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Author name code: temmer
ADS astronomy entries on 2022-09-14
author:"Temmer, Manuela"
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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: SODA - Satellite Orbit DecAy near-real time forecast
Authors: Drescher, Lukas; Temmer, Manuela; Mayer-Gürr,
Torsten; Krauss, Sandro; Kroisz, B. Sofia; Behzadpour, Saniya;
Süsser-Rechberger, Barbara
2022cosp...44..826D Altcode:
Based on the results by Krauss et al. (2018, 2020), we investigate
the correlation between the interplanetary magnetic field of ICMEs
and the variation of the neutral density in the thermosphere. Within
the FFG funded project SWEETS (space weather effects on low Earth
orbiting satellites) we analyze a large sample of about 300 ICMEs
(interplanetary coronal mass ejections) from 2002 to 2017 and how they
relate to the orbit decay of satellites. The density estimates are
based on accelerometer measurements (CHAMP, GRAACE, GRACE-FO) as well
as on kinematic orbits of the satellite missions Swarm, TerraSAR-X,
Tandem-X and Sentinel 1, 3. Thus, our investigations covering altitudes
between 300 to 800 km. We find that strong magnetic field variations in
the Bz component trigger geomagnetic storms which lead to an increase
in the neutral density and subsequently the aerodynamic drag. As
a result, the satellites at very low altitudes may drop by several
tens to a hundred of meters during an extreme ICME event. From the
statistical study we derive an empirical relation between Bz value and
orbit drop for satellites in a normalized height of 490km. Using that
relation, we established a tool that enables to detect potential orbit
drops in near real-time. This forecast/nowcast service, called SODA
(Satellite Orbit DecAy) is implemented in the ESA Ionospheric Weather
SSP program/Ionospheric Weather Expert Service Centre (I-ESC).
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Title: Determination of CME orientation and consequences for their
propagation
Authors: Martinic, Karmen; Vrsnak, Bojan; Veronig, Astrid; Dumbovic,
Mateja; Temmer, Manuela
2022cosp...44.2441M Altcode:
The configuration of the interplanetary magnetic field and features
of the related ambient solar wind in the ecliptic and meridional
plane are different. Therefore, one can expect that the orientation
of the flux rope axis of a coronal mass ejection (CME) influences
the propagation of the CME itself. However, the determination of the
CME's orientation remains a challenging task to perform. This study
aims to provide a reference to different CME orientation determination
methods in the near-Sun environment. Also, it aims to investigate the
non-radial flow in the sheath region of the interplanetary CME (ICME)
in order to provide the first proxy to relate the ICME orientation
with its propagation. We investigated 22 isolated CME-ICME events
in the period 2008-2015. We first determined the CME orientation in
the near-Sun environment using a 3D reconstruction of the CME with
the graduated cylindrical shell (GCS) model applied to coronagraphic
images provided by the STEREO and SOHO missions. The CME orientation
in the near-Sun environment was determined using an ellipse fitting
technique to the CME outer front as determined from the SOHO/LASCO
coronagraph. In the near-Earth environment, we obtained the orientation
of the corresponding ICME using in-situ plasma and field data and also
investigated the non-radial flow in its sheath region. The ability of
GCS and ellipse fitting to determine the CME orientation is found to be
limited to reliably distinguish only between the high or low inclination
of the events. Most of the CME-ICME pairs under investigation were
found to be characterized by a low inclination. The majority of
CME-ICME pairs have a consistent estimation of tilt from remote and
in situ data. The observed non-radial flows in the sheath region show
a greater y-direction to z-direction flow ratio for high-inclination
events indicating that CME orientation could have an impact to the
CME propagation.
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Title: Development and evaluation of Drag-Based Ensemble Model (DBEM)
Authors: Čalogović, Jaša; Vrsnak, Bojan; Veronig, Astrid; Dumbovic,
Mateja; Temmer, Manuela
2022cosp...44.3443C Altcode:
The Drag-based Model (DBM) is a well-known 2D analytical model for
simulating the heliospheric propagation of Coronal Mass Ejections
(CMEs). Main output is the prediction of the CME arrival time and
speed at Earth or any other given target in the solar system. Due to a
very short computational time of DBM (< 0.01s), the probabilistic
Drag-Based Ensemble Model (DBEM) was developed by making an ensemble
of n different input parameters to account for possible variability
(uncertainties) in the input parameters. Using such an approach
to obtain the distribution and significance of the DBM results,
the DBEM determines the CME hit chance, most probable arrival times
and speeds, quantifies the prediction uncertainties and calculates
the confidence intervals. As an important tool for space weather
forecasters, the fully operational DBM/DBEM web application is
integrated as one of the ESA Space Situational Awareness portal services
(https://swe.ssa.esa.int/current-space-weather). In the last few years,
DBM/DBEM has been constantly improved with various new features such as
Graduated Cylindrical Shell (GCS) option for the CME geometry input,
the CME propagation visualizations as well as a new DBEM version
employing the variable solar wind speeds. The model development,
new features and the corresponding model evaluations will be presented.
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Title: How properties of large-scale solar wind structures drive
magnetosheath jet properties
Authors: Koller, Florian; Temmer, Manuela; Preisser, Luis; Roberts,
Owen; Weiss, B. Stefan; Plaschke, Ferdinand
2022cosp...44.1611K Altcode:
The Earth's magnetosheath consists of turbulent, shocked solar wind
(SW) plasma. Magnetosheath jets are dynamic pressure enhancements
which are frequently observed within this region. They travel
anti-sunward from the bow shock to the Earth's magnetopause and can be
geoeffective. While several generation mechanisms have been proposed,
jets are generally linked to processes at the quasi-parallel bow shock
and the foreshock. Our goal is to analyze, how these jets are related to
large-scale SW structures, in particular coronal mass ejections (CMEs)
as well as stream interaction regions (SIRs) and associated high speed
streams (HSSs). We use jets detected by the THEMIS spacecraft between
2008 to 2020. The number of detected jets is lower during the passing
of CMEs. Significantly more jets are observed during SIRs and HSSs. We
find that jets are unlikely to appear during a mix of low Alfvénic Mach
numbers and high IMF cone angles, which are SW conditions often found
during CMEs and their associated sheaths. These conditions may inhibit
the formation of a well-defined foreshock and therefore affecting the
jet generation. We analyze whether jets differ during each type of
large-scale SW structure and discuss the different possible origin
mechanisms.
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Title: Magnetosheath jets during a CME and SIR passage: A case study.
Authors: Preisser, Luis; Temmer, Manuela; Roberts, Owen; Koller,
M. Florian; Plaschke, Ferdinand
2022cosp...44.1642P Altcode:
Large scale solar wind (SW) structures called Coronal Mass Ejections
(CMEs) and Stream Interaction Regions (SIRs) travel through
the interplanetary medium, where they might impact the Earth's
magnetosphere. Jets are localized structures characterized by an
enhancement in dynamic pressure observed propagating through the
Earth's magnetosheath (EMS) transporting mass, momentum and energy
and being able to reach and perturb the Earth's magnetopause. Although
jets have been studied since 20 years, how the different SW conditions
triggered by CMEs and SIRs change the production of jets in the EMS,
is a topic that is just beginning to be explored. In this case study we
characterize jets observed by THEMIS during a CME and a SIR passage. We
find clear differences in number and size between the jets associated
with the CME regions arriving at the EMS as well as in comparison with
the characteristics of jets associated with the SIR passage. Comparing
WIND and THEMIS data we discuss how these differences are linked to
the SW conditions and with different jet generation mechanisms.
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Title: Understanding our capabilities in observing and modelling
Coronal Mass Ejections
Authors: Verbeke, Christine; Mays, M. Leila; Riley, Pete; Mierla,
Marilena; Cremades, Hebe; Dumbovic, Mateja; Temmer, Manuela; Scolini,
Camilla; Hinterreiter, Jürgen; Paouris, Evangelos; Palmerio, Erika;
Kay, Christina; Balmaceda, Laura
2022cosp...44.3441V Altcode:
Coronal Mass Ejections (CMEs) are large-scale eruptions of plasma and
magnetic fields from the Sun. They are considered to be the main drivers
of strong space weather events at Earth and their arrival time and
associated shocks are one of the key aspects of space weather. Multiple
models have been developed over the past decades to be able to predict
the propagation of CMEs in the interplanetary space and their arrival
time at Earth. Such models require input from observations, which can
be used to fit the CME to an appropriate structure. The forecasting
of CME arrival has proven to be exceedingly challenging. One of the
major setbacks is the uncertainty of the CME observational input. When
determining input parameters for CME propagation models, it is common
procedure to derive kinematic parameters from remote-sensing data. The
resulting parameters can be used as inputs for the CME propagation
models to obtain an arrival prediction time of the CME f.e. at
Earth. However, when fitting the CME structure to obtain the needed
parameters for simulations, different geometric structures and also
different parts of the CME structure can be fitted. These aspects,
together with the fact that 3D reconstructions strongly depend on the
subjectivity and judgement of the scientist performing them, may lead
to uncertainties in the fitted parameters. Up to now, no large study
has tried to map these uncertainties and to evaluate how they affect the
modelling of CMEs. We will discuss these limits in the scope of the CME
input analysis that is performed by the ISSI Bern team on "Understanding
Our Capabilities In Observing and Modelling Coronal Mass Ejections".
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Title: Evolution of ICME sheath and leading-edge structure in the
inner heliosphere
Authors: Temmer, Manuela; Bothmer, Volker
2022cosp...44.1439T Altcode:
We investigate a data sample of 40 interplanetary CME (ICME) events
from Helios 1 and 2 data that cover the distance range 0.3-1au. For
comparison, we add a sample of 5 ICMEs observed with Parker Solar
Probe during 2018-2021. From the solar wind plasma and magnetic field
measurements, we extract the ICME sub-structures sheath, leading-edge,
and magnetic ejecta. We analyze their characteristic parameters as
function of distance and present the main findings of this study: a)
the average starting distance for actual sheath formation appears to
be located at a distance of about 13 Rs; b) the sheath density becomes
dominant over the magnetic ejecta density beyond 38 Rs; c) the sheath
size could be related to the ambient solar wind density and magnetic
ejecta characteristics; d) a local linear relation between sheath
density and ambient solar wind speed was found; e) the leading-edge
does not increase in size over distance and might be an isolated
structure wedged in between sheath and magnetic ejecta. With Parker
Solar Probe approaching the Sun as close as 10Rs, we will certainly
detect more CME events to obtain measurements that might re-affirm
the presented results. The current findings can be applied to help
improve CME propagation models.
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Title: Stellar CME search using large datasets: Balmer line
asymmetries in optical SDSS spectra
Authors: Koller, Florian; Odert, Petra; Leitzinger, Martin; Veronig,
Astrid; Temmer, Manuela; Beck, Paul G.
2022cosp...44.1386K Altcode:
On the Sun, a strong correlation between highly energetic flares
and coronal mass ejections (CMEs) has been well established. Highly
energetic flares have also been frequently detected on all late-type
stars. However, the association with CMEs proved to be difficult in the
stellar case. Large datasets are a necessity to increase the probability
of detecting these sparse events. In order to find stellar flares
and associated CMEs, we used optical spectra provided by the Sloan
Digital Sky Survey (SDSS) data release 14. The sample consisted of F,
G, K, and M main-sequence type stars, resulting in available spectra
for more than 630 000 stars. We made use of the individual spectral
exposures provided by the SDSS. Flares were detected by searching for
significant amplitude changes in the Hα and Hβ spectral lines. We
searched for CMEs by identifying asymmetries in the Balmer lines
caused by the Dopplereffect, which indicate plasma motions in the line
of sight. We detected 281 flares on late-type stars (spectral types
K3 - M9) and calculated their Hα flare energies. Six possible CME
candidates were identified that show excess flux in Balmer line wings,
five of which show red wing enhancements. Our mass estimates for the
CME candidates range from 6×10$ ^{16}$ -‑ 6×10$ ^{18}$g, and the
highest projected velocities are 300 -‑ 700km s$ ^{‑1}$. Our low
detection rate of CMEs agrees with previous studies.
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Title: Galactic cosmic rays as signatures of interplanetary transients
Authors: Dumbovic, Mateja; Kühl, Patrick; Heber, Bernd; Vrsnak,
Bojan; Temmer, Manuela; Kirin, Anamarija; Hörlöck, Malte; Jensen,
Stefan; Benko, Ilona; Kramaric, Luka
2022cosp...44.1255D Altcode:
Coronal mass ejections (CMEs), interplanetary shocks, and corotating
interaction regions (CIRs) drive heliospheric variability, causing
various interplanetary as well as planetary disturbances. One of
their very common in-situ signatures are short-term reductions in
the galactic cosmic ray (GCR) flux (i.e. Forbush decreases), which
are measured by ground-based instruments at Earth and Mars, as well
as various spacecraft throughout the heliosphere (most recently
by Solar Orbiter). In general, interplanetary magnetic structures
interact with GCRs producing depressions in the GCR flux. Therefore,
different types of interplanetary magnetic structures cause different
types of Forbush decreases, allowing us to distinguish between
them. We recently developed and employed two different analytical
models to explain CME-related and CIR-related Forbush decreases,
using an expansion-diffusion and the convection-diffusion approaches,
respectively. We used observation-based generic CME and CIR profiles
as the theoretical background for the models and tested the models on
various case studies. Moreover, the CME-related Forbush decrease model
(ForbMod, Dumbovic et al., 2018; 2020) is brought one step further, as
it also considers the energy dependance of the detector with which the
measurements are made. ForbMod is tested through model-to-observations
comparison to analyse to how many CMEs it is applicable and could
ultimately provide a helpful tool to analyse Forbush decreases. With
new modelling efforts, as well as observational analysis we are one
step closer in utilizing GCR measurements to provide information
on interplanetary transients, especially where other measurements
(e.g. plasma, magnetic field) are lacking.
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Title: Acceleration and Expansion of a Coronal Mass Ejection in the
High Corona: Role of Magnetic Reconnection
Authors: Zhuang, Bin; Lugaz, Noé; Temmer, Manuela; Gou, Tingyu;
Al-Haddad, Nada
2022ApJ...933..169Z Altcode: 2022arXiv220602090Z
The important role played by magnetic reconnection in the early
acceleration of coronal mass ejections (CMEs) has been widely
discussed. However, as CMEs may have expansion speeds comparable to
their propagation speeds in the corona, it is not clear whether and
how reconnection contributes to the true acceleration and expansion
separately. To address this question, we analyze the dynamics of a
moderately fast CME on 2013 February 27, associated with a continuous
acceleration of its front into the high corona, even though its speed
had reached ~700 km s<SUP>-1</SUP>, which is faster than the solar
wind. The apparent acceleration of the CME is found to be due to its
expansion in the radial direction. The true acceleration of the CME,
i.e., the acceleration of its center, is then estimated by taking into
account the expected deceleration caused by the drag force of the solar
wind acting on a fast CME. It is found that the true acceleration and
the radial expansion have similar magnitudes. We find that magnetic
reconnection occurs after the eruption of the CME and continues during
its propagation in the high corona, which contributes to its dynamic
evolution. Comparison between the apparent acceleration related to the
expansion and the true acceleration that compensates the drag shows
that, for this case, magnetic reconnection contributes almost equally
to the expansion and to the acceleration of the CME. The consequences
of these measurements for the evolution of CMEs as they transit from
the corona to the heliosphere are discussed.
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Title: Observations of CME source regions/lower-atmospheric
manifestations
Authors: Temmer, Manuela
2022cosp...44.1357T Altcode:
The Sun is an active star that influences the Earth as well as the
entire solar system. Most dynamic phenomena are observed as coronal
mass ejections (CMEs). While CMEs frequently occur at the Sun,
they are obviously less numerous when it comes to stars. Do we miss
specific observing techniques? This talk will give an overview on
the diverse manifestations of CME related signatures on the Sun that
are observed during the CME early evolution phase. Strong and fast
events can be most clearly related to their source regions that often
show bright flare emissions as the reconnection process starts which
drives the CME. In the wake of the eruption, CMEs expand and leave low
atmospheric footprints, such as disappearing filaments or dark dimming
regions, and may generate coronal waves. Weak and slow CMEs might not be
detected by such footprints as they start from higher up in the corona
(stealth CMEs). In the radio wavelength, typical signatures of type
II and III bursts can give hint to propagating shocks and the opening
of magnetic field. The ambient conditions in which the CME erupts,
such as strong overlying closed magnetic fields, nearby coronal holes
(open magnetic field) or multiple eruptions (transient open field),
may alter the ability to generate specific signatures.
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Title: From CME - CH proximity on the Sun to ICME - CIR interaction
at Earth: a case study
Authors: Geyer, Paul; Dumbovic, Mateja; Temmer, Manuela
2022cosp...44.1121G Altcode:
The interaction between interplanetary coronal mass ejections (ICMEs)
and corotating interaction regions (CIRs) leads to a variety of
changes both in the trajectory and the morphology of the former. This
means that the solar wind (SW) conditions at Earth's orbit due to
interacting heliospheric structures may deviate significantly from the
case of sole ICME or CIR passage. Studying the interaction of these
large-scale structures in the heliosphere thus provides a basis for a
more accurate space weather prediction of the associated near-Earth
effects and enhances the accuracy of CME propagation models. The
eruption of a flare related CME southwest to the center of the solar
disk was observed by SDO/AIA on February 4, 2014. A coronal hole (CH)
east of the disk center is also present at that time. The CME is listed
by the DONKI database and associated to the in-situ magnetic field and
plasma signatures detected at L1 3 days later. After the arrival of a
fast forward shock on February 7, 2014 typical sheath properties are
observed, followed by a region of low fluctuations, plasma beta and
temperature - typical ICME signatures. A SW flow angle reversal is
observed at the beginning of this interval, indicating east-west flow
deflection normally observed around stream interfaces. The region of
typical ICME signatures is interrupted by a phase of decreased field
magnitude simultaneously occurring with the disturbance of the flow
speed. Finally, at the trailing part of the in-situ event we observe
the passage of a high-speed stream. The proximity of the coronal source
regions of ICME and CIR clearly results in their interaction and thus
morphological changes visible in plasma and magnetic field data. This
view is also supported by WSA-ENLIL simulations showing the coincident
arrival and apparent merging of the CIR and ICME at Earth. The
separation of two intervals of weak magnetic field fluctuations by a
region of strong fluctuations indicates a fundamental rearrangement of
the magnetic field associated with the ICME. This is supported by the
non-bidirectional electron pitch angle data. The complexity of this
event demonstrates the need to study the interaction of the coronal
source regions and their respective SW structures in a holistic way.
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Title: Determination of coronal mass ejection orientation and
consequences for their propagation
Authors: Martinić, K.; Dumbović, M.; Temmer, M.; Veronig, A.;
Vršnak, B.
2022A&A...661A.155M Altcode: 2022arXiv220410112M
Context. The configuration of the interplanetary magnetic field
and features of the related ambient solar wind in the ecliptic
and meridional plane are different. Therefore, one can expect that
the orientation of the flux-rope axis of a coronal mass ejection
(CME) influences the propagation of the CME itself. However, the
determination of the CME orientation, especially from image data,
remains a challenging task to perform. Aim. This study aims to provide
a reference to different CME orientation determination methods in
the near-Sun environment. Also, it aims to investigate the non-radial
flow in the sheath region of the interplanetary CME (ICME) in order
to provide the first proxy to relate the ICME orientation with its
propagation. <BR /> Methods: We investigated 22 isolated CME-ICME
events in the period 2008-2015. We determined the CME orientation in
the near-Sun environment using the following: (1) a 3D reconstruction
of the CME with the graduated cylindrical shell (GCS) model applied
to coronagraphic images provided by the STEREO and SOHO missions;
and (2) an ellipse fitting applied to single spacecraft data from
SOHO/LASCO C2 and C3 coronagraphs. In the near-Earth environment,
we obtained the orientation of the corresponding ICME using in situ
plasma and field data and also investigated the non-radial flow in
its sheath region. <BR /> Results: The ability of GCS and ellipse
fitting to determine the CME orientation is found to be limited to
reliably distinguish only between the high or low inclination of the
events. Most of the CME-ICME pairs under investigation were found to
be characterized by a low inclination. For the majority of CME-ICME
pairs, we obtain consistent estimations of the tilt from remote and
in situ data. The observed non-radial flows in the sheath region show
a greater y direction to z direction flow ratio for high-inclination
events, indicating that the CME orientation could have an impact on
the CME propagation.
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Title: Magnetosheath Jet Occurrence Rate in Relation to CMEs and SIRs
Authors: Koller, Florian; Temmer, Manuela; Preisser, Luis; Plaschke,
Ferdinand; Geyer, Paul; Jian, Lan K.; Roberts, Owen W.; Hietala,
Heli; LaMoury, Adrian T.
2022JGRA..12730124K Altcode:
Magnetosheath jets constitute a significant coupling effect between
the solar wind (SW) and the magnetosphere of the Earth. In order to
investigate the effects and forecasting of these jets, we present the
first-ever statistical study of the jet production during large-scale
SW structures like coronal mass ejections (CMEs), stream interaction
regions (SIRs) and high speed streams (HSSs). Magnetosheath data from
Time History of Events and Macroscale Interactions during Substorms
(THEMIS) spacecraft between January 2008 and December 2020 serve as
measurement source for jet detection. Two different jet definitions
were used to rule out statistical biases induced by our jet detection
method. For the CME and SIR + HSS lists, we used lists provided by
literature and expanded on incomplete lists using OMNI data to cover
the time range of May 1996 to December 2020. We find that the number and
total time of observed jets decrease when CME-sheaths hit the Earth. The
number of jets is lower throughout the passing of the CME-magnetic
ejecta (ME) and recovers quickly afterward. On the other hand, the
number of jets increases during SIR and HSS phases. We discuss a few
possibilities to explain these statistical results.
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Title: How the area of solar coronal holes affects the properties
of high-speed solar wind streams near Earth: An analytical model
Authors: Hofmeister, Stefan J.; Asvestari, Eleanna; Guo, Jingnan;
Heidrich-Meisner, Verena; Heinemann, Stephan G.; Magdalenic, Jasmina;
Poedts, Stefaan; Samara, Evangelia; Temmer, Manuela; Vennerstrom,
Susanne; Veronig, Astrid; Vršnak, Bojan; Wimmer-Schweingruber, Robert
2022A&A...659A.190H Altcode: 2022arXiv220315689H
Since the 1970s it has been empirically known that the area of
solar coronal holes affects the properties of high-speed solar wind
streams (HSSs) at Earth. We derive a simple analytical model for the
propagation of HSSs from the Sun to Earth and thereby show how the
area of coronal holes and the size of their boundary regions affect
the HSS velocity, temperature, and density near Earth. We assume that
velocity, temperature, and density profiles form across the HSS cross
section close to the Sun and that these spatial profiles translate
into corresponding temporal profiles in a given radial direction due
to the solar rotation. These temporal distributions drive the stream
interface to the preceding slow solar wind plasma and disperse with
distance from the Sun. The HSS properties at 1 AU are then given by
all HSS plasma parcels launched from the Sun that did not run into
the stream interface at Earth distance. We show that the velocity
plateau region of HSSs as seen at 1 AU, if apparent, originates from
the center region of the HSS close to the Sun, whereas the velocity
tail at 1 AU originates from the trailing boundary region. Small
HSSs can be described to entirely consist of boundary region plasma,
which intrinsically results in smaller peak velocities. The peak
velocity of HSSs at Earth further depends on the longitudinal width
of the HSS close to the Sun. The shorter the longitudinal width of
an HSS close to the Sun, the more of its "fastest" HSS plasma parcels
from the HSS core and trailing boundary region have impinged upon the
stream interface with the preceding slow solar wind, and the smaller
is the peak velocity of the HSS at Earth. As the longitudinal width
is statistically correlated to the area of coronal holes, this also
explains the well-known empirical relationship between coronal hole
areas and HSS peak velocities. Further, the temperature and density
of HSS plasma parcels at Earth depend on their radial expansion from
the Sun to Earth. The radial expansion is determined by the velocity
gradient across the HSS boundary region close to the Sun and gives
the velocity-temperature and density-temperature relationships at
Earth their specific shape. When considering a large number of HSSs,
the assumed correlation between the HSS velocities and temperatures
close to the Sun degrades only slightly up to 1 AU, but the correlation
between the velocities and densities is strongly disrupted up to 1
AU due to the radial expansion. Finally, we show how the number of
particles of the piled-up slow solar wind in the stream interaction
region depends on the velocities and densities of the HSS and preceding
slow solar wind plasma.
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Title: Dynamic Time Warping as a Means of Assessing Solar Wind
Time Series
Authors: Samara, E.; Laperre, B.; Kieokaew, R.; Temmer, M.; Verbeke,
C.; Rodriguez, L.; Magdalenić, J.; Poedts, S.
