set of selected events exhibiting clear
signatures of deflection. With the help of remote imaging observations
provided by the SOHO, STEREO and SDO missions, and in-situ measurements
recorded by Wind, ACE, and Messenger. We show that such signatures are
evidence of hidden effects such as rotation, changes in the direction
of propagation, and/or interaction with other magnetic obstacles.
---------------------------------------------------------
Title: How Many CMEs Have Flux Ropes? Deciphering the Signatures
of Shocks, Flux Ropes, and Prominences in Coronagraph Observations
of CMEs
Authors: Vourlidas, A.; Lynch, B. J.; Howard, R. A.; Li, Y.
2013SoPh..284..179V Altcode: 2012arXiv1207.1599V
We intend to provide a comprehensive answer to the question on whether
all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve
this, we present a synthesis of the LASCO CME observations over the
last 16 years, assisted by 3D MHD simulations of the breakout model,
EUV and coronagraphic observations from STEREO and SDO, and statistics
from a revised LASCO CME database. We argue that the bright loop
often seen as the CME leading edge is the result of pileup at the
boundary of the erupting flux rope irrespective of whether a cavity
or, more generally, a three-part CME can be identified. Based on
our previous work on white light shock detection and supported
by the MHD simulations, we identify a new type of morphology, the
`two-front' morphology. It consists of a faint front followed by
diffuse emission and the bright loop-like CME leading edge. We show
that the faint front is caused by density compression at a wave
(or possibly shock) front driven by the CME. We also present highly
detailed multi-wavelength EUV observations that clarify the relative
positioning of the prominence at the bottom of a coronal cavity with
a clear flux rope structure. Finally, we visually check the full LASCO
CME database for flux rope structures. In the process, we classify the
events into two clear flux rope classes (`three-part', and `Loop'),
jets and outflows (no clear structure). We find that at least 40 %
of the observed CMEs have clear flux rope structures and that ∼ 29 %
of the database entries are either misidentifications or inadequately
measured and should be discarded from statistical analyses. We propose
a new definition for flux rope CMEs (FR-CMEs) as a coherent magnetic,
twist-carrying coronal structure with angular width of at least
40<SUP>∘</SUP> and able to reach beyond 10 R<SUB>⊙</SUB> which
erupts on a time scale of a few minutes to several hours. We conclude
that flux ropes are a common occurrence in CMEs and pose a challenge
for future studies to identify CMEs that are clearly not FR-CMEs.
---------------------------------------------------------
Title: On the relationship between interplanetary coronal mass
ejections and magnetic clouds
Authors: Kilpua, Emilia; Isavnin, Alexey; Vourlidas, Angelos; Koskinen,
Hannu; Rodriguez, Luciano
2013EGUGA..15.2827K Altcode:
The relationship of magnetic clouds (MCs) to interplanetary coronal
mass ejections (ICMEs) is still an open issue in space research. The
view that all ICMEs would originate as magnetic flux ropes has received
increasing attention, although near the orbit of the Earth only about
one-third of ICMEs show clear MC signatures and often the MC occupies
only a portion of the ICME. We have performed a systematic comparison
of the cases where ICME and MC signatures coincided and where ICME
signatures extended significantly beyond the MC boundaries. We found
clear differences in the ICME properties (eg., speed, magnetic field
magnitude), in the ambient solar wind structure, and in the solar
cycle dependence for these two event types. We show that the MC and
the regions of ICME-related plasma in front and behind the MC have
all distinct characteristics enforcing the conception that they have
intrinsically different origin or evolve differently. Erosion of
magnetic flux in front of the ICME may also reconfigure the initial
three-part CME seen in white-light images to a more complex ICME,
but the geometrical effect (i.e. the encounter through the CME leg
and/or far from the flux rope center) has little contribution to the
observed mismathch in the MC and ICME boundary times. We will also
discuss ramifications to CME and space weather research.
---------------------------------------------------------
Title: Probing the origin of solar energetic particles by combining
solar and heliospheric imagery with in-situ measurements from
the STEREO spacecraft (Arne Richter Award for Outstanding Young
Scientists Lecture)
Authors: Rouillard, Alexis P.; Tylka, Allan; Vourlidas, Angelos; Ng,
Chee K.
2013EGUGA..1513908R Altcode:
The Solar-Terrestrial Relations Observatory (STEREO), launched in 2006,
is equipped with cameras that are observing the Sun and heliosphere
from two vantage points. The orbital configuration of the spacecraft
reached in 2011-2012 provides an unprecedented opportunity to track
the expansion of Coronal Mass Ejections and their associated pressure
waves in 3-D. We will present a series of analyses that combine
ultraviolet and white-light images obtained by STEREO and the Solar
Dynamics Observatory (SDO) to track, in the lower corona, the spatial
and temporal evolution of pressure waves associated with the onset
of CMEs. We use in-situ measurements of the onset of solar energetic
particle events (SEPs) to determine their release time near the Sun. We
concentrate on the proton-rich events detected by the near-Earth
spacecraft and the STEREOs during 2011 and 2012. We use a simple model
of the distribution of interplanerary magnetic field lines to determine
the footpoint locations of field lines connecting the lower corona to
the points of in-situ measurements. We (1) determine the height and
spatial extent of the pressure waves at the SEP release times, (2)
compare the longitudinal extent of SEP events with the extent of the
pressure waves, (3) compare the kinematic properties of pressure waves
launched over widely separated longitudes. We discuss the successes
and challenges faced when interpreting these observations in terms of
the acceleration of particles at coronal shocks.
---------------------------------------------------------
Title: Three-dimensional evolution of ejected flux ropes from the
Sun to 1 AU
Authors: Isavnin, Alexey; Vourlidas, Angelos; Kilpua, Emilia K. J.
2013EGUGA..15.3239I Altcode:
Studying the evolution of magnetic clouds entrained in coronal
mass ejections using in-situ data is a difficult task since only
a limited number of observational points is available at large
heliocentric distances. Remote sensing observations can, however,
provide important information for events close to the Sun. In this
work we estimate the flux rope orientation first by studying the
associated prominences and/or post-eruptive arcades using STEREO/EUVI
and SOHO/EIT observations, then in the close vicinity of the Sun using
forward modeling of STEREO/SECCHI and SOHO/LASCO coronagraph images
of coronal mass ejections and, finally, in-situ using Grad-Shafranov
reconstruction of the magnetic cloud at 1 AU. We show that it is
possible to reconstruct the three-dimensional orientation and geometry
of the flux rope in each of these three stages of its evolution. Thus,
we are able to measure changes in the orientation of the erupted
flux ropes as they propagate from the Sun to 1 AU. In contrast to
past studies, our method allows one to deduce the evolution of the
three-dimensional orientation of individual flux ropes rather than on
a statistical basis. We study 15 magnetic clouds observed during the
minimum following Solar Cycle 23 and the rise of Solar Cycle 24. The
results of our analysis confirm earlier studies showing that the flux
ropes tend to deflect towards the solar equatorial plane. We also
find evidence of rotation on their travel from the Sun to 1 AU. We
further compare the orientations of the studied flux ropes with the
local orientation of the heliospheric current sheet using global MHD
simulations of the solar corona.
---------------------------------------------------------
Title: Tracking the momentum flux of a CME and quantifying its
influence on geomagnetically induced currents at Earth
Authors: Savani, Neel; Vourlidas, Angelos; Pullkinen, Antti
2013EGUGA..15.2314S Altcode:
We investigate a CME propagating towards Earth on 29 March 2011. This
event is specifically chosen for its predominately northward directed
magnetic field, so that the influence from the momentum flux onto
Earth can be isolated. We focus our study on understanding how a
small Earth-directed segment propagates. Mass images are created from
the white-light cameras onboard STEREO which are also converted into
mass height-time maps (mass J-maps). The mass tracks on these J-maps
correspond to the sheath region between the CME and its associated shock
front as detected by in situ measurements at L1. A time-series of mass
measurements from the STEREO COR-2A instrument are made along the Earth
propagation direction. Qualitatively, this mass time-series shows a
remarkable resemblance to the L1 in situ density series. The in situ
measurements are used as inputs into a 3D magnetospheric space weather
simulation from CCMC. These simulations display a sudden compression
of the magnetosphere from the large momentum flux at the leading edge
of the CME and predictions are made for the time-derivative of the
magnetic field (dB/dt) on the ground. The predicted dB/dt were then
compared with observations from specific equatorially-located ground
stations and show notable similarity. This study of the momentum of a
CME from the Sun down to its influence on magnetic ground stations on
Earth is presented as preliminary proof of concept, such that future
attempts may try to use remote sensing to create density and velocity
time-series as inputs to magnetospheric simulations.
---------------------------------------------------------
Title: Derivation of the Magnetic Field in a Coronal Mass Ejection
Core via Multi-frequency Radio Imaging
Authors: Tun, Samuel D.; Vourlidas, A.
2013ApJ...766..130T Altcode:
The magnetic field within the core of a coronal mass ejection (CME)
on 2010 August 14 is derived from analysis of multi-wavelength radio
imaging data. This CME's core was found to be the source of a moving
type IV radio burst, whose emission is here determined to arise
from the gyrosynchrotron process. The CME core's true trajectory,
electron density, and line-of-sight depth are derived from stereoscopic
observations, constraining these parameters in the radio emission
models. We find that the CME carries a substantial amount of mildly
relativistic electrons (E < 100 keV) in a strong magnetic field (B
< 15 G), and that the spectra at lower heights are preferentially
suppressed at lower frequencies through absorption from thermal
electrons. We discuss the results in light of previous moving type
IV burst studies, and outline a plan for the eventual use of radio
methods for CME magnetic field diagnostics.
---------------------------------------------------------
Title: CME propagation analysis using remote and in-situ observations
Authors: Nieves-Chinchilla, Teresa; Stenborg, Guillermo; Vourlidas,
Angelos; Savani, Neel P.; Hidalgo, Miguel A.; Vena, Luis A.; Szabo,
Adam; Colaninno, Robin C.
2013enss.confE..50N Altcode:
Coronal mass ejections (CMEs) are the main drivers of Space
Weather. Accurate forecasting of their likely geo-effectiveness requires
accurate tracking of their morphological and kinematical evolution
throughout the interplanetary medium. However, single view-point
observations depend on strong assumptions to model the development of
the CME; the most common hypotheses are those of radial propagation and
self-similar expansion. The use of different view-points show that, at
least for some cases, those assumptions may not be valid. Analyses of
remote sensing and in-situ data show signatures of strong deflection,
over-expansion and/or large deformation. These behaviors could hide
effects as rotation, deviation from radial propagation, or interaction
with other magnetic obstacles. Understanding the 3D development and
evolution of CME features is therefore of utmost importance to help
establish the connection between remote and in-situ observations,
and hence improve forecasting of Space Weather. In this work, we
present the analysis of a set of selected events exhibiting clear
signatures of deflection. With the help of remote imaging observations
provided by the SOHO, STEREO and SDO missions, and in-situ measurements
recorded by Wind, ACE, and Messenger. We show that such signatures are
evidence of hidden effects such as rotation, changes in the direction
of propagation, and/or interaction with other magnetic obstacles.
---------------------------------------------------------
Title: First direct EUV observation and multi-temperature analysis
of a coherent, wave-like propagating disturbance along pseudo-open
field lines above a sunspot
Authors: Stenborg, Guillermo; Stekel, Tardelli; Vourlidas, Angelos;
Howard, Russell
2013enss.confE..55S Altcode:
We report the first direct observation (along with a comprehensive
kinematical characterization) of a wave-like front recorded in
several SDO AIA channels. The front propagates coherently along a
bundle of pseudo-open field lines with origin on an active region
sunspot. Wavelet-processing of AIA images makes the wave-like
disturbance clearly discernible with the naked eye. The disturbance
propagates with an average plane-of-sky phase velocity of 50 km/sec
in the 131 Å, 171 Å, 193 Å, 211 Å, 304 Å and 335 Å channels,
exhibiting a 3 min periodicity in all cases. Its origin could be
tracked down to a higher-than-average intensity point inside the umbra
of the corresponding spot (i.e., an umbral dot) observed in the 1600
Å and 1700 Å AIA channels. The intensity of the source oscillates in
phase with the wave-like phenomenon observed in the other channels. We
speculate on the magneto-acoustic nature of the wave.
---------------------------------------------------------
Title: Direct Evidence for a Fast Coronal Mass Ejection Driven by the
Prior Formation and Subsequent Destabilization of a Magnetic Flux Rope
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2013ApJ...764..125P Altcode: 2012arXiv1211.7211P
Magnetic flux ropes play a central role in the physics of coronal
mass ejections (CMEs). Although a flux-rope topology is inferred for
the majority of coronagraphic observations of CMEs, a heated debate
rages on whether the flux ropes pre-exist or whether they are formed
on-the-fly during the eruption. Here, we present a detailed analysis
of extreme-ultraviolet observations of the formation of a flux rope
during a confined flare followed about 7 hr later by the ejection of
the flux rope and an eruptive flare. The two flares occurred during
2012 July 18 and 19. The second event unleashed a fast (>1000 km
s<SUP>-1</SUP>) CME. We present the first direct evidence of a fast
CME driven by the prior formation and destabilization of a coronal
magnetic flux rope formed during the confined flare on July 18.
---------------------------------------------------------
Title: Multi-Spacecraft Observations of the Longitudinal Properties
of Solar Energetic Particle Events
Authors: Mewaldt, R. A.; Cohen, C. M.; Mason, G. M.; von Rosenvinge,
T. T.; Gomez-Herrero, R.; Vourlidas, A.; Wiedenbeck, M. E.
2012AGUFMSH23B..02M Altcode:
During the recent rise in solar activity, the twin STEREO spacecraft, in
combination with near-Earth assets (e.g., ACE, GOES, RHESSI, SDO, SOHO,
and Wind) have provided ~360° coverage of solar energetic particle
(SEP) events, coronal mass ejections (CMEs), shocks, and other aspects
of solar eruptions. This combination has provided an unprecedented
opportunity to observe how the properties of SEP events vary with
longitude. Initial results indicate that particles are distributed in
longitude more easily than was earlier appreciated. Indeed, most recent
large SEP events associated with CME-driven shocks are observed by both
STEREOs and ACE, even as these spacecraft are separated by >100° in
longitude. This talk will discuss longitudinal, intensity, composition,
and spectral variations of large SEP events and compare them with models
and previous studies. Small 3He-rich flares associated with flares and
coronal jets are also found to be distributed more broadly in longitude
than reported in single-point studies. Recent observations, issues, and
proposed explanations for SEP longitudinal variations will be reviewed.
---------------------------------------------------------
Title: Kinematics of Earth Impacting Coronal Mass Ejections
Authors: Colaninno, R. C.; Vourlidas, A.
2012AGUFMSH31A2210C Altcode:
With the data from the STEREO mission, we are able to continuously
monitor Coronal Mass Ejections (CMEs) as they progress from the Sun to
Earth. However, even with continuous monitoring with remote sensing
observations, we are still unable to accurately predict the arrival
or terrestrial impact of a CME. In this study, we analyze nine CMEs
from the Sun to Earth as observed in both the remote sensing and in
situ data sets. In this study, we track nine CMEs from the Sun to 70%
- 98% of the distance to Earth with the remote sensing data. We use the
Graduate Cyclical Shell (GCS) model to estimate the position of each CME
as it is observed in the inner heliosphere. From the derived kinematics,
we compare the predicted arrival times and impact velocities with the in
situ data. We consider different method for fitting the kinematics and
the modeled geometry of the CME to improve the predicted arrival time.
---------------------------------------------------------
Title: The relation between the properties of pressure variations
in the lower corona and solar energetic particle events
Authors: Rouillard, A. P.; Vourlidas, A.; Tylka, A. J.; Cohen, C. M.;
Mewaldt, R. A.; Mason, G. M.; Thernisien, A. F.
2012AGUFMSH24A..07R Altcode:
We combine ultraviolet and white-light images obtained by the Solar
Dynamics Observatory (SDO) and the Solar-Terrestrial Relations
Observatory (STEREO) to track, in the lower corona, the spatial and
temporal evolution of pressure waves associated with the onset of
Coronal Mass Ejections (CMEs). We use in-situ measurements of the onset
of solar energetic particle events (SEPs) to determine their release
time near the Sun. We concentrate on the proton-rich events detected
by the near-Earth spacecraft and the STEREOs during 2011 and 2012. We
use a simple model of the distribution of interplanerary magnetic field
lines to determine the foopoint locations of field lines connecting the
lower corona to the points of in-situ measurements. We (1) determine
the height and spatial extent of the pressure waves at the SEP release
times, (2) compare the longitudinal extent of SEP events with the
extent of the pressure waves, (3) compare the kinematic properties of
pressure waves launched over widely separated longitudes. We discuss
the successes and challenges faced when interpreting these observations
in terms of the acceleration of particles at coronal shocks.
---------------------------------------------------------
Title: Super-elastic collision of large-scale magnetized plasmoids
in the heliosphere
Authors: Shen, Chenglong; Wang, Yuming; Wang, Shui; Liu, Ying;
Liu, Rui; Vourlidas, Angelos; Miao, Bin; Ye, Pinzhong; Liu, Jiajia;
Zhou, Zhenjun
2012NatPh...8..923S Altcode: 2014arXiv1412.7375S
A super-elastic collision is an unusual process in which some mechanism
causes the kinetic energy of the system to increase. Most studies
have focused on solid-like objects, and have rarely considered
gases or liquids, as the collision of these is primarily a mixing
process. However, magnetized plasmoids are different from ordinary
gases--as cross-field diffusion is effectively prohibited--but it
remains unclear how they behave during a collision. Here we present
a comprehensive picture of a unique collision between two coronal
mass ejections in the heliosphere, which are the largest magnetized
plasmoids erupting from the Sun. Our analysis reveals that these two
magnetized plasmoids collided as if they were solid-like objects,
with a likelihood of 73% that the collision was super-elastic. The
total kinetic energy of the plasmoid system increased by about 6.6%
through the collision, significantly influencing its dynamics.
---------------------------------------------------------
Title: Super-elastic Collision between Two Coronal Mass Ejections
in the Heliosphere
Authors: Wang, Y.; Shen, C.; Wang, S.; Liu, Y.; Liu, R.; Vourlidas,
A.; Miao, B.; Liu, J.; Zhou, Z.
2012AGUFMSH21C..02W Altcode:
Super-elastic collision is an abnormal collisional process, in which
some particular mechanisms cause the kinetic energy of the system
increasing. Most studies in this aspect focus on solid-like objects,
but they rarely consider gases or liquids, as the collision of the
latter is primarily a mixing process. With cross-field diffusion being
effectively prohibited, magnetized plasmoids are different from ordinary
gases. But it remains unclear how they act during a collision. Here we
present the global picture of a unique collision between two coronal
mass ejections in the heliosphere, which are the largest magnetized
plasmoids erupting from the Sun. Our analysis for the first time reveals
that these two magnetized plasmoids collided like solid-like objects
with a 75% likelihood of being super-elastic. Their total kinetic
energy surprisingly increased by about 6.9% through the collision,
which significantly influenced the dynamics of the plasmoids.
---------------------------------------------------------
Title: A Comparison of Solar Energetic Particle Events with the
Properties of Coronal Mass Ejections
Authors: Kahler, S. W.; Vourlidas, A.
2012AGUFMSH23B..07K Altcode:
Gradual solar energetic particle (SEP) events observed at 1 AU are
produced by shocks driven by coronal mass ejections (CMEs). Our
limited characterizations of the remotely imaged CMEs and of their
associated SEP events observed in situ must be improved to increase
our ability to forecast SEP events and to understand better the
physical connections between the two phenomena. We carry out a
statistical comparison of properties of 115 SEP events with those
of their associated CMEs observed over the past solar cycle. Improved
measurements of white-light CME images enable us to improve calculations
of the masses and energies of CMEs using both leading edge and center-
of-mass kinematics. These values are used in statistical comparisons
with the peak 20-MeV intensities, the energy power-law spectral indices,
the 2-MeV/nuc H/He ratios, and calculated total energies of SEP events
observed on the Wind spacecraft. The large dynamical ranges of the SEP
parameters allow us to look for statistical trends in the data that
could give us physical insights into the physics of SEP production as
well as possible SEP prediction tools.
---------------------------------------------------------
Title: Combining remote and in-situ observations to learn about
CME evolution
Authors: Nieves-Chinchilla, T.; Stenborg, G.; Vourlidas, A.; Colaninno,
R. C.; Szabo, A.; Hidalgo, M. A.; Lepping, R. P.; Collinson, G. A.;
Boardsen, S. A.; Anderson, B. J.; Korth, H.; Barabash, S.; Zhang,
T.; Frahm, R. A.; Coates, A. J.; Shane, N.
2012AGUFMSH21C..04N Altcode:
Multi-spacecraft observations of CME/ICMEs are critical sources
of information to learn about the CME initiation, propagation,
and evolution from the Sun through the heliosphere. However, the
investigation has been undertaken from two, quite separate points of
view, namely remote sensing and in-situ observations. In recent years,
the availability of heliospheric imaging has provided a big impetus
to link the events as observed from these two perspectives. However,
a comprehensive and coordinated analysis of the multi-view point data,
using different techniques and models, is still far of being completely
understood. In this work, we demonstrate the discrepancy between these
two points of view using a thorough analysis of imaging and in-situ
observations at many inner heliospheric locations. We will show that
the measurements of the distortion of the ICMEs is strongly affected
by projection effects and that in-situ reconstructions of the CME
structure are highly dependent on the selection of the magnetic field
boundary. Therefore, both the cross section distortion and expansion,
and, therefore, the CME evolution, are still unclear. We use a
combination of remote (SOHO, STEREO, SDO) and in-situ (Wind, ACE, VEX,
MESSENGER) observations to show the potential this approach has to shed
light into the dynamical interaction of CMEs with the solar wind during
their propagation and development through the interplanetary medium.
---------------------------------------------------------
Title: Simulate the Coronal Mass Ejection on 2011 March 7 from
Chromosphere to 1 AU
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Oran, R.;
Sokolov, I.; Toth, G.; Gombosi, T. I.; Vourlidas, A.; Liu, Y.; Sun, X.
2012AGUFMSH33E..04J Altcode:
On 2011 March 7, a fast CME (> 2000 km/s) occurred in NOAA
11164. This event is also associated with a Solar Energetic Particle
(SEP) event. In this study, we present the magnetohydrodynamics
simulation results of this event. We initiate the CME by using the
Titov-Demoulin flux rope model. The background solar wind starts
from chromosphere with heat conduction and radiative cooling. The
solar wind is driven by Alfven-wave pressure and heated by Alfven-wave
dissipation. The magnetic field of the inner boundary is specified with
a synoptic magnetogram from SDO/HMI. In order to produce the physically
correct CME structures and CME-driven shocks, the electron and proton
temperatures are separated so that the electron heat conduction
is explicitly treated in conjunction with proton shock heating. We
simulate the CME propagation to 1 AU. A comprehensive validation work
is done by using the remote as well as the in-situ observation from
SOHO, STEREOA/B, ACE, and WIND. Our result shows that the new model
can reproduce most of the observed features near the Sun and in the
heliosphere. The CME-driven shock is well reproduced, which is important
for modeling the SEP event with diffusive shock acceleration.
---------------------------------------------------------
Title: Space weather effects of Cycle 24 SEP events
Authors: Cohen, C. M.; Mewaldt, R. A.; Mason, G. M.; Vourlidas, A.
2012AGUFMSH44B..03C Altcode:
When coronal mass ejections (CMEs) are fast and massive enough
they can generate interplanetary shocks that accelerate particles
to tens or hundreds of MeV/nucleon. These solar energetic particle
(SEP) events are a space weather hazard to astronauts and sensitive
space-based equipment. If the CME is directed towards Earth and impacts
the magnetosphere it can trigger a geomagnetic storm, resulting
in a variety of detrimental effects on communication systems and
power grids. Although to date, solar cycle 24 has not produced many
large-fluence SEP events nor many geoeffective CMEs, we will compare
the activity experienced so far to the most significant events of
cycle 23. Possible implications for the remainder of the cycle will
also be discussed.
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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: Exploring Small Spatial Scales in the Transition Region
and Solar Corona with the Very High Angular Resolution Imaging
Spectrometer (VERIS)
Authors: Chua, D. H.; Korendyke, C. M.; Vourlidas, A.; Brown, C. M.;
Tun-Beltran, S.; Klimchuk, J. A.; Landi, E.; Seely, J.; Davila, J. M.;
Hagood, R.; Roberts, D.; Shepler, E.; Feldman, R.; Moser, J.; Shea, J.
2012AGUFMSH33A2217C Altcode:
Theoretical and experimental investigations of the transition region
and coronal loops point to the importance of processes occurring on
small spatial scales in governing the strong dynamics and impulsive
energy release in these regions. As a consequence, high spatial,
temporal, and temperature resolution over a broad temperature range,
and accuracy in velocity and density determinations are all critical
observational parameters. Current instruments lack one or more of these
properties. These observational deficiencies have created a wide array
of opposing descriptions of coronal loop heating and questions such
as whether or not the plasma within coronal loops is multi-thermal or
isothermal. High spectral and spatial resolution spectroscopic data
are absolutely required to resolve these controversies and to advance
our understanding of the dynamics within the solar atmosphere. We
will achieve this with the Very High Angular Resolution Imaging
Spectrometer (VERIS) sounding rocket payload. VERIS consists of an
off-axis paraboloid telescope feeding a very high angular resolution,
extreme ultraviolet (EUV) imaging spectrometer that will provide
the first ever, simultaneous sub-arcsecond (0.16 arcsecond/pixel)
spectra in bright lines needed to study plasma structures in the
transition region, quiet corona, and active region core. It will do
so with a spectral resolution of >5000 to allow Doppler velocity
determinations to better than 3 km/s. VERIS uses a novel two-element,
normal incidence optical design with highly reflective, broad wavelength
coverage EUV coatings to access a spectral range with broad temperature
coverage (0.03-15 MK) and density-sensitive line ratios. Combined with
Hinode Solar Optical Telescope (SOT) and ground based observatories,
VERIS will deliver simultaneous observations of the entire solar
atmosphere from the photosphere to the multi-million degree corona
at sub-arcsecond resolution for the first time ever, allowing us to
understand the missing link between chromospheric structures and the
corona. VERIS will be launched from White Sands Missile Range in early
2013. This paper presents a progress report on the VERIS payload and
a summary of observations planned to further our understanding of
the fine-scale structure of individual coronal loops and the heating
mechanisms operating within them.
---------------------------------------------------------
Title: Preface
Authors: Fleck, Bernhard; Heber, Bernd; Vourlidas, Angelos; van
Driel-Gesztelyi, Lidia; Mandrini, Cristina H.; Leibacher, John
2012SoPh..281....1F Altcode: 2012SoPh..tmp..223F
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Topology of Active Regions and Coronal Holes:
Implications for Coronal Outflows and the Solar Wind
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin,
P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.;
Stenborg, G.; Vourlidas, A.; Brooks, D. H.
2012SoPh..281..237V Altcode: 2012SoPh..tmp..228V
During 2 - 18 January 2008 a pair of low-latitude opposite-polarity
coronal holes (CHs) were observed on the Sun with two active regions
(ARs) and the heliospheric plasma sheet located between them. We use
the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows
and measure their velocities. Solar-Terrestrial Relations Observatory
(STEREO) imaging is also employed, as are the Advanced Composition
Explorer (ACE) in-situ observations, to assess the resulting impacts on
the solar wind (SW) properties. Magnetic-field extrapolations of the two
ARs confirm that AR plasma outflows observed with EIS are co-spatial
with quasi-separatrix layer locations, including the separatrix of a
null point. Global potential-field source-surface modeling indicates
that field lines in the vicinity of the null point extend up to the
source surface, enabling a part of the EIS plasma upflows access
to the SW. We find that similar upflow properties are also observed
within closed-field regions that do not reach the source surface. We
conclude that some of plasma upflows observed with EIS remain confined
along closed coronal loops, but that a fraction of the plasma may be
released into the slow SW. This suggests that ARs bordering coronal
holes can contribute to the slow SW. Analyzing the in-situ data, we
propose that the type of slow SW present depends on whether the AR is
fully or partially enclosed by an overlying streamer.
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Title: Global Energetics of Thirty-eight Large Solar Eruptive Events
Authors: Emslie, A. G.; Dennis, B. R.; Shih, A. Y.; Chamberlin, P. C.;
Mewaldt, R. A.; Moore, C. S.; Share, G. H.; Vourlidas, A.; Welsch,
B. T.
2012ApJ...759...71E Altcode: 2012arXiv1209.2654E
We have evaluated the energetics of 38 solar eruptive events observed
by a variety of spacecraft instruments between 2002 February
and 2006 December, as accurately as the observations allow. The
measured energetic components include: (1) the radiated energy in
the Geostationary Operational Environmental Satellite 1-8 Å band,
(2) the total energy radiated from the soft X-ray (SXR) emitting
plasma, (3) the peak energy in the SXR-emitting plasma, (4) the
bolometric radiated energy over the full duration of the event,
(5) the energy in flare-accelerated electrons above 20 keV and in
flare-accelerated ions above 1 MeV, (6) the kinetic and potential
energies of the coronal mass ejection (CME), (7) the energy in solar
energetic particles (SEPs) observed in interplanetary space, and
(8) the amount of free (non-potential) magnetic energy estimated
to be available in the pertinent active region. Major conclusions
include: (1) the energy radiated by the SXR-emitting plasma exceeds,
by about half an order of magnitude, the peak energy content of the
thermal plasma that produces this radiation; (2) the energy content
in flare-accelerated electrons and ions is sufficient to supply the
bolometric energy radiated across all wavelengths throughout the event;
(3) the energy contents of flare-accelerated electrons and ions are
comparable; (4) the energy in SEPs is typically a few percent of the
CME kinetic energy (measured in the rest frame of the solar wind);
and (5) the available magnetic energy is sufficient to power the CME,
the flare-accelerated particles, and the hot thermal plasma.
---------------------------------------------------------
Title: A Study of the Heliocentric Dependence of Shock Standoff
Distance and Geometry using 2.5D Magnetohydrodynamic Simulations of
Coronal Mass Ejection Driven Shocks
Authors: Savani, N. P.; Shiota, D.; Kusano, K.; Vourlidas, A.;
Lugaz, N.
2012ApJ...759..103S Altcode: 2012arXiv1209.1990S
We perform four numerical magnetohydrodynamic simulations in
2.5 dimensions (2.5D) of fast coronal mass ejections (CMEs)
and their associated shock fronts between 10 Rs and 300 Rs. We
investigate the relative change in the shock standoff distance, Δ,
as a fraction of the CME radial half-width, D <SUB>OB</SUB> (i.e.,
Δ/D <SUB>OB</SUB>). Previous hydrodynamic studies have related the
shock standoff distance for Earth's magnetosphere to the density
compression ratio (DR; ρ <SUB>u</SUB>/ρ <SUB>d</SUB>) measured
across the bow shock. The DR coefficient, k <SUB>dr</SUB>, which is
the proportionality constant between the relative standoff distance
(Δ/D <SUB>OB</SUB>) and the compression ratio, was semi-empirically
estimated as 1.1. For CMEs, we show that this value varies linearly
as a function of heliocentric distance and changes significantly
for different radii of curvature of the CME's leading edge. We find
that a value of 0.8 ± 0.1 is more appropriate for small heliocentric
distances (<30 Rs) which corresponds to the spherical geometry of
a magnetosphere presented by Seiff. As the CME propagates its cross
section becomes more oblate and the k <SUB>dr</SUB> value increases
linearly with heliocentric distance, such that k <SUB>dr</SUB> =
1.1 is most appropriate at a heliocentric distance of about 80 Rs. For
terrestrial distances (215 Rs) we estimate k <SUB>dr</SUB> = 1.8 ± 0.3,
which also indicates that the CME cross-sectional structure is generally
more oblate than that of Earth's magnetosphere. These alterations to
the proportionality coefficients may serve to improve investigations
into the estimates of the magnetic field in the corona upstream of a
CME as well as the aspect ratio of CMEs as measured in situ.
---------------------------------------------------------
Title: Three-Dimensional Properties of Coronal Mass Ejections from
STEREO/SECCHI Observations
Authors: Bosman, E.; Bothmer, V.; Nisticò, G.; Vourlidas, A.; Howard,
R. A.; Davies, J. A.
2012SoPh..281..167B Altcode: 2012SoPh..tmp..234B
We identify 565 coronal mass ejections (CMEs) between January 2007
and December 2010 in observations from the twin STEREO/SECCHI/COR2
coronagraphs aboard the STEREO mission. Our list is in full
agreement with the corresponding SOHO/LASCO CME Catalog
(http://cdaw.gsfc.nasa.gov/CME_list/) for events with angular
widths of 45<SUP>∘</SUP> and up. The monthly event rates behave
similarly to sunspot rates showing a three- to fourfold rise between
September 2009 and March 2010. We select 51 events with well-defined
white-light structure and model them as three-dimensional (3D) flux
ropes using a forward-modeling technique developed by Thernisien,
Howard and Vourlidas (Astrophys. J. 652, 763 - 773, 2006). We derive
their 3D properties and identify their source regions. We find that
the majority of the CME flux ropes (82 %) lie within 30<SUP>∘</SUP>
of the solar equator. Also, 82 % of the events are displaced from their
source region, to a lower latitude, by 25<SUP>∘</SUP> or less. These
findings provide strong support for the deflection of CMEs towards
the solar equator reported in earlier observations, e.g. by Cremades
and Bothmer (Astron. Astrophys.422, 307 - 322, 2004).
---------------------------------------------------------
Title: On the Nature and Genesis of EUV Waves: A Synthesis of
Observations from SOHO, STEREO, SDO, and Hinode (Invited Review)
Authors: Patsourakos, Spiros; Vourlidas, Angelos
2012SoPh..281..187P Altcode: 2012SoPh..tmp...93P; 2012arXiv1203.1135P
A major, albeit serendipitous, discovery of the SOlar and
Heliospheric Observatory mission was the observation by the Extreme
Ultraviolet Telescope (EIT) of large-scale extreme ultraviolet (EUV)
intensity fronts propagating over a significant fraction of the Sun's
surface. These so-called EIT or EUV waves are associated with eruptive
phenomena and have been studied intensely. However, their wave nature
has been challenged by non-wave (or pseudo-wave) interpretations and
the subject remains under debate. A string of recent solar missions
has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving the question of their nature. With
this review, we gather the current state-of-the-art knowledge in the
field and synthesize it into a picture of an EUV wave driven by the
lateral expansion of the CME. This picture can account for both wave
and pseudo-wave interpretations of the observations, thus resolving
the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion on several remaining open
questions in the field of EUV waves research.
---------------------------------------------------------
Title: Uncovering the Birth of a Coronal Mass Ejection from
Two-Viewpoint SECCHI Observations
Authors: Vourlidas, A.; Syntelis, P.; Tsinganos, K.
2012SoPh..280..509V Altcode: 2012arXiv1201.0162V; 2012SoPh..tmp...27V
We investigate the initiation and formation of Coronal Mass Ejections
(CMEs) via a detailed two-viewpoint analysis of low corona observations
of a relatively fast CME acquired by the SECCHI instruments aboard
the STEREO mission. The event which occurred on 2 January 2008, was
chosen because of several unique characteristics. It shows upward
motions for at least four hours before the flare peak. Its speed and
acceleration profiles exhibit a number of inflections which seem to
have a direct counterpart in the GOES light curves. We detect and
measure, in 3D, loops that collapse toward the erupting channel while
the CME is increasing in size and accelerates. We suggest that these
collapsing loops are our first evidence of magnetic evacuation behind
the forming CME flux rope. We report the detection of a hot structure
which becomes the core of the white light CME. We observe and measure
unidirectional flows along the erupting filament channel which may
be associated with the eruption process. Finally, we compare these
observations to the predictions from the standard flare-CME model
and find a very satisfactory agreement. We conclude that the standard
flare-CME concept is a reliable representation of the initial stages
of CMEs and that multi-viewpoint, high cadence EUV observations can
be extremely useful in understanding the formation of CMEs.
---------------------------------------------------------
Title: Intercomparison of the LASCO-C2, SECCHI-COR1, SECCHI-COR2,
and Mk4 Coronagraphs
Authors: Frazin, Richard A.; Vásquez, Alberto M.; Thompson, William
T.; Hewett, Russell J.; Lamy, Philippe; Llebaria, Antoine; Vourlidas,
Angelos; Burkepile, Joan
2012SoPh..280..273F Altcode: 2012SoPh..tmp..140F
In order to assess the reliability and consistency of white-light
coronagraph measurements, we report on quantitative comparisons between
polarized brightness [pB] and total brightness [B] images taken by
the following white-light coronagraphs: LASCO-C2 on SOHO, SECCHI-COR1
and -COR2 on STEREO, and the ground-based MLSO-Mk4. The data for this
comparison were taken on 16 April 2007, when both STEREO spacecraft were
within 3.1<SUP>∘</SUP> of Earth's heliographic longitude, affording
essentially the same view of the Sun for all of the instruments. Due
to the difficulties of estimating stray-light backgrounds in COR1 and
COR2, only Mk4 and C2 produce reliable coronal-hole values (but not
at overlapping heights), and these cannot be validated without rocket
flights or ground-based eclipse measurements. Generally, the agreement
between all of the instruments' pB values is within the uncertainties
in bright streamer structures, implying that measurements of bright
CMEs also should be trustworthy. Dominant sources of uncertainty and
stray light are discussed, as is the design of future coronagraphs
from the perspective of the experiences with these instruments.
---------------------------------------------------------
Title: Secondary Waves and/or the "Reflection" from and "Transmission"
through a Coronal Hole of an Extreme Ultraviolet Wave Associated with
the 2011 February 15 X2.2 Flare Observed with SDO/AIA and STEREO/EUVI
Authors: Olmedo, Oscar; Vourlidas, Angelos; Zhang, Jie; Cheng, Xin
2012ApJ...756..143O Altcode: 2012arXiv1206.6137O
For the first time, the kinematic evolution of a coronal wave over the
entire solar surface is studied. Full Sun maps can be made by combining
images from the Solar Terrestrial Relations Observatory satellites,
Ahead and Behind, and the Solar Dynamics Observatory, thanks to the wide
angular separation between them. We study the propagation of a coronal
wave, also known as the "Extreme Ultraviolet Imaging Telescope" wave,
and its interaction with a coronal hole (CH) resulting in secondary
waves and/or reflection and transmission. We explore the possibility
of the wave obeying the law of reflection. In a detailed example, we
find that a loop arcade at the CH boundary cascades and oscillates as
a result of the extreme ultraviolet (EUV) wave passage and triggers
a wave directed eastward that appears to have reflected. We find that
the speed of this wave decelerates to an asymptotic value, which is less
than half of the primary EUV wave speed. Thanks to the full Sun coverage
we are able to determine that part of the primary wave is transmitted
through the CH. This is the first observation of its kind. The kinematic
measurements of the reflected and transmitted wave tracks are consistent
with a fast-mode magnetohydrodynamic wave interpretation. Eventually,
all wave tracks decelerate and disappear at a distance. A possible
scenario of the whole process is that the wave is initially driven by
the expanding coronal mass ejection and subsequently decouples from
the driver and then propagates at the local fast-mode speed.
---------------------------------------------------------
Title: Erratum: "Initiation and Development of the White-light
and Radio Coronal Mass Ejection on 2001 April 15" <A
href="/abs/2012ApJ...750..147D">(2012, ApJ, 750, 147)</A>
Authors: Démoulin, P.; Vourlidas, A.; Pick, M.; Bouteille, A.
2012ApJ...754..156D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Science Highlights from the First Three Years of CME
Observations from STEREO/SECCHI
Authors: Vourlidas, A.
2012ASPC..454..367V Altcode:
Since early 2007, the SECCHI experiment aboard the STEREO mission
has been observing the Sun and the heliosphere from two varying
vantage points using EUV disk imagers, coronagraphs and heliospheric
imagers. Despite the prolonged solar minimum, the unprecedented
coverage of solar eruptions from the low corona to beyond 1 AU is
providing many new and fundamental insights into the physics of CME
formation, initiation and propagation. Here, I highlight a few key
results and outline possible scientific synergies between the STEREO
and the Hinode payloads.
---------------------------------------------------------
Title: Magnetic topology, coronal outflows, and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas,
Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea;
Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa,
Marc; Brooks, David
2012cosp...39.1173M Altcode: 2012cosp.meet.1173M
During 2-18 January 2008 a pair of low-latitude opposite polarity
coronal holes were observed on the Sun flanked by two ARs with
the heliospheric plasma sheet between them. Hinode/EUV Imaging
Telescope (EIS) is used to locate AR-related outflows and measure their
velocities. The Advanced Composition Explorer (ACE) in-situ observations
are employed to assess the resulting impacts on the interplanetary solar
wind (SW). Magnetic field extrapolations of the two ARs confirm that AR
plasma outflows observed with EIS are co-spatial with quasi-separatrix
layer locations, including the separatrix of a null point. Global
potential field source-surface modeling indicates that field lines
in the vicinity of the null point extend up to the source-surface,
enabling a part of the EIS plasma upflows access to the SW. Similar
upflow magnitude is also observed within closed field regions. Though
part of the plasma upflows observed with EIS remain confined along
closed coronal loops, a subset of them are indeed able to make their
imprint in the slow SW, making ARs bordering coronal holes a slow
SW contributor.
---------------------------------------------------------
Title: Future Remote-Sensing Observations of CMEs from out of the
Ecliptic
Authors: Lugaz, Noé; Roussev, Ilia; Liewer, Paulett; Vourlidas,
Angelos; Downs, Cooper
2012cosp...39.1116L Altcode: 2012cosp.meet.1116L
In the past four decades, Coronal Mass Ejections (CMEs) have been
observed remotely with coronagraphs primarily from Earth or L1. More
recently, using SMEI and STEREO/SECCHI, CMEs are now routinely observed
to larger distances (up to 1 AU and beyond) and from directions away
from the Sun-Earth line. We will review some of the new techniques,
which have been devised to analyze these observations and discuss
how they might be adapted to observations from out-of-ecliptic. We
will also present simulated white-light and extreme-ultraviolet (EUV)
images of CMEs as they would appear from different orbits above the
ecliptic. Taking advantage of the fact that, in MHD simulations,
the plasma parameters are known in at each time-step in the full 3-D
volume, we will discuss how multiple viewpoints might help reveal the
3-D nature of CMEs and associated phenomena.
---------------------------------------------------------
Title: The Longitudinal Properties of a Solar Energetic Particle
Event Investigated Using Modern Solar Imaging
Authors: Rouillard, A. P.; Sheeley, N. R.; Tylka, A.; Vourlidas,
A.; Ng, C. K.; Rakowski, C.; Cohen, C. M. S.; Mewaldt, R. A.; Mason,
G. M.; Reames, D.; Savani, N. P.; StCyr, O. C.; Szabo, A.
2012ApJ...752...44R Altcode:
We use combined high-cadence, high-resolution, and multi-point imaging
by the Solar-Terrestrial Relations Observatory (STEREO) and the Solar
and Heliospheric Observatory to investigate the hour-long eruption of a
fast and wide coronal mass ejection (CME) on 2011 March 21 when the twin
STEREO spacecraft were located beyond the solar limbs. We analyze the
relation between the eruption of the CME, the evolution of an Extreme
Ultraviolet (EUV) wave, and the onset of a solar energetic particle
(SEP) event measured in situ by the STEREO and near-Earth orbiting
spacecraft. Combined ultraviolet and white-light images of the lower
corona reveal that in an initial CME lateral "expansion phase," the
EUV disturbance tracks the laterally expanding flanks of the CME,
both moving parallel to the solar surface with speeds of ~450 km
s<SUP>-1</SUP>. When the lateral expansion of the ejecta ceases, the
EUV disturbance carries on propagating parallel to the solar surface
but devolves rapidly into a less coherent structure. Multi-point
tracking of the CME leading edge and the effects of the launched
compression waves (e.g., pushed streamers) give anti-sunward speeds
that initially exceed 900 km s<SUP>-1</SUP> at all measured position
angles. We combine our analysis of ultraviolet and white-light images
with a comprehensive study of the velocity dispersion of energetic
particles measured in situ by particle detectors located at STEREO-A
(STA) and first Lagrange point (L1), to demonstrate that the delayed
solar particle release times at STA and L1 are consistent with the
time required (30-40 minutes) for the CME to perturb the corona over a
wide range of longitudes. This study finds an association between the
longitudinal extent of the perturbed corona (in EUV and white light)
and the longitudinal extent of the SEP event in the heliosphere.
---------------------------------------------------------
Title: Uncloaking Structures and Dynamic Phenomena on EUV images
via a multi-resolution based image-processing technique
Authors: Stenborg, Guillermo Adrian; Vourlidas, Angelos; Howard,
Russell
2012shin.confE.213S Altcode:
Groundbreaking observations of the low solar corona at extreme
ultraviolet (EUV) wavelengths have been provided by the EIT instrument
on board SOHO for more than 15 years. At the beginning of 2007, the
EUVI instruments on board the twin STEREO spacecraft opened doors
and commenced to image the EUV low corona with an improved cadence
and spatial resolution from two vantage points off the Sun-Earth
line. Since February 2010, the AIA instrument on board the Solar
Dynamics Observatory observes the low EUVI corona at a 10 sec cadence in
8 wavelengths. Despite the increasing quality of the EUV observations,
they have not been fully exploited. A customized wavelet-based image
cleaning and enhancing technique that exploits the multi-scale nature
of the observed solar features has been developed (Stenborg et al.,
2008) to maximize the scientific return of the EIT observations. We
have now adapted it to work with STEREO/EUVI and SDO/AIA images. Its
application has already helped unveil phenomena only theorized before,
as well as revealed phenomena that have not found a satisfactory
explanation yet. In this presentation, we make a brief survey of the
new products, and recent related discoveries, in particular with regard
to its relevance to the prominence/cavity/CME expansion paradigm.
---------------------------------------------------------
Title: Remote and in situ observations of an unusual Earth-directed
coronal mass ejection from multiple viewpoints
Authors: Nieves-Chinchilla, T.; Colaninno, R.; Vourlidas, A.; Szabo,
A.; Lepping, R. P.; Boardsen, S. A.; Anderson, B. J.; Korth, H.
2012JGRA..117.6106N Altcode: 2012JGRA..11706106N
During June 16-21, 2010, an Earth-directed coronal mass ejection (CME)
event was observed by instruments onboard STEREO, SOHO, MESSENGER and
Wind. This event was the first direct detection of a rotating CME
in the middle and outer corona. Here, we carry out a comprehensive
analysis of the evolution of the CME in the interplanetary medium
comparing in situ and remote observations, with analytical models and
three-dimensional reconstructions. In particular, we investigate the
parallel and perpendicular cross section expansion of the CME from
the corona through the heliosphere up to 1 AU. We use height-time
measurements and the Gradual Cylindrical Shell (GCS) technique to
model the imaging observations, remove the projection effects, and
derive the 3-dimensional extent of the event. Then, we compare the
results with in situ analytical Magnetic Cloud (MC) models, and with
geometrical predictions from past works. We find that the parallel
(along the propagation plane) cross section expansion agrees well with
the in situ model and with the Bothmer and Schwenn (1998) empirical
relationship based on in situ observations between 0.3 and 1 AU. Our
results effectively extend this empirical relationship to about 5 solar
radii. The expansion of the perpendicular diameter agrees very well with
the in situ results at MESSENGER (∼0.5 AU) but not at 1 AU. We also
find a slightly different, from Bothmer and Schwenn (1998), empirical
relationship for the perpendicular expansion. More importantly,
we find no evidence that the CME undergoes a significant latitudinal
over-expansion as it is commonly assumed. Instead, we find evidence that
effects due to CME rotation and expansion can be easily confused in the
images leading to a severe overestimation of the proper 3D size of the
event. Finally, we find that the reconstructions of the CME morphology
from the in situ observations at 1 AU are in agreement with the remote
sensing observations but they show a big discrepancy at MESSENGER. We
attribute this discrepancy to the ambiguity of selecting the proper
boundaries due to the lack of accompanying plasma measurements.
---------------------------------------------------------
Title: The influence of CME momentum onto the Earth's Magnetosphere
Authors: Savani, Neel P.; Vourlidas, A.
2012shin.confE..12S Altcode:
Recent observations have been able to track the white light structures
of CMEs from remote observations of the corona out to planetary bodies,
where comparative studies with in situ measurements have been made. The
majority of these studies have focused on achieving consistent results
for parameters such as the arrival time, propagation direction and
the orientation of a possible magnetic flux rope topology. In this
study we focus on estimating mass and momentum of the CME for both the
structure in its entirety and for the narrow slit which travels over
Earth. We track the mass profile of the CME through the Heliospheric
Imagers onboard STEREO and monitor the resulting in situ measurements
at L1. We test the hypothesis that the sudden increase in momentum of
the solar wind instigates a geomagnetic disturbance and affects the
initial phase of the magnetic activity indices.
---------------------------------------------------------
Title: Three-dimensional evolution of erupted flux ropes from the
Sun to 1AU
Authors: Isavnin, Alexey; Vourlidas, Angelos; Kilpua, Emilia K. J.
2012shin.confE..83I Altcode:
Studying the evolution of magnetic clouds entrained in by coronal mass
ejections using in-situ data is a difficult task since only a limited
number of observational points is at hand. In this work we estimate the
flux rope orientation first in the close vicinity of the Sun (2-20Rs)
using forward modeling of STEREO/SECCHI and SOHO/LASCO coronagraph
images of coronal mass ejections and then in situ using Grad-Shafranov
reconstruction of the magnetic cloud. Thus, we are able to measure
changes in the orientation of individual erupted flux ropes as they
propagated from the Sun to 1AU. We use this method to study 15 magnetic
clouds observed during the minimum following the Solar Cycle 23 and
the rise of the Solar Cycle 24. Our analysis of these selected events
shows that flux ropes tend to deflect towards the solar equatorial
plane on their travel from the Sun to 1AU and also experience rotation.
---------------------------------------------------------
Title: Study of the coronal thermal response to an EUV wave
Authors: Olmedo, Oscar A.; Vourlidas, Angelos; Stenborg, Guillermo
2012shin.confE.102O Altcode:
In this work we use observations from the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamic Observatory to study, in high-temporal
cadence, the temperature response of the corona to the passage of
EUV waves. We use the flux ratios of the six AIA EUV channels and
DEM to study how the temperature of the disturbed plasma evolves with
time. During our investigation we found that there is an appreciable
amount of stray light scatter, particularly in the 131 and 94 Angstrom
AIA channels, due to the flare associated with the EUV wave. We explore
several methods in an attempt to suppress this scatter.
---------------------------------------------------------
Title: Are There Connections in Eruptive Events Across Time and Space?
Authors: Vourlidas, Angelos
2012shin.confE.158V Altcode:
Coronal Mass Ejections (CMEs) from different source regions occur
sometimes in close temporal proximity. Repeated eruptive flares occur
sometimes at the same location in an active region. Are these eruptions
related somehow? Can eruptions 'communicate' across large distances
or in across time or are they simply chance occurrences? In this talk,
I will discuss how observations of 'sympathetic' CMEs and 'homologous'
flares relate to the questions above.
---------------------------------------------------------
Title: Initiation and Development of the White-light and Radio
Coronal Mass Ejection on 2001 April 15
Authors: Démoulin, P.; Vourlidas, A.; Pick, M.; Bouteille, A.
2012ApJ...750..147D Altcode:
The 2001 April 15 event was one of the largest of the last solar
cycle. A former study established that this event was associated
with a coronal mass ejection (CME) observed both at white light
and radio frequencies. This radio CME is illuminated by synchrotron
emission from relativistic electrons. In this paper, we investigate
the relation of the radio CME to its extreme-ultraviolet (EUV) and
white-light counterpart and reach four main conclusions. (1) The radio
CME corresponds to the white-light flux rope cavity. (2) The presence
of a reconnecting current sheet behind the erupting flux rope is framed,
both from below and above, by bursty radio sources. This reconnection is
the source of relativistic radiating electrons which are injected down
along the reconnected coronal arches and up along the flux rope border
forming the radio CME. (3) Radio imaging reveals an important lateral
overexpansion in the low corona; this overexpansion is at the origin of
compression regions where type II and III bursts are imaged. (4) Already
in the initiation phase, radio images reveal large-scale interactions
of the source active region (AR) with its surroundings, including
another AR and open magnetic fields. Thus, these complementary radio,
EUV, and white-light data validate the flux rope eruption model of CMEs.
---------------------------------------------------------
Title: A decade of coronagraphic and spectroscopic studies of
CME-driven shocks
Authors: Vourlidas, Angelos; Bemporad, Alessandro
2012AIPC.1436..279V Altcode: 2012arXiv1207.1603V
Shocks driven by Coronal Mass Ejections (CMEs) are primary agents of
space weather. They can accelerate particles to high energies and
can compress the magnetosphere thus setting in motion geomagnetic
storms. For many years, these shocks were studied only in-situ when
they crossed over spacecraft or remotely through their radio emission
spectra. Neither of these two methods provides information on the
spatial structure of the shock nor on its relationship to its driver,
the CME. In the last decade, we have been able to not only image
shocks with coronagraphs but also measure their properties remotely
through the use of spectroscopic and image analysis methods. Thanks to
instrumentation on STEREO and SOHO we can now image shocks (and waves)
from the low corona, through the inner heliosphere, to Earth. Here,
we review the progress made in imaging and analyzing CME-driven shocks
and show that joint coronagraphic and spectrscopic observations are
our best means to understand shock physics close to the Sun.
---------------------------------------------------------
Title: High spatial resolution VAULT H-Lyα observations and
multiwavelength analysis of an active region filament
Authors: Vial, J. -C.; Olivier, K.; Philippon, A. A.; Vourlidas, A.;
Yurchyshyn, V.
2012A&A...541A.108V Altcode:
Context. The search for the fine structure of prominences has
received considerable new attention thanks to the Swedish Solar
Telescope (SST) Hα pictures that provide an unsurpassed spatial
resolution. Recently, it has been shown that the filaments' coronal
environment, at least for quiescent filaments, is perturbed by either
cool absorbing material (in the EUV) or an "emissivity blocking"
(actually a lack of transition region and coronal material). <BR />
Aims: The aim is to assess the fine structure in an active region
filament and to determine the nature of the EUV absorption or lack
of emission phenomena, using the very optically thick line H-Lyα,
formed at a temperature higher than Hα. <BR /> Methods: We performed
a multiwavelength study where high-resolution imaging in the H-Lyα
line (VAULT) was analysed and compared with observations of an active
region filament in Hα (BBSO) and EUV lines (EIT and TRACE). <BR />
Results: As for the SST data, small-scale structures were detected at
a typical scale of about one to two arcseconds with, for some cuts,
an indication of fine scales down to 0.4 arcsec in the optically thick
H-Lyα line. The filament intensity relative to the intensity of the
(active) region it is embedded in is about 0.2 in H-Lyα. This ratio
(Lymanα ratio intensity or "LRI") is the lowest value compared to
other lines, e.g. Hα. The filament environment was also investigated
and evidence of an UV extension was found. The comparison of spatial
cuts in different lines across the filament shows evidence of strong
absorption, and consequently of cool plasma on one side of the filament,
but not on the other (that side is obscured by the filament itself). <BR
/> Conclusions: The absence of very fine structure in H-Lyα compared
to Hα is explained by the formation temperature of the H-Lyα line
(~20 000 K), where the transition regions of the thin threads begin to
merge. From the detection of H-Lyα absorption on the observable side of
the filament side, we derive the presence of absorbing (cool) material
and possibly also of emissivity blocking (or coronal void). This poses
the question whether these absorption effects are typical of active
region filaments. <P />Appendix A is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Global Energetics of Large Solar Eruptive Events
Authors: Dennis, Brian R.; Emslie, A. G.; Chamberlin, P. C.; Mewaldt,
R. A.; Moore, C. S.; Share, G. H.; Shih, A. Y.; Vourlidas, A.;
Welsch, B.
2012AAS...22041002D Altcode:
We have evaluated the energetics of the larger solar eruptive events
recorded with a variety of spacecraft instruments between February
2002 and December 2006. All of the energetically important components
of the flares and of the accompanying coronal mass ejections and
solar energetic particles have been evaluated as accurately as
the observations allow. These components include the following:
(1) the total energy in the high temperature plasma determined from
the RHESSI thermal X-ray observations; (2) the total energies in
accelerated electrons above 20 keV and ions above 1 MeV from RHESSI
hard X-ray and gamma-ray observations, respectively; (3) the potential
and kinetic energies of the CME from SOHO/LASCO observations; (4)
the solar energetic particle (SEP) energy estimates from in situ
measurements on ACE, GOES, and SOHO; (5) the total radiated energy
from the SORCE/TSI measurements where available, and otherwise from
the Flare Irradiance Spectral Model (FISM). The results are assimilated
and discussed relative to the probable amount of nonpotential magnetic
energy estimated to be available in the flaring active regions from
MDI line-of-sight magnetograms.
---------------------------------------------------------
Title: Observation of “Transmission” of an EUV Wave Through a
Coronal Hole
Authors: Olmedo, Oscar; Vourlidas, A.; Zhang, J.; Cheng, X.
2012AAS...22052120O Altcode:
We present for the first time what appears to be the “transmission”
of an EUV wave through a coronal hole. Though this effect had not
previously been observed, numerical simulations indicate that EUV
waves can cross coronal holes. The EUV wave event studied in this
work occurred on 2011 February 15 and was associated with an X class
flare. It is seen that the part of the wave that crosses the coronal
hole appears to accelerate relative to the part over the quiet Sun. This
observation is fully consistent with the behavior of a fast-mode
wave since the fast-mode speed will be higher in a coronal hole
(due to its reduced plasma density) than in the quiet Sun at a given
height. These observations are hard to reconcile with a pure pseudo-wave
interpretation of EUV waves. Our findings indicate that we accept either
all EUV waves as fast-mode waves or the hybrid interpretation of EUV
waves where the coronal mass ejections outer envelope, observed as a
pseudo-wave, triggers a fast-mode wave seen later on in the event. In
the latter scenario the EUV wave should look to propagate continuously
as the coronal mass ejection leaves behind a fast-mode wave in its
wake. And it is this fast-mode wave that crosses the coronal hole.
---------------------------------------------------------
Title: The Current Status of Research on Coronal Mass Ejections
Authors: Vourlidas, Angelos
2012AAS...22030401V Altcode:
Coronal Mass Ejections (CMEs) are the main drivers of Space Weather and
have been the focus of intense research since the mid-1990's. Since
2007, CMEs have even been studied stereoscopically by the STEREO
mission. We now have observations spanning more than one solar cycle,
3D information, simultaneous remote and in-situ observations, a wide
wavelength coverage, and quite sophisticated MHD simulations. In
this talk, I will review our current status of knowledge on the CME
phenomenon with an emphasis on the open issues on the geoeffectiveness
of these events.
---------------------------------------------------------
Title: CME mass evolution derived from stereoscopic observations of
STEREO/SECCHI instruments COR1 and COR2
Authors: Bein, B.; Temmer, M.; Vourlidas, A.; Veronig, A.
2012EGUGA..14.7174B Altcode:
The STEREO mission consists of two nearly identical spacecraft STEREO-A
and STEREO-B, which observe simultaneously the Sun from two different
vantage points. We use observations from both coronagraphs, COR1 and
COR2 of the SECCHI instrument suite aboard STEREO-A and STEREO-B,
to derive the CME mass evolution for a height range from 1.4 to 15
RSun. Due to the fact that we have observations from two different
vantage points, we measure not only the projected mass but can
estimate the 'true' CME mass evolution with height. We developed a
fit function, which considers the mass increase based on the geometry
of the instrument (mass hidden behind the occulter) and a possible
'real' mass increase with height. The fit parameters are compared with
characteristic CME quantities.
---------------------------------------------------------
Title: Type II Radio Emission from Shock Formation In The Low
Corona on 13-Jun-2010: Combined Observations from the ARTEMIS-IV
Radiospectrograph and SDO/AIA
Authors: Kouloumvakos, A.; Vourlidas, A.; Preka-Papadema, P.; Hillaris,
A.; Caroubalos, C.; Moussas, X.; Tsitsipis, P.; Kontogeorgos, A.
2012hell.confQ..12K Altcode:
High cadence observations in the low corona from AIA imagers combined
with radiospectrograph high-resolution recordings give a new perspective
of shock formation in the low corona. Using ARTEMIS-IV observations
of drifting type-II metric radio emission and ultra-high resolution
observations from the AIA imagers we present direct observation of
shock formation in the EUV and its association to the accompanying
type-II during the 13-Jun-2010 Event. We will show that, in this case,
the coronal expansion driven by the formation of the CME ejecta is
responsible for both EUV and radio emissions.
---------------------------------------------------------
Title: STEREO and SDO observations of several solar jets
Authors: Tsinganos, K.; Moschou, S.; Vourlidas, A.
2012hell.conf...13T Altcode:
We present an analysis of recent observations of several solar jets
observed at the solar limb with STEREO A/B and the Solar Dynamics
Observatory (SDO). We construct fitted height-time diagrams at all
wavelengths and calculate the temporal evolution of the jet speed
and acceleration. The first case is a large solar jet observed on
06/30/2010, simultaneously by STEREO & SDO in the north solar pole,
at many wavelengths, from 171 to 304 Angstroms. It has a precursor
and lasts in total for about 60 minutes, while the main jet reaches a
height of 0.3 Ro and a maximum speed of about 250 km/sec. The second
sample contains a set of four solar limb jets observed 5 days earlier
than the previous one, i.e., 06/25/2010. All jets are observed with
SDO while two of them are simultaneously observed with STEREO. Two
jets have a precursor and last from 60 - 120 minutes, reaching heights
of less than 0.2 Ro. Finally, we analyse a jet observed by STEREO on
11/12/2008 in 174, 195, 284 and 304 Angstroms. The jet reaches a height
of 0.25 Ro and a maximum speed of about 150 km/sec. Magnetograms during
the jet appearances show the corresponding magnetic topologies. The
velocities involved are smaller than the escape speed from the sun at
each radius. The results are preliminarily discussed in relation to
possible jet formation mechanisms.
---------------------------------------------------------
Title: New Views of the Solar Corona from STEREO and SDO
Authors: Vourlidas, A.
2012hell.conf....6V Altcode:
In the last few years, we have been treated to an unusual visual feast
of solar observations of the corona in EUV wavelengths. The observations
from the two vantage points of STEREO/SECCHI are now capturing the
entire solar atmosphere simultaneously in four wavelengths. The SDO/AIA
images provide us with arcsecond resolution images of the full visible
disk in ten wavelengths. All these data are captured with cadences of
a few seconds to a few minutes. In this talk, I review some intriguing
results from our first attempts to deal with these observations which
touch upon the problems of coronal mass ejection initiation and solar
wind generation. I will also discuss data processing techniques that
may help us recover even more information from the images. The talk
will contain a generous portion of beautiful EUV images and movies of
the solar corona.
---------------------------------------------------------
Title: Constraining a Model for EUV Wave Formation with SDO and
STEREO Quadrature Observations
Authors: Patsourakos, S.; Vourlidas, A.; Olmedo, O.
2012hell.conf....7P Altcode:
The generation mechanism(s) of large-scale propagating intensity fronts
seen in the EUV, often called EUV waves, in association with impulsive
Coronal Mass Ejection (CMEs) is currently a matter of debate. The strong
lateral expansion which some impulsive CMEs undergo during their early
phases, when they are observed in the inner corona by EUV imagers, is
one possible mechanism for the generation of EUV waves. One impulsive
CME - EUV wave pair was observed during 15 February 2011 in quadrature
by SDO and STEREO. The source active region was close to disk center
as seen by SDO and at the limb as seen by STEREO. This configuration
allowed us to determine the kinematics of the EUV wave and of the
early EUV CME by AIA/SDO and EUVI/STEREO respectively. The detailed
kinematics of the early EUV CME (height and radius evolution of the
erupting flux) were then used to constrain a simple model of EUV wave
formation, invoking the erupting flux as the wave driver. The ground
tracks of the EUV wave as predicted by this data-driven model were
then compared with those of the observed wave.
---------------------------------------------------------
Title: On the initiation of Coronal Mass Ejections observed by
STEREO/EUVI
Authors: Syntelis, P.; Tsinganos, K.; Vourlidas, A.; Gontikakis, C.
2012hell.confR..14S Altcode:
This study examines different stages of a Coronal Mass Ejection's (CME)
initiation in NOAA Active Region (AR) 10980, observed on January 2,
2008 by STEREO's Extreme UltraViolet Imager (EUVI). We identify a
first phase consisting of an upward motion, which at 1.58R? reaches the
velocity of 70 (4) km/s. Those measurements are extrapolated to later
time frames to examine whether this initial acceleration drives the
CME's propagation later on. We also identify an ascending new flux-rope
beneath the CME. During the CME's rise, there are indications that
some adjacent loops incline to the main CME body. At the later phase
of the initiation, some moving blob-like structures appear along the
CME flanks. Propagation speeds of these blobs are measured. These
blobs could be indications that a siphon flow exists along the CME.
---------------------------------------------------------
Title: Investigation of the Formation and Separation of an
Extreme-ultraviolet Wave from the Expansion of a Coronal Mass Ejection
Authors: Cheng, X.; Zhang, J.; Olmedo, O.; Vourlidas, A.; Ding, M. D.;
Liu, Y.
2012ApJ...745L...5C Altcode: 2011arXiv1112.4540C
We address the nature of EUV waves through direct observations of the
formation of a diffuse wave driven by the expansion of a coronal mass
ejection (CME) and its subsequent separation from the CME front. The
wave and the CME on 2011 June 7 were well observed by the Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory. Following the
solar eruption onset, marked by the beginning of the rapid increasing
of the CME velocity and the X-ray flux of accompanying flare, the CME
exhibits a strong lateral expansion. During this impulsive expansion
phase, the expansion speed of the CME bubble increases from 100
km s<SUP>-1</SUP> to 450 km s<SUP>-1</SUP> in only six minutes. An
important finding is that a diffuse wave front starts to separate
from the front of the expanding bubble shortly after the lateral
expansion slows down. Also a type II burst is formed near the time of
the separation. After the separation, two distinct fronts propagate
with different kinematic properties. The diffuse front travels across
the entire solar disk, while the sharp front rises up, forming the CME
ejecta with the diffuse front ahead of it. These observations suggest
that the previously termed EUV wave is a composite phenomenon and
driven by the CME expansion. While the CME expansion is accelerating,
the wave front is cospatial with the CME front, thus the two fronts are
indiscernible. Following the end of the acceleration phase, the wave
moves away from the CME front with a gradually increasing distance
between them.
---------------------------------------------------------
Title: CMEs in the the Interplanetary Medium : analysis from the
Sun to 1 AU
Authors: Colaninno, R. C.; Vourlidas, A.; Nieves-Chinchilla, T.
2011AGUFMSH23A1946C Altcode:
For many years, white light coronagraphs have provided information on
the near Sun evolution of coronal mass ejections (CMEs). More recently,
the Heliospheric Imager (HI) instruments aboard the STEREO mission are
providing crucial remote sensing information on the interplanetary
evolution of these events. Data from in situ instruments complete
the overall characterization of interplanetary CMEs. In this work,
we present an analysis of a CME from near the Sun to 1 AU using
combined data from multiple spacecraft. We compare the propagation and
evolution as observed in remote sensing data with in situ observations
and derived parameters.
---------------------------------------------------------
Title: Uncovering the Wave Nature of the EIT Wave for the 2010 January
17 Event through Its Correlation to the Background Magnetosonic Speed
Authors: Zhao, X. H.; Wu, S. T.; Wang, A. H.; Vourlidas, A.; Feng,
X. S.; Jiang, C. W.
2011ApJ...742..131Z Altcode:
An EIT wave, which typically appears as a diffuse brightening that
propagates across the solar disk, is one of the major discoveries
of the Extreme ultraviolet Imaging Telescope on board the Solar
and Heliospheric Observatory. However, the physical nature of the
so-called EIT wave continues to be debated. In order to understand
the relationship between an EIT wave and its associated coronal wave
front, we investigate the morphology and kinematics of the coronal mass
ejection (CME)-EIT wave event that occurred on 2010 January 17. Using
the observations of the SECCHI EUVI, COR1, and COR2 instruments on
board the Solar Terrestrial Relations Observation-B, we track the shape
and movements of the CME fronts along different radial directions to a
distance of about 15 solar radii (R<SUB>s</SUB> ); for the EIT wave,
we determine the propagation of the wave front on the solar surface
along different propagating paths. The relation between the EIT wave
speed, the CME speed, and the local fast-mode characteristic speed is
also investigated. Our results demonstrate that the propagation of
the CME front is much faster than that of the EIT wave on the solar
surface, and that both the CME front and the EIT wave propagate faster
than the fast-mode speed in their local environments. Specifically,
we show a significant positive correlation between the EIT wave speed
and the local fast-mode wave speed in the propagation paths of the
EIT wave. Our findings support that the EIT wave under study is a
fast-mode magnetohydrodynamic wave.
---------------------------------------------------------
Title: Measurement of the Fast-Mode Wave Speed Using Full Sun Map
observations of Coronal Wave Events
Authors: Olmedo, O. A.; Vourlidas, A.; Zhang, J.; Cheng, X.
2011AGUFMSH12A..06O Altcode:
In this study we use observations from AIA on SDO, and EUVI on STEREO to
study the propagation of coronal "waves" over the entire solar surface
by constructing full Sun maps from all three telescopes. By tracing
paths that originate at the active region and reflect from the coronal
hole boundary we are able to predict the trajectory that "wave" will
take upon reflection. We compare the events that took place on 13 and 15
February 2011, from the same active region, and find that the reflected
waves have comparable speeds (~280-300 km/s), yet had different
incident speeds (~400 vs. ~600 km/s respectively). We interpret the
reflected wave as propagating at the fast-mode wave speed. Finally,
the high-cadence AIA observations allow us to examine the temporal
evolution of the wave in great detail. We compare the evolution of
the intensity/thermal response of the several wavelength observations.
---------------------------------------------------------
Title: A comparative study of the evolving morphology of 2.5-D
simulated CMEs to Earth's magnetosphere
Authors: Savani, N. P.; Shiota, D.; Kusano, K.; Lugaz, N.; Vourlidas,
A.
2011AGUFMSH22A..03S Altcode:
Our understanding of the evolving morphology of coronal mass
ejections (CMEs) has advanced significantly after remote-sensing
observations became available from the wide fields-of-view from
STEREO/SECCHI. However, the most practical way to relate the shock
parameters up and downstream to the CME morphology remains with the
numerical MHD models. We present 2.5-D numerical investigations of fast
CMEs and its associated shock between 10Rs and 250Rs. We display the
axis-symmetric results of the CMEs from different speeds and magnetic
field strength along the axis of the flux rope structure. We discuss
the relationship between the Mach number and density ratio over the
shock to the aspect ratio of CMEs. The sheath distance and the size
of the CME perpendicular to the spacecraft direction of travel are
related to those values estimated from Earth's magnetosphere.
---------------------------------------------------------
Title: The longitudinal properties of solar energetic particle events
investigated using modern solar imaging.
Authors: Rouillard, A. P.; Sheeley, N. R.; Tylka, A. J.; Vourlidas,
A.; Ng, C. K.; Mason, G. M.; Cohen, C. M.
2011AGUFMSH33D..03R Altcode:
On 2011 March 21, the Solar-Terrestrial Relations Observatory
(STEREO) imaged the launch (at ~02:10UT) and outward propagation of
a fast (>1300 km s-1) and wide (latitudinal extent greater than
90 degrees) coronal mass ejection (CME) which emerged W135 degrees
(behind the west-limb as viewed from near-Earth spacecraft). Protons
with energies exceeding 90 MeV were first detected by the STEREO-Ahead
(STA) spacecraft and a few minutes later by near-Earth orbiting
spacecraft. Velocity dispersion analyses of energetic electrons, protons
and heavier ions, put the solar particle release (SPR) times along
magnetic field lines connected to STA at ~02:30UT and along magnetic
field lines connected to near-Earth spacecraft at ~ 03:00UT. The
spatial evolution of a pressure wave and its associated shock forming
around the CME could be tracked using (critical) high-cadence and
high-resolution STA (extreme ultraviolet and white-light) images. We
demonstrate that the delay between the SEP onset at STA and Earth is
consistent with the time required for the pressure wave to propagate
from the launch-site of the CME to the base of coronal streamers that
are magnetically connected to near-Earth spacecraft. By considering
measured shock speeds and inferred shock geometries along different
longitudes and by deriving spectra of energetic protons, this study
also presents some interpretation of the longitudinal variability of
the SEP event in terms of the evolution of the compression wave. Time
permitting, we will also summarise the results of similar analyses
carried out for the other energetic CME events in 2010 and 2011.
---------------------------------------------------------
Title: Plasma Outflows Within Polar Coronal Plumes
Authors: Raouafi, N.; Stenborg, G.; Vourlidas, A.
2011AGUFMSH13B1959R Altcode:
Plasma outflow velocities within polar coronal plumes and their
contribution to the fast solar wind are a matter of controversy. We
investigate the plasma dynamics within plumes through the analysis
of high cadence and spatial resolution observations from the Solar
Dynamic Observatory (SDO) jointly with STEREO and Hinode data. This
analysis allows us to address the source of heating and plasma
acceleration inside polar plumes and therefore obtain constraint on
the contribution of plumes to the fast solar wind. Our results provide
important constraints of theoretical model dealing with the formation
and evolution of polar coronal plumes.
---------------------------------------------------------
Title: The role of CMEs in the lateral spread of electron events in
the inner heliosphere
Authors: Nieves-Chinchilla, T.; Gómez-Herrero, R.; Colaninno, R. C.;
Vourlidas, A.; Szabo, A.
2011AGUFMSH31B2001N Altcode:
This work focuses on the study of the role played by solar wind
transient events in the longitudinal spread of particles during some
SEP events. We have selected SEP events observed simultaneously by
STEREO and/or ACE/Wind that show an increase in the flux of nearly
relativistic electrons. We combine in situ and remote sensing analysis
to identify the 3D morphology, position, and kinematics of CMEs that
could facilitate the lateral spread.
---------------------------------------------------------
Title: Observations of the White Light Corona from Solar Orbiter
and Solar Probe Plus
Authors: Howard, R. A.; Thernisien, A. F.; Vourlidas, A.; Plunkett,
S. P.; Korendyke, C. M.; Sheeley, N. R.; Morrill, J. S.; Socker,
D. G.; Linton, M. G.; Liewer, P. C.; De Jong, E. M.; Velli, M. M.;
Mikic, Z.; Bothmer, V.; Lamy, P. L.
2011AGUFMSH43F..06H Altcode:
The SoloHI instrument on Solar Orbiter and the WISPR instrument on Solar
Probe+ will make white light coronagraphic images of the corona as the
two spacecraft orbit the Sun. The minimum perihelia for Solar Orbiter
is about 60 Rsun and for SP+ is 9.5 Rsun. The wide field of view of the
WISPR instrument (about 105 degrees radially) corresponds to viewing
the corona from 2.2 Rsun to 20 Rsun. Thus the entire Thomson hemisphere
is contained within the telescope's field and we need to think of
the instrument as being a traditional remote sensing instrument and
then transitioning to a local in-situ instrument. The local behavior
derives from the fact that the maximum Thomson scattering will favor
the electron plasma close to the spacecraft - exactly what the in-situ
instruments will be sampling. SoloHI and WISPR will also observe
scattered light from dust in the inner heliosphere, which will be an
entirely new spatial regime for dust observations from a coronagraph,
which we assume to arise from dust in the general neighborhood of about
half way between the observer and the Sun. As the dust grains approach
the Sun, they evaporate and do not contribute to the scattering. A
dust free zone has been postulated to exist somewhere inside of 5 Rsun
where all dust is evaporated, but this has never been observed. The
radial position where the evaporation occurs will depend on the
precise molecular composition of the individual grains. The orbital
plane of Solar Orbiter will gradually increase up to about 35 degrees,
enabling a very different view through the zodiacal dust cloud to test
the models generated from in-ecliptic observations. In this paper we
will explore some of the issues associated with the observation of
the dust and will present a simple model to explore the sensitivity
of the instrument to observe such evaporations.
---------------------------------------------------------
Title: Deriving the Physical Parameters of a Solar Ejection with an
Isotropic Magnetohydrodynamic Evolutionary Model
Authors: Berdichevsky, Daniel B.; Stenborg, Guillermo; Vourlidas,
Angelos
2011ApJ...741...47B Altcode:
The time-space evolution of a ~50° wide coronal mass ejection (CME)
on 2007 May 21 is followed remotely with the Solar Terrestrial
Relations Observatory heliospheric imager HI-1, and measured in
situ near Venus by the MESSENGER and Venus-Express spacecraft. The
paper compares the observations of the CME structure with a simple,
analytical magnetohydrodynamic force-free solution. It corresponds to
a self-similar evolution, which gives a consistent picture of the main
spatial-temporal features for both remote and in situ observations. Our
main findings are (1) the self-similar evolution allows us to map the
CME bright front into about 1/3 of the whole interplanetary counterpart
of the coronal mass ejection (ICME, i.e., corresponding to the in situ
observed passage of the plasma and magnetic field structure), in good
quantitative agreement with the imaging measurements, (2) the cavity
following the CME front maps into the rest of the ICME structure, 80%
or more of which is consistent with a force free, cylindrically shaped
flux rope, and (3) time and space conditions constrain the translational
speed of the FR center to 301 km s<SUP>-1</SUP>, and the expansion
speed of the FR core to 26 km s<SUP>-1</SUP>. A careful determination
of the ICME cross-section and volume allows us to calculate the mass
of the CME bright region (4.3 ± 1.1 10<SUP>14</SUP> g) from the
in situ measurements of the proton number density, which we assume
to be uniform inside the bright region, of excellent agreement with
the value estimated from the SECCHI HI-1 observations for the same
structure. We provide model estimates for several global parameters
including FR helicity (~2 × 10<SUP>26</SUP> Weber<SUP>2</SUP>).
---------------------------------------------------------
Title: A study of coronal mass ejections and the subsurface structure
at their source regions
Authors: Baldner, C.; Chen, J.; Vourlidas, A.
2011sdmi.confE.104B Altcode:
Coronal mass ejection (CME) is one of the most violent phenomena
in the solar atmosphere. One of the possible sources to cause such
violent eruption could be the magnetic flux and energy from below
the photosphere, However, due to the large difference in scales,
the subsurface and the atmosphere of the Sun have often been studied
separately. In this study, our objective is to combine the studies in
both fields in the hope to connect the subsurface magnetic fields to
the dynamics in the atmosphere. We selected a system of three active
regions, AR10987, AR10988 and AR10989, for this study. These three
active regions were located approximately at a same latitude and almost
equally separated. Two CMEs were detected from this group during our
observation period. We compared the CMEs with different CME models
both qualitatively and quantitatively. The best-matched model was
then used to deduce the possible driving mechanism of the CMEs. For
the study of the subsurface structure, we employed the techniques of
local helioseismology to obtain both the thermal and magnetic structural
properties. I will discuss our results in this presentation.
---------------------------------------------------------
Title: Recent Advances in Heliophysics from Space-Based Observations
Authors: Vourlidas, A.
2011Ippa....2...37V Altcode:
The Sun is the only star we can observe in detail and on the other hand,
solar variability drives the heliosphere and influences the environment
around our planet. Over the last 10-15 years, a large number of space
missions have been providing a smorgasbord of observations from the
photosphere to the outer reaches of the heliosphere. As a consequence,
solar and space physics are being integrated into a joint research
field, called heliophysics, and are tackling the mysteries of the
Sun and the heliosphere with great success. In this short review, I
discuss a few of those exciting advances in an attempt to capture the
spirit of progress that permeates the field. Due to space restrictions,
I left out many major results which may be addressed in future articles.
---------------------------------------------------------
Title: Forward Modeling of a CME Driven Shock : When is a Halo CME
not a CME?
Authors: Colaninno, Robin C.; Olmedo, Oscar; Thernisien, Arnaud;
Vourlidas, Angelos
2011shin.confE...2C Altcode:
In this work, we use the a forward modeling technique to model both a
CME and the resulting CME driven shock observed on 24 February 2011. We
incorporate coronagraph data from STEREO-SECCHI and SOHO LASCO to fit
the forward model. The 24 February 2011 CME and shock were directed
towards the STEREO-B spacecraft. From SOHO-LASCO, we can see the CME
driving the shock edge on. However, in both the STEREO-A and B fields
of view, the CME is hidden behind the occulter. The shock was also
measured in-situ at STEREO-B. If this event had been seen from only
the STEREO-A and B points of view, it might have been identified as a
weak halo CME or incorrectly associated with a secondary slow CME. The
implications of this event for space weather predications are discussed.
---------------------------------------------------------
Title: Interpreting the Properties of Solar Energetic Particle Events
by Using Combined Imaging and Modeling of Interplanetary Shocks
Authors: Rouillard, A. P.; Odstřcil, D.; Sheeley, N. R.; Tylka, A.;
Vourlidas, A.; Mason, G.; Wu, C. -C.; Savani, N. P.; Wood, B. E.;
Ng, C. K.; Stenborg, G.; Szabo, A.; St. Cyr, O. C.
2011ApJ...735....7R Altcode:
Images of the solar corona obtained by the Solar-Terrestrial Relations
Observatory (STEREO) provide high-cadence, high-resolution observations
of a compression wave forming ahead of a fast (940 km s<SUP>-1</SUP>)
coronal mass ejection (CME) that erupted at ~9:00 UT on 2010 April
03. The passage of this wave at 1 AU is detected in situ by the Advanced
Composition Explorer and Wind spacecraft at 08:00 UT on April 05 as a
shock followed by a turbulent and heated sheath. These unprecedented and
complementary observations of a shock-sheath region from the Sun to 1 AU
are used to investigate the onset of a Solar Energetic Particle (SEP)
event measured at the first Lagrange point (L1) and at STEREO-Behind
(STB). The spatial extent, radial coordinates, and speed of the ejection
are measured from STEREO observations and used as inputs to a numerical
simulation of the CME propagation in the background solar wind. The
simulated magnetic and plasma properties of the shock and sheath region
at L1 agree very well with the in situ measurements. These simulation
results reveal that L1 and STB are magnetically connected to the western
and eastern edges of the driven shock, respectively. They also show
that the 12 hr delay between the eruption time of the ejection and the
SEP onset at L1 corresponds to the time required for the bow shock to
reach the magnetic field lines connected with L1. The simulated shock
compression ratio increases along these magnetic field lines until
the maximum flux of high-energy particles is observed.
---------------------------------------------------------
Title: The Reflection of Coronal Waves from Coronal Holes Seen in
Full Sun Synoptic Maps
Authors: Olmedo, Oscar; Olmedo, Oscar; Vourlidas, Angelos; Zhang,
Jie; Cheng, Xin
2011shin.confE..76O Altcode:
We demonstrate the wave nature of
---------------------------------------------------------
Title: The First Observation of a Rapidly Rotating Coronal Mass
Ejection in the Middle Corona
Authors: Vourlidas, A.; Colaninno, R.; Nieves-Chinchilla, T.;
Stenborg, G.
2011ApJ...733L..23V Altcode:
In this Letter, we present the first direct detection of a
rotating coronal mass ejection (CME) in the middle corona (5-15 R
<SUB>sun</SUB>). The CME rotation rate is 60° day<SUP>-1</SUP>, which
is the highest rate reported yet. The Earth-directed event was observed
by the STEREO/SECCHI and SOHO/LASCO instruments. We are able to derive
the three-dimensional morphology and orientation of the CME flux rope
by applying a forward-fitting model to simultaneous observations from
three vantage points (SECCHI-A, -B, LASCO). Surprisingly, we find that
even such rapidly rotating CME does not result in significant projection
effects (variable angular width) in any single coronagraph view. This
finding may explain the prevalent view of constant angular width for
CMEs above 5 R <SUB>sun</SUB> and the lack of detections of rotating
CMEs in the past. Finally, the CME is a "stealth" CME with very weak low
corona signatures as viewed from Earth. It originated from a quiet-Sun
neutral line. We tentatively attribute the fast rotation to a possible
disconnection of one of the CME footpoints early in the eruption. We
discuss the implications of such rotations to space weather prediction.
---------------------------------------------------------
Title: CME reconstruction: Pre-STEREO and STEREO era
Authors: Thernisien, A.; Vourlidas, A.; Howard, R. A.
2011JASTP..73.1156T Altcode:
Since the first observations of coronal mass ejections (CMEs) in 1970s,
their three-dimensional (3D) morphology has been a key ingredient for
understanding their origin and evolution. The determination of their
3D structure using a single viewpoint, however posed a challenge
because only their 2D projection on the sky plane is observed. The
operation of the STEREO mission with its unique capability of imaging
the inner heliosphere from two viewpoints has greatly improved this
situation. It is therefore timely to review the pre-STEREO efforts in
3D CME reconstruction and compare them with the first STEREO results
in this area. Our paper focuses on the techniques relevant to the
CME morphology: forward modeling, polarimetric, spectroscopic, direct
inversion. We also discuss the limitations and considerations involved
in each technique.
---------------------------------------------------------
Title: Euv Imaging Of Shock Formation In The Low Corona With Sdo/aia
Authors: Vourlidas, Angelos; Patsourakos, S.; Kouloumvakos, T.
2011SPD....42.0907V Altcode: 2011BAAS..43S.0907V
Shock generation in the low corona has long been inferred by spectral
observations of drifting so-called type-II radio emission in the
metric wavelengths. Type-IIs occur with coronal mass ejections (CMEs)
and/or flares but not consistently. Therefore, the exact relationship
has been difficult to pin down, mostly because of the lack of radio
imaging capability and of the low cadence of EUV observations in the
low corona during the flare/CME formation. The advent of ultra-high
observations from the AIA imagers has changed all that. In this talk,
we present several direct observations of shock formation in the EUV
and their association to the accompanying type-IIs. We will show that
the coronal expansion driven by the formation of the CME ejecta is
responsible for both EUV and radio emissions.
---------------------------------------------------------
Title: Viewing The Entire Sun With STEREO And SDO
Authors: Thompson, William T.; Gurman, J. B.; Kucera, T. A.; Howard,
R. A.; Vourlidas, A.; Wuelser, J.; Pesnell, D.
2011SPD....42.1835T Altcode: 2011BAAS..43S.1835T
On 6 February 2011, the two Solar Terrestrial Relations Observatory
(STEREO) spacecraft were at 180 degrees separation. This allowed the
first-ever simultaneous view of the entire Sun. Combining the STEREO
data with corresponding images from the Solar Dynamics Observatory
(SDO) allows this full-Sun view to continue for the next eight years. We
show how the data from the three viewpoints are combined into a single
heliographic map. Processing of the STEREO beacon telemetry allows
these full-Sun views to be created in near-real-time, allowing tracking
of solar activity even on the far side of the Sun. This is a valuable
space-weather tool, not only for anticipating activity before it rotates
onto the Earth-view, but also for deep space missions in other parts of
the solar system. Scientific use of the data includes the ability to
continuously track the entire lifecycle of active regions, filaments,
coronal holes, and other solar features. There is also a significant
public outreach component to this activity. The STEREO Science Center
produces products from the three viewpoints used in iPhone/iPad and
Android applications, as well as time sequences for spherical projection
systems used in museums, such as Science-on-a-Sphere and Magic Planet.
---------------------------------------------------------
Title: New Results Revealed By Enhanced Extreme-Ultraviolet Images
Authors: Stenborg, Guillermo A.; Vourlidas, A.; Howard, R.
2011SPD....42.1809S Altcode: 2011BAAS..43S.1809S
Groundbreaking observations of the low solar corona at extreme
ultraviolet (EUV) wavelengths have been provided by the EIT instrument
on board SOHO for more than 15 years. At the beginning of 2007, the
EUVI instruments onboard the twin STEREO S/C opened doors and commenced
to image the EUV low corona with a better cadence and better spatial
resolution from two vantage points off the Sun-Earth line. And now,
since February 2010 the AIA instrument on board the Solar Dynamics
Observatory observes the low EUVI corona at a 10 sec cadence in 8
wavelengths. Despite the increasing quality of the EUV observations,
they have not been fully exploited. A customized wavelet-based image
cleaning and enhancing technique that exploits the multi-scale nature
of the observed solar features has been developed (Stenborg et al.,
2008) to maximize the scientific return of the EIT observations. We
have now adapted it to work with STEREO/EUVI and SDO/AIA images. Its
application has already helped unveil phenomena only theorized before,
as well as revealed phenomena that have not found a satisfactory
explanation yet. In this presentation, a brief survey of the new
products and recent discoveries will be shown.
---------------------------------------------------------
Title: Solar Eruptive Events (SEE) Mission for the Next Solar Maximum
Authors: Lin, Robert P.; Krucker, S.; Caspi, A.; Hurford, G.; Dennis,
B.; Holman, G.; Christe, S.; Shih, A. Y.; Bandler, S.; Davila, J.;
Milligan, R.; Kahler, S.; Weidenbeck, M.; Doschek, G.; Vourlidas,
A.; Share, G.; Raymond, J.; McConnell, M.; Emslie, G.
2011SPD....42.2204L Altcode: 2011BAAS..43S.2204L
Major solar eruptive events consisting of both a large flare and a
near simultaneous large fast coronal mass ejection (CME), are the most
powerful explosions and also the most powerful and energetic particle
accelerators in the solar system, producing solar energetic particles
(SEPs) up to tens of GeV for ions and 10s-100s of MeV for electrons. The
intense fluxes of escaping SEPs are a major hazard for humans in space
and for spacecraft. Furthermore, the solar plasma ejected at high speed
in the fast CME completely restructures the interplanetary medium,
producing the most extreme space weather in geospace, at other planets,
and in the heliosphere. Thus, the understanding of the flare/CME
energy release process and of the related particle acceleration
processes in SEEs is a major goal in Heliophysics. Here we present
a concept for a Solar Eruptive Events (SEE) mission, consisting of a
comprehensive set of advanced new instruments on the single spacecraft
in low Earth orbit, that focus directly on the coronal energy release
and particle acceleration in flares and CMEs. SEE will provide new
focussing hard X-ray imaging spectroscopy of energetic electrons in the
flare acceleration region, new energetic neutral atom (ENA) imaging
spectroscopy of SEPs being accelerated by the CME at altitudes above
2 solar radii, gamma-ray imaging spectroscopy of flare-accelerated
energetic ions, plus detailed EUV/UV/Soft X-ray diagnostics of the
plasmas density, temperature, and mass motions in the energy release and
particle acceleration regions. Together with ground-based measurements
of coronal magnetic fields from ATST, FASR, and COSMO, SEE will enable
major breakthroughs in our understanding of the fundamental physical
processes involved in major solar eruptive events.
---------------------------------------------------------
Title: Study of the Coronal Wave Event of February 15, 2011 Over
the Entire Solar Surface.
Authors: Olmedo, Oscar; Vourlidas, A.; Zhang, J.; Cheng, X.
2011SPD....42.1834O Altcode: 2011BAAS..43S.1834O
We investigate the coronal wave associated with the February 15, 2011
X-class flare. The flare occurred at 1:44 UT in active region NOAA
11158. We use observations from the Atmospheric Imaging Assembly (AIA)
aboard Solar Dynamics Observatory, and the Extreme Ultraviolet Image
(EUVI) aboard the Solar Terrestrial Relations Observatory to study
the propagation of the coronal wave over the entire solar surface with
the help of full Sun synoptic maps. The high-cadence AIA observations
allow us to examine the temporal evolution of the wave in great
detail. Our investigation focuses on two aspects: (i) The apparent
transmission and reflection of the wave through a coronal hole, and
(ii) the thermal response in the corona during the coronal wave passage.
---------------------------------------------------------
Title: Erratum: "Comprehensive Analysis of Coronal Mass
Ejection Mass and Energy Properties Over a Full Solar Cycle" <A
href="/abs/2010ApJ...722.1522V">(2010, ApJ, 722, 1522)</A>
Authors: Vourlidas, A.; Howard, R. A.; Esfandiari, E.; Patsourakos,
S.; Yashiro, S.; Michalek, G.
2011ApJ...730...59V Altcode:
No abstract at ADS
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Title: A novel technique to measure intensity fluctuations in EUV
images and to detect coronal sound waves nearby active regions
Authors: Stenborg, G.; Marsch, E.; Vourlidas, A.; Howard, R.;
Baldwin, K.
2011A&A...526A..58S Altcode:
Context. In the past years, evidence for the existence of outward-moving
(Doppler blue-shifted) plasma and slow-mode magneto-acoustic propagating
waves in various magnetic field structures (loops in particular) in
the solar corona has been found in ultraviolet images and spectra. Yet
their origin and possible connection to and importance for the mass and
energy supply to the corona and solar wind is still unclear. There has
been increasing interest in this problem thanks to the high-resolution
observations available from the extreme ultraviolet (EUV) imagers on
the Solar TErrestrial RElationships Observatory (STEREO) and the EUV
spectrometer on the Hinode mission. <BR /> Aims: Flows and waves exist
in the corona, and their signatures appear in EUV imaging observations
but are extremely difficult to analyse quantitatively because of their
weak intensity. Hence, such information is currently available mostly
from spectroscopic observations that are restricted in their spatial
and temporal coverage. To understand the nature and origin of these
fluctuations, imaging observations are essential. Here, we present
measurements of the speed of intensity fluctuations observed along
apparently open field lines with the Extreme UltraViolet Imagers (EUVI)
onboard the STEREO mission. One aim of our paper is to demonstrate that
we can make reliable kinematic measurements from these EUV images,
thereby complementing and extending the spectroscopic measurements
and opening up the full corona for such an analysis. Another aim is to
examine the assumptions that lead to flow versus wave interpretation
for these fluctuations. <BR /> Methods: We have developed a novel
image-processing method by fusing well established techniques for
the kinematic analysis of coronal mass ejections (CME) with standard
wavelet analysis. The power of our method lies with its ability
to recover weak intensity fluctuations along individual magnetic
structures at any orientation , anywhere within the full solar disk ,
and using standard synoptic observing sequences (cadence <3 min)
without the need for special observation plans. <BR /> Results: Using
information from both EUVI imagers, we obtained wave phase speeds
with values on the order of 60-90 km s<SUP>-1</SUP>, compatible with
those obtained by other previous measurements. Moreover, we studied the
periodicity of the observed fluctuations and established a predominance
of a 16-min period, and other periods that seem to be multiples of
an underlying 8-min period. <BR /> Conclusions: The validation of our
analysis technique opens up new possibilities for the study of coronal
flows and waves, by extending it to the full disk and to a larger
number of coronal structures than has been possible previously. It
opens up a new scientific capability for the EUV observations from
the recently launched Solar Dynamics Observatory. Here we clearly
establish the ubiquitous existence of sound waves which continuously
propagate along apparently open magnetic field lines. <P />Movies 1
and 2 (Figs. 12 and 13) are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Evidence for a current sheet forming in the wake of a coronal
mass ejection from multi-viewpoint coronagraph observations
Authors: Patsourakos, S.; Vourlidas, A.
2011A&A...525A..27P Altcode: 2010arXiv1010.0323P
Context. Ray-like features observed by coronagraphs in the wake
of coronal mass ejections (CMEs) are sometimes interpreted as the
white light counterparts of current sheets (CSs) produced by the
eruption. The 3D geometry of these ray-like features is largely
unknown and its knowledge should clarify their association to the
CS and place constraints on CME physics and coronal conditions. <BR
/> Aims: If these rays are related to field relaxation behind CMEs,
therefore representing current sheets, then they should be aligned to
the CME axis. With this study we test these important implications for
the first time. <BR /> Methods: An example of such a post-CME ray was
observed by various coronagraphs, including these of the Sun Earth
Connection Coronal and Heliospheric investigation (SECCHI) onboard
the Solar Terrestrial Relations Observatory (STEREO) twin spacecraft
and the Large Angle Spectrometric Coronagraph (LASCO) onboard the
Solar and Heliospheric Observatory (SOHO). The ray was observed in
the aftermath of a CME which occurred on 9 April 2008. The twin STEREO
spacecraft were separated by about 48° on that day. This significant
separation combined with a third “eye” view supplied by LASCO allow
for a truly multi-viewpoint observation of the ray and of the CME. We
applied 3D forward geometrical modeling to the CME and to the ray as
simultaneously viewed by SECCHI-A and B and by SECCHI-A and LASCO,
respectively. <BR /> Results: We found that the ray can be approximated
by a rectangular slab, nearly aligned with the CME axis, and much
smaller than the CME in both terms of thickness and depth (≈0.05
and 0.15 R<SUB>⊙</SUB> respectively). The ray electron density and
temperature were substantially higher than their values in the ambient
corona. We found that the ray and CME are significantly displaced
from the associated post-CME flaring loops. <BR /> Conclusions:
The properties and location of the ray are fully consistent with
the expectations of the standard CME theories for post-CME current
sheets. Therefore, our multi-viewpoint observations supply strong
evidence that the observed post-CME ray is indeed related to a post-CME
current sheet. <P />Movies are only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: The Wide Field Imager for Solar PRobe (WISPR)
Authors: Plunkett, S. P.; Howard, R. A.; Vourlidas, A.; Korendyke,
C. M.; Socker, D. G.; Morrill, J. S.; Sheeley, N. R.; Linton, M.;
Liewer, P. C.; de Jong, E. M.; Mikic, Z.
2010AGUFMSH11B1622P Altcode:
The Wide Field Imager for Solar PRobe (WISPR) will image the
Thomson-scattered light from the coronal plasma in the inner corona,
with unprecedented spatial resolution, cadence, and sensitivity. WISPR
follows on the SECCHI Heliospheric Imager (HI) aboard the STEREO
mission, and addresses all four key objectives in the Solar Probe Plus:
Report of the STDT (2008): (1) Determine the structure and dynamics of
the magnetic fields at the sources of the fast and slow solar wind, (2)
Trace the flow of energy that heats the solar corona and accelerates
the SW, (3) explore the mechanisms that accelerate and transport
energetic particles, (4) explore dusty plasma phenomena and their
influence on the solar wind and energetic particle formation. Situated
in the ram direction of the Solar Probe Plus (SPP) spacecraft (S/C),
WISPR will have the unique ability to image the coronal structures when
they are close to the Sun, as they approach, and as they pass over the
spacecraft. As a remote sensor, WISPR will connect the structures close
to the Sun to the spacecraft and provide important spatial and temporal
information; measuring, for example, the properties of the structures
generating the shocks and SEPs that will be measured in a few minutes at
the S/C. Since the S/C is embedded in the corona, WISPR and the in situ
instruments will measure for the first time the same plasma. Also as
the SPP transits through the corona, the rapidly-varying viewpoint and
high spatial resolution of WISPR will enable tomographic imaging of the
corona, and lead to higher fidelity and finer scale 3D reconstructions
than are possible with the STEREO mission or single-view rotational
tomography. The wide field of view will include at times other inner
heliospheric probes (e.g. Solar Orbiter) and will image the outflowing
wind that is impinging on that probe. In addition to this standard
imaging mode, WISPR opens a new capability for imaging instruments,
the measurement of pressure turbulence by employing a high cadence mode
(~1 sec) to image a small region in the corona. For the first time,
the slopes of the power spectral density from images can be compared
directly to the density and magnetic field fluctuations seen in situ as
a function of coronal spatial structure and heliocentric distance. In
addition, the 1 sec cadence can be generated anywhere within the WISPR
field, enabling the study of the transition of the solar wind injected
at the tops of the helmet streamers to inertial dissipation scales.
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Title: The Genesis of an Impulsive CME observed by AIA on SDO
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2010AGUFMSH14A..03P Altcode:
Understanding the first moments in the life-time of Coronal Mass
Ejections (CMEs), i.e. their genesis, represents possibly the key to
unlock the physical processes responsible for their initiation. After
this critical interval, which could last as little as few minutes for
the most impulsive events, differences between various CME models become
minimal. The recent launch of the SDO mission and the availability of
high-quality EUV imaging from AIA in particular, opened a new avenue
into CME initiation investigations with its unprecedented image cadence
and multi-wavelength simultaneous coverage. We here report on AIA
observations of an impulsive CME-flare-EUV wave event which took place
during 13 June 2010. All the important dynamics (e.g., rise phase of
the flare, impulsive acceleration of the CME) had a duration of only
10 minutes making this event a perfect showcase event for AIA. Taking
advantage of the unique aspects of AIA data (12 sec cadence and 7
different EUV channels) we present a detailed analysis of this event
which includes: (1) its kinematic behavior (acceleration profile);
(2) radial and expansion speeds; (3) relationships between (1) and (2)
with the flare energy release; (4) multi-temperature evolution of the
early CME. All the above supply new strong constraints for the physics
of impulsive CMEs.
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Title: The Genesis of an Impulsive Coronal Mass Ejection Observed
at Ultra-high Cadence by AIA on SDO
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2010ApJ...724L.188P Altcode: 2010arXiv1010.5234P
The study of fast, eruptive events in the low solar corona is one
of the science objectives of the Atmospheric Imaging Assembly (AIA)
imagers on the recently launched Solar Dynamics Observatory (SDO), which
take full disk images in 10 wavelengths with arcsecond resolution and
12 s cadence. We study with AIA the formation of an impulsive coronal
mass ejection (CME) which occurred on 2010 June 13 and was associated
with an M1.0 class flare. Specifically, we analyze the formation of
the CME EUV bubble and its initial dynamics and thermal evolution in
the low corona using AIA images in three wavelengths (171 Å, 193 Å,
and 211 Å). We derive the first ultra-high cadence measurements
of the temporal evolution of the CME bubble aspect ratio (=bubble
height/bubble radius). Our main result is that the CME formation
undergoes three phases: it starts with a slow self-similar expansion
followed by a fast but short-lived (~70 s) period of strong lateral
overexpansion which essentially creates the CME. Then the CME undergoes
another phase of self-similar expansion until it exits the AIA field of
view. During the studied interval, the CME height-time profile shows a
strong, short-lived, acceleration followed by deceleration. The lateral
overexpansion phase coincides with the deceleration phase. The impulsive
flare heating and CME acceleration are closely coupled. However,
the lateral overexpansion of the CME occurs during the declining
phase and is therefore not linked to flare reconnection. In addition,
the multi-thermal analysis of the bubble does not show significant
evidence of temperature change.
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Title: Temporal evolution and spatial variation of the solar wind
from multi-spacecraft measurements
Authors: Opitz, A.; Wurz, P.; Fedorov, A.; Sauvaud, J.; Luhmann, J. G.;
Riley, P.; Szego, K.; Russell, C. T.; Galvin, A. B.; Rouillard, A. P.;
Vourlidas, A.; van Driel-Gesztelyi, L.
2010AGUFMSH33C..07O Altcode:
We study the temporal evolution and the spatial variation of the solar
wind on different scales. The analyzed multi-spacecraft (STEREO, VEX,
SOHO, MEX, and other spacecraft) measurements were obtained between 2007
and 2010 during solar minimum in the inner heliosphere. We derived
the temporal and spatial variability of the different solar wind
parameters (proton bulk velocity, electron core density, etc). These
results support prediction of the solar wind parameters for different
heliospheric positions and help to derive its validity range. In order
to explain occasional deviations from the nominal solar wind evolution
we use imaging data and modeling results.
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Title: Causes, Occurrences, and Consequences of Extreme Solar Particle
Events (Invited)
Authors: Mewaldt, R. A.; Cohen, C. M.; Mason, G. M.; Vourlidas, A.
2010AGUFMSH52A..01M Altcode:
This talk will discuss the conditions that result in extreme solar
energetic particle (SEP) events, their frequency of occurrence,
and some of their consequences. It will argued that the largest
SEP events are accelerated by shocks driven by fast coronal mass
ejections (CMEs), and that they require CMEs with kinetic energies
exceeding 10<SUP>32</SUP> ergs that encounter an abundant population
of suprathermal seed particles. The occurrence frequency of extreme
SEP events will be investigated using in-situ, ground-based, and polar
ice-core data. Finally, we discuss some of the potential consequences
of extreme SEP events for humans and hardware in space.
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Title: Kinematic Characterization Of In/out Pairs As Seen In Secchi
Authors: Baldwin, K. L.; Vourlidas, A.; Zhang, J.; Linton, M.
2010AGUFMSH23B1853B Altcode:
This study investigates the kinematic properties of the “in/out
pair” coronal features seen in Thompson scattered, white-light
coronagraph images. Frequently, the pairs occur as the after-math of
solar coronal mass ejections appearing at first as a pin hole tear along
the streamer axis. The tear appears consistently at around 5 solar
radii. Due to the timing and location of these events, it is likely
that the pairs are indicators of magnetic reconnection at the trailing
edge of CMEs. Using the SECCHI COR1/COR2 instruments in combination with
the LASCO C2 data, we are able to calculate the 3D location as well as
the true speed of the pairs using elongation-time map (so-called JMAP)
capabilities. The inflow portion of the pairs are seen in both SECCHI
and LASCO coronagraphs and travel at approximately 100 km/s. While,
the outflow portion take the shape of the outflow of the preceding
storm and travel faster than 200 km/s. The images used in this analysis
were processed using a running difference technique. Previous images
subtraction highlights the proper motions of the intensity enhancements,
while removing background effects. These results may shed light on
the processes of magnetic reconnection following solar storms.
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Title: Importance of Heliospheric Evolution to Understand CME
Geo-effectiveness
Authors: Lugaz, N.; Roussev, I. I.; Vourlidas, A.; Gombosi, T. I.
2010AGUFMSH51C1695L Altcode:
The properties of coronal mass ejections (CMEs) as they leave the
corona (around 5-15 Rsun), are an important indication of their
potential geo-effectiveness. It is, for example, the case for their
speed, direction and orientation. However, during the heliosopheric
propagation, these properties can change dramatically. Here, we present
cases, when a CME expected geo-effectivness is significantly modified
during its propagation and when the speed, direction and orientation of
a CME at 1 AU can not simply be predicted directly from the properties
in the corona. We focus on 3-D MHD simulations of CMEs as well as the
analysis of heliospheric observations by STEREO/SECCHI. We present
instances of shock-shock interaction, shock-CME interaction as well
as cases when a CME is deflected in the heliosphere.
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Title: Simulations of Overexpanding CME Cavities
Authors: Kliem, B.; Forbes, T.; Vourlidas, A.; Patsourakos, S.
2010AGUFMSH51A1661K Altcode:
Coronal mass ejection (CME) cavities seen in white-light coronagraphs
expand nearly self similarly in the outer corona and inner solar
wind. Little is known about their initial expansion in the inner
corona. A two-phase evolution, consisting of an initial overexpansion
up to a heliocentric front height of about 1.5 solar radii, followed by
nearly self-similar expansion, was recently discovered in STEREO/SECCHI
observations of a fast CME (Patsourakos et al. 2010). The overexpansion
is expressed as a decrease of the cavity aspect ratio (center height
by radius) by at least a factor of 2 during the rise phase of the
main CME acceleration. We present MHD simulations of erupting flux
ropes that show the initial overexpansion of a cavity in line with
the observed evolution. The contributions of ideal-MHD expansion and
of magnetic reconnection to the growth of the flux rope and cavity
in the simulations will be quantified to identify the primary cause
of the overexpansion. This assesses the diagnostic potential of the
overexpansion for the change of flux rope current and the role of
magnetic reconnection in the early evolution of CMEs.
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Title: Interpreting SDO/AIA observations of EUV waves, a comprehensive
analysis with direct comparison to global MHD simulations
Authors: Downs, C.; Roussev, I. I.; Vourlidas, A.; van der Holst,
B.; Lugaz, N.