2022ApJ...927..187S Altcode: 2021arXiv210907873S
Over the last decades, international attempts have been made to
develop realistic space weather prediction tools aiming to forecast
the conditions on the Sun and in the interplanetary environment. These
efforts have led to the development of appropriate metrics to assess the
performance of those tools. Metrics are necessary to validate models, to
compare different models, and to monitor the improvements to a certain
model over time. In this work, we introduce dynamic time warping (DTW)
as an alternative way of evaluating the performance of models and,
in particular, of quantifying the differences between observed and
modeled solar wind time series. We present the advantages and drawbacks
of this method, as well as its application to Wind observations and
EUHFORIA predictions at Earth. We show that DTW can warp sequences
in time, aiming to align them with the minimum cost by using dynamic
programming. It can be applied for the evaluation of modeled solar wind
time series in two ways. The first calculates the sequence similarity
factor, a number that provides a quantification of how good the forecast
is compared to an ideal and a nonideal prediction scenario. The second
way quantifies the time and amplitude differences between the points
that are best matched between the two sequences. As a result, DTW
can serve as a hybrid metric between continuous measurements (e.g.,
the correlation coefficient) and point-by-point comparisons. It is
a promising technique for the assessment of solar wind profiles,
providing at once the most complete evaluation portrait of a model.
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Title: Generic profile of a long-lived corotating interaction region
and associated recurrent Forbush decrease
Authors: Dumbović, M.; Vršnak, B.; Temmer, M.; Heber, B.; Kühl, P.
2022A&A...658A.187D Altcode: 2022arXiv220109623D
Context. Corotating interaction regions (CIRs), formed by the
interaction of slow solar wind and fast streams that originate from
coronal holes (CHs), produce recurrent Forbush decreases, which are
short-term depressions in the galactic cosmic ray (GCR) flux. <BR />
Aims: Our aim is to prepare a reliable set of CIR measurements to be
used as a textbook for modeling efforts. For that purpose, we observe
and analyse a long-lived CIR, originating from a single CH, recurring
in 27 consecutive Carrington rotations 2057-2083 in the time period
from June 2007-May 2009. <BR /> Methods: We studied the in situ
measurements of this long-lived CIR as well as the corresponding
depression in the cosmic ray (CR) count observed by SOHO/EPHIN
throughout different rotations. We performed a statistical analysis,
as well as the superposed epoch analysis, using relative values of the
key parameters: the total magnetic field strength, B, the magnetic
field fluctuations, dBrms, plasma flow speed, v, plasma density, n,
plasma temperature, T, and the SOHO/EPHIN F-detector particle count,
and CR count. <BR /> Results: We find that the mirrored CR count-time
profile is correlated with that of the flow speed, ranging from moderate
to strong correlation, depending on the rotation. In addition, we
find that the CR count dip amplitude is correlated to the peak in the
magnetic field and flow speed of the CIR. These results are in agreement
with previous statistical studies. Finally, using the superposed epoch
analysis, we obtain a generic CIR example, which reflects the in situ
properties of a typical CIR well. <BR /> Conclusions: Our results are
better explained based on the combined convection-diffusion approach of
the CIR-related GCR modulation. Furthermore, qualitatively, our results
do not differ from those based on different CHs samples. This indicates
that the change of the physical properties of the recurring CIR from one
rotation to another is not qualitatively different from the change of
the physical properties of CIRs originating from different CHs. Finally,
the obtained generic CIR example, analyzed on the basis of superposed
epoch analysis, can be used as a reference for testing future models.
---------------------------------------------------------
Title: Characteristics and evolution of sheath and leading edge
structures of interplanetary coronal mass ejections in the inner
heliosphere based on Helios and Parker Solar Probe observations
Authors: Temmer, Manuela; Bothmer, Volker
2022arXiv220204391T Altcode:
Aims: We statistically investigate the plasma and magnetic field
characteristics of the upstream regions of interplanetary coronal mass
ejections (ICMEs) and their evolution as function of distance to the Sun
in the inner heliosphere. We use a sample of 40 well-observed ICMEs from
Helios 1/2 (0.3-1au) and 5 from Parker Solar Probe (0.32-0.75au). For
each event we identify four main density structures, namely shock,
sheath, leading edge (LE), and magnetic ejecta (ME) itself. Methods:
We derive separately for each structure averaged plasma and magnetic
field parameter values as well as duration and place the results
into comparison with the upstream solar wind (SW) to investigate the
interrelation between the different density structures. Results:
The sheath structure presumably consists of compressed plasma due
to the turbulent SW material following the shock. The sheath lies
ahead of a region of compressed ambient SW, the LE, which is typically
found directly in front of the magnetic driver and seems to match the
bright leading edge commonly observed in remote sensing observations of
CMEs. The sheath becomes denser than the ambient SW at about 0.06au,
which we interpret as the average starting distance for actual sheath
formation. Between 0.09-0.28au the sheath structure density starts to
dominate over the density within the ME. The ME density seems to fall
below the ambient SW density over 0.45-1.07au. Besides the well-known
expansion of the ME, the sheath size shows a weak positive correlation
with distance, while the LE seems not to expand with distance from the
Sun. We further find a moderate anti-correlation between sheath density
and local SW plasma speed upstream of the ICME shock. An empirical
relation is derived connecting the ambient SW speed with sheath and LE
density that can be used for modeling of ICME evolution. Constraints
to those results are given.
---------------------------------------------------------
Title: Validation scheme for solar coronal models: Constraints from
multi-perspective observations in EUV and white light
Authors: Wagner, A.; Asvestari, E.; Temmer, M.; Heinemann, S. G.;
Pomoell, J.
2022A&A...657A.117W Altcode: 2021arXiv211001893W; 2021arXiv211001893A
Context. In this paper, we present a validation scheme to investigate
the quality of coronal magnetic field models, which is based on
comparisons with observational data from multiple sources. <BR />
Aims: Many of these coronal models may use a range of initial
parameters that produce a large number of physically reasonable
field configurations. However, that does not mean that these
results are reliable and comply with the observations. With an
appropriate validation scheme, which is the aim of this work,
the quality of a coronal model can be assessed. <BR /> Methods:
The validation scheme was developed with the example of the EUropean
Heliospheric FORecasting Information Asset (EUHFORIA) coronal model. For
observational comparison, we used extreme ultraviolet and white-light
data to detect coronal features on the surface (open magnetic field
areas) and off-limb (streamer and loop) structures from multiple
perspectives (Earth view and the Solar Terrestrial Relations Observatory
- STEREO). The validation scheme can be applied to any coronal model
that produces magnetic field line topology. <BR /> Results: We show
its applicability by using the validation scheme on a large set of
model configurations, which can be efficiently reduced to an ideal
set of parameters that matches best with observational data. <BR />
Conclusions: We conclude that by using a combined empirical visual
classification with a mathematical scheme of topology metrics, a very
efficient and objective quality assessment for coronal models can
be performed.
---------------------------------------------------------
Title: On the influence of CMEs and SIRs on the generation of
magnetosheath jets
Authors: Koller, Florian; Temmer, Manuela; Preisser, Luis; Plaschke,
Ferdinand; Roberts, Owen
2021AGUFMSH25G..34K Altcode:
Magnetosheath jets are dynamic pressure enhancements observed in
the Earths magnetosheath. They are significant coupling elements
between the solar wind and the magnetosphere of the Earth. Jets are
frequently generated at the Earths bow shock and travel downstream
to the magnetopause, where they can trigger reconnection and initiate
geomagnetic substorms. It is so far unexplored how these jets relate to
large scale solar wind structures that are associated to the solar cycle
and solar activity. To gain insights into these relations, we analyze
jet generation during the passing of coronal mass ejections (CMEs)
and stream interaction regions (SIRs). In our statistical analysis,
we use magnetosheath jets detected by the THEMIS spacecraft between
2008 to 2020, and identify all overlaps with CME and SIR intervals. We
report that magnetosheath jets can be generated at all times, but they
appear much more frequently during SIRs, while the numbers of observed
jets decrease significantly during CMEs. To explain this statistical
difference, we inspect how the solar wind conditions related to the
observed jets differ during CMEs and SIRs.
---------------------------------------------------------
Title: Characteristics of magnetosheath jets during an CME passage.
Authors: Preisser, Luis; Plaschke, Ferdinand; Koller, Florian; Temmer,
Manuela; Roberts, Owen
2021AGUFMSH25G..32P Altcode:
Jets are localized enhancements in the dynamic pressure observed
downstream of the Earths bow shock which propagate through the Earths
magnetosheath (EMS) transporting mass, momentum and energy. Coronal
Mass Ejections (CMEs) are large scale solar wind events traveling
through the interplanetary medium. As the CME crosses the EMS,
its structure (upstream side shock/sheath magnetic ejecta) changes
the magnetosheath environment. How these changes in the EMS region
produced by the passage of a CME affect the production of jets is a
topic not yet explored. In this work we characterize jets observed
by THEMIS spacecraft during such a passage. We find differences in
number and size between jets located in the CME upstream region and
those located in the corresponding CME downstream region. Comparing
WIND and THEMIS A, D, E data we discuss how these differences can be
associated to different jet generation mechanisms and if they are or
not related with the transmission of the CME structure into the EMS.
---------------------------------------------------------
Title: The 2019 International Women's Day Event: A Two-step Solar
Flare with Multiple Eruptive Signatures and Low Earth Impact
Authors: Dumbovic, Mateja; Veronig, Astrid; Podladchikova, Tatiana;
Thalmann, Julia; Chikunova, Galina; Dissauer, Karin; Magdalenic,
Jasmina; Temmer, Manuela; Guo, Jingnan; Samara, Evangelia
2021AGUFMSH32A..08D Altcode:
We present a detailed analysis of an eruptive event that occurred on
early 2019 March 8 in active region AR 12734, to which we refer as the
International Women's day event. The event under study is intriguing in
several aspects: 1) low-coronal eruptive signatures come in ”pairs” (a
double-peak flare, two coronal dimmings, and two EUV waves); 2) although
the event is characterized by a complete chain of eruptive signatures,
the corresponding coronagraphic signatures are weak; 3) although
the source region of the eruption is located close to the center of
the solar disc and the eruption is thus presumably Earth-directed,
heliospheric signatures are very weak with little Earth-impact. We
analyze a number of multi-spacecraft and multi-instrument (both
remote-sensing and in situ) observations, including Soft X-ray,
(extreme-) ultraviolet (E)UV), radio and white-light emission, as well
as plasma, magnetic field and particle measurements. We employ 3D NLFF
modeling to investigate the coronal magnetic field configuration in and
around the active region, the GCS model to make a 3D reconstruction of
the CME geometry and the 3D MHD numerical model EUHFORIA to model the
background state of the heliosphere. Our results indicate two subsequent
eruptions of two systems of sheared and twisted magnetic fields,
which merge already in the upper corona and start to evolve further
out as a single entity. The large-scale magnetic field significantly
influences both, the early and the interplanetary evolution of the
structure. During the first eruption the stability of the overlying
field was disrupted which enabled the second eruption. We find that
during the propagation in the interplanetary space the large-scale
magnetic field, i.e. , the location of heliospheric current sheet
between the AR and the Earth likely influences propagation and the
evolution of the erupted structure(s).
---------------------------------------------------------
Title: The Dynamic Time Warping Technique as an Alternative Way to
Evaluate Space Weather Predictions
Authors: Samara, Evangelia; Chane, Emmanuel; Laperre, Brecht; Kieokaew,
Rungployphan; Temmer, Manuela; Verbeke, Christine; Rodriguez, Luciano;
Magdalenic, Jasmina; Poedts, Stefaan
2021AGUFMSH55C1860S Altcode:
In this work, the Dynamic Time Warping (DTW) technique is presented
as an alternative method to quantify differences between observed
and modeled time series in solar wind forecasting. The method was
initially developed for speech recognition purposes and over the years
it met great interest by other scientific fields. In the frame of this
study, we show for the first time how we can apply DTW to assess the
performance of modeled time series produced by space weather forecasting
tools. Dynamic Time Warping can quantify how similar two time series
are by providing a temporal alignment between them, in an optimal
way, under certain restrictions. We further discuss the benefits and
limitations of this method compared to other widely used metrics and
we show examples on how the technique is applied to predicted solar
wind time series modeled by EUHFORIA.
---------------------------------------------------------
Title: Quantifying Capabilities in Observing Coronal Mass Ejections
Authors: Verbeke, Christine; Mays, M.; Kay, Christina; Mierla,
Marilena; Riley, Pete; Palmerio, Erika; Dumbovic, Mateja; Scolini,
Camilla; Temmer, Manuela; Paouris, Evangelos; Hinterreiter, Jurgen;
Balmaceda, Laura; Cremades, Hebe
2021AGUFMSH55C1854V Altcode:
Coronal Mass Ejections (CMEs) are large-scale eruptions of plasma
and magnetic fields from the Sun. They are considered to be the main
drivers of strong space weather events at Earth. Multiple models have
been developed over the past decades to predict the propagation of
CMEs and their possible arrival time at Earth. Such models require
input from observations, which can be used to fit the CME to an
appropriate structure.When determining parameters associated to
the CME structure, it is common procedure to derive such kinematic
parameters from remote-sensing data. The resulting parameters can be
used as input for CME propagation models to obtain an arrival time
prediction of the CME e.g. at Earth. However, different geometric
structures and different parts of the CME structure can be fitted,
and these aspects, together with the fact that most 3D reconstructions
are performed by a scientist, creating a subjectivity of the fit, may
lead to uncertainties in the fitted parameters. To our knowledge, so
far, no large scale study has tried to map these uncertainties and how
these affect the modelling of arrival time models.As a start for this
work, we focused on the effect cause by the influence and subjectivty
of the performing scientist. We have designed a synthetic situation
where the true geometric parameters are known in order to quantify
such uncertainties for the first time and discuss the results. We
explore further work of the associated ISSI team.
---------------------------------------------------------
Title: Earth-affecting solar transients: a review of progresses in
solar cycle 24
Authors: Zhang, Jie; Temmer, Manuela; Gopalswamy, Nat; Malandraki,
Olga; Nitta, Nariaki V.; Patsourakos, Spiros; Shen, Fang; Vršnak,
Bojan; Wang, Yuming; Webb, David; Desai, Mihir I.; Dissauer, Karin;
Dresing, Nina; Dumbović, Mateja; Feng, Xueshang; Heinemann, Stephan
G.; Laurenza, Monica; Lugaz, Noé; Zhuang, Bin
2021PEPS....8...56Z Altcode: 2020arXiv201206116Z
This review article summarizes the advancement in the studies of
Earth-affecting solar transients in the last decade that encompasses
most of solar cycle 24. It is a part of the effort of the International
Study of Earth-affecting Solar Transients (ISEST) project, sponsored
by the SCOSTEP/VarSITI program (2014-2018). The Sun-Earth is an
integrated physical system in which the space environment of the
Earth sustains continuous influence from mass, magnetic field, and
radiation energy output of the Sun in varying timescales from minutes to
millennium. This article addresses short timescale events, from minutes
to days that directly cause transient disturbances in the Earth's
space environment and generate intense adverse effects on advanced
technological systems of human society. Such transient events largely
fall into the following four types: (1) solar flares, (2) coronal mass
ejections (CMEs) including their interplanetary counterparts ICMEs,
(3) solar energetic particle (SEP) events, and (4) stream interaction
regions (SIRs) including corotating interaction regions (CIRs). In
the last decade, the unprecedented multi-viewpoint observations of
the Sun from space, enabled by STEREO Ahead/Behind spacecraft in
combination with a suite of observatories along the Sun-Earth lines,
have provided much more accurate and global measurements of the size,
speed, propagation direction, and morphology of CMEs in both 3D and over
a large volume in the heliosphere. Many CMEs, fast ones, in particular,
can be clearly characterized as a two-front (shock front plus ejecta
front) and three-part (bright ejecta front, dark cavity, and bright
core) structure. Drag-based kinematic models of CMEs are developed to
interpret CME propagation in the heliosphere and are applied to predict
their arrival times at 1 AU in an efficient manner. Several advanced
MHD models have been developed to simulate realistic CME events from
the initiation on the Sun until their arrival at 1 AU. Much progress
has been made on detailed kinematic and dynamic behaviors of CMEs,
including non-radial motion, rotation and deformation of CMEs, CME-CME
interaction, and stealth CMEs and problematic ICMEs. The knowledge
about SEPs has also been significantly improved. An outlook of how to
address critical issues related to Earth-affecting solar transients
concludes this article.
---------------------------------------------------------
Title: Space weather: the solar perspective
Authors: Temmer, Manuela
2021LRSP...18....4T Altcode: 2021arXiv210404261T
The Sun, as an active star, is the driver of energetic phenomena that
structure interplanetary space and affect planetary atmospheres. The
effects of Space Weather on Earth and the solar system is of increasing
importance as human spaceflight is preparing for lunar and Mars
missions. This review is focusing on the solar perspective of the Space
Weather relevant phenomena, coronal mass ejections (CMEs), flares,
solar energetic particles (SEPs), and solar wind stream interaction
regions (SIR). With the advent of the STEREO mission (launched in
2006), literally, new perspectives were provided that enabled for the
first time to study coronal structures and the evolution of activity
phenomena in three dimensions. New imaging capabilities, covering the
entire Sun-Earth distance range, allowed to seamlessly connect CMEs
and their interplanetary counterparts measured in-situ (so called
ICMEs). This vastly increased our knowledge and understanding of the
dynamics of interplanetary space due to solar activity and fostered the
development of Space Weather forecasting models. Moreover, we are facing
challenging times gathering new data from two extraordinary missions,
NASA's Parker Solar Probe (launched in 2018) and ESA's Solar Orbiter
(launched in 2020), that will in the near future provide more detailed
insight into the solar wind evolution and image CMEs from view points
never approached before. The current review builds upon the Living
Reviews article by Schwenn from 2006, updating on the Space Weather
relevant CME-flare-SEP phenomena from the solar perspective, as observed
from multiple viewpoints and their concomitant solar surface signatures.
---------------------------------------------------------
Title: HI-based CME Modeling and the Influence of the Drag-force on
the CME Frontal Shape
Authors: Amerstorfer, Tanja; Hinterreiter, Jurgen; Temmer, Manuela;
Weiss, Andreas; Bauer, Maike; Moestl, Christian; Barnard, Luke; Reiss,
Martin; Pomoell, Jens; Amerstorfer, Ute
2021AGUFMSH33A..03A Altcode:
Modeling the evolution of coronal mass ejections through the inner
heliosphere is still just as challenging as imprecise.A small fleet
of spacecraft is currently operating in an orbit around the Sun and
offers the possibility to verify model results by comparing them to
in situ arrivals at different heliocentric distances, longitudes and
latitudes.However, deformations of a CME front can be very local making
them hard to model and difficult to verify. These distortions are mainly
caused by the interaction of CME and ambient solar wind and lead to
large differences between different propagation models. With the help
of heliospheric imagers it is possible to constrain the elongation of
the CME front to a certain degree. Additionally, these observations
can be utilized to derive information on the CME kinematics, the CME
mass and the drag-force exerted by the solar wind. We present the
first HI-based CME model allowing a CME front to react to the ambient
solar wind in a local manner leading to frontal deformations. Three
different ambient solar wind models serve as input to the model and
underline the need of more precise solar wind modeling in order to
improve CME arrival prediction models.
---------------------------------------------------------
Title: Searching for flares and associated CMEs on cool stars using
Balmer lines in SDSS spectra
Authors: Koller, Florian; Leitzinger, Martin; Temmer, Manuela; Odert,
Petra; Beck, Paul; Veronig, Astrid
2021AGUFM.U43B..04K Altcode:
Flares and coronal mass ejections (CMEs) shape the environment of stars
and can severely affect the atmospheres and therefore the habitability
of exoplanets. In the case of our Sun, we find that highly energetic
flares and CMEs are strongly correlated. While we find frequent
and highly energetic flares on all late-type stars, determining
the association with stellar CMEs proves to be more difficult. To
further constrain the activity of late-type main-sequence stars, we
aimed to detect and classify stellar flares and potential stellar CME
signatures. For that, we used optical spectra provided by the Sloan
Digital Sky Survey (SDSS) data release 14. The sample was constrained
to all F, G, K, and M main-sequence type stars, which resulted in
available spectra for more than 630 000 stars. We made use of the
individual spectral exposures provided by the SDSS. To automatically
detect flares, we searched for significant amplitude changes in the
$H\alpha$ and $H\beta$ spectral lines after a Gaussian profile was fit
to each line core. We searched for CMEs by identifying asymmetries in
the Balmer lines caused by the Dopplereffect, which indicate plasma
motions in the line of sight. We report 281 flares on late-type stars
(spectral types K3 M9). Six possible CME candidates were identified
that show excess flux in Balmer line wings. We calculated $H\alpha$
Flare energies and estimated the masses of the CME candidates. The
$H\alpha$ flare energies we derived range from $3 \times 10^{28}
- 2 \times 10^{33}$ erg. We find that the $H\alpha$ flare energy
increases with earlier types, while the fraction of flaring times
increases with later types. Our mass estimates for the CME candidates
range from $6 \times 10^{16} - 6 \times 10^{18}$ g, and the highest
projected velocities are $\sim 300 - 700$ km s$^{-1}$. We conclude
that our low detection rate of CMEs agrees with previous studies,
suggesting that the CME occurrence rate that can be detected with
optical spectroscopy is low for late-type main-sequence stars.
---------------------------------------------------------
Title: Drag-Based CME Modeling With Heliospheric Images Incorporating
Frontal Deformation: ELEvoHI 2.0
Authors: Hinterreiter, Jürgen; Amerstorfer, Tanja; Temmer, Manuela;
Reiss, Martin A.; Weiss, Andreas J.; Möstl, Christian; Barnard,
Luke A.; Pomoell, Jens; Bauer, Maike; Amerstorfer, Ute V.
2021SpWea..1902836H Altcode: 2021arXiv210808075H
The evolution and propagation of coronal mass ejections (CMEs) in
interplanetary space is still not well understood. As a consequence,
accurate arrival time and arrival speed forecasts are an unsolved
problem in space weather research. In this study, we present the ELlipse
Evolution model based on HI observations (ELEvoHI) and introduce a
deformable front to this model. ELEvoHI relies on heliospheric imagers
(HI) observations to obtain the kinematics of a CME. With the newly
developed deformable front, the model is able to react to the ambient
solar wind conditions during the entire propagation and along the
whole front of the CME. To get an estimate of the ambient solar wind
conditions, we make use of three different models: Heliospheric Upwind
eXtrapolation model (HUX), Heliospheric Upwind eXtrapolation with
time dependence model (HUXt), and EUropean Heliospheric FORecasting
Information Asset (EUHFORIA). We test the deformable front on a CME
first observed in STEREO-A/HI on February 3, 2010 14:49 UT. For this
case study, the deformable front provides better estimates of the
arrival time and arrival speed than the original version of ELEvoHI
using an elliptical front. The new implementation enables us to study
the parameters influencing the propagation of the CME not only for
the apex, but for the entire front. The evolution of the CME front,
especially at the flanks, is highly dependent on the ambient solar
wind model used. An additional advantage of the new implementation is
given by the possibility to provide estimates of the CME mass.
---------------------------------------------------------
Title: How to Estimate the Far-Side Open Flux Using STEREO Coronal
Holes
Authors: Heinemann, Stephan G.; Temmer, Manuela; Hofmeister, Stefan
J.; Stojakovic, Aleksandar; Gizon, Laurent; Yang, Dan
2021SoPh..296..141H Altcode: 2021arXiv210902375H
Global magnetic field models use as input synoptic data, which usually
show "aging effects" as the longitudinal 360<SUP>∘</SUP> information
is not obtained simultaneously. Especially during times of increased
solar activity, the evolution of the magnetic field may yield large
uncertainties. A significant source of uncertainty is the Sun's magnetic
field on the side of the Sun invisible to the observer. Various methods
have been used to complete the picture: synoptic charts, flux-transport
models, and far side helioseismology. In this study, we present a new
method to estimate the far-side open flux within coronal holes using
STEREO EUV observations. First, we correlate the structure of the
photospheric magnetic field as observed with the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory (HMI/SDO)
with features in the transition region. From the 304 Å intensity
distribution, which we found to be specific to coronal holes, we derive
an empirical estimate for the open flux. Then we use a large sample of
313 SDO coronal hole observations to verify this relation. Finally,
we perform a cross-instrument calibration from SDO to STEREO data
to enable the estimation of the open flux at solar longitudes not
visible from Earth. We find that the properties of strong unipolar
magnetic elements in the photosphere, which determine the coronal
hole's open flux, can be approximated by open fields in the transition
region. We find that structures below a threshold of 78 % (STEREO)
or 94 % (SDO) of the solar disk median intensity as seen in 304 Å
filtergrams are reasonably well correlated with the mean magnetic
flux density of coronal holes (cc=sp 0.59 ). Using the area covered
by these structures (A<SUB>OF</SUB>) and the area of the coronal hole
(A<SUB>CH</SUB>), we model the open magnetic flux of a coronal hole
as |Φ<SUB>CH</SUB>|=0.25 A<SUB>CH</SUB>exp (0.032 A<SUB>OF</SUB>)
with an estimated uncertainty of 40 to 60 %.
---------------------------------------------------------
Title: Coronal Hole Detection and Open Magnetic Flux
Authors: Linker, Jon A.; Heinemann, Stephan G.; Temmer, Manuela;
Owens, Mathew J.; Caplan, Ronald M.; Arge, Charles N.; Asvestari,
Eleanna; Delouille, Veronique; Downs, Cooper; Hofmeister, Stefan J.;
Jebaraj, Immanuel C.; Madjarska, Maria S.; Pinto, Rui F.; Pomoell,
Jens; Samara, Evangelia; Scolini, Camilla; Vršnak, Bojan
2021ApJ...918...21L Altcode: 2021arXiv210305837L
Many scientists use coronal hole (CH) detections to infer open
magnetic flux. Detection techniques differ in the areas that they
assign as open, and may obtain different values for the open magnetic
flux. We characterize the uncertainties of these methods, by applying
six different detection methods to deduce the area and open flux of
a near-disk center CH observed on 2010 September 19, and applying
a single method to five different EUV filtergrams for this CH. Open
flux was calculated using five different magnetic maps. The standard
deviation (interpreted as the uncertainty) in the open flux estimate
for this CH ≍ 26%. However, including the variability of different
magnetic data sources, this uncertainty almost doubles to 45%. We
use two of the methods to characterize the area and open flux for
all CHs in this time period. We find that the open flux is greatly
underestimated compared to values inferred from in situ measurements
(by 2.2-4 times). We also test our detection techniques on simulated
emission images from a thermodynamic MHD model of the solar corona. We
find that the methods overestimate the area and open flux in the
simulated CH, but the average error in the flux is only about 7%. The
full-Sun detections on the simulated corona underestimate the model
open flux, but by factors well below what is needed to account for
the missing flux in the observations. Under-detection of open flux in
coronal holes likely contributes to the recognized deficit in solar
open flux, but is unlikely to resolve it.
---------------------------------------------------------
Title: Modelling a multi-spacecraft coronal mass ejection encounter
with EUHFORIA
Authors: Asvestari, E.; Pomoell, J.; Kilpua, E.; Good, S.;
Chatzistergos, T.; Temmer, M.; Palmerio, E.; Poedts, S.; Magdalenic, J.
2021A&A...652A..27A Altcode: 2021arXiv210511831A
Context. Coronal mass ejections (CMEs) are a manifestation of the
Sun's eruptive nature. They can have a great impact on Earth, but also
on human activity in space and on the ground. Therefore, modelling
their evolution as they propagate through interplanetary space is
essential. <BR /> Aims: EUropean Heliospheric FORecasting Information
Asset (EUHFORIA) is a data-driven, physics-based model, tracing
the evolution of CMEs through background solar wind conditions. It
employs a spheromak flux rope, which provides it with the advantage of
reconstructing the internal magnetic field configuration of CMEs. This
is something that is not included in the simpler cone CME model used
so far for space weather forecasting. This work aims at assessing the
spheromak CME model included in EUHFORIA. <BR /> Methods: We employed
the spheromak CME model to reconstruct a well observed CME and compare
model output to in situ observations. We focus on an eruption from 6
January 2013 that was encountered by two radially aligned spacecraft,
Venus Express and STEREO-A. We first analysed the observed properties of
the source of this CME eruption and we extracted the CME properties as
it lifted off from the Sun. Using this information, we set up EUHFORIA
runs to model the event. <BR /> Results: The model predicts arrival
times from half to a full day ahead of the in situ observed ones,
but within errors established from similar studies. In the modelling
domain, the CME appears to be propagating primarily southward, which
is in accordance with white-light images of the CME eruption close
to the Sun. <BR /> Conclusions: In order to get the observed magnetic
field topology, we aimed at selecting a spheromak rotation angle for
which the axis of symmetry of the spheromak is perpendicular to the
direction of the polarity inversion line (PIL). The modelled magnetic
field profiles, their amplitude, arrival times, and sheath region length
are all affected by the choice of radius of the modelled spheromak.
---------------------------------------------------------
Title: Multi-channel coronal hole detection with convolutional
neural networks
Authors: Jarolim, R.; Veronig, A. M.; Hofmeister, S.; Heinemann,
S. G.; Temmer, M.; Podladchikova, T.; Dissauer, K.
2021A&A...652A..13J Altcode: 2021arXiv210414313J
Context. A precise detection of the coronal hole boundary is of
primary interest for a better understanding of the physics of coronal
holes, their role in the solar cycle evolution, and space weather
forecasting. <BR /> Aims: We develop a reliable, fully automatic
method for the detection of coronal holes that provides consistent
full-disk segmentation maps over the full solar cycle and can perform
in real-time. <BR /> Methods: We use a convolutional neural network
to identify the boundaries of coronal holes from the seven extreme
ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA)
and from the line-of-sight magnetograms provided by the Helioseismic
and Magnetic Imager (HMI) on board the Solar Dynamics Observatory
(SDO). For our primary model (Coronal Hole RecOgnition Neural Network
Over multi-Spectral-data; CHRONNOS) we use a progressively growing
network approach that allows for efficient training, provides detailed
segmentation maps, and takes into account relations across the full
solar disk. <BR /> Results: We provide a thorough evaluation for
performance, reliability, and consistency by comparing the model
results to an independent manually curated test set. Our model shows
good agreement to the manual labels with an intersection-over-union
(IoU) of 0.63. From the total of 261 coronal holes with an area
> 1.5 × 10<SUP>10</SUP> km<SUP>2</SUP> identified during
the time-period from November 2010 to December 2016, 98.1% were
correctly detected by our model. The evaluation over almost the full
solar cycle no. 24 shows that our model provides reliable coronal
hole detections independent of the level of solar activity. From a
direct comparison over short timescales of days to weeks, we find
that our model exceeds human performance in terms of consistency
and reliability. In addition, we train our model to identify coronal
holes from each channel separately and show that the neural network
provides the best performance with the combined channel information,
but that coronal hole segmentation maps can also be obtained from
line-of-sight magnetograms alone. <BR /> Conclusions: The proposed
neural network provides a reliable data set for the study of solar-cycle
dependencies and coronal-hole parameters. Given the fast and robust
coronal hole segmentation, the algorithm is also highly suitable for
real-time space weather applications. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140640/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: 2019 International Women's Day event. Two-step solar flare
with multiple eruptive signatures and low Earth impact
Authors: Dumbović, M.; Veronig, A. M.; Podladchikova, T.; Thalmann,
J. K.; Chikunova, G.; Dissauer, K.; Magdalenić, J.; Temmer, M.; Guo,
J.; Samara, E.
2021A&A...652A.159D Altcode: 2021arXiv210615417D
Context. We present a detailed analysis of an eruptive event that
occurred on 2019 March 8 in the active region AR 12734, which we
refer as the International Women's Day event. The event under study
is intriguing based on several aspects: (1) low-coronal eruptive
signatures come in `pairs', namely, there is a double-peaked flare,
two coronal dimmings, and two extreme ultraviolet (EUV) waves; (2)
although the event is characterized by a complete chain of eruptive
signatures, the corresponding coronagraphic signatures are weak;
and (3) although the source region of the eruption is located close
to the center of the solar disc and the eruption is thus presumably
Earth-directed, heliospheric signatures are very weak with very weak
Earth impact. <BR /> Aims: In order to understand the initiation and
evolution of this particular event, we performed a comprehensive
analysis using a combined observational-modeling approach. <BR />
Methods: We analyzed a number of multi-spacecraft and multi-instrument
(both remote-sensing and in situ) observations, including soft X-ray,
EUV, radio and white-light emission, as well as plasma, magnetic field,
and particle measurements. We employed 3D nonlinear force-free modeling
to investigate the coronal magnetic field configuration in and around
the active region, the graduated cylindrical shell model to make a 3D
reconstruction of the CME geometry, and the 3D magnetohydrodynamical
numerical model EUropean Heliospheric FORecasting Information Asset
to model the background state of the heliosphere. <BR /> Results:
Our results reveal a two-stage C1.3 flare, associated with two
EUV waves that occur in close succession and two-stage coronal
dimmings that evolve co-temporally with the flare and type II and
III radio bursts. Despite its small GOES class, a clear drop in
magnetic free energy and helicity is observed during the flare. White
light observations do not unambiguously indicate two separate CMEs,
but rather a single entity most likely composed of two sheared and
twisted structures corresponding to the two eruptions observed in the
low corona. The corresponding interplanetary signatures are that of
a small flux rope swith indications of strong interactions with the
ambient plasma, which result in a negligible geomagnetic impact. <BR
/> Conclusions: Our results indicate two subsequent eruptions of
two systems of sheared and twisted magnetic fields, which already
begin to merge in the upper corona and start to evolve further out
as a single entity. The large-scale magnetic field significantly
influences both the early and the interplanetary evolution of the
structure. During the first eruption, the stability of the overlying
field was disrupted, enabling the second eruption. We find that during
the propagation in the interplanetary space the large-scale magnetic
field, that is, the location of heliospheric current sheet between the
AR and the Earth, is likely to influence propagation, along with the
evolution of the erupted structure(s). <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140752/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Probabilistic Drag-Based Ensemble Model (DBEM) Evaluation
for Heliospheric Propagation of CMEs
Authors: Čalogović, Jaša; Dumbović, Mateja; Sudar, Davor; Vršnak,
Bojan; Martinić, Karmen; Temmer, Manuela; Veronig, Astrid M.
2021SoPh..296..114C Altcode: 2021arXiv210706684C
The Drag-based Model (DBM) is a 2D analytical model for heliospheric
propagation of Coronal Mass Ejections (CMEs) in ecliptic plane
predicting the CME arrival time and speed at Earth or any other given
target in the solar system. It is based on the equation of motion and
depends on initial CME parameters, background solar wind speed, w and
the drag parameter γ . A very short computational time of DBM (<
0.01 s) allowed us to develop the Drag-Based Ensemble Model (DBEM)
that takes into account the variability of model input parameters
by making an ensemble of n different input parameters to calculate
the distribution and significance of the DBM results. Thus the DBEM
is able to calculate the most likely CME arrival times and speeds,
quantify the prediction uncertainties and determine the confidence
intervals. A new DBEMv3 version is described in detail and evaluated
for the first time determining the DBEMv3 performance and errors by
using various CME-ICME lists and it is compared with previous DBEM
versions, ICME being a short-hand for interplanetary CME. The analysis
to find the optimal drag parameter γ and ambient solar wind speed
w showed that somewhat higher values (γ ≈0.3 ×10<SUP>−7</SUP>
km<SUP>−1</SUP>, w ≈ 425 km s<SUP>−1</SUP>) for both of these DBEM
input parameters should be used for the evaluation than the previously
employed ones. Based on the evaluation performed for 146 CME-ICME pairs,
the DBEMv3 performance with mean error (ME) of −11.3 h, mean absolute
error (MAE) of 17.3 h was obtained. There is a clear bias towards
the negative prediction errors where the fast CMEs are predicted to
arrive too early, probably due to the model physical limitations and
input errors (e.g. CME launch speed). This can be partially reduced by
using larger values for γ resulting in smaller prediction errors (ME
=−3.9 h, MAE = 14.5 h) but at the cost of larger prediction errors
for single fast CMEs as well as larger CME arrival speed prediction
errors. DBEMv3 showed also slight improvement in the performance for
all calculated output parameters compared to the previous DBEM versions.
---------------------------------------------------------
Title: Drag-based model (DBM) tools for forecast of coronal mass
ejection arrival time and speed
Authors: Dumbović, Mateja; Čalogović, Jaša; Martinić, Karmen;
Vršnak, Bojan; Sudar, Davor; Temmer, Manuela; Veronig, Astrid
2021FrASS...8...58D Altcode: 2021arXiv210314292D
Forecasting the arrival time of coronal mass ejections (CMEs) and
their associated shocks is one of the key aspects of space weather
research and predictions. One of the commonly used models is, due
to its simplicity and calculation speed, the analytical drag-based
model (DBM) for heliospheric propagation of CMEs. DBM relies on
the observational fact that slow CMEs accelerate whereas fast CMEs
decelerate, and is based on the concept of MHD drag, which acts to
adjust the CME speed to the ambient solar wind. Although physically
DBM is applicable only to the CME magnetic structure, it is often used
as a proxy for the shock arrival. In recent years, the DBM equation
has been used in many studies to describe the propagation of CMEs
and shocks with different geometries and assumptions. Here we give
an overview of the five DBM versions currently available and their
respective tools, developed at Hvar Observatory and frequently used
by researchers and forecasters. These include: 1) basic 1D DBM, a 1D
model describing the propagation of a single point (i.e. the apex of
the CME) or concentric arc (where all points propagate identically); 2)
advanced 2D self-similar cone DBM, a 2D model which combines basic DBM
and cone geometry describing the propagation of the CME leading edge
which evolves self-similarly; 3) 2D flattening cone DBM, a 2D model
which combines basic DBM and cone geometry describing the propagation
of the CME leading edge which does not evolve self-similarly; 4)
DBEMv1, an ensemble version of the 2D flattening cone DBM which uses
CME ensembles as an input and 5) DBEMv3, an ensemble version of the
2D flattening cone DBM which creates CME ensembles based on the input
uncertainties. All five versions have been tested and published in
recent years and are available online or upon request. We provide an
overview of these five tools, of their similarities and differences,
as well as discuss and demonstrate their application.
---------------------------------------------------------
Title: Properties of stream interaction regions at Earth and Mars
during the declining phase of SC 24
Authors: Geyer, Paul; Temmer, Manuela; Guo, Jingnan; Heinemann,
Stephan G.
2021A&A...649A..80G Altcode: 2021arXiv210205948G
<BR /> Aims: We inspect the evolution of stream interaction regions
(SIRs) from Earth to Mars, covering the distance range 1-1.5 AU, over
the declining phase of solar cycle 24 (2014-2018). So far, studies
only analyzed SIRs measured at Earth and Mars at different times. We
compare existing catalogs for both heliospheric distances and arrive at
a clean dataset for the identical time range. This allows a well-sampled
statistical analysis and for the opposition phases of the planets an
in-depth analysis of SIRs as they evolve with distance. <BR /> Methods:
We use in situ solar wind data from OMNI and the Mars Atmosphere and
Volatile EvolutioN spacecraft as well as remote sensing data from Solar
Dynamics Observatory. A superposed epoch analysis is performed for bulk
speed, proton density, temperature, magnetic field magnitude and total
perpendicular pressure. Additionally, a study of events during the
two opposition phases of Earth and Mars in the years 2016 and 2018 is
conducted. SIR related coronal holes with their area as well as their
latitudinal and longitudinal extent are extracted and correlated to
the maximum bulk speed and duration of the corresponding high speed
solar wind streams following the stream interaction regions. <BR />
Results: We find that while the entire solar wind high speed stream
shows no expansion as it evolves from Earth to Mars, the crest of
the high speed stream profile broadens by about 17%, and the magnetic
field and total pressure by about 45% around the stream interface. The
difference between the maximum and minimum values in the normalized
superposed profiles increases slightly or stagnates from 1-1.5 AU
for all parameters, except for the temperature. A sharp drop at zero
epoch time is observed in the superposed profiles for the magnetic
field strength at both heliospheric distances. The two opposition
phases reveal similar correlations of in situ data with coronal hole
parameters for both planets. Maximum solar wind speed has a stronger
dependence on the latitudinal extent of the respective coronal hole
than on its longitudinal extent. We arrive at an occurrence rate of
fast forward shocks three times higher at Mars than at Earth.
---------------------------------------------------------
Title: Current status of project SWEETS: Estimating thermospheric
neutral mass densities from satellite data at various altitudes
Authors: Krauss, Sandro; Suesser-Rechberger, Barbara; Behzadpour,
Saniya; Mayer-Guerr, Torsten; Temmer, Manuela; Kroisz, Sofia;
Drescher, Lukas
2021EGUGA..23.4174K Altcode:
Within the project SWEETS (funded by the FFG Austria) it is intended
to develop a forecasting model, to predict the expected impact of solar
events, like coronal mass ejections (CMEs), on satellites at different
altitudes between 300-800 km. For the realization, scientific data,
such as kinematic orbit information and accelerometer measurements, from
a wide variety of satellites are incorporated. Based on the evaluation
of the impact of several hundred solar events on the thermosphere the
forecasting will be realized through a joint analysis and evaluation
of solar wind plasma and magnetic field data observed at the Lagrange
point L1.In this contribution we show first preliminary results of
thermospheric densities estimates based on kinematic orbit information
for different satellite missions (e.g., TerraSAR-X, TanDEM-X, Swarm A-C,
GRACE, GRACE-FO, CHAMP). To validate the outcome, we compare the results
with state-of-the-art thermospheric models as well as with densities
estimated from accelerometer measurements if available. Finally,
for some specific CME events we will perform a comparison between
the post-processed density estimates and results from our preliminary
forecasting tool.
---------------------------------------------------------
Title: Statistical study of CMEs, lateral overexpansion and SEP events
Authors: Adamis, Alexandros; Veronig, Astrid; Podladchikova, Tatiana;
Dissauer, Karin; Miteva, Rositsa; Guo, Jingnan; Haberle, Veronika;
Dumbovic, Mateja; Temmer, Manuela; Kozarev, Kamen; Magdalenic, Jasmina;
Kay, Christina
2021EGUGA..23.3216A Altcode:
We present a statistical study on the early evolution of coronal mass
ejections (CMEs), to better understand the effect of CME (over)-
expansion and how it relates to the production of Solar Energetic
Particle (SEP) events. We study the kinematic CME characteristics
in terms of their radial and lateral expansion, from their early
evolution in the Sun"s atmosphere as observed in EUV imagers and
coronagraphs. The data covers 72 CMEs that occurred in the time range of
July 2010 to September 2012, where the twin STEREO spacecraft where in
quasiquadrature to the Sun-Earth line. From the STEREO point-of-view,
the CMEs under study were observed close to the limb. We calculated
the radial and lateral height (width) versus time profiles and
derived the corresponding peak and mean velocities, accelerations,
and angular expansion rates, with particular emphasis on the role
of potential lateral overexpansion in the early CME evolution. We
find high correlations between the radial and lateral CME velocities
and accelerations. CMEs that are associated tend to be located at
the high-value end of the distributions of velocities, widths, and
expansion rates compared to nonSEP associated events.
---------------------------------------------------------
Title: Statistical relations between in-situ measured Bz component
and thermospheric density variations
Authors: Kroisz, Sofia; Drescher, Lukas; Temmer, Manuela; Krauss,
Sandro; Süsser-Rechberger, Barbara; Mayer-Gürr, Torsten
2021EGUGA..23.4773K Altcode:
Through advanced statistical investigation and evaluation of solar
wind plasma and magnetic field data, we investigate the statistical
relation between the magnetic field Bz component, measured at L1,
and Earth"s thermospheric neutral density. We will present preliminary
results of the time series analyzes using in-situ plasma and magnetic
field measurements from different spacecraft in near Earth space (e.g.,
ACE, Wind, DSCOVR) and relate those to derived thermospheric densities
from various satellites (e.g., GRACE, CHAMP). The long and short term
variations and dependencies in the solar wind data are related to
variations in the neutral density of the thermosphere and geomagnetic
indices. Special focus is put on the specific signatures that stem from
coronal mass ejections and stream or corotating interaction regions. The
results are used to develop a novel short-term forecasting model called
SODA (Satellite Orbit DecAy). This is a joint study between TU Graz
and University of Graz funded by the FFG Austria (project "SWEETS").
---------------------------------------------------------
Title: Multi-Channel Coronal Hole Detection with Convolutional
Neural Networks
Authors: Jarolim, Robert; Veronig, Astrid; Hofmeister, Stefan;
Heinemann, Stephan; Temmer, Manuela; Podladchikova, Tatiana; Dissauer,
Karin
2021EGUGA..23.1490J Altcode:
Being the source region of fast solar wind streams, coronal holes are
one of the key components which impact space weather. The precise
detection of the coronal hole boundary is an important criterion
for forecasting and solar wind modeling, but also challenges our
current understanding of the magnetic structure of the Sun. We use
deep-learning to provide new methods for the detection of coronal holes,
based on the multi-band EUV filtergrams and LOS magnetogram from the
AIA and HMI instruments onboard the Solar Dynamics Observatory. The
proposed neural network is capable to simultaneously identify full-disk
correlations as well as small-scale structures and efficiently combines
the multi-channel information into a single detection. From the
comparison with an independent manually curated test set, the model
provides a more stable extraction of coronal holes than the samples
considered for training. Our method operates in real-time and provides
reliable coronal hole extractions throughout the solar cycle, without
any additional adjustments. We further investigate the importance of
the individual channels and show that our neural network can identify
coronal holes solely from magnetic field data.
---------------------------------------------------------
Title: Comparative study of halo CME arrival predictions
Authors: Yordanova, Emiliya; Dumbovic, Mateja; Temmer, Manuela;
Scolini, Camilla; Magdalenic, Jasmina; Thompson, William J.;
Sorriso-Valvo, Luca; Dimmock, Andrew P.; Rosenqvist, Lisa
2021EGUGA..2314187Y Altcode:
Halo coronal mass ejections (CMEs) are one of the most effective
drivers of intense geomagnetic storms. Despite the recent advances
in space weather forecasting, the accurate arrival prediction of
halo CMEs remains a challenge. This is because in general CMEs
interact with the background solar wind during their propagation in
the interplanetary space. In addition, in the case of halo CMEs,
the accurate estimation of their kinematics is difficult due
to projection effects in the plane-of-sky.In this study, we are
revisiting the arrival of twelve geoeffective Earth-directed fast
halo CMEs using an empirical and a numerical approaches. For this
purpose we refine the input to the Drag-based Model (DBM) and to
the EUropean Heliospheric Forecasting Information Asset (EUHFORIA),
which are recently available for users from the ESA Space Situational
Awareness Portal (http://swe.ssa.esa.int).The DBM model has been tested
using different values for the input drag parameter. On average, the
predicted arrival times are confined in the range of ± 10 h. The
closest arrival to the observed one has been achieved with a drag
value higher than the recommended for fast CMEs. Setting a higher
drag also helped to obtain a closer to the observed CME arrival
speed prediction. These results suggest that the exerted solar wind
drag was higher than expected. Further, we are searching for clues
about the CME propagation by performing EUHFORIA runs using the same
CME kinematics. Preliminary results show that both models perform
poorly for CMEs that have possibly undergone CME-CME interaction,
underlying again the importance of taking into account the state of
the interplanetary space in the CME forecast.
---------------------------------------------------------
Title: Deriving CME volume and density from remote sensing data
Authors: Temmer, Manuela; Holzknecht, Lukas; Dumbovic, Mateja;
Vrsnak, Bojan; Sachdeva, Nishtha; Heinemann, Stephan G.; Dissauer,
Karin; Scolini, Camilla; Asvestari, Eleanna; Veronig, Astrid M.;
Hofmeister, Stefan
2021EGUGA..23.2535T Altcode:
Using combined STEREO-SOHO white-light data, we present a method to
determine the volume and density of a coronal mass ejection (CME) by
applying the graduated cylindrical shell model (GCS) and deprojected
mass derivation. Under the assumption that the CME mass is roughly
equally distributed within a specific volume, we expand the CME
self-similarly and calculate the CME density for distances close to the
Sun (15-30 Rs) and at 1 AU. The procedure is applied on a sample of 29
well-observed CMEs and compared to their interplanetary counterparts
(ICMEs). Specific trends are derived comparing calculated and in-situ
measured proton densities at 1 AU, though large uncertainties are
revealed due to the unknown mass and geometry evolution: i) a moderate
correlation for the magnetic structure having a mass that stays
rather constant and ii) a weak correlation for the sheath density by
assuming the sheath region is an extra mass - as expected for a mass
pile-up process - that is in its amount comparable to the initial
CME deprojected mass. High correlations are derived between in-situ
measured sheath density and the solar wind density and solar wind speed
as measured 24 hours ahead of the arrival of the disturbance. This
gives additional confirmation that the sheath-plasma indeed stems from
piled-up solar wind material. While the CME interplanetary propagation
speed is not related to the sheath density, the size of the CME may
play some role in how much material is piled up.
---------------------------------------------------------
Title: Constraining the CME parameters of the spheromak flux rope
implemented in EUHFORIA
Authors: Asvestari, Eleanna; Pomoell, Jens; Kilpua, Emilia; Good,
Simon; Chatzistergos, Theodosios; Temmer, Manuela; Palmerio, Erika;
Poedts, Stefaan; Magdalenic, Jasmina
2021EGUGA..23.3291A Altcode:
Coronal mass ejections (CMEs) are primary drivers of space weather
phenomena. Modelling the evolution of the internal magnetic field
configuration of CMEs as they propagate through the interplanetary
space is an essential part of space weather forecasting. EUHFORIA
(EUropean Heliospheric FORecasting Information Asset) is a data-driven,
physics-based model, able to trace the evolution of CMEs and CME-driven
shocks through realistic background solar wind conditions. It employs
a spheromak-type magnetic flux rope that is initially force-free,
providing it with the advantage of modelling CME as magnetised
structures. For this work we assessed the spheromak CME model
employed in EUHFORIA with a test CME case study. The selected CME
eruption occurred on the 6th of January 2013 and was encountered
by two spacecraft, Venus Express and STEREO--A, which were radially
aligned at the time of the CME passage. Our focus was to constrain
the input parameters, with particular interest in: (1) translating
the angular widths of the graduated cylindrical shell (GCS) fitting
to the spheromak radius, and (2) matching the observed magnetic field
topology at the source region. We ran EUHFORIA with three different
spheromak radii. The model predicts arrival times from half to a full
day ahead of the one observed in situ. We conclude that the choice
of spheromak radius affected the modelled magnetic field profiles,
their amplitude, arrival times, and sheath region length.