2010AGUFMSH11A1614D Altcode:
In this work we present an analysis of two EUV waves observed by the
Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory
(SDO) in the context of thermodynamic MHD simulations of the global
Solar Corona. Due to the extreme advances in cadence, resolution,
and bandpass coverage in the EUV regime, the AIA instrument offers an
unprecedented ability to observe the dynamics of large scale coronal
wave-like transients known as EUV waves. However, the complexity of
the corona, coupled with line-of-sight (LOS) projection of structures,
can often make the physical nature of EUV waves difficult to interpret
directly. To provide a comprehensive physical analysis and further
compliment observational insight, we employ a global MHD model
that captures the thermodynamic structure of the low corona for
the conditions of a given solar rotation (the LC component of the
SWMF). This provides a self-consistent framework to characterize
both the pre-event conditions as well as the time-dependent dynamics
of the eruption itself using a CME eruption model. A key feature of
this model is the ability to synthesize the multi-filter response
of the SDO/AIA instrument directly from model data, which allows
for direct interpretation of AIA observations with full knowledge of
the 3D magnetic and thermodynamic structures in the simulations. We
focus on the interpretation of the stark thermodynamic signatures
in the multi-filter AIA data within the propagating EUV wave front
(unambiguous now due to the high uniform cadence of the AIA band-passes)
and address the non-linear interaction of the EUV wave front with
neighboring regions in the ambient corona.
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Title: Kinematic analysis and comparison of the CME and its related
EIT wave for January 10, 2010 event
Authors: Zhao, X.; Wu, S.; Wang, A.; Vourlidas, A.
2010AGUFMSH23B1844Z Altcode:
EIT wave, typically appearing as a diffuse brightening propagating
across the Sun, is one of the major discoveries of the Extreme
ultraviolet Imaging Telescope (EIT) on SOHO. But the physical nature
of the so-called EIT wave is strongly debated. In order to understand
the relationship between the EIT wave and its related Coronal mass
ejection (CME), we investigate the morphology and kinematics of the
CME-EIT wave event happened on January 10, 2010. Using the observations
of SECCHI/EUVI, SECCHI/COR1 and SECCHI/COR2 onboard the STEREO-B,
we track the shape and movements of the CME fronts along different
radial directions to the distance of about 15 solar radii; While for
the EIT wave, we determine the propagation of the wave front on the
solar surface along different propagation directions. Our tracking
results demonstrate that the CME front propagation is much faster
than the propagation of the EIT wave on the surface. While this CME
exhibits deceleration during its moving out, the EIT wave propagates
at nearly constant speed. We also compare their propagation speeds to
the characteristic speeds, and find out that both the CME and the EIT
wave propagate beyond and with the fast-mode speed.
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Title: White Light and Radio Emission of CME-Shocks: their Evolution
in the Interplanetary Medium
Authors: Ontiveros, V.; Corona-Romero, P.; Gonzalez-Esparza, A.;
Aguilar-Rodriguez, E.; Vourlidas, A.
2010AGUFMSH23B1845O Altcode:
We analysed fast Coronal Mass Ejections (CMEs) driving shocks close
to the solar surface and their evolution in the interplanetary (IP)
medium. For each event we derived the CME kinematics and the shock
strength from coronograph images, and the shock speeds in the IP medium
from their type II radio burst emissions. We studied these events with
an analytical model to illuminate their IP evolution.
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Title: The Birth of Coronal Mass Ejections As Seen by STEREO and SDO
Authors: Vourlidas, A.; Patsourakos, S.
2010AGUFMSH21C..07V Altcode:
Despite observations of thousands of coronal mass ejections (CMEs),
the details of their formation still elude us. Impulsive CMEs, in
particular, originate low in the corona, and form within 10-15 mins
while accelerating rapidly. This region of the corona is regularly
observed by EUV imagers but the rapid CME evolution requires high
cadence and relatively large fields of view. Thanks to the operation of
the STEREO and SDO missions, we are currently in a unique position to
address the problem of CME formation. The two missions provide almost
simultaneous observations from three viewpoints with 3 EUV imagers. The
EUV instruments observe in the same (or similar) channels and have
highly complimentary cadences and fields of view. In this paper, we
discuss a coherent picture of the birth of CMEs based on a study of the
first few-minute evolution of several impulsive CMEs. These CMEs seem
to first undergo an non-linear expansion followed by a self-similar
phase. We discuss the implication for CME initiation models.
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Title: Imaging the Solar Wind with SoloHI
Authors: Howard, R. A.; Vourlidas, A.; Plunkett, S. P.; Korendyke,
C. M.; McMullin, D. R.; Liewer, P. C.; Velli, M. M.; Solohi
2010AGUFMSH11B1627H Altcode:
Imaging outflows in the corona have been observed with the SOHO/LASCO
instrument, since 1996. With the launch of the STEREO mission in
2006, these outflows can be followed into the heliosphere, with the
SECCHI/Heliospheric Imager. For the Solar Orbiter mission, we have
proposed an instrument called the Solar Orbiter Heliospheric Imager
(SoloHI) to be able to image the solar wind and the density fluctuations
in the wind and thus provide the link between the in-situ and remote
sensing measurements. The nature of the Thomson scattering process
integrates along a particular look direction but the scattering is a
maximum on the Thomson sphere - the locus of points that form a right
angle between the look direction and the solar vector. The experience
from SECCHI/HI shows that the density fluctuations are easily visible
and can be tracked back into the low corona, enabling a coupling
between the solar wind plasma crossing the spacecraft and the source
region in the corona. However, the SECCHI/HI observations have low
cadence and long integration times. As a new observing mode for SoloHI,
we have implemented a capability to readout a subset of the image at
a time cadence of about 1 second. Thus small scale fluctuations can
be observed in addition to the large scale fluctuations observed from
SECCHI/HI. This will enable us to determine the spectral index of the
density fluctuations over an unprecedented range of heights (from 5 to
135 Rsun) to compare with the in-situ determinations of the spectral
index. This may indicate whether the fluctuations are generated close
to the sun and convected out by the solar wind or are generated within
the solar wind.
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Title: Capturing the Three-Dimensional Motion of the 16 June 2010
CME in the STEREO-SECCHI Observations using Scene Flow
Authors: Colaninno, R. C.; Vourlidas, A.
2010AGUFMSH23B1856C Altcode:
The motion of coronal mass ejections (CMEs) in the heliosphere is
governed by the complex interactions of the magnetic field and gas
pressure both internal and external to the CME. The two-viewpoint
observations of the Sun Earth Connection Coronal and Heliospheric
Investigation (SECCHI) instrument suite abroad the Solar TErrestrial
RElations Observatory (STEREO) mission is a unique resource for
studying these forces throughout the heliosphere. To access the fullest
potential of these data, we first need to apply advanced image analysis
tools to deal with the three-dimensional data. Here, we present the
application of the computer vision technique of scene flow on the
CME observed by SECCHI on 10 June 2010. Scene flow methods estimate
the three-dimensional motion of points in the field of view using
multiple camera sequences. We use a scene flow algorithm to estimate the
three-dimensional velocity at every point on a surface of the 10 June
2010 CME. We discuss how these technique can be used in future research.
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Title: Reconstructing CMEs with Coordinated Imaging and In Situ
Observations: Global Structure, Kinematics, and Implications for
Space Weather Forecasting
Authors: Liu, Y.; Thernisien, A. F.; Luhmann, J. G.; Vourlidas, A.;
Davies, J. A.; Lin, R. P.; Bale, S.
2010AGUFMSH23B1861L Altcode:
We reconstruct the global structure and kinematics of coronal mass
ejections (CMEs) using coordinated imaging and in situ observations
from multiple vantage points. A forward modeling technique, which
assumes a rope-like morphology for CMEs, is used to determine the
global structure (including orientation and propagation direction)
from coronagraph observations. We reconstruct the corresponding
structure from in situ measurements at 1 AU with the Grad-Shafranov
(GS) method, which gives the flux-rope orientation, cross section
and a rough knowledge of the propagation direction. CME kinematics
(propagation direction and radial distance) during the transit from
the Sun to 1 AU are studied with a geometric triangulation technique,
which provides an unambiguous association between solar observations
and in situ signatures; a track fitting approach is invoked when
data are available from only one spacecraft. We show how the results
obtained from imaging and in situ data can be compared by applying
these methods to some events, especially Earth-directed ones. This
merged imaging and in situ study shows important consequences and
implications for CME research as well as space weather forecasting:
(1) CME propagation directions can be determined to a relatively good
precision as shown by the consistency between different methods; (2)
the geometric triangulation technique shows a promising capability to
link solar observations with corresponding in situ signatures at 1 AU
and to predict CME arrival at the Earth; (3) the flux rope within CMEs,
which has the most hazardous southward magnetic field, cannot be imaged
at large distances due to expansion; (4) the flux-rope orientation
derived from in situ measurements at 1 AU may have a large deviation
from that determined by coronagraph image modeling; (5) we find, for
the first time, that CMEs undergo a westward migration with respect
to the Sun-Earth line at their acceleration phase, which we suggest
as a universal feature produced by the magnetic field connecting the
Sun and ejecta. Importance of having dedicated spacecraft at L4 and
L5, which are well situated for the triangulation concept, is also
discussed based on the results.
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Title: Connecting CME expansion from Sun to 1 AU
Authors: Nieves-Chinchilla, T.; Colaninno, R. C.; Vourlidas, A.;
Szabo, A.; Vinas, A. F.; Davila, J. M.
2010AGUFMSH23B1841N Altcode:
EUV disk imagers and white light coronagraphs have provided for many
years information on the early formation and evolution of coronal
mass ejections (CMEs). More recently, the novel heliospheric imaging
instruments aboard the STEREO mission are providing crucial remote
sensing information on the interplanetary evolution of these events
while in situ instruments complete the overall characterization of the
interplanetary CMEs. In this work, we present an analysis of CMEs from
the Sun to the interplanetary medium using combined data from SDO, SOHO,
STEREO, WIND, and ACE spacecraft. From the remote sensing analysis,
the most notable feature of a CME observed in the SECCHI suite of
instruments field of view is its elliptic cross section. However, most
of the models for in situ modeling impose the circular cross-section
geometry. In this work, we link the remote sensing observations with
the in situ data through an analytical in situ model which incorporates
the distortion in the cross-section. In this study, different aspects
such as the ambient solar wind, magnetic field configurations, plasma
parameters, etc, have been taken into account in order to cover the
widest spectrum of possible scenarios.
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Title: Examining Periodic Solar-Wind Density Structures Observed in
the SECCHI Heliospheric Imagers
Authors: Viall, Nicholeen M.; Spence, Harlan E.; Vourlidas, Angelos;
Howard, Russell
2010SoPh..267..175V Altcode: 2010arXiv1009.5885V; 2010SoPh..tmp..174V
We present an analysis of small-scale, periodic, solar-wind density
enhancements (length scales as small as ≈ 1000 Mm) observed
in images from the Heliospheric Imager (HI) aboard STEREO-A. We
discuss their possible relationship to periodic fluctuations
of the proton density that have been identified at 1 AU using
in-situ plasma measurements. Specifically, Viall, Kepko, and Spence
(J. Geophys. Res.113, A07101, 2008) examined 11 years of in-situ
solar-wind density measurements at 1 AU and demonstrated that not
only turbulent structures, but also nonturbulent, periodic density
structures exist in the solar wind with scale sizes of hundreds to
one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper
(Geophys. Res. Lett.36, L23102, 2009) analyzed the α-to-proton
solar-wind abundance ratio measured during one such event of periodic
density structures, demonstrating that the plasma behavior was highly
suggestive that either temporally or spatially varying coronal source
plasma created those density structures. Large periodic density
structures observed at 1 AU, which were generated in the corona, can
be observable in coronal and heliospheric white-light images if they
possess sufficiently high density contrast. Indeed, we identify such
periodic density structures as they enter the HI field of view and
follow them as they advect with the solar wind through the images. The
smaller, periodic density structures that we identify in the images
are comparable in size to the larger structures analyzed in-situ at 1
AU, yielding further evidence that periodic density enhancements are
a consequence of coronal activity as the solar wind is formed.
---------------------------------------------------------
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: Toward understanding the early stages of an impulsively
accelerated coronal mass ejection. SECCHI observations
Authors: Patsourakos, S.; Vourlidas, A.; Kliem, B.
2010A&A...522A.100P Altcode: 2010arXiv1008.1171P
Context. The expanding magnetic flux in coronal mass ejections (CMEs)
often forms a cavity. Studies of CME cavities have so far been limited
to the pre-event configuration to evolved CMEs at great heights, and
to two-dimensional imaging data. <BR /> Aims: Quantitative analysis of
three-dimensional cavity evolution at CME onset can reveal information
that is relevant to the genesis of the eruption. <BR /> Methods:
A spherical model was simultaneously fit to Solar Terrestrial
Relations Observatory (STEREO) Extreme Ultraviolet Imager (EUVI)
and Inner Coronagraph (COR1) data of an impulsively accelerated CME
on 25 March 2008, which displays a well-defined extreme ultraviolet
(EUV) and white-light cavity of nearly circular shape already at low
heights h ≈ 0.2 R_⊙. The center height h(t) and radial expansion
r(t) of the cavity were obtained in the whole height range of the main
acceleration. We interpret them as the axis height and as a quantity
proportional to the minor radius of a flux rope. <BR /> Results:
The three-dimensional expansion of the CME exhibits two phases in
the course of its main upward acceleration. From the first h and r
data points, taken shortly after the onset of the main acceleration,
the erupting flux shows an overexpansion compared to its rise, as
expressed by the decrease in the aspect ratio from κ = h/r ≈ 3
to κ ≈ (1.5-2). This phase is approximately coincident with the
impulsive rise in the acceleration and is followed by a phase of very
gradual change in the aspect ratio (a nearly self-similar expansion)
toward κ ~ 2.5 at h ~ 10 R_⊙. The initial overexpansion of the CME
cavity can be caused by flux conservation around a rising flux rope
of decreasing axial current and by the addition of flux to a growing,
or by even newly formed, flux rope by magnetic reconnection. Further
analysis will be required to decide which of these contributions is
dominant. The data also suggest that the horizontal component of the
impulsive cavity expansion (parallel to the solar surface) triggers the
associated EUV wave, which subsequently detaches from the CME volume.
---------------------------------------------------------
Title: Reconstructing Coronal Mass Ejections with Coordinated
Imaging and in Situ Observations: Global Structure, Kinematics,
and Implications for Space Weather Forecasting
Authors: Liu, Ying; Thernisien, Arnaud; Luhmann, Janet G.; Vourlidas,
Angelos; Davies, Jackie A.; Lin, Robert P.; Bale, Stuart D.
2010ApJ...722.1762L Altcode: 2010arXiv1009.1414L
We reconstruct the global structure and kinematics of coronal mass
ejections (CMEs) using coordinated imaging and in situ observations
from multiple vantage points. A forward modeling technique, which
assumes a rope-like morphology for CMEs, is used to determine the
global structure (including orientation and propagation direction) from
coronagraph observations. We reconstruct the corresponding structure
from in situ measurements at 1 AU with the Grad-Shafranov method,
which gives the flux-rope orientation, cross section, and a rough
knowledge of the propagation direction. CME kinematics (propagation
direction and radial distance) during the transit from the Sun to
1 AU are studied with a geometric triangulation technique, which
provides an unambiguous association between solar observations and
in situ signatures; a track fitting approach is invoked when data are
available from only one spacecraft. We show how the results obtained
from imaging and in situ data can be compared by applying these
methods to the 2007 November 14-16 and 2008 December 12 CMEs. This
merged imaging and in situ study shows important consequences and
implications for CME research as well as space weather forecasting:
(1) CME propagation directions can be determined to a relatively good
precision as shown by the consistency between different methods; (2)
the geometric triangulation technique shows a promising capability to
link solar observations with corresponding in situ signatures at 1 AU
and to predict CME arrival at the Earth; (3) the flux rope within CMEs,
which has the most hazardous southward magnetic field, cannot be imaged
at large distances due to expansion; (4) the flux-rope orientation
derived from in situ measurements at 1 AU may have a large deviation
from that determined by coronagraph image modeling; and (5) we find,
for the first time, that CMEs undergo a westward migration with respect
to the Sun-Earth line at their acceleration phase, which we suggest is
a universal feature produced by the magnetic field connecting the Sun
and ejecta. The importance of having dedicated spacecraft at L4 and
L5, which are well situated for the triangulation concept, is also
discussed based on the results.
---------------------------------------------------------
Title: Comprehensive Analysis of Coronal Mass Ejection Mass and
Energy Properties Over a Full Solar Cycle
Authors: Vourlidas, A.; Howard, R. A.; Esfandiari, E.; Patsourakos,
S.; Yashiro, S.; Michalek, G.
2010ApJ...722.1522V Altcode: 2010arXiv1008.3737V
The LASCO coronagraphs, in continuous operation since 1995, have
observed the evolution of the solar corona and coronal mass ejections
(CMEs) over a full solar cycle with high-quality images and regular
cadence. This is the first time that such a data set becomes available
and constitutes a unique resource for the study of CMEs. In this paper,
we present a comprehensive investigation of the solar cycle dependence
on the CME mass and energy over a full solar cycle (1996-2009) including
the first in-depth discussion of the mass and energy analysis methods
and their associated errors. Our analysis provides several results
worthy of further studies. It demonstrates the possible existence of
two event classes: "normal" CMEs reaching constant mass for >10
R <SUB>sun</SUB> and "pseudo"-CMEs which disappear in the C3 field
of view. It shows that the mass and energy properties of CME reach
constant levels and therefore should be measured only above ~10 R
<SUB>sun</SUB>. The mass density (g/R <SUP>2</SUP> <SUB>sun</SUB>)
of CMEs varies relatively little (< order of magnitude) suggesting
that the majority of the mass originates from a small range in coronal
heights. We find a sudden reduction in the CME mass in mid-2003 which
may be related to a change in the electron content of the large-scale
corona and we uncover the presence of a 6 month periodicity in the
ejected mass from 2003 onward.
---------------------------------------------------------
Title: Sun to 1 AU propagation and evolution of a slow
streamer-blowout coronal mass ejection
Authors: Lynch, B. J.; Li, Y.; Thernisien, A. F. R.; Robbrecht, E.;
Fisher, G. H.; Luhmann, J. G.; Vourlidas, A.
2010JGRA..115.7106L Altcode: 2010JGRA..11507106L
We present a comprehensive analysis of the evolution of the classic,
slow streamer-blowout CME of 1 June 2008 observed by the STEREO twin
spacecraft to infer relevant properties of the pre-eruption source
region which includes a substantial portion of the coronal helmet
streamer belt. The CME was directed ∼40° East of the Sun-Earth
line and the Heliospheric Imager observations are consistent with
the CME propagating essentially radially to 1 AU. The elongation-time
J-map constructed from the STEREO-A HI images tracks the arrival of two
density peaks that bound the magnetic flux rope ICME seen at STEREO-B on
6 June 2008. From the STEREO-A elongation-time plots we measure the ICME
flux rope radial size R<SUB>c</SUB>(t) and find it well approximated by
the constant expansion value V<SUB>exp</SUB> = 24.5 km/s obtained from
the STEREO-B declining velocity profile within the magnetic cloud. The
flux rope spatial orientation, determined by forward modeling fits to
the STEREO COR2 and HI1 data, approaches the observed 1 AU flux rope
orientation and suggests large-scale rotation during propagation, as
predicted by recent numerical simulations. We compare the ICME flux
content to the PFSS model coronal field for Carrington Rotation 2070
and find sufficient streamer belt flux to account for the observed
ICME poloidal/twist flux if reconnection during CME initiation process
is responsible for the conversion of overlying field into the flux
rope twist component in the standard fashion. However, the PFSS model
field cannot account for the ICME toroidal/axial flux component. We
estimate the field strength of the pre-eruption sheared/axial component
in the low corona and the timescales required to accumulate this
energized pre-eruption configuration via differential rotation and
flux cancelation by supergranular diffusion at the polarity inversion
line. We show that both mechanisms are capable of generating the
desired shear component over time periods of roughly 1-2 months. We
discuss the implications for slow streamer-blowout CMEs arising as
a natural consequence of the corona's re-adjustment to the long term
evolutionary driving of the photospheric fields.
---------------------------------------------------------
Title: MHD Simulation of the 2008 December 12 CME: Comparison with
STEREO Observations
Authors: Jin, Meng; Manchester, Ward; van der Holst, Bart; Frazin,
Richard; Gombosi, Tamas; Vourlidas, Angelos; Liu, Ying; Vasquez,
Alberto
2010shin.confE.147J Altcode:
We model the 2008 December 12 coronal mass ejection (CME) from its
active region origin and follow its propagation to 1AU. This CME
is ideal for study for it erupted from near disk center producing
a magnetic cloud that passed the Earth 5 days later as observed by
Wind. The resulting ICME passed between the STEREO spacecraft and was
well observed by COR1 and COR2 coronagraphs as well as the HI1 and HI2
imagers. We compare our numerical model to these extensive observations
to understand and verify the three-dimensional (3-D) structure of
the ejected plasma. We employ a new advanced two-temperature model
of the solar wind, which combines improved thermodynamics along with
the treatment of Afven waves. The model address both field-aligned
electron and ion heat conduction with collisional coupling between
the two species. Alfven waves heat the ions, which then transfer
their energy to electrons, which transport the energy far into the
corona. We use numerous observations to specify boundary conditions
for the numerical model, including MDI synoptic magnetograms and 3-D
tomographic reconstructions of coronal temperature and density based
on STEREO EUVI data.
---------------------------------------------------------
Title: Reconstructing CMEs with Coordinated Imaging and In Situ
Observations: Global Structure, Kinematics, and Implications for
Space Weather Forecasting
Authors: Liu, Ying; Thernisien, Arnaud; Luhmann, Janet G.; Vourlidas,
Angelos; Davies, Jackie A.; Lin, Robert P.; Bale, Stuart D.
2010shin.confE.136L Altcode:
We reconstruct the global structure and kinematics of coronal mass
ejections (CMEs) using coordinated imaging and in situ observations. We
will first briefly review and discuss various techniques with which
to convert elongation measurements to radial distances, a challenge in
determining CME kinematics. We will then discuss what CME properties we
can compare between white light observations and in situ measurements,
and show how to determine the properties and make the comparison. Both
case studies (including the 2008 December 12 and 2010 April 3 events)
and a statistical analysis will be presented. Consequences and
implications for CME research and space weather forecasting resulting
from this merged imaging and in situ study will be discussed based on
the results.
---------------------------------------------------------
Title: Comparing Techniques to Derive the Direction of Propagation
of CMEs
Authors: Lugaz, Noe; Roussev, I. I.; Vourlidas, A.
2010shin.confE.137L Altcode:
Using data from SECCHI and the HIs, it is possible to derive the
direction of propagation of CMEs in addition to their speed with
a variety of methods. When the 2 STEREO spacecraft separation is
optimal, it is possible to derive the CME direction using simultaneous
observations from the twin spacecraft and also, using observations from
only one spacecraft with fitting methods. This makes it possible to
compare and validate different analyses techniques. Here, we propose a
new fitting method and compare the results from these two methods with
those from two stereoscopic methods. We address one possible source of
errors of fitting methods: the assumption of radial propagation. Using
stereoscopic methods, we find that at least 7 of 12 studied CMEs had
small or negligible heliospheric deflection.
---------------------------------------------------------
Title: Kinematic Characterization of In/Out Pairs as seen in SECCHI
Images
Authors: Baldwin, Katherine; Vourlidas, Angelos; Linton, Mark; Howard,
Russell; Stenborg, Guillermo
2010shin.confE.148B Altcode:
This study investigates the kinematic properties of the 'in/out pair'
coronal features seen in Thompson scattered, white-light coronagraph
images. Frequently, the pairs occur as the aftermath of solar coronal
mass ejections appearing at first as a pin hole tear along the streamer
axis. The tear appears consistently at around 5 solar radii. Due
to the timing and location of these events, it is likely that the
pairs are indicators of magnetic reconnection at the trailing edge
of CMEs. Using the SECCHI COR1/COR2 instruments in combination with
the LASCO C2 data, we are able to calculate the 3D location as well as
the true speed of the pairs using elongation-time map (so-called JMAP)
capabilities. The inflow portion of the pairs are seen in both SECCHI
and LASCO coronagraphs and travel at approximately 100 km/s. While,
the outflow portion take the shape of the outflow of the preceding
storm and travel faster than 200 km/s. The images used in this analysis
were processed using a running difference technique. Previous images
subtraction highlights the proper motions of the intensity enhancements,
while removing background effects. These results may shed light on
the processes of magnetic reconnection following solar storms.
---------------------------------------------------------
Title: Determining the Azimuthal Properties of Coronal Mass Ejections
from Multi-Spacecraft Remote-Sensing Observations with STEREO SECCHI
Authors: Lugaz, N.; Hernandez-Charpak, J. N.; Roussev, I. I.; Davis,
C. J.; Vourlidas, A.; Davies, J. A.
2010ApJ...715..493L Altcode: 2010arXiv1004.0945L
We discuss how simultaneous observations by multiple heliospheric
imagers (HIs) can provide some important information about the azimuthal
properties of coronal mass ejections (CMEs) in the heliosphere. We
propose two simple models of CME geometry that can be used to derive
information about the azimuthal deflection and the azimuthal expansion
of CMEs from SECCHI/HI observations. We apply these two models to four
CMEs well observed by both STEREO spacecraft during the year 2008. We
find that in three cases, the joint STEREO-A and B observations are
consistent with CMEs moving radially outward. In some cases, we are
able to derive the azimuthal cross section of the CME fronts, and we
are able to measure the deviation from self-similar evolution. The
results from this analysis show the importance of having multiple
satellites dedicated to space weather forecasting, for example, in
orbits at the Lagrangian L4 and L5 points.
---------------------------------------------------------
Title: Examining Periodic Solar Wind Density Structures in SECCHI HI1A
Authors: Viall, Nicholeen; Vourlidas, A.; Spence, H.; Howard, R.
2010AAS...21630303V Altcode:
We present an analysis of small-scale periodic solar wind density
enhancements observed in SECCHI HI1. We discuss their possible
relationship to periodic fluctuations of the proton density observed
in-situ with the Wind SWE data. Viall et al. [2008] used 11 years
of solar wind density measurements at 1 AU and demonstrated that in
addition to turbulent fluctuations, non-turbulent periodic density
structures with length scales of tens to hundreds of megameters exist in
the solar wind. Event studies of the periodic density structures reveal
instances in which the density structures have alpha/proton abundance
ratio changes associated with the density structures. Specifically,
the alpha density varies with the same periodicity as the protons,
but in antiphase. For those events, this strongly suggests either time
varying or spatially varying coronal source plasma that created the
density structures. If such periodic density structures observed at 1
AU are generated in the corona, then they may be observable in SECCHI
HI1 data. We identify periodic density structures as they convect
with the solar wind into the field of view of SECCHI HI and follow
the train of structures as a function of time. The periodic density
structures we analyze are comparable in size to the larger structures
identified in-situ at 1 AU. <P />This research was supported through
NASA Grant No. NNG05GK65G and an appointment to the NASA Postdoctoral
Program at the Goddard Space Flight Center, administered by Oak Ridge
Associated Universities through a contract with NASA.
---------------------------------------------------------
Title: Kinematic Characterization Of In/out Pairs As Seen In Secchi
Authors: Baldwin, Katherine; Vourlidas, A.; Linton, M.
2010AAS...21640625B Altcode:
This study investigates the kinematic properties of the "in/out pair”
coronal features seen in Thompson scattered, white-light coronagraph
images. Frequently, the pairs occur as the after-math of solar coronal
mass ejections appearing at first as a pin hole tear along the streamer
axis. The tear appears consistently at around 5 solar radii. Due
to the timing and location of these events, it is likely that the
pairs are indicators of magnetic reconnection at the trailing edge
of CMEs. Using the SECCHI COR1/COR2 instruments in combination with
the LASCO C2 data, we are able to calculate the 3D location as well as
the true speed of the pairs using elongation-time map (so-called JMAP)
capabilities. The inflow portion of the pairs are seen in both SECCHI
and LASCO coronagraphs and travel at approximately 100 km/s. While,
the outflow portion take the shape of the outflow of the preceding
storm and travel faster than 200 km/s. The images used in this analysis
were processed using a running difference technique. Previous images
subtraction highlights the proper motions of the intensity enhancements,
while removing background effects. These results may shed light on
the processes of magnetic reconnection following solar storms.
---------------------------------------------------------
Title: Tracking of Coronal White-Light Events by Texture
Authors: Goussies, N.; Stenborg, G.; Vourlidas, A.; Howard, R.
2010SoPh..262..481G Altcode: 2010SoPh..tmp....8G
The extraction of the kinematic properties of coronal mass ejections
(CMEs) from white-light coronagraph images involves a significant
degree of user interaction: defining the edge of the event, separating
the core from the front or from nearby unrelated structures, etc. To
contribute towards a less subjective and more quantitative definition,
and therefore better kinematic characterization of such events,
we have developed a novel image-processing technique based on the
concept of "texture of the event". The texture is defined by the
so-called gray-level co-occurrence matrix, and the technique consists
of a supervised segmentation algorithm to isolate a particular region
of interest based upon its similarity with a pre-specified model. Once
the event is visually defined early in its evolution, it is possible to
automatically track the event by applying the segmentation algorithm to
the corresponding time series of coronagraph images. In this paper we
describe the technique, present some examples, and show how the coronal
background, the core of the event, and even the associated shock (if
one exists) can be identified for different kind of CMEs detected by
the LASCO and SECCHI coronagraphs.
---------------------------------------------------------
Title: Intermittent release of transients in the slow solar wind:
1. Remote sensing observations
Authors: Rouillard, A. P.; Davies, J. A.; Lavraud, B.; Forsyth, R. J.;
Savani, N. P.; Bewsher, D.; Brown, D. S.; Sheeley, N. R.; Davis,
C. J.; Harrison, R. A.; Howard, R. A.; Vourlidas, A.; Lockwood, M.;
Crothers, S. R.; Eyles, C. J.
2010JGRA..115.4103R Altcode: 2010JGRA..11504103R
The Heliospheric Imager (HI) instruments on board the STEREO spacecraft
are used to analyze the solar wind during August and September 2007. We
show how HI can be used to image the streamer belt and, in particular,
the variability of the slow solar wind which originates inside and
in the vicinity of the streamer belt. Intermittent mass flows are
observed in HI difference images, streaming out along the extension of
helmet streamers. These flows can appear very differently in images:
plasma distributed on twisted flux ropes, V-shaped structures, or
“blobs.” The variety of these transient features may highlight the
richness of phenomena that could occur near helmet streamers: emergence
of flux ropes, reconnection of magnetic field lines at the tip of
helmet streamers, or disconnection of open magnetic field lines. The
plasma released with these transient events forms part of the solar
wind in the higher corona; HI observations show that these transients
are frequently entrained by corotating interaction regions (CIRs),
leading to the formation of larger, brighter plasma structures in HI
images. This entrainment is used to estimate the trajectory of these
plasma ejecta. In doing so, we demonstrate that successive transients
can be entrained by the same CIR in the high corona if they emanate
from the same corotating source. Some parts of the streamers are more
effective sources of transients than others. Surprisingly, evidence
is given for the outflow of a recurring twisted magnetic structure,
suggesting that the emergence of flux ropes can be recurrent.
---------------------------------------------------------
Title: Geometric Triangulation of Imaging Observations to Track
Coronal Mass Ejections Continuously Out to 1 AU
Authors: Liu, Ying; Davies, Jackie A.; Luhmann, Janet G.; Vourlidas,
Angelos; Bale, Stuart D.; Lin, Robert P.
2010ApJ...710L..82L Altcode: 2010arXiv1001.1352L
We describe a geometric triangulation technique, based on
time-elongation maps constructed from imaging observations, to track
coronal mass ejections (CMEs) continuously in the heliosphere and
predict their impact on the Earth. Taking advantage of stereoscopic
imaging observations from the Solar Terrestrial Relations Observatory,
this technique can determine the propagation direction and radial
distance of CMEs from their birth in the corona all the way to 1
AU. The efficacy of the method is demonstrated by its application to
the 2008 December 12 CME, which manifests as a magnetic cloud (MC)
from in situ measurements at the Earth. The predicted arrival time
and radial velocity at the Earth are well confirmed by the in situ
observations around the MC. Our method reveals non-radial motions and
velocity changes of the CME over large distances in the heliosphere. It
also associates the flux-rope structure measured in situ with the
dark cavity of the CME in imaging observations. Implementation of
the technique, which is expected to be a routine possibility in the
future, may indicate a substantial advance in CME studies as well as
space weather forecasting.
---------------------------------------------------------
Title: Extreme Ultraviolet Observations and Analysis of
Micro-Eruptions and Their Associated Coronal Waves
Authors: Podladchikova, O.; Vourlidas, A.; Van der Linden, R. A. M.;
Wülser, J. -P.; Patsourakos, S.
2010ApJ...709..369P Altcode:
The Solar Terrestrial Relations Observatory EUV telescopes have
uncovered small-scale eruptive events, tentatively referred to as
"mini-CMEs" because they exhibit morphologies similar to large-scale
coronal mass ejections (CMEs). Coronal waves and widespread diffuse
dimmings followed by the expansion of the coronal waves are the most
brightly manifestations of large-scale CMEs. The high temporal and
spatial resolution of the EUV data allows us to detect and analyze
these eruptive events, to resolve their fine structure, and to show that
the observed "mini-waves" have a strong similarity to the large-scale
"EIT' waves. Here, we analyze a micro-event observed on 2007 October 17
by the Sun Earth Connection Coronal and Heliospheric Investigation EUV
Imager (EUVI) in 171 Å (Fe IX) with a 2.5 minute cadence. The mini-CME
differs from its large-scale counterparts by having smaller geometrical
size, a shorter lifetime, and reduced intensity of coronal wave and
dimmings. The small-scale coronal wave develops from micro-flaring
sites and propagate up to a distance of 40,000 km in a wide angular
sector of the quiet Sun over 20 minutes. The area of the small-scale
dimming is two orders of magnitude smaller than for large-scale
events. The average speed of the small-scale coronal wave studied is
14 km s<SUP>-1</SUP>. Our observations give strong indications that
small-scale EUV coronal waves associated with the micro-eruptions
propagate in the form of slow mode waves almost perpendicular to the
background magnetic field.
---------------------------------------------------------
Title: MHD Simulation of the 2008 December 12 CME: Comparison with
STEREO Observations
Authors: Manchester, Ward, IV; van der Holst, Bart; Frazin, Richard;
Gombosi, Tamas; Vourlidas, Angelos; Liu, Ying; Vásquez, Alberto
2010cosp...38.1857M Altcode: 2010cosp.meet.1857M
We model the 2008 December 12 coronal mass ejection (CME) from its
active region origin and follow its propagation to 1AU. This CME
is ideal for study for it erupted from near disk center producing
a magnetic cloud that passed the Earth 5 days later as observed by
Wind. The resulting ICME passed between the STEREO spacecraft and was
well observed by COR1 and COR2 coronagraphs as well as the HI1 and HI2
imagers. We compare our numerical model to these extensive observations
to understand and verify the three-dimensional (3-D) structure of
the ejected plasma. We employ a new advanced two-temperature model
of the solar wind, which combines improved thermodynamics along with
the treatment of Afven waves. The model address both field-aligned
electron and ion heat conduction with collisional coupling between
the two species. Alfven waves heat the ions, which then transfer
their energy to electrons, which transport the energy far into the
corona. We use numerous observations to specify boundary conditions
for the numerical model, including MDI synoptic magnetograms and 3-D
tomographic reconstructions of coronal temperature and density based
on STEREO EUVI data.
---------------------------------------------------------
Title: The Structure and Dynamics of the Upper Chromosphere and Lower
Transition Region as Revealed by the Subarcsecond VAULT Observations
Authors: Vourlidas, A.; Sanchez Andrade-Nuño, B.; Landi, E.;
Patsourakos, S.; Teriaca, L.; Schühle, U.; Korendyke, C. M.;
Nestoras, I.
2010SoPh..261...53V Altcode: 2009arXiv0912.2272V
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a
sounding rocket payload built to study the crucial interface between
the solar chromosphere and the corona by observing the strongest line
in the solar spectrum, the Ly α line at 1216 Å. In two flights, VAULT
succeeded in obtaining the first ever subarcsecond ( 0.5\hbox{$^”$}
) images of this region with high sensitivity and cadence. Detailed
analyses of those observations contributed significantly to new
ideas about the nature of the transition region. Here, we present
a broad overview of the Ly α atmosphere as revealed by the VAULT
observations and bring together past results and new analyses from the
second VAULT flight to create a synthesis of our current knowledge
of the high-resolution Ly α Sun. We hope that this work will serve
as a good reference for the design of upcoming Ly α telescopes and
observing plans.
---------------------------------------------------------
Title: Coronal sound waves on open magnetic field lines originating
near solar active regions
Authors: Stenborg, Guillermo; Marsch, Eckart; Vourlidas, Angelos;
Howard, Russell; Baldwin, Katherine
2010cosp...38.1814S Altcode: 2010cosp.meet.1814S
In the past years, evidence for the existence of outward-moving plasma
and slow-mode magne-toacoustic waves propagating in various magnetic
field structures (loops in particular) in the solar corona has been
found, yet their origin and possible connection with the mass and energy
supply to the corona and solar wind is still unclear. These results
were obtained by the high-resolution observations available from the
extreme ultraviolet (EUV) imagers on the STEREO and Hinode missions,
and from data obtained by the ultraviolet spectrometer on Hinode. Here,
we present the first measurements of intensity fluctuations observed by
the Extreme Ultra-Violet Imagers (EUVI) onboard the Solar TErrestrial
RElationships Observatory (STEREO) mission along apparently open
field lines near solar active regions. We demonstrate that one can
make reliable kinematic measurements (speed, acceleration) from these
EUV images, thereby complementing and extending the spectroscopic
measurements. We have developed a series of image-processing steps
to recover the weak intensity fluctuations along individual magnetic
structures, de-projected them and produced distance-time maps. They
can be analysed by use of well established techniques adapted from the
kinematic analysis of Coronal Mass Ejection (CME), and by standard
methods of wavelet analysis. We obtained wave phase speeds with
values on the order of 100 km/s. We also studied the periodicity
of the observed fluctuations and established a predominance of a
16-minutes period, as well as other periods being multi-ples of the
8-minutes period that appears to be the basic value. Thus we clearly
established the ubiquitous existence of sound waves which seem to
emanate continuously on open coronal fields.
---------------------------------------------------------
Title: Evidence for extended acceleration of solar flare ions from 1-8
MeV solar neutrons detected with the MESSENGER Neutron Spectrometer
Authors: Feldman, William C.; Lawrence, David J.; Goldsten, John O.;
Gold, Robert E.; Baker, Daniel N.; Haggerty, Dennis K.; Ho, George C.;
Krucker, SäM.; Lin, Robert P.; Mewaldt, Richard A.; Murphy, Ronald
J.; Nittler, Larry R.; Rhodes, Edgar A.; Slavin, James A.; Solomon,
Sean C.; Starr, Richard D.; Vilas, Faith; Vourlidas, Angelos
2010JGRA..115.1102F Altcode: 2010JGRA..11501102F
Neutrons produced on the Sun during the M2 flare on 31 December 2007
were observed at 0.48 AU by the MESSENGER Neutron Spectrometer. These
observations are the first detection of solar neutrons inside 1 AU. This
flare contained multiple acceleration episodes as seen in type III
radio bursts. After these bursts ended, both the energetic particle and
neutron fluxes decayed smoothly to background with an e-folding decay
time of 2.84 h, spanning a 9 h time period. This time is considerably
longer than the mean lifetime of a neutron, which indicates that
either the observed neutrons were generated in the spacecraft by solar
energetic particle protons, or they originated on the Sun. If most of
the neutrons came from the Sun, as our simulations of neutron production
on the spacecraft show, they must have been continuously produced. A
likely explanation of their long duration is that energetic ions were
accelerated over an extended time period onto closed magnetic arcades
above the corona and then slowly pitch angle-scattered by coronal
turbulence into their chromospheric loss cones. Because of their
relatively low energy loss in the Neutron Spectrometer (0.5-7.5 MeV),
most of these neutrons beta decay to energetic protons and electrons
close to the Sun, thereby forming an extended seed population available
for further acceleration by subsequent shocks driven by coronal mass
ejections in interplanetary space.
---------------------------------------------------------
Title: Heatwaves on the Sun
Authors: Robbrecht, Eva; Wang, Yi-Ming; Vourlidas, Angelos;
Patsourakos, Spiros
2010cosp...38.1791R Altcode: 2010cosp.meet.1791R
Dimmings have been observed for several years now, but their
interpretation is still problematic. A dimming is an observational
effect of diminished brightness with respect to pre-event images, which
is usually interpreted as a density depletion. But not all dimmings are
what they appear to be. In this paper we report on an unusual "dimming
wave" which is not a density depletion but rather a heat wave. Thanks
to the stereoscopic view from the SECCHI/EUVI imagers we are able not
only to uncover the nature of the wave, but also to understand its
three dimensional evolution and its relationship to a quiet sun CME.
---------------------------------------------------------
Title: Kinematic characterization of In/Out pairs as seen in SECCHI
images
Authors: Baldwin, Katherine; Vourlidas, Angelos
2010cosp...38.1864B Altcode: 2010cosp.meet.1864B
This study investigates the kinematic properties of the "in/out pair"
coronal features seen in Thompson scattered, white-light coronagraph
images. Frequently, the pairs occur as the after-math of solar coronal
mass ejections appearing at first as a pin hole tear along the streamer
axis. The tear appears consistently at around 5 solar radii. Due
to the timing and location of these events, it is likely that the
pairs are indicators of magnetic reconnection at the trailing edge
of CMEs. Using the SECCHI COR1/COR2 instruments in combination with
the LASCO C2 data, we are able to calculate the 3D location as well as
the true speed of the pairs using elongation-time map (so-called JMAP)
capabilities. The inflow portion of the pairs are seen in both SECCHI
and LASCO coronagraphs and travel at approximately 100 km/s. While,
the outflow portion take the shape of the outflow of the preceding
storm and travel faster than 200 km/s. The images used in this
analysis were processed using a running difference technique. Previous
images subtraction highlights the proper motions of the intensity
enhance-ments, while removing background effects. These results may shed
light on the processes of magnetic reconnection following solar storms.
---------------------------------------------------------
Title: MHD Modeling of CMEs and CIRs and Comparison with White Light
Observations from STEREO/SECCHI
Authors: Lugaz, Noé; Roussev, Ilia; Vourlidas, Angelos; Manchester,
Ward, IV; Gombosi, Tamas
2010cosp...38.1869L Altcode: 2010cosp.meet.1869L
Interplanetary coronal mass ejections (iCMEs) have complex magnetic and
density structures, the result of their interaction with the structured
solar wind, in particular with corotating interaction regions (CIRs),
and also with previous eruptions. iCMEs and CIRs are been pri-marily
measured in situ and studied via numerical simulations in the previous
three decades, but, in the past five years, they have also been revealed
through remote-sensing observations by heliospheric imagers. To
understand and analyze these observations often requires the use of
numerical modeling. Numerical simulations can be used to determine
the origin of a complex ejecta observed near Earth or to analyze the
origin, speed and extent of density structures observed remotely. In
this talk, we review recent efforts to use numerical simulations
of CMEs and CIRs for the analysis of line-of-sight images produced
by STEREO/SECCHI in order to in-vestigate the density structure,
energetics and kinematics of iCMEs in interplanetary space. We also
discuss how numerical simulations can be used to test different methods
for the derivation of iCME properties from remote observations and
to predict and explain observational effects. In particular, we use
a series of numerical simulations to test and compare some of the
methods used to determine CME position, speed and direction from
white-light observations. Finally, we show how numerical simulations
are an essential tool for understanding the properties of iCMEs and
for maximizing the return of heliospheric missions such as STEREO.
---------------------------------------------------------
Title: On the 3-D reconstruction of Coronal Mass Ejections using
coronagraph data
Authors: Mierla, M.; Inhester, B.; Antunes, A.; Boursier, Y.; Byrne,
J. P.; Colaninno, R.; Davila, J.; de Koning, C. A.; Gallagher, P. T.;
Gissot, S.; Howard, R. A.; Howard, T. A.; Kramar, M.; Lamy, P.;
Liewer, P. C.; Maloney, S.; Marqué, C.; McAteer, R. T. J.; Moran, T.;
Rodriguez, L.; Srivastava, N.; St. Cyr, O. C.; Stenborg, G.; Temmer,
M.; Thernisien, A.; Vourlidas, A.; West, M. J.; Wood, B. E.; Zhukov,
A. N.
2010AnGeo..28..203M Altcode:
Coronal Mass ejections (CMEs) are enormous eruptions of magnetized
plasma expelled from the Sun into the interplanetary space, over the
course of hours to days. They can create major disturbances in the
interplanetary medium and trigger severe magnetic storms when they
collide with the Earth's magnetosphere. It is important to know their
real speed, propagation direction and 3-D configuration in order to
accurately predict their arrival time at the Earth. Using data from
the SECCHI coronagraphs onboard the STEREO mission, which was launched
in October 2006, we can infer the propagation direction and the 3-D
structure of such events. In this review, we first describe different
techniques that were used to model the 3-D configuration of CMEs in
the coronagraph field of view (up to 15 R⊙). Then, we apply these
techniques to different CMEs observed by various coronagraphs. A
comparison of results obtained from the application of different
reconstruction algorithms is presented and discussed.
---------------------------------------------------------
Title: The Evolution Of The Brightness Of The White Light Corona
Over A Solar Cycle
Authors: Howard, R. A.; Battams, K.; Vourlidas, A.; Morrill, J. S.;
Stenborg, G.
2009AGUFMSH13C..04H Altcode:
The LASCO C2 and C3 coronagraphs on the SOHO mission have been operating
almost continuously since 1996. This long period covers two solar minima
and one maximum. It has been reported that the solar wind magnetic
field and pressure is abnormally low. We have asked whether there is
any difference in the brightness, which is directly related to the
electron content. We have generated plots of the total intensity for
the entire 13 year period. Comparison over this long period is possible
due to the excellent, absolute calibration of the coronagraphs using
star transits. We find a solar cycle dependence of about 20%. However,
we do not see a significant decrease of the current minimum compared
to the previous one. Rather, the total intensity (summed over all
position angles) is ~5% higher this minimum than previously due to a
slightly broader streamer “belt” now than previously. In contrast,
CMEs are about 2x less massive at the current minimum than the previous
one. The CME average mass dramatically decreased from 2002 to 2004 by
a factor of 5. This CME decrease corresponded to the average CME width
becoming narrower. We note that the intensity structure of the current
minimum did not achieve the simple structure of the previous minimum.
---------------------------------------------------------
Title: Kinematical characterization of intensity fluctuations observed
in STEREO EUVI images: 1. On-disk case
Authors: Baldwin, K. L.; Stenborg, G.; Vourlidas, A.; Howard, R. A.
2009AGUFMSH41B1650B Altcode:
Enhanced, wavelet processed STEREO/EUVI images reveal intermittent
intensity fluctuations traveling outwards along apparently-open
field lines nearby active region coronal holes. The phenomenon has
been observed and quantified using data from instruments on other
missions. However, much debate still exists in the solar community
about the physical cause and exact quantitative nature of the
fluctuations. The STEREO/EUVI continuous coverage, full-disk imaging
allows for the first time a more comprehensive study. In particular,
we found that the phenomenon persists for as long as the topological
configuration of the source region remains constant. In order to
shed light on an understanding of the nature of the fluctuations, we
have devised a method to determine the kinematical parameters of these
apparent outflows. In this work, we introduce the method, report on the
average plane-of-sky speed found for a set of selected dates, infer
the true velocity by taking advantage of the STEREO two-point view,
and discuss the possible scenarios that can explain the phenomenon.
---------------------------------------------------------
Title: Dependence of CME Propagation on Parameters of the Ejecta
and Ambient Solar Wind
Authors: Li, Y.; Lynch, B. J.; Luhmann, J. G.; Krauss-Varban, D.;
Thernisien, A.; Vourlidas, A.; MacNeice, P. J.
2009AGUFMSH41A1632L Altcode:
CME propagation through the heliosphere has been one of the
most uncertain problems, due to its complex nature and sparse
observations in the vast space. CME travel time, speed and trajectory
have been often unpredictable, because they may be modified going
through ambient solar wind streams and IMF structure. All of these
parameters are important for understanding CMEs and their space weather
consequences. Direct observations of CME propagation through to 1AU have
only become a reality since the recent STEREO Heliospheric Imager (HI)
observations. Based on a few strategically selected CMEs that vary in
parameter space and situated in different solar wind/IMF conditions,
we perform several CCMC ENLIL with cone model simulations to study the
propagation. Comparisons between modeling results including CME driven
shock properties, travel time, 3D trajectory, and distortion of the
ejecta (limited to the model approximation) will be made. Comparisons
are also made between modeling, HI imaging results, and observed
in-situ parameters when available.
---------------------------------------------------------
Title: Geometric Triangulation of Imaging Observations to Track CMEs
Continuously Out to 1 AU (Invited)
Authors: Liu, Y.; Davies, J.; Luhmann, J. G.; Lin, R. P.; Bale, S.;
Vourlidas, A.
2009AGUFMSH43A..04L Altcode:
We describe a geometric triangulation technique, based on
time-elongation maps constructed from imaging observations, to track
coronal mass ejections (CMEs) continuously in the heliosphere and
predict their impact on the Earth. Taking advantage of stereoscopic
imaging observations from STEREO, this technique can precisely determine
the propagation direction and radial distance of CMEs from their
birth in the corona all the way to 1 AU. The efficacy of the method
is demonstrated by its application to the 2008 December 12 CME, which
manifests as a magnetic cloud (MC) from in situ measurements at the
Earth. The predicted arrival time and radial velocity at the Earth are
well confirmed by the in situ observations around the MC. Implementation
of the technique, which is expected to be a routine possibility in
the future, indicates a substantial advance in CME studies as well as
space weather forecasting.
---------------------------------------------------------
Title: STEREO observations of interplanetary coronal mass ejections
and prominence deflection during solar minimum period
Authors: Kilpua, E. K. J.; Pomoell, J.; Vourlidas, A.; Vainio, R.;
Luhmann, J.; Li, Y.; Schroeder, P.; Galvin, A. B.; Simunac, K.
2009AnGeo..27.4491K Altcode:
In this paper we study the occurrence rate and solar origin of
interplanetary coronal mass ejections (ICMEs) using data from the
two Solar TErrestrial RElation Observatory (STEREO) and the Wind
spacecraft. We perform a statistical survey of ICMEs during the
late declining phase of solar cycle 23. Observations by multiple,
well-separated spacecraft show that even at the time of extremely
weak solar activity a considerable number of ICMEs were present in the
interplanetary medium. Soon after the beginning of the STEREO science
mission in January 2007 the number of ICMEs declined to less than one
ICME per month, but in late 2008 the ICME rate clearly increased at each
spacecraft although no apparent increase in the number of coronal mass
ejections (CMEs) occurred. We suggest that the near-ecliptic ICME rate
can increase due to CMEs that have been guided towards the equator
from their high-latitude source regions by the magnetic fields in
the polar coronal holes. <BR /><BR /> We consider two case studies to
highlight the effects of the polar magnetic fields and CME deflection
taking advantage of STEREO observations when the two spacecraft were in
the quadrature configuration (i.e. separated by about 90 degrees). We
study in detail the solar and interplanetary consequences of two CMEs
that both originated from high-latitude source regions on 2 November
2008. The first CME was slow (radial speed 298 km/s) and associated with
a huge polar crown prominence eruption. The CME was guided by polar
coronal hole fields to the equator and it produced a clear flux rope
ICME in the near-ecliptic solar wind. The second CME (radial speed 438
km/s) originated from an active region 11007 at latitude 35° N. This
CME propagated clearly north of the first CME and no interplanetary
consequences were identified. The two case studies suggest that slow
and elongated CMEs have difficulties overcoming the straining effect
of the overlying field and as a consequence they are guided by the
polar coronal fields and cause in-situ effects close to the ecliptic
plane. The 3-D propagation directions and CME widths obtained by using
the forward modelling technique were consistent with the solar and
in-situ observations.
---------------------------------------------------------
Title: Examining Solar Wind Number Density Structures Observed in
SECCHI HI 1
Authors: Viall, N. M.; Spence, H. E.; Vourlidas, A.; Howard, R. A.
2009AGUFMSH13B1516V Altcode:
We present an analysis of small-scale periodic solar wind density
enhancements observed in SECCHI HI 1. We discuss their possible
relationship to periodic fluctuations of the proton density observed
in-situ with the Wind SWE data. Viall et al. [2008] used 11 years
of solar wind density measurements at 1 AU and demonstrated that in
addition to turbulent fluctuations, non-turbulent, periodic density
structures exist in the solar wind. In the slow wind, periodic
density structures occurred most often with radial length-scales of
approximately 73, 120, 136 and 180 Mm. In the fast wind, periodic
density structures occurred most often with radial length-scales
of approximately 187, 270 and 400 Mm. Event studies of the periodic
density structures reveal instances in which the density structures
have alpha/proton abundance ratio changes associated with the density
structures. Specifically, the alpha density varies with the same
periodicity as the protons, but in antiphase. For those events, this
strongly suggests either time varying or spatially varying coronal
source plasma that created the density structures. If such periodic
density structures observed at 1 AU are generated in the corona,
then they may be observable in SECCHI HI1 data. For instance, larger
scale plasmoids have been observed in the corona [e.g. Sheeley et al.,
2009] and it is plausible that smaller, periodic structures may exist
as well. We identify periodic density structures as they convect with
the solar wind into the field of view of SECCHI HI and follow the train
of structures as a function of time. The periodic density structures
we analyze are comparable in size to the larger structures identified
in-situ at 1 AU.
---------------------------------------------------------
Title: Determining CME azimuthal properties from stereoscopic
heliospheric observations
Authors: Lugaz, N.; Hernandez, J. N.; Roussev, I. I.; Vourlidas, A.