---------------------------------------------------------
Title: CME arrival time predictions with a deformable front
Authors: Hinterreiter, Jürgen; Amerstorfer, Tanja; Reiss, Martin A.;
Weiss, Andreas J.; Möstl, Christian; Temmer, Manuela; Bauer, Maike;
Bailey, Rachel L.; Amerstorfer, Ute V.
2021EGUGA..23.5830H Altcode:
We present the first results of our newly developed CME arrival
prediction model, which allows the CME front to deform and adapt to
the changing solar wind conditions. Our model is based on ELEvoHI
and makes use of the WSA/HUX (Wang-Sheeley-Arge/Heliospheric Upwind
eXtrapolation) model combination, which computes large-scale ambient
solar wind conditions in the interplanetary space. With an estimate of
the solar wind speed and density, we are able to account for the drag
exerted on different parts of the CME front. Initially, our model relies
on heliospheric imager observations to confine an elliptical CME front
and to obtain an initial speed and drag parameter for the CME. After
a certain distance, each point of the CME front is propagating based
on the conditions in the heliosphere. In this case study, we compare
our results to previous arrival time predictions using ELEvoHI with
a rigid CME front. We find that the actual arrival time at Earth and
the arrival time predicted by the new model are in very good agreement.
---------------------------------------------------------
Title: Evolution of stream interaction regions from 1 to 1.5 AU
Authors: Geyer, Paul; Temmer, Manuela; Guo, Jingnan; Heinemann, Stephan
2021EGUGA..2312513G Altcode:
We inspect the evolution of stream interaction regions from Earth to
Mars for the declining solar cycle 24. In particular, the opposition
phases of the two planets are analyzed in more detail. So far, there
is no study comparing the long-term properties of stream interaction
regions and accompanying high-speed streams at both planets for the
same time period. We build a catalogue covering a dataset of all
measured stream interaction regions at Earth and Mars for the time
period December 2014 - November 2018. The number of events (>120)
allows for a strong statistical basis. To build the catalogue we use
near-earth OMNI data as well as measurements from the Mars Atmosphere
and Volatile EvolutioN (MAVEN) spacecraft. For the opposition phase,
we additionally use image data from the Solar Dynamics Observatory
to complement the in-situ observations. Bulk speed, proton density,
temperature, magnetic field magnitude and total perpendicular pressure
are statistically evaluated using a superposed epoch analysis. For
the opposition phase, coronal holes that are linked to individual
streams are identified. The extracted coronal hole areas (using CATCH)
and their longitudinal/latitudinal extension are correlated to the
duration and maximum bulk speed of the high-speed stream following
the passage of a stream interaction region. We find that an expansion
of the stream interface from 1 to 1.5 AU is most visible in magnetic
field and total perpendicular pressure. The duration of the high-speed
stream does not increase significantly from Earth to Mars, however,
the stream crest seems to increase. The amplitudes of the SW parameters
are found to only slightly increase or stagnate from 1 - 1.5 AU. We
arrive at similar correlation coefficients for both planets with the
properties of the related coronal holes. There is a stronger linking
of maximum bulk speed to latitudinal extent of the coronal hole than
to the longitudinal. On average, the occurrence rate of fast forward
shocks increases from Earth to Mars.
---------------------------------------------------------
Title: Why are ELEvoHI CME Arrival Predictions Different if Based
on STEREO A or STEREO B Heliospheric Imager Observations?
Authors: Hinterreiter, Jürgen; Amerstorfer, Tanja; Reiss, Martin
A.; Möstl, Christian; Temmer, Manuela; Bauer, Maike; Amerstorfer,
Ute V.; Bailey, Rachel L.; Weiss, Andreas J.; Davies, Jackie A.;
Barnard, Luke A.; Owens, Mathew J.
2021SpWea..1902674H Altcode: 2021arXiv210207478H
Accurate forecasting of the arrival time and arrival speed of
coronal mass ejections (CMEs) is an unsolved problem in space weather
research. In this study, a comparison of the predicted arrival times
and speeds for each CME based, independently, on the inputs from the
two STEREO vantage points is carried out. We perform hindcasts using
ELlipse Evolution model based on Heliospheric Imager observations
(ELEvoHI) ensemble modeling. An estimate of the ambient solar wind
conditions is obtained by the Wang Sheeley Arge/Heliospheric Upwind
eXtrapolation (WSA/HUX) model combination that serves as input to
ELEvoHI. We carefully select 12 CMEs between February 2010 and July
2012 that show clear signatures in both STEREO A and STEREO B HI time
elongation maps, that propagate close to the ecliptic plane, and that
have corresponding in situ signatures at Earth. We find a mean arrival
time difference of 6.5 h between predictions from the two different
viewpoints, which can reach up to 9.5 h for individual CMEs, while the
mean arrival speed difference is 63 km s<SUP>−1</SUP>. An ambient
solar wind with a large speed variance leads to larger differences
in the STEREO A and STEREO B CME arrival time predictions (cc =
0.92). Additionally, we compare the predicted arrivals, from both
spacecraft, to the actual in situ arrivals at Earth and find a mean
absolute error of 7.5 ± 9.5 h for the arrival time and 87 ± 111 km
s<SUP>−1</SUP> for the arrival speed. There is no tendency for one
spacecraft to provide more accurate arrival predictions than the other.
---------------------------------------------------------
Title: Search for flares and associated CMEs on late-type
main-sequence stars in optical SDSS spectra
Authors: Koller, Florian; Leitzinger, Martin; Temmer, Manuela; Odert,
Petra; Beck, Paul G.; Veronig, Astrid
2021A&A...646A..34K Altcode: 2020arXiv201200786K
<BR /> Aims: This work aims to detect and classify stellar flares and
potential stellar coronal mass ejection (CME) signatures in optical
spectra provided by the Sloan Digital Sky Survey (SDSS) data release
14. The sample is constrained to all F, G, K, and M main-sequence
type stars, resulting in more than 630 000 stars. This work makes
use of the individual spectral exposures provided by the SDSS. <BR
/> Methods: An automatic flare search was performed by detecting
significant amplitude changes in the Hα and Hβ spectral lines after
a Gaussian profile was fit to the line core. CMEs were searched for
by identifying asymmetries in the Balmer lines caused by the Doppler
effect of plasma motions in the line of sight. <BR /> Results: We
identified 281 flares on late-type stars (spectral types K3 - M9). We
identified six possible CME candidates showing excess flux in Balmer
line wings. Flare energies in Hα were calculated and masses of the
CME candidates were estimated. The derived Hα flare energies range
from 3 × 10<SUP>28</SUP> - 2 × 10<SUP>33</SUP> erg. The Hα flare
energy increases with earlier types, while the fraction of flaring times
increases with later types. Mass estimates for the CME candidates are
in the range of 6 × 10<SUP>16</SUP> - 6 × 10<SUP>18</SUP> g, and the
highest projected velocities are ~300-700 km s<SUP>-1</SUP>. <BR />
Conclusions: The low detection rate of CMEs we obtained agrees with
previous studies, suggesting that for late-type main-sequence stars the
CME occurrence rate that can be detected with optical spectroscopy is
low. <P />Table C.1 is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A34">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A34</A>
---------------------------------------------------------
Title: Quo vadis, European Space Weather community?
Authors: Lilensten, Jean; Dumbović, Mateja; Spogli, Luca; Belehaki,
Anna; Van der Linden, Ronald; Poedts, Stefaan; Barata, Teresa; Bisi,
Mario M.; Cessateur, Gaël; De Donder, Erwin; Guerrero, Antonio;
Kilpua, Emilia; Korsos, Marianna B.; Pinto, Rui F.; Temmer, Manuela;
Tsagouri, Ioanna; Urbář, Jaroslav; Zuccarello, Francesca
2021JSWSC..11...26L Altcode:
This paper was written by a group of European researchers believing
that now is the right time to frame the Space Weather and Space
Climate discipline in Europe for future years. It is devoted to
openly discussing the organisation and sustainability of the European
Space Weather community and its assets in the (near) future. More
specifically, we suggest that the European Space Weather community
lacks a uniting organisation to help the community to sustain and
develop the successful efforts made thus far. Our aim is not to draw
a complete and exhaustive panorama of Space Weather throughout the
world, nor even throughout Europe. It is not a new white paper on the
science and applications: there exist many (e.g. Tsurutani et al.,
2020 Nonlinear Processes Geophys 27(1): 75-119); nor another roadmap:
several important have been published recently (e.g. Schrijver et al.,
2015. Adv Space Res 55(12): 2745-2807; Opgenoorth et al., 2019. J Space
Weather Space Clim 9: A37). Our aim is to question our practices and
organisation in front of several changes that have occurred in the
recent years and to set the ground to provide coordinated answers
to these questions being posed in Europe, and to make these answers
discussed throughout the world. This group was assembled first through
a series of sessions devoted to the sustainability of Space Weather
research during the European Space Weather Week (ESWW) series of
meetings, specifically: ESWW 14 (2017), ESWW 15 (2018), and ESWW 16
(2019). It then grew from discussions and personal contacts. The authors
do not pretend to identify the full range of opinions in Europe,
although they do come from 13 different European countries with a
large span of ages (around half are below the age of 40 years old at
the time of writing) with a good gender balance ending with a diverse
mix of young and motivated scientists and senior people who have played
a role in shaping the Space Weather community in Europe. The questions
and the propositions to organise Space Weather in Europe in the future
result from their discussions through these meetings and through remote
meetings during the pandemic. We wish to share them with all those who
consider themselves as members of the European Space Weather community
and/or are interested in its future and to propose actions. We do this,
bearing in mind that Europe plays a key international role in Space
Weather which extends beyond the ESA and EU/EC geographic area.
---------------------------------------------------------
Title: Statistical Approach on Differential Emission Measure of
Coronal Holes using the CATCH Catalog
Authors: Heinemann, Stephan G.; Saqri, Jonas; Veronig, Astrid M.;
Hofmeister, Stefan J.; Temmer, Manuela
2021SoPh..296...18H Altcode: 2021arXiv210213396H
Coronal holes are large-scale structures in the solar atmosphere
that feature a reduced temperature and density in comparison to the
surrounding quiet Sun and are usually associated with open magnetic
fields. We perform a differential emission measure analysis on the
707 non-polar coronal holes in the Collection of Analysis Tools for
Coronal Holes (CATCH) catalog to derive and statistically analyze
their plasma properties (i.e. temperature, electron density, and
emission measure). We use intensity filtergrams of the six coronal EUV
filters from the Atmospheric Imaging Assembly onboard the Solar Dynamics
Observatory, which cover a temperature range from ≈10<SUP>5.5</SUP> to
10<SUP>7.5</SUP>K. Correcting the data for stray and scattered light, we
find that all coronal holes have very similar plasma properties with an
average temperature of 0.94 ±0.18 MK, a mean electron density of (2.4
±0.7 )×10<SUP>8</SUP>cm−<SUP>3</SUP>, and a mean emission measure
of (2.8 ±1.6 )×10<SUP>26</SUP>cm−<SUP>5</SUP>. The temperature
distribution within the coronal holes was found to be largely uniform,
whereas the electron density shows a 30 to 40% linear decrease from the
boundary towards the inside of the coronal hole. At distances greater
than 20″ (≈15 Mm) from the nearest coronal hole boundary, the
density also becomes statistically uniform. The coronal hole temperature
may show a weak solar-cycle dependency, but no statistically significant
correlation of plasma properties with solar-cycle variations could be
determined throughout the observed period between 2010 and 2019.
---------------------------------------------------------
Title: Towards solving the source to impact chain of Space Weather
processes
Authors: Temmer, Manuela
2021cosp...43E.643T Altcode:
Space Weather is of global and major interest that sustains an exciting
and wealthy interdisciplinary research community. In that respect,
science and development of forecasting tools needs to understand the
chain of action that causes Space Weather, starting from processes at
the Sun, in interplanetary space, and impact at Earth. The initiative
called iSWAT (international Space Weather Action Teams) aims towards
tackling the broad spectrum of issues and addresses individual
communities to form interdisciplinary partnerships maximizing
return on investments to national and international space weather
programs. With that iSWAT fosters information and knowledge exchange
between international research groups on solar-, heliospheric- and
geo-space in order to improve existing and to develop new models. In
that broad spectrum of topics, I will specifically focus on the modeling
of the background solar wind and embedded coronal mass ejections.
---------------------------------------------------------
Title: Deriving CME Density From Remote Sensing Data and Comparison
to In Situ Measurements
Authors: Temmer, M.; Holzknecht, L.; Dumbović, M.; Vršnak, B.;
Sachdeva, N.; Heinemann, S. G.; Dissauer, K.; Scolini, C.; Asvestari,
E.; Veronig, A. M.; Hofmeister, S. J.
2021JGRA..12628380T Altcode: 2020arXiv201106880T
We determine the three dimensional geometry and deprojected mass of 29
well observed coronal mass ejections (CMEs) and their interplanetary
counterparts (ICMEs) using combined Solar Terrestrial Relations
Observatory Solar and Heliospheric Observatory white light data. From
the geometry parameters, we calculate the volume of the CME for the
magnetic ejecta (flux rope type geometry) and sheath structure (shell
like geometry resembling the (I)CME frontal rim). Working under the
assumption that the CME mass is roughly equally distributed within a
specific volume, we expand the CME self similarly and calculate the CME
density for distances close to the Sun (15-30 Rs) and at 1 AU. Specific
trends are derived comparing calculated and in situ measured proton
densities at 1 AU, though large uncertainties are revealed due to the
unknown mass and geometry evolution: (1) a moderate correlation for
the magnetic structure having a mass that stays rather constant (cc
≈ 0.56 - 0.59), and (2) a weak correlation for the sheath density (cc
≈ 0.26) by assuming the sheath region is an extra mass—as expected
for a mass pile up process—that is in its amount comparable to the
initial CME deprojected mass. High correlations are derived between in
situ measured sheath density and the solar wind density (cc ≈ -0.73)
and solar wind speed (cc ≈ 0.56) as measured 24 h ahead of the arrival
of the disturbance. This gives additional confirmation that the sheath
plasma indeed stems from piled up solar wind material. While the CME
interplanetary propagation speed is not related to the sheath density,
the size of the CME may play some role in how much material could be
piled up.
---------------------------------------------------------
Title: Improving Understanding and Assessment of the Ambient
Solar Wind
Authors: Reiss, Martin; Moestl, Christian; Linker, Jon; Mullinix,
Richard; Rastaetter, Lutz; Temmer, Manuela; Arge, Charles; MacNeice,
Peter; Wiegand, Chiu; Muglach, Karin; Ko, Kuen
2021cosp...43E2398R Altcode:
The Sun's magnetic field drives the evolving ambient solar wind flow
and the magnetic field embedded within it. Thus, studying the magnetic
field configuration in the solar atmosphere is of crucial importance
for improving our understanding of and ultimately predicting space
weather from Sun to Earth. Coronal holes are regions of low intensity
emission in EUV and X-ray images. Coronal holes are closely associated
with open magnetic field lines, along which the solar wind accelerates
to supersonic speeds. Therefore, they play a central role in shaping
the structure of the heliosphere and defining key properties in
interplanetary space, such as the solar wind bulk speed, magnetic field
strength, and field orientation. Answering vital research questions
related to the ambient solar wind requires an interdisciplinary strategy
and the coordinated collaboration of international partners. Here we
present the COSPAR ISWAT activities for improving the understanding
and assessment of the evolving ambient solar wind flow embedded in
the 'Coronal Hole Boundary Working Team' and the 'Ambient Solar
Wind Validation Team'. Specifically, we present our progress in
evaluating the uncertainty of coronal hole boundary locations in
solar observations, and our progress in establishing an online hub for
validation of ambient solar wind models. In context, we demonstrate
the first application of a new online platform enabling developers
and end-users to directly assess the quality of state-of-the-art
solar wind model solutions. To conclude, we present the objectives,
current status and roadmaps of both action teams, and discuss the main
challenges we face in the realization of our objectives.
---------------------------------------------------------
Title: Life-time evolution and magnetic structure of coronal holes
Authors: Heinemann, Stephan; Pomoell, Jens; Temmer, Manuela; Bourdin,
Philippe
2021cosp...43E1024H Altcode:
The study of the evolution of coronal holes (CHs) is especially
important in the context of high--speed solar wind streams
emanating from them. Slow and high speed stream interaction
regions may deliver large amount of energy into the Earth's
magnetosphere-termosphere-ionosphere system system, cause geomagnetic
storms, and shape interplanetary space. The open magnetic structure,
its evolution and interplay with the local and global fields strongly
defines the coronal and solar wind properties. Only by understanding
these we can attempt to create a full picture of our heliosphere. By
statistically investigating the long--term evolution of 16 well
observed CHs, which are distributed in time over a full solar cycle,
we aim to reveal processes that drive the observed changes in the
CH parameters. We use remote sensing image data from SDO and focus
on coronal, morphological and underlying photospheric magnetic field
characteristics as well as investigate the evolution of the associated
high--speed streams from in-situ measurements. The analysis of the
observational data is supported by modeling, based on synthetic data
in order to simulate the small-scale magnetic field topology in 3
dimensions. We find that the CH area evolution mostly shows a rough
trend of growing to a maximum followed by a decay. No correlation of
the area evolution to the evolution of the signed magnetic flux and
signed magnetic flux density enclosed in the projected coronal hole
area was found. From this we conclude that the magnetic flux within
the extracted coronal hole boundaries is not the main cause for its
area evolution. This is supported by the model results. Change rates
of the signed mean magnetic flux density and the signed magnetic flux
are derived to be dependent on the solar cycle rather than on the
evolution of the individual CH. This clearly hints towards that the
global magnetic field gives significant contribution to the evolution
of open magnetic field structures on the Sun. The velocities of the
high speed streams emanating from the CHs are found to be linearly
related to the area of the individual CH, however the slopes vary.
---------------------------------------------------------
Title: Forecasting the arrival time of coronal mass ejections
Authors: Dumbovic, Mateja; Mays, M. Leila; Riley, Pete; Mierla,
Marilena; Kay, Christina; Vrsnak, Bojan; Veronig, Astrid; Cremades,
Hebe; Čalogović, Jaša; Verbeke, Christine; Temmer, Manuela; Sudar,
Davor; Scolini, Camilla; Hinterreiter, Jürgen; Paouris, Evangelos;
Palmerio, Erika; Balmaceda, Laura
2021cosp...43E1038D Altcode:
Forecasting the arrival time of coronal mass ejections (CMEs) and their
associated shocks is one of the key aspects of space weather. In recent
years many models have been developed by various research groups aiming
to forecast CME arrival time. The models differ based on the input,
approach, assumptions and complexity ranging from simple empirical and
analytical to complex numerical and machine learning models. One of the
commonly used models is, due to its simplicity and calculation speed,
the analytical drag-based (ensemble) model [DB(E)M] for heliospheric
propagation of CMEs. DB(E)M relies on the observational fact that
slow CMEs accelerate whereas fast CMEs decelerate, and is based on
the concept of MHD drag, which acts to adjust the CME speed to the
ambient solar wind. However, regardless of the model, forecasting CME
arrival time has proven to be exceedingly challenging. One of the major
setbacks is the uncertainty of the CME observational input, which
is still substantial despite state-of-the-art remote observational
capacities such as high-resolution EUV imagers and stereoscopic
observations. Another major setback is the uncertainty in the CME
propagation itself, due to e.g. unrealistic background solar wind
and/or complex interactions. These limits will be discussed in the
scope of DB(E)M and the CME input analysis performed by the ISSI Bern
team on the "Understanding Our Capabilities In Observing And Modeling
Coronal Mass Ejections".
---------------------------------------------------------
Title: Stereoscopic view on CMEs; differences in predicted CME
arrivals based on STEREO-A/STEREO-B HI data
Authors: Hinterreiter, Jürgen; Moestl, Christian; Amerstorfer, Ute;
Amerstorfer, Tanja; Temmer, Manuela; Reiss, Martin; Bailey, Rachel;
Weiss, Andreas J.; Bauer, Maike
2021cosp...43E1039H Altcode:
Over the last decades numerous models to predict the arrival times
and speeds of CMEs (coronal mass ejections) have been developed. They
range from computationally very fast drag-based models to expensive
MHD models. However, uncertainties in the forecasts are large for all
the models available so far. In this study, we use ELEvoHI (ELlipse
Evolution model based on Heliospheric Imager observations) ensemble
modeling for CME post-event arrival prediction. The model assumes an
elliptical shape of the CME front within the ecliptic plane and makes
use of time-elongation profiles provided by HI (Heliospheric Imager)
onboard the STEREO (Solar TErrestrial RElations Observatory) twin
spacecraft. In addition, ELEvoHI utilizes an ambient solar wind provided
by the Wang-Sheeley-Arge model to account for the drag force that is
exerted on the CME during the propagation in the heliosphere. For
this study, we carefully select 12 CMEs between February 2010 and
July 2012. The CMEs have to fulfill the following three criteria: 1)
clear signatures in STEREO-A and STEREO-B HI images, 2) corresponding
in-situ signature, and 3) propagation close to the ecliptic plane. Based
on typical input data we analyze the arrival times and speeds of each
CME using STEREO-A and STEREO-B time-elongation profiles and compare
them with each other. The results show differences up to 10 hours and
200 km/s. We give possible reasons for the discrepancies in relation
to the input data and dependencies on the two vantage points.
---------------------------------------------------------
Title: ISWAT H2 Cluster: CME structure, evolution and propagation
through heliosphere
Authors: Verbeke, Christine; Mays, M. Leila; Temmer, Manuela; Kay,
Christina
2021cosp...43E2417V Altcode:
Coronal mass ejections (CMEs) are energetically the most powerful
phenomena in the solar system. Most of the times related to solar
flare emissions, CMEs consist of magnetic field and plasma that is
impulsively ejected into interplanetary space. To make progress in
improving current state-of-the-art CME propagation models, validation
and scientific peer-review qualification is needed. iSWAT is an
international, community driven effort and provides the required
platform to challenge currentmodels and to exchange our experience
with peers in order to improve our work. We give an overview on the
available teams in the H2 cluster and their aims for the H2 cluster.
---------------------------------------------------------
Title: Observational study of CME propagation and geo-effectiveness
Authors: Temmer, Manuela
2021cosp...43E1784T Altcode:
Coronal mass ejections (CMEs) are the most powerful dynamic phenomena in
our solar system. The propagation behavior of these transient events in
interplanetary space is strongly dependent on their initial parameters,
like size and mass, kinematics, and the ambient solar wind structure. As
CMEs evolve, different structures are observed, typically covering a
shock-sheath region and a driver, pre-sumably consisting of a magnetic
flux rope. The structures can be observed and distinguished partly in
remote sensing image data and more clearly from in-situ measurements
by their different character-istics. Both structures undergo changes
on their way from Sun to Earth that modifies the degree of impact and
geoeffectiveness. While during propagation presumably mass is built up
in the sheath's front region, the orientation of the interplanetary
magnetic field affects the magnetic structure by re-ducing or
increasing the amount of magnetic flux due to reconnection with the
interplanetary magnetic field. When hitting Earth, differences in
the magnetospheric responses are found between the magnetic and the
shock-sheath region. This talk will review different perspectives of
CME evolution in inter-planetary space and their interaction with the
solar wind, with special aspects from new solar missions Parker Solar
Probe and Solar Orbiter.
---------------------------------------------------------
Title: Statistical Analysis of SDO-era Coronal Holes using CATCH
Authors: Heinemann, Stephan; Temmer, Manuela
2021cosp...43E1014H Altcode:
Coronal holes are regions of open magnetic field configuration in the
solar corona and can be observed as large-scale dark structures in the
extreme ultraviolet and X-ray spectrum. Deriving reliably the coronal
hole boundary is crucial, as its area, underlying magnetic field, and
other properties such as shape and intensity, give important hints
towards high speed solar wind acceleration processes. In this study
we present a new threshold-based extraction method that is modulated
using the intensity gradient along the coronal hole boundary. It is
implemented as a user-friendly SSWIDL-GUI and is part of the official
distribution. The Collection of Analysis Tools for Coronal Holes
(CATCH) enables the user to download data, perform guided coronal hole
extraction and analyze the underlying photospheric magnetic field. We
used CATCH to evaluate all non-polar coronal holes of the SDO-era. We
used 193 Å filtergrams taken by the Atmospheric Imaging Assembly
(AIA) and line-of-sight magnetograms taken by the Heliospheric and
Magnetic Imager (HMI), both on board the Solar Dynamics Observatory
(SDO) to investigate 707 coronal holes near the central meridian during
the time period of 2010 and 2019. We find coronal holes distributed
across latitudes of $\pm 60^\circ$ and sizes between $1.6\times10^9$
km$^{2}$. to $1.8\times10^{11}$ km$^{2}$. The absolute value of the
mean signed magnetic field strength is on average of 2.9$\pm$1.9 G. We
find no distinct trend towards a preferred hemisphere in abundance
or size. Variations in the local and global conditions significantly
change the threshold needed for reliable coronal hole extraction and
thus, we can highlight the importance of individually assessing and
extracting coronal holes.
---------------------------------------------------------
Title: The COSPAR ISWAT initiative for open validation analysis for
models of the evolving ambient solar wind
Authors: Reiss, Martin; Kuznetsova, Maria; Mullinix, Richard;
Rastaetter, Lutz; Temmer, Manuela; MacNeice, Peter; Wiegand, Chiu;
Muglach, Karin
2021cosp...43E2363R Altcode:
Validation analysis plays a critical role in applied space weather
research and prediction. First and foremost to inform developers and
users of space weather models about the strengths and weaknesses of
the models, and also to provide an unbiased assessment of progress
over time. Here we present the activities of the Ambient Solar Wind
Validation Team embedded in the COSPAR ISWAT initiative. The objective
of this action team is to establish an online hub for validation
analysis of ambient solar wind models in correspondence with the
space weather community, allowing developers and end-users to directly
assess the quality of state-of-the-art model solutions. To this end,
we choose and agree on a set of comprehensive validation metrics
reflecting the community needs and integrate them into the existing
Comprehensive Assessment of Models and Events using Library Tools
(CAMEL) web application hosted by NASA's Community Coordinated Modelling
Center. CAMEL is an interactive visualization tool allowing developers
and users to compare space weather and space science model output to
observations. Specifically, we make use of CAMEL to quantitatively
assess the relationship between state-of-the-art solar wind model
solutions and observational data in terms of point-to-point statistics
and more advanced event-based validation measures. In this presentation,
we will demonstrate the first application of the new online platform
with examples of state-of-the-art model solutions. We will also discuss
the main challenges we face in the realization of our objectives,
and present the current status and the roadmap of the action team.
---------------------------------------------------------
Title: Estimating the magnetic flux within an eruptive flux rope
Authors: Temmer, Manuela; Rodriguez, Luciano; Dissauer, Karin; Veronig,
Astrid; Tschernitz, Johannes; Thalmann, Julia K.; Hinterreiter, Jürgen
2021cosp...43E1741T Altcode:
Erupting magnetic flux ropes develop into coronal mass ejections (CMEs)
as they evolve and finally propagate into interplanetary space. Those
large scale eruptions are observed to be frequently related to dynamic
surface phenomena such as coronal waves and dimming regions. The better
we are able to estimate initial CME parameters such as kinematics,
geometry, and magnetic properties, the more precisely we can feed
state-of-the-art CME propagation models and with that improve CME
forecasting. In that respect, we report on a well-observed flare-CME
event from 1 October 2011 focusing on the dynamic evolution of the
CME and its embedded magnetic field. Using combined STEREO and SDO
observations together with nonlinear force-free (NLFF) modeling we
derive separately the flare reconnection and dimming flux. We find
that already before the start of the impulsive flare phase magnetic
reconnection was ongoing, that added magnetic flux to the flux rope
before its final eruption. As the dimming evolves over a longer time
span than the flaring phase, we find that the dimming flux increases by
more than 25% after the end of the flare. This indicates that magnetic
flux is still added to the flux rope after eruption and that the derived
flare reconnection flux is most probably a lower limit for estimating
the magnetic flux within the flux rope.
---------------------------------------------------------
Title: Modeling Coronal Mass Ejections with EUHFORIA
Authors: Verbeke, Christine; Schmieder, Brigitte; Rodriguez, Luciano;
Poedts, Stefaan; Magdalenic, Jasmina; Pomoell, Jens; Temmer, Manuela;
Asvestari, Eleanna; Scolini, Camilla; Heinemann, Stephan; Hinterreiter,
Jürgen; Samara, Evangelia
2021cosp...43E2358V Altcode:
Fully understanding the origin and evolution of Coronal Mass Ejections
(CMEs) from the Sun to the Earth remains a major topic in current
solar-terrestrial physics and is of key importance to improve our space
weather prediction capabilities. CMEs can drive strong space weather
disturbances at Earth, and their dynamical pressure, magnetic field
configuration and interaction with the solar wind can significantly
alter their arrival time and impact at Earth. One of the key parameters
that determine the geo-effectiveness of the CME is its internal magnetic
configuration. With the EUHFORIA inner-heliosphere magnetohydrodynamics
model, we can model a magnetised CME using a Linear Force Free Spheromak
(LFFS) model, in order to model the internal magnetic structure of
the CME throughout the inner heliosphere. In this talk, we present
an overview of the model assessment efforts that have been made
with EUHFORIA over the past years. We discuss the validation of the
solar wind, as well as the development of the LFFS model. We focus
on determining the sensitivity of the LFFS model input parameters,
as well as some case studies to show our improved modeling of the
CME magnetic field structures at Earth. Finally, we discuss current
limitations and future improvements of the EUHFORIA model.
---------------------------------------------------------
Title: CME evolution and the corresponding Forbush decrease: modelling
vs multi-spacecraft observation
Authors: Dumbovic, Mateja; Moestl, Christian; Podladchikova, Tatiana;
Guo, Jingnan; Heber, Bernd; Vrsnak, Bojan; Dissauer, Karin; Veronig,
Astrid; Amerstorfer, Tanja; Temmer, Manuela; Carcaboso, Fernando;
Kirin, Anamarija
2021cosp...43E1747D Altcode:
One of the very common in-situ signatures of interplanetary coronal
mass ejections (ICMEs), as well as other interplanetary transients are
Forbush decreases (FDs), i.e. short-term reductions in the galactic
cosmic ray (GCR) flux. FD phenomena are caused by the interaction
of GCRs with a magnetic structure, therefore it is expected that
different types of interplanetary substructures cause different types
of GCR time profiles, allowing us to distinguish between shock/sheath,
flux rope and SIR-type of FDs. Moreover, since the interaction of
GCRs and CME magnetic structure (i.e. flux rope) occurs all the
way from Sun to Earth, FDs reflect the evolutionary properties of
CMEs. We apply modelling to different ICME regions in order to obtain
a generic FD profile. We model the shock/sheath-related FD using the
propagating diffusive barrier (PDB) model, the flux-rope-related FD
using the diffusion model for the expanding flux rope (ForbMod),
and the exponential time profile approximates the recovery after
the event. The modeled generic FD profile qualitatively agrees with
our current observation-based understanding of FDs. In addition, we
test ForbMod against a set of multi-spacecraft observations of the
same ICME. We find a reasonable agreement of the ForbMod model with
multi-spacecraft measurements, indicating that modelled FDs reflect
well the flux rope evolution.
---------------------------------------------------------
Title: Evolution of coronal mass ejections and the corresponding
Forbush decreases: modelling vs. multi-spacecraft observations
Authors: Dumbovic, M.; Vrsnak, B.; Guo, J.; Heber, B.; Dissauer, K.;
Carcaboso-Morales, F.; Temmer, M.; Veronig, A.; Podladchikova, T.;
Moestl, C.; Amerstorfer, T.; Kirin, A.
2020AGUFMSH046..08D Altcode:
One of the very common in situ signatures of interplanetary coronal
mass ejections (ICMEs), as well as other interplanetary transients,
are Forbush decreases (FDs), i.e. short-term reductions in the galactic
cosmic ray (GCR) flux. A two-step FD is often regarded as a textbook
example, which presumably owes its specific morphology to the fact that
the measuring instrument passed through the ICME head-on, encountering
first the shock front (if developed), then the sheath and finally the
CME magnetic structure. The interaction of GCRs and the shock/sheath
region, as well as the CME magnetic structure, occurs all the way from
Sun to Earth, therefore, FDs are expected to reflect the evolutionary
properties of CMEs and their sheaths. We apply modelling to different
ICME regions in order to obtain a generic two-step FD profile, which
qualitatively agrees with our current observation-based understanding of
FDs. We next adapt the models for energy dependence to enable comparison
with different GCR measurement instruments (as they measure in different
particle energy ranges). We test these modelling efforts against a
set of multi-spacecraft observations of the same event, using the
Forbush decrease model for the expanding flux rope (ForbMod). We find
a reasonable agreement of the ForbMod model for the GCR depression
in the CME magnetic structure with multi-spacecraft measurements,
indicating that modelled FDs reflect well the CME evolution.
---------------------------------------------------------
Title: Drag-based Forecast for CME Arrival
Authors: Yordanova, E.; Jaklovsky, S.; Dumbovic, M.; Temmer, M.;
Dimmock, A. P.; Rosenqvist, L.
2020AGUFMSH0030013Y Altcode:
The accurate estimation of the CME arrival times at 1 AU is of key
importance for space weather forecast. It is a challenging issue, since
when a CME expands, it inevitably interacts with the solar corona and
the ambient solar wind occupying the interplanetary space. This often
results in modification of the CME's plasma properties and propagation
path. There are various approaches in use for arrival time prediction -
either based on MHD modeling or empirical relations between parameters
measured from coronagraphs and in-situ at L1. Here, we investigate the
performance of the recent Drag Based Ensemble Model (DBEM, Dumbović et
al., 2018; Žic et al., 2015) available for users from the ESA Space
Situational Awareness Portal (http://swe.ssa.esa.int). DBEM provides
an ensemble of probabilistic predictions for CME arrivals based on the
Drag-Based Model (DBM, Vršnak et al., 2013) which assumes that the
propagation of a CME is dependent solely on the magnetohydrodynamic
drag (in analogy to the aerodynamic drag) exerted to the CME from the
ambient solar wind. <P />We have selected to test a set of twelve
geoeffective Earth-directed fast halo CMEs. For the model runs, we
use as input CMEs' shock speed and the velocity of the respective
preceding solar wind measured by WIND spacecraft. We perform test
runs with values of the drag parameter: (0.1, 0.2 and 0.3)x10<SUP>-7
</SUP>km<SUP>-1</SUP>. Overall, the model produced a wide distribution
of arrival times. The predictions were rather good, being confined in
the range of ± 10 h. In addition, the model provides prediction for
the CME arrival speeds, which in our case seem to be overestimated for
all drag values. The closest predicted arrival time to about -2.5 h
on average, was achieved by setting the drag value to 0.2x10<SUP>-7
</SUP>km<SUP>-1</SUP>. When matching also the predicted to the
observed arrival speeds, the best average result was achieved with drag
parameter 0.3x10<SUP>-7 </SUP>km<SUP>-1</SUP>, corresponding to +4.5
h CME arrival time. These drag values are higher than the recommended
0.1x10<SUP>-7 </SUP>km<SUP>-1</SUP> for fast CMEs, suggesting that the
exerted solar wind drag was higher than anticipated. This implies that
further improvement in the CME arrival forecast requires more detailed
and precise knowledge of the preconditioning of the interplanetary
space through which the CMEs are propagating. <P />References:
<P />Dumbović, M., et al., The Drag-based Ensemble Model (DBEM)
for Coronal Mass Ejection Propagation. Astrophys. J., 854:180,
2018 <P />Žic, M. et al., Heliospheric Propagation of Coronal Mass
Ejections: Drag-based Model Fitting. Astrophys. J. Suppl., 218:32,
2015 <P />Vršnak, B., et al., Propagation of Interplanetary Coronal
Mass Ejections: The Drag-Based Model, Solar Phys. 285:295-315, 2013
---------------------------------------------------------
Title: CME-CME Interactions as Sources of CME Helio-Effectiveness:
the Early September 2017 Events
Authors: Scolini, C.; Chané, E.; Temmer, M.; Pomoell, J.; Kilpua,
K. E. J.; Dissauer, K.; Veronig, A.; Palmerio, E.; Dumbovic, M.; Guo,
J.; Rodriguez, L.; Poedts, S.
2020AGUFMSH0440017S Altcode:
Coronal Mass Ejections (CMEs) are the main source of intense space
weather disturbances in the heliosphere. It is known that the
capability of individual CMEs to drive strong space weather events
at Earth (called "geo-effectiveness") and other locations (here
referred to as "helio-effectiveness") primarily depends on their
speed, density, and magnetic field strength and orientation at the
impact location. Moreover, previous studies established that CME--CME
interactions can significantly alter the properties of individual
CMEs, in such a way that their geo-effectiveness is often dramatically
amplified. However, the actual quantification of this amplification has
been rarely investigated, and previous studies have mostly focused on
the near-Earth region only, i.e. without considering its full space-time
evolution as the CMEs propagate to 1 AU and beyond. <P />Here, we
present a study on the role of CME--CME interactions as sources of CME
helio-effectiveness by performing simulations of complex CME events
with the EUHFORIA heliospheric model. As a case study, we consider
a sequence of CMEs observed in early September 2017. As their source
region rotated on the solar disk, CMEs were launched over a wide range
of longitudes, interacting with each other and paving the way for the
propagation of the following ones. At Earth, their interaction resulted
in an intense geomagnetic storm. Using initial parameters derived
from remote-sensing observations, we perform global simulations of
magnetised CMEs with EUHFORIA, investigating how their interactions
affected the propagation and internal properties of individual CME
structures. Taking advantage of 3D simulation outputs, we quantify
the amplification of the helio-effectiveness of the individual CMEs
involved, as a function of the interaction phase and of the location
within the CME structure. Additionally, we explore the possibility of
the existence of a "helio-effectiveness amplification zone", i.e. a
characteristic heliocentric distance at which CME--CME interactions have
the highest probability to develop into helio-effective events. Results
from this study benchmark our current prediction capabilities in
the case of complex CME events, and provide new insights on their
large-scale evolution and potential impact throughout the heliosphere.
---------------------------------------------------------
Title: Characteristics of a long-lived CIR and the corresponding
depression in the GCR flux
Authors: Dumbovic, M.; Vrsnak, B.; Temmer, M.; Heber, B.
2020AGUFMSH0440026D Altcode:
We observe a long-lived CIR recurring in 27 consecutive Carrington
rotations 2057-2083 in the time period from June 2007 - May 2009. We
characterize the in situ measurements of this long-lived CIR as well as
the corresponding depression in the GCR count observed by SOHO/EPHIN,
and analyze them throughout different rotations. We find that the
behavior of the flow speed peak roughly shows a rising phase and
a declining phase. This is similar to the evolutionary profile of
some observed coronal hole areas, but without a clear peak. The GCR
count evolutionary profile roughly follows that of the flow speed
peak, but moreover we find that the inverted GCR count time-profile
matches very well with that of the flow speed throughout different
rotations. We perform a statistical analysis and find the GCR count
amplitude correlated to the peak in the magnetic field and flow
speed, as expected based on previous statistical studies. In order
to characterize a generic CIR profile for modelling purposes, we
perform the superposed epoch analysis using relative values of the
key parameters. Based on the observed properties we propose a simple
analytical model starting from the basic Fokker-Planck equation.
---------------------------------------------------------
Title: COSPAR International Space Weather Action Teams: Addressing
Challenges Across the Field of Space Weather.
Authors: Kuznetsova, M. M.; Belehaki, A.; Bisi, M. M.; Bruinsma, S.;
Fung, S. F.; Glover, A.; Grande, M.; Guo, J.; Jun, I.; Linker, J.;
Mann, I. R.; Masson, A.; Mendoza, A. M. M.; Murray, S. A.; Nandy, D.;
Opgenoorth, H. J.; Pevtsov, A. A.; Plainaki, C.; Reiss, M.; Sutton,
E. K.; Temmer, M.; Usoskin, I. G.; Yao, Z.; Yardley, S.; Zheng, Y.
2020AGUFMSH0030022K Altcode:
Advanced predictions of space weather impacts require improved
understanding and modeling capabilities of coupled chains of space
environment processes. It is necessary to assemble parts of the
source-to-impact puzzle by identifying, addressing and solving
problems focused on specific physical domains, and then to connect
all validated solutions from space weather origins on the sun to
impacts on coupled geospace system, humans and technologies. To
address the need for multi-disciplinary international space weather
research community connecting experts in space weather phenomena
across all domains and experts in space environment impact,
the COSPAR Panel on Space Weather facilitated establishment of
a network of International Space Weather Action Teams (ISWAT, <A
href="https://www.iswat-cospar.org">https://www.iswat-cospar.org</A>,
@IswatCosparOrg). ISWAT serves as a global hub for community coordinated
topical collaborations focused on different aspects of space weather
including advancing understanding, assessment and improvement of
modeling capabilities, transitioning advances in research to operations,
optimized utilization of available observations, and generating inputs
to future instrumentation deployment. Action teams are building
blocks of ISWAT initiative. ISWAT action teams are organized into
domain-based ISWAT clusters. Action teams are working in coordinated
effort across physical domain and across borders. The primary ISWAT
goal is to advance space weather predictive capabilities based on best
science available. The ISWAT currently includes more than 250 active
participants and more than 50 action teams. The presentation will
overview the outcome from the COSPAR ISWAT Inaugural Working Meeting
in February 2020, highlight recent progress in advancing physics-based
predictive capabilities and discuss plans for transforming COSPAR space
weather Roadmap into a living document maintained by the community.
---------------------------------------------------------
Title: Exploration and Forecasting of Thermospheric Variations at
Different Altitudes Within the Framework of Project SWEETS
Authors: Krauss, S.; Suesser-Rechberger, B.; Temmer, M.; Mayer-Guerr,
T.; Drescher, L.; Kroisz, S.
2020AGUFMSM050..09K Altcode:
Owing to advances in solar research in the recent decades, today we know
that coronal mass ejections (CMEs) cause the most comprehensive spectrum
of space weather disturbances. These huge clouds of magnetized plasma
are propagating from the solar corona into interplanetary space with
typical transit times that range between two and five days, depending on
the initial speed, the mass, the size as well as the speed and density
of the surrounding solar wind plasma. During strong geomagnetic storms,
induced by CMEs, the neutral density of the Earth's thermosphere is
subject to strong fluctuations and, thus, a critical parameter for low
Earth-orbiting satellites. The enhanced energy input from the solar
wind to the magnetosphere causes heating and expansion of the Earth's
thermosphere, which affects Earth-orbiting satellites in such a way
that the drag force acting on the spacecraft is enhanced and leads
to an additional storm induced orbit decay. <P />Within the project
SWEETS (FFG funded) it is intended to develop a forecasting model, to
predict the expected impact of solar events on satellites at different
altitudes between 300-800 km. For the realization, scientific data,
such as kinematic orbit information and accelerometer measurements,
from a wide variety of satellites will be incorporated. Through a
joint analysis and evaluation of solar wind plasma and magnetic field
data observed at the Lagrange point L1, first preliminary results of
predicted thermospheric density increases and associated satellite
orbit decay rates are shown.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Search for flares and CMEs in
SDSS data (Koller+, 2021)
Authors: Koller, F.; Leitzinger, M.; Temmer, M.; Odert, P.; Beck,
P. G.; Veronig, A.
2020yCat..36460034K Altcode:
This file contains the complete list of flares found by this work
and their most important derived or collected parameters. The
in-depth description of the derivation of these parameters is given
in the article. <P />The optical spectra by SDSSS data release 14
(2018ApJS..235...42A) that we used in this work consist of several
single spectra, which are combined to a final coadded spectrum for each
observed object. We used the single spectra to find temporal changes
in Balmer lines, indicating flaring events. With the latest GAIA data
release (2018A&A...616A...1G), we were able to derive energy and
luminosity values for the flares. We focused on the Halpha Balmer line
due to the better S/N. Our methods were based on line fitting algorithms
to detect changes from one observation to another. <P />Similar to
the work by Hilton et al. (2010, Cat. J/AJ/140/1402) we give stellar
coordinates as RAdeg and DEdeg as the first parameters to distinguish
between the objects. In addition to that, the Plate-MJD-Fiber number
serves as a unique identifier for the flaring SDSS spectrum. The stellar
position is not enough because objects can be observed multiple times
at different surveys by SDSS, resulting in different sets of single
spectra. The method and the categorization of the S/N bins are defined
in the article. <P />The spectral type classified by SDSS and by
other literature is given. The distance and the source for the value
is given when possible. The defined quiet flag and the consideration
flag give insight on the reliability of the derived values. Whether a
flare was also detected in Hilton et al. (2010, Cat. J/AJ/140/1402) is
given in a separate column. The flare energy, the luminosity, and the
associated errors were derived using the SDSS spectra as is described
in the article (see Sect.4.2.2) and given here in units of W and W/s
(J). <P />The peak spectrum and the spectrum used in the calculation as
the reference are given. Their number refer to the chronological order
of the single spectra. The number of available single spectra (in the
optical red domain containing Halpha) and the number of single spectra
in a flaring state are given. The overall time of these flaring spectra
is summed and given in units of minutes. <P />Additional comments made
during the visual inspection of all flaring spectra are added. <P />(1
data file).
---------------------------------------------------------
Title: A new method for estimating global coronal wave properties
based on their interaction with solar coronal holes
Authors: Piantschitsch, I.; Terradas, J.; Temmer, M.
2020A&A...641A..21P Altcode: 2020arXiv200607293P
Among the effects of interactions between global coronal waves (CWs)
and coronal holes (CHs) is the formation of reflected and transmitted
waves. Observations of such events provide us with measurements
of different CW parameters, such as phase speed and intensity
amplitudes. However, several of these parameters are provided with
only intermediate observational quality, whereas other parameters,
such as the phase speed of transmitted waves, can hardly be observed
in general. We present a new method to estimate crucial CW parameters,
such as density and phase speed of reflected as well as transmitted
waves, Mach numbers and density values of the CH's interior, by using
analytical expressions in combination with the most basic and most
accessible observational measurements available. The transmission and
reflection coefficients were derived from linear theory and used to
calculate estimations for phase speeds of incoming, reflected, and
transmitted waves. The obtained analytical expressions were validated
by performing numerical simulations of CWs interacting with CHs. This
new method enables us to determine in a fast and straightforward way
reliable CW and CH parameters from basic observational measurements
which provides a powerful tool to better understand the observed
interaction effects between CWs and CHs.
---------------------------------------------------------
Title: Solar Flare-CME Coupling throughout Two Acceleration Phases
of a Fast CME
Authors: Gou, Tingyu; Veronig, Astrid M.; Liu, Rui; Zhuang, Bin;
Dumbović, Mateja; Podladchikova, Tatiana; Reid, Hamish A. S.; Temmer,
Manuela; Dissauer, Karin; Vršnak, Bojan; Wang, Yuming
2020ApJ...897L..36G Altcode: 2020arXiv200611707G
Solar flares and coronal mass ejections (CMEs) are closely coupled
through magnetic reconnection. CMEs are usually accelerated impulsively
within the low solar corona, synchronized with the impulsive flare
energy release. We investigate the dynamic evolution of a fast CME and
its associated X2.8 flare occurring on 2013 May 13. The CME experiences
two distinct phases of enhanced acceleration, an impulsive one with a
peak value of ∼5 km s<SUP>-2</SUP>, followed by an extended phase with
accelerations up to 0.7 km s<SUP>-2</SUP>. The two-phase CME dynamics
is associated with a two-episode flare energy release. While the first
episode is consistent with the "standard" eruption of a magnetic flux
rope, the second episode of flare energy release is initiated by the
reconnection of a large-scale loop in the aftermath of the eruption
and produces stronger nonthermal emission up to γ-rays. In addition,
this long-duration flare reveals clear signs of ongoing magnetic
reconnection during the decay phase, evidenced by extended hard X-ray
bursts with energies up to 100-300 keV and intermittent downflows
of reconnected loops for >4 hr. The observations reveal that the
two-step flare reconnection substantially contributes to the two-phase
CME acceleration, and the impulsive CME acceleration precedes the most
intense flare energy release. The implications of this non-standard
flare/CME observation are discussed.
---------------------------------------------------------
Title: Evolution of Coronal Mass Ejections and the Corresponding
Forbush Decreases: Modeling vs. Multi-Spacecraft Observations
Authors: Dumbović, Mateja; Vršnak, Bojan; Guo, Jingnan; Heber,
Bernd; Dissauer, Karin; Carcaboso, Fernando; Temmer, Manuela; Veronig,
Astrid; Podladchikova, Tatiana; Möstl, Christian; Amerstorfer, Tanja;
Kirin, Anamarija
2020SoPh..295..104D Altcode: 2020arXiv200602253D
One of the very common in situ signatures of interplanetary coronal
mass ejections (ICMEs), as well as other interplanetary transients,
are Forbush decreases (FDs), i.e. short-term reductions in the galactic
cosmic ray (GCR) flux. A two-step FD is often regarded as a textbook
example, which presumably owes its specific morphology to the fact that
the measuring instrument passed through the ICME head on, encountering
first the shock front (if developed), then the sheath, and finally the
CME magnetic structure. The interaction of GCRs and the shock/sheath
region, as well as the CME magnetic structure, occurs all the way from
Sun to Earth, therefore, FDs are expected to reflect the evolutionary
properties of CMEs and their sheaths. We apply modeling to different
ICME regions in order to obtain a generic two-step FD profile, which
qualitatively agrees with our current observation-based understanding
of FDs. We next adapt the models for energy dependence to enable
comparison with different GCR measurement instruments (as they measure
in different particle energy ranges). We test these modeling efforts
against a set of multi-spacecraft observations of the same event, using
the Forbush decrease model for the expanding flux rope (ForbMod). We
find a reasonable agreement of the ForbMod model for the GCR depression
in the CME magnetic structure with multi-spacecraft measurements,
indicating that modeled FDs reflect well the CME evolution.