2009AGUFMSH41A1636L Altcode:
We discuss how remote-sensing observations by multiple white-light
imagers can provide some information about the azimuthal deflection
and azimuthal expansion of Coronal Mass Ejections (CMEs) as they
propagate in the heliosphere. Our analysis focuses on one CME which
was well observed by the SECCHI/HIs onboard STEREO-A and B on April
26-28, 2008. By considering two simple models of CME geometry and
using simultaneous observations from the two different viewpoints,
we show that the observations can be best understood by modeling the
CME as a propagating sphere of expanding radius on a fixed radial
trajectory. Preliminary analysis shows that the CME expansion is
self-similar from 0.2 AU until 0.5 AU and slows down afterwards. An
alternative explanation of the observations is a deflection towards
the east of a bubble CME. While observational effects may play a role,
the results from these two models are corroborated by the non-detection
of the CME at L1, where a CME hit was expected based on its initial
width and direction.
---------------------------------------------------------
Title: Kinematical characterization of intensity fluctuations observed
in STEREO EUVI images: II. Off-disk case
Authors: Stenborg, G. A.; Baldwin, K.; Vourlidas, A.; Howard, R. A.
2009AGUFMSH41B1651S Altcode:
Coherent quasi-periodic perturbations in brightness along polar plumes
have been found with the Extreme ultraviolet Imager Telescope (EIT)
onboard the SOlar and Heliospheric Observatory (SOHO). Unfortunately,
without the use of high cadence EIT campaigns from SOHO, a systematic
study of such phenomenon was not feasible due to the high temporal
resolution required for this analysis. The advent of the Solar
TErrestrial RElationships Observatory (STEREO) mission with its higher
spatial and temporal resolution imagers resolved this issue. The
twin Extreme UltraViolet Imagers (EUVI) aboard STEREO allowed for
simultaneous, high cadence views of the plume structures from two view
points. In our enhanced, wavelet processed STEREO/EUVI images, we have
found persistent and quasi-steady intensity fluctuations apparently
traveling outward above polar coronal holes. The projected plane-of-sky
linear speed ranges from 70 to 150 km/sec for these above-the-limb
fluctuations. Additionally, some cases exhibit an acceleration pattern
very close to the limb. In this work, we introduce the method developed
to systematically measure the kinematical parameters of the phenomenon,
we compute several parameters for pre-selected dates, and we discuss
the existence of an apparent quasi-periodic pattern observed in the
Height-Time maps. Finally, we relate our quantitative findings to
previous works.
---------------------------------------------------------
Title: Sun to 1 AU Propagation of a Slow Streamer-Blowout Coronal
Mass Ejection
Authors: Lynch, B. J.; Li, Y.; Thernisien, A. F.; Robbrecht, E.;
Luhmann, J. G.; Vourlidas, A.
2009AGUFMSH41A1635L Altcode:
We present the time history and evolution of the 3-dimensional size,
shape, and orientation of the slow, classic streamer blowout CME of
2008 Jun 01 by combining STEREO-A remote imaging of its interplanetary
propagation with in situ STEREO-B plasma and field measurements at
1~AU. The STEREO-A HI coverage allows unambigious identification of
the CME white light front-cavity structure and the resulting ICME flux
rope boundaries in running difference images. The elongation-time tracks
predict the arrival of the ICME at STEREO-B on 2008 June 06 remarkably
well. Starting from the simplest in situ flux rope model for the
coherent magnetic cloud field structure, we utilize the unprecedented
coverage of the coronal and heliospheric imaging observations to obtain
important corrections for the ICME flux rope geometry. MHD modeling
results obtained from the NASA Community Coordinated Modeling Center
for the ambient heliopsheric solar wind stream structure and a simple
CME-like density-pulse propagation are used to verify the overall
propagation direction and characterize some of the observed evolutionary
properties. The ICME radial expansion, i.e. the time evolution of
the flux rope radius Rc(t) from the STEREO-A elongation-time plots,
is well approximated by the standard treatment of constant radial
expansion Vexp = 24.5 km/s measured from the in situ bulk velocity
profile. The 3-dimensional spatial orientation of the ICME flux rope
determined by forward modeling in the inner heliosphere shows excellent
agreement with the observed 1~AU flux rope orientation and evidence
for large scale rotation of the ICME flux rope during its propagation,
as predicted by recent numerical simulations. In addition, measurements
of the CME's latitudinal angular width allows us to improve the estimate
the actual flux rope cross-sectional area and measurements of the CME's
longitudinal extent allows us to estimate a more realistic CME “loop
length". These geometric quantities are used to improve the estimates of
the ICME in situ toroidal and poloidal magnetic fluxes, ΦT and ΦP. The
in situ flux values are then compared to the magnetic fluxes inferred
from this event's source region, which includes a substantial portion of
the large scale coronal helmet streamer belt. We conlude by discussing
our results in the context of both CME initiation and the physical
mechanism(s) that energize the pre-eruption configuration. Support
for this work was provided by NASA HGI NNX08AJ04G.
---------------------------------------------------------
Title: Geoeffective CME-driven Shocks: Comparison Between Imaging
Data and in-situ Observations
Authors: Ontiveros, V.; Gonzalez-Esparza, A.; Vourlidas, A.
2009AGUFMSH41A1630O Altcode:
Fast Coronal Mass Ejections (CMEs) drive shock waves that can be
recognized in the coronagraph images. Properties of the shock and
the CME, such as density compression ratio, mass, kinetic energy, and
the direction of propagation, can be measured from these images. The
aim of this study is: (1) to compare these properties with in-situ
measurements of the large scale Shock-Sheath-CME structure in the
interplanetary medium, and (2) to track back to the Sun geoeffective
parameters of the CME-shock, that have been recognized as the main
cause of moderate and intense geomagnetic storms.
---------------------------------------------------------
Title: A Review of Coronagraphic Observations of Shocks Driven by
Coronal Mass Ejections
Authors: Vourlidas, Angelos; Ontiveros, Veronica
2009AIPC.1183..139V Altcode: 2009arXiv0908.1996V
The existence of shocks driven by Coronal Mass Ejections (CMEs)
has always been assumed based on the superalfvenic speeds for
some of these events and on indirect evidence such as radio
bursts and distant streamer deflections. However, the direct
signature of the plasma enhancement at the shock front has escaped
detection until recently. Since 2003, work on LASCO observations
has shown that CME-driven shocks can be detected by white light
coronagraph observations from a few solar radii to at least 20
R<SUB>sun</SUB>. Shock properties, such as the density compression ratio
and their direction can be extracted from the data. We review this work
here and demonstrate how to recognize the various shock morphologies
in the images. We also discuss how the two-viewpoint coronagraph
observations from the STEREO mission allow the reconstruction of the
3D envelope of the shock revealing some interesting properties of the
shocks (e.g., anisotropic expansion).
---------------------------------------------------------
Title: First Measurements of the Mass of Coronal Mass Ejections from
the EUV Dimming Observed with STEREO EUVI A+B Spacecraft
Authors: Aschwanden, Markus J.; Nitta, Nariaki V.; Wuelser,
Jean-Pierre; Lemen, James R.; Sandman, Anne; Vourlidas, Angelos;
Colaninno, Robin C.
2009ApJ...706..376A Altcode:
The masses of coronal mass ejections (CMEs) have traditionally been
determined from white-light coronagraphs (based on Thomson scattering
of electrons), as well as from extreme ultraviolet (EUV) dimming
observed with one spacecraft. Here we develop an improved method
of measuring CME masses based on EUV dimming observed with the dual
STEREO/EUVI spacecraft in multiple temperature filters that includes
three-dimensional volume and density modeling in the dimming region
and background corona. As a test, we investigate eight CME events with
previous mass determinations from STEREO/COR2, of which six cases are
reliably detected with the Extreme Ultraviolet Imager (EUVI) using our
automated multi-wavelength detection code. We find CME masses in the
range of m <SUB>CME</SUB> = (2-7) × 10<SUP>15</SUP> g. The agreement
between the two EUVI/A and B spacecraft is m<SUB>A</SUB> /m<SUB>B</SUB>
= 1.3 ± 0.6 and the consistency with white-light measurements by COR2
is m <SUB>EUVI</SUB>/m <SUB>COR2</SUB> = 1.1 ± 0.3. The consistency
between EUVI and COR2 implies no significant mass backflows (or inflows)
at r < 4 R <SUB>sun</SUB> and adequate temperature coverage for the
bulk of the CME mass in the range of T ≈ 0.5-3.0 MK. The temporal
evolution of the EUV dimming allows us to also model the evolution
of the CME density n<SUB>e</SUB> (t), volume V(t), height-time h(t),
and propagation speed v(t) in terms of an adiabatically expanding
self-similar geometry. We determine e-folding EUV dimming times of
t<SUB>D</SUB> = 1.3 ± 1.4 hr. We test the adiabatic expansion model
in terms of the predicted detection delay (Δt ≈ 0.7 hr) between
EUVI and COR2 for the fastest CME event (2008 March 25) and find good
agreement with the observed delay (Δt ≈ 0.8 hr).
---------------------------------------------------------
Title: The Impact of Geometry on Observations of CME Brightness
and Propagation
Authors: Morrill, J. S.; Howard, R. A.; Vourlidas, A.; Webb, D. F.;
Kunkel, V.
2009SoPh..259..179M Altcode:
Coronal mass ejections (CMEs) have a significant impact on space
weather and geomagnetic storms and so have been the subject of numerous
studies. Most CME observations have been made while these events are
near the Sun (e.g., SOHO/LASCO). Recent data from the Coriolis/SMEI
and STEREO/SECCHI-HI instruments have imaged CMEs farther into the
heliosphere. Analyses of CME observations near the Sun measure the
properties of these events by assuming that the emission is in the
plane of the sky and hence the speed and mass are lower limits to
the true values. However, this assumption cannot be used to analyze
optical observations of CMEs far from the Sun, such as observations from
SMEI and SECCHI-HI, since the CME source is likely to be far from the
limb. In this paper we consider the geometry of observations made by
LASCO, SMEI, and SECCHI. We also present results that estimate both CME
speed and trajectory by fitting the CME elongations observed by these
instruments. Using a constant CME speed does not generally produce
profiles that fit observations at both large and small elongation,
simultaneously. We include the results of a simple empirical model
that alters the CME speed to an estimated value of the solar wind
speed to simulate the effect of drag on the propagating CME. This
change in speed improves the fit between the model and observations
over a broad range of elongations.
---------------------------------------------------------
Title: What Is the Nature of EUV Waves? First STEREO 3D Observations
and Comparison with Theoretical Models
Authors: Patsourakos, S.; Vourlidas, A.; Wang, Y. M.; Stenborg, G.;
Thernisien, A.
2009SoPh..259...49P Altcode: 2009arXiv0905.2189P
One of the major discoveries of the Extreme ultraviolet Imaging
Telescope (EIT) on SOHO was the intensity enhancements propagating
over a large fraction of the solar surface. The physical origin(s)
of the so-called EIT waves is still strongly debated with either
wave (primarily fast-mode MHD waves) or nonwave (pseudo-wave)
interpretations. The difficulty in understanding the nature of EUV waves
lies in the limitations of the EIT observations that have been used
almost exclusively for their study. They suffer from low cadence and
single temperature and viewpoint coverage. These limitations are largely
overcome by the SECCHI/EUVI observations onboard the STEREO mission. The
EUVI telescopes provide high-cadence, simultaneous multitemperature
coverage and two well-separated viewpoints. We present here the first
detailed analysis of an EUV wave observed by the EUVI disk imagers on 7
December 2007 when the STEREO spacecraft separation was ≈ 45°. Both a
small flare and a coronal mass ejection (CME) were associated with the
wave. We also offer the first comprehensive comparison of the various
wave interpretations against the observations. Our major findings are
as follows: (1) High-cadence (2.5-minute) 171 Å images showed a strong
association between expanding loops and the wave onset and significant
differences in the wave appearance between the two STEREO viewpoints
during its early stages; these differences largely disappeared later;
(2) the wave appears at the active region periphery when an abrupt
disappearance of the expanding loops occurs within an interval of 2.5
minutes; (3) almost simultaneous images at different temperatures
showed that the wave was most visible in the 1 - 2 MK range and
almost invisible in chromospheric/transition region temperatures; (4)
triangulations of the wave indicate it was rather low lying (≈ 90
Mm above the surface); (5) forward-fitting of the corresponding CME as
seen by the COR1 coronagraphs showed that the projection of the best-fit
model on the solar surface was inconsistent with the location and size
of the co-temporal EUV wave; and (6) simulations of a fast-mode wave
were found in good agreement with the overall shape and location of the
observed wave. Our findings give significant support for a fast-mode
interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the CME.
---------------------------------------------------------
Title: Deriving the radial distances of wide coronal mass ejections
from elongation measurements in the heliosphere - application to
CME-CME interaction
Authors: Lugaz, N.; Vourlidas, A.; Roussev, I. I.
2009AnGeo..27.3479L Altcode: 2009arXiv0909.0534L
We present general considerations regarding the derivation of the
radial distances of coronal mass ejections (CMEs) from elongation
angle measurements such as those provided by SECCHI and SMEI, focusing
on measurements in the Heliospheric Imager 2 (HI-2) field of view
(i.e. past 0.3 AU). This study is based on a three-dimensional (3-D)
magneto-hydrodynamics (MHD) simulation of two CMEs observed by SECCHI
on 24-27 January 2007. Having a 3-D simulation with synthetic HI
images, we are able to compare the two basic methods used to derive CME
positions from elongation angles, the so-called "Point-P" and "Fixed-φ"
approximations. We confirm, following similar works, that both methods,
while valid in the most inner heliosphere, yield increasingly large
errors in HI-2 field of view for fast and wide CMEs. Using a simple
model of a CME as an expanding self-similar sphere, we derive an
analytical relationship between elongation angles and radial distances
for wide CMEs. This relationship is simply the harmonic mean of the
"Point-P" and "Fixed-φ" approximations and it is aimed at complementing
3-D fitting of CMEs by cone models or flux rope shapes. It proves
better at getting the kinematics of the simulated CME right when we
compare the results of our line-of-sights to the MHD simulation. Based
on this approximation, we re-analyze the J-maps (time-elongation maps)
in 26-27 January 2007 and present the first observational evidence
that the merging of CMEs is associated with a momentum exchange from
the faster ejection to the slower one due to the propagation of the
shock wave associated with the fast eruption through the slow eruption.
---------------------------------------------------------
Title: No Trace Left Behind: STEREO Observation of a Coronal Mass
Ejection Without Low Coronal Signatures
Authors: Robbrecht, Eva; Patsourakos, Spiros; Vourlidas, Angelos
2009ApJ...701..283R Altcode: 2009arXiv0905.2583R
The availability of high-quality synoptic observations of the
extreme-ultraviolet (EUV) and visible corona during the SOHO mission
has advanced our understanding of the low corona manifestations of
coronal mass ejections (CMEs). The EUV imager/white light coronagraph
connection has been proven so powerful, it is routinely assumed that if
no EUV signatures are present when a CME is observed by a coronagraph,
then the event must originate behind the visible limb. This assumption
carries strong implications for space weather forecasting but has not
been put to the test. This paper presents the first detailed analysis
of a frontside, large-scale CME that has no obvious counterparts in
the low corona as observed in EUV and Hα wavelengths. The event was
observed by the SECCHI instruments onboard the STEREO mission. The
COR2A coronagraph observed a slow flux-rope-type CME, while an
extremely faint partial halo was observed in COR2B. The event evolved
very slowly and is typical of the streamer-blowout CME class. EUVI A
171 Å images show a concave feature above the east limb, relatively
stable for about two days before the eruption, when it rises into
the coronagraphic fields and develops into the core of the CME. None
of the typical low corona signatures of a CME (flaring, EUV dimming,
filament eruption, waves) were observed in the EUVI B images, which we
attribute to the unusually large height from which the flux rope lifted
off. This interpretation is supported by the CME mass measurements
and estimates of the expected EUV dimming intensity. Only thanks to
the availability of the two viewpoints we were able to identify the
likely source region. The event originated along a neutral line over
the quiet-Sun. No active regions were present anywhere on the visible
(from STEREO B) face of the disk. Leaving no trace behind on the solar
disk, this observation shows unambiguously that a CME eruption does
not need to have clear on-disk signatures. Also it sheds light on the
question of "mystery" geomagnetic storms, storms without clear solar
origin (formerly called problem storms). We discuss the implications
for space weather monitoring. Preliminary inspection of STEREO data
indicates that events like this are not uncommon, particularly during
the ongoing period of deep solar minimum.
---------------------------------------------------------
Title: CME-driven shocks: Formation and deformation
Authors: Liu, Ying; Luhmann, J. G.; Lin, R. P.; Bale, S. D.;
Richardson, J. D.; Manchester, W. B.; Kasper, J. C.; Vourlidas, A.
2009shin.confE.123L Altcode:
We discuss the formation and deformation of CME-driven shocks
by combining high-cadence imaging observations of the corona and
coordinated in situ measurements. Various shock signatures in the
corona, including remote deflection of coronal structures, a weak edge
ahead of the CME front in white light and coronal metric type II bursts,
are used to investigate the distance and time of shock formation,
a puzzle lasting for several decades. Early CME kinematics obtained
from high-cadence observations are compared with a certain range of
Alfven speeds determined from band splitting of type II bursts and
motion of plasma blobs in the post-CME plasma sheet. CMEs and their
preceding shocks can also be deformed by coronal structures that act
like density/field obstacles as well as solar wind speed gradient when
the solar wind momentum dominates the magnetic force. The curvature of
CMEs/shocks resulting from this distortion is studied in terms of the
elevation angle of their normals and plasma deflection flows in CME
sheaths and is compared with global MHD simulations. Multi-spacecraft
measurements of specific events coordinated by MHD propagation of the
solar wind are also examined in order to probe the global structure
of CME-driven shocks.
---------------------------------------------------------
Title: Origins of Solar Minimum CMEs with ICMEs
Authors: Li, Yan; Luhmann, J. G.; Lynch, B. J.; Toy, V.; Thernisien,
A.; Vourlidas, A.; Kilpua, E.; Jian, L.
2009shin.confE.167L Altcode:
We study a group of approximately one dozen CMEs occurred during the
current solar minimum in order to understand their associations (or lack
of) with coronal activity (e.g., flares, prominences/filaments). These
CMEs are the sources of all the significant ICMEs that were detected
by spacecraft at 1AU between Jan 2007 and Sept 2008. They make up only
a small fraction of the total CME population in various catalogs in
this time span. Most CMEs in this group are slow eruptions and have no
association with flares. For some of these CMEs, we cannot identify
any associated solar activity on the disk. What gave rise to this
group of solar minimum CMEs and what can we learn from them?
---------------------------------------------------------
Title: Examining Solar Wind Number Density Structures Observed in
SECCHI HI 1
Authors: Viall, Nicholeen Mary; Spence, Harlan E.; Vourlidas, Angelos;
Howard, Russ
2009shin.confE.133V Altcode:
We explore small-scale quasi-periodic solar wind density fluctuations
observed in SECCHI HI 1. We discuss their possible relationship to
periodic fluctuations of the proton density observed in-situ with the
Wind SWE data. Viall et al. [2008] used 11 years of solar wind density
measurements at 1 AU and demonstrated that in addition to turbulent
fluctuations, non-turbulent, periodic density structures exist in the
solar wind. In the slow wind, periodic density structures occurred most
often with radial length-scales of approximately 73, 120, 136 and 180
Mm. In the fast wind, periodic density structures occurred most often
with radial length-scales of approximately 187, 270 and 400 Mm. Event
studies of the periodic density structures reveal instances in which the
density structure has alpha/proton abundance ratio changes associated
with the density structures. Specifically, the alpha density varies
with the same periodicity as the protons, but in antiphase. This
strongly suggests either time varying or spatially varying coronal
source plasma that created the density structures. If such periodic
density structures observed at 1AU are generated in the corona, then
they may be observable in SECCHI HI1 data. For instance, larger scale
plasmoids have been observed in the corona [e.g. Sheeley et al., 2009]
and it is plausible that smaller, quasi-periodic structures may exist
as well. We identify quasi-periodic density structures in the SECCHI HI1
images that are comparable in size to those identified in-situ at 1AU.
---------------------------------------------------------
Title: Tracking CMEs/shocks and predicting their arrival time at
the Earth
Authors: Liu, Ying; Luhmann, J. G.; Lin, R. P.; Bale, S. D.; Davies,
J. A.; Thernisien, A.; Vourlidas, A.
2009shin.confE..59L Altcode:
Coronal mass ejections (CMEs) have been recognized as primary drivers
of interplanetary disturbances. Of central importance in space weather
forecasting is to track CMEs and their preceding shocks from the Sun
continuously out to 1 AU. We will discuss and evaluate three different
strategies for this purpose, specifically (1) frequency drift of type
II bursts to track CME-driven shocks; (2) MHD propagation of observed
solar wind disturbances; and (3) geometric triangulation of white-light
features observed by wide-angle coronagraphs and heliospheric imagers
from vantage points off the Sun-Earth line. Event studies together with
implications for instrumentation will be presented to demonstrate the
capabilities with which the impact of a solar storm on the Earth can
be predicted with small ambiguities.
---------------------------------------------------------
Title: Kinematics of CMEs observed in SECCHI HI: Fast solar wind
acceleration of CMEs?
Authors: Colaninno, Robin Crescenza; Vourlidas, Angelos
2009shin.confE.166C Altcode:
The SECCHI HI instruments allow us to observe CMEs from 15 solar
radii to 1 AU. In these data, we often see a fast lateral expansion
of the CME. This lateral expansion causes a pancaking effect where the
angular extent of the CME becomes much larger than its radial extent. A
possible cause of this pancaking is an interaction of the CME with the
fast solar wind. By fitting a geometric surface to the two viewpoints
of STEREO data, we are able to infer the shape and direction of the
CME at low coronal heights. By using the HI data and extrapolating
the directional information from the geometric model, we can estimate
the position of the CME as it moves in the solar wind. Here we will
combine this data with Predictive Science's heliospheric models to
discover if CMEs are interacting with the fast solar wind.
---------------------------------------------------------
Title: On Magnetic Donuts and Croissants: The Structure of the Slow
Solar Wind as Revealed from the SECCHI Telescopes on STEREO
Authors: Vourlidas, Angelos
2009shin.confE.132V Altcode:
The SECCHI telescopes aboard the STEREO mission have been providing
continuous imaging of the corona and inner heliosphere since
2007. The observations have already provided important clues about
the magnetic, croissant-like, nature of CMEs. However, the extended
solar minimum allows us an opportunity to observe the quiescent solar
wind as well. I review the status of solar wind analysis based on the
SECCHI observations some of which show that donut-like structures are
propagating in the wind. I also discuss the role of such observations in
discriminating among the various theories for the solar wind generation.
---------------------------------------------------------
Title: "Extreme Ultraviolet Waves" are Waves: First Quadrature
Observations of an Extreme Ultraviolet Wave from STEREO
Authors: Patsourakos, Spiros; Vourlidas, Angelos
2009ApJ...700L.182P Altcode: 2009arXiv0905.2164P
The nature of coronal mass ejection (CME)-associated low corona
propagating disturbances, "extreme ultraviolet (EUV) waves," has been
controversial since their discovery by EIT on SOHO. The low-cadence,
single-viewpoint EUV images and the lack of simultaneous inner corona
white-light observations have hindered the resolution of the debate
on whether they are true waves or just projections of the expanding
CME. The operation of the twin EUV imagers and inner corona coronagraphs
aboard STEREO has improved the situation dramatically. During early
2009, the STEREO Ahead (STA) and Behind (STB) spacecrafts observed
the Sun in quadrature having a ≈90° angular separation. An EUV
wave and CME erupted from active region 11012, on February 13, when
the region was exactly at the limb for STA and hence at disk center
for STB. The STEREO observations capture the development of a CME
and its accompanying EUV wave not only with high cadence but also in
quadrature. The resulting unprecedented data set allowed us to separate
the CME structures from the EUV wave signatures and to determine without
doubt the true nature of the wave. It is a fast-mode MHD wave after all.
---------------------------------------------------------
Title: Dynamic Lyα jets
Authors: Koza, J.; Rutten, R. J.; Vourlidas, A.
2009A&A...499..917K Altcode: 2008arXiv0807.4889K
Context: The solar chromosphere and transition region are highly
structured and complex regimes. A recent breakthrough has been
the identification of dynamic fibrils observed in Hα as caused
by field-aligned magnetoacoustic shocks. <BR />Aims: We seek to
find whether such dynamic fibrils are also observed in Lyα. <BR
/>Methods: We used a brief sequence of four high-resolution Lyα
images of the solar limb taken by the Very high Angular resolution
ULtraviolet Telescope (VAULT), which displays many extending and
retracting Lyα jets. We measured their top trajectories and fitted
parabolas to the 30 best-defined ones. <BR />Results: Most jet tops move
supersonically. Half of them decelerate, sometimes superballistically,
the others accelerate. This bifurcation may arise from incomplete
sampling of recurrent jets. <BR />Conclusions: The similarities between
dynamic Lyα jets and Hα fibrils suggest that the magnetoacoustic
shocks causing dynamic Hα fibrils also affect dynamic Lyα jets.
---------------------------------------------------------
Title: Morphology and density structure of post-CME current sheets
Authors: Vršnak, B.; Poletto, G.; Vujić, E.; Vourlidas, A.; Ko,
Y. -K.; Raymond, J. C.; Ciaravella, A.; Žic, T.; Webb, D. F.;
Bemporad, A.; Landini, F.; Schettino, G.; Jacobs, C.; Suess, S. T.
2009A&A...499..905V Altcode: 2009arXiv0902.3705V
Context: Eruption of a coronal mass ejection (CME) drags and “opens”
the coronal magnetic field, presumably leading to the formation
of a large-scale current sheet and field relaxation by magnetic
reconnection. <BR />Aims: We analyze the physical characteristics
of ray-like coronal features formed in the aftermath of CMEs, to
confirm whether interpreting this phenomenon in terms of a reconnecting
current sheet is consistent with observations. <BR />Methods: The study
focuses on measurements of the ray width, density excess, and coronal
velocity field as a function of the radial distance. <BR />Results: The
morphology of the rays implies that they are produced by Petschek-like
reconnection in the large-scale current sheet formed in the wake of
CME. The hypothesis is supported by the flow pattern, often showing
outflows along the ray, and sometimes also inflows into the ray. The
inferred inflow velocities range from 3 to 30 km s<SUP>-1</SUP>, and
are consistent with the narrow opening-angle of rays, which add up to a
few degrees. The density of rays is an order of magnitude higher than
in the ambient corona. The density-excess measurements are compared
with the results of the analytical model in which the Petschek-like
reconnection geometry is applied to the vertical current sheet, taking
into account the decrease in the external coronal density and magnetic
field with height. <BR />Conclusions: The model results are consistent
with the observations, revealing that the main cause of the density
excess in rays is a transport of the dense plasma from lower to higher
heights by the reconnection outflow.
---------------------------------------------------------
Title: Coronal Mass Ejections and Global Coronal Magnetic Field
Reconfiguration
Authors: Liu, Ying; Luhmann, Janet G.; Lin, Robert P.; Bale, Stuart
D.; Vourlidas, Angelos; Petrie, Gordon J. D.
2009ApJ...698L..51L Altcode:
We investigate the role of coronal mass ejections (CMEs) in the global
coronal magnetic field reconfiguration, a debate that has lasted for
about two decades. Key evidence of the coronal field restructuring
during the 2007 December 31 CME is provided by combining imaging
observations from widely separated spacecraft with the potential-field
source-surface (PFSS) model, thanks to the extraordinarily quiet
Sun at the present solar minimum. The helmet streamer, previously
disrupted by the CME, re-forms but is displaced southward permanently;
the preexisting heliospheric plasma sheet (HPS) is also disrupted as
evidenced by the concave-outward shape of the CME. The south polar
coronal hole shrinks considerably. Plasma blobs moving outward along
the newly formed HPS suggest the occurrence of magnetic reconnection
between the fields blown open by the CME and the ambient adjacent open
fields. A streamer-like structure is also observed in the wake of the
CME and interpreted as a plasma sheet where the thin post-CME current
sheet is embedded. These results are important for understanding the
coronal field evolution over a solar cycle as well as the complete
picture of CME initiation and propagation.
---------------------------------------------------------
Title: First Determination of the True Mass of Coronal Mass Ejections:
A Novel Approach to Using the Two STEREO Viewpoints
Authors: Colaninno, Robin C.; Vourlidas, Angelos
2009ApJ...698..852C Altcode: 2009arXiv0903.4344C
The twin Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) COR2 coronagraphs of the Solar Terrestrial Relations
Observatory (STEREO) provide images of the solar corona from two
viewpoints in the solar system. Since their launch in late 2006, the
STEREO Ahead (A) and Behind (B) spacecraft have been slowly separating
from Earth at a rate of 22fdg5 per year. By the end of 2007, the two
spacecraft were separated by more than 40° from each other. At that
time, we began to see large-scale differences in the morphology and
total intensity between coronal mass ejections (CMEs) observed with
SECCHI-COR2 on STEREO-A and B. Due to the effects of the Thomson
scattering geometry, the intensity of an observed CME is dependent
on the angle it makes with the observed plane of the sky. From the
intensity images, we can calculate the integrated line-of-sight electron
density and mass. We demonstrate that it is possible to simultaneously
derive the direction and true total mass of the CME if we make the
simple assumption that the same mass should be observed in COR2-A and B.
---------------------------------------------------------
Title: The Polarimetric Performance of the SECCHI/COR2 Coronagraphs
on the Stereo Mission
Authors: Baldwin, Katherine; Vourlidas, A.
2009SPD....40.1805B Altcode:
The COR2 coronagraphs have been observing the corona in polarized light
since January 2007. The COR2 observations are used widely for estimates
of the density and 3D structure of the corona and for the localization
of coronal mass ejections. The characterization of the polarimetric
performance of the instrument is very important for these analyses
but also for observations involving the total brightness only. This
is because the polarizer is placed permanently in the optical train of
the telescope and therefore affects every COR2 image. In this paper, we
give a report on our polarization calibrations, including instrumental
polarization and provide estimates for the expected accuracy of COR2
polarimetric analysis on the estimation of coronal density and the
localization of structures.
---------------------------------------------------------
Title: Study of the 2007 April 20 CME-Comet Interaction Event with
an MHD Model
Authors: Jia, Y. D.; Russell, C. T.; Jian, L. K.; Manchester, W. B.;
Cohen, O.; Vourlidas, A.; Hansen, K. C.; Combi, M. R.; Gombosi, T. I.
2009ApJ...696L..56J Altcode: 2009arXiv0903.4942J
This study examines the tail disconnection event on 2007 April
20 on comet 2P/Encke, caused by a coronal mass ejection (CME) at a
heliocentric distance of 0.34 AU. During their interaction, both the CME
and the comet are visible with high temporal and spatial resolution by
the STEREO-A spacecraft. Previously, only current sheets or shocks have
been accepted as possible reasons for comet tail disconnections, so it
is puzzling that the CME caused this event. The MHD simulation presented
in this work reproduces the interaction process and demonstrates how
the CME triggered a tail disconnection in the April 20 event. It
is found that the CME disturbs the comet with a combination of a
180° sudden rotation of the interplanetary magnetic field (IMF),
followed by a 90° gradual rotation. Such an interpretation applies
our understanding of solar wind-comet interactions to determine the
in situ IMF orientation of the CME encountering Encke.
---------------------------------------------------------
Title: Two Years of the STEREO Heliospheric Imagers. Invited Review
Authors: Harrison, Richard A.; Davies, Jackie A.; Rouillard, Alexis
P.; Davis, Christopher J.; Eyles, Christopher J.; Bewsher, Danielle;
Crothers, Steve R.; Howard, Russell A.; Sheeley, Neil R.; Vourlidas,
Angelos; Webb, David F.; Brown, Daniel S.; Dorrian, Gareth D.
2009SoPh..256..219H Altcode:
Imaging of the heliosphere is a burgeoning area of research. As
a result, it is awash with new results, using novel applications,
and is demonstrating great potential for future research in a wide
range of topical areas. The STEREO (Solar TErrestrial RElations
Observatory) Heliospheric Imager (HI) instruments are at the heart
of this new development, building on the pioneering observations of
the SMEI (Solar Mass Ejection Imager) instrument aboard the Coriolis
spacecraft. Other earlier heliospheric imaging systems have included
ground-based interplanetary scintillation (IPS) facilities and the
photometers on the Helios spacecraft. With the HI instruments, we now
have routine wide-angle imaging of the inner heliosphere, from vantage
points outside the Sun-Earth line. HI has been used to investigate the
development of coronal mass ejections (CMEs) as they pass through the
heliosphere to 1 AU and beyond. Synoptic mapping has also allowed us to
see graphic illustrations of the nature of mass outflow as a function
of distance from the Sun - in particular, stressing the complexity of
the near-Sun solar wind. The instruments have also been used to image
co-rotating interaction regions (CIRs), to study the interaction of
comets with the solar wind and CMEs, and to witness the impact of CMEs
and CIRs on planets. The very nature of this area of research - which
brings together aspects of solar physics, space-environment physics,
and solar-terrestrial physics - means that the research papers are
spread among a wide range of journals from different disciplines. Thus,
in this special issue, it is timely and appropriate to provide a review
of the results of the first two years of the HI investigations.
---------------------------------------------------------
Title: Forward Modeling of Coronal Mass Ejections Using STEREO/SECCHI
Data
Authors: Thernisien, A.; Vourlidas, A.; Howard, R. A.
2009SoPh..256..111T Altcode:
We describe a forward modeling method developed to study the coronal
mass ejections observed with STEREO/SECCHI. We present a survey of
26 CMEs modeled with this method. We selected most of the bright
events observed since November 2007 to August 2008, after when the
separation was greater than 40° degrees, thus showing noticeable
differences between the two views. From these stereoscopic observations
and using a geometric model of a flux rope, we are able to determine
the three-dimensional direction of propagation, the three-dimensional
velocity and acceleration of the CME front, and in most of the cases the
flux rope orientation and length. We define a merit function that allows
us to partially automate the fit, as well as perform a sensitivity
analysis on the model parameters. We find a precision on the longitude
and latitude to be of a maximum of ±17° and ±4°, respectively,
for a 10% decrease of the merit function but a precision on the flux
rope orientation and length to be almost one order of magnitude larger,
showing that these parameters are more difficult to estimate using only
coronagraph data. Finally, comparison with independent measurements
shows a good agreement with the direction and speed we estimated.
---------------------------------------------------------
Title: Solar - Terrestrial Simulation in the STEREO Era: The 24 -
25 January 2007 Eruptions
Authors: Lugaz, N.; Vourlidas, A.; Roussev, I. I.; Morgan, H.
2009SoPh..256..269L Altcode: 2009arXiv0902.2004L
The SECCHI instruments aboard the recently launched STEREO spacecraft
enable for the first time the continuous tracking of coronal mass
ejections (CMEs) from the Sun to 1 AU. We analyze line-of-sight
observations of the 24 - 25 January 2007 CMEs and fill the 20-hour gap
in SECCHI coverage in 25 January by performing a numerical simulation
using a three-dimensional magneto-hydrodynamic (MHD) code, the Space
Weather Modeling Framework (SWMF). We show how the observations reflect
the interaction of the two successive CMEs with each other and with
the structured solar wind. We make a detailed comparison between
the observations and synthetic images from our model, including
time-elongation maps for several position angles. Having numerical
simulations to disentangle observational from physical effects, we are
able to study the three-dimensional nature of the ejections and their
evolution in the inner heliosphere. This study reflects the start of a
new era where, on one hand, models of CME propagation and interaction
can be fully tested by using heliospheric observations and, on the
other hand, observations can be better interpreted by using global
numerical models.
---------------------------------------------------------
Title: The Sub-arcsecond Structure Of The Upper Chromosphere:
Results From The 2nd Flight Of The Nrl Vault Sounding Rocket Payload
Authors: Sanchez-Andrade Nuno, Bruno; Vourlidas, A.; Korendyke, C.
2009SPD....40.2901S Altcode:
The Very high Angular resolution ULtraviolet Telescope (VAULT) is an Lya
spectroheliograph flown on a sounding rocket. The payload is capable of
obtaining Lya filtergrams with a spatial resolution of around 0.33” (
200 km) over an extended field of view (535” x 235”) . The instrument
is tuned to the Ly-a line because it forms at the boundary of the upper
chromosphere low corona. On its last flight, on 14 June 2002, VAULT
observed an area around NOAA AR 9997 & 9998 with a rich variety
of features: quiet Sun network, limb spicules, filaments, prominences
and plage. <P />The observing campaign incorporated a wide variety of
ground-based and space-borne instruments. The level 0.9 VAULT data is
open and available from http://wwwsolar.nrl.navy.mil/rockets/vault .We
have recently releseased SolarSoft-compatible software for easy access
and processing of the data. <P />This contribution showcases the data
capabilities and availability. We present contrast-enhanced images by
means of wavelet image processing. The images reveal in extraordinary
detail the dynamics of the smallest solar scales (200-300 km). We
observe flows along thin threads on the prominence, exploding events
on the plage and even in the quiet sun regions.
---------------------------------------------------------
Title: No trace left behind: STEREO Observation of a Coronal Mass
Ejection Lacking Low Coronal Signatures
Authors: Vourlidas, Angelos; Robbrecht, E.; Patsourakos, S.
2009SPD....40.2104V Altcode:
The availability of high quality synoptic observations of the EUV and
visible corona during the SOHO mission has advanced our understanding
of the low corona manifestations of CMEs. The EUV imager/White light
coronagraph connection has been proven so powerful, it is routinely
assumed that if no EUV signatures are present when a CME is observed
by a coronagraph, then the event must originate behind the visible
limb. This assumption carries strong implications for space weather
forecasting but has not been put to the test. This paper presents the
first detailed analysis of a frontside, large-scale CME that has no
obvious counterparts in the low corona. The event was observed by the
SECCHI instruments on the STEREO mission. The COR2A coronagraph observed
the event as a typical flux-rope type CME, while an extremely faint
partial halo was observed in COR2B. The event evolved very slowly and
is typical of the streamer-blowout CME class. EUVI-A 171A images show
a concave feature above the east limb, relatively stable for about
two days before the eruption, when it rises into the coronagraphic
fields and develops into the core of the CME. None of the typical low
corona signatures of a CME (flaring, EUV dimming, filament eruption,
waves) were observed. Thanks to the two STEREO viewpoints we were able
to identify the likely source region. The event originated along a
quiet sun neutral line. No active regions were present anywhere on the
visible face of the disk. Leaving no trace behind, this observation
shows unambiguously that a CME eruption does not need to have clear
on-disk signatures. Also it sheds light on the question of `mystery'
geomagnetic storms; storms without clear solar origin. Preliminary
inspection of STEREO data indicates that events like this are not
uncommon, particularly during the ongoing period of deep solar minimum.
---------------------------------------------------------
Title: Quadrature STEREO Observations Determine the Nature of
EUV Waves
Authors: Kliem, Bernhard; Patsourakos, S.; Vourlidas, A.; Ontiveros, V.
2009SPD....40.2603K Altcode:
One of the major discoveries of EIT on SOHO was the observation of
large-scale EUV intensity disturbances which travel over significant
fractions of the solar disk. These `EUV waves' are associated with
CME onsets and can be either an MHD wave triggered by the eruption or
the footprints of the associated CME, which currently is a subject of
intense debate. EUV waves are better observed when their source region
is close to disk center, whereas CME onsets and CMEs in general are
better observed off-limb. Therefore, simultaneous multi-viewpoint
observations of EUV waves are best suited to clarify the nature of
these transients and to determine their true relationship with CMEs. <P
/>We present here the first quadrature STEREO observations of an EUV
wave. The wave was observed on 2009 February 13 by both satellites,
which were at a separation of 90 degrees. The wave originated from
an erupting active region near disk center as seen from SC B and
propagated over almost the entire visible solar disk. For SC A the
active region was at the east limb and showed a small erupting bubble,
expanding impulsively in both radial and lateral directions and inducing
deflections of nearby and remote coronal structures. We present high
cadence EUVI and COR1 measurements of both the wave (SC B), and the
expanding EUV bubble (SC A), and of the resulting white-light CME (SC A;
COR1). These would allow to quantify for the first time the true sizes
and expansion characteristics of both the EUV wave and the associated
CME. <P />Finally, we search for wave-associated features in 3D MHD
simulations of CME onsets based on ideal MHD instabilities. These are
compared with the STEREO observations.
---------------------------------------------------------
Title: Reconstruction of CME-Driven Shocks Using STEREO Observations
Authors: Vourlidas, A.; Ontiveros, Veronica; Riley, P.
2009SPD....40.2212V Altcode:
Recent work has shown that CME-driven shocks can easily be detected by
white light coronagraph observations from a few solar radii above the
surface to at least 20 Rs. However, the shock emission suffers from the
same projection effects at the CME emission making precise measurements
of the shock properties difficult and prone to assumptions. The two
viewpoint observations from the SECCHI/COR2 coronagraphs aboard the
STEREO mission offer an unprecedented opportunity to reconstruct the
3D envelope of the shock using the same procedures applied to the
successful reconstruction of the CME itself. Due to the low solar
activity over the last years, there have been only a handful of
white lght shock candidates observed with SECCHI. We examine the
most prominent one, associated with the eruption on December 31,
2007. We find that the shock does not evolve isotropically but it is
influenced by the large scale coronal magnetic field configuration. To
study this interaction in more detail, we employ a sophisticated
thermodynamic model of the corona to derive a 3d distribution of the
Alfvén speed around the eruption site. We find that we can account
for the coronagraph observations only if the shape of the shock closely
matches that of the surrounding magnetic field.
---------------------------------------------------------
Title: First Measurements of the Mass of Coronal Mass Ejections from
the EUV Dimming Observed with Stereo EUVI A and B Spacecraft
Authors: Aschwanden, Markus J.; Nitta, N. V.; Wuelser, J.; Lemen,
J. R.; Sandman, A.; Vourlidas, A.; Colaninno, R. C.
2009SPD....40.2116A Altcode:
The masses of Coronal Mass Ejections (CMEs) have traditionally
been determined from white-light coronagraphs, based on the Thomson
scattering of electrons. Here we develop a new method of measuring CME
masses from the EUV dimming seen with EUV imaging telescopes in multiple
temperature filters. As a test we compare the CME masses measured by
STEREO/EUVI A and B with those previously determined by STEREO/COR2, for
a set of 8 CME events of which we detected 7 with EUVI and determined
the masses in 6 cases. We find CME masses in the range of m = (2-7)
x 10(15) g. The agreement between the two EUVI/A and B spacecraft is
mA/mB =1.3 +/- 0.6 and the consistency with white-light measurements
by COR2 is mEUVI/mCOR2 = 1.1 +/- 0.3. The consistency between EUVI
and COR2 implies no significant mass backflows (or inflows) at r <
4 R and adequate temperature coverage for the bulk of the CME mass
in the range of T = 0.5-3.0 MK. The temporal evolution of the EUV
dimming allows us also to model the evolution of the CME density,
volume, height-time, and propagation speed in terms of an adiabatically
expanding self-similar geometry. We test this model with the predicted
detection delay between EUVI and COR2 for the 2008-Mar-25 event.
---------------------------------------------------------
Title: Large-scale Structures Caused by Interacting Coronal
Mass Ejections: Their Formation and Detection as Revealed by MHD
Simulations
Authors: Lugaz, N.; Roussev, I. I.; Vourlidas, A.
2009EGUGA..11.6510L Altcode:
The interaction of successive coronal mass ejections (CMEs) on their way
to Earth (and other planets) has been a leading cause of large-scale
and long-lived structures resulting in intense geo-magnetic storms
during past solar cycles. Associated with the interaction, the merging
of shock waves, which creates denser sheaths and the compression of the
magnetic field in ejecta are expected to result in unusal responses of
the magnetosphere. Here, we present results of magneto-hydrodynamic
simulations of geo-effective events from the years 2000 and 2001
with the Space Weather Modeling Framework (SWMF). Our focus is on
the propagation and interaction of successive CMEs from the Sun to
the Earth and the understanding of the mechanisms which may result
in larger and more geo-effective structures. We will also present
simulations showing how the Heliospheric Imagers onboard STEREO will
help predicting complex ejecta during solar cycle 24.
---------------------------------------------------------
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: Driving Currents for Flux Rope Coronal Mass Ejections
Authors: Subramanian, Prasad; Vourlidas, Angelos
2009ApJ...693.1219S Altcode: 2008arXiv0810.4210S
We present a method for measuring electrical currents enclosed by flux
rope structures that are ejected within solar coronal mass ejections
(CMEs). Such currents are responsible for providing the Lorentz
self-force that propels CMEs. Our estimates for the driving current
are based on measurements of the propelling force obtained using data
from the LASCO coronagraphs aboard the SOHO satellite. We find that
upper limits on the currents enclosed by CMEs are typically around
10<SUP>10</SUP> A. We estimate that the magnetic flux enclosed by the
CMEs in the LASCO field of view is a few times 10<SUP>21</SUP> Mx.
---------------------------------------------------------
Title: POLAR investigation of the Sun—POLARIS
Authors: Appourchaux, T.; Liewer, P.; Watt, M.; Alexander, D.;
Andretta, V.; Auchère, F.; D'Arrigo, P.; Ayon, J.; Corbard, T.;
Fineschi, S.; Finsterle, W.; Floyd, L.; Garbe, G.; Gizon, L.; Hassler,
D.; Harra, L.; Kosovichev, A.; Leibacher, J.; Leipold, M.; Murphy,
N.; Maksimovic, M.; Martinez-Pillet, V.; Matthews, B. S. A.; Mewaldt,
R.; Moses, D.; Newmark, J.; Régnier, S.; Schmutz, W.; Socker, D.;
Spadaro, D.; Stuttard, M.; Trosseille, C.; Ulrich, R.; Velli, M.;
Vourlidas, A.; Wimmer-Schweingruber, C. R.; Zurbuchen, T.
2009ExA....23.1079A Altcode: 2008ExA...tmp...40A; 2008arXiv0805.4389A
The POLAR Investigation of the Sun (POLARIS) mission uses a combination
of a gravity assist and solar sail propulsion to place a spacecraft
in a 0.48 AU circular orbit around the Sun with an inclination of 75°
with respect to solar equator. This challenging orbit is made possible
by the challenging development of solar sail propulsion. This first
extended view of the high-latitude regions of the Sun will enable
crucial observations not possible from the ecliptic viewpoint or from
Solar Orbiter. While Solar Orbiter would give the first glimpse of
the high latitude magnetic field and flows to probe the solar dynamo,
it does not have sufficient viewing of the polar regions to achieve
POLARIS’s primary objective: determining the relation between the
magnetism and dynamics of the Sun’s polar regions and the solar cycle.
---------------------------------------------------------
Title: Quantitative Measurements of Coronal Mass Ejection-Driven
Shocks from LASCO Observations
Authors: Ontiveros, Veronica; Vourlidas, Angelos
2009ApJ...693..267O Altcode: 2008arXiv0811.3743O
In this paper, we demonstrate that coronal mass ejection (CME)-driven
shocks can be detected in white light coronagraph images and in which
properties such as the density compression ratio and shock direction
can be measured. Also, their propagation direction can be deduced via
simple modeling. We focused on CMEs during the ascending phase of solar
cycle 23 when the large-scale morphology of the corona was simple. We
selected events which were good candidates to drive a shock due to their
high speeds (V > 1500 km s<SUP>-1</SUP>). The final list includes 15
CMEs. For each event, we calibrated the LASCO data, constructed excess
mass images, and searched for indications of faint and relatively
sharp fronts ahead of the bright CME front. We found such signatures
in 86% (13/15) of the events and measured the upstream/downstream
densities to estimate the shock strength. Our values are in agreement
with theoretical expectations and show good correlations with the CME
kinetic energy and momentum. Finally, we used a simple forward modeling
technique to estimate the three-dimensional shape and orientation of
the white light shock features. We found excellent agreement with
the observed density profiles and the locations of the CME source
regions. Our results strongly suggest that the observed brightness
enhancements result from density enhancements due to a bow-shock
structure driven by the CME.
---------------------------------------------------------
Title: Multispacecraft Observations of Magnetic Clouds and Their
Solar Origins between 19 and 23 May 2007
Authors: Kilpua, E. K. J.; Liewer, P. C.; Farrugia, C.; Luhmann,
J. G.; Möstl, C.; Li, Y.; Liu, Y.; Lynch, B. J.; Russell, C. T.;
Vourlidas, A.; Acuna, M. H.; Galvin, A. B.; Larson, D.; Sauvaud, J. A.
2009SoPh..254..325K Altcode: 2008SoPh..tmp..194K
We analyze a series of complex interplanetary events and their solar
origins that occurred between 19 and 23 May 2007 using observations
by the STEREO and Wind satellites. The analyses demonstrate the new
opportunities offered by the STEREO multispacecraft configuration
for diagnosing the structure of in situ events and relating them to
their solar sources. The investigated period was characterized by
two high-speed solar wind streams and magnetic clouds observed in
the vicinity of the sector boundary. The observing satellites were
separated by a longitudinal distance comparable to the typical radial
extent of magnetic clouds at 1 AU (fraction of an AU), and, indeed,
clear differences were evident in the records from these spacecraft. Two
partial-halo coronal mass ejections (CMEs) were launched from the same
active region less than a day apart, the first on 19 May and the second
on 20 May 2007. The clear signatures of the magnetic cloud associated
with the first CME were observed by STEREO B and Wind while only STEREO
A recorded clear signatures of the magnetic cloud associated with the
latter CME. Both magnetic clouds appeared to have interacted strongly
with the ambient solar wind and the data showed evidence that they were
a part of the coronal streamer belt. Wind and STEREO B also recorded
a shocklike disturbance propagating inside a magnetic cloud that
compressed the field and plasma at the cloud's trailing portion. The
results illustrate how distant multisatellite observations can reveal
the complex structure of the extension of the coronal streamer into
interplanetary space even during the solar activity minimum.
---------------------------------------------------------
Title: The CME-ICME Connection and Interplanetary Structure During
Solar Minimum
Authors: Li, Y.; Lynch, B. J.; Luhmann, J. G.; Kilpua, E.; Toy, V.;
Vourlidas, A.; Russell, C. T.; Galvin, A. B.
2008AGUFMSH13B1542L Altcode:
When an interplanetary transient (ICME) exhibits a large angle and
smooth rotation in the IMF vector, it is classified as a magnetic cloud
(MC) and commonly interpreted as the signature of a magnetic flux
rope. On the average bout a third of ICME ejecta are MCs, although
the fraction seems to be larger during the quiet phase of the solar
cycle. Non-flux rope ICMEs are likely (1) distorted during the transit
through heliosphere, (2) observed at an unfavorable crossing angle
if the ICME structure has spatial variation, (3) or are simply have a
more complex internal structure. Five Magnetic Clouds (MC) have been
found from a total of nine ICMEs observed during 2007 January 01 to 2008
August 31, when the separation of STEREO A (STA) and B (STB) spacecraft
varied between 0.05 to 70.35 degrees heliolongitude. We investigate the
four best MCs using observations from three spacecraft (STA, STB and
ACE). The first MC seems to have been detected by all three spacecraft
(STA and STB 40.4 degrees apart), while the latter three were detected
by only one of the STEREO spacecraft and sometimes by ACE. From
the inferred flux rope orientation at each crossing and the spatial
variation of the ICME properties, we interpret how each MC flux rope was
situated relative to the spacecraft, and its connection to the Sun from
corresponding coronal and heliospheric modeling results. Each of the
MCs can be associated at low confidence (in contrary to expectations
for solar minimum time) with a CME observed by coronagraphs on board
STEREO and/or SOHO. All potential parent CMEs were very slow in the 200
km/s range (plane-of-sky), but the speeds of the MCs were between ~390
and ~480 km/s, indicating acceleration in the heliosphere. Solar disk
activities are minor around the four CMEs, with no GOES x-ray flares,
and two possibly associated filament eruptions. Some CME structures
appear to form in the coronagraph field of view rather than rising from
below. Several low/mid- latitude coronal holes and a highly warped
coronal streamer arcade and source surface neutral line dominate the
coronal structure during the period of the study. Previous studies
have shown that the MC fluxrope orientation may be aligned with the
large-scale coronal streamer arcades. Estimated MC orientations are
discussed and compared with events during the previous solar minimum,
which exhibited a more dipolar coronal structure. This work was
supported, in part, by NASA NNG06GE51G, NNX08AJ04G, and NAS5-03131.
---------------------------------------------------------
Title: Multipoint Analysis of Meso-scale Structures in the Ambient
Solar Wind: STEREO-A, -B, and L1 Observations
Authors: Spence, H. E.; Viall, N. M.; Vourlidas, A.; Howard, R. A.;
Simunac, K.; Kistler, L. M.; Galvin, A. B.; Kasper, J. C.; Lazarus,
A. J.
2008AGUFMSH12A..06S Altcode:
We explore sources of apparent time-dependence of meso-scale structures
(those lasting two to three days and less) in the ambient solar wind
through analysis of measurements from STEREO-A, -B, and L1 spacecraft
(WIND, ACE, and SOHO). In early 2008, stable corotating interaction
regions and high-speed streams provided excellent boundaries and
features for co-registering the large-scale, corotating solar wind
observed by several heliospheric spacecraft separated in solar orbital
phase near 1 AU. During this period, STEREO-B (located 23 degrees behind
the Earth in heliographic longitude) first observed the large-scale
corotating stream structures, followed by the WIND, ACE, and SOHO
spacecraft at Earth, then finally by STEREO-A (located 22 degrees ahead
of the Earth in heliographic longitude). Conspicuous similarities
in the macro-scale solar wind flow dominate the comparison between
spacecraft observations and permit us to time-adjust the observed flow
features reasonably well by assuming a simple corotating solar wind
source. While the co-registered, large-scale solar wind structure agrees
well, mesoscale flow features can exhibit large measured differences
at the various spacecraft. We focus on one such interesting feature
which exhibits apparent time dependence. Though this few-day-long,
significant flow speed event is observed by the PLASTIC experiments
on both STEREO-A and STEREO-B, it is not seen at the L1 spacecraft
which the STEREO spacecraft bracket in space and time. We explore
potential sources of the apparent time dependence of this meso-scale
feature. Latitudinal differences in the multipoint measurements is one
source that could account for the apparent mesoscale flow structure
variability. We also explore explicit time variation of the solar wind's
source, by analyzing relevant coronal holes observed simultaneously
by the STEREO spacecraft imagers. This event and analysis underscores
that multipoint heliospheric observations and analysis reveals the
existence of mesoscale structure in the solar wind and can be used to
constrain its possible source(s).
---------------------------------------------------------
Title: STEREO ICMEs and their Solar Source Regions Near Solar Minimum
Authors: Toy, V.; Li, Y.; Luhmann, J. G.; Schroeder, P.; Vourlidas,
A.; Jian, L. K.; Russell, C. T.; Galvin, A. B.; Simunac, K.; Acuna,
M.; Sauvaud, J. A.; Skoug, R.; Petrie, G.
2008AGUFMSH23A1620T Altcode:
Although the quiet activity period surrounding the current solar minimum
has prevailed since the launch of STEREO in October 2006, there have
been at least 9 clear in-situ detections of ICMEs (Interplanetary
Coronal Mass Ejections) by one or more spacecraft during the time
the imagers were also operating. These observations provide unusually
complete data sets for evaluating helio-longitude extent of the ICMEs
and for identifying the probable solar cause(s) of the events. In
this poster we present information on these ICMEs from the IMPACT and
PLASTIC and ACE in-situ investigations, together with solar images
from STEREO and SOHO that seem to capture the causative activity at
the Sun. We find that even though the Sun was very quiet in '07-'08,
with few active regions visible in GONG and SOHO magnetograms, there
were numerous CME candidates that erupted through the near-equatorial
helmet streamers. Most events could be identified with EUV disk activity
as well as a coronagraph CME, even if the associated active region
was very small or weak. Old cycle active regions, new and decayed,
continued to maintain a warp in the large-scale helmet streamer belt
that was a frequent site of the eruptions. However, the warp in the
streamer belt may simply indicate that the active region(s) present
is(are) sufficiently strong to affect the large scale quiet coronal
field structure. Overall we see no gross differences between the solar
activity and ICME causes during this and the previous solar activity
minimum, when the Streamer belt was less warped due to the existence
of stronger solar polar fields.
---------------------------------------------------------
Title: Comparison of MHD Simulations of CME Evolution and Structure
with Coronagraph Observations
Authors: Manchester, W. B.; Vourlidas, A.; Jai, Y.; Lugaz, N.; Roussev,
I.; Gombosi, T.; Opher, M.
2008AGUFMSH11A..07M Altcode:
Coronal mass ejections (CMEs) expel significant amounts of plasma into
interplanetary space producing large-scale variations in density that
are manifest in coronagraph images. A limitation of these images is
that they present two-dimensional projections of three-dimensional
structures that are challenging to interpret. The circumstances are
even more complex when CMEs are observed at large elongation and
the location of preferential scattering is significantly curved. To
address the interpretation of such coronagraph images, we examine
the Thomson-scattered white-light appearance of 3D MHD simulations
of CMEs to identify and reproduce features observed by LASCO and
SECCHI coronagraphs. We find close quantitative comparison with
LASCO observations and produce shapes at large elongations as seen
by SECCHI. We find evidence of shock propagation, magnetic clouds,
CME pancaking, and complex time evolution as CMEs propagate at large
elongation past the Thomson sphere. A key point is to determine how the
3-D structure of CMEs is affected by propagation through a structured
solar wind.
---------------------------------------------------------
Title: Interactions of Multiple CMEs with Complex Interplanetary
Medium as Revealed by STEREO
Authors: Lugaz, N.; Vourlidas, A.; Roussev, I. I.
2008AGUFMSH13B1553L Altcode:
Since the launch of STEREO in November 2006, continuous white-light
observations of solar transients on their way to the Earth have been
made possible. STEREO/SECCHI observations have also revealed the
complexity and dynamic structure of the interplanetary medium. In this
talk, we will discuss the significance of 3-D numerical simulations
in the interpretation of observations taken by SECCHI. Our focus will
be on a series of two ejections on January, 24-25, 2007, which have
been simulated with the Space Weather Modeling Framework (SWMF). We
will discuss the appearance of coronal mass ejections (CMEs) and
dense streams in the Heliospheric Imagers' field-of-view. Detailed
comparisons between the real and simulated time-elongation plots
will be presented. We will also discuss how observations of CME-CME
interaction can be distinguished from the interaction of CMEs with
dense streams in the solar wind using the simulations.
---------------------------------------------------------
Title: STEREO Observations of a post-CME Current Sheet
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2008AGUFMSH13B1552P Altcode:
Ray-like features in the wake of Coronal Mass Ejections (CMEs) are
often interpreted as current sheets produced by the eruption. The 3D
geometry of such post-CME current sheets is largely unknown and its
knowledge should place important constraints on CME physics and coronal
conditions. An example of a post-CME current sheet was observed on April
9th 2008, in the aftermath of the 'cartwheel' CME, which was observed
by Hinode, SoHO, STEREO and TRACE. The CME and the corresponding current
sheet were well-observed by both STEREO spacecraft, which were separated
by about 48 degrees the day of the event. We present here an analysis
of the 3D morphology of the current sheet using data from the COR1 and
COR2 coronagraphs from both STEREO spacecraft. We will attempt various
forward models (e.g., slabs, cylinders) of the current sheet as seen by
the COR1 and COR2 coronagraphs from both STEREO spacecraft. This will
characterize the 3D geometry of the current sheet and more precisely
its shape and its real width and length. Our forward modeling will also
supply the radial variation of the density along the current sheet. This
information will supply some estimates of the temperature and magnetic
field distributions in and out the current sheet respectively.
---------------------------------------------------------
Title: First STEREO observation of a quiet sun CME
Authors: Robbrecht, E.; Patsourakos, S.; Vourlidas, A.
2008AGUFMSH13B1560R Altcode:
Streamer-blowouts form a particular class of CMEs characterized by a
slow rise and swelling of the streamer that can last for days. While
they are more massive than the average CME, their slow development
complicates their association with features/activity in the low
corona and hampers studies on their initiation mechanism(s). This
paper reports on the first observation from 2 viewpoints of a streamer
blowout CME. The event was observed by the SECCHI/COR2 A instrument
as a typical flux-rope type CME, while a very faint partial halo was
observed in COR2-B. The CME erupted from the east limb in the COR2 A
field of view. EUVI-171 A images show a bright feature above the limb,
traveling from the southern hemisphere towards the equator after which
it slowly rises into the coronagraphic fields of view developing into
the flux-rope structure CME. At the time of eruption the separation
between the two STEREO spacecraft is sufficiently large (54 deg) to
observe the source region face-on in STEREO-B. However, inspection of
EUVI B data didn't reveal any particular source region, other than the
quiet sun. No flaring activity could be related to the eruption. This
observation shows unambiguously that a CME eruption does not necessarily
have clear on-disk signature. Also it sheds light on the long-standing
question of the necessity of having a flare for producing a CME. This
result supplies strong constraints for CME initiation models. This type
of observation could not have been achieved without the multi-viewpoint
observations by STEREO.
---------------------------------------------------------
Title: Propagation and Decoupling of ICMEs and interplanetary shocks
Authors: Gonzalez-Esparza, A.; Aguilar-Rodriguez, E.;
Ontiveros-Hernandez, V.; Corona-Romero, P.; Vourlidas, A.
2008AGUFMSH13B1558G Altcode:
The tracking of a solar storm from the Sun to 1~AU is one of the
crucial issues for space weather forecasting. We use white light, remote
radio and in-situ measurements to study the propagation of ICME/shock
events. We compare these observations with two simple 1-D HD models:
analytical and numerical, which focus on the transferring of momentum
from the CME to the shock. The aim of the study is to understand how
a fast CME/shock decelerates in the interplanetary medium.
---------------------------------------------------------
Title: Evidence for the Magnetic Trapping of Solar-Flare Ions
from 1-8-MeV Solar Neutrons Detected with the MESSENGER Neutron
Spectrometer
Authors: Feldman, W. C.; Lawrence, D. J.; Goldsten, J. O.; Gold, R. E.;
Baker, D. N.; Haggerty, D. K.; Krucker, S.; Lin, R. P.; Murphy, R. J.;
Nittler, L. R.; Slavin, J. A.; Solomon, S. C.; Starr, R. D.; Vilas,
F.; Vourlidas, A.
2008AGUFM.U12A..02F Altcode:
Neutrons produced on the Sun during the M2 flare on 31 December 2007
were observed throughout an approximately 10-hour period at 0.48 AU
by the MESSENGER Neutron Spectrometer. This flare contained multiple
acceleration episodes as seen in Type III radio bursts and fine
structure in the energetic-particle environment at MESSENGER. After
these bursts ended, both the energetic-particle and neutron fluxes
decayed smoothly to background with an e-folding decay time of 2.84
hours. The fact that this time is considerably longer than the mean
life of a neutron (886 s) indicates that neutrons at the Sun must have
been continuously produced. A likely explanation is that a considerable
fraction of the energetic ions accelerated during the flare remained
trapped on closed magnetic arcades high in the corona and were slowly
pitch-angle scattered by coronal turbulence into their chromospheric
loss cones. Subsequent interactions with chromospheric ions generated
neutrons that scatter to form a population of upward-going albedo
neutrons.
---------------------------------------------------------
Title: Observations and analysis of the April 9, 2008 CME using
STEREO, Hinode TRACE and SoHO data
Authors: Reeves, K. K.; Patsourakos, S.; Stenborg, G.; Miralles, M.;
Deluca, E.; Forbes, T.; Golub, L.; Kasper, J.; Landi, E.; McKenzie,
D.; Narukage, N.; Raymond, J.; Savage, S.; Su, Y.; van Ballegooijen,
A.; Vourlidas, A.; Webb, D.
2008AGUFMSH12A..04R Altcode:
On April 9, 2008 a CME originating from an active region behind the limb
was well-observed by STEREO, Hinode, TRACE and SoHO. Several interesting
features connected to this eruption were observed. (1) The interaction
of the CME with open field lines from a nearby coronal hole appeared
to cause an abrupt change in the direction of the CME ejecta. (2) The
prominence material was heated, as evidenced by a change from absorption
to emission in the EUV wavelengths. (3) Because the active region was
behind the limb, the X-Ray Telescope on Hinode was able to take long
enough exposure times to observe a faint current- sheet like structure,
and it was able to monitor the dynamics of the plasma surrounding this
structure. This event is also being studied in the context of activity
that occurred during the Whole Heliosphere Interval (WHI).
---------------------------------------------------------
Title: Mass Measurements of Coronal Mass Ejections Using the
SECCHI-COR2 Coronagraphs
Authors: Colaninno, R. C.; Vourlidas, A.; Thernisien, A.
2008AGUFMSH13B1549C Altcode:
The twin Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) COR2 coronagraphs of the Solar Terrestrial Relations
Observatory (STEREO) provide images of the solar corona from two view
points in the solar system. Since their launch in late 2006, the STEREO
Ahead (A) and Behind (B) spacecraft have been slowing separating from
Earth at a rate of 22.5 degrees per year. By the end of 2007, the two
spacecraft were separated by more than 40 degrees from each other. At
this time, we began to see large- scale differences in the morphology
and total intensity between coronal mass ejections (CMEs) observed
with SECCHI-COR2 on STEREO-A and B. Because the CME emission is due to
Thomson scattering, the intensity of an observed CME is dependent on the
angle it makes with the observed plane-of-the-sky. From the intensity
images, we can calculate the integrated line of sight electron density
and mass. We demonstrate that is is possible to simultaneously derive
the direction and true total mass of the CME if we make the simple
assumption that the same mass should be observed in COR2-A and B.
---------------------------------------------------------
Title: Calibration Results for the COR2 Instrument Aboard the STEREO
Satellite
Authors: Baldwin, K.; Vourlidas, A.
2008AGUFMSH13B1532B Altcode:
We report on the calibration status of the COR2 internally occulting
coronagraphs aboard the Solar Terrestrial Relations Observatory
(STEREO) satellites. The COR2 instruments are part of the Sun Earth
Connection Coronal and Heliospheric Investigation (SECCHI) instrument
package aboard STEREO. The field of view of the COR2 instruments
extends from 2.5 to 15 solar radii and its linear spectral filter
transmits from 650nm to 750nm. All pre-flight optical calibration
efforts were preformed at the Naval Research Laboratory's Solar
Coronagraph Optical Test Chamber (SCOTCH), including: a vignetting
function, calculation of stray light effects and image quality. To
verify the instrument performance in flight we have developed a star
fitting routine to extract the intensity of various stars as they
transverse the telescope's field of view. Using the pre- flight and
in-flight results in combination with star positions and star counts,
we derived calibration factors for the external/internal geometric and
photometric calibration. Specifically, calibration efforts include
pointing corrections, distortion and vignetting. Calibrations will
be implemented to improve the accuracy of scientific calculations
performed using the COR2 data set.
---------------------------------------------------------
Title: Three-dimensional MHD Simulation of the 2003 October 28
Coronal Mass Ejection: Comparison with LASCO Coronagraph Observations
Authors: Manchester, Ward B., IV; Vourlidas, Angelos; Tóth, Gábor;
Lugaz, Noé; Roussev, Ilia I.; Sokolov, Igor V.; Gombosi, Tamas I.;
De Zeeuw, Darren L.; Opher, Merav
2008ApJ...684.1448M Altcode: 2008arXiv0805.3707M
We numerically model the coronal mass ejection (CME) event of 2003
October 28 that erupted from AR 10486 and propagated to Earth in less
than 20 hr, causing severe geomagnetic storms. The magnetohydrodynamic
(MHD) model is formulated by first arriving at a steady state corona
and solar wind employing synoptic magnetograms. We initiate two
CMEs from the same active region, one approximately a day earlier
that preconditions the solar wind for the much faster CME on the
28th. This second CME travels through the corona at a rate of
over 2500 km s<SUP>-1</SUP>, driving a strong forward shock. We
clearly identify this shock in an image produced by the Large Angle
Spectrometric Coronagraph (LASCO) C3 and reproduce the shock and its
appearance in synthetic white-light images from the simulation. We
find excellent agreement with both the general morphology and the
quantitative brightness of the model CME with LASCO observations. These
results demonstrate that the CME shape is largely determined by its
interaction with the ambient solar wind and may not be sensitive to the
initiation process. We then show how the CME would appear as observed
by wide-angle coronagraphs on board the Solar Terrestrial Relations
Observatory (STEREO) spacecraft. We find complex time evolution of
the white-light images as a result of the way in which the density
structures pass through the Thomson sphere. The simulation is performed
with the Space Weather Modeling Framework (SWMF).
---------------------------------------------------------
Title: The Brightness of Density Structures at Large Solar Elongation
Angles: What Is Being Observed by STEREO SECCHI?
Authors: Lugaz, N.; Vourlidas, A.; Roussev, I. I.; Jacobs, C.;
Manchester, W. B., IV; Cohen, O.
2008ApJ...684L.111L Altcode: 2008arXiv0808.0198L
We discuss features of coronal mass ejections (CMEs) that are specific
to heliospheric observations at large elongation angles. Our analysis
is focused on a series of two eruptions that occurred on 2007 January
24-25, which were tracked by the Heliospheric Imagers (HIs) on board
STEREO. Using a three-dimensional (3D) magnetohydrodynamic simulation
of these ejections with the Space Weather Modeling Framework (SWMF),
we illustrate how the combination of the 3D nature of CMEs, solar
rotation, and geometry associated with the Thomson sphere results in
complex effects in the brightness observed by the HIs. Our results
demonstrate that these effects make any in-depth analysis of CME
observations without 3D simulations challenging. In particular,
the association of bright features seen by the HIs with fronts of
CME-driven shocks is far from trivial. In this Letter, we argue that,
on 2007 January 26, the HIs observed not only two CMEs, but also a
dense corotating stream compressed by the CME-driven shocks.
---------------------------------------------------------
Title: Dynamic Fibrils in Ly-alpha
Authors: Koza, J.; Rutten, R. J.; Vourlidas, A.; Suetterlin, P.
2008ESPM...12.2.16K Altcode:
We have detected dynamic fibrils (DFs) in Ly-alpha filtergrams taken
with the rocket-borne Very high Angular resolution ULtraviolet Telescope
(VAULT). Although the data consist of only a 1-min sequence of 4
images taken near the solar limb during the second VAULT flight, they
enable us to identify and study the time evolution of over 50 DFs. Most
show parabolic trajectories in their angular extent, with supersonic
maximum velocities. The measured decelerations vary from sub-ballistic
to super-ballistic. The similarities with DFs seen in Halpha suggest a
common cause, possibly the presence of hot transition-region interfaces
around cool oscillation-fed jets.
---------------------------------------------------------
Title: STEREO and RHESSI Observations of Electron Acceleration in
a Partially Disk-Occulted Solar Flare
Authors: Krucker, S.; Wuelser, J. -P.; Vourlidas, A.; Davila, J.;
Thompson, W. T.; White, S.; Lin, R. P.
2008ESPM...12.2.84K Altcode:
RHESSI hard X-ray observations of partially-disk occulted solar flares
provide crucial information on faint coronal hard X-ray sources in the
absence of generally much brighter emissions from footpoints of flare
loops. Coronal hard X-ray sources can differ fundamentally from the
classical footpoint sources of the flare impulsive phase and provide
unique information about the supra-thermal electrons closest to the
site in the corona where their acceleration is believed to occur. The
different view-angles provided by the STEREO spacecraft allow us to put
the partially occulted hard X-ray sources observed by RHESSI in context
with the EUV flare ribbons and the EUV emission from CME observed by
STEREO/EUVI. <P />In this presentation we report on the GOES C8 flare
observed on December 31, 2007 peaking around 01:11UT. From Earth-view
(RHESSI), the flare occurs about 12 degrees behind the eastern limb
giving an occultation height of 16 Mm. From STEREO B, the flare
ribbons are seen on the disk (about 10 degrees from the limb), while
the flare is highly occulted (130 Mm) for STEREO A observations so
that emissions related to the associated CME are seen. Despite the
occultation, RHESSI observes strong non-thermal emissions up to 100
keV that entirely originate from the corona. Initially, the coronal
hard X-ray emission is seen from above the EUV flare ribbons similar
to what is reported in the Masuda flare. Later on, emissions from a
radially extended (approximately 20 Mm) source is seen. The radial
extension is in the same direction as the current sheet of the outward
moving CME suggesting that the HXR emission might be a direct signature
of electrons accelerated in the reconnection process.
---------------------------------------------------------
Title: Solar-terrestrial Simulations in the STEREO Era
Authors: Lugaz, N.; Roussev, I.; Vourlidas, A.
2008ESPM...12..5.2L Altcode:
Due to the scarcity of heliospheric observations, over the past decade
global 3-D numerical simulations have become increasingly important in
studying the propagation of coronal mass ejections (CMEs) from the Sun
to the Earth. Since the launch of STEREO in November 2006, continuous
white-light observations of solar transients on their way to the Earth
in near-real time have become possible. <P />In this talk, we will
discuss the significance of 3-D simulations in the interpretation
of observations taken by the Heliospheric Imagers. We will focus on
a series of two ejections in January, 24-25, 2007, which have been
simulated with the Space Weather Modeling Framework (SWMF). We will
present detailed comparisons between real and simulated time-elongation
plots and discuss the appearance of CME-CME interaction in real and
synthetic observations.
---------------------------------------------------------
Title: Physical parameters along the boundaries of a mid-latitude
streamer and in its adjacent regions
Authors: Susino, R.; Ventura, R.; Spadaro, D.; Vourlidas, A.; Landi, E.
2008A&A...488..303S Altcode:
Context: Coronal streamers appear to be strictly associated with the
generation of the slow solar wind, even if a firm identification of
the sources of the particle flux within these structures is still an
unresolved issue. <BR />Aims: The purpose of this work is to contribute
to a better knowledge of the physical characteristics of streamers and
of their surroundings in a wide range of heliocentric distances and
at both high radial and latitudinal resolutions. <BR />Methods: The
analysis is based on spectral observations of a narrow, mid-latitude
streamer performed with UVCS/SOHO during one week in May 2004: H i
Lyα and O vi resonance doublet line intensities and profiles were
obtained at different heliocentric distances and latitudes. In addition,
white-light polarized brightness images were taken in the same days
of observation, through the LASCO/SOHO C2 coronagraph. <BR />Results:
The radial variations in electron density and temperature, H i and O
vi kinetic temperatures, and outflow velocities were derived from the
observed line intensities, profiles, and O vi line intensity ratios
between 1.6 and 5.0 R_⊙, in two regions, 2-3 arcmin wide, located
along the boundaries and in a narrow strip (5-10 arcmin) outside
the streamer structure. Significantly high kinetic temperatures and
outflow velocities were found in the out-of-streamer region above 3.0
R_⊙ for the O vi ions and, for the first time, H i atoms, compared
to those obtained along the streamer boundaries. Moreover, the O vi
kinetic temperatures and velocities turn out much higher than the H
i ones at any heliocentric distance in all the observed regions. A
higher anisotropy is also noticed for the O vi kinetic temperature
in the region flanking the streamer. <BR />Conclusions: The slow
coronal wind is found to flow with significantly different speeds and
kinetic temperatures along the boundaries of the streamer and in the
out-of-streamer regions at all heights, above 3.0-3.5 R_⊙. This fact,
consistent with previous studies, indicates that two components of
slow wind probably form in the observed regions: one originates just
above the streamer cusp and flows with velocities a little higher than
100 km s<SUP>-1</SUP>, while the other flows along the open magnetic
field lines flanking the streamer with velocities slightly lower than
the slow wind asymptotic heliospheric value of ~400 km s<SUP>-1</SUP>,
around 5.0 R_⊙.
---------------------------------------------------------
Title: How Efficient are Coronal Mass Ejections at Accelerating
Solar Energetic Particles?
Authors: Mewaldt, R. A.; Cohen, C. M. S.; Giacalone, J.; Mason,
G. M.; Chollet, E. E.; Desai, M. I.; Haggerty, D. K.; Looper, M. D.;
Selesnick, R. S.; Vourlidas, A.
2008AIPC.1039..111M Altcode:
The largest solar energetic particle (SEP) events are thought to
be due to particle acceleration at a shock driven by a fast coronal
mass ejection (CME). We investigate the efficiency of this process
by comparing the total energy content of energetic particles with the
kinetic energy of the associated CMEs. The energy content of 23 large
SEP events from 1998 through 2003 is estimated based on data from
ACE, GOES, and SAMPEX, and interpreted using the results of particle
transport simulations and inferred longitude distributions. CME data
for these events are obtained from SOHO. When compared to the estimated
kinetic energy of the associated coronal mass ejections (CMEs), it
is found that large SEP events can extract ~10% or more of the CME
kinetic energy. The largest SEP events appear to require massive,
very energetic CMEs.
---------------------------------------------------------
Title: The Solar Magnetic Field and Coronal Dynamics of the Eruption
on 2007 May 19
Authors: Li, Y.; Lynch, B. J.; Stenborg, G.; Luhmann, J. G.; Huttunen,
K. E. J.; Welsch, B. T.; Liewer, P. C.; Vourlidas, A.
2008ApJ...681L..37L Altcode:
The solar eruption on 2007 May 19, from AR 10956 near solar disk
center, consisted of a B9.5 flare (12:48 UT), a filament eruption,
an EUV dimming, a coronal wave, and a multifront CME. The eruption
was observed by the twin STEREO spacecraft at a separation angle of
8.5°. We report analysis of the source region photospheric magnetic
field and its preeruption evolution using MDI magnetograms, the coronal
magnetic field topology estimated via PFSS modeling, and the coronal
dynamics of the eruption through STEREO EUVI wavelet-enhanced anaglyph
movies. Despite its moderate magnitude and size, AR 10956 was a complex
and highly nonpotential active region with a multipolar configuration,
and hosted frequent flares, multiple filament eruptions, and CMEs. In
the 2 days prior to the May 19 eruption, the total unsigned magnetic
flux of the region decreased by ~17%. We interpret the photospheric
magnetic field evolution, the coronal field topology, and the observed
coronal dynamics in the context of current models of CME initiation
and discuss the prospects for future MHD modeling inspired by these
analyses.
---------------------------------------------------------
Title: STEREO SECCHI Stereoscopic Observations Constraining the
Initiation of Polar Coronal Jets
Authors: Patsourakos, S.; Pariat, E.; Vourlidas, A.; Antiochos, S. K.;
Wuelser, J. P.
2008ApJ...680L..73P Altcode: 2008arXiv0804.4862P
We report on the first stereoscopic observations of polar coronal jets
made by the EUVI/SECCHI imagers on board the twin STEREO spacecraft. The
significantly separated viewpoints (~11°) allowed us to infer the 3D
dynamics and morphology of a well-defined EUV coronal jet for the first
time. Triangulations of the jet's location in simultaneous image pairs
led to the true 3D position and thereby its kinematics. Initially the
jet ascends slowly at ≈10-20 km s<SUP>-1</SUP> and then, after an
apparent "jump" takes place, it accelerates impulsively to velocities
exceeding 300 km s<SUP>-1</SUP> with accelerations exceeding the solar
gravity. Helical structure is the most important geometrical feature
of the jet which shows evidence of untwisting. The jet structure
appears strikingly different from each of the two STEREO viewpoints:
face-on in one viewpoint and edge-on in the other. This provides
conclusive evidence that the observed helical structure is real and
does not result from possible projection effects of single-viewpoint
observations. The clear demonstration of twisted structure in polar jets
compares favorably with synthetic images from a recent MHD simulation of
jets invoking magnetic untwisting as their driving mechanism. Therefore,
the latter can be considered as a viable mechanism for the initiation
of polar jets.
---------------------------------------------------------
Title: The Encounter of Comet Encke with a Coronal Mass Ejection:
A Unique Cosmic Collision
Authors: Vourlidas, A.
2008Ippa....2d..14V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: STEREO small ICME activity and the connection to the
large-scale coronal structure during the solar activity minimum
Authors: Huttunen, K. E.; Luhmann, J. G.; Gosling, J. T.; Li, Y.;
Larson, D.; Schroeder, P.; Elliot, H.; Petrie, G.; Vourlidas, A.;
Galvin, A. B.; Russell, C. T.
2008AGUSMSH21A..06H Altcode:
We have investigated ICME activity during the solar activity minimum
from March 2007 to December 2007 using observations from the STEREO
and Wind spacecraft. During this period the angular separation of
the twin STEREO satellites increased from about 1 to 44 degrees while
Wind was located at the L1 point. At solar minimum the interplanetary
medium is dominated by recurrent high-speed streams, but slow solar
wind frequently includes ICME events. These slow ICMEs tend to have
shorter durations and weaker magnetic fields than typical ICMEs at
1 AU. We will discuss the properties of these small ICMEs and their
scale-sizes. In addition we will relate the ICMEs to the large-scale
coronal structure using the GONG magnetogram synoptic maps. We also
discuss the possible connection of these events to the transient
outflows from coronal streamers identified originally by SOHO/LASCO
and currently observed by the STEREO/SECCHI imagers.
---------------------------------------------------------
Title: Understanding the Initiation of Polar Coronal Jets with
STEREO/SECCHI Stereoscopic Observations
Authors: Vourlidas, A.; Patsourakos, S.; Pariat, E.; Antiochos, S.
2008AGUSMSH23A..02V Altcode:
Polar coronal jets are collimated transient ejections of plasma
occurring in polar coronal holes. The kinematics and mostly the 3D
morphology of jets place strong constraints on the physical mechanism(s)
responsible for their initiation, and were not accessible before
the STEREO mission. We report on the first stereoscopic observations
of polar coronal jets made by the EUVI/SECCHI imagers on-board the
twin STEREO spacecraft at spacecraft separations of ~ 11° and ~
45°. Triangulations of the jet locations in simultaneous image pairs
led to the true 3D position and thereby their kinematics. The most
important geometrical feature of the observed jets is helical structures
showing evidence of untwisting. The jet structure appear strikingly
different from each of the two STEREO viewpoints: face-on in the
one viewpoint and edge-on in the other. This provides solid evidence
that the observed helical structure is real and not resulting from
possible projection effects of single viewpoint observations. The clear
demonstration of twisted structure in polar jets compares favorably
with synthetic images from a recent MHD simulation of jets invoking
magnetic untwisting as their driving mechanism.
---------------------------------------------------------
Title: Initiation and Evolution of CMEs from Helmet Streamers
Authors: Liu, Y.; Luhmann, J.; Odstrcil, D.; Li, Y.; Vourlidas, A.;
Lin, R.; Bale, S.
2008AGUSMSH31A..04L Altcode:
A traditional picture for CME eruptions is that the closed magnetic
fields underneath a helmet streamer are destabilized to produce
a CME. At the tip of the streamer belt is the heliospheric plasma
sheet (HPS) which is characterized by slow, dense and cold solar
wind. An important point, missed by early CME observations, is that
CMEs disrupting the streamer belt and moving through the HPS would
be distorted into a concave-outward shape by the interaction with
the HPS. For the first time, the interaction between CMEs and the
preexisting HPS is clearly imaged by SECCHI and LASCO from the Sun out
to several tens of solar radii. The 31 December 2007 CME first appears
as a bulge swelling from the base of a streamer and pushing EUV plumes
aside, consistent with the traditional scenario for CME initiation;
the CME then quickly becomes concave-outward owing to the interaction
with the preexisting HPS. The streamer reforms after the CME but seems
a little displaced. A similar picture is observed for the 5 September
2005 CME. The CME source regions are underneath the streamer belt as
revealed by the PFSS modeled coronal fields; an MHD model using the
observed photospheric magnetic fields as input gives a bi-modal ambient
solar wind, consistent with the observed concave-outward shape. We also
discuss deflection flows ahead of the CMEs and how CMEs regulate the
global field configuration of the Sun based on the observations. These
results are important for understanding the complete picture of CME
initiation and propagation.
---------------------------------------------------------
Title: Stereoscopic Analysis of STEREO/EUVI Observations of May 19,
2007 Erupting Filament
Authors: Liewer, P. C.; Dejong, E. M.; Hall, J. R.; Huttunen, K. J.;
Howard, R. A.; Vourlidas, A.; Thompson, W. T.
2008AGUSMSH23A..04L Altcode:
A filament eruption, associated with a B9.5 flare, was observed
by the Solar TERrestrial Relations Observatory (STEREO) on May 19,
2007, beginning at about 13 UT in AR10956. Analysis of remote and
in situ observations indicate that this event is the most probable
source of an interplanetary magnetic cloud observed by the Wind and
STEREO B spacecraft on 2007 May 21-22. Here, we use observations from
the SECCHI/EUVI telescopes to analyze the behavior of the filament
before and during the eruption and to study its relation to other
solar signatures of the CME event. At this time, STEREO A and B were
sufficiently separated to determine the three- dimensional structure
of the filament using stereoscopy. The filament could be followed
in SECCHI/EUVI 304 Angstrom stereoscopic data from about 12 hours
before to about 2 hours after the eruption. Although the filament
has episodes of activity during this period, no dramatic pre-eruption
warning signal is seen. Other results from stereoscopic analysis of
STEREO/ EUVI data will also be presented. Copyright 2008 California
Institute of Technology. Government sponsorship acknowledged.
---------------------------------------------------------
Title: Physical Properties of a Coronal Streamer at 2.5 Solar Radii
Authors: Uzzo, M.; Strachan, L.; Kohl, J.; Vourlidas, A.
2008AGUSMSH51B..03U Altcode:
In this presentation the plasma properties of a streamer observed in
April of 2007 at 2.5 solar radii are examined. The data comes from
observations conducted by the Ultraviolet Coronagraph Spectrometer
(UVCS) and the Large Angle Spectroscopic Coronagraph (LASCO) C2
instrument aboard the Solar and Heliospheric Observatory (SOHO). From
the UV spectral profiles the proton and oxygen kinetic temperatures can
be derived as a function of latitude across the streamer. The observed
line intensities are used to calculate the photospheric normalized
absolute elemental abundances for O, S, N and Fe. The abundances
are analyzed with respect to the FIP effect and compared to in situ
measurements at SOHO. An estimate for the electron density is determined
from both the UV data and the polarized white light data from LASCO C2.
---------------------------------------------------------
Title: Imaging the Heliosphere at Solar Minimum: SECCHI Observations
During the Whole Heliosphere Interval
Authors: Plunkett, S. P.; Howard, R. A.; Vourlidas, A.; Stenborg,
G. A.; Thompson, W. T.
2008AGUSMSH51A..07P Altcode:
We present remotely sensed imaging observations of the inner heliosphere
from the SECCHI experiment on the STEREO mission during the Whole
Heliosphere Interval in March and April 2008. These observations reveal
the large-scale structure and dynamics of the heliosphere near solar
minimum, extending from the surface of the Sun to beyond 1 AU, from
two vantage points in the ecliptic plane separated by about 50 degrees.
---------------------------------------------------------
Title: On the Origins of Coronal Mass Ejections during Solar Minimum
using STEREO Observations
Authors: Li, Y.; Luhmann, J. G.; Lynch, B. J.; Huttunen, E.; Toy,
V.; Vourlidas, A.; Petrie, G.
2008AGUSMSH43A..08L Altcode:
This study addresses the question of the origins of CMEs at the current
solar minimum. It is a common consensus that it should be straight
forward to track a CME from its source to 1AU during solar quiet times
when the solar wind and IMF structure is less complex and fewer CMEs
and other coronal activity occur. In reality, total of 1249 CMEs from
January to October 2007 are reported on the LASCO CME catalog. Only ~23%
(292) CMEs are wider than 30deg and ~2% (28) CMEs wider than 90deg
from L1 view point. Most CMEs in the catalog are narrow or jet-like
and are classified as poor events. Majority of the CMEs are slow with
only one event over 1000km/s. But it has not been an easy task to
relate a CME to its source during this period. Using an appropriate
set of events and images from three viewing angles from STEREO A/B and
SOHO at L1, we determine the sources of the CMEs and their locations
on the Sun and in the large scale coronal field. Among other issues,
we discuss the implications of our results to CME generation/origin,
specifically, whether CMEs always originate from photospheric magnetic
neutral lines? Whether some CMEs originate higher in the corona with
no signature on the solar disk?
---------------------------------------------------------
Title: The Sun as the Source of Heliospheric "Space Weather": A CISM
Integrated Model Perspective and STEREO Inspiration
Authors: Luhmann, J. G.; Li, Y.; Lynch, B.; Lee, C. O.; Huttunen, E.;
Liu, Y.; Toy, V.; Odstrcil, D.; Riley, P.; Linker, J.; Mikic, Z.; Arge,
C.; Petrie, G.; Zhao, X.; Liu, Y.; Hoeksema, T.; Owens, M.; Galvin,
A.; Simunac, K.; Howard, R.; Vourlidas, A.; Jian, L. K.; Russell, C. T.
2008AGUSMSH31C..01L Altcode:
Models developed under the Center for Integrated Space weather
Modeling (CISM) represent one effort that is underway to realistically
simulate the Sun's physical controls over interplanetary conditions,
or heliospheric "space weather", in three dimensions. This capability
is critical for interpreting the latest observations from STEREO,
whose goal is to enable connections to be made between what is
observed in the heliosphere via distributed in-situ measurements
and what is observed in the corona and heliosphere via imaging from
separated 1 AU perspectives. The ways in which the CISM models are
enabling the exploitation of STEREO and other observations toward
increased understanding of the solar wind and coronal activity and
its consequences are described. In particular, the models allow the
identification of the sources of structures in the solar wind, and
analyses of how the coronal context of the observed CMEs plays a key
role in determining the ultimate terrestrial (and other planetary)
response .
---------------------------------------------------------
Title: Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI)
Authors: Howard, R. A.; Moses, J. D.; Vourlidas, A.; Newmark, J. S.;
Socker, D. G.; Plunkett, S. P.; Korendyke, C. M.; Cook, J. W.; Hurley,
A.; Davila, J. M.; Thompson, W. T.; St Cyr, O. C.; Mentzell, E.;
Mehalick, K.; Lemen, J. R.; Wuelser, J. P.; Duncan, D. W.; Tarbell,
T. D.; Wolfson, C. J.; Moore, A.; Harrison, R. A.; Waltham, N. R.;
Lang, J.; Davis, C. J.; Eyles, C. J.; Mapson-Menard, H.; Simnett,
G. M.; Halain, J. P.; Defise, J. M.; Mazy, E.; Rochus, P.; Mercier,
R.; Ravet, M. F.; Delmotte, F.; Auchere, F.; Delaboudiniere, J. P.;
Bothmer, V.; Deutsch, W.; Wang, D.; Rich, N.; Cooper, S.; Stephens,
V.; Maahs, G.; Baugh, R.; McMullin, D.; Carter, T.
2008SSRv..136...67H Altcode: 2008SSRv..tmp...64H
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) is a five telescope package, which has been developed for
the Solar Terrestrial Relation Observatory (STEREO) mission by the
Naval Research Laboratory (USA), the Lockheed Solar and Astrophysics
Laboratory (USA), the Goddard Space Flight Center (USA), the University
of Birmingham (UK), the Rutherford Appleton Laboratory (UK), the
Max Planck Institute for Solar System Research (Germany), the Centre
Spatiale de Leige (Belgium), the Institut d’Optique (France) and the
Institut d’Astrophysique Spatiale (France). SECCHI comprises five
telescopes, which together image the solar corona from the solar disk to
beyond 1 AU. These telescopes are: an extreme ultraviolet imager (EUVI:
1 1.7 R<SUB>⊙</SUB>), two traditional Lyot coronagraphs (COR1: 1.5 4
R<SUB>⊙</SUB> and COR2: 2.5 15 R<SUB>⊙</SUB>) and two new designs
of heliospheric imagers (HI-1: 15 84 R<SUB>⊙</SUB> and HI-2: 66 318
R<SUB>⊙</SUB>). All the instruments use 2048×2048 pixel CCD arrays
in a backside-in mode. The EUVI backside surface has been specially
processed for EUV sensitivity, while the others have an anti-reflection
coating applied. A multi-tasking operating system, running on a PowerPC
CPU, receives commands from the spacecraft, controls the instrument
operations, acquires the images and compresses them for downlink
through the main science channel (at compression factors typically
up to 20×) and also through a low bandwidth channel to be used for
space weather forecasting (at compression factors up to 200×). An
image compression factor of about 10× enable the collection of images
at the rate of about one every 2 3 minutes. Identical instruments,
except for different sizes of occulters, are included on the STEREO-A
and STEREO-B spacecraft.
---------------------------------------------------------
Title: Heliospheric Images of the Solar Wind at Earth
Authors: Sheeley, N. R., Jr.; Herbst, A. D.; Palatchi, C. A.; Wang,
Y. -M.; Howard, R. A.; Moses, J. D.; Vourlidas, A.; Newmark, J. S.;
Socker, D. G.; Plunkett, S. P.; Korendyke, C. M.; Burlaga, L. F.;
Davila, J. M.; Thompson, W. T.; St. Cyr, O. C.; Harrison, R. A.;
Davis, C. J.; Eyles, C. J.; Halain, J. P.; Wang, D.; Rich, N. B.;
Battams, K.; Esfandiari, E.; Stenborg, G.
2008ApJ...675..853S Altcode:
During relatively quiet solar conditions throughout the spring and
summer of 2007, the SECCHI HI2 white-light telescope on the STEREO
B solar-orbiting spacecraft observed a succession of wave fronts
sweeping past Earth. We have compared these heliospheric images with
in situ plasma and magnetic field measurements obtained by near-Earth
spacecraft, and we have found a near perfect association between the
occurrence of these waves and the arrival of density enhancements
at the leading edges of high-speed solar wind streams. Virtually
all of the strong corotating interaction regions are accompanied by
large-scale waves, and the low-density regions between them lack such
waves. Because the Sun was dominated by long-lived coronal holes and
recurrent solar wind streams during this interval, there is little
doubt that we have been observing the compression regions that are
formed at low latitude as solar rotation causes the high-speed wind
from coronal holes to run into lower speed wind ahead of it.
---------------------------------------------------------
Title: SECCHI Observations of the Sun's Garden-Hose Density Spiral
Authors: Sheeley, N. R., Jr.; Herbst, A. D.; Palatchi, C. A.; Wang,
Y. -M.; Howard, R. A.; Moses, J. D.; Vourlidas, A.; Newmark, J. S.;
Socker, D. G.; Plunkett, S. P.; Korendyke, C. M.; Burlaga, L. F.;
Davila, J. M.; Thompson, W. T.; St. Cyr, O. C.; Harrison, R. A.;
Davis, C. J.; Eyles, C. J.; Halain, J. P.; Wang, D.; Rich, N. B.;
Battams, K.; Esfandiari, E.; Stenborg, G.
2008ApJ...674L.109S Altcode:
The SECCHI HI2 white-light imagers on the STEREO A and B spacecraft
show systematically different proper motions of material moving outward
from the Sun in front of high-speed solar wind streams from coronal
holes. As a group of ejections enters the eastern (A) field of view,
the elements at the rear of the group appear to overrun the elements
at the front. (This is a projection effect and does not mean that the
different elements actually merge.) The opposite is true in the western
(B) field; the elements at the front of the group appear to run away
from the elements at the rear. Elongation/time maps show this effect
as a characteristic grouping of the tracks of motion into convergent
patterns in the east and divergent patterns in the west, consistent
with ejections from a single longitude on the rotating Sun. Evidently,
we are observing segments of the "garden-hose" spiral made visible
when fast wind from a low-latitude coronal hole compresses blobs of
streamer material being shed at the leading edge of the hole.
---------------------------------------------------------
Title: A Fresh View of the Extreme-Ultraviolet Corona from the
Application of a New Image-Processing Technique
Authors: Stenborg, Guillermo; Vourlidas, Angelos; Howard, Russell A.
2008ApJ...674.1201S Altcode:
The Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar
and Heliospheric Observatory (SOHO) has provided (and continues
to provide) the solar physics community with an unprecedented view
of the extreme-ultraviolet (EUV) transition region and corona. In
particular, it has observed EUV bright points, coronal holes, loops,
and arcades, as well as dynamical events such as flares, EIT waves,
and mass ejections. However, the multiscale nature of the observed
solar features has not been fully exploited so far. In this paper,
we introduce a technique to enhance the EUV features based on their
multiscale nature, show a few examples of features not revealed with
standard image-processing techniques (and therefore not previously
noticed in the EIT data set), and make the solar physics community
aware of the availability of the full EIT data set as processed with
this novel technique.
---------------------------------------------------------
Title: Simulating the interaction of the 2007 April 19 CME with
Comet Encke
Authors: Manchester, Ward, IV; Gombosi, Tamas; Frazin, Richard;
Vourlidas, Angelos; Toth, Gabor; Cohen, Ofer; Hansen, Kenneth; Sokolov,
Igor; van der Holst, Bart
2008cosp...37.1896M Altcode: 2008cosp.meet.1896M
We model the propagation of a coronal mass ejection (CME) that was
observed with LASCO on April 19, 2007. The resulting ICME was observed
with SECCHI (STEREO A) to impact comet Encke on April 20. We compare the
results of our three-dimensional global MHD simulation of this event
with both sets of coronagraph observations. In particular, we make
synthetic Thomson-scattered white light images from the simulation to
quantitatively compare to the coronagraph images made with LASCO and
SECCHI. We then propagate the CME into interplanetary space where it
interacts with comet Encke. We simulate the complex response of the
cometary plasma to the CME impact.
---------------------------------------------------------
Title: Large solar energetic particle events of solar cycle 23
Authors: Mewaldt, R. A.; Chollet, Eileen; Cohen, Christina; Looper,
Mark; Mason, Glenn; Vourlidas, Angelos; Giacalone, Joe; Haggerty,
Dennis; Desai, Mihir; Selesnick, Richard
2008cosp...37.2020M Altcode: 2008cosp.meet.2020M
We present the results of a survey of the largest solar energetic
particle (SEP) events of Solar Cycle 23, based on data from ACE, GOES,
SAMPEX, SOHO, and STEREO. The fluence spectra of the 25 largest proton
events (as measured by >30 MeV protons) have been fit with common
spectral shapes, and their spectral slopes and breaks determined. The
spectral characteristics are compared with other signatures including
Fe/O, He/H and total energy content, as well as selected solar and
interplanetary parameters. Estimates of the total energy content
of accelerated particles are made using the results of new particle
transport simulations. When compared to the estimated kinetic energy
of the associated CMEs it is found that SEPs frequently extract ∼10
per cent of the CME kinetic energy. Finally, we compare SEP fluences
from solar cycle 23 to those measured during the past 50 years.
---------------------------------------------------------
Title: Stereoscopic Analysis of STEREO/EUVI Observations of May 19,
2007 Erupting Filament
Authors: Liewer, Paulett; Luhmann, Janet G.; Huttunen, Emilia; Li,
Yan; Howard, R. A.; Thompson, W. T.; Dejong, E. M.; Hall, J. R.;
Falconer, D. A.; Vourlidas, Angelos
2008cosp...37.1778L Altcode: 2008cosp.meet.1778L
A filament eruption, associated with a double coronal mass ejection
(CME), was observed by the Solar TERrestrial Relations Observatory
(STEREO) on May 19, 2007, beginning at about 13 UT in AR10956. Analysis
of remote and in situ observations indicate that this event is the
most probable source of an interplanetary magnetic cloud observed
by the Wind and STEREO B spacecraft on 2007 May 21-22. Here, we use
observations from the SECCHI/EUVI telescopes to analyze the behavior of
the filament before and during the eruption and to study its relation
to other solar signatures of the CME event. At this time, STEREO A
and B were sufficiently separated to determine the three-dimensional
structure of the filament using stereoscopy. The filament could be
followed in SECCHI/EUVI 304 Angstrom stereoscopic data from about
12 hours before to about 2 hours after the eruption. Although the
filament has episodes of activity during this period, no dramatic
pre-eruption warning signal is seen. We also present an evaluation of
a magnetogram-based CME-prediction measure for AR 10956 for the May
17-20, 2007 period and compare it with observed CME activity.
---------------------------------------------------------
Title: Solar Polar Imager: Observing Solar Activity from a New
Perspective
Authors: Liewer, P. C.; Ayon, J.; Alexander, D.; Kosovichev, A.;
Mewaldt, R. A.; Socker, D. G.; Vourlidas, A.
2008nssv.book....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Forward modeling reconstruction techniques applied to
STEREO-SECCHI data
Authors: Thernisien, A. F.; Howard, R. A.; Vourlidas, A.
2007AGUFMSH32A0778T Altcode:
In past works, forward modeling techniques have been successfully used
to study the morphology and the electron density of streamers and flux
rope coronal mass ejections. Nevertheless, these studies have been done
using SOHO-LASCO data. The STEREO mission, launched in October 2007,
provide now 2 new points of view in addition to the one provided by
SOHO. Besides the Lyot coronagraphs aboard the STEREO-SECCHI instrument
package, the Heliospheric Imagers, also part of the SECCHI package,
provide now a new and extended view of the corona, from 7 degrees
elongation to almost 90 degrees. In this study, we will make use of
the 3 points of view provided by these two missions to constrain better
the three-dimensional reconstruction of CMEs, from few solar radii, up
to Earth orbit. We will present the results concerning the morphology,
dynamics and electron density obtained for different recent CME events.
---------------------------------------------------------
Title: How do CME-Shocks Look Like?: Study of Shock Geometry.
Authors: Ontiveros, V.; Vourlidas, A.
2007AGUFMSH31A0223O Altcode:
We use raytracing software to simulate white light coronagraph images of
common 3D shock-like geometries, i.e. spherical and bow-shock type. We
obtain the density profiles for different projections, shock thickness,
and background and upstream densities. The results are compared to
density profiles obtained from analyzing LASCO coronagraph images
of CMEs that are good candidates to drive a shock due to their high
velocities (V>1500 km/s). This work is funded by the LWS TR&T
program.
---------------------------------------------------------
Title: Multipoint Analysis by STEREO and WIND of the Magnetic Cloud
on May 21-23, 2007
Authors: Huttunen, K. E.; Luhmann, J. G.; Li, Y.; Lynch, B.; Liu,
Y.; Schroeder, P.; Bale, S. D.; Lee, C. O.; Lin, R. P.; Vourlidas,
A.; Farrugia, C.; Galvin, A. B.; Acuna, M. H.; Howard, R. A.; Kaiser,
M.; Mewaldt, R. A.; Sauvaud, J.; Wiedenbeck, M.
2007AGUFMSH42A..03H Altcode:
We will present multi-spacecraft observations by STEREO A and B and WIND
of a magnetic cloud in the interplanetary space on May 21-23, 2007. At
that time the angular separation between STEREO A and B was nearly 10
degrees. The differences in the observed magnetic field signatures
at the locations of the spacecrafts suggest that they crossed the
different parts of the magnetic cloud. STEREO B observed a very clear
rotation of the magnetic field direction and presumably crossed the
cloud close to the center whereas STEREO A likely traversed the leg of
the magnetic cloud. Although the magnetic field maximum within this
cloud was ~17 nT it did not produce significant geomagnetic response
since the Z-component of the magnetic field was orientated northward. We
will analyze the structure of the magnetic cloud at each spacecraft in
order to deduce its larger-scale structure and orientation. In addition,
we will study the solar source region of the magnetic cloud as well
as the coronagraph and radio wave observations.
---------------------------------------------------------
Title: The source region magnetic conditions of solar eruption events
observed by multi spacecraft
Authors: Li, Y.; Lynch, B. J.; Welsch, B. T.; Stenborg, G. A.;
Vourlidas, A.; Luhmann, J. G.; Fisher, G. H.
2007AGUFMSH32A0773L Altcode:
The magnetic connectivity, topology and properties including magnetic
flux changes, magnetic gradient and flow field from LCT of three
active regions will be derived from photospheric magnetograms and
synoptic maps to understand the initiation condition of eruptions/flares
originated from the regions and the potential impact on the heliosphere
and magnetosphere. The three active regions are AR10930 in December
2006 and AR10953 and AR10956 in May 2007. AR10930 and AR10956 are
responsible for the two Magnetic Clouds observed by IMPACT on STEREO
A/B during the first half year of the mission. The associated coronal
CME/flare/filament activities will be studied using solar imaging
data from SOHO, STEREO, BBSO and HINODE. We will analyze photospheric
magnetograms and synoptic maps from MDI and GONG. Vector magnetic
field observations from HINODE and SOLIS are currently being sought
and if available will be value added information for initiation of the
eruptions. PFSS model field line tracing based on the synoptic maps
gives the magnetic topology and connectivity in the active region and
the global large scale field. The large scale field results including
regions with closed arcades and fields open to the interplanetary
space give the context and relative location of the source region of
the eruptions.
---------------------------------------------------------
Title: Modeling STEREO White-Light Observations of CMEs with 3D
MHD Simulations
Authors: Manchester, M. B.; Vourlidas, A.; Toth, G.; Lugaz, N.;
Sokolov, I.; Gombosi, T.; de Zeeuw, D.; Opher, M.
2007AGUFMSH32A0785M Altcode:
We model the Thomson-scattered white-light appearance of a variety of
3D MHD models of CMEs during solar minimum to reproduce large-scale
features of SECCHI observations. We create a gallery of expected CME
shapes at large elongations as seen by SECCHI. We examine evidence of
shock propagation, magnetic clouds, CME pancaking, and complex time
evolution as CMEs propagate at large elongation past the Thomson
sphere. A key point is to determine how the structure of CMEs and
CME-driven shocks are affected by interaction with the ambient solar
wind. MHD models are performed with BATSRUS and SWMF, and formulated
by first arriving at a steady state corona and solar wind employing
synoptic magnetograms. We initiate CMEs from active regions low in
the corona with magnetic flux ropes.
---------------------------------------------------------
Title: Using Global MHD Models to Interpret STEREO Observations
Authors: Riley, P.; Mikic, Z.; Linker, J. A.; Odstrcil, D.; Luhmann,
J. G.; Vourlidas, A.
2007AGUFMSH32A0788R Altcode:
The STEREO mission presents a unique opportunity to combine both
remote and in situ observations from multiple vantage points,
and, in particular, to provide simultaneous limb and disk-centered
observations. In spite of this wealth of data, the system remains
remarkably under-sampled, and reconstructing 3-D structure from
the observations remains a formidable task. In this presentation we
use global MHD models, which reproduce the eruption and evolution of
specific CME events through the corona and past the orbit of Earth, to
explore the relationship between the various remote sensing and in situ
observations that would be seen at the two STEREO spacecraft. These
simulations were developed as part of our contribution to NASA's
Living With a Star TR&T focused science topic on the relationship
between ICMEs and their solar sources. Our model, which incorporates
coronal heating, thermal conduction, and radiation, is capable of
reproducing a wide variety of measurements, ranging from (polarized)
brightness and emission images to in situ time series of magnetic
and plasma parameters. Moreover, we can construct quantities that
are either not directly observable, or can only be inferred locally,
such as the Alfven speed, the location of the heliospheric current
sheet, and the three-dimensional topology of the magnetic field. We
believe that the combination of sophisticated modeling results and
the exciting new measurements from the STEREO mission will allow us
to address fundamental questions concerning the origin and evolution
of CMEs, ultimately allowing us to develop predictive capabilities
related to their potential to generate space weather effects.
---------------------------------------------------------
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: Towards a Better Understanding of CME Onsets with SECCHI
on STEREO
Authors: Patsourakos, S.; Vourlidas, A.
2007AGUFMSH32A0779P Altcode:
Observations of the first minutes in the life of Coronal Mass Ejections
(CMEs) represent the main key into identifying the physical mechanism(s)
behind them. Previous observations of CME onsets were limited by factors
such as low cadence, small field of view, single-temperature coverage,
and lack of 3D information. These limitations are significantly
mitigated by the availability of SECCHI observations onboard the
STEREO mission. We analyze a series of high-cadence, multi-temperature
observations of CME onsets taken with the EUVI/SECCHI imagers tied with
high-cadence coronagraphic COR1/SECCHI observations. We discuss how
our perception of well-known features pertinent to CME onsets such as
dimmings, EIT waves and cavities is shaped by the unique characteristics
of SECCHI observations, and of the 3D information available in STEREO
obervations in particular. We finally discuss how the generic elements
of our observations compare with the expectations of CME models in an
attempt to place some constraints on them.
---------------------------------------------------------
Title: The Physical Properties of Coronal Streamers. II.