---------------------------------------------------------
Title: A statistical study of the long-term evolution of coronal
hole properties as observed by SDO
Authors: Heinemann, S. G.; Jerčić, V.; Temmer, M.; Hofmeister,
S. J.; Dumbović, M.; Vennerstrom, S.; Verbanac, G.; Veronig, A. M.
2020A&A...638A..68H Altcode: 2019arXiv190702795H; 2019arXiv190702795J
Context. Understanding the evolution of coronal holes is especially
important when studying the high-speed solar wind streams that emanate
from them. Slow- and high-speed stream interaction regions may deliver
large amounts of energy into the Earth's magnetosphere-ionosphere
system, cause geomagnetic storms, and shape interplanetary space. <BR
/> Aims: By statistically investigating the long-term evolution of
well-observed coronal holes we aim to reveal processes that drive
the observed changes in the coronal hole parameters. By analyzing 16
long-living coronal holes observed by the Solar Dynamic Observatory,
we focus on coronal, morphological, and underlying photospheric magnetic
field characteristics, and investigate the evolution of the associated
high-speed streams. <BR /> Methods: We use the Collection of Analysis
Tools for Coronal Holes to extract and analyze coronal holes using
193 Å EUV observations taken by the Atmospheric Imaging Assembly as
well as line-of-sight magnetograms observed by the Helioseismic and
Magnetic Imager. We derive changes in the coronal hole properties and
look for correlations with coronal hole evolution. Further, we analyze
the properties of the high-speed stream signatures near 1AU from OMNI
data by manually extracting the peak bulk velocity of the solar wind
plasma. <BR /> Results: We find that the area evolution of coronal
holes shows a general trend of growing to a maximum followed by a
decay. We did not find any correlation between the area evolution
and the evolution of the signed magnetic flux or signed magnetic
flux density enclosed in the projected coronal hole area. From this
we conclude that the magnetic flux within the extracted coronal
hole boundaries is not the main cause for its area evolution. We
derive coronal hole area change rates (growth and decay) of (14.2
± 15.0)×10<SUP>8</SUP> km<SUP>2</SUP> per day showing a reasonable
anti-correlation (cc<SUB>Pearson</SUB> = -0.48) to the solar activity,
approximated by the sunspot number. The change rates of the signed mean
magnetic flux density (27.3 ± 32.2 mG day<SUP>-1</SUP>) and the signed
magnetic flux (30.3 ± 31.5 10<SUP>18</SUP> Mx day<SUP>-1</SUP>) were
also found to be dependent on solar activity (cc<SUB>Pearson</SUB> =
0.50 and cc<SUB>Pearson</SUB> = 0.69 respectively) rather than on the
individual coronal hole evolutions. Further we find that the relation
between coronal hole area and high-speed stream peak velocity is
valid for each coronal hole over its evolution, but we see significant
variations in the slopes of the regression lines.
---------------------------------------------------------
Title: Prediction of CME arrivals; differences based on stereoscopic
heliospheric imager data
Authors: Hinterreiter, Jürgen; Amerstorfer, Tanja; Reiss, Martin A.;
Temmer, Manuela; Möstl, Christian; Bauer, Maike; Amerstorfer, Ute V.;
Bailey, Rachel L.; Weiss, Andreas J.
2020EGUGA..22.7829H Altcode:
Forecasting the arrival time and speed of CMEs is of high
importance. However, uncertainties in the forecasts are high. We present
the results of post-event prediction of CME arrivals using ELEvoHI
(ELlipse Evolution model based on Heliospheric Imager observations)
ensemble modeling. The model uses time-elongation profiles provided by
HI (Heliospheric Imager) onboard STEREO (Solar TErrestrial RElations
Observatory) and assumes an elliptical shape of the CME front. The
drag force exerted by the ambient solar wind is an essential factor
influencing the dynamic evolution of CMEs in the heliosphere. To
account for this effect, ELEvoHI utilizes the modeled ambient solar
wind provided by the Wang-Sheeley-Arge model. We carefully select 12
CMEs between February 2010 and July 2012, which show clear signatures
in STEREO-A and STEREO-B HI images, have a corresponding in-situ
signature, and propagate close to the ecliptic plane. As input to
ELEvoHI, we make use of STEREO-A and STEREO-B time-elongation profiles
for each CME and compare the predicted arrival times and speeds based
on both vantage points with each other. We present our model results
and discuss possible reasons for the differences in the arrival times
of up to 15 hours.
---------------------------------------------------------
Title: Magnetic Flux Emergence in a Coronal Hole
Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova,
Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma,
Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván;
Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea;
Kontogiannis, Ioannis; Cid, Consuelo
2020SoPh..295...64P Altcode: 2020arXiv200611779P
A joint campaign of various space-borne and ground-based observatories,
comprising the Japanese Hinode mission (Hinode Observing Plan 338,
20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum
Tower Telescope (VTT), investigated numerous targets such as pores,
sunspots, and coronal holes. In this study, we focus on the coronal
hole region target. On 24 September 2017, a very extended non-polar
coronal hole developed patches of flux emergence, which contributed
to the decrease of the overall area of the coronal hole. These flux
emergence patches erode the coronal hole and transform the area into a
more quiet-Sun-like area, whereby bipolar magnetic structures play an
important role. Conversely, flux cancellation leads to the reduction
of opposite-polarity magnetic fields and to an increase in the area
of the coronal hole.
---------------------------------------------------------
Title: Using Forbush decreases at Earth and Mars to measure the
radial evolution of ICMEs
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
Robert F.; Dumbović, Mateja; Janvier, Miho; Démoulin, Pascal;
Veronig, Astrid; Temmer, Manuela; Papaioannou, Athanasios; Dasso,
Sergio; Hassler, Donald M.; Zeitlin, Cary J.
2020EGUGA..22.7838V Altcode:
Interplanetary coronal mass ejections (ICMEs), large clouds of plasma
and magnetic field regularly expelled from the Sun, are one of the
main drivers of space weather effects in the solar system. While
the prediction of their arrival time at Earth and other locations
in the heliosphere is still a complex task, it is also necessary to
further understand the time evolution of their geometric and magnetic
structure, which is even more challenging considering the limited number
of available observation points.Forbush decreases (FDs), short-term
drops in the flux of galactic cosmic rays (GCR), can be caused by the
shielding from strong and/or turbulent magnetic structures in the solar
wind, such as ICMEs and their associated shock/sheath regions. In the
past, FD observations have often been used to determine the arrival
times of ICMEs at different locations in the solar system, especially
where sufficient solar wind plasma and magnetic field measurements are
not (or not always) available. One of these locations is Mars, where the
Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory
(MSL) mission's Curiosity rover has been continuously measuring GCRs and
FDs on the surface for more than 7 years.In this work, we investigate
whether FD data can be used to derive additional information about the
ICME properties than just the arrival time by performing a statistical
study based on catalogs of FDs observed at Earth or Mars. In particular,
we find that the linear correlation between the FD amplitude and the
maximum steepness, which was already seen at Earth by previous authors
(Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars,
but with a different proprtionality factor.By consulting physics-based
analytical models of FDs, we find that this quantity is not expected to
be influenced by the different energy ranges of GCR particles observed
by the instruments at Earth and Mars. Instead, we suggest that the
difference in FD characteristics at the two planets is caused by the
radial enlargement of the ICMEs, and particularly their sheath regions,
as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening
factor derived from our analysis extends observations for the evolution
closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger
heliocentric distances and is consistent with these results.
---------------------------------------------------------
Title: Analysis of a severe geomagnetic storm on August 26, 2018
and the related effects on the GRACE-FO mission
Authors: Krauss, Sandro; Temmer, Manuela; Behzadpour, Saniya; Lhotka,
Christoph
2020EGUGA..22.3499K Altcode:
On August 20, 2018 a complex interplanetary coronal mass ejections
(ICME) occurred on the Sun, which subsequently triggered an unexpected
large geomagnetic storm on August 25. We present a detailed analysis of
the ICME eruption and explore the occurred perturbation of the neutral
mass density in the upper Earth's atmosphere. The analysis is based on
accelerometer observations from the satellite mission GRACE Follow-On as
well as interplanetary magnetic field measurements by the DSCOVR and ACE
spacecraft. Through the evaluation of solar observations by the SECCHI
instrument on-board of the STEREO-A satellite in form of white-light,
the early evolution of the ICME can be aptly illustrated. Furthermore,
due to the heating and the subsequent expansion of the thermosphere
also the drag force acting on the spacecraft is enhanced. This leads
to an additional storm induced orbit decay, which we calculate by
means of variations in the semi-major axis. The findings are compared
with predictions from our preliminary thermospheric forecasting tool,
which is based on the study by Krauss et al. 2018.
---------------------------------------------------------
Title: Understanding our capabilities in observing and modelling
Coronal Mass Ejections
Authors: Verbeke, Christine; Mierla, Marilena; Mays, M. Leila;
Kay, Christina; Dumbovic, Mateja; Temmer, Manuela; Palmerio, Erika;
Paouris, Evangelos; Cremades, Hebe; Riley, Pete; Scolini, Camilla;
Hinterreiter, Juergen
2020EGUGA..2220456V Altcode:
Coronal Mass Ejections (CMEs) are large-scale eruptions of plasma and
magnetic fields from the Sun. They are considered to be the main drivers
of strong space weather events at Earth. Multiple models have been
developed over the past decades to be able to predict the propagation
of CMEs and their arrival time at Earth. Such models require input
from observations, which can be used to fit the CME to an appropriate
structure.When determining input parameters for CME propagation
models, it is common procedure to derive kinematic parameters from
remote-sensing data. The resulting parameters can be used as inputs for
the CME propagation models to obtain an arrival prediction time of the
CME f.e. at Earth. However, when fitting the CME structure to obtain the
needed parameters for simulations, different geometric structures and
also different parts of the CME structure can be fitted. These aspects,
together with the fact that 3D reconstructions strongly depend on the
subjectivity and judgement of the scientist performing them, may lead
to uncertainties in the fitted parameters. Up to now, no large study
has tried to map these uncertainties and to evaluate how they affect
the modelling of CMEs. Fitting a large set of CMEs within a selected
period of time, we aim to investigate the uncertainties in the CME
fittings in detail. Each event is fitted multiple times by different
scientists. We discuss statistics on uncertainties of the fittings. We
also present some first results of the impact of these uncertainties
on CME propagation modelling.Acknowledgements: This work has been
partly supported by the International Space Science Institute (ISSI)
in the framework of International Team 480 entitled: Understanding
Our Capabilities In Observing And Modelling Coronal Mass Ejections'.
---------------------------------------------------------
Title: Observation-based modelling of magnetised CMEs in the inner
heliosphere with EUHFORIA
Authors: Scolini, Camilla; Pomoell, Jens; Chané, Emmanuel; Poedts,
Stefaan; Rodriguez, Luciano; Kilpua, Emilia; Temmer, Manuela;
Verbeke, Christine; Dissauer, Karin; Veronig, Astrid; Palmerio, Erika;
Dumbović, Mateja
2020EGUGA..22.1777S Altcode:
Coronal Mass Ejections (CMEs) are the primary source of strong
space weather disturbances at Earth and other locations in the
heliosphere. Understanding the physical processes involved in their
formation at the Sun, propagation in the heliosphere, and impact
on planetary bodies is therefore critical to improve current space
weather predictions throughout the heliosphere. The capability of CMEs
to drive strong space weather disturbances at Earth and other planetary
and spacecraft locations primarily depends on their dynamic pressure,
internal magnetic field strength, and magnetic field orientation at
the impact location. In addition, phenomena such as the interaction
with the solar wind and other solar transients along the way, or
the pre-conditioning of interplanetary space due to the passage of
previous CMEs, can significantly modify the properties of individual
CMEs and alter their ultimate space weather impact. Investigating
and modeling such phenomena via advanced physics-based heliospheric
models is therefore crucial to improve the space weather prediction
capabilities in relation to both single and complex CME events. In this
talk, we present our progress in developing novel methods to model CMEs
in the inner heliosphere using the EUHFORIA MHD model in combination
with remote-sensing solar observations. We discuss the various
observational techniques that can be used to constrain the initial
CME parameters for EUHFORIA simulations. We present current efforts
in developing more realistic magnetised CME models aimed at describing
their internal magnetic structure in a more realistic fashion. We show
how the combination of these two approaches allows the investigation of
CME propagation and evolution throughout the heliosphere to a higher
level of detail, and results in significantly improved predictions of
CME impact at Earth and other locations in the heliosphere. Finally,
we discuss current limitations and future improvements in the context
of studying space weather events throughout the heliosphere.
---------------------------------------------------------
Title: The impact of coronal hole characteristics and solar cycle
activity in reconstructing coronal holes with EUHFORIA
Authors: Asvestari, E.; Heinemann, S. G.; Temmer, M.; Pomoell, J.;
Kilpua, E.; Magdalenic, J.; Poedts, S.
2020JPhCS1548a2004A Altcode:
Modelling with high accuracy the open magnetic field and the fast solar
wind in the heliosphere is essential for space weather forecasting
purposes. Primary sources of open magnetic field flux are Coronal
Holes (CH), uni-polar regions that appear as dark patches in the
solar corona when observed in X-ray and extreme-ultraviolet (EUV)
images due to having significantly lower density and temperature
to their surroundings. Therefore, when assessing how well the open
magnetic field and the fast solar wind are modelled one can look at
how well the model performs on one of its fundamental functions, that
of reconstructing coronal hole areas. In this study we investigate how
the CH morphology (i.e. latitudinal position of the centre of mass,
area, intensity, elongation) and the solar variability, from high to
low activity periods, can affect the results. We also investigated the
possibility that the model is reconstructing CHs that are systematically
shifted with respect to their observed position. The study is applied
on 15 CHs exhibiting different latitudinal position and geometry. We
compare the modelled CH areas with boundaries obtained by remote sensing
EUV observations using the CATCH tool (Collection of Analysis Tools for
Coronal Holes). We found no apparent effect of the CH characteristics
on the modelling capabilities. In addition, solar cycle activity seems
not to have any effect either. However, we emphasize that our sample
is small and this outcome highlights the need for an extended research.
---------------------------------------------------------
Title: CME evolution and the corresponding Forbush decrease: modelling
vs multi-spacecraft observation
Authors: Dumbovic, Mateja; Vrsnak, Bojan; Guo, Jingnan; Heber, Bernd;
Dissauer, Karin; Carcaboso-Morales, Fernando; Temmer, Manuela; Veronig,
Astrid; Podladchikova, Tatiana; Möstl, Christian; Amerstorfer, Tanja;
Kirin, Anamarija
2020EGUGA..2210446D Altcode:
One of the very common in-situ signatures of ICMEs, as well as other
interplanetary transients are Forbush decreases (FDs), i.e. short-term
reductions in the galactic cosmic ray (GCR) flux. A two-step FD is
often regarded as a textbook example, which presumably owns its specific
morphology to the fact that the measuring instrument passed through the
ICME head-on, encountering first the shock front (if developed), then
the sheath and finally the magnetic structure. The interaction of GCRs
and the shock/sheath region as well as CME magnetic structure occurs all
the way from Sun to Earth, therefore, FDs are expected to reflect the
evolutionary properties of CMEs and their sheaths. We apply modelling
to different ICME regions in order to obtain a generic two-step FD
profile, which qualitatively agrees with our current observation-based
understanding of FDs. We next adapt the models for energy dependence
to enable comparison with different GCR measurement instruments
(as they measure in different particle energy ranges). We test these
modelling efforts against a set of multi-spacecraft observations of
the same event.
---------------------------------------------------------
Title: Exploring Thermospheric Variations Triggered by Severe
Geomagnetic Storm on 26 August 2018 Using GRACE Follow-On Data
Authors: Krauss, S.; Behzadpour, S.; Temmer, M.; Lhotka, C.
2020JGRA..12527731K Altcode:
With the successful launch of the satellite mission Gravity Recovery
and Climate Experiment (GRACE) Follow-On in May 2018 the opportunity
arises to resume the analysis of accelerometer data regarding space
weather induced perturbations of the Earth's thermosphere. On
21 August 2018 a complex interplanetary coronal mass ejections
occurred on the Sun, which subsequently triggered an unexpected
large geomagnetic storm on 26 August. We present a detailed analysis
of the interplanetary coronal mass ejection eruption and explore
the occurred perturbation of the neutral mass density in the upper
Earth's atmosphere. Due to the heating and the subsequent expansion
of the thermosphere also the drag force acting on the spacecraft
is enhanced. This leads to an additional storm-induced orbit
decay, which we calculate by means of variations in the semimajor
axis. The evaluation is based on the utilization of accelerometer
measurements from GRACE Follow-On. For the reduction of disturbing
nongravitational forces we implemented a physical shadow function,
which incorporates the Earth's oblateness and the atmospheric refraction
and extinction. Additionally, the estimation of Earth's reradiation
is now based on hourly measurements by the Clouds and the Earth's
Radiant Energy System. The resulting atmospheric densities and orbit
decays are compared with predictions from our preliminary thermospheric
forecasting tool, which is based on the study by Krauss et al. (2018, <A
href="https://doi.org/10.1029/2018JA025778">https://doi.org/10.1029/2018JA025778</A>).
The evaluation shows that the maximum estimated orbit decay triggered
by the geomagnetic storm on 26 August is in the order of approximately
8.2 m and thus in good accordance with the forecasted value (9.5
m)—predicted with a lead time of about 60 min.
---------------------------------------------------------
Title: Relating CME density derived from remote sensing data to CME
sheath solar wind plasma pile up as measured in-situ
Authors: Temmer, Manuela; Holzknecht, Lukas; Dumbovic, Mateja; Vrsnak,
Bojan; Sachdeva, Nishtha; Heinemann, Stephan; Dissauer, Karin; Scolini,
Camilla; Asvestari, Eleanna; Veronig, Astrid; Hofmeister, Stefan
2020EGUGA..22.3341T Altcode:
For better estimating the drag force acting on coronal mass ejections
(CMEs) in interplanetary space and ram-pressure at planets, improved
knowledge of the evolution of CME density/mass is highly valuable. We
investigate a sample of 29 well observed CME-ICME events, for which
we determine the de-projected 3D mass (STEREO-A and -B data), and the
CME volume using GCS modeling (STEREO, SoHO). Expanding the volume to
1AU distance, we derive the density and compare the results to in-situ
proton density measurements separately for the ICME sheath and magnetic
structure. A fair agreement between calculated and measured density is
derived for the magnetic structure as well for the sheath if taking
into account mass pile up of solar wind plasma. We give evidence and
observational assessment that during the interplanetary propagation
of a CME 1) the magnetic structure has rather constant mass and 2)
the sheath region at the front of the driver is formed from piled-up
mass that is rather depending on the solar wind density ahead of the
CME, than on the CME speed.
---------------------------------------------------------
Title: Comparing the Properties of ICME-Induced Forbush Decreases
at Earth and Mars
Authors: Freiherr von Forstner, Johan L.; Guo, Jingnan;
Wimmer-Schweingruber, Robert F.; Dumbović, Mateja; Janvier, Miho;
Démoulin, Pascal; Veronig, Astrid; Temmer, Manuela; Papaioannou,
Athanasios; Dasso, Sergio; Hassler, Donald M.; Zeitlin, Cary J.
2020JGRA..12527662F Altcode: 2020arXiv200303157V
Forbush decreases (FDs), which are short-term drops in the flux
of galactic cosmic rays, are caused by the shielding from strong
and/or turbulent magnetic structures in the solar wind, especially
interplanetary coronal mass ejections (ICMEs) and their associated
shocks, as well as corotating interaction regions. Such events can be
observed at Earth, for example, using neutron monitors, and also at
many other locations in the solar system, such as on the surface of
Mars with the Radiation Assessment Detector instrument onboard Mars
Science Laboratory. They are often used as a proxy for detecting the
arrival of ICMEs or corotating interaction regions, especially when
sufficient in situ solar wind measurements are not available. We
compare the properties of FDs observed at Earth and Mars, focusing
on events produced by ICMEs. We find that FDs at both locations show
a correlation between their total amplitude and the maximum hourly
decrease, but with different proportionality factors. We explain this
difference using theoretical modeling approaches and suggest that it is
related to the size increase of ICMEs, and in particular their sheath
regions, en route from Earth to Mars. From the FD data, we can derive
the sheath broadening factor to be between about 1.5 and 1.9, agreeing
with our theoretical considerations. This factor is also in line with
previous measurements of the sheath evolution closer to the Sun.
---------------------------------------------------------
Title: CME-CME Interactions as Sources of CME Geoeffectiveness:
The Formation of the Complex Ejecta and Intense Geomagnetic Storm
in 2017 Early September
Authors: Scolini, Camilla; Chané, Emmanuel; Temmer, Manuela; Kilpua,
Emilia K. J.; Dissauer, Karin; Veronig, Astrid M.; Palmerio, Erika;
Pomoell, Jens; Dumbović, Mateja; Guo, Jingnan; Rodriguez, Luciano;
Poedts, Stefaan
2020ApJS..247...21S Altcode: 2019arXiv191110817S
Coronal mass ejections (CMEs) are the primary sources of intense
disturbances at Earth, where their geoeffectiveness is largely
determined by their dynamic pressure and internal magnetic field,
which can be significantly altered during interactions with other
CMEs in interplanetary space. We analyze three successive CMEs that
erupted from the Sun during 2017 September 4-6, investigating the
role of CME-CME interactions as a source of the associated intense
geomagnetic storm (Dst_{min}=-142 nT on September 7). To quantify
the impact of interactions on the (geo)effectiveness of individual
CMEs, we perform global heliospheric simulations with the European
Heliospheric Forecasting Information Asset (EUHFORIA) model, using
observation-based initial parameters with the additional purpose of
validating the predictive capabilities of the model for complex CME
events. The simulations show that around 0.45 au, the shock driven by
the September 6 CME started compressing a preceding magnetic ejecta
formed by the merging of two CMEs launched on September 4, significantly
amplifying its B<SUB>z</SUB> until a maximum factor of 2.8 around 0.9
au. The following gradual conversion of magnetic energy into kinetic
and thermal components reduced the B<SUB>z</SUB> amplification until
its almost complete disappearance around 1.8 au. We conclude that a
key factor at the origin of the intense storm triggered by the 2017
September 4-6 CMEs was their arrival at Earth during the phase of
maximum B<SUB>z</SUB> amplification. Our analysis highlights how the
amplification of the magnetic field of individual CMEs in spacetime due
to interaction processes can be characterized by a growth, a maximum,
and a decay phase, suggesting that the time interval between the CME
eruptions and their relative speeds are critical factors in determining
the resulting impact of complex CMEs at various heliocentric distances
(helioeffectiveness).
---------------------------------------------------------
Title: Differential Emission Measure Plasma Diagnostics of a
Long-Lived Coronal Hole
Authors: Saqri, Jonas; Veronig, Astrid M.; Heinemann, Stephan G.;
Hofmeister, Stefan J.; Temmer, Manuela; Dissauer, Karin; Su, Yang
2020SoPh..295....6S Altcode: 2020arXiv200102259S
We use Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA) data to reconstruct the plasma properties from differential
emission measure (DEM) analysis for a previously studied long-lived,
low-latitude coronal hole (CH) over its lifetime of ten solar
rotations. We initially obtain a non-isothermal DEM distribution with
a dominant component centered around 0.9 MK and a secondary smaller
component at 1.5 - 2.0 MK. We find that deconvolving the data with
the instrument point spread function (PSF) to account for long-range
scattered light reduces the secondary hot component. Using the 2012
Venus transit and a 2013 lunar eclipse to test the efficiency of this
deconvolution, significant amounts of residual stray light are found
for the occulted areas. Accounting for this stray light in the error
budget of the different AIA filters further reduces the secondary hot
emission, yielding CH DEM distributions that are close to isothermal
with the main contribution centered around 0.9 MK. Based on these DEMs,
we analyze the evolution of the emission measure (EM), density, and
averaged temperature during the CH's lifetime. We find that once the CH
is clearly observed in EUV images, the bulk of the CH plasma reveals
a quite constant state, i.e. temperature and density reveal no major
changes, whereas the total CH area and the photospheric magnetic fine
structure inside the CH show a distinct evolutionary pattern. These
findings suggest that CH plasma properties are mostly "set" at the CH
formation or/and that all CHs have similar plasma properties.
---------------------------------------------------------
Title: Comparing the Properties of ICME-Induced Forbush Decreases
at Earth and Mars
Authors: Freiherr von Forstner, J. L.; Guo, J.; Wimmer-Schweingruber,
R. F.; Dumbovic, M.; Janvier, M.; Demoulin, P.; Veronig, A.; Temmer,
M.; Hassler, D.; Zeitlin, C.