Authors: Uzzo, M.; Strachan, L.; Vourlidas, A.
2007ApJ...671..912U Altcode:
In this paper the plasma properties of three streamers observed in
2003 by the Ultraviolet Coronagraph Spectrometer (UVCS) are presented
for five heights from 1.75 to 5.0 R<SUB>solar</SUB>. The kinetic
temperatures for protons (T<SUB>k,p</SUB>) and the O<SUP>5+</SUP> ions
(T<SUB>k,O</SUB>) are derived as a function of height with preferential
heating of O<SUP>5+</SUP> over protons recorded. By examining how
T<SUB>k,p</SUB> varies with latitude at each height, an idea of
the magnetic field morphology is found. At 1.75 R<SUB>solar</SUB>
the elemental abundances (O, S, Ar, and Fe), electron temperature,
and electron density are derived from the UV spectral data. All three
streamers were quiescent with typical abundance values; however,
no depleted cores were found. The first ionization potential (FIP)
effect was detected for all three streamers with a bias of ~4. This is
consistent with slow solar wind in situ measurements, thereby supporting
the hypothetical connection between the two. All three streamers had a
higher than expected electron temperature. The electron densities above
1.75 R<SUB>solar</SUB> are derived from the Large Angle Spectroscopic
Coronagraph (LASCO) C2 polarized brightness data. Estimates for the
O<SUP>5+</SUP> outflow velocities are obtained using the O VI λ1032
over λ1037 intensity ratios and the estimated electron densities. All
three streamers showed evidence of significant outflows at 4.0 and
5.0 R<SUB>solar</SUB>.
---------------------------------------------------------
Title: Heliospheric Streamers: Comparison Between Model Calculations
and SECCHI Observations
Authors: Howard, R. A.; Thernisien, A.; Vourlidas, A.; Morrill, J. S.;
MacNiece, P.
2007AGUFMSH42A..04H Altcode:
We have generated a time dependent 3-dimensional description of the
electron density distribution out to 1 AU using the ENLIL model at
the Community Coordinated Modeling Center (CCMC). Using this electron
density description we have computed the brightness measurements that
would be observed by coronagraphic instruments such as SECCHI using
the Raytrace package. We compare the computed images with the actual
SECCHI observations of streamers/heliospheric current sheet.
---------------------------------------------------------
Title: A New View of the Extreme Ultraviolet Corona from
Wavelet-Processed EUV Images
Authors: Stenborg, G. A.; Vourlidas, A.; Howard, R. A.
2007AGUFMSH14B..04S Altcode:
Our knowledge of the structure and dynamics of the extreme ultraviolet
solar corona has greatly increased over the last 11 years thanks to
the observations from the Extreme-ultraviolet Imaging Telescope (EIT)
aboard the SOHO spacecraft. The EIT images have revealed the early
phases of coronal mass ejections (CMEs), discovered coronal waves
associated with CMEs, recorded impressive post-CME loop systems and
eruptive prominences, and detected reconnection at the base of coronal
hole plumes, among other things. It would be natural to think that,
by now, the EIT instrument has exhausted its discovery potential. We
will demonstrate in this presentation that this is not the case. We
have developed a wavelet-based image enhancement technique that exploits
the multi-scale nature of the observed solar features, and treated the
entire EIT database accordingly. The technique allowed us to remove
the instrumental stray light background and enhance the fine coronal
structures at the same time. The final images reveal such a wealth of
structures and dynamics that they seem to have been obtained by a new
instrument. The clarity of the enhanced images allows us to identify
numerous and potentially interesting phenomena that were previously
obscured by a background level that includes stray light and image
noise. A few examples will be presented here, including application to
the STEREO EUVI images. This presentation aims to bring the availability
of this resource and its potential for significant discoveries to the
attention of the solar physics community.
---------------------------------------------------------
Title: Direct Imaging of the Heliospheric Plasma Sheet from the
SECCHI telescopes on the STEREO Mission
Authors: Vourlidas, A.; Riley, P.
2007AGUFMSH21A0283V Altcode:
We report the first ever direct imaging observations of the fine scale
structure of the solar wind in the inner heliosphere. The observations
were obtained by the Sun-Earth Connection Coronal and Heliospheric
Investigation (SECCHI) instrument suite on the Solar Terrestrial
Relations Observatory (STEREO) mission. The SECCHI telescopes can
trace the coronal plasma from its origins at the solar corona to the
Earth's neighborhood. Besides coronal mass ejections, the images also
reveal the fine scale structure of the heliospheric plasma sheet during
quiet periods. Here, we will show the evolution of these structures
from the inner corona to the inner heliosphere. We will also include
comparisons with large-scale MHD models of the heliosphere and discuss
the importance of such observations for understanding the physics of
the solar wind.
---------------------------------------------------------
Title: Physical parameters of a mid-latitude streamer during the
declining phase of the solar cycle
Authors: Spadaro, D.; Susino, R.; Ventura, R.; Vourlidas, A.; Landi, E.
2007A&A...475..707S Altcode:
Context: Investigating the physical properties of solar coronal
streamers is important for understanding their role in the global
magnetic structure of the extended solar atmosphere, as well as in the
generation of the slow solar wind. <BR />Aims: We hope to contribute as
completely as possible to the ongoing SOHO instruments campaign devoted
to the study of the physical characteristics of coronal streamers at
various heliocentric distances. <BR />Methods: We analyzed ultraviolet
H I Lyα and O VI resonance doublet lines observed by UVCS/SOHO in
a narrow, mid-latitude streamer structure along different lines
of sight during a week in May 2004 and made nearly simultaneous
white-light polarized brightness measurements from the LASCO/SOHO C2
coronagraph. <BR />Results: Electron densities and temperatures, H
I and O VI kinetic temperatures, and outflow velocities were derived
from the line intensities and widths, as well as from the O VI line
intensity ratio in the 1.6-5 R<SUB>⊙</SUB> range of heights, limited
to the central region of the streamer. To our knowledge, the H I outflow
velocities obtained in this work are the first ones determined inside a
streamer structure. They are significantly lower than those of the O VI
ions. This, together with the O VI kinetic temperatures that are much
higher than the H I ones, suggest that the absorption of Alfvén waves
at the ion cyclotron frequency might also occur inside streamers. <BR
/>Conclusions: In comparison with other streamers described in the
literature, the structure examined in this work generally exhibits lower
electron density and neutral hydrogen kinetic temperature. Conversely,
the O VI kinetic temperature and outflow velocity radial profiles are
consistent with the results for the other examined streamers.
---------------------------------------------------------
Title: First Direct Observation of the Interaction between a Comet
and a Coronal Mass Ejection Leading to a Complete Plasma Tail
Disconnection
Authors: Vourlidas, Angelos; Davis, Chris J.; Eyles, Chris J.;
Crothers, Steve R.; Harrison, Richard A.; Howard, Russell A.; Moses,
J. Daniel; Socker, Dennis G.
2007ApJ...668L..79V Altcode:
This a discovery report of the first direct imaging of the interaction a
comet with a coronal mass ejection (CME) in the inner heliosphere with
high temporal and spatial resolution. The observations were obtained
by the Sun-Earth Connection Coronal and Heliospheric Investigation
(SECCHI) Heliospheric Imager-1 (HI-1) aboard the STEREO mission. They
reveal the extent of the plasma tail of comet 2P/Encke to unprecedented
lengths and allow us to examine the mechanism behind a spectacular
tail disconnection event. Our preliminary analysis suggests that the
disconnection is driven by magnetic reconnection between the magnetic
field entrained in the CME and the interplanetary field draped around
the comet and not by pressure effects. Further analysis is required
before we can conclude whether the reconnection occurs on the day side
or on the tail side of the comet. However, the observations offer
strong support to the idea that large-scale tail disconnections are
magnetic in origin. The online movie reveals a wealth of interactions
between solar wind structures and the plasma tail beyond the collision
with the CME. Future analyses of this data set should provide critical
insights on the structure of the inner heliosphere.
---------------------------------------------------------
Title: Erratum: “Identification of a Peculiar Radio Source
in the Aftermath of Large Coronal Mass Ejection Events” (<A
href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>)
Authors: Vourlidas, Angelos; Pick, Monique; Hoang, Sang; Démoulin,
Pascal
2007ApJ...665L.179V Altcode:
In our recent Letter (A. Vourlidas et al. [<A
href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>], hereafter
Paper I), we determined the azimuth and elevation of our radio source
with a direction-finding algorithm (Paper I, Fig. 4) assuming that
the source emission dominates over the galactic background. This is
generally true for type III emissions that are mainly used for these
analyses. However, this condition does not necessarily hold for weaker
emissions such as the broadband continuum source in our Letter. As the
source intensity decreases to near the Galactic background level, the
source direction shifts toward the direction of the Galactic center. It
is therefore important to subtract the background before deriving
source directions, which we did not do in Paper I. This correction
has now been applied to the WIND WAVES data reported in Figure 4
of Paper I. As a result, there is no more significant drift in the
source elevation or azimuth. The radio continuum source remains along
the ecliptic plane as do other radio bursts observed in association
with this coronal mass ejection (CME) event. <P />This correction
does not significantly alter our proposed scenarios for the origin of
the broadband source. The emission could still arise from electrons
injected in nearby structures originating from interactions between
the expanding CME and closed coronal loops or from the closing down of
previously opened loops. Our velocity estimations are also unaffected
by the corrections on the source location. They still suggest that
the continuum propagates too slowly to be the CME shock. However, we
must point out that M. J. Reiner, M. L. Kaiser, & J.-L. Bougeret
(<A href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>) modeled
this event as a type II source deriving an initial speed of 3000 km
s<SUP>-1</SUP>, a strong deceleration of 41 ms<SUP>-2</SUP> lasting
for about 15 hr, followed by an almost constant propagation to the
Earth. As the authors acknowledge in their paper, these parameters
were obtained using a simple generic speed profile. Currently, there
are no independent observations or theoretical predictions that
show such a velocity profile for interplanetary CMEs. On the other
hand, patchy, drifting structures that are typical signatures of
interplanetary type II bursts are clearly seen in the radio spectrum
after 14:30 UT but at a higher frequency than that of our continuum
source. Similar patchy emissions are seen until a shock signature at
Earth on September 24 at 21:00 UT. So a type II source is present in
the spectrum. <P />Our initial intention with this work was to bring
attention to the possibility that the conventional interpretation,
as type II emission from a CME-driven shock, for low-frequency
drifting continua might not hold true for all cases. We suggested
in Paper I that the emission mechanism of this continuum could be
gyrosynchrotron from nonthermal electrons. Recently, T. S. Bastian
(ApJ, 665, 805 [2007]) proposed incoherent synchrotron emission from
electrons entrained in the CME as an alternative explanation for such
smooth type II-like sources. Therefore, we may be confronted with
a new phenomenon, and we clearly need more studies to pin down the
physical mechanism. <P />We are grateful to M. Reiner for pointing
out the need for correction of our direction-finding results and for
providing a preprint of M. J. Reiner, M. L. Kaiser, & J.-L. Bougeret
(<A href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>).
---------------------------------------------------------
Title: The Quiet Sun Network at Subarcsecond Resolution: VAULT
Observations and Radiative Transfer Modeling of Cool Loops
Authors: Patsourakos, S.; Gouttebroze, P.; Vourlidas, A.
2007ApJ...664.1214P Altcode:
One of the most enigmatic regions of the solar atmosphere is the
transition region (TR), corresponding to plasmas with temperatures
intermediate of the cool, few thousand K, chromosphere and the hot,
few million K, corona. The traditional view is that the TR emission
originates from a thin thermal interface in hot coronal structures,
connecting their chromosphere with their corona. This paradigm fails
badly for cool plasmas (~T<10<SUP>5</SUP> K), since it predicts
emission orders of magnitude less than what it is observed. It was
therefore proposed that the “missing” TR emission could originate from
tiny, isolated from the hot corona, cool loops at TR temperatures. A
major problem in investigating this proposal is the very small sizes
of the hypothesized cool loops. Here, we report the first spatially
resolved observations of subarcsecond-scale looplike structures seen
in the Lyα line made by the Very High Angular Resolution Ultraviolet
Telescope (VAULT). The subarcsecond (~0.3") resolution of VAULT allows
us to directly view and resolve looplike structures in the quiet Sun
network. We compare the observed intensities of these structures with
simplified radiative transfer models of cool loops. The reasonable
agreement between the models and the observations indicates that an
explanation of the observed fine structure in terms of cool loops
is plausible.
---------------------------------------------------------
Title: Progress Toward A Very High Angular Resolution Imaging
Spectrometer (VERIS)
Authors: Korendyke, Clarence M.; Vourlidas, A.; Landi, E.; Seely,
J.; Klimchuck, J.
2007AAS...210.2604K Altcode: 2007BAAS...39Q.324K
Recent imaging at arcsecond (TRACE) and sub-arcsecond (VAULT) spatial
resolution clearly show that structures with fine spatial scales
play a key role in the physics of the upper solar atmosphere. Both
theoretical and observational considerations point to the importance
of small spatial scales, impulsive energy release, strong dynamics,
and extreme plasma nonuniformity. Fundamental questions regarding the
nature, structure, properties and dynamics of loops and filamentary
structures in the upper atmosphere have been raised. <P />To address
these questions, we are developing a next generation, VEry high
angular Resolution Imaging Spectrometer (VERIS) as a sounding rocket
instrument. VERIS will obtain the necessary high spatial resolution,
high fidelity measurements of plasma temperatures, densities and
velocities. With broad simultaneous temperature coverage, the VERIS
observations will directly address unresolved issues relating to
interconnections of various temperature solar plasmas. VERIS will
provide the first ever subarcsecond spectra of transition region and
coronal structures. It will do so with a sufficient spectral resolution
of to allow centroided Doppler velocity determinations to better than 3
km/s. VERIS uses a novel two element, normal incidence optical design
with highly reflective EUV coatings to access a spectral range with
broad temperature coverage (0.03-15 MK) and density-sensitive line
ratios. Finally, in addition to the spectra, VERIS will simultaneously
obtain spectrally pure slot images (10x150 arcsec) in the +/-1 grating
orders, which can be combined to make instantaneous line-of-sight
velocity maps with 8km/s accuracy over an unprecedented field of
view. <P />The VERIS program is beginning the second year of its
three year development cycle. All design activities and reviews are
complete. Fabrication of all major components has begun. Brassboard
electronics cards have been fabricated, assembled and tested. The paper
presents the essential scientific characteristics of the instrument.
---------------------------------------------------------
Title: The Impact of Geometry on CME Observations Made by SEECHI
Authors: Morrill, J.; Kunkel, V.; Halain, J. P.; Harrison, R. A.;
Howard, R. A.; Moses, J. D.; Newmark, J.; Plunkett, S.; Socker, D.;
Wang, D.; Vourlidas, A.
2007AGUSMSH41A..11M Altcode:
Optical observations of Coronal Mass Ejections (CME's) during the past
several decades have generally been confined to events observed near
the sun. Although events originating from most regions of the sun can
be observed, the assumption has often made that the CME is propagating
in the plane-of-the-sky. This assumption is generally adequate to give
lower limits of CME mass and speed. However, continuous observations
of CME's are now being made from very near the solar surface to
large distances from the sun by the SECCHI instrument on STEREO. When
CME's are observed at great distances from the sun, plane-of-the-sky
assumptions are not adequate for analysis of these events. In this
presentation we will discuss some recent observations made by the
SEECHI instruments and the impact of geometry on our interpretation
of these events.
---------------------------------------------------------
Title: Energetics of solar coronal mass ejections
Authors: Subramanian, P.; Vourlidas, A.
2007A&A...467..685S Altcode: 2007astro.ph..1160S
Aims:We investigate whether solar coronal mass ejections are driven
mainly by coupling to the ambient solar wind or through the release
of internal magnetic energy. <BR />Methods: We examine the energetics
of 39 flux-rope like coronal mass ejections (CMEs) from the Sun using
data in the distance range ~2-20 R<SUB>⊙</SUB> from the Large Angle
Spectroscopic Coronograph (LASCO) aboard the Solar and Heliospheric
Observatory (SOHO). This comprises a complete sample of the best
examples of flux-rope CMEs observed by LASCO in 1996-2001. <BR
/>Results: We find that 69% of the CMEs in our sample experience a
clearly identifiable driving power in the LASCO field of view. For
those CMEs that are driven, we examine if they might be deriving most
of their driving power by coupling to the solar wind. We do not find
conclusive evidence in favor of this hypothesis. On the other hand,
we find that their internal magnetic energy is a viable source of the
required driving power. We have estimated upper and lower limits on
the power that can possibly be provided by the internal magnetic field
of a CME. We find that, on average, the lower limit to the available
magnetic power is around 74% of what is required to drive the CMEs,
while the upper limit can be as much as an order of magnitude larger.
---------------------------------------------------------
Title: The Sun To The Earth, A Panoramic View From SECCHI: Overview
Authors: Moses, John Daniel; Newmark, J.; Howard, R. A.; Plunkett,
S.; Socker, D.; Wang, D.; Vourlidas, A.; Halain, J.; Harrison, R. A.;
Eyles, C. J.; Davila, J.; Lemen, J.; Wuelser, J.
2007AAS...21011904M Altcode: 2007BAAS...39..244M
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) is the remote sensing component of the STEREO mission
to explore the source, initiation, and propagation through the
heliosphere of Coronal Mass Ejections (CMEs). To achieve this goal,
SECCHI must continuously observe CMEs from two different perspectives
beginning with the pre-event coronal configuration and ending with the
propagation of the event out of the inner heliosphere. Thus, each of
the two STEREO observatories carries a suite of SECCHI telescopes with
5 different fields of view providing an uninterrupted view of coronal
and Heliospheric phenomena from the solar chromosphere to 1 AU. This
is the first panoramic view of the inner heliosphere dedicated to
observing the spatial and temporal scales characteristic of CMEs at
elongation angles from 0 to almost 90 degrees. <P />We present first
results from the SECCHI imaging suite with emphasis on the unprecedented
panoramic views of the heliosphere. We show direct observations of
CMEs and the solar wind from initiation on the Sun throughout the inner
heliosphere to 1 AU. The SECCHI suite performance exceeds that necessary
to achieve the Level 1 STEREO science objectives. Thus, as the STEREO
spacecraft separate to provide views from different directions we can
anticipate breakthrough observations for issues currently unresolved
by plane-of-sky projections through optically thin structures. <P
/>The most current information on SECCHI can be obtained from the
STEREO mission website at http://stereo.gsfc.nasa.gov and the SECCHI
website at http://secchi.nrl.navy.mil. The NRL participation in the
STEREO mission is supported by NASA under S-13631-Y, and by the Office
of Naval Research.
---------------------------------------------------------
Title: Chromospheric Science with the STEREO Mission
Authors: Vourlidas, A.
2007ASPC..368..633V Altcode:
The STEREO mission, launched in October 2006 comprises two spacecraft
drifting at opposite directions from Earth. STEREO carries a suite of
solar telescopes to provide, for the first time, stereoscopic views
CMEs and of the corona including the cool, upper chromospheric line
of He II at 304 Å. In my talk, I give an overview of the mission and
its science objectives and discuss the areas where STEREO can provide
important contributions to chromospheric science questions.
---------------------------------------------------------
Title: The SECCHI Experiment on the STEREO Mission
Authors: Howard, R. A.; Moses, J. D.; Vourlidas, A.; Newmark, J. S.;
Socker, D. G.; Wang, D.; Plunkett, S. P.; Baugh, R.; McMullin, D. R.;
Davila, J. M.; Thompson, W. T.; Lemen, J. R.; Wuelser, J.; Harrison,
R. A.; Waltham, N. R.; Davis, C. J.; Eyles, C. J.; Defise, J.; Halain,
J.; Bothmer, V.; Delaboudiniere, J.; Auchere, F.; Mercier, R.; Ravet,
M. F.
2007AGUSMSH33A..01H Altcode:
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of an
extreme ultraviolet (EUV) imager, two white light coronagraphs, and
two telescopes that comprise the heliospheric imager. SECCHI will
observe coronal mass ejections (CMEs) from their birth at the sun,
through the corona and into the heliosphere. A complete instrument
suite is being carried on each of the two STEREO spacecraft, which
will provide the first sampling of a CME from two vantage points. The
spacecraft, launched 25 October 2006, are orbiting the Sun, one Ahead
of the Earth and the other Behind, each separating from Earth at about
22 degrees per year. The varying separation means that we will have
different observational capabilities as the spacecraft separate and
therefore differing science goals. The primary science objectives
all are focused on understanding the physics of the CME process
their initiation, 3D morphology, propagation, interaction with the
interplanetary medium and space weather effects. By observing the CME
from multiple viewpoints with UV and coronagraphic telescopes and by
combining these observations with radio and in-situ observations from
the other instruments on STEREO as well as from other satellites and
ground based observatories operating at the same time, answers to some
of the outstanding questions will be obtained. We will show some of
the initial results.
---------------------------------------------------------
Title: Seeing the Heliosphere with New Eyes: First Results from the
SECCHI Experiment on STEREO
Authors: Vourlidas, A.
2007AGUSMSH33A..02V Altcode:
The STEREO mission was launched on October, 2006 with the main objective
to study Coronal Mass Ejections (CMEs) from their initiation in the
solar corona to their arrival at Earth using a suite of remote sensing
and in-situ instruments on two, almost identical, spacecraft. The
mission objectives are mainly addressed by the imaging experiment,
named Sun-Earth Connection Coronal & Heliospheric Investigation
(SECCHI), which comprises a suite of five telescopes; an EUVI full disk
imager, two coronagraphs covering the range from 1.5 to 15 solar radii,
and two heliospheric imagers observing along the Sun-Earth LINE from
15 solar radii to the Earth's orbit and beyond. It is the first time
that such imaging capabilities are available and they will certainly
lead to important advances in our understanding of the CME initiation,
propagation, and its three-dimensional configuration. In this talk,
we will showcase the observations and initial results from the first
months of operations of the SECCHI telescopes. We will also discuss
the instrument performance and synergies with existing observatories
(e.g., SOHO). SECCHI was built by a consortium of US and European
institutions under the direction of the Solar Physics Branch at the
U.S. Naval Research Laboratory.
---------------------------------------------------------
Title: Forward Modeling Of Cme Events Applied To STEREO-SECCHI Data.
Authors: Thernisien, Arnaud; Howard, R. A.; Vourlidas, A.
2007AAS...210.2807T Altcode: 2007BAAS...39R.136T
We have implemented a simple flux rope CME model. With this purely
geometric model, we were able to reproduce 30 different CME events
observed with SOHO-LASCO. We were also able to determine locally the
electron density profile in the CME leading edge. The STEREO mission,
launched in October 2006, is made of two twin spacecrafts that observe
the Sun from two points of view. In this presentation, I will describe
how we applied our forward modeling technique to the simulation of
CME events observed from 2 or 3 different points of view, by using
STEREO-SECCHI data and also SOHO-LASCO.
---------------------------------------------------------
Title: Signatures of CMEs Shocks on LASCO Observations
Authors: Ontiveros, V. Z.; Vourlidas, A.
2007AGUSMSH23A..03O Altcode:
We report on our efforts to establish reliable markers of CME-driven
shocks in white light coronograph images. For this study, we looked
at events during the ascending phase of solar cycle 23 when the
overall morphology of the white light corona is simple. We isolated
events that will be good candidates to drive a shock due to their high
velocities (V>1500 km/s). The list includes 15 CMEs. For each event
we calibrated the LASCO images and searched for indications of faint
sharp fronts ahead of the bright CME front. We report our findings of
the analysis of the front morphology, the distant streamer deflections,
and the mass and energetics of these events. This work is funded by
the LWS TR&T program
---------------------------------------------------------
Title: The Physical Properties of Three Coronal Streamers from 2003
Authors: Uzzo, Michael; Strachan, L.; Vourlidas, A.
2007AAS...210.3002U Altcode: 2007BAAS...39..142U
In this presentation we examine the plasma properties of three streamers
observed in April, May and September of 2003 by two instruments,
UVCS and LASCO, onboard the SOHO spacecraft. The properties are the
electron density, electron temperature, elemental abundances, oxygen
outflow velocity, proton kinetic temperature and oxygen kinetic
temperature. These properties are then mapped onto the respective
streamer with regards to height above the solar disk (1.75, 2.5, 3.0,
4.0 and 5.0 Ro) and latitude. The photospheric normalized absolute
elemental abundances of O, Fe, Ar and S are derived at 1.75 Ro. The
first ionization potential (FIP) bias measured within these streamers
are compared to the results measured in situ within the slow solar wind.
---------------------------------------------------------
Title: Stereo Observations Of The Solar Corona Using The Secchi
Experiment
Authors: Plunkett, Simon P.; Howard, R. A.; Moses, J. D.; Vourlidas,
A.; Socker, D.; Newmark, J.; Wang, D.; Baugh, R.; Davila, J.;
Thompson, W.; St. Cyr, O. C.; Lemen, J.; Wuelser, J. P.; Harrison,
R. A.; Waltham, N.; Davis, C. J.; Eyles, C. J.; Defise, J. M.; Halain,
J. P.; Bothmer, V.; Delaboudiniere, J. P.; Auchere, F.; Mercier, R.;
Ravet, M. F.
2007AAS...21011901P Altcode: 2007BAAS...39..243P
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of an
extreme ultraviolet (EUV) imager, two white light coronagraphs,
and two telescopes that comprise the heliospheric imager. The main
objective of SECCHI is to observe coronal mass ejections (CMEs) from
their birth at the sun, through the corona and into the heliosphere. A
complete instrument suite is being carried on each of the two STEREO
spacecraft, which will provide the first sampling of a CME from two
vantage points as the spacecraft separate from each other at the rate
of about 45 degrees per year. We will show examples of some of the
data and some of the initial stereo results.
---------------------------------------------------------
Title: The Sun To The Earth, A Panoramic View From SECCHI: CME
Observations Through The Inner Heliosphere
Authors: Newmark, Jeffrey; Moses, J. D.; Howard, R. A.; Plunkett, S.;
Socker, D.; Wang, D.; Vourlidas, A.; Halain, J. P.; Harrison, R. A.;
Eyles, C. J.; Davila, J.; Lemen, J.; Wuelser, J. P.
2007AAS...21011905N Altcode: 2007BAAS...39..244N
The STEREO SECCHI telescope suite is returning unprecedented viewsvof
the Sun and inner heliosphere. The SECCHI instruments on each of the two
STEREO spacecraft are observing Coronal Mass Ejections (CMEs) from their
initiation, through the corona, and into interplanetary space beyond the
Earth's orbit. We present a first analysis of a CME throughout the inner
heliosphere. We focus on the propagation characteristics of the CME
and the morphological properties of the CME as viewed from STEREO. <P
/>This first glimpse of a CME in the heliosphere clearly demonstrates
the anticipated scientific returns that future STEREO observations
(at larger angular separations) of CMEs in interplanetary space will
provide. <P />The most current information can be obtained on the STEREO
mission website at http://stereo.gsfc.nasa.gov and the SECCHI website
at http://secchi.nrl.navy.mil. The NRL participation on SECCHI is
supported by NASA under S-13631-Y, and by the Office of Naval Research.
---------------------------------------------------------
Title: Simulated CMEs and Predictions for STEREO
Authors: Manchester, M. B.; Vourlidas, A.; Gombosi, T.; Sokolov,
I. V.; Cohen, O.; Toth, G.
2007AGUSMSH41A..06M Altcode:
We compare results of our global MHD simulations of CMEs propagating
from Sun-to-Earth to observations made with STEREO. We model a number
of events of varying degree of complexity, and model the observations
that are made by the SECCHI coronagraph suite and in situ observations
by IMPACT and PLASTIC. We make synthetic Thomson-scattered white light
images from the simulations as they would appear to the COR1, COR2,
and wide-angle coronagraphs HI1 and HI2. We identify shock structures
in the coronagraph images and follow their evolution to Earth orbit. At
large elongation, we find complex time evolution of the white- light
images as a result of three-dimensional structures encountering large
variations in scattering efficiency as they pass through the Thomson
sphere. We then compare the modeled ICME plasma structures with
observations from PLASTIC. We also model solar energetic particles
and compare them with IMPACT observations.
---------------------------------------------------------
Title: Features and Properties of Coronal Mass Ejection/Flare
Current Sheets
Authors: Lin, J.; Li, J.; Forbes, T. G.; Ko, Y. -K.; Raymond, J. C.;
Vourlidas, A.
2007ApJ...658L.123L Altcode:
Solar eruptions occur when magnetic energy is suddenly converted into
heat and kinetic energy by magnetic reconnection in a current sheet
(CS). It is often assumed that CSs are too thin to be observable
because the electric resistivity η<SUB>e</SUB> in CSs is taken
to be very small. In this work, we show the implications for the
CS thickness d estimated from observations of three eruptions by
the UVCS and the LASCO experiments on SOHO. We infer the effective
η<SUB>e</SUB> causing the rapid reconnection, which predicts much
faster reconnection in a thick CS than that caused by the classical
and anomalous resistivities. We find that in these events CSs are
observable and have extremely large values of d and η<SUB>e</SUB>,
implying that large-scale turbulence is operating within CSs. We also
discuss the properties of the so-called hyperresistivity caused by
the tearing mode and the relation to our results.
---------------------------------------------------------
Title: Identification of a Peculiar Radio Source in the Aftermath
of Large Coronal Mass Ejection Events
Authors: Vourlidas, Angelos; Pick, Monique; Hoang, Sang; Démoulin,
Pascal
2007ApJ...656L.105V Altcode:
We report the discovery of a new radio feature associated with coronal
mass ejection (CME) events. The feature is a low-frequency (<1 MHz),
relatively wide (~300 kHz) continuum that appears just after the main
phase of the eruptive event, lasts for several hours, and exhibits a
slow negative frequency drift. So far, we have identified this radio
signature in a handful of CME events and suspect it might be a common
occurrence. The radio continuum starts almost simultaneously with the
commonly observed decimetric type IV stationary continuum (also called
flare continuum), but the two seem unrelated. The emission mechanism,
whether plasma emission or gyroresonance, is unclear at the moment. On
the basis of our preliminary analysis, we interpret this radio continuum
as the lateral interaction of the CME with magnetic structures. Another
possibility is that this continuum traces the reconfiguration of
large-scale loop systems, such as streamers. In other words, it could
be the large-scale counterpart of the post-CME arcades seen over active
region neutral lines after big CME events. This Letter aims to bring
attention to this feature and attract more research into its nature.
---------------------------------------------------------
Title: S ynergies With The Solar Orbiter Mission: Remote Sensing
Studies Of The Corona And Coronal Transients
Authors: Vourlidas, A.
2007ESASP.641E..14V Altcode:
Currently, the Solar Orbiter (SolO) mission is planned to start its
science observations around the next solar minimum (2018-2020) and
extend to the maximum of cycle 25. Given the demanding deep space
orbit and the restrictions on spacecraft resources, the mission will
likely include a modest instrument payload designed to fully address
a focused set of solar physics problems. Hopefully, SolO will not be
the only solar mission op- erating at the time. The scientific return
of the SolO mission will be greatly enhanced by joint observational
programs with other instruments, both space-borne and gound- based
ones. In this paper, I concentrate on obser- vations of the outer
corona and of coronal mass ejections and discuss a few examples of
synergistic science at the time of the SolO mission with an emphasis
on the unique characteristics of the SolO orbit.
---------------------------------------------------------
Title: A Radio Burst and Its Associated CME on March 17, 2002
Authors: Yan, Y.; Pick, M.; Wang, M.; Krucker, S.; Vourlidas, A.
2006SoPh..239..277Y Altcode: 2006SoPh..tmp...78Y
In this study, we present a detailed analysis, based on multiwavelength
observations and magnetic field extrapolation, of a radio and X-ray
event observed on March 17, 2002. This event was accompanied by a
Coronal Mass Ejection (CME) observed by the Large-Angle Spectrometric
Coronagraph (LASCO) aboard SOHO. During the main event, the Reuven
Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) mission observed
a hard X-ray emission correlated in time with the development of a type
III burst group. The CME development, the hard X-ray emission, and the
type III burst group appear to be closely associated. The multifrequency
Nançay Radioheliograph (NRH) shows that the type III bursts are
produced at a distance from the active region that progressively
increases with time. Their emitting sources are distributed along
the western edge of the CME. We conclude the type III electron beams
propagate in the interface region between the ascending CME and the
neighboring open field lines. Due to the development of the CME,
this region becomes progressively highly compressed. By measuring,
at each frequency, the shift versus time of the type III positions, we
estimate that the electron density in this compression region increased
roughly by a factor of 10 over a few minutes. Another signature of
this compression region is a narrow white light feature interpreted
as a coronal shock driven by the CME lateral expansion.
---------------------------------------------------------
Title: Analysis of the Velocity Field of CMEs Using Optical Flow
Methods
Authors: Colaninno, Robin C.; Vourlidas, Angelos
2006ApJ...652.1747C Altcode:
Optical flow is a powerful image processing tool for measuring motion in
digital images. The optical flow algorithm provides an estimate of the
velocity vector at every pixel from a pair of successive images. Here
we present an application of this method to images of coronal mass
ejections (CMEs). The technique is first tested and validated on a
simulated CME. It is then applied to several CMEs observed with the
LASCO C2 coronagraph to derive their velocity fields. The resulting
velocity measurements allow us to visualize the evolution of the
CME plasma and to separate the “bulk” velocity from the expansion
velocity of a given CME. To our knowledge, this is the first time that
such information has been extracted from CME observations. We discuss
the limitations and accuracy of our optical flow method and propose
further improvements.
---------------------------------------------------------
Title: Which CMEs are associated with Proton Events?
Authors: Vourlidas, A.; Cane, H. V.; Richardson, I.
2006AGUFMSH41B..05V Altcode:
We investigate the properties of CMEs associated with medium-sized
proton events. We calibrated the LASCO C2 and C3 images for 69 events
and looked for patterns in the CME morphology (e.g, CME shape, extent,
speed) and the existence or not of a white light shock. The preliminary
analysis seems to suggest that proton events are associated with a
particular subset of CMEs. We report our results and our preliminary
interpretations.
---------------------------------------------------------
Title: CME Brightness at Large Elongations: Application to LASCO
and SMEI Observations
Authors: Vourlidas, A.; Webb, D. F.; Morrill, J. S.; Jackson, B. V.
2006AGUFMSH32A..03V Altcode:
The traditional analysis of the CME brightness relied on the assumption
that all lines of sight through the CME were parallel due to the large
distance between the observer and the event. However, this assumption
is not correct when CME observations at large distances from the
Sun are concerned. In a recent paper (Vourlidas & Howard 2006)
we have outlined the proper geometry and presented a few theoretical
predictions about the brightness evolution of CME launched at various
angles relative to the Sun-observer line. In this talk, we use LASCO
and SMEI observations of the same events to test our predictions and
see how we can use our theoretical framework to interpret the observed
CME structures.
---------------------------------------------------------
Title: The SECCHI Experiment on the STEREO Mission
Authors: Howard, R. A.; Moses, D.; Vourlidas, A.; Newmark, J.; Socker,
D. G.; Plunkett, S.; Wang, D.; Baugh, R.; McMullin, D.; Davila, J.;
St. Cyr, C.; Thompson, W. T.; Lemen, J.; Wuelser, J.; Harrison, R. A.;
Waltham, N. R.; Davis, C.; Eyles, C. J.; Defise, J.; Halain, J.;
Bothmer, V.; Delaboudiniere, J.; Auchere, F.; Mercier, R.; Ravet, M.
2006AGUFMSM12A..02H Altcode:
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of an
extreme ultraviolet (EUV) imager, two white light coronagraphs, and
two telescopes that comprise the heliospheric imager. SECCHI will
observe coronal mass ejections (CMEs) from their birth at the sun,
through the corona and into the heliosphere. A complete instrument
suite is being carried on each of the two STEREO spacecraft, which
will provide the first sampling of a CME from two vantage points. The
spacecraft will orbit the Sun, one Ahead of the Earth and the other
Behind, each separating from Earth at about 22 degrees per year. The
varying separation means that we will have different observational
capabilities as the spacecraft separate and therefore differing science
goals. The primary science objectives all are focused on understanding
the physics of the CME process their initiation, 3D morphology,
propagation, interaction with the interplanetary medium and space
weather effects. By observing the CME from multiple viewpoints with UV
and coronagraphic telescopes and by combining these observations with
radio and in-situ observations from the other instruments on STEREO as
well as from other satellites and ground based observatories operating
at the same time, answers to some of the outstanding questions will
be obtained. STEREO follows the very successful SOHO mission. SOHO's
success was primarily due to the highly complementary nature of the
instruments, but it was partly due to the very stable platform. The
L1 orbit enables an extremely stable thermal environment and thus
very stable pointing, as well as uninterrupted solar viewing. The
STEREO will have both of these characteristics, but in addition will
have multi-viewpoint viewing of CMEs, which will greatly enhance the
many discoveries that SOHO data have produced. We have been developing
techniques to interpret the observations from multiple viewpoints and
to perform 3-dimensional deconvolution of the CME observations using
forward modeling and inversion techniques. A continuous downlink of
STEREO data will provide a low-resolution, real- time view from all
of the instruments. The full data are downlinked once a day and will
be available about 24 hours later. We will present some preliminary
results from the instrument, which is expected to be launched in
October/November, 2006
---------------------------------------------------------
Title: Modeling of Flux Rope Coronal Mass Ejections
Authors: Thernisien, A. F. R.; Howard, R. A.; Vourlidas, A.
2006ApJ...652..763T Altcode:
We present a forward-modeling technique for flux rope-like CMEs using
an empirically defined model of a flux rope, the graduated cylindrical
shell (GCS). To compare it with white-light coronagraph observations,
we assume an electron distribution through the GCS and derive synthetic
images in total and polarized brightness for various projections
of the model using a Thomson scattering ray-tracing program. We
test our forward modeling technique on 34 LASCO CMEs analyzed by
Cremades & Bothmer. We are able to reproduce the CME morphology
and derive the electron density (at the CME front) of these events
using multi-instrument observations (MDI, Hα, EIT, LASCO) under the
assumption of self-similar expansion. This study suggests that a flux
rope-like structure is a good description for these events. We also find
that we need to invoke a deflection and/or rotation of the structure
relative to the position and orientation of the source region in most
cases. Finally, we demonstrate an original technique to fit the electron
density of the CME leading edge. We find that, on average, the peak
of the density at the CME front is 7.5 times that in the equatorial
model of Saito et al., and can reach ~22 times the model in some cases.
---------------------------------------------------------
Title: Theoretical Investigation of the Onsets of Type II Radio
Bursts during Solar Eruptions
Authors: Lin, Jun; Mancuso, Salvatore; Vourlidas, Angelos
2006ApJ...649.1110L Altcode:
On the basis of previous works, we investigated coronal mass ejection
(CME) propagations and the consequent type II radio bursts invoked
by the CME-driven shocks. The results indicate that the onset of type
II bursts depends on the local Alfvén speed (or the magnetoacoustic
wave speed in the non-force-free environment), which is governed
by both the magnetic field and the plasma density. This determines
that the type II burst cannot appear at any altitude. Instead,
its onset positions can never be lower than a critical height for
the given coronal environment, which consequently determines the
start frequencies of the emission: for an eruption taking place in
the magnetic configuration with a background field of 100 G, the
onset of type II bursts should occur at around 0.5 R<SUB>solar</SUB>
from the solar surface, and the corresponding start frequency of the
fundamental component is about 150 MHz. This result is consistent with
similar estimates based on observations that bring the corresponding
frequency to a few hundred MHz. Our results further indicate that the
onset of type II bursts depends on the rate of magnetic reconnection
as well. When magnetic reconnection during the eruption is not fast
enough, a type II burst may not occur at all even if the associated CME
is fast (say, faster than 800 km s<SUP>-1</SUP>). This may account for
the fast and radio-quiet CMEs. Related to these results, properties of
the associated solar flares and type III radio bursts, especially those
used as the precursors of the type II radio bursts, are also discussed.
---------------------------------------------------------
Title: The Flux-Rope Scaling of the Acceleration of Coronal Mass
Ejections and Eruptive Prominences
Authors: Chen, J.; Marqué, C.; Vourlidas, A.; Krall, J.; Schuck, P. W.
2006ApJ...649..452C Altcode:
The new flux-rope scaling law of the acceleration of coronal mass
ejections (CMEs) derived by Chen & Krall is quantitatively
tested by comparing the theoretical prediction with the near-Sun
acceleration profiles of 13 eruptive prominences (EPs) and four CMEs. A
CME and associated EP are assumed to be organized by an underlying
magnetic flux rope (MFR) with specific structural and geometrical
relationships. The scaling law states that if the initial structure
is a flux rope with a footpoint separation distance of S<SUB>f</SUB>,
then the height Z<SUB>max</SUB> at which the acceleration measured at
the centroid of the apex reaches maximum scales with S<SUB>f</SUB>. The
primary source of prominence data is the radio data from the archive
of the Nobeyama Radio Observatory. A number of Hα events are also
included. For CMEs, previously published events with good coverage of
the initial acceleration are used. For each event, observed quantities
are used to determine S<SUB>f</SUB> and Z<SUB>max</SUB>. It is shown
that for the events included in the present study, Z<SUB>max</SUB>
scales with S<SUB>f</SUB> in accordance with the scaling law. The
result is consistent with the hypothesis that the preeruption magnetic
structure underlying a CME and the associated EP is a flux rope driven
by the toroidal Lorentz hoop force. The scaling law may constitute
a quantitative observable discriminator of the preeruption magnetic
geometry underlying CMEs/EPs and the driving force.
---------------------------------------------------------
Title: Detections of CME-Driven Shocks with LASCO
Authors: Vourlidas, A.
2006ESASP.617E..23V Altcode: 2006soho...17E..23V
No abstract at ADS
---------------------------------------------------------
Title: Physical Properties of a 2003 April Quiescent Streamer
Authors: Uzzo, M.; Strachan, L.; Vourlidas, A.; Ko, Y. -K.; Raymond,
J. C.
2006ApJ...645..720U Altcode:
In 2003 April, the Ultraviolet Coronagraph Spectrometer (UVCS)
on board the Solar and Heliospheric Observatory (SOHO) observed
a quiescent streamer in an effort to derive the physical plasma
parameters across the streamer and as a function of height (from
1.75 to 5.0 R<SUB>solar</SUB>). Values for the electron temperature,
proton and O<SUP>5+</SUP> kinetic temperatures, elemental abundances,
and O<SUP>5+</SUP> outflow velocity were derived. The presence of
the first ionization potential (FIP) effect was also explored. These
plasma parameters were compared to those derived for other previously
reported active region and quiescent streamers. The photospheric
normalized absolute elemental abundances for O, Si, S, Ar, and Fe
were derived at 1.75 R<SUB>solar</SUB>. The remaining parameters were
derived at five heights up to 5.0 R<SUB>solar</SUB>. To calculate the
electron density above 2.2 R<SUB>solar</SUB> the polarized brightness
data from another SOHO instrument, the Large Angle Spectroscopic
Coronagraph (LASCO) C2 detector, was employed. The streamer was
located above a complex filament structure and had a slightly higher
electron temperature compared to what is typically found for quiescent
streamers. This streamer did exhibit the customary FIP effect, but
no abundance-depleted core typically found for such stable quiescent
streamers was detected. The perpendicular kinetic temperature for
the protons and the O<SUP>5+</SUP> ions did not vary across the
streamer. This differs from two other quiescent streamer comparison
cases, in which the O<SUP>5+</SUP> kinetic temperature did decrease at
the core structure. The O<SUP>5+</SUP> outflow velocities were similar
to those observed in an equatorial streamer from solar minimum.
---------------------------------------------------------
Title: Forward Modeling Technique for the Reconstruction of the
Solar Corona
Authors: Thernisien, Arnaud; Howard, R. A.; Vourlidas, A.
2006SPD....37.0818T Altcode: 2006BAAS...38..233T
We present a forward modeling technique for the reconstruction of
structures such as streamers and CMEs observed with SOHO-LASCO. This
technique relies on the computation of a synthetic image of brightness
from an assumed electron density model. By iteratively comparing
the reconstructed model and the data image, we are able to fit the
parameters of the model, such as the position, the shape aspect
parameters and the electron density.Streamers are observed as bright
and quasi radial shapes. We show how it is possible to determine the
electron density in these regions by modeling the streamer as a simple
slab. We also show that we can reconstruct its three dimensional
morphology using data 7 days apart.We present a model of flux rope
CME that we were able to fit to 34 structured CME events observed on
SOHO-LASCO. LASCO only provides the projection of the 3D CME structure,
so many parameters of our model cannot be determined directly. We
made use of information provided by multiple instrument (MDI, Halpha,
EIT) in order to constrain our reconstruction, and also assumed self
similar expansion (Cremades and Bothmer, A&A 2004).Finally, by
combining the two models, streamer and CME, we present a case study
of a streamer deflected by a CME during the eruption. We show how,
by using our simulation software, we can change the observer point
of view and look at the modeled event as if it was seen from Earth,
and compare to a halo CME.
---------------------------------------------------------
Title: Analysis of the Velocity Field of CMEs Using Optical Flow
Methods
Authors: Colaninno, Robin C.; Vourlidas, A.
2006SPD....37.2404C Altcode: 2006BAAS...38..251C
Optical flow is a powerful image processing tool for measuring motion
in digital images. The optical flow algorithm estimates a velocity
vector at every image pixel from a pair of successive images. Here
we present the application of this method on images of coronal mass
ejections (CMEs). The technique is first tested and validated on a
simulated CME. Then it is applied to several CMEs observed with the
LASCO-C2 coronagraph to derive their velocity fields. The resulting
velocity measurements allow us to separate the 'bulk' velocity from the
expansion velocity of a given CME. To our knowledge, this is the first
time that such information has been extracted from CME observations. We
discuss the limitations and accuracy of our optical flow method and
propose further improvements.
---------------------------------------------------------
Title: Investigations of the Reconnecting Current Sheets in Solar
Eruptions
Authors: Lin, Jun; Li, J.; Forbes, T. G.; Ko, Y.; Raymond, J. C.;
van Ballegooijen, A. A.; Vourlidas, A.
2006SPD....37.0826L Altcode: 2006BAAS...38..235L
Observations and theories continuously provide evidence of formation
and development of the reconnecting current sheets during major
eruptions. Because the high electric conductivity and the force-free
environment of the solar corona, the current sheet is usually
confined in a small volume compared to the other structures involved
in the eruption in order to allow the energy conversion or magnetic
reconnection to take place at a plausible rate. The work investigating
the sizes, especially thickness, of the current sheet developed by the
eruption in reality was never conducted before since it is believed
that the current sheet is too thin to be observable. It has often been
stated that the thickness is limited either by the Lamor radius of
particles, which is about tens of meters in the coronal environment, or
by the mean-free-path of particles in the region where the interaction
between particles and ion-acoustic waves occurs. In the latter case,
the particle mean-free-path is a few kilometers. Here we use a set
of unique observations provided by the UVCS and LASCO experiments
on SOHO to determine the thickness, d, and furthermore the electric
resistivity, eta<SUB>e</SUB>, of the current sheets for three eruptive
events. We find that d ranges from 1.0 x 10<SUP>4</SUP> km to 6.0
x 10<SUP>5</SUP> km, and eta<SUB>e</SUB> from 1.0 x 10<SUP>5</SUP>
ohm m to 4.0 x 10<SUP>6</SUP> ohm m. These values of eta<SUB>e</SUB>
are 12-14 orders of magnitude greater than the classical collisional
resistivity, 4-6 orders of magnitude greater than estimates of anomalous
resistivity, and even 1-3 orders greater than those often used for solar
flares. The existence of such large values for d and eta<SUB>e</SUB>
suggests that large scale turbulent processes are operating within
the current sheet. Understanding how a high level of turbulence can
develop so rapidly is a challenging goal for future research.
---------------------------------------------------------
Title: On The CME Brightness At Large Elongations: Implications For
Secchi Observations
Authors: Vourlidas, Angelos; Howard, R. A.
2006SPD....37.2503V Altcode: 2006BAAS...38..252V
The SECCHI instrument suite aboard the STEREO mission will allow us
to follow a coronal mass ejection (CME) continuously from the Sun to
Earth for the first time. The comparison of the CME emission among the
various instruments is not as easy as one might think. This is because
the telescopes record the Thomson scattered emission from the CME
plasma which has a rather sensitive dependence on the geometry between
the observer and the scattering material. Here, we will describe the
proper treatment of the Thomson scattered emission, compare the CME
brightness over a large range of elongation angles and discuss the
implications for observations.
---------------------------------------------------------
Title: The Proper Treatment of Coronal Mass Ejection Brightness:
A New Methodology and Implications for Observations
Authors: Vourlidas, Angelos; Howard, Russell A.
2006ApJ...642.1216V Altcode:
With the complement of coronagraphs and imagers in the SECCHI suite,
we will follow a coronal mass ejection (CME) continuously from the
Sun to Earth for the first time. The comparison, however, of the CME
emission among the various instruments is not as easy as one might
think. This is because the telescopes record the Thomson-scattered
emission from the CME plasma, which has a rather sensitive dependence
on the geometry between the observer and the scattering material. Here
we describe the proper treatment of the Thomson-scattered emission,
compare the CME brightness over a large range of elongation angles,
and discuss the implications for existing and future white-light
coronagraph observations.
---------------------------------------------------------
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: Multi-Wavelength Observations of CMEs and Associated Phenomena.
Report of Working Group F
Authors: Pick, M.; Forbes, T. G.; Mann, G.; Cane, H. V.; Chen, J.;
Ciaravella, A.; Cremades, H.; Howard, R. A.; Hudson, H. S.; Klassen,
A.; Klein, K. L.; Lee, M. A.; Linker, J. A.; Maia, D.; Mikic,
Z.; Raymond, J. C.; Reiner, M. J.; Simnett, G. M.; Srivastava, N.;
Tripathi, D.; Vainio, R.; Vourlidas, A.; Zhang, J.; Zurbuchen, T. H.;
Sheeley, N. R.; Marqué, C.
2006SSRv..123..341P Altcode: 2006SSRv..tmp...60P
This chapter reviews how our knowledge of CMEs and CME-associated
phenomena has been improved, since the launch of the SOHO mission,
thanks to multi-wavelength analysis. The combination of data obtained
from space-based experiments and ground based instruments allows us
to follow the space-time development of an event from the bottom of
the corona to large distances in the interplanetary medium. Since CMEs
originate in the low solar corona, understanding the physical processes
that generate them is strongly dependant on coordinated multi-wavelength
observations. CMEs display a large diversity in morphology and kinematic
properties, but there is presently no statistical evidence that those
properties may serve to group them into different classes. When a CME
takes place, the coronal magnetic field undergoes restructuring. Much
of the current research is focused on understanding how the corona
sustains the stresses that allow the magnetic energy to build up and
how, later on, this magnetic energy is released during eruptive flares
and CMEs. Multi-wavelength observations have confirmed that reconnection
plays a key role during the development of CMEs. Frequently, CMEs
display a rather simple shape, exhibiting a well known three-part
structure (bright leading edge, dark cavity and bright knot). These
types of events have led to the proposal of the ‘`standard model’'
of the development of a CME, a model which predicts the formation
of current sheets. A few recent coronal observations provide some
evidence for such sheets. Other more complex events correspond to
multiple eruptions taking place on a time scale much shorter than the
cadence of coronagraph instruments. They are often associated with
large-scale dimming and coronal waves. The exact nature of these waves
and the physical link between these different manifestations are not
yet elucidated. We also discuss what kind of shocks are produced during
a flare or a CME. Several questions remain unanswered. What is the
nature of the shocks in the corona (blast-wave or piston-driven?) How
they are related to Moreton waves seen in Hα? How they are related
to interplanetary shocks? The last section discusses the origin of
energetic electrons detected in the corona and in the interplanetary
medium. “Complex type III-like events,”which are detected at
hectometric wavelengths, high in the corona, and are associated with
CMEs, appear to originate from electrons that have been accelerated
lower in the corona and not at the bow shock of CMEs. Similarly,
impulsive energetic electrons observed in the interplanetary medium
are not the exclusive result of electron acceleration at the bow shocks
of CMEs; rather they have a coronal origin.
---------------------------------------------------------
Title: Calibration of the Soho/Lasco C3 White Light Coronagraph
Authors: Morrill, J. S.; Korendyke, C. M.; Brueckner, G. E.; Giovane,
F.; Howard, R. A.; Koomen, M.; Moses, D.; Plunkett, S. P.; Vourlidas,
A.; Esfandiari, E.; Rich, N.; Wang, D.; Thernisien, A. F.; Lamy, P.;
Llebaria, A.; Biesecker, D.; Michels, D.; Gong, Q.; Andrews, M.
2006SoPh..233..331M Altcode:
We present a detailed review of the calibration of the LASCO C3
coronagraph on the SOHO satellite. Most of the calibration has been
in place since early in the mission and has been utilized to varying
degrees as required by specific analysis efforts. However, using
observational data from the nearly decade-long database of LASCO images,
we have re-evaluated and improved many aspects of the calibration. This
includes the photometric calibration, vignetting function, geometric
distortion, stray light, and exposure and observation times. Using this
comprehensive set of corrections we have generated and made available a
set of calibrated coronal images along with a set of periodic background
images to ease the accessibility and use of the LASCO database.
---------------------------------------------------------
Title: Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study
Authors: Vourlidas, Angelos; Gary, Dale E.; Shibasaki, Kiyoto
2006PASJ...58...11V Altcode:
We investigate the sunspot gyroresonance emission at 17 GHz using the
synoptic database of the Nobeyama Radioheliograph. Our statistical
study is based on full disk observations obtained during the maximum
of Cycle 22 (1992-94). We study the center-to-limb variation of the
brightness and polarization of the sunspot radio emission and present
some cases of polarization reversal. We find that the radio emission
is most likely 3rd-harmonic gyroresonance emission arising from 2000
G fields in transition region, or low corona temperatures.
---------------------------------------------------------
Title: Properties of the Post-CME Current Sheets in Solar Eruptions
Authors: Lin, J.; Li, J.; Forbes, T. G.; Ko, Y. -K.; Raymond, J. C.;
van Ballegooijen, A. A.; Vourlidas, A.
2006cosp...36..198L Altcode: 2006cosp.meet..198L
Solar eruptions constitute the most violent energy release process in
the solar system They are are created when magnetic energy is suddenly
converted into heat and kinetic energy by magnetic reconnection in
a field reversal region or current sheet The effective electrical
resistivity eta e of the sheet plasma plays a crucial role in energy
conversion Here we present the results for the current sheet thickness
d and eta e determined by analyzing a set of unique data for three
eruptions observed by the UVCS and the LASCO experiments on SOHO Such a
work was never conducted before since it is believed that the current
sheet is too thin to be observable The extremely large values of d
and eta e obtained in this work suggest that the current sheet in
solar eruptions is observable in some circumstances and large-scale
turbulence is operating within the current sheet This constitutes a
challenging goal for future research on the magnetic energy conversion
occurring in both space and laboratory
---------------------------------------------------------
Title: Multi-Wavelength Observations of CMEs and Associated Phenomena
Authors: Pick, M.; Forbes, T. G.; Mann, G.; Cane, H. V.; Chen, J.;
Ciaravella, A.; Cremades, H.; Howard, R. A.; Hudson, H. S.; Klassen,
A.; Klein, K. L.; Lee, M. A.; Linker, J. A.; Maia, D.; Mikic,
Z.; Raymond, J. C.; Reiner, M. J.; Simnett, G. M.; Srivastava, N.;
Tripathi, D.; Vainio, R.; Vourlidas, A.; Zhang, J.; Zurbuchen, T. H.;
Sheeley, N. R.; Marqué, C.
2006cme..book..341P Altcode:
This chapter reviews how our knowledge of CMEs and CME-associated
phenomena has been improved, since the launch of the SOHO mission,
thanks to multi-wavelength analysis. The combination of data obtained
from space-based experiments and ground based instruments allows us
to follow the space-time development of an event from the bottom of
the corona to large distances in the interplanetary medium. Since
CMEs originate in the low solar corona, understanding the physical
processes that generate them is strongly dependant on coordinated
multi-wavelength observations. CMEs display a large diversity in
morphology and kinematic properties, but there is presently no
statistical evidence that those properties may serve to group them
into different classes. When a CME takes place, the coronal magnetic
field undergoes restructuring. Much of the current research is focused
on understanding how the corona sustains the stresses that allow the
magnetic energy to build up and how, later on, this magnetic energy is
released during eruptive flares and CMEs. Multiwavelength observations
have confirmed that reconnection plays a key role during the development
of CMEs. Frequently, CMEs display a rather simple shape, exhibiting a
well known three-part structure (bright leading edge, dark cavity and
bright knot). These types of events have led to the proposal of the
"standard model" of the development of a CME, a model which predicts
the formation current sheets. A few recent coronal observations provide
some evidence for such sheets. Other more complex events correspond
to multiple eruptions taking place on a time scale much shorter than
the cadence of coronagraph instruments. They are often associated with
large-scale dimming and coronal waves. The exact nature of these waves
and the physical link between these different manifestations are not
yet elucidated. We also discuss what kind of shocks are produced during
a flare or a CME. Several questions remain unanswered. What is the
nature of the shocks in the corona (blast-wave or piston-driven?) How
they are related to Moreton waves seen in Hα? How they are related
to interplanetary shocks? The last section discusses the origin of
energetic electrons detected in the corona and in the interplanetary
medium. "Complex type III-like events," which are detected at
hectometric wavelengths, high in the corona, and are associated with
CMEs, appear to originate from electrons that have been accelerated
lower in the corona and not at the bow shock of CMEs. Similarly,
impulsive energetic electrons observed in the interplanetary medium
are not the exclusive result of electron acceleration at the bow shocks
of CMEs; rather they have a coronal origin.
---------------------------------------------------------
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: The SECCHI Experiment on the STEREO Mission
Authors: Howard, R.; Moses, D.; Vourlidas, A.; Davila, J.; Lemen, J.;
Harrison, R.; Eyles, C.; Defise, J. -M.; Bothmer, V.; Ravet, M. -F.;
Secchi Team
2006cosp...36..870H Altcode: 2006cosp.meet..870H
The Sun Earth Connection Coronal and Heliospheric Investigation SECCHI
on the NASA Solar Terrestrial Relations Observatory STEREO mission
is a suite of remote sensing instruments consisting of an extreme
ultraviolet EUV imager two white light coronagraphs and two telescopes
that comprise the heliospheric imager SECCHI will observe coronal mass
ejections CMEs from their birth at the sun through the corona and into
the heliosphere A complete instrument suite is being carried on each
of the two STEREO spacecraft which will provide the first sampling of
a CME from two vantage points The spacecraft will orbit the Sun one
Ahead of the Earth and the other Behind each separating from Earth at
about 22 degrees per year The varying separation means that we will
have different observational capabilities as the spacecraft separate
and therefore differing science goals The primary science objectives
all are focused on understanding the physics of the CME process -
their initiation 3D morphology propagation interaction with the
interplanetary medium and space weather effects By observing the CME
from multiple viewpoints with UV and coronagraphic telescopes and by
combining these observations with radio and in-situ observations from
the other instruments on STEREO as well as from other satellites and
ground based observatories operating at the same time answers to some
of the outstanding questions will be obtained STEREO follows the very
successful SOHO mission SOHO s success was primarily due to the highly
complementary nature of the instruments but it was
---------------------------------------------------------
Title: A Review of White Light Streamers at the End of Cycle 23
Authors: Vourlidas, Angelos
2006IAUS..233..197V Altcode:
This is a brief review of the quiescent large scale visible corona with
an emphasis on the origin, structure and role of streamers in the solar
wind. The review is mostly based on results from the last 10 years of
the SOHO mission and the goal is to provide a coherent picture of what
is known about streamers at the end of the current cycle.
---------------------------------------------------------
Title: A Flux-Rope Scaling of CME and Prominence Acceleration
Authors: Marque, C.; Chen, J.; Vourlidas, A.; Krall, J.; Schuck, P.
2005AGUFMSH13A0293M Altcode:
It has been known that coronal mass ejections (CMEs) and eruptive
prominences (EPs) are closely associated with each other. A major
question concerning CMEs and EPS is the magnetic geometry that underlies
the eruptive plasma structures. It is now well established that many
CMEs can be explained as erupting magnetic flux ropes. However, the
coronal magnetic field cannot be directly measured at this time,
and therefore the flux rope hypothesis has not been confirmed by
magnetic field data. A second unresolved question is the structural
relationship between the closely associated CMEs and EPs. Recently,
it was theoretically found [1] that the height at which a CME or an
EP attains maximum acceleration scales with the footpoint separation
distance (S_f) of the underlying magnetic flux rope. This scaling law
is characteristic of an erupting flux rope and is universal in that it
depends only the flux rope geometry and the Lorentz force acting on
the structure. It was shown to be well satisfied based on comparison
with a small number of CMEs and EPs, indicating that the erupting
structures in these events were initially flux ropes or evolved into
flux ropes early enough. In the present paper, we present results of a
study using a larger sample of events. In this study, we have analyzed
CME events detected by LASCO, for which footpoints are determined
by observational proxies such as magnetic neutral line length, and
EPs seen in Hα and radio data, for which footpoint locations are
observable. We find that CMEs and EPs in this large sample also satisfy
the flux-rope scaling law. The results are consistent with the model
structure with the bright CME rim at Z+2a and the prominence at Z-a,
where Z is the height of the centroid and a is the minor radius of the
flux rope, both defined at the apex of the flux rope. <P />1. Chen,
J. and J. Krall, JGR, 108 (A11), 2003
---------------------------------------------------------
Title: Testing the Predictions of the Catastrophe Model: Comparisons
with Measurements of LASCO Flux Rope CMEs
Authors: Vourlidas, A.; Lin, J.
2005AGUFMSH11C..05V Altcode:
The search for the initiation mechanism of coronal mass ejections
(CMEs)has led to two classes of models. Those that assume a preexisting
magnetic flux rope and those that form such a flux rope during the
eruption process. Which of these two classes comes closer to reality
can only be found by comparing the model predictions to observed CME
properties. Here, we concentrate on the predictions of a preexisting
flux rope model (catastrophe model) in Lin et al (2004). Specifically,
we compare the evolution of mass, speed and magnetic energy of the CME
as predicted in the model to similar measurements/estimates of flux rope
CMEs seen by the LASCO coronagraphs. We find interesting similarities
between predictions and observations and we discuss the implications
for improvements to the model. Ref: Lin, J. et al, ApJ, 602, 422, 2004
---------------------------------------------------------
Title: Fast coronal mass ejection environments and the production
of solar energetic particle events
Authors: Kahler, S. W.; Vourlidas, A.
2005JGRA..11012S01K Altcode:
The search continues for coronal environmental factors that determine
whether a fast coronal mass ejection (CME) results in a solar
energetic particle (SEP) event at 1 AU. From a plot of peak 20 MeV
SEP intensities versus associated CME speeds we select for comparison
two groups of fast, wide, western hemisphere CMEs observed with the
LASCO coronagraph from 1998 to 2002. The SEP-rich CME group produced
the largest observed SEP events, and the SEP-poor CME group produced
the smallest or no observed SEP events. The major differences are that
the SEP-rich CMEs are brighter and more likely to be streamer blowouts
and to follow colocated CMEs within 12 or 24 hours. The SEP-poor CMEs
are fainter and less likely to interact with streamers or to follow
preceding colocated CMEs. Thus we confirm the recent result that the
SEP event peak intensities are higher when the associated driver CMEs
are preceded within a day by wide CMEs at the same locations. However,
the enhanced brightness, and therefore mass, of the SEP-rich CMEs
appears to be their most dominant characteristic and suggests that
either large longitudinal and latitudinal extents or high densities
are needed for fast CMEs to produce SEPs.
---------------------------------------------------------
Title: Relationships between CME brightness and in-situ plasma
parameters observed at 1 AU
Authors: Xie, H.; St. Cyr, C.; Lara, A.; Vourlidas, A.
2005AGUFMSH51C1225X Altcode:
In this study, we investigate the relationships between the CME
brightness observed by LASCO coronagraphs and the plasma density
in the solar wind disturbance region, i.e, the interplanetary shock
and the associated interplanetary CME (ICME) region. We derive the
excess density and fluxes of mass, momentum and energy of a CME via the
brightness of LASCO images, which is proportional to the plasma density
of the CME, subtracting a background (a pre-event image) brighness. The
excess density and fluxes of the solar wind disturbance was obtained
by integrating the in-situ measured excess (above a ambient level)
density, momentum, and energy over the duration of the disturbance. We
find that there are good correlations between the excess density, and
fluxes of mass, momentum and energy of CME in the corona and those in
the ICME region. Also, we examine the effects of the CME interaction
and thomson scattering on the correlation analysis results.
---------------------------------------------------------
Title: SEP Acceleration Efficiency of CMEs
Authors: Howard, R. A.; Vourlidas, A.; Mewaldt, R. E.
2005AGUFMSH14A..02H Altcode:
We investigate the efficiency of coronal mass ejections (CMEs) in
accelerating solar energetic particles (SEPs) by comparing their
respective kinetic energy budgets. Our SEP sample comprises a list
of 20-30 well-observed events whose energy spectra are obtained by
combining data from multiple in-situ instruments. The corresponding
CMEs were observed with the LASCO coronagraphs. Calibrated images were
used for the mass and velocity measurements. Because most of these
events correspond to fast and extended CMEs, extra care was taken
during the measurements to isolate the ejecta from other signatures
usually associated with these type of events. The CME masses were
corrected to the first order, for projection effects assuming radial
propagation from the corresponding source regions. The implications
for the acceleration efficiency of CMEs derived from the comparison
between CME and SEP energies are discussed.
---------------------------------------------------------
Title: Modelling of CMES for the STEREO Mission
Authors: Howard, R. A.; Thernisien, A. F.; Marque, Ch.; Vourlidas,
A.; Patel, N.
2005ESASP.592..727H Altcode: 2005soho...16E.147H; 2005ESASP.592E.147H
No abstract at ADS
---------------------------------------------------------
Title: Solar Polar Imager: Observing Solar Activity from a New
Perspective
Authors: Alexander, D.; Sandman, A.; Liewer, P.; Ayon, J.; Goldstein,
B.; Murphy, N.; Velli, M.; Floyd, L.; Moses, D.; Socker, D.; Vourlidas,
A.; Garbe, G.; Suess, S.; Hassler, D.; Kosovichev, A.; Mewaldt, R.;
Neugebauer, M.; Ulrich, R.; Zurbuchen, T.
2005ESASP.592..663A Altcode: 2005soho...16E.131A; 2005ESASP.592E.131A
No abstract at ADS
---------------------------------------------------------
Title: How Efficient are Coronal Mass Ejections at Accelerating
Solar Energetic Particles?
Authors: Mewaldt, R. A.; Cohen, C. M. S.; Mason, G. M.; Haggerty,
D. K.; Looper, M. D.; Vourlidas, A.; Desai, M. I.; Giacalone, J.;
Labrador, A. W.; Leske, R. A.; Mazur, J. E.
2005ESASP.592...67M Altcode: 2005soho...16E..10M; 2005ESASP.592E..10M
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: Structure and Organization of the Upper Chromosphere
Authors: Korendyke, C. M.; Landi, E.; Vourlidas, A.
2005AGUSMSH12A..05K Altcode:
Over its past two flights, the VAULT sounding rocket instrument
obtained a series of subarcsecond resolution images of the solar
disk. These Lyman alpha images resolve and separate structures in
the upper chromosphere. The observed plasmas are concentrated in
larger diameter, optically thick loops. The images taken near the limb
unambiguously identify the height of the upper chromosphere in the quiet
sun. An unexpected level of evolution and activity is present in the
"quiet sun" at small spatial scales. The third flight of the payload
will investigate the interconnectivity of the observed structures with
the photosphere.
---------------------------------------------------------
Title: On the Evolution of CME Mass
Authors: Howard, R. A.; Vourlidas, A.
2005AGUSMSH53A..05H Altcode:
Calculating the total mass of a CME is a standard technique that has
been used for several decades and which SOHO/LASCO has refined and
automated. The total mass of a CME is only that material that arises
from below the occulting disk. It doesn't consider any mass that has
been swept up from within the field of view and moved, since we always
consider a "pre-event" coronal state. In this paper we turn to the
question of swept up material and investigate the evolution in height of
the volume density of the region at the CME front. Often the post-CME
corona is "cleaned out", meaning that it is very dim compared to the
pre-event and general background. We thus assume that the material has
been swept up by the CME expansion through that volume. Can LASCO detect
that swept up mass? To investigate this we have selected only events
that have a clearly defined leading and trailing edge to the CME front,
and which in an ideal sense are examples of the "three-part" CME. We
calculated the mass of those LASCO events, which also gives the column
electron density. We convert that electron content to a volume density
in a narrow region at the center of the front, by approximating the
shape as a small section of a sphere. This enables us to say that the
depth along the line of sight is the same as the angular latitudinal
span, which we take to be on the order of a few degrees. We find that
the volume density in such events decreases with increasing height by
a simple power law with an exponent of -3. This is exactly what would
be expected for purely radial expansion and no pileup of material in
the front. We will discuss why the pileup isn't observed by LASCO and
where implications for the height origin of these CMEs. We will also
discuss the implications for the upcoming STEREO mission.
---------------------------------------------------------
Title: Modeling of the Radio Metric Emission of the Quiet Sun Corona
Using Potential Field Source Surface Extrapolations
Authors: Marque, C.; Wang, Y.; Thernisien, A. F.; Howard, R. A.;
Vourlidas, A.
2005AGUSMSH24A..05M Altcode:
We present the result of a modeling of the Quiet Sun corona in the
metric radio range (F~150-450 MHz). At these frequencies, the radio
emission is dominated by non-thermal emissions (plasma emissions)
due to populations of accelerated electrons, and, when the solar
activity is low or moderate, by the thermal emission of the corona
(bremsstrahlung). While this emission mechanism is well known, depending
only on the electron density and temperature, the difficulties arise
from the refraction that affects the radio waves propagating in the
corona, which depends on the electron density distribution. In order
to build a realistic description of the electron and temperature
distribution in the corona for a given date, we have used Potential
Field Source Surface extrapolations, based on synoptic maps of the
photospheric magnetic field. The density and temperature distribution is
based on scaling laws which depend on the field strength as well as the
length of the loops. We use radio data from the Nancay Radioheliograph
to constraint the free parameters of these scaling laws, and make
qualitative and quantitative comparisons between the radio images and
the simulations.
---------------------------------------------------------
Title: The Mass Properties of Coronal Mass Ejections: Evolution
& Statistics
Authors: Vourlidas, A.; Howard, R.
2005AGUSMSP44A..04V Altcode:
A defining property of a Coronal Mass Ejection (CME) is naturally its
mass. The LASCO observations of 1000s of CMEs over the last 8 years
allow us to constrain statistically the "typical" CME mass but also to
examine its evolution as a function of time during each event. Such
work could not be done in the past due to the lower cadence and
instrument sensitivity. Our analysis of the CME mass properties has
revealed some interesting and maybe unexpected results. For example,
close to half of the observed CMEs seem to blend into the background
before reaching 30 Rs. In this paper, we will discuss our findings
for the LASCO CME sample from 1996 to 2004.
---------------------------------------------------------
Title: Detection and Diagnostics of a Coronal Shock Wave Driven by
a Partial-Halo Coronal Mass Ejection on 2000 June 28
Authors: Ciaravella, A.; Raymond, J. C.; Kahler, S. W.; Vourlidas,
A.; Li, J.
2005ApJ...621.1121C Altcode:
A fast partial-halo coronal mass ejection (CME) was observed on 2000
June 28 by instruments on the SOHO spacecraft. The CME leading edge
and filamentary cold core were detected over the northwest limb at 2.32
R<SUB>solar</SUB> by the SOHO UV Coronagraph Spectrometer (UVCS). The
broad profile of the O VI λ1032 line gives evidence of a shock front at
the leading edge, supporting the identification of white-light CME sharp
leading edges as fast-mode shocks. Line-of-sight speeds are as high as
1500 km s<SUP>-1</SUP>, comparable to the projected speed obtained from
LASCO. Pumping of the O VI λ1032 by Lyβ (v=1810 km s<SUP>-1</SUP>)
and of O VI λ1037 by O VI λ1032 (v=1648 km s<SUP>-1</SUP>) were
detected, which provide diagnostics of outflow speed and density. The
angle of the ejecta with the plane of the sky is obtained, combining
the projected speed from LASCO with the line-of sight-speed, and
varies between 7° and 46°. In the latter case the projected height
of 2.32 R<SUB>solar</SUB> was at an actual heliocentric distance of
3.6 R<SUB>solar</SUB>. An associated solar energetic particle (SEP)
event was observed at the L1 point following this CME. The abundance
and charge-state data are consistent with a gradual shock-accelerated
SEP event. A type II radio burst was observed at the same time the
shock front was detected by UVCS.
---------------------------------------------------------
Title: Energetics of Coronal Mass Ejections
Authors: Subramanian, Prasad; Vourlidas, Angelos
2005IAUS..226..314S Altcode: 2005astro.ph..2057S
We examine the energetics of the best examples of flux-rope CMEs
observed by LASCO in 1996-2001. We find that 69% of the CMEs in our
sample experience a driving power in the LASCO field of view. For
these CMEs which are driven, we examine if they might be deriving
most of their driving energy by coupling to the solar wind. We do
not find conclusive evidence to support this hypothesis. We adopt two
different methods to estimate the energy that can possibly be released
by the internal magnetic fields of the CMEs. We find that the internal
magnetic fields are a viable source of driving power for these CMEs.
---------------------------------------------------------
Title: What Fraction of the Kinetic Energy of Coronal Mass Ejections
goes into Accelerating Solar Energetic Particles?
Authors: Mewaldt, R. A.; Cohen, C. M. S.; Mason, G. M.; Haggety,
D. K.; Looper, M. D.; Vourlidas, A.; Desai, M. I.; Giacalone, J.;
Labrador, A. W.; Leske, R. A.; Mazur, J. E.
2005ICRC....1..129M Altcode: 2005ICRC...29a.129M
No abstract at ADS
---------------------------------------------------------
Title: Error Estimates in the Measurements of Mass and Energy in
White Light CMEs
Authors: Vourlidas, Angelos
2005IAUS..226...76V Altcode:
Due to the optically thin nature of the white light emission, all
measurements of the energetics and dynamics of a CME are based on
sky-plane projected quantities. The extent and distribution of the CME
material along the line of sight is unknown. Thus, CME measurements
have an inherent degree of uncertainty. In this paper, I identify the
various (possible) sources of errors associated with measurements of
CME mass and energy (e.g., instrumental, random, projections effects,
etc) and give an error budget for the final measurements. I apply these
errors to the statistics of mass and energy for several thousand CMEs
observed with LASCO in 1996-2003.
---------------------------------------------------------
Title: Calibration Results for the STEREO/SECCHI COR2 Coronagraphs
Authors: Vourlidas, A.; Plunkett, S.; Korendyke, C.; Gong, Q.; Socker,
D.; Howard, R.
2004AGUFMSH21B0409V Altcode:
The two SECCHI instrument suites aboard the upcoming STEREO mission
include the COR2 coronagraphs which observe the middle/outer corona;
namely, from 2.5 to 15 solar radii. As of the end of August 2004,
both COR2 instruments have been assembled and delivered to the SECCHI
project and their perfomance has been measured and analyzed. The
coronagraphs have met (and in some cases, exceeded) their performance
requirements. Here, we present in detail the results of the calibration
(photometry, polarization, stray light levels, etc) of the COR2
coronagraphs. We compare these new coronagraphs to the LASCO ones
and discuss how they will contribute to the scientific success of the
STEREO mission.
---------------------------------------------------------
Title: Planetary Auroral Storms Trace a CME-driven Interplanetary
Shock Throughout the Solar System, from the Sun to Saturn at 9 AU
Authors: Prange, R.; Pallier, L.; Hansen, K. C.; Howard, R.; Vourlidas,
A.; Courtin, R.; Parkinson, C.
2004AGUFM.P51A1419P Altcode:
Hubble Space Telescope FUV images taken in December 2000 revealed
for the first time au auroral storm on Saturn. The Sun, the Earth,
Jupiter and Saturn were practically aligned at that time, allowing the
solar wind plasma to flow by all three planets successively within ~1
month. Observations of Jupiter coordinated with Cassini measurements
in the nearby solar wind were also executed during this period. Using
a recently developped MHD code and solar wind measurements in the
Earth vicinity, we establish that (1) the strong auroral event on
Saturn was related to the interaction of an interplanetary shock with
its magnetosphere, (2) this shock was initiated by a series of CMEs
on the Sun observed by SOHO. We follow the propagation of the shock
throughout the solar system, from the Earth where auroral storms are
recorded, to Jupiter where the auroral activity is strongly enhanced,
and to Saturn where it ultimately activates the observed unusual polar
source. This is the first report of consecutive auroral responses to a
propagating interplanetary shock. It indicates that shocks retain their
properties and their ability to trigger planetary auroral activity
thoughout the solar system, thereby unifying our understanding of
solar-planetary interactions. We discuss also the similarities and
differences observed between the planetary auroral responses.
---------------------------------------------------------
Title: Modeling of CME Visibility for the STEREO Mission
Authors: Howard, R. A.; Patel, N. S.; Thernisien, A.; Marque, C.;
Vourlidas, A.
2004AGUFMSH21D..06H Altcode:
One of the objectives of the STEREO mission is to determine the
three-dimensional configuration of CMEs. The STEREO mission consists
of two identical spacecraft, one leading Earth and the other trailing
Earth, which will separate from each other at the rate of about 45
degrees per year. To understand the visibility of CMEs and the ability
to discern the 3D structure, we have been developing a "forward
modeling" capability (RAYTRACE) described in another paper at this
meeting. This capability complements the inversion technique we have
also been developing. Using RAYTRACE we may compute synthetic total
and polarized brightness images using the Thomson scattering formulae
from an assumed electron density model. Several (geometric) models of a
CME have been defined - loop, spherical shell, cylindrical shell and a
graduated cylindrical shell (GCS). Since the GCS model is a reasonable
simulation of a flux-rope CME, we have used it to investigate the
appearance of a CME as a function of STEREO separation angle. In this
model the angular size in the two directions, the height of the leading
edge, the orientation of the structure in the corona and the radial
electron density distribution can be specified. We present the results
of this study and compare the simulations with observed CMEs from LASCO.
---------------------------------------------------------
Title: Modelling of the Quiet Sun Emission in the Metric Radio Range
Authors: Marque, C.; Wang, Y.; Thernisien, A. F.; Howard, R. A.;
Vourlidas, A.; Patel, N. S.
2004AGUFMSH21B0424M Altcode:
The thermal emission from the Quiet Sun can be mapped in the metric
radio range when the solar activity is low, and plasma emissions
due to non-maxwellian distributions of electrons are weak or
non-existent. This occurs mainly in the vicinity of the solar cycle
minimum. Metric radio observations have been used in the past to infer
the mean coronal temperature, and to map and study large scale coronal
structures. Earlier simulations using symmetrical electron density
distributions and uniform temperatures were succesful to depict some
of the properties of the Quiet Sun emission but are not suitable in
detailed comparisons with observations, and furthermore, they predict
limb brightening in the high frequency range of the metric domain
(150-450 MHz), which has not been observed so far. In this paper,
we present simulations of the Quiet Sun emission based on Potential
Field Source Surface extrapolations, which are used to build a global
density and temperature model of the corona at a given date. Scaling
laws involving the loop footpoint field strength and loop length govern
the density and temperature distribution in this model. Synthetic
radio images are then computed using raytracing techniques, taking into
account the refraction of radio waves in the corona, and are compared
with actual observations provided by the Nancay Radioheliograph.
---------------------------------------------------------
Title: Raytracing Software for the Simulation of the Solar K-Corona
Authors: Thernisien, A. F.; Patel, N. S.; Howard, R. A.; Marqué,
C.; Vourlidas, A.
2004AGUFMSH21B0404T Altcode:
In this talk we will present RAYTRACE, a raytracing software
developed at the U.S. Naval Research Laboratory. The program is an
implementation of the Thomson scattering equations applied to the
solar corona (Billings 1966). Synthetic coronal images in total or
polarized brightness can be calculated using models of various coronal
structures. We have implemented many models for quiescent and dynamic
coronal stuctures such as streamers, the heliospheric current sheet
(HCS), jets and CMEs. The models are generally analytic representations
of the volume electron density, but a generic data cube of electron
density can also be used. The core of the program has been written in
C++ pimarily for computation speed. An earlier version was written
in IDL, but was quite slow. Due to the processing speed of common
computers, a high resolution image (512 x 512) of the HCS streamer belt
for instance can be generated in less than 1 minute (Pentium 4, 2.5 GHz,
512 Mb RAM, Linux OS). A graphical user interface has been developed
in IDL and allows the user to easily enter the parameters required for
each model, specifying the position and orientation of the observer and
structure, the size and resolution of the images, and then to visualize
the output and compare the results to actual coronal images obtained
by SOHO/LASCO and in the future by the STEREO/SECCHI coronagraphs
(COR1 and COR2). Some of the main features of the front-end interface
include mesh plot positioning of structures in space, parameter tuning
for the structures and movie making. Different studies have already
been done using this software, such as the inversion of the electron
density of the streamer belt or the modeling of CMEs for the STEREO
mission (presented in another paper at this meeting).
---------------------------------------------------------
Title: An interplanetary shock traced by planetary auroral storms
from the Sun to Saturn
Authors: Prangé, Renée; Pallier, Laurent; Hansen, Kenneth C.;
Howard, Russ; Vourlidas, Angelos; Courtin, Régis; Parkinson, Chris
2004Natur.432...78P Altcode:
A relationship between solar activity and aurorae on Earth
was postulated long before space probes directly detected plasma
propagating outwards from the Sun. Violent solar eruption events trigger
interplanetary shocks that compress Earth's magnetosphere, leading
to increased energetic particle precipitation into the ionosphere and
subsequent auroral storms. Monitoring shocks is now part of the `Space
Weather' forecast programme aimed at predicting solar-activity-related
environmental hazards. The outer planets also experience aurorae,
and here we report the discovery of a strong transient polar emission
on Saturn, tentatively attributed to the passage of an interplanetary
shock-and ultimately to a series of solar coronal mass ejection (CME)
events. We could trace the shock-triggered events from Earth, where
auroral storms were recorded, to Jupiter, where the auroral activity
was strongly enhanced, and to Saturn, where it activated the unusual
polar source. This establishes that shocks retain their properties and
their ability to trigger planetary auroral activity thoughout the Solar
System. Our results also reveal differences in the planetary auroral
responses on the passing shock, especially in their latitudinal and
local time dependences.
---------------------------------------------------------
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: Radio Observations of Coronal Mass Ejection4
Authors: Vourlidas, Angelos
2004ASSL..314..223V Altcode:
In this chapter we review the status of CME observations in radio
wavelengths with an emphasis on imaging. It is an area of renewed
interest since 1996 due to the upgrade of the Nançay Radioheliograph
in conjunction with the continuous coverage of the solar corona from
the EIT and LASCO instruments aboard SOHO. Also covered are analyses
of Nobeyama Radioheliograph data and spectral data from a plethora of
spectrographs around the world. We will point out the shortcomings of
the current instrumentation and the ways that FASR could contribute. A
summary of the current understanding of the physical processes that
are involved in the radio emission from CMEs is be given.
---------------------------------------------------------
Title: Electron Density Inversion and Modeling of a streamer using
EIT-LASCO Data of January 2004
Authors: Thernisien, A. F.; Howard, R. A.; Marqué, Ch.; Vourlidas, A.
2004AAS...204.7101T Altcode: 2004BAAS...36Q.797T
We present in this poster the electron density characterisation of a
streamer observed by LASCO under 2 different angles of view. At the
end of January 2004, due to a favorable configuration of the Solar
corona, we are able to observe a streamer, first, from the side, and
then, 7 days later, from the face. Using electron density inversion
technics we have determined the density profiles characterising the
lenght and the thickness of the streamer. Those density profiles were
then used to refine a 3D model of a streamer that is compared to LASCO
observations using ray tracing technics.
---------------------------------------------------------
Title: Mass and Kinetic Energy Distributions of Coronal Mass Ejections
in 1996-2002
Authors: Vourlidas, A.; Patsourakos, S.
2004AAS...204.7303V Altcode: 2004BAAS...36..800V
We present the mass and kinetic energy distributions of coronal mass
ejections observed by LASCO between 1996 and 2002. The sample includes
more than 4000 events. Events with projected widths larger than 120
deg were excluded because of uncertainties in the calculation of the
mass and speed for such large events. <P />We compare the LASCO mass
and energy distribution to similar distributions from Solwind and
soft x-ray flares. In particular, we find that the CME kinetic energy
distribution follows a power law similar to the one found for solar
flares. The implications of our findings are discussed in the paper.
---------------------------------------------------------
Title: Simulations of the Quiet Sun Emission at Metric and Decimetric
Radio Wavelengths
Authors: Marqué, C.; Wang, Y. M.; Thernisien, A. F.; Vourlidas, A.;
Howard, R. A.
2004AAS...204.7104M Altcode: 2004BAAS...36Q.797M
In the metric and decimetric radio range, solar emission is dominated
by non-thermal radiation from electron populations accelerated during
flares or continuous processes. When the solar activity is low, mainly
during the solar cycle minimum, the thermal emission from the corona
can be mapped, and structures such as coronal holes, active regions
or filament cavities can be observed. The radio thermal emission is
sensitive to the electron density and temperature, and radio rays
suffer refraction effects when their frequency is close to the local
plasma frequency. A model of the electron density and temperature
distribution is thus needed to compute the thermal radiation at a
given frequency. Axisymetric and homogeneous electron density models
have been successfully used for the last fourty years to described
the basic properties of this thermal emission. Nevertheless, these
density models are not suitable for describing the corona at a given
date. <P />We present in this poster more realistic simulations using
a Potential Field Source Surface extrapolation and realistic electron
density distributions. Assuming hydrostatic equilibrium, the density
is determined by the strength of the magnetic field and the length of
the magnetic loops: n=n0(B,L)*f(r). Different n0 and f functions are
used and the corresponding results are compared to real data.
---------------------------------------------------------
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: Coronal Mass Ejection Masses From CMEs Identified in
Interplanetary Scintillation (IPS) Tomography and LASCO Coronagraph
Images
Authors: Rappoport, S. A.; Jackson, B. V.; Hick, P. P.; Buffington,
A.; Vourlidas, A.
2004AAS...204.3802R Altcode: 2004BAAS...36..712R
To optimize the information from individual radio source observations
of the sky covering large elongations, we have developed a
Computer-Assisted Tomography (CAT) program. We fit STELab (Nagoya
University, Japan) interplanetary scintillation (IPS) observations to a
time-dependent, three-dimensional heliospheric model. These observations
allow us to create "sky maps" covering 10 to 80 degrees in elongation,
in which we can track CMEs observed earlier in LASCO coronagraph
images. These events have approximately the same shapes and extents as
observed closer to the Sun. Here we map several CMEs in 3-dimensions as
they move outward to 1 AU. Masses for each of the events are determined
from the reconstruction analysis and are compared with plane of the
sky masses obtained from calibrated LASCO coronagraph images.
---------------------------------------------------------
Title: A Study of the Kinematic Evolution of Coronal Mass Ejections
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Vourlidas, A.
2004ApJ...604..420Z Altcode:
We report the kinematic properties of a set of three coronal
mass ejections (CMEs) observed with the LASCO (Large Angle and
Spectrometric Coronagraph) on the Solar and Heliospheric Observatory
(SOHO) spacecraft, which showed characteristics of impulsive,
intermediate, and gradual acceleration, respectively. The first CME
had a 30 minute long fast acceleration phase during which the average
acceleration was about 308 m s<SUP>-2</SUP> this acceleration took
place over a distance of about 3.3 R<SUB>solar</SUB> (from 1.3 to
4.6 R<SUB>solar</SUB>, height measured from disk center). The CME
characterized by intermediate acceleration had a long acceleration
phase of about 160 minutes during which the average acceleration was
about 131 m s<SUP>-2</SUP> the CME traveled a distance of at least
4.3 R<SUB>solar</SUB>, reaching a height of 7.0 R<SUB>solar</SUB> at
the end of the acceleration phase. The CME characterized by gradual
acceleration had no fast acceleration phase. Instead, it displayed a
persistent weak acceleration lasting more than 24 hr with an average
acceleration of only 4.0 m s<SUP>-2</SUP> throughout the LASCO field
of view (from 1.1 to 30 R<SUB>solar</SUB>). This study demonstrates
that the final velocity of a CME is determined by a combination of
acceleration magnitude and acceleration duration, both of which can
vary significantly from event to event. The first two CME events were
associated with soft X-ray flares. We found that in the acceleration
phase there was close temporal correlation both between the CME velocity
and the soft X-ray flux of the flare and between the CME acceleration
and derivative of the X-ray flux. These correlations indicate that
the CME large-scale acceleration and the flare particle acceleration
are strongly coupled physical phenomena occurring in the corona.
---------------------------------------------------------
Title: Solar Physics from Space for the Next Solar Cycle
Authors: Vourlidas, Angelos; Patsourakos, Spiros
2004hell.conf...78V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Masses and Energetics of CMEs Observed by SOHO/LASCO
Authors: Howard, R. A.; Morrill, J.; Vourlidas, A.; Buzasi, D.;
Esfandiari, E.; Rich, N.; Thernisien, A.
2003AGUFMSH41B0460H Altcode:
The LASCO data base contains over 5000 CMEs, observed from 1996-2001. We
have developed an automated procedure to calibrate the associated LASCO
images and to calculate the CME properties. Of the total number of
CMEs, we have been able to calculate the mass and energetics of about
80% of the total number of events. Here we report on the analysis of
the mass and energy properties of over 3000 CMEs and compare them to
previous observations of CMEs.
---------------------------------------------------------
Title: Direct Detection of a Coronal Mass Ejection-Associated Shock
in Large Angle and Spectrometric Coronagraph Experiment White-Light
Images
Authors: Vourlidas, A.; Wu, S. T.; Wang, A. H.; Subramanian, P.;
Howard, R. A.
2003ApJ...598.1392V Altcode: 2003astro.ph..8367V
The Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 and
C3 coronagraphs recorded a unique coronal mass ejection (CME) on 1999
April 2. The event did not have the typical three-part CME structure
and involved a small-filament eruption without any visible overlying
streamer ejecta. The event exhibited an unusually clear signature of a
wave propagating at the CME flanks. The speed and density of the CME
front and flanks were consistent with the existence of a shock. To
better establish the nature of the white-light wave signature,
we employed a simple MHD simulation using the LASCO measurements
as constraints. Both the measurements and the simulation strongly
suggest that the white-light feature is the density enhancement from
a fast-mode MHD shock. In addition, the LASCO images clearly show
streamers being deflected when the shock impinges on them. It is the
first direct imaging of this interaction.
---------------------------------------------------------
Title: Comparisons Between Noise Storm Emissions and CME Events
Authors: Marque, C.; Vourlidas, A.
2003AGUFMSH21B0119M Altcode:
In this poster, we present preliminary comparisons between noise
storm emissions and CME occurrences as observed with the Nançay
Radioheliograph and the LASCO coronagraph on board SOHO. We looked
for modifications of the noise storm parameters (flux) and possible
appearances or disappearances temporarily associated with CME initiation
and propagation in the low corona. On-disk EUV images have also been
used to locate the area where the CMEs were originating from.
---------------------------------------------------------
Title: LASCO C2 and C3 Level-1 Images: Calibration and Pipeline
Processing
Authors: Thernisien, A. F.; Morrill, J.; Llebaria, A.; Rich, N.;
Vourlidas, A.; Esfandiari, E.; Wang, D.; Korendyke, C.; Moses, D.;
Biesecker, D.; Bout, M.; Lamy, P.; Howard, R. A.
2003AGUFMSH41B0461T Altcode:
The LASCO C2 and C3 coronagraphs have provided coronal observations
since May, 1996. Initial calibrations have been available during most
of this time period. We have subsequently completed a re-evaluation
and refinement of these calibration procedures. We are now able
to present the final version of the level-1 data using the latest
improvements from in-flight calibration results. Further details
on the LASCO calibration and level-1 data access are presented at
http://lasco-www.nrl.navy.mil/level_1/lascocal_index.html. In this
presentation we will sum up the different aspects of the LASCO
C2-C3 image corrections such as vignetting, absolute photometry,
time corrections, geometric distortion, sun center position, and
spacecraft orientation.
---------------------------------------------------------
Title: Physical Parameters of the 2000 February 11 Coronal Mass
Ejection: Ultraviolet Spectra versus White-Light Images
Authors: Ciaravella, A.; Raymond, J. C.; van Ballegooijen, A.;
Strachan, L.; Vourlidas, A.; Li, J.; Chen, J.; Panasyuk, A.
2003ApJ...597.1118C Altcode:
We present spectra of a three-part coronal mass ejection (CME) observed
by the Ultraviolet Coronagraph Spectrometer aboard SOHO on 2000
February 11. Images of the CME in different spectral lines show how
the morphology depends on the temperature, density, and outflow speed
of the ejected plasma. The H I Lyα is the line that best resembles
the white-light data, although it can be rather different where the
outflow speed severely dims its radiative component. We estimate the
ranges of temperature and density in the front, prominence core, and
void. We also estimate the outflow speed that is the true speed of the
ejecta as obtained from the Doppler dimming technique, its component
projected on the plane of the sky, and the line-of-sight speed for the
three components of the CME. The plasma in the front was denser, cooler,
and more depleted in O and Si than the ambient coronal streamer. These
characteristics indicate that it originated in the closed field core
of the pre-CME streamer. The leading edge was not the projection of
a simple spherical shell onto the plane of the sky. The line profiles
suggest a wide looplike structure, although a more complete shell that
was brighter in some areas could also match the data. The prominence has
a structure in temperature and density with the hotter top end emitting
in the Mg X and Si XII lines while the bottom end was much cooler and
visible only in the H I Lyman lines. Emission in the void was rather
faint. The outflow speed obtained from Doppler dimming of the radiative
lines, the line-of-sight speed measured from the Doppler shift of the
lines, and the plane-of-the-sky speed estimated from the comparison
of the images taken at 2.3 and 2.6 R<SUB>solar</SUB> give speeds much
lower than those estimated at greater heights (>4 R<SUB>solar</SUB>)
from LASCO and indicate a stronger acceleration at lower heights.
---------------------------------------------------------
Title: Constraints on Coronal Mass Ejection Dynamics from Simultaneous
Radio and White-Light Observations
Authors: Reiner, M. J.; Vourlidas, A.; Cyr, O. C. St.; Burkepile,
J. T.; Howard, R. A.; Kaiser, M. L.; Prestage, N. P.; Bougeret, J. -L.
2003ApJ...590..533R Altcode:
Simultaneous radio and white-light observations are used to deduce
information on the dynamics of two coronal mass ejection (CME)
events that occurred about 2 hr apart on 2001 January 20 and that were
associated with eruptions from the same active region on the Sun. The
analysis combines both space-based and ground-based data. The radio
data were obtained from the WAVES experiment on the Wind spacecraft and
from the Culgoora radiospectrograph in Australia. The white-light data
were from the LASCO experiment on SOHO and from the Mk4 coronameter at
the Mauna Loa Solar Observatory. For these CME events we demonstrate
that the frequency drift rate of the type II radio emissions, generated
by the shocks driven by the white-light CMEs, are consistent with the
plane-of-sky height-time measurements, provided that the propagation
direction of the CMEs and their associated radio sources was along
a radial line from the Sun at a solar longitude of ~E50°. These
results imply that the “true” CME speeds were estimated to be ~1.4
times higher than the measured plane-of-sky speeds and that the CMEs
originated from solar eruptions centered near E50°. This CME origin
is consistent with the known active region and flare site associated
with these two CME events. Furthermore, we argue that the type II
radio emissions generated by these CMEs must have originated in
enhanced density regions of the corona. We investigate whether the
type II radiation could have originated in one or more dense coronal
streamers, whose densities were estimated from the polarization
brightness measurements made by LASCO at that time. Finally, we use
these radio and white-light observations to speculate about the dynamics
and scales involved in the interaction between these two CMEs.
---------------------------------------------------------
Title: Filament Eruptions in the Metric Radio Range
Authors: Marqué, Ch.; Vourlidas, A.
2003SPD....34.2302M Altcode: 2003BAAS...35R.851M
The aim of this paper is to show that metric radio diagnostics can be
used to study the motion and behavior of eruptive filaments from the
site of the eruption up to the coronagraphic field of view, allowing
a complete coverage of these events at medium and high altitudes. <P
/>I will illustrate this with an example of a filament eruption that
occurred on May 27th 2002 ansd I will discuss the radio observations
in terms of interaction with coronal structures and filament cavity
detection. <P />Ch. Marqué is funded by a NASA contract to NRL.
---------------------------------------------------------
Title: High-Resolution Views of the Solar Atmosphere
Authors: Vourlidas, A.; Korendyke, C.
2003SPD....34.2009V Altcode: 2003BAAS...35..845V
The study of many of the outstanding phenomena of the solar atmosphere
(coronal heating, flares and coronal mass ejection) has persistently
shown that observations of physical processes at ever smaller scales
are needed for their understanding. Here I report on the results from
the latest NRL sounding rocket payload, the Very Advanced ULtraviolet
Telescope (VAULT). In two successful flights, the instrument achieved
0.33 arcsecond resolution, the highest ever from a space platform. VAULT
obtained spectrally pure images of the upper chromosphere/lower
transition region in the Lya line (1216A). A number of space-borne
and ground-based obsrvatories supported the VAULT flights. The first
results from the analysis of these datasets will be presented.
---------------------------------------------------------
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: Mass and energy properties of LASCO CMEs
Authors: Vourlidas, A.; Buzasi, D.; Howard, R. A.; Esfandiari, E.
2002ESASP.506...91V Altcode: 2002svco.conf...91V; 2002ESPM...10...91V
We present measurements of the dynamical (mass, potential energy) and
kinetic (speed, kinetic energy) properties of coronal mass ejections
(CMEs). The sample includes the majority of white light CMEs observed
between 1996-2000. In particular, we investigate the mass and energy
distributions of CMEs and compare it to similar analyses from past
coronagraphs.
---------------------------------------------------------
Title: Observations of CMEs in the Rising and Declining Phases of
Solar Cycle 23
Authors: Howard, R. A.; Plunkett, S. P.; St. Cyr, O. C.; Vourlidas, A.
2002AGUSMSH41A..02H Altcode:
The most complete observations of CMEs throughout a solar cycle,
previously, were conducted from 1979 through 1989 using a combination
of the P78-1/Solwind and SMM coronagraphs. Aside from the variation
in the occurrence rate of CMEs throughout the cycle, perhaps the most
interesting effect of the solar cycle was the occurrence of CMEs in
the outer corona along the magnetic neutral line. The LASCO experiment
on the SOHO satellite has been observing the solar corona since the
start of cycle 23, except for a brief 4-month hiatus in 1998. The new
observations have several important improvements over the previous
ones - increased sensitivity, increased spatial coverage and continuous
solar viewing. In this paper, we examine the nature of CME observations
during the rising and declining phases to determine if there is a
difference between the CMEs that occur during these two phases.
---------------------------------------------------------
Title: Calibration of the LASCO C3 Coronal Images
Authors: Morrill, J.; Biesecker, D.; Esfandiari, A.; Korendyke, C.;
Moses, D.; Rich, N.; Vourlidas, A.; Wang, D.; Howard, R. A.; Lamy,
P.; Llebaria, A.; Thernisien, A.
2002AAS...200.5503M Altcode: 2002BAAS...34R.732M
The LASCO C3 coronagraph has provided coronal observations since May,
1996. Preliminary calibrations have been available during most of this
time period. However, some aspects of the calibration have required
re-evaluation and we are just completing a complete review of the
calibration procedure for these images. In this presentation we will
discuss the steps required to correct LASCO C3 images. This includes
corrections required by both optical and electrical characteristics
of the instrument as well as timimg and spacecraft pointing driven
correctons.
---------------------------------------------------------
Title: Radio Signatures of Coronal Mass Ejections
Authors: Vourlidas, A.
2002AAS...200.4906V Altcode: 2002BAAS...34..722V
The SOHO mission and in particular the LASCO/EIT imaging of the near-Sun
enviroment brought the study of coronal mass ejections (CMEs) to the
forefront of solar physics research. Solar radiophysics, especially in
low frequencies have benefited from the renewed interest on outer corona
events and the availability of new or renovated radio instruments both
in space and on the ground. Now spectrometric and imaging observations
of CMEs and related phenomena are routinely available and their analysis
has begun to contribute important insights to the physics of CMEs. In
this paper, I review the significant amount of radio CME work that has
accumulated since the beggining of the current solar cycle and outline
the ways in which radio coronal observations could become even more
important in the future.
---------------------------------------------------------
Title: Solar energetic electron events and coronal shocks
Authors: Klassen, A.; Bothmer, V.; Mann, G.; Reiner, M. J.; Krucker,
S.; Vourlidas, A.; Kunow, H.
2002A&A...385.1078K Altcode:
Mildly relativistic electrons appear during the solar energetic particle
events. A detailed investigation on the origin of such electrons is
presented for four particlular solar events. The mildly relativistic
electrons have been detected at energies of 0.25-0.7 MeV by COSTEP/SOHO
and below 0.392 MeV by Wind 3-DP experiments. Coronal shocks associated
with these electron events are identified from the metric-to-decametric
solar type II radio bursts. All selected events were associated with
solar activity at western longitudes, so that the magnetic footpoints
connecting the spacecraft with the Sun were close to the flare/shock/CME
site. The associated type II bursts were accompanied by so-called shock
accelerated (SA) type III bursts appearing to be emerging from the type
II emission site. We found: (1) that all of the 0.25-0.7 MeV electron
events were released during or after, but never simultaneously with the
onset of type II bursts and CMEs. The time delay between the type II
burst onset and the release of the mildly relativistic electrons is in
the range of 11.5-45 min; (2) that the mildly relativistic electrons
were released rather at the end of SA type III bursts or somewhat
later; (3) that the mildly relativistic electrons were released when
the associated type II burst and the CME reached a certain height
(h ~ 1-4 R_s) above the photosphere. For the four events studied,
it is concluded that mildly relativistic electrons at 0.25-0.7 MeV
energies measured in the interplanetary medium from solar energetic
particle events are accelerated by coronal shock waves, commonly in
association with white-light CMEs.
---------------------------------------------------------
Title: Solar Phenomena Associated with “EIT Waves”
Authors: Biesecker, D. A.; Myers, D. C.; Thompson, B. J.; Hammer,
D. M.; Vourlidas, A.
2002ApJ...569.1009B Altcode:
In an effort to understand what an “EIT wave” is and what its causes
are, we have looked for correlations between the initiation of EIT
waves and the occurrence of other solar phenomena. An EIT wave is
a coronal disturbance, typically appearing as a diffuse brightening
propagating across the Sun. A catalog of EIT waves, covering the period
from 1997 March through 1998 June, was used in this study. For each
EIT wave, the catalog gives the heliographic location and a rating
for each wave, where the rating is determined by the reliability of
the observations. Since EIT waves are transient, coronal phenomena, we
have looked for correlations with other transient, coronal phenomena:
X-ray flares, coronal mass ejections (CMEs), and metric type II radio
bursts. An unambiguous correlation between EIT waves and CMEs has been
found. The correlation of EIT waves with flares is significantly weaker,
and EIT waves frequently are not accompanied by radio bursts. To
search for trends in the data, proxies for each of these transient
phenomena are examined. We also use the accumulated data to show the
robustness of the catalog and to reveal biases that must be accounted
for in this study.
---------------------------------------------------------
Title: Analysis of Lasco Observations of Streamer Blowout Events
Authors: Vourlidas, A.; Howard, R. A.; Morrill, J. S.; Munz, S.
2002stma.conf..201V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Correlation between Coronal and Lower Transition Region
Structures at Arcsecond Scales
Authors: Vourlidas, A.; Klimchuk, J. A.; Korendyke, C. M.; Tarbell,
T. D.; Handy, B. N.
2001ApJ...563..374V Altcode:
We compare the morphology of active region structures observed in
the 171 Å (T~9×10<SUP>5</SUP> K) and Lyα (T~2×10<SUP>4</SUP> K)
lines. The coronal data were obtained by the Transition Region and
Coronal Explorer (TRACE) in support of the Very High Angular Resolution
Ultraviolet Telescope (VAULT) sounding rocket launch, which acquired
subarcsecond resolution images of an active region in the Lyα line,
on 1999 May 7. Using a pair of calibrated, nearly simultaneous images,
we find that: (i) a very good correlation exists between the Lyα and
171 Å intensities in the TRACE moss regions, (ii) we can identify
several identical structures in some (but not all) moss areas, and
(iii) the correlations are greatly reduced at the footpoints of the
171 Å large-scale loops. We derive a lower limit for the Lyα emission
measure, under the assumption of effectively optically thin emission,
and compare it to the 171 Å emission measure. As in previous studies,
we find an excess of Lyα material compared to the amount expected
for a thermal conduction-dominated corona-chromosphere transition
region, even for structures that appear to be identical in the two
wavelengths. This result implies that some other mechanism besides
classical heat conduction from the corona must contribute to the
observed Lyα intensities. The observations do not support the idea
of a physically distinct cool loop component within active regions.
---------------------------------------------------------
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: Tracing shock waves from the corona to 1 AU: Type II radio
emission and relationship with CMEs
Authors: Leblanc, Yolande; Dulk, George A.; Vourlidas, Angelos;
Bougeret, Jean-Louis
2001JGR...10625301L Altcode:
We report on 10 type II bursts observed with ground-based spectrographs
in the meter-decameter range, and with the Radio and Plasma Wave
Investigation on the Wind spacecraft from 13.8 to 0.01 MHz. We have
selected events with contemporaneous observations of flares and
of coronal mass ejections (CMEs) by Large-Angle and Spectrometric
Coronagraph (LASCO) telescopes. We trace the history of each event from
the time of the impulsive phase of the flare, the CME liftoff time, and
the start time of the radio bursts. We derive the speed of the type II
shock by using a coronal/solar wind density model, and the height-time
progression is compared with that of the CME as observed in the plane of
the sky and then converted into the radial direction. For most events
a shock at 1 AU was observed in situ. The results show the following:
(1) All type II bursts occurred within 2 or 3 min of the impulsive
phase of a flare. (2) The speeds of the disturbances from the time
of the flares to the time of the shocks at 1 AU were very similar to
the speeds of the type II-emitting shocks; they were in the range of
600 to 1300 kms<SUP>-1</SUP>. (3) When the type II burst was observed
far out in the solar wind, the progression of the type II source had
about the same speed in the solar wind as in the corona. (4) The CME
liftoffs were before the flares and the type II bursts by 1-24 min
for most of the selected events. As a consequence, in the corona,
the type II bursts, being behind the fronts of the CMEs, are usually
blast waves. (5) When a shock and CME material are observed at 1 AU,
the time of arrival implies a deceleration of the CME in the solar wind,
as is observed in the LASCO data. (6) Somewhere in the solar wind the
shocks very likely become piston-driven, related to the CME.
---------------------------------------------------------
Title: Coronal Mass Ejection of 2000 July 14 Flare Event: Imaging
from Near-Sun to Earth Environment
Authors: Manoharan, P. K.; Tokumaru, M.; Pick, M.; Subramanian,
P.; Ipavich, F. M.; Schenk, K.; Kaiser, M. L.; Lepping, R. P.;
Vourlidas, A.