2019AGUFMSH41D3339F Altcode:
Forbush decreases (FDs), short-term drops in the flux of galactic
cosmic rays (GCR), can be caused by the shielding from strong and/or
turbulent magnetic structures in the solar wind, i.e. interplanetary
coronal mass ejections (ICMEs) and their associated shocks as well
as corotating interaction regions (CIRs). FDs are often used as a
proxy for detecting the arrival of ICMEs or CIRs at locations where
sufficient in situ solar wind measurements are not or not always
available, such as at Mars. The Radiation Assessment Detector (RAD)
onboard the Mars Science Laboratory (MSL) mission's Curiosity rover
has been continuously measuring the GCR environment on the surface
of Mars for more than 7 years since its landing in August 2012 and is
thus an excellent source for measurements of FDs at Mars (see e.g. <A
href="https://doi.org/10.1051/0004-6361/201732087">Guo et al. 2018,
A&A</A>). <P />Based on the large catalog of FDs at Mars compiled
by <A href="https://doi.org/10.1007/s11207-019-1454-2">Papaioannou et
al. (2019, Solar Physics)</A> as well as results from our previous
work (<A href="https://doi.org/10.1029/2018SW002138">Freiherr von
Forstner et al., 2019, Space Weather</A>), we study the parameters
of FDs at Mars and their relations, focusing on events produced by
ICMEs. We then compare these data with catalogs of terrestrial FDs,
investigating whether and to what extent the differences of certain FD
characteristics between the two planets, at two different heliospheric
distances, are related to the evolution of ICMEs between Earth and
Mars. <P />Our results show that there is a linear correlation between
the FD amplitude (drop percentage) and the maximum hourly GCR decrease
during the FD, which was already found at Earth by previous authors (<A
href="https://doi.org/10.1017/S1743921309029676">Belov et al., 2008</A>,
<A href="https://doi.org/10.1134/S0016793212030024">Abunin et al.,
2012</A>). However, this correlation has a different proprtionality
factor at Mars than at Earth, especially for ICME-induced events. As
we do not find a clear dependence of this relationship on the observed
GCR energy range, we suggest that this difference is probably caused by
the expansion of the ICME sheath region as it propagates outward from
1 AU to ∼1.5 AU. The expansion factor derived from our analysis is in
line with expansion factors of ICME sheaths within the inner heliosphere
observed by <a href="https://doi.org/10.1029/2018JA025949>Janvier
et al. (2019, JGR Space Physics).
---------------------------------------------------------
Title: A study of the role of CME-CME interactions on CME
geo-effectiveness with EUHFORIA
Authors: Scolini, C.; Poedts, S.; Rodriguez, L.; Temmer, M.; Dumbovic,
M.; Guo, J.; Veronig, A.; Dissauer, K.; Palmerio, E.; Kilpua, K. E. J.;
Pomoell, J.
2019AGUFMSH43D3368S Altcode:
Coronal Mass Ejections (CMEs) are the main source of strong space
weather disturbances at Earth and other locations in the solar
system. While their impact is largely determined by their dynamic
pressure and magnetic field, interactions with other CMEs can
significantly alter their individual characteristics and enhance their
(geo-)effectiveness. As observations in the heliosphere are limited,
investigating such phenomena via physics-based models is therefore
crucial to advance our understanding of complex CME events, and to
assess the prediction capabilities at various locations. <P />Here we
present a comprehensive study of the role of CME-CME interactions on
their (geo-)effectiveness, by performing simulations of complex CME
events with the EUHFORIA heliospheric solar wind and CME propagation
model. As a case study, we consider a sequence of 6 CMEs observed during
the unusually active week of 4-10 September 2017. As their source region
moved on the solar disk due to the rotation, CMEs were launched over
a wide range of longitudes, interacting with each other while paving
the way for the propagation of the following ones. CME signatures were
observed at Mars and at Earth, where intense disturbances and space
weather events were triggered by CME-CME interactions. Using input
parameters derived from multi-spacecraft remote-sensing observations
of CMEs and their source region, we perform global simulations of the
event using the spheromak CME model in EUHFORIA, and we investigate how
their interactions affected the evolution of single CME structures and
the in-situ properties at Earth and Mars. <P />Results from this case
study are complemented by a parametric study of CME-CME interactions,
performed by running a set of simulations varying the initial CME
parameters (e.g. speed, waiting time, magnetic field properties,
density…), with the aim of quantifying the effect of such changes on
their propagation and interaction. Results will benchmark our current
prediction capabilities in the case of complex CME events and provide
insights on their large-scale evolution in the heliosphere.
---------------------------------------------------------
Title: Improving Modelling Areas of Open-Closed Flux in the Corona
Using Remote Sensing Observations
Authors: Asvestari, E.; Heinemann, S.; Temmer, M.; Pomoell, J.;
Kilpua, K. E. J.; Magdalenic, J.; Poedts, S.
2019AGUFMSH13A..09A Altcode:
Modelling the open magnetic field in the heliosphere with high
accuracy is essential for space weather forecasting purposes. Primary
source of open magnetic field are Coronal Holes (CH). Therefore, when
assessing how well we model the open magnetic field one needs to test
how well the model performs on one of its fundamental functions, that
of reconstructing coronal hole areas. For our study, we used EUHFORIA
(European heliospheric forecasting information asset) model which
employs an empirical solar wind model that combines the Potential
Field Source Surface (PFSS) and the Schatten Current Sheet (SCS)
models. Two important free parameters of the PFSS and the SCS models
are the source surface height (the outer boundary of the PFSS) and the
height of the inner boundary of SCS. Although, a commonly used value
for the source surface height is that of 2.5 solar radii, a wider range
of allowed heights ranging from 1.5 to 3.25 solar radii exist. Here, we
investigate the optimal heights that one should preselect in the model
aiming for better reconstruction of open flux areas. We vary the source
surface height within the interval [1.4, 3.2]Rs with a step of 0.1Rs,
and the SCS inner boundary height within the interval [1.3, 2.8]Rs with
the same step, where Rs is one solar radius. The study is applied on 15
CH exhibiting different latitudinal position and geometry. We compare
the modelled open flux areas with CH boundaries extracted using remote
sensing EUV observations and CATCH (Collection of analysis tools for
coronal holes). This study indicates that lower values of the two
boundary heights improve the modelling results. EUV image data from
instruments having a wide field of view, such as SUVI on board GOES-R,
and SWAP on board PROBA2, offer unprecedented possibility to actually
observe the heights below which closed loops exist in the corona,
and therefore further constrain the height choices in the model by
providing a lower limit.
---------------------------------------------------------
Title: Genesis and impulsive evolution of the fast CME associated
with the X8.2 flare on 2017 September 10
Authors: Veronig, A.; Podladchikova, T.; Dissauer, K.; Temmer, M.;
Seaton, D. B.; Long, D.; Guo, J.; Vrsnak, B.; Harra, L. K.; Kliem, B.
2019AGUFMSH13A..02V Altcode:
The X8.2 event of 2017 September 10 provides unique observations to
study the genesis, magnetic morphology, impulsive dynamics and shock
formation in a very fast coronal mass ejection (CME). As will be
discussed in this presentation, fundamental insight in the processes
of magnetic reconnection, CME acceleration and shock formation are
provided through EUV observations of the middle corona. <P />Combining
the large field-of-view and high-cadence imagery from GOES-16/SUVI
and SDO/AIA EUV, respectively, we identify a hot (T ≈ 10-15 MK)
bright rim around a quickly expanding cavity, embedded inside a much
larger CME shell (T ≈ 1-2 MK). The CME shell develops from a dense
set of large AR loops (>0.5Rs) and seamlessly evolves into the
CME front observed in LASCO C2. The strong lateral overexpansion
of the CME shell acts as a piston initiating the fast and globally
propagating EUV shock wave. The hot cavity rim is demonstrated to be
a manifestation of the dominantly poloidal flux and frozen-in plasma
added to the rising flux rope by magnetic reconnection in the current
sheet beneath. The same structure is later observed as the core of the
white-light CME, challenging the traditional interpretation of the CME
three-part morphology (Veronig et al. 2018). <P />The large amount of
added magnetic flux suggested by these observations can explain the
extreme accelerations of the radial and lateral expansion of the CME
shell and cavity, all reaching values up to 5-10 km s<SUP>-2</SUP>. The
acceleration peaks occur simultaneously with the first RHESSI 100-300
keV hard X-ray burst of the associated flare, further underlining the
importance of the reconnection process for the impulsive CME evolution
in the low and middle corona.
---------------------------------------------------------
Title: International Scientific Coordination on Space Weather:
A COSPAR Panel on Space Weather Perspective
Authors: Bisi, M. M.; Kuznetsova, M. M.; Temmer, M.; Opgenoorth, H. J.;
Belehaki, A.; Bruinsma, S.; Glover, A.; Heynderickx, D.; Linker, J.;
Mann, I. R.; Murray, S. A.; Nandy, D.
2019AGUFMSM31C3543B Altcode:
The understanding and prediction of space-weather phenomena and
their respective impact(s) on society have been widely-acknowledged
as an international challenge and something that requires a global
coordination and focus. In order to address this need to form
more-formal worldwide collaboration and coordination, and to maximise
return on such efforts (particularly scientifically), the Committee
on Space Research (COSPAR) Panel on Space Weather (PSW) has created a
network of International Space Weather Action Teams (ISWATs). <P />The
COSPAR PSW ISWAT initiative is capitalising on established efforts by
engaging existing national and international "teams" and "facilitates"
to form individual ISWATs that are being grouped into clusters
by domains/themes related to different aspects of solar/coronal,
heliospheric, ionospheric/atmospheric, and planetary space-weather
phenomena. The initiative also includes overarching themes such as
dealing with large data sets and model/scientific validations. The
ISWAT initiative places a strong encouragement for scientists to go
beyond their funding borders to form ISWATs better suited to address
challenges that one individual or small group/team may not be able to
address alone. <P />The ISWAT initiative serves as a global hub for
community coordinated topical focused collaborations and as a global
community voice for the next generation of both scientific and strategic
planning - this includes an update of the COSPAR/ILWS space weather
scientific roadmap (to transform the roadmap into a living document)
and to potentially provide an operational roadmap in parallel. <P
/>This presentation will re-introduce the ISWAT initiative, review
its current status and plans for community-wide campaigns, highlight
the overarching current plans for PSW, and place a focus on two key
space-weather areas: the ambient heliosphere/background solar wind
(designated as ISWAT theme H1) and CME structure, evolution and
propagation through heliosphere (designated as ISWAT theme H2).
---------------------------------------------------------
Title: Showcasing the just released ISWAT website
(http://www.iswat-cospar.org) built with a content management platform
to serve as an online presence for the ISWAT (International Space
Weather Action Teams) - community driven effort hosted by the COSPAR
Panel on Space Weather.
Authors: Mendoza, A. M. M.; Kuznetsova, M.; Opgenoorth, H. J.;
Belehaki, A.; Bisi, M. M.; Bruinsma, S.; Heynderickx, D.; Linker,
J.; Mann, I. R.; Murray, S. A.; Nandy, D.; Temmer, M.
2019AGUFMSM31C3181M Altcode:
We will showcase the just released ISWAT website (<A
href="http://www.iswat-cospar.org/">http://www.iswat-cospar.org</A>)
built with a content management platform to serve as an online
presence for the <P />ISWAT (International Space Weather Action
Teams) - community driven effort hosted by the COSPAR Panel on Space
Weather. <P />The website was created to represent ISWAT overarching
goal to serve as a global hub for topical collaborations and focused
on different aspects of space weather. <P />The homepage main's ISWAT
image menu shows ISWAT clusters that cover Solar (S), Heliosphere
(H) and Geospace (G) domains. Each cluster (S1-S3, H1-H4, G1-G3)
<P />shown in the image is links to dedicated webpages that contain
information about cluster goals and links to entry pages of registered
action teams. <P />The "Join ISWAT" link contains 2 interactive forms
for joining ISWAT mailing list and for registration of established and
emerging international teams focused on different <P />aspects of space
weather. After the registration is confirmed by cluster moderator a link
to a new team entry page is added to a submitted cluster site. A team
start entry <P />team page will contain information submitted during
registration that may include a link to an external team page as an
option. Another interactive form to join a <P />registered ISWAT team
will be added in the near future. <P />Future planned additions include
a Forum to create threaded discussion boards to encourage discussions
on global coordination of space weather and invite community inputs
to global space weather roadmap updates. <P />The website will be
eventually maintained and facilitated by the COSPAR Panel on Space
Weather Chairs/Vice-chairs, ISWAT cluster moderators, and ISWAT team
<P />representatives.
---------------------------------------------------------
Title: International Scientific Coordination on Space Weather:
A COSPAR Panel on Space Weather Perspective
Authors: Kuznetsova, M.; Bisi, M. M.; Kusano, K.; Fuller-Rowell,
T. J.; Mann, I.; Belehaki, A.; Minow, J. I.; Munoz-Jaramillo, A.;
Masson, A.; Bruinsma, S.; Bisi, M. M.; Kuznetsova, M. M.; Temmer, M.;
Opgenoorth, H. J.; Belehaki, A.; Bruinsma, S.; Glover, A.; Heynderickx,
D.; Linker, J.; Mann, I. R.; Murray, S. A.; Nandy, D.
2019AGUFMSM31C3543K Altcode:
The understanding and prediction of space-weather phenomena and
their respective impact(s) on society have been widely-acknowledged
as an international challenge and something that requires a global
coordination and focus. In order to address this need to form
more-formal worldwide collaboration and coordination, and to maximise
return on such efforts (particularly scientifically), the Committee
on Space Research (COSPAR) Panel on Space Weather (PSW) has created a
network of International Space Weather Action Teams (ISWATs). <P />The
COSPAR PSW ISWAT initiative is capitalising on established efforts by
engaging existing national and international "teams" and "facilitates"
to form individual ISWATs that are being grouped into clusters
by domains/themes related to different aspects of solar/coronal,
heliospheric, ionospheric/atmospheric, and planetary space-weather
phenomena. The initiative also includes overarching themes such as
dealing with large data sets and model/scientific validations. The
ISWAT initiative places a strong encouragement for scientists to go
beyond their funding borders to form ISWATs better suited to address
challenges that one individual or small group/team may not be able to
address alone. <P />The ISWAT initiative serves as a global hub for
community coordinated topical focused collaborations and as a global
community voice for the next generation of both scientific and strategic
planning - this includes an update of the COSPAR/ILWS space weather
scientific roadmap (to transform the roadmap into a living document)
and to potentially provide an operational roadmap in parallel. <P
/>This presentation will re-introduce the ISWAT initiative, review
its current status and plans for community-wide campaigns, highlight
the overarching current plans for PSW, and place a focus on two key
space-weather areas: the ambient heliosphere/background solar wind
(designated as ISWAT theme H1) and CME structure, evolution and
propagation through heliosphere (designated as ISWAT theme H2).
---------------------------------------------------------
Title: Assessing the Performance of EUHFORIA Modeling the Background
Solar Wind
Authors: Hinterreiter, Jürgen; Magdalenic, Jasmina; Temmer, Manuela;
Verbeke, Christine; Jebaraj, Immanuel Christopher; Samara, Evangelia;
Asvestari, Eleanna; Poedts, Stefaan; Pomoell, Jens; Kilpua, Emilia;
Rodriguez, Luciano; Scolini, Camilla; Isavnin, Alexey
2019SoPh..294..170H Altcode: 2019arXiv190707461H
In order to address the growing need for more accurate space-weather
predictions, a new model named EUHFORIA (EUropean Heliospheric
FORecasting Information Asset) was recently developed. We present
the first results of the performance assessment for the solar-wind
modeling with EUHFORIA and identify possible limitations of its present
setup. Using the basic EUHFORIA 1.0.4 model setup with the default input
parameters, we modeled background solar wind (no coronal mass ejections)
and compared the obtained results with Advanced Composition Explorer
(ACE) in-situ measurements. For the purposes of statistical study we
developed a technique of combining daily EUHFORIA runs into continuous
time series. The combined time series were derived for the years 2008
(low solar activity) and 2012 (high solar activity), from which in-situ
speed and density profiles were extracted. We find for the low-activity
phase a better match between model results and observations compared to
the high-activity time interval considered. The quality of the modeled
solar-wind parameters is found to be rather variable. Therefore, to
better understand the results obtained we also qualitatively inspected
characteristics of coronal holes, i.e. the sources of the studied fast
streams. We discuss how different characteristics of the coronal holes
and input parameters to EUHFORIA influence the modeled fast solar wind,
and suggest possibilities for the improvement of the model.
---------------------------------------------------------
Title: Refining halo CME forecast
Authors: Yordanova, E.; Werner, E.; Temmer, M.; Dimmock, A. P.;
Rosenqvist, L.
2019AGUFMSH32A..07Y Altcode:
Halo CMEs are strongly geoeffective due to their direct propagation
towards Earth. Therefore, it is of critical importance to accurately
predict their arrival time. However, there are certain difficulties
that make this task challenging. Usually, the quality of estimation
of halo CME kinematics from coronagraph images suffers from projection
effects in the plane-of-sky. In addition, the state of the background
solar wind through which the CME is propagating should also be
accounted for. <P />In this study, we refine the WSA-ENLIL+Cone model
prediction by investigating one of the model input parameters, namely,
the density enhancement factor (dcld). This parameter represents the
density enhancement of the leading edge of the CME cone relative to the
density enhancement of the fast solar wind. The default input is dcld
equal to 4, which often results in higher amplitudes and earlier CME
arrival times. We take instead the ratio between the density enhancement
at the shock produced by the halo CME and the ambient solar wind and
revisit the model predictions for already existing WSA-ENLIL+Cone
runs. The new forecast results shows significant improvement in the
arrival time estimation, suggesting that the custom dcld factor may
be useful in space weather operational setting.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Coronal hole parameters
(Heinemann+, 2019)
Authors: Heinemann, S. G.; Temmer, M.; Heinemann, N.; Dissauer, K.;
Samara, E.; Jercic, V.; Hofmeister, S. J.; Veronig, A. M.
2019yCatp058029401H Altcode:
Coronal hole parameters such as morphological properties, the intensity,
boundary stability as well as properties of the underlying photospheric
magnetic field and its fine structure are presented. 718 coronal holes
between 2010 and 2019 have been extracted and analyzed from 193A
filtergrams taken by AIA/SDO. For each coronal hole the following
parameters are given (including uncertainties). Date, Threshold,
Category Factor, Area, Intensity (Mean + Median), Position, Extension,
Mean Magnetic Field Strength (Signed + Unsigned), Magnetic Flux (Signed
+ Unsigned), Flux Balance, Skewness (Magnetic Field Distribution),
Flux Tube Number (Weak + Strong), Flux Tube Area Ratio (Weak + Strong),
Flux Tube Flux Ratio (Weak + Strong). <P />(1 data file).
---------------------------------------------------------
Title: Reconstructing Coronal Hole Areas With EUHFORIA and Adapted
WSA Model: Optimizing the Model Parameters
Authors: Asvestari, E.; Heinemann, S. G.; Temmer, M.; Pomoell, J.;
Kilpua, E.; Magdalenic, J.; Poedts, S.
2019JGRA..124.8280A Altcode: 2019arXiv190703337A
The adopted Wang-Sheeley-Arge (WSA) model embedded in EUHFORIA
(EUropean Heliospheric FORecasting Information Asset) is compared to
EUV observations. According to the standard paradigm, coronal holes are
sources of open flux; thus, we use remote sensing EUV observations and
CATCH (Collection of Analysis Tools for Coronal Holes) to extract CH
areas and compare them to the open flux areas modeled by EUHFORIA. From
the adopted WSA model we employ only the Potential Field Source Surface
(PFSS) model for the inner corona and the Schatten Current Sheet
(SCS) model for the outer (PFSS+SCS). The height, R<SUB>ss</SUB>, of
the outer boundary of the PFSS, known as the source surface, and the
height, R<SUB>i</SUB>, of the inner boundary of the SCS are important
parameters affecting the modeled CH areas. We investigate the impact
the two model parameters can have in the modeled results. We vary
R<SUB>ss</SUB> within the interval [1.4, 3.2]R<SUB>⊙</SUB> with
a step of 0.1R<SUB>⊙</SUB>, and R<SUB>i</SUB> within the interval
[1.3, 2.8]R<SUB>⊙</SUB> with the same step, and the condition that
R<SUB>i</SUB><R<SUB>ss</SUB>. This way we have a set of 184 initial
parameters to the model, and we assess the model results for all these
possible height pairs. We conclude that the default heights used so
far fail in modeling accurately CH areas and lower heights need to
be considered.
---------------------------------------------------------
Title: Statistical Analysis and Catalog of Non-polar Coronal Holes
Covering the SDO-Era Using CATCH
Authors: Heinemann, Stephan G.; Temmer, Manuela; Heinemann, Niko;
Dissauer, Karin; Samara, Evangelia; Jerčić, Veronika; Hofmeister,
Stefan J.; Veronig, Astrid M.
2019SoPh..294..144H Altcode: 2019arXiv190701990H
Coronal holes are usually defined as dark structures seen in the extreme
ultraviolet and X-ray spectrum which are generally associated with
open magnetic fields. Deriving reliably the coronal hole boundary is
of high interest, as its area, underlying magnetic field, and other
properties give important hints as regards high speed solar wind
acceleration processes and compression regions arriving at Earth. In
this study we present a new threshold-based extraction method,
which incorporates the intensity gradient along the coronal hole
boundary, which is implemented as a user-friendly SSW-IDL GUI. The
Collection of Analysis Tools for Coronal Holes (CATCH) enables the
user to download data, perform guided coronal hole extraction and
analyze the underlying photospheric magnetic field. We use CATCH
to analyze non-polar coronal holes during the SDO-era, based on 193
Å filtergrams taken by the Atmospheric Imaging Assembly (AIA) and
magnetograms taken by the Heliospheric and Magnetic Imager (HMI),
both on board the Solar Dynamics Observatory (SDO). Between 2010 and
2019 we investigate 707 coronal holes that are located close to the
central meridian. We find coronal holes distributed across latitudes
of about ±60<SUP>∘</SUP>, for which we derive sizes between 1.6
×10<SUP>9</SUP> and 1.8 ×10<SUP>11</SUP><SUP>km2</SUP>. The absolute
value of the mean signed magnetic field strength tends towards an
average of 2.9 ±1.9 G. As far as the abundance and size of coronal
holes is concerned, we find no distinct trend towards the northern
or southern hemisphere. We find that variations in local and global
conditions may significantly change the threshold needed for reliable
coronal hole extraction and thus, we can highlight the importance of
individually assessing and extracting coronal holes.
---------------------------------------------------------
Title: Photospheric magnetic structure of coronal holes
Authors: Hofmeister, Stefan J.; Utz, Dominik; Heinemann, Stephan G.;
Veronig, Astrid; Temmer, Manuela
2019A&A...629A..22H Altcode: 2019arXiv190903806H
In this study, we investigate in detail the photospheric magnetic
structure of 98 coronal holes using line-of-sight magnetograms of
SDO/HMI, and for a subset of 42 coronal holes using HINODE/SOT G-band
filtergrams. We divided the magnetic field maps into magnetic elements
and quiet coronal hole regions by applying a threshold at ±25 G. We
find that the number of magnetic bright points in magnetic elements
is well correlated with the area of the magnetic elements (cc =
0.83 ± 0.01). Further, the magnetic flux of the individual magnetic
elements inside coronal holes is related to their area by a power law
with an exponent of 1.261 ± 0.004 (cc = 0.984 ± 0.001). Relating
the magnetic elements to the overall structure of coronal holes, we
find that on average (69 ± 8)% of the overall unbalanced magnetic
flux of the coronal holes arises from long-lived magnetic elements
with lifetimes > 40 h. About (22 ± 4)% of the unbalanced magnetic
flux arises from a very weak background magnetic field in the quiet
coronal hole regions with a mean magnetic field density of about
0.2-1.2 G. This background magnetic field is correlated to the flux
of the magnetic elements with lifetimes of > 40 h (cc = 0.88 ±
0.02). The remaining flux arises from magnetic elements with lifetimes
< 40 h. By relating the properties of the magnetic elements to the
overall properties of the coronal holes, we find that the unbalanced
magnetic flux of the coronal holes is completely determined by
the total area that the long-lived magnetic elements cover (cc =
0.994 ± 0.001). <P />Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201935918/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: EVE Flare Diagnostics of in situ Observed Electron Events
Authors: Miteva, R.; Samwel, S. W.; Veronig, A.; Koleva, K.; Dechev,
M.; Dissauer, K.; Temmer, M.; Kozarev, K.; Zabunov, S.
2019simi.conf..196M Altcode:
We present a comparative study between SDO/EVE flare intensity and the
peak intensity of solar energetic electrons and protons over solar
cycle 24 (2010–2017). For the analysis we selected flare emission
in three EUV wavelengths: 94, 133 and 304 Å. Data from 103–175 and
175–315 keV ACE/EPAM energy channels are used to identify and analyze
the flux of the in situ observed electrons. SOHO/ERNE data in five
energy channels (17–22, 26–32, 40–51, 64–80, 101–131 MeV) is
used for the proton signatures of the so-identified electron events. We
calculated Pearson correlation coefficients between the electron and
proton particle fluxes and the flare EUV intensities, and compare the
results with the respective correlations between particle flux and
the solar flare GOES class and speed of the coronal mass ejections.
---------------------------------------------------------
Title: STEREOCat Speed de-projection of SEP-Related CMEs
Authors: Tsvetkov, Ts.; Miteva, R.; Temmer, M.; Petrov, N.
2019simi.conf..207T Altcode:
Particles accelerated to high energies by solar eruptive phenomena
can reach the Earth moving along the interplanetary magnetic field
lines. We use a list of 156 SOHO ERNE 20 MeV solar energetic particle
(SEP) events from solar cycle 24 (2009–2017) with identified solar
origin (e.g. flares and CMEs). The aim of this study is to evaluate
the 3D parameters of SEP-related CMEs and estimate if they can give
us a better insight of SEP production than the previously used 2D
velocities. The 3D kinematic properties of the CME set are explored
using observations from STEREO SECCHI and SOHO LASCO coronagraphs
based on the STEREOCat analysis tool.