2001ApJ...559.1180M Altcode:
We report the results of our investigation of interplanetary effects
caused by the large solar flare (X5.7/3B) that occurred on 2000
July 14. In association with this event a bright, fast, halo coronal
mass ejection (CME) was observed. The analysis of multiwavelength,
high-cadence images obtained from the Nançay Radioheliograph shows
the on-disk signatures of the initiation of the CME at low-coronal
heights, <=2 R<SUB>solar</SUB>. The formation of the CME inferred
from the radio data indicates a nearly developed halo at the low
corona. The white-light images and CME follow-up measurements in the
interplanetary medium also show, in agreement with the radio data,
the propagation of the fully developed halo CME. The inference on
the consequences of the CME in the inner heliosphere is from the
interplanetary scintillation (IPS) observations obtained with the
Ooty Radio Telescope and multiantenna system at the Solar-Terrestrial
Environment Laboratory. Scintillation measurements at Ooty on a grid
of a large number of radio sources provided an opportunity to image
the disturbance associated with the CME at different distances from
the Sun before its arrival at the near-Earth space. The scintillation
data in particular also played a crucial role in understanding the
radial evolution of the speed of the CME in the inner heliosphere. The
“speed-distance” plot indicates a two-level deceleration: (1) a low
decline in speed at distances within or about 100 solar radii and
(2) a rapid decrease at larger distances from the Sun. The linear
increase in the size of the CME with radial distance is also briefly
discussed. The expansion of the CME, formation of the halo in the low
corona, and its speed history in the interplanetary medium suggest a
driving energy, which is likely supplied by the twisted magnetic flux
rope system associated with the CME.
---------------------------------------------------------
Title: The Coronal Mass Ejection of 1998 April 20: Direct Imaging
at Radio Wavelengths
Authors: Bastian, T. S.; Pick, M.; Kerdraon, A.; Maia, D.; Vourlidas,
A.
2001ApJ...558L..65B Altcode:
We observed the fast coronal mass ejection (CME) of 1998 April 20
with the radioheliograph at Nançay, France, between 164 and 432
MHz. Spectroscopic data were obtained between 40 and 800 MHz by the
spectrometer at Tremsdorf, Germany, and between 20 kHz and 14 MHz
with the WAVES instrument on board the Wind spacecraft. Energetic
particle data were obtained from the Wind 3D Plasma and Energetic
Particle experiment. The CME was observed in white light by the
Large-Angle Spectrometric COronagraph experiment on board the Solar and
Heliospheric Observatory spacecraft. For the first time, the expanding
CME loops are imaged directly at radio wavelengths. We show that the
radio-emitting CME loops are the result of nonthermal synchrotron
emission from electrons with energies of ~0.5-5 MeV interacting
with magnetic fields of ~0.1 to a few gauss. They appear nearly
simultaneously with the onset of an associated type II radio burst,
shock-accelerated type III radio bursts, and the initiation of a solar
energetic particle event. We suggest possible sources of the energetic
electrons responsible for this “radio CME” and point out diagnostic
uses for synchrotron emission from CME loops.
---------------------------------------------------------
Title: Determination of three-dimensional structure of coronal
streamers and relationship to the solar magnetic field
Authors: Liewer, P. C.; Hall, J. R.; De Jong, M.; Socker, D. G.;
Howard, R. A.; Crane, P. C.; Reiser, P.; Rich, N.; Vourlidas, A.
2001JGR...10615903L Altcode:
We have determined the location, in three dimensions, of eight
quasi-stable coronal “streamers” from an analysis of Solar
and Heliospheric Observatory (SOHO) Large-Angle and Spectrometric
Coronagraph images acquired over approximately one solar rotation. We
use the locations to attempt to determine the solar origin of the
streamers. Comparison of the streamers' locations (longitude and
latitude at the R~2.5R<SUB>S</SUB> source surface) with that of the
current sheet computed from a potential source surface model show
that all of the streamers lie in or near the heliospheric current
sheet. We assume that the streamers coincide with magnetic field lines
and use a potential source surface magnetic model to map the location
of the streamers from the source surface (R~2.5R<SUB>S</SUB>) to the
photosphere. We find that many of the streamers are associated with
strong magnetic field active regions. When a streamer and its associated
active region are visible simultaneously, the active region is seen
to be bright in the SOHO extreme ultraviolet imaging telescope (EIT)
EUV full disk images. This, and other evidence, leads us to conclude
that many of the bright streamers are the result of scattering from
regions of enhanced density associated with active region outflow,
and not a result of line-of-sight viewing through folds in a warped
current sheet with uniform density.
---------------------------------------------------------
Title: SOHO Observations of a Coronal Mass Ejection
Authors: Akmal, Arya; Raymond, John C.; Vourlidas, Angelos; Thompson,
Barbara; Ciaravella, A.; Ko, Y. -K.; Uzzo, M.; Wu, R.
2001ApJ...553..922A Altcode:
We describe a coronal mass ejection (CME) observed on 1999 April 23 by
the Ultraviolet Coronagraph Spectrometer (UVCS), the Extreme-Ultraviolet
Imaging Telescope (EIT), and the Large-Angle and Spectrometric
Coronagraphs (LASCO) aboard the Solar and Heliospheric Observatory
(SOHO). In addition to the O VI and C III lines typical of UVCS spectra
of CMEs, this 480 km s<SUP>-1</SUP> CME exhibits the forbidden and
intercombination lines of O V at λλ1213.8 and 1218.4. The relative
intensities of the O V lines represent an accurate electron density
diagnostic not generally available at 3.5 R<SUB>solar</SUB>. By
combining the density with the column density derived from LASCO,
we obtain the emission measure of the ejected gas. With the help
of models of the temperature and time-dependent ionization state of
the expanding gas, we determine a range of heating rates required to
account for the UV emission lines. The total thermal energy deposited
as the gas travels to 3.5 R<SUB>solar</SUB> is comparable to the
kinetic and gravitational potential energies. We note a core of colder
material radiating in C III, surrounded by hotter material radiating
in the O V and O VI lines. This concentration of the coolest material
into small regions may be a common feature of CMEs. This event thus
represents a unique opportunity to describe the morphology of a CME,
and to characterize its plasma parameters.
---------------------------------------------------------
Title: High-resolution Imaging of the Upper Solar Chromosphere:
First Light Performance of the Very-high-Resolution Advanced
ULtraviolet Telescope
Authors: Korendyke, C. M.; Vourlidas, A.; Cook, J. W.; Dere, K. P.;
Howard, R. A.; Morrill, J. S.; Moses, J. D.; Moulton, N. E.; Socker,
D. G.
2001SoPh..200...63K Altcode:
The Very-high-resolution Advanced ULtraviolet Telescope (VAULT)
experiment was successfully launched on 7 May 1999 on a Black Brant
sounding rocket vehicle from White Sands Missile Range. The instrument
consists of a 30 cm UV diffraction limited telescope followed by a
two-grating, zero-dispersion spectroheliograph tuned to isolate the
solar Lα emission line. During the flight, the instrument successfully
obtained a series of images of the upper chromosphere with a limiting
resolution of ∼ 0.33 arc sec. The resulting observations are the
highest-resolution images of the solar atmosphere obtained from space
to date. The flight demonstrated that sub-arc second ultraviolet
images of the solar atmosphere are achievable with a high-quality,
moderate-aperture space telescope and associated optics. Herein,
we describe the payload and its in-flight performance.
---------------------------------------------------------
Title: Solar Phenomena Associated With EIT Waves
Authors: Myers, D. C.; Biesecker, D. A.; Thompson, B. J.; Vourlidas, A.
2001AGUSM..SH51B03M Altcode:
Observations with the Extreme Ultraviolet Imaging Telescope (EIT)
on SOHO revealed the existence of transient waves which appear to
propagate across the disk from a localized starting point. These EIT
waves may be the coronal counterpart of previously discovered Moreton
waves. Moreton waves have long been thought to be associated with
solar flares, though this may have been because flares are more easily
observed than other phenomena, such as Coronal Mass Ejections. EIT
waves are observed much more often than Moreton waves, though this
may also be due to detection efficiency. In this study, we hope to
gain a better understanding of EIT waves, and in particular their
initiation, through their relationship to other solar events. This
study uses a complete catalog of EIT waves observed from March, 1997
to June, 1998; a period in which 175 waves were found. For each wave,
the following ancillary data sets were examined for co-temporal and
co-spatial events: GOES X-ray Monitor, LASCO Coronagraph, and Type II
radio burst data. EIT waves are classified according to a system which
measures the reliability of the existence of the event. We investigate
the rate at which each class of EIT wave is associated with flares,
CMEs and Type II events. Data are further divided into limb and disk
events in order to correct for detection efficiency and biases. An
investigation of EUV dimmings is also included as they offer clues to
the relationship between EIT waves, flares and CME's.
---------------------------------------------------------
Title: Issues on the Morphological Studies of LASCO CMEs
Authors: Vourlidas, A.
2001AGUSM..SH42A03V Altcode:
Over the last 5 years, the phenomenon of coronal mass ejections (CMEs)
has been under intense investigation from a variety of instruments. The
correlation between remote sensing observations (CMEs) and in situ
measurements (ICMEs) remains uncertain due to the lack of coverage
between 30 Rs and the Earth. Nevertheless, there have been several
efforts to directly relate structures in CMEs and ICMEs. This approach
can be problematic, however, at least from the coronagraphic point
of view. In this talk, I will present some of the issues arising in
LASCO CME observations (morphology, evolution, sources, instrumental
restrictions) that could invalidate the assumptions for direct
correspondance between CMEs and ICMEs.
---------------------------------------------------------
Title: Ultra-High Resolution Observations of the Upper Chromosphere:
First Results From the NRL VAULT Sounding Rocket Payload
Authors: Vourlidas, A.; Korendyke, C. M.; Dere, K. P.; Klimchuk, J. A.
2001AGUSM..SP61A03V Altcode:
The Very high resolution Advanced ULtraviolet Telescope (VAULT) is
a new spectroscopic imaging instrument. The instrument was launched
on May 7, 1999 as a sounding rocket payload. The goal of the first
VAULT flight was to obtain sub-arcsecond images of the Sun in the
light of Lya (1216 Å). VAULT directly imaged an active region plage,
fliaments and the fine structures in the supergranule boundaries and
network with the unprecented spatial resolution of 0.33 arcseconds. We
present the VAULT images and the first results from the comparison of
the Lya data to observations from other instruments and in particular
with a sequence of TRACE 171 Å images taken during the VAULT flight.
---------------------------------------------------------
Title: Comparison of Type II Radio Emissions with CME Dynamics
Measured by the LASCO White-light Coronagraph
Authors: Reiner, M. J.; St. Cyr, O. C.; Vourlidas, A.; Kaiser, M. L.;
Prestage, N. P.
2001AGUSM..SH61A03R Altcode:
We compare the observed frequency drift rate of metric and decametric
type II radio emissions with the CME dynamics measured by the LASCO
coronagraph. The radio data relate to the "true" CME/shock height and
"true" CME projected liftoff time, but require knowledge of the coronal
density profile since the observed radio frequency is related to the
plasma density in the source region. The coronagraph data, on the other
hand, measure the CME projected height and liftoff time. We attempt to
determine the "true" dynamics of a CME by requiring consistency between
the radio and white-light data. The technique will be illustrated for a
CME observed on January 20, 2001 for which there were both well-defined
frequency-drifting metric and decametric type II radio emissions. On
this day there were two CMEs ejected from the sun about 2 hours apart,
with the second CME overtaking and interacting with the first. We will
also demonstrate how, in this case, the required consistency between the
radio and white-light data can indicate changes in the coronal density
profile encountered by the CME-driven shocks for these two CME events.
---------------------------------------------------------
Title: Deriving the Electron Density of the Solar Corona from the
Inversion of Total Brightness Measurements
Authors: Hayes, A. P.; Vourlidas, A.; Howard, R. A.
2001ApJ...548.1081H Altcode:
Usually, the electron density structure of the white-light solar
corona is estimated from the inversion of polarized brightness
measurements. The inversion technique was developed in the 1950s and has
remained largely unchanged since. Here, for the first time, we expand
this technique to total brightness observations to take advantage
of the extensive Large Angle and Spectrometric Coronagraphs (LASCO)
archive. We compare our technique to both theoretical coronal models and
actual observations and show that it is as robust and accurate as the
widely used polarized brightness inversion. The quantitative analysis
of white-light coronal data critically depends on the removal of the
F corona. We briefly describe an improved F corona model we derived
using the LASCO time series data.
---------------------------------------------------------
Title: In-flight performance of the Very high Angular resolution
ULtraviolet Telescope sounding rocket payload
Authors: Korendyke, Clarence M.; Vourlidas, A.; Cook, John W.; Dere,
Kenneth P.; Feldman, R.; Howard, Russell A.; Lilley, D. N.; Morrill,
Jeff S.; Moses, J. Daniel; Moulton, Norman E.; Moye, Robert W.;
Roberts, D. E.; Shepler, E. L.; Smith, J. K.; Socker, Dennis G.;
Spears, T. R.; Waymire, R. S.; Brown, Wayne E.; Tarbell, Theodore D.;
Berger, Tom; Handy, Brian N.
2000SPIE.4139..340K Altcode:
The Very high Angular Resolution ULtraviolet Telescope experiment was
successfully launched on May 7, 1999 on a Black Brant sounding rocket
vehicle from White Sands Missile Range. The instrument consists of a
30 cm UV diffraction limited telescope followed by a double grating
spectroheliograph tuned to isolate the solar Lyman (alpha) emission
line. During the flight, the instrument successfully obtained a series
of images of the upper chromosphere with a limiting resolution of
approximately 0.33 arc-seconds. The resulting observations are the
highest resolution images of the solar atmosphere obtained from space
to date. The flight demonstrated that subarc-second ultraviolet images
of the solar atmosphere are achievable with a high quality, moderate
aperture space telescope and associated optics. Herein, we describe
the payload and its in- flight performance.
---------------------------------------------------------
Title: Flare- and coronal mass ejection (CME)-associated type II
bursts and related radio emissions
Authors: Leblanc, Yolande; Dulk, George A.; Vourlidas, Angelos;
Bougeret, Jean-Louis
2000JGR...10518225L Altcode:
We report on two events that occurred within 6 hours of each other on
November 3, 1997. They were observed with ground-based spectrographs
in the meter to decameter range and with the WAVES experiment on the
Wind spacecraft at longer wavelengths. Complementary observations
were made with Extreme Ultraviolet Imaging Telescope (EIT) and
Large Angle and Spectrometric Coronagraph (LASCO) experiments on the
Solar and Heliospheric Observatory (SOHO). The two events are very
similar in many ways: both consist of type III bursts, type II shocks,
shock-accelerated type III bursts proceeding from the type II to low
frequencies, and type IV continuum. Flares and coronal mass ejections
(CMEs) are associated with the two events. We trace the history of
the two events from the time of the impulsive phase of the flare,
which is coincident with the start time of the radio bursts and 10 to
30 min after the CME liftoff from the Sun. We derive the height-time
progression of the type II shocks by using a coronal-solar wind density
model and compare it with the progression of the CME in the plane of
the sky. The results show that the speeds of the type II shocks in the
low corona were high, 900-950 km s<SUP>-1</SUP>. Then, at a height
of ~2R<SUB>S</SUB>, the fast shocks decelerate and become slower
shocks, <~380 km s<SUP>-1</SUP>. We discuss (1) the relationship
between these type II shocks, flares and CMEs, including the apparent
deceleration of the type II shocks, (2) the hypotheses of blast wave
versus piston-driven shocks, (3) the acceleration of electrons at the
shock front producing the shock-accelerated type III bursts, and (4)
the acceleration of electrons that become trapped in the expanding
loops of the CME and emit type IV continuum.
---------------------------------------------------------
Title: Simultaneous SOHO and Ground-Based Observations of a Large
Eruptive Prominence and Coronal Mass Ejection
Authors: Plunkett, S. P.; Vourlidas, A.; Šimberová, S.; Karlický,
M.; Kotrč, P.; Heinzel, P.; Kupryakov, Yu. A.; Guo, W. P.; Wu, S. T.
2000SoPh..194..371P Altcode:
Coronal mass ejections (CMEs) are frequently associated with
erupting prominences near the solar surface. A spectacular eruption
of the southern polar crown prominence was observed on 2 June 1998,
accompanied by a CME that was well-observed by the LASCO coronagraphs
on SOHO. The prominence was observed in its quiescent state and was
followed throughout its eruption by the SOHO EIT and later by LASCO
as the bright, twisted core of the CME. Ground-based Hα observations
of the prominence were obtained at the Ondřejov Observatory in the
Czech Republic. A great deal of fine structure was observed within
the prominence as it erupted. The prominence motion was found to
rotate about its axis as it moved outward. The CME contained a helical
structure that is consistent with the ejection of a magnetic flux rope
from the Sun. Similar structures have been observed by LASCO in many
other CMEs. The relationship of the flux rope to other structures in
the CME is often not clear. In this event, the prominence clearly lies
near the trailing edge of the structure identified as a flux rope. This
structure can be observed from the onset of the CME in the low corona
all the way out to the edge of the LASCO field of view. The initiation
and evolution of the CME are modeled using a fully self-consistent,
3D axisymmetric, MHD code.
---------------------------------------------------------
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: Large-Angle Spectrometric Coronagraph Measurements of the
Energetics of Coronal Mass Ejections
Authors: Vourlidas, A.; Subramanian, P.; Dere, K. P.; Howard, R. A.
2000ApJ...534..456V Altcode:
We examine the energetics of coronal mass ejections (CMEs) with data
from the large-angle spectrometric coronagraphs (LASCO) on SOHO. The
LASCO observations provide fairly direct measurements of the mass,
velocity, and dimensions of CMEs. Using these basic measurements,
we determine the potential and kinetic energies and their evolution
for several CMEs that exhibit flux-rope morphologies. Assuming flux
conservation, we use observations of the magnetic flux in a variety
of magnetic clouds near the Earth to determine the magnetic flux and
magnetic energy in CMEs near the Sun. We find that the potential and
kinetic energies increase at the expense of the magnetic energy as
the CME moves out, keeping the total energy roughly constant. This
demonstrates that flux-rope CMEs are magnetically driven. Furthermore,
since their total energy is constant, the flux-rope parts of the CMEs
can be considered a closed system above ~2 R<SUB>solar</SUB>.
---------------------------------------------------------
Title: Determination of Three-Dimensional Geometry of Coronal
Streamers using LASCO Data
Authors: Liewer, P. C.; Hall, J. R.; De Jong, E. M.; Socker, D. G.;
Howard, R. A.; Crane, P.; Reiser, P.; Rich, N. B.; Vourlidas, A.
2000SPD....31.1501L Altcode: 2000BAAS...32..848L
The structure of the outer corona as revealed by the SOHO/LASCO
coronagraphs is dominated by bright ray-like streamers which may
persist for days or weeks. From analysis of approximately 1 month of
SOHO/LASCO C3 coronagraph images, we have determined in three-dimensions
the locations of 8 bright ray-like radial “streamers" seen in the
outer corona (R > 3 R<SUB>SUN</SUB>). Comparison of the steamers'
locations (longitude and latitude at the source surface) with that
of the current sheet as computed from a potential-source-surface
model shows that all of the streamers lie in or near the heliospheric
current sheet. The potential-source-surface magnetic model is used to
map the locations of the streamers from the source surface (R = 2.5
R<SUB>SUN</SUB>) to the photosphere. We find that many of the streamers
are associated with strong magnetic field active regions. When the
streamers and active region are both visible, the active regions are
seen to be bright in the SOHO/EIT data. From a previous analysis of
SOHO/LASCO C2&C3 images near solar minimum, Wang et al. (1997)
found that the bright streamers seen in the coronagraph images were
the results of line-of-sight viewing of a convoluted or "folded"
uniform density heliospheric plasma sheet and not a result of coronal
density enhancements. In our analysis of a more active SUN, not all of
the steamers lie at folds in the current sheet. This, along with their
associations with active regions, leads us to conclude that some of the
bright streamers are apparently the result of scattering from regions
of enhanced density, associated with active region outflow, and not
a result of line-of-sight viewing, consistent with the suggestion by
Wang et al. (2000). Wang, Y.-M. et al., Ap. J. 485, 875 (1997). Wang,
Y.-M., Sheeley, N. R., Jr., and Rich, N. B., Geophys. Res. Lett. 27,
149 (2000).
---------------------------------------------------------
Title: Model for Radio Thermal Emission at 328 and 1446 MHz from
EUV Observations
Authors: Cook, J. W.; Newmark, J. S.; Vourlidas, A.
2000SPD....31.0221C Altcode: 2000BAAS...32..814C
We have modeled the contribution to solar radio emission at 328 and
1446 MHz from free-free thermal bremsstrahlung emission, using a full
disk differential emission measure (DEM) map of the Sun. The DEM map
is produced from four EUV images (171 A, 195 A, 284 A, and 304 A)
for a selected day from the EIT instrument on the SOHO satellite,
using a method developed previously by Cook, Newmark, and Moses. The
EIT instrument images the Sun out to 1.4 R, with a pixel size of 2.6
arc sec and spatial resolution of 2 pixels. We perform the radiative
transfer calculation, determining the optical depth scale for free-free
emission and the emergent absolute intensity for each pixel in the
field-of-view using the individual DEM of that pixel, and transforming
integrals over the line-of-sight into integrals over temperature
via the DEM. We can compare our model calculation with the VLA radio
observations of Vourlidas from 1998 January 31. Our model is in good
agreement outside of active regions, where free-free emission should
truly be the dominant emission mechanism. In areas such as sunspots,
where the strong magnetic field leads to additional gyro resonance
radiation, the difference between the observed total intensity and our
calculated thermal component should be a good estimate of the nonthermal
gyro radiation. This work is supported by NASA under W-19,348 and by
the Office of Naval Research.
---------------------------------------------------------
Title: Solar Phenomena Associated With EIT Waves
Authors: Myers, D. C.; Biesecker, D. A.; Vourlidas, A.; Thompson, B. J.
2000SPD....31.0273M Altcode: 2000BAAS...32..824M
In an effort to understand what causes an "EIT wave" or what effects
an EIT wave might have, we are investigating whether EIT waves
can be associated directly with any other solar phenomena. An EIT
wave is a coronal disturbance, typically appearing as a bright rim,
observed to propagate across the Sun. Waves at the solar limb are
identified by the deflections of magnetic fields that they cause. We
have taken a working catalogue of "EIT waves" and determined what,
if any, solar phenomena are associated with each wave. We have thus
far looked for an association with GOES X-ray flares and with LASCO
coronal mass ejections. This poster shows the work accomplished thus
far, in particular, that there is a strong association with GOES flux
increases and that waves with a higher quality rating tend to have
a higher GOES flux level. We also plan to determine if there is an
association with radio transients, particularly type II events. The
EIT wave catalogue was compiled by examining EIT difference images of
the Sun from the start of higher cadence images (24-March-1997). Each
wave is classified by a quality rating from 0 to 6. The quality rating
describes a confidence level that the given times contain an EIT wave,
with 0 being the lowest certainty and 6 the highest. The catalogue of
EIT waves, and this study, are still being expanded and will eventually
encompass all EIT waves observed with a high image cadence from 1996
through 1998.
---------------------------------------------------------
Title: Comets C/1999 J6, C/1999 U5, C/1999 W1, C/1999 Y3
Authors: Biesecker, D. A.; Hammer, D.; Marsden, B. G.; Oates, M.;
Vourlidas, A.
2000IAUC.7386....1B Altcode: 2000IAUC.7386Q...1B
Further to IAUC 7376 and 7383, D. A. Biesecker reports observations
(measures by D. Hammer and himself, reductions by B. G. Marsden)
of four more comets seen in 1999 SOHO data, all but C/1999 J6 being
presumed Kreutz sungrazers. Comets C/1999 J6 (visible in both C2 and
C3 data) and C/1999 U5 (visible in only the C3 telescope) show no
tail. However, C/1999 W1 and C/1999 Y3, which were both visible with
only the C2 telescope, did show tails. Selected V magnitudes from
Biesecker for C/1999 J6: May 10.750 UT, 8.1; 10.833, 7.3; 10.935,
6.5; 11.088, 5.9; 11.269, 5.5, 11.338, 4.9; 11.462, 5.1. Comet C/1999
J6 was first noted by M. Oates via the SOHO Web page; C/1999 U5 and
C/1999 W1 were discovered by Biesecker, and C/1999 Y3 was discovered
by A. Vourlidas of the SOHO team. Full astrometry and orbital elements
appear on the MPECs indicated below. 1999 UT R.A. (2000) Decl. MPEC
Comet May 10.726 3 05.0 +15 48 2000-F30 C/1999 J6 Oct. 31.495 14 06.8
-17 27 2000-F31 C/1999 U5 Nov. 23.188 15 55.1 -22 06 2000-F32 C/1999
W1 Dec. 21.496 18 04.0 -25 03 2000-F33 C/1999 Y3
---------------------------------------------------------
Title: Sungrazing Comets
Authors: Hammer, D.; Marsden, B. G.; Lewis, D.; Vourlidas, A.; Schenk,
K.; Lovejoy, T.; Biesecker, D. A.
2000IAUC.7376....2H Altcode: 2000IAUC.7376R...1H; 2000IAUC.7376B...1H
Biesecker also reports observations (measures by D. Hammer and himself,
reductions by B. G. Marsden) of some older Kreutz sungrazing comets seen
in SOHO C3 data; full astrometry and parabolic orbital elements appear
on the MPECs indicated below. Comet C/1999 O2 developed a short tail,
C/1999 O3 had a short tail evident, C/1999 Q3 showed a tail, and C/1999
R3 showed evidence for a tail; the other four comets showed no evident
tail. Comets C/1999 O2 and C/1999 P4 were discovered by D. Lewis,
C/1999 P5 by A. Vourlidas, C/1999 Q2 and C/1999 R3 by K. Schenk,
and C/1999 Q3 by Biesecker, while comets C/1999 O3 and C/1999 Q1 were
first noted by T. Lovejoy via the SOHO Web page. 1999 UT R.A. (2000)
Decl. MPEC Comet July 21.888 7 49.5 +18 13 2000-E28 C/1999 O2 31.446 8
22.4 +16 25 2000-E29 C/1999 O3 Aug. 9.429 8 58.2 +14 39 2000-E30 C/1999
P4 12.138 9 06.3 +13 30 2000-E31 C/1999 P5 23.821 9 51.1 +10 39 2000-E32
C/1999 Q1 24.471 9 54.2 +10 11 2000-E33 C/1999 Q2 30.738 10 10.4 +
7 49 2000-E34 C/1999 Q3 Sept. 4.863 10 25.5 + 5 40 2000-E35 C/1999 R3
---------------------------------------------------------
Title: COMET C/19
Authors: Vourlidas, A.; Hammer, D.; Biesecker, D.; Marsden, B. G.
2000MPEC....E...31V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: COMET C/19
Authors: Vourlidas, A.; Hammer, D.; Biesecker, D.; Marsden, B. G.
2000MPEC....F...33V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: LASCO and EIT Observations of Coronal Mass Ejections
Authors: Dere, K. P.; Vourlidas, A.; Subramanian, Prasad
2000astro.ph..2061D Altcode:
We present a brief overview of LASCO and EIT observations of CMEs. We
discuss CME energetics, the relation of CMEs to streamers and conclude
with some insights into the source regions of CMEs.
---------------------------------------------------------
Title: Development of Coronal Mass Ejections: Radio Shock Signatures
Authors: Maia, Dalmiro; Pick, Monique; Vourlidas, Angelos; Howard,
Russel
2000ApJ...528L..49M Altcode:
We present observational imaging evidence for the existence of metric
radio bursts closely associated with the front edge of coronal mass
ejections (CMEs). These radio bursts drift in frequency similarly to
type II bursts. They are weak and usually go undetected on spectrograph
data. We find the same measured projected velocity for the displacement
of, respectively, the radio source (when observed at two or more
frequencies) and the CME leading edge. The position of the emitting
source coincides with the CME leading edge. Among the events analyzed,
the fastest of them, with a velocity over 1400 km s<SUP>-1</SUP>,
was associated with interplanetary type II bursts.
---------------------------------------------------------
Title: Coronal Mass Ejections and Large Scale Structure of the Corona
Authors: Maia, D.; Vourlidas, A.; Pick, M.; Howard, R.; Schwenn, R.;
Lamy, P.
2000AdSpR..25.1843M Altcode:
A comparative study of two events accompanied by both a flare and a
CME has been performed. The data analysis has been made by comparing
the observations of the LASCO/SOHO coronagraphs with those of the
Nancay radioheliograph. The observations show a clear connection
between coronal green and red line transient activity, burst radio
emission and the CME development which is due to successive loop
interactions. Signatures of these interactions are given by the radio
emission. One can identify successive sequences in the evolution
of the coronal restructuring leading to the full development of the
CME. Identification and timing of these sequences result from the radio
emission analysis. For flare-CME events , the evolution takes place
in the low corona and is extremely fast of the order, on a few minutes
---------------------------------------------------------
Title: LASCO/Nancay Observations of the CME on 20 April 1998: White
Light Sources of Type-II Radio Emission
Authors: Vourlidas, A.; Maia, D.; Pick, M.; Howard, R. A.
1999ESASP.448.1003V Altcode: 1999ESPM....9.1003V; 1999mfsp.conf.1003V
No abstract at ADS
---------------------------------------------------------
Title: LASCO Measurements of the Energetics of Coronal Mass Ejections
Authors: Vourlidas, Angelos; Subramanian, Prasad; Dere, K. P.; Howard,
R. A.
1999astro.ph.12069V Altcode:
We examine the energetics of Coronal Mass Ejections (CMEs) with data
from the LASCO coronagraphs on SOHO. The LASCO observations provide
fairly direct measurements of the mass, velocity and dimensions of
CMEs. Using these basic measurements, we determine the potential and
kinetic energies and their evolution for several CMEs that exhibit a
flux-rope morphology. Assuming flux conservation, we use observations
of the magnetic flux in a variety of magnetic clouds near the Earth
to determine the magnetic flux and magnetic energy in CMEs near the
Sun. We find that the potential and kinetic energies increase at the
expense of the magnetic energy as the CME moves out, keeping the total
energy roughly constant. This demonstrates that flux rope CMEs are
magnetically driven. Furthermore, since their total energy is constant,
the flux rope parts of the CMEs can be considered to be a closed system
above $\sim$ 2 $R_{\sun}$.
---------------------------------------------------------
Title: Calibrated H I Lyman α Observations with TRACE
Authors: Handy, B. N.; Tarbell, T. D.; Wolfson, C. J.; Korendyke,
C. M.; Vourlidas, A.
1999SoPh..190..351H Altcode:
Since shortly after launch in April 1998, the Transition Region and
Coronal Explorer (TRACE) observatory has amassed a collection of H
i Lα (1216 Å) observations of the Sun that have been not only of
high spatial and temporal resolution, but also span a duration in
time never before achieved. The Lα images produced by TRACE are,
however, composed of not only the desired line emission, but also
local ultraviolet continuum and longer wavelength contamination. This
contamination has frustrated attempts to interpret TRACE observations
in H i Lα. The Very Advanced Ultraviolet Telescope (VAULT) sounding
rocket payload was launched from White Sands Missile range 7 May 1999
at 20:00 UT. The VAULT telescope for this flight was a dedicated H i
Lα imaging spectroheliograph. We use TRACE observations in the 1216
Å and 1600 Å channels along with observations from the VAULT flight
to develop a method for removing UV continuum and longer wavelength
contamination from TRACE Lα images.
---------------------------------------------------------
Title: Development Of Coronal Mass Ejections : Radio Shock Signatures
Authors: Maia, D.; Pick, M.; Vourlidas, A.
1999ESASP.446..473M Altcode: 1999soho....8..473M
This study presents joint observations of Coronal Mass Ejections
from the EIT telescope and LASCO coronagraphs on SOHO and from the
Nan ay Radioheliograph. The contribution of radio observations to the
present knowledge of origin and development of CMEs will be reviewed. In
particular, this study will focuss on the following points : - The radio
detection in the corona of the leading edge of CMEs and the association
with shocks ; - The identification of successive sequences leading to
the full development of CMEs and the timing of these sequences. The
radio detection of coronal waves- The radio counterpart seen in
projection over the solar disk of halo CME events.
---------------------------------------------------------
Title: Sungrazing Comets
Authors: Biesecker, D. A.; Marsden, B. G.; Vourlidas, A.
1999IAUC.7204....1B Altcode: 1999IAUC.7204A...1B; 1999IAUC.7204Q...1B
D. A. Biesecker, SM&A Corporation and Goddard Space Flight Center,
reports observations of three more apparent Kreutz sungrazing comets
found in images taken with both the C2 and C3 coronagraphs aboard
SOHO. Astrometric measurements made by Biesecker (and reduced by
B. G. Marsden), together with orbital elements by Marsden, are given on
MPECs 1999-M08 (C/1999 K9), 1999-M09 (C/1999 K10), and 1999-M10 (C/1999
L4). 1999 UT R.A. (2000) Decl. Comet May 23.698 4 03.8 +18 13 C/1999
K9 31.698 4 33.4 +19 47 C/1999 K10 June 1.448 4 33.9 +19 37 C/1999
L4 Comets C/1999 K9 and C/1999 L4 were discovered by A. Vourlidas;
C/1999 K10 was discovered by Biesecker. No tail is evident for C/1999
K9 on images obtained during May 23-24. No tail is visible in the May
31-June 1 images of C/1999 K10; this object was extremely faint in the
C3 images. A faint tail is visible is visible in the June 1 images of
C/1999 L4, which was again very difficult to measure in the C3 frames.
---------------------------------------------------------
Title: Large-scale structure and coronal dynamics from joint radio,
SOHO/EIT and coronagraph observations
Authors: Pick, M.; Maia, D.; Vourlidas, A.; Benz, A. O.; Howard, R.;
Thompson, B. J.
1999AIPC..471..649P Altcode: 1999sowi.conf..649P
This study presents joint observations of an `halo' coronal mass
ejection from the EIT telescope and LASCO coronagraphs on SOHO, from
the Nançay Radioheliograph (NRH) and the Zurich ETH radiospectrograph
(Phoenix-2). This event includes different manifestations: a coronal
wave and a dimming region detected by EIT, a CME showing bright discrete
portions above east and west limbs. Radio signatures of all these
manifestations are found and the interpretation is briefly discussed.
---------------------------------------------------------
Title: Radio signatures of a fast coronal mass ejection development
on November 6, 1997
Authors: Maia, D.; Vourlidas, A.; Pick, M.; Howard, R.; Schwenn, R.;
Magalhães, A.
1999JGR...10412507M Altcode:
The Oporto radiospectrograph and the Nançay radioheliograph recorded
a radio event on November 6, 1997, closely related in time with a flare
on National Oceanic and Atmospheric Administration (NOAA) active region
8100. At the beginning of the event the radio sources are located on a
rather small volume in the vicinity of the flare site. In a timescale of
only a few minutes the radio emission sites spread over a large volume
in the corona, covering a range of 100° in heliolatitude. During the
period of the radio event the Large Angle and Spectrometric Coronagraph
(LASCO) on board the Solar and Heliospheric Observatory (SOHO) observed
an extremely fast coronal mass ejection (CME), with a velocity around
2000 kms<SUP>-1</SUP>. This CME presents the particularity of having
a fast lateral expansion, giving it a shape reminiscent of a “coat
hanger.” There is a very good association between the latitudinal
extent and time development of the CME seen by LASCO and the radio
sources recorded by the radio instruments.
---------------------------------------------------------
Title: LASCO Measurements of Erupting Flux Ropes
Authors: Vourlidas, A.; Subramanian, P.; Dere, K. P.; Howard, R. A.
1999AAS...19410103V Altcode: 1999BAAS...31..998V
It is commonly assumed that Coronal Mass Ejections from the Sun are
magnetically driven. We address this question with data from the LASCO
coronagraphs aboard the SOHO spacecraft. These observations provide
fairly direct measurements of the energetics of CMEs. We determine
the kinetic and gravitational energies and their evolution for several
helical CMEs. We estimate the evolution of the magnetic energy based on
the conservation of magnetic flux and observations of magnetic clouds
near the Earth. From the magnitude and variation of these three forms
of energy, we examine the energetics of CMEs from the perspective that
they are driven through their internal magnetic energy.
---------------------------------------------------------
Title: The Increase in Mass of CMEs due to Propagation
Authors: Howard, R. A.; Dere, K. P.; Sheeley, N. R., Jr.; Subramanian,
P.; Vourlidas, A.; Wang, D.
1999AAS...19410102H Altcode: 1999BAAS...31..998H
The question we would like to address is whether coronal mass ejections
snowplow ambient material. Some of the CMEs observed by the LASCO
coronagraph on SOHO have a clearly defined loop-like front, meaning
that the trailing edge of the front can be clearly defined. We measure
the mass in the front of the CME in this subclass. We find that for
some of the events, the mass in the leading edge increases, implying
that the CME is indeed "snowplowing" ambient material. If there is a
significant increase in mass, then the CME frontal speed might decrease
to conserve momentum. We estimate the amount of ambient material,
using a model of coronal densities, and find that it is consistent
with the mass increase. We can also estimate the height in the corona,
below the occulting disk, from where the original material in the CME
is released. These concepts as well as conditions for when the mass
increases will be discussed.
---------------------------------------------------------
Title: IDL-based Database of Solar Active Regions
Authors: Gary, D. E.; Grechnev, V. V.; Shabarova, L. V.; Vourlidas,
A.; Nishio, M.
1999ASPC..172..391G Altcode: 1999adass...8..391G
A database on solar active regions has been implemented in IDL
(Interactive Data Language). The observational parameters of the regions
are stored in a multi-level structure array that is distributed as a
standard IDL save file. Convenient access to the data is provided by an
application equipped with a graphical user interface (GUI). A variety
of search modes are implemented. Full-disk 17 GHz radio maps produced
by the Nobeyama Radioheliograph provide the basis for the database.
---------------------------------------------------------
Title: Nonthermal Radio Signatures of Coronal Disturbances with and
without Coronal Mass Ejections
Authors: Aurass, H.; Vourlidas, A.; Andrews, M. D.; Thompson, B. J.;
Howard, R. H.; Mann, G.
1999ApJ...511..451A Altcode:
This study presents data on two events from the Extreme-UV Imaging
Telescope (EIT) and the Large Angle and Spectroscopic Coronagraph
instruments (C1, C2, and C3), Geostationary Operational Environmental
Satellite (GOES) soft X-ray data, and 40-800 MHz radio spectra of the
Astrophysical Institute Potsdam. At first glance, the two events appear
similar. However, one event decays after a flare-related ejection of
cold and hot matter into the lower corona causing only brightness
changes in EIT and C1, while the other event marks the onset of a
coronal mass ejection (CME) that propagates with a leading-edge speed
of ~530 km s<SUP>-1</SUP> between 2 and 30 R<SUB>solar</SUB>. The
radio data reveal two differences between the CME and non-CME events:
(1) a characteristic faint type III burst group in the time interval
with the first clearly CME-related structural change in the coronagraph
images and (2) a continuum emission with a frequency drift during the
passage of the CME matter through the C1 field of view. Furthermore,
we show that the radio spectral data can provide essential information
on the timing of the early stages of CME formation and the initial
mass motions associated with the ejection.
---------------------------------------------------------
Title: Comet C/1998 K7 (SOHO)
Authors: Vourlidas, A.; Gregory, S.; Biesecker, D. A.; Williams,
G. V.; Marsden, B. G.
1999MPEC....A...24V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Near-Sun Comets
Authors: Biesecker, D.; Williams, G. V.; Schenk, K.; Stezelberger,
S.; Vourlidas, A.
1998IAUC.6952....1B Altcode: 1998IAUC.6952Q...1B; 1998IAUC.6952A...1B
D. Biesecker, Space Applications Corporation, NASA Goddard Space Flight
Center, reports provisional data (reduced by G. V. Williams) on nine
more comets found in C3 coronagraphic data. Except for the first comet
(2 deg from the sun at its closest with maximum tail length 0.5 deg),
they appear to be Kreutz sungrazers and were also observed by C2. Orbit
computations are deferred until more definitive astrometry can be
done. Comets X/1998 G3, G4, K10 and K11 (these last two having 0.5-deg
tails and being among the brightest Kreutz comets, with K11 following
K10 along the Kreutz track 4 hr later) were discovered by K. Schenk; H2
and K9 (the latter not showing a tail) by S. Stezelberger; J2 and K8 by
Biesecker; and K7 by A. Vourlidas. 1998 UT R.A. (2000) Decl. Apr. 10.526
1 42.2 +12 06 X/1998 G3 10.526 1 29.9 + 5 43 X/1998 G4 29.113 2 45.5
+11 31 X/1998 H2 May 10.323 3 21.5 +14 38 X/1998 J2 16.406 3 42.0 +16
05 X/1998 K7 19.240 3 49.7 +17 07 X/1998 K8 27.742 4 23.0 +17 53 X/1998
K9 31.073 4 37.0 +17 27 X/1998 K10 30.706 4 39.1 +16 50 X/1998 K11
---------------------------------------------------------
Title: The November 6, 1997 event: Radio signatures of the CME
development
Authors: Maia, D.; Vourlidas, A.; Pick, M.; Howard, R.; Schwenn, R.;
Magalhaes, A.; Carneiro, J.; Agostinho, R.
1998cee..workE..57M Altcode:
The analysis of the November 6, 1997 event has taken advantage of the
new capabilities of the OPorto Radiospectrograph and of the Nanccay
Radioheliograph. The evolution of this event shows successive phases
in time scales of a fraction of a second. It is shown that the CME
observed by the LASCO/SOHO coronograph is the result of successive
interactions of multiple loop systems which occur over a latitude range
of about 100<SUP>circ</SUP>. These magnetic loop interactions lead to
the creation of several electron acceleration sites which are widely
separated in the corona. There is a close correspondance between the
evolution of the CME seen by LASCO and the extend of radio sources
seen by the radioheliograph. The association with particles detected
by in situ measurements in the interplanetary medium is also presented.
---------------------------------------------------------
Title: Solar origin of accelerated particles detected in the corona
and in the interplanetary medium
Authors: Pick, M.; Maia, D.; Howard, R.; Vourlidas, A.
1998cee..workE..58P Altcode:
We discuss the solar origin of accelerated particles detected in
the corona and in the interplanetary medium. This synthesis lies on
the study of several events which have been observed by the Nanccay
Radioheliograph and the LASCO/SOHO instrument. The in-situ measurements
of particles in the interplanetary medium have been made by ULYSSES,
WIND, ACE and SOHO.
---------------------------------------------------------
Title: Nonthermal Radio Signatures of Coronal Disturbances with and
without Mass Ejections
Authors: Aurass, H.; Vourlidas, A.; Andrews, M. D.; Thompson, B. J.;
Howard, R. H.; Mann, G.
1998cee..workE..20A Altcode:
We show that the radio signature of nonthermal electrons can be a
sensitive indicator of small scale energy release related to topological
changes in coronal magneto-plasma structures. We compare two events
using images from the Extreme-UV Imaging Telescope (EIT) and the Large
Angle and Spectroscopic Coronagraph (LASCO) instruments, GOES soft
X-ray data, and 40--800 MHz radio spectra of the AI Potsdam. At first
glance, both events appear similar. One event decays after a prominence
eruption causing only brightness changes in the EIT and C1 images. But
the other event marks the onset of a large coronal mass ejection (CME)
that propagates with a speed of ~530kms^{-1} between 2--30 R_odot. The
CME formation is accompanied by an unspectacular faint group of metric
drift bursts starting in the spectral range 170--200 MHz (at a height
1.20-1.25 R_odot) and lasts for ~3 min. During the CME lift-off,
the frequency drift of an associated type IV continuum translates to
a speed of ~90kms^{-1}. The same speed is obtained from the height
change of leading CME features in LASCO-C1. The non-CME event is
accompanied by a non-drifting continuum and lacks any type III burst
activity. We offer a number of explanations for the CME absence. Also,
in the non-CME case we show that the post-prominence eruption current
sheet can be detected in the EIT and C1 images. Its lower part appears
as a bright blob in EIT on the top of a loop arcade. The brightness
of this blob corresponds to a soft X-ray long duration event (LDE)
decay. Our study suggests that prominence eruptions and soft X-ray
LDEs are insufficient to reveal a CME.
---------------------------------------------------------
Title: The Structure of "halo" Coronal Mass Ejections
Authors: Vourlidas, A.; Howard, R. A.; Dere, K. P.; Passwaters, S. E.
1997AAS...191.7305V Altcode: 1997BAAS...29.1321V
We investigate the relation between the structure of "halo" coronal
mass ejections (CMEs) and the global coronal structure. In particular,
we compare two "halo" events which occured on October 21, 1997 and were
observed with the SoHO/LASCO coronographs at a high cadence. Although
the two CME occured at different locations on the solar disk, they
both exhibit similar morphology which appear to be influenced by the
global coronal structure. By comparing the data from the coronaraphs,
EIT and magnetograms, we will attempt to decipher the interplay between
the ejected material and the surrounding corona.
---------------------------------------------------------
Title: The Structure of the Solar Corona above Sunspots as Inferred
from Radio, X-Ray, and Magnetic Field Observations
Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J.
1997ApJ...489..403V Altcode:
We present observations of a solar active region, NOAA/USAF no. 7123,
during 1992 April 3-10. The database includes high-angular-resolution
radio, soft X-ray, magnetograph, and Hα observations. The radio
observations include VLA maps in the Stokes I and V parameters at 4.7
and 8.4 GHz. The soft X-ray observations were obtained by the Soft
X-Ray Telescope on board the Yohkoh satellite, the magnetograms were
obtained at Kitt Peak, Mt. Wilson, and Big Bear, and the Hα data were
obtained at Big Bear. <P />The lead sunspot in the active region is
studied here. In particular, the polarization properties and brightness
temperature spectrum are used to constrain the thermal structure of the
corona over the sunspot. It is found that the 4.7 GHz emission of the
sunspot is polarized in the sense of the ordinary mode, in contradiction
with simple gyroresonance models that predict that the spot should be
polarized in the sense of the extraordinary mode. We model the spectral
and temporal evolution of the polarization structure in two frequencies,
4.7 and 8.4 GHz, using gyroresonance models to fit one-dimensional
brightness temperature profiles across the spot in each polarization
and frequency. The constraints provided by the X-ray and magnetic
field observations help us to derive a qualitatively self-consistent
picture for the daily evolution of the spot. We attribute the excess
of the o-mode emission to the magnetic field configuration and to the
temperature inhomogeneities across the spot. Namely, we find that (1)
the umbral and penumbral environments are distinct, with the X-rays and
the o-mode radio emission coming from the hotter penumbral loops, while
the observed x-mode emission originates from the cooler umbral loops;
(2) there exist temperature inhomogeneities in both the radial and
vertical direction over the spot; and (3) the umbral magnetic field
remains more confined in the corona than that predicted by a dipole
model. Instead, a field configuration based on the magnetohydrostatic
equilibrium model of Low gives a better agreement with the observations.
---------------------------------------------------------
Title: Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study
Authors: Vourlidas, A.; Gary, D. E.; Shibasaki, K.
1997SPD....28.0134V Altcode: 1997BAAS...29..885V
Our statistical study is based on a compilation of the daily Nobeyama
Radioheliograph full-disk maps obtained at 17 GHz between July 1992 --
December 1994. It includes 533 active regions, 20% of which appear to
have gyroresonance cores during some part of their disk crossing. At
least one of the regions reaches coronal temperatures (T>10(6)
K) while several others show a polarization reversal at the extreme
limb. Our study indicates that the gyroresonance cores are polarized
in the sense of the x-mode and are due to s=3 (B=2024 G) and/or s=4
(B=1518 G) gyroresonance absorption in the transition region and/or
corona. We also investigate the dependence between various physical
quantities such as brightness temperature, degree of polarization,
spot area, photospheric magnetic field and heliographic longitude and
comment on the polarization reversals at the limb. A more detailed
study of individual active regions, that have been also observed with
the Owens Valley Solar Array, will follow.
---------------------------------------------------------
Title: Multiband VLA Observations of Solar Active Regions:
Implications for the Distribution of Coronal Plasma
Authors: Vourlidas, A.; Bastian, T. S.
1996ApJ...466.1039V Altcode:
We present high-quality radio observations of a solar active region
(NOAA/USAF region 5131) made by the Very Large Array in the 0.33, 1.5,
4.7, and 8.4 0Hz frequency bands. The observations were made during
the IAU-sanctioned International Solar Month on 1988 September 1 and
4. In addition to the radio maps, the database includes images from the
Solar Maximum Mission Soft X-ray Polychromator in the Fe XVII line,
photo spheric magnetograms, and Hα filtergrams. Because coverage in
only a single wavelength is available, the soft X-ray data are used for
qualitative comparisons. <P />We identify those areas of the active
region from which the radio emission is predominantly due to thermal
bremsstrahlung emission. To account for the observed four-point
radio spectra in these areas, we examine three different models,
which characterize the corona in terms of a single plasma component,
two components, and multiple components. The latter differs somewhat
from past models. In particular, we take explicit account of the
highly inhomogeneous structure of active regions through a multilayer
slab model in which the thermal distribution is constrained by the
generic form of the differential emission measure. While multicomponent
models provide the best agreement with the observations, we find that a
complete model must include both free-free and gyroresonance opacity. We
compare our radio data and model results with those resulting from
previous studies.
---------------------------------------------------------
Title: On the Peculiar Radio Polarization of a Sunspot and the
Distibution of the Coronal Plasma
Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J.
1996AAS...188.3602V Altcode: 1996BAAS...28..873V
A comprehensive set of microwave, soft x-ray and magnetic observations
of solar active region NOAA/USAF 7123 was obtained during 4--9 April,
1992. The observations show an unusual 4.7 GHz source which is polarized
in the sense of the ordinary mode over the umbra of the leading spot. A
detailed analysis of the daily radio and soft X-ray maps of the spot
indicates that (i) the umbral magnetic field is strongly confined,
(ii) the umbral and penumbral loops have distinct atmospheres and (iii)
temperature gradients may exist both radially and vertically over the
spot. A possible scenario for the temporal evolution of the spot is
also presented.
---------------------------------------------------------
Title: On the radio polarization from sunspots
Authors: Vourlidas, Angelos
1996PhDT........23V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Joint Radio and Soft X-Ray Imaging of an `Anemone' Active
Region
Authors: Vourlidas, A.; Bastian, T. S.; Nitta, N.; Aschwanden, M. J.
1996SoPh..163...99V Altcode:
The Very Large Array and the Soft X-ray Telescope (SXT) aboard the
Yohkoh satellite jointly observed the rapid growth and decay of a
so-called `anemone' active region on 3-6 April, 1992 (AR 7124). The
VLA obtained maps of the AR 7124 at 1.5, 4.7, and 8.4 GHz. In general,
discrete coronal loop systems are rarely resolved at 1.5 GHz wavelengths
because of limited brightness contrast due to optical depth effects and
wave scattering. Due to its unusual anemone-like morphology, however,
several discrete loops or loop systems are resolved by both the VLA
at 1.5 GHz and the SXT in AR 7124.
---------------------------------------------------------
Title: Active Region 7123: Its Peculiar Radio Polarization and the
Distribution of the Umbral Coronal Plasma
Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J.
1995AAS...18710105V Altcode: 1995BAAS...27.1426V
A comprehensive set of microwave and soft x-ray observations of solar
active region 7123 was obtained during 3--10 April, 1992. Here, we
present a detailed analysis of the polarized radio emission from the
sunspot-associated component of AR 7123. We use the VLA observations
at 1.5, 4.7 and 8.4 GHz, supported by the available x-ray and magnetic
data. We concentrate on understanding the 4.7 GHz o-mode polarization
over the umbra of the leading spot of AR 7123 and its variation
with aspect angle within the physical context provided by the x-ray
observations (SXT/Yohkoh) and past work on umbral atmospheres.
---------------------------------------------------------
Title: Aspect Angle Dependence of the Polarized Radio Emission from
AR 7123
Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J.; Nitta, N.
1995SPD....26..701V Altcode: 1995BAAS...27..965V
No abstract at ADS
---------------------------------------------------------
Title: Joint Radio and Soft X-ray Imaging of an “Anemone” Active
Region
Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M.; Nitta, N.
1994AAS...185.8609V Altcode: 1994BAAS...26Q1465V
The Very Large Array and the Soft X-ray Telescope aboard the Yohkoh
satellite observed the rapid growth and decay of a so-called “anemone”
active region on 3-6 April (AR 7124). In general, discrete coronal
loop systems are rarely resolved at radio wavelengths due to optical
depth effects and scattering. In the case of AR 7124, however, several
discrete loops or loop systems are resolved by both the VLA and the SXT,
probably due to its unusual “anemone”-like morphology. Furthermore,
the region exhibited a significant amount of variability, especially
on April 3, marked by many subflares and intensity changes as has been
reported in flare patrol observations. In the present study, physical
parameters derived from multiband radio and soft x-ray techniques for
discrete loops are compared. The temporal evolution of these parameters
is also examined.
---------------------------------------------------------
Title: A Multiband Study of Radio Emission from Solar Active Regions
Authors: Vourlidas, Angelos; Bastian, T. S.
1994ASPC...68..369V Altcode: 1994sare.conf..369V
No abstract at ADS
---------------------------------------------------------
Title: The Structure of Solar Active Regions
Authors: Vourlidas, A.; Bastian, T. S.
1992AAS...180.4204V Altcode: 1992BAAS...24..796V
In past years, x-ray observations of solar active regions have
lead to the expectation of greater brightness temperatures at radio
wavelengths than those typically observed. It has been suggested that
cool plasma in the corona along the line of sight attenuates radio
emission via free-free absorption. If such plasma is present, it has
consequences for both the microwave spectrum and its polarization
properties. In order to test these ideas, high quality radio and x-ray
maps are required. We present a comprehensive set of observations of
a large solar active region (NOAO/USAF number 5131) made during the
IAU sanctioned International Solar Month in September, 1988. The VLA
was used to image the Sun in the 90, 20, 6 and 3.6 cm bands between
1--4 September. To improve the image quality we used the technique of
frequency synthesis at 3.6, 6 and 20 cm. The final maps are among the
best in dynamic range yet obtained. In addition to the radio maps, the
data base includes images from the SMM XRP in Fe XVII, magnetograms,
and Hα observations. We reconcile the x-ray and radio observations
with a simple model which differs somewhat from past models. Rather than
relying on a screen of cool plasma between the source and the observer,
we take explicit account of the highly inhomogeneous structure of solar
active regions. We briefly compare and contrast the consequences of
this model with existing models.