---------------------------------------------------------
Title: CME-HSS Interaction and Characteristics Tracked from Sun
to Earth
Authors: Heinemann, Stephan G.; Temmer, Manuela; Farrugia, Charles J.;
Dissauer, Karin; Kay, Christina; Wiegelmann, Thomas; Dumbović, Mateja;
Veronig, Astrid M.; Podladchikova, Tatiana; Hofmeister, Stefan J.;
Lugaz, Noé; Carcaboso, Fernando
2019SoPh..294..121H Altcode: 2019arXiv190810161H
In a thorough study, we investigate the origin of a remarkable plasma
and magnetic field configuration observed in situ on June 22, 2011, near
L1, which appears to be a magnetic ejecta (ME) and a shock signature
engulfed by a solar wind high-speed stream (HSS). We identify the
signatures as an Earth-directed coronal mass ejection (CME), associated
with a C7.7 flare on June 21, 2011, and its interaction with a HSS,
which emanates from a coronal hole (CH) close to the launch site of the
CME. The results indicate that the major interaction between the CME and
the HSS starts at a height of 1.3 R⊙ up to 3 <SUB>R⊙</SUB>. Over
that distance range, the CME undergoes a strong north-eastward
deflection of at least 30<SUP>∘</SUP> due to the open magnetic field
configuration of the CH. We perform a comprehensive analysis for the
CME-HSS event using multi-viewpoint data (from the Solar TErrestrial
RElations Observatories, the Solar and Heliospheric Observatory and the
Solar Dynamics Observatory), and combined modeling efforts (nonlinear
force-free field modeling, Graduated Cylindrical Shell CME modeling,
and the Forecasting a CME's Altered Trajectory - ForeCAT model). We aim
at better understanding its early evolution and interaction process as
well as its interplanetary propagation and related in situ signatures,
and finally the resulting impact on the Earth's magnetosphere.
---------------------------------------------------------
Title: Assessment and recommendations for a consolidated European
approach to space weather - as part of a global space weather effort
Authors: Opgenoorth, Hermann J.; Wimmer-Schweingruber, Robert F.;
Belehaki, Anna; Berghmans, David; Hapgood, Mike; Hesse, Michael;
Kauristie, Kirsti; Lester, Mark; Lilensten, Jean; Messerotti, Mauro;
Temmer, Manuela
2019JSWSC...9A..37O Altcode:
Over the last 10-20 years there has been an ever-increasing
international awareness of risks to modern society from adverse and
potentially harmful - and in extreme cases even disastrous - space
weather events. Many individual countries and even international
organisations like the United Nations (UN) have begun to increase
their activities in preparing for and mitigating effects of adverse
space weather. As in the rest of the world there is also in Europe an
urgent need for coordination of Space Weather efforts in individual
countries as well as in and among European organisations such as
the European Space Agency (ESA) and the European Union (EU). This
coordination should not only improve our ability to meet space weather
risks, but also enable Europe to contribute to on-going global space
weather efforts. While space weather is a global threat, which needs a
global response, it also requires tailored regional and trans-regional
responses that require coordination at all levels. Commissioned by
the European Space Science Committee (ESSC) of the European Science
Foundation, the authors - together with ex-officio advice from ESA
and the EU - have over two years assessed European activities in the
realm of space weather and formulated a set of recommendations to ESA,
the EU and their respective member states, about how to prepare Europe
for the increasing impact of adverse space weather effects on man-made
infrastructure and our society as a whole. We have also analysed
parallel international activities worldwide, and we give advice how
Europe could incorporate its future activities into a global scheme.
---------------------------------------------------------
Title: Spectroscopy and Differential Emission Measure Diagnostics
of a Coronal Dimming Associated with a Fast Halo CME
Authors: Veronig, Astrid M.; Gömöry, Peter; Dissauer, Karin; Temmer,
Manuela; Vanninathan, Kamalam
2019ApJ...879...85V Altcode: 2019arXiv190601517V
We study the coronal dimming caused by the fast halo CME (deprojected
speed v = 1250 km s<SUP>-1</SUP>) associated with the C3.7 two-ribbon
flare on 2012 September 27, using Hinode/EIS spectroscopy and Solar
Dynamics Observatory (SDO)/AIA Differential Emission Measure (DEM)
analysis. The event reveals bipolar core dimmings encompassed by
hook-shaped flare ribbons located at the ends of the flare-related
polarity inversion line, and marking the footpoints of the erupting
filament. In coronal emission lines of log T [K] = 5.8-6.3, distinct
double-component spectra indicative of the superposition of a stationary
and a fast upflowing plasma component with velocities up to 130 km
s<SUP>-1</SUP> are observed at these regions, which were mapped by the
scanning EIS slit close in time to their impulsive dimming onset. The
outflowing plasma component is found to be of the same order as and
even dominant over the stationary one, with electron densities in the
upflowing component of 2 × 10<SUP>9</SUP> cm<SUP>-3</SUP> at log T
[K] = 6.2. The density evolution in core-dimming regions derived from
SDO/AIA DEM analysis reveals impulsive reductions by 40%-50% within
≲10 minutes and remains at these reduced levels for hours. The
mass-loss rate derived from the EIS spectroscopy in the dimming
regions is of the same order as the mass increase rate observed in the
associated white-light CME (1 × 10<SUP>12</SUP> g s<SUP>-1</SUP>),
indicating that the CME mass increase in the coronagraphic field of
view results from plasma flows from below and not from material piled
up ahead of the outward-moving and expanding CME front.
---------------------------------------------------------
Title: Unusual Plasma and Particle Signatures at Mars and STEREO-A
Related to CME-CME Interaction
Authors: Dumbović, Mateja; Guo, Jingnan; Temmer, Manuela; Mays,
M. Leila; Veronig, Astrid; Heinemann, Stephan G.; Dissauer, Karin;
Hofmeister, Stefan; Halekas, Jasper; Möstl, Christian; Amerstorfer,
Tanja; Hinterreiter, Jürgen; Banjac, Saša; Herbst, Konstantin; Wang,
Yuming; Holzknecht, Lukas; Leitner, Martin; Wimmer–Schweingruber,
Robert F.
2019ApJ...880...18D Altcode: 2019arXiv190602532D
On 2017 July 25 a multistep Forbush decrease (FD) with a remarkable
total amplitude of more than 15% was observed by Mars Science
Laboratory/Radiation Assessment Detector at Mars. We find that these
particle signatures are related to very pronounced plasma and magnetic
field signatures detected in situ by STEREO-A on 2017 July 24, with
a higher-than-average total magnetic field strength reaching more
than 60 nT. In the observed time period STEREO-A was at a relatively
small longitudinal separation (46°) to Mars, and both were located at
the back side of the Sun as viewed from Earth. We analyze a number of
multispacecraft and multi-instrument (both in situ and remote-sensing)
observations and employ modeling to understand these signatures. We
find that the solar sources are two coronal mass ejections (CMEs)
that erupted on 2017 July 23 from the same source region on the back
side of the Sun as viewed from Earth. Moreover, we find that the
two CMEs interact nonuniformly, inhibiting the expansion of one of
the CMEs in the STEREO-A direction, whereas allowing it to expand
more freely in the Mars direction. The interaction of the two CMEs
with the ambient solar wind adds up to the complexity of the event,
resulting in a long, substructured interplanetary disturbance at Mars,
where different substructures correspond to different steps of the FD,
adding up to a globally large-amplitude FD.
---------------------------------------------------------
Title: Heliospheric Evolution of Magnetic Clouds
Authors: Vršnak, B.; Amerstorfer, T.; Dumbović, M.; Leitner, M.;
Veronig, A. M.; Temmer, M.; Möstl, C.; Amerstorfer, U. V.; Farrugia,
C. J.; Galvin, A. B.
2019ApJ...877...77V Altcode: 2019arXiv190408266V
The interplanetary evolution of 11 magnetic clouds (MCs) recorded by at
least two radially aligned spacecraft is studied. The in situ magnetic
field measurements are fitted to a cylindrically symmetric Gold-Hoyle
force-free uniform-twist flux-rope configuration. The analysis
reveals that in a statistical sense, the expansion of the studied
MCs is compatible with self-similar behavior. However, individual
events expose a large scatter of expansion rates, ranging from very
weak to very strong expansion. Individually, only four events show an
expansion rate compatible with isotropic self-similar expansion. The
results indicate that the expansion has to be much stronger when
the MCs are still close to the Sun than in the studied 0.47-4.8 au
distance range. The evolution of the magnetic field strength shows a
large deviation from the behavior expected for the case of isotropic
self-similar expansion. In the statistical sense, as well as in most
of the individual events, the inferred magnetic field decreases much
slower than expected. Only three events show behavior compatible
with self-similar expansion. There is also a discrepancy between the
magnetic field decrease and the increase of the MC size, indicating that
magnetic reconnection and geometrical deformations play a significant
role in the MC evolution. About half of the events show a decay of the
electric current as expected for self-similar expansion. Statistically,
the inferred axial magnetic flux is broadly consistent with remaining
constant. However, events characterized by a large magnetic flux show
a clear tendency toward decreasing flux.
---------------------------------------------------------
Title: Three-dimensional Reconstructions of Extreme-ultraviolet Wave
Front Heights and Their Influence on Wave Kinematics
Authors: Podladchikova, Tatiana; Veronig, Astrid M.; Dissauer, Karin;
Temmer, Manuela; Podladchikova, Olena
2019ApJ...877...68P Altcode: 2019arXiv190409427P
EUV waves are large-scale disturbances in the solar corona initiated
by coronal mass ejections. However, solar EUV images show only the
wave front projections along the line of sight of the spacecraft. We
perform 3D reconstructions of EUV wave front heights using multipoint
observations from STEREO-A and STEREO-B, and we study their evolution
to properly estimate the EUV wave kinematics. We develop two different
methods to solve the matching problem of the EUV wave crest on
pairs of STEREO-A/B images by combining epipolar geometry with the
investigation of perturbation profiles. The proposed approaches are
applicable at the early and maximum stage of the event when STEREO-A/B
see different facets of the EUV wave, but also at the later stage when
the wave front becomes diffusive and faint. The techniques developed
are demonstrated on two events observed at different separations of
the STEREO spacecraft (42° and 91°). For the 2007 December 7 event,
we find that the emission of the EUV wave front mainly comes from a
height range up to 90-104 Mm, decreasing later to 7-35 Mm. Including
the varying height of the EUV wave front allows us to correct the
wave kinematics for the projection effects, resulting in velocities
in the range of 217-266 km s<SUP>-1</SUP>. For the 2009 February 13
event, the wave front height almost doubled from 54 to 93 Mm over 10
minutes, and the velocity derived is 205-208 km s<SUP>-1</SUP>. In
the two events under study, the corrected speeds differ by up to 25%
from the uncorrected ones, depending on the wave front height evolution.
---------------------------------------------------------
Title: Investigating the evolution and interactions of the September
2017 CME events with EUHFORIA
Authors: Scolini, Camilla; Rodriguez, Luciano; Temmer, Manuela; Guo,
Jingnan; Dumbovic, Mateja; Pomoell, Jens; Poedts, Stefaan
2019shin.confE...1S Altcode:
Coronal Mass Ejections (CMEs) are the primary source of strong
space weather disturbances at Earth and other locations in the
heliosphere. While their (geo-)effectiveness is largely determined
by their dynamic pressure and magnetic field, phenomena such as
the interaction with other transients (CMEs, CIRs…), or the
pre-conditioning of interplanetary space due to preceding CMEs,
can significantly alter the properties of single CME events and
influence their (geo-)effectiveness. Investigating such phenomena
via physics-based models is crucial to improve our understanding of
interacting CME events, and to assess the prediction capability of
extreme space weather events at various locations in the heliosphere. <P
/>We present a comprehensive analysis of the CME events that erupted
from AR12673 during the unusually active week of September 4-10,
2017, using the EUHFORIA heliospheric model. As AR12673 rotated on
the solar disk, CMEs were launched over a wide range of longitudes,
interacting with each other and paving the way for the propagation
of following CMEs. CME signatures were observed at both Earth and
Mars, and associated particle events were reported at Earth, Mars,
and STEREO-A. At Earth, an intense geomagnetic storm triggered by
a CME sheath interacting with a preceding ejecta was recorded on
September 8, 2017. <P />Using parameters derived from remote-sensing
and multi-spacecraft observations of the CMEs and their source
region, we simulate the events with both traditional cone CME model,
and with a more realistic flux-rope CME model. We investigate how
CME-CME interactions affect the spatial and temporal evolution of CME
shocks, sheaths and ejecta in the heliosphere, and we compare simulation
results with in-situ measurements at Earth and Mars. This study will not
only benchmark current prediction capabilities in the case of complex
CME events, but will also provide better insights on the large-scale
evolution of complex CME events throughout the heliosphere.
---------------------------------------------------------
Title: ELEvoHI ensemble modeling: CME arrival prediction based on
heliospheric imager observations
Authors: Hinterreiter, Jürgen; Amerstorfer, Tanja; Temmer, Manuela;
Möstl, Christian; Reiss, Martin; Amerstorfer, Ute; Bailey, Rachel
2019EGUGA..21.9132H Altcode:
We present a statistical study on CME arrival prediction using ELEvoHI
(ELlipse Evolution model based on Heliospheric Imager observations)
ensemble modeling. ELEvoHI is the current state-of-the-art HI
elongation fitting method that utilizes heliospheric imager data
obtained by the STEREO (Solar TErrestrial RElations Observatory)
twin spacecraft assuming that the drag force exerted by the ambient
solar wind is the dominant force influencing the CME propagation in
the IP-space. The HI time-elongation profiles needed by ELEvoHI as
well as the in-situ data for validating the results are taken from
the FP7 HELCATS project. GCS (Graduated Cylindrical Shell) fitting
is applied for each CME separately. We perform a cut in the ecliptic
plane, based on the GCS fit, to derive the initial values needed
for the ELEvoHI ensemble modeling. In this study, we select CMEs
in a 12-month interval (June 2009 to June 2010) corresponding to a
location of STEREO-B close to Lagrange point 5 (60° trailing Earth),
making the model results valuable for future studies (STEREO-A near
L5 in mid 2020) and for a planned L5 mission. Our analysis contains
two parts: First, a contingency table (hit/false alarms/misses) with
the corresponding skill scores and second the times and speeds for the
predicted and observed Earth arriving events. The statistical results
are compared to other studies and will serve as benchmark for future
enhanced ELEvoHI versions.
---------------------------------------------------------
Title: Genesis, magnetic morphology and impulsive evolution of
the coronal mass ejection associated with the X8.2 flare on 2017
September 10
Authors: Veronig, Astrid; Podladchikova, Tatiana; Dissauer, Karin;
Temmer, Manuela; Seaton, Daniel; Long, David; Guo, Jingnan; Vrsnak,
Bojan; Harra, Louise; Kliem, Bernhard
2019EGUGA..21.9243V Altcode:
The extreme X8.2 event of 2017 September 10 provides unique observations
to study the genesis, magnetic morphology, impulsive dynamics and
shock formation in a very fast coronal mass ejection (CME). Combining
GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot (T ≈ 10-15
MK) bright rim around a quickly expanding cavity, embedded inside a
much larger CME shell (T ≈ 1-2 MK). The CME shell develops from a
dense set of large AR loops (>0.5Rs) and seamlessly evolves into
the CME front observed in LASCO C2. The strong lateral overexpansion
of the CME shell acts as a piston initiating the fast EUV shock
wave. The hot cavity rim is demonstrated to be a manifestation of
the dominantly poloidal flux and frozen-in plasma added to the rising
flux rope by magnetic reconnection in the current sheet beneath. The
same structure is later observed as the core of the white-light CME,
challenging the traditional interpretation of the CME three-part
morphology. The large amount of added magnetic flux suggested by these
observations explains the extreme accelerations of the radial and
lateral expansion of the CME shell and cavity, all reaching values
up to 5-10 km s-2. The acceleration peaks occur simultaneously with
the first RHESSI 100-300 keV hard X-ray burst of the associated flare,
further underlining the importance of the reconnection process for the
impulsive CME evolution. Finally, the much higher radial propagation
speed of the flux rope in relation to the CME shell causes a distinct
deformation of the white-light CME front and shock.
---------------------------------------------------------
Title: Statistics of Coronal Dimmings Associated with Coronal Mass
Ejections. II. Relationship between Coronal Dimmings and Their
Associated CMEs
Authors: Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova, T.
2019ApJ...874..123D Altcode: 2018arXiv181001589D
We present a statistical study of 62 coronal dimming events associated
with Earth-directed coronal mass ejections (CMEs) during the
quasi-quadrature period of STEREO and the Solar Dynamics Observatory
(SDO). This unique setting allows us to study both phenomena in great
detail and compare characteristic quantities statistically. Coronal
dimmings are observed on-disk by the SDO/Atmospheric Imaging Assembly
and the Helioseismic and Magnetic Imager, while the CME kinematics
during the impulsive acceleration phase is studied close to the limb
with STEREO/EUVI and COR, minimizing projection effects. The dimming
area, its total unsigned magnetic flux, and its total brightness,
reflecting properties of the total dimming region at its final extent,
show the highest correlations with the CME mass (c ∼ 0.6-0.7). Their
corresponding time derivatives, describing the dynamics of the dimming
evolution, show the strongest correlations with the CME peak velocity
(c ∼ 0.6). The highest correlation of c = 0.68 ± 0.08 is found
with the mean intensity of dimmings, indicating that the lower the
CME starts in the corona, the faster it propagates. No significant
correlation between dimming parameters and the CME acceleration was
found. However, for events where high-cadence STEREO observations were
available, the mean unsigned magnetic field density in the dimming
regions tends to be positively correlated with the CME peak acceleration
(c = 0.42 ± 0.20). This suggests that stronger magnetic fields result
in higher Lorentz forces providing stronger driving force for the CME
acceleration. Specific coronal dimming parameters correlate with both
CME and flare quantities providing further evidence for the flare-CME
feedback relationship. For events in which the CME occurs together
with a flare, coronal dimmings statistically reflect the properties
of both phenomena.
---------------------------------------------------------
Title: Importance of heliospheric imager track quality for CME
arrival prediction accuracy
Authors: Amerstorfer, Tanja; Hinterreiter, Jürgen; Möstl, Christian;
Davies, Jackie A.; Amerstorfer, Ute V.; Reiss, Martin A.; Temmer,
Manuela; Bailey, Rachel L.; Harrison, Richard A.
2019EGUGA..21.7373A Altcode:
Operational CME arrival prediction is mainly conducted using
magnetohydrodynamic models based on coronagraph observations and
magnetograms. Although the Solar TErrestrial RElations Observatory with
its heliospheric imagers (HI) provides the possibility to trace a CME's
propagation along its path from the Sun to 1 AU, these data can hardly
be used to predict CME arrivals in real time (except for a few events
in an early phase of the mission). One of the main reasons for that
is a large number of data gaps in beacon data, which is available in
near real time (in contrast to the complete science data), impeding a
proper measurement of the CME front. With regard to a possible future L5
mission carrying HIs we investigate the most suitable way of extracting
the time-elongation track of CMEs from HI observations leading to
a prediction with the highest possible accuracy. As a first step to
reach this goal, we use time-elongation tracks measured from STEREO/HI
science data and provided by the FP7 HELCATS team as well as tracks
derived using time-elongation maps and tracks measured directly in an
HI image time series. These time-elongation tracks are further used as
input to our CME ensemble prediction tool ELEvoHI (ELlipse Evolution
model based on HI data), which assumes a drag-based interplanetary
CME propagation and an elliptical CME frontal shape. ELEvoHI produces
post-event predictions of arrival times and speeds at 1 AU for all
tracks of each CME under study. By comparing the prediction results from
several ways of tracking we attempt to deduce a preferable approach
for future studies, e.g. when using data from Parker Solar Probe's
Wide-Field Imager for Solar Probe (WISPR), and maybe for future real
time predictions when STEREO-A approaches the L5 point.
---------------------------------------------------------
Title: Observational assessment on CME mass pile up in interplanetary
space
Authors: Temmer, Manuela; Holzknecht, Lukas; Dumbovic, Mateja;
Vrsnak, Bojan
2019EGUGA..21.9578T Altcode:
Coronal mass ejections (CMEs) propagating in the heliosphere are
exposed to a drag force due to the ambient solar wind. Mass pile-up
in interplanetary space can have strong effects on the drag force,
and with that on the CME propagation time and energy input to the
magnetosphere. For a sample of well observed events, we determine
the de-projected 3D mass and its evolution up to a distance range
of about 15Rs using combined STEREO-SECCHI COR1 and COR2 data, for
which no pile-up at the CME front is found (see also Bein et al.,
2013). Applying the GCS forward fitting model (Thernisien et al., 2006,
2009) on COR2 data, we obtain the volume of the CMEs. Working under the
assumption that the CME mass is constant beyond 15Rs and that the CME
undergoes self-similar expansion, we estimate the CME density at the
distance of 1AU. The results are compared to in-situ proton density
data measured for the associated ICME's sheath and magnetic structure
for which we derive a trend towards a mass increase at the CME front.
---------------------------------------------------------
Title: Investigating the evolution and interactions of the September
2017 CME events with EUHFORIA
Authors: Scolini, Camilla; Rodriguez, Luciano; Temmer, Manuela; Guo,
Jingnan; Dumbovic, Mateja; Pomoell, Jens; Poedts, Stefaan
2019EGUGA..21.1337S Altcode:
Coronal Mass Ejections (CMEs) and their Interplanetary counterparts
(ICMEs) are the primary source of strong space weather disturbances at
Earth and other places in the heliosphere. Key parameters determining
the geo-effectiveness of CMEs are their plasma dynamic pressure
and internal magnetic field intensity and orientation. In addition,
phenomena such as the interaction with other CME structures along the
way, or the pre-conditioning of interplanetary (IP) space due to the
passage of previous CMEs, can significantly modify the properties of
single CME events and influence their geo-effectiveness. Therefore,
investigating and modeling such phenomena via physics-based heliospheric
models is crucial in order to assess and improve our space weather
prediction capability in relation to complex CME events. In this regard,
we present a comprehensive analysis of the CME events that erupted from
AR 12673 during the unusually active week of September 4-10, 2017, with
the aim of validating for the first time the prediction capabilities
of the EUHFORIA model in the case of complex CME events. As AR 12673
rotated along with the solar disk, CMEs were launched over a wide
range of longitudes, interacting with each other and paving the way
for the propagation of the following CMEs. Following the eruptions,
ICME-related signatures were observed at both Earth and Mars,
while associated particle events were reported at Earth, Mars, and
STEREO-A. In terms of impact on Earth, an intense geomagnetic storm,
triggered by a strong southward magnetic field associated to an ICME
sheath, was recorded on September 8, 2017. In order to study these
CME-CME interactions and their influence on the geo-effectiveness of
single CMEs, we simulate the events using the EUHFORIA model. With
the intent of preserving a predictive approach, we use kinematic,
geometric and magnetic input parameters for the CMEs as derived from
remote-sensing and multi-spacecraft observations of the CMEs and
their source regions. We model CMEs first using an over-simplified
cone model, and then a more realistic flux- rope model so to quantify
the improvement in the prediction of the interplanetary magnetic field
and CME geo-effectiveness at Earth in the latter case. Furthermore,
we investigate the modelling of CME-CME interactions considering the
spatial and temporal evolution of ICMEs in terms of their shocks,
sheaths and ejecta structures in the heliosphere, and we quantify the
impact of such phenomena on the propagation and evolution of single
CME events. Results from this study will not only benchmark our
current prediction capabilities in the case of complex CME events,
but will also provide better insights on the large-scale evolution
and interaction of complex CME events in the inner heliosphere.
---------------------------------------------------------
Title: Stellar CMEs from an observational point of view
Authors: Leitzinger, Martin; Odert, Petra; Vida, Krisztian; Koller,
Florian; Veronig, Astrid; Korhonen, Heidi; Guenther, Eike; Hanslmeier,
Arnold; Temmer, Manuela; Dissauer, Karin; Greimel, Robert; Kriskovics,
Levente; Lammer, Helmut
2019EGUGA..21.6786L Altcode:
Stellar activity is mainly characterized by the high energy phenomena
such as outbreaks of radiation (flares) and sporadic expulsions
of particles into the astrosphere termed coronal mass ejections
(CMEs). Both phenomena are known to cause space weather in our solar
system. On stars, flares and their parameters are well determined,
in contrast to CMEs; their parameters are still not determined
statistically. Both phenomena may have severe effects on planetary
atmospheres and, in addition, stellar CMEs may play an important
role in stellar mass and angular momentum loss and therefore in
stellar evolution. Flares are directly detectable from photometric
observations, whereas the detection of CMEs requires different
observational methods. CMEs have different signatures in different
wavelength regimes. Most of the stellar CMEs were detected so far
using the method of Doppler-shifted Balmer flux which is accessible via
spectroscopic measurements. Several observational programs have been
carried out and are planned for the future, including new observations
and archival data. Also several attempts to detect stellar CMEs via
radio emission have been carried out in the past decades. Finally,
the X-ray regime may provide a valuable data pool to look for so-called
dimmings, well-known from the Sun, which are closely related to CMEs and
which are detectable in X-ray light curves. So far stellar CMEs have
been detected rarely and only a handful of distinct events is known,
mainly for dMe stars. We report on past, ongoing and future campaigns
of stellar CMEs on F-, G-, K-, and M-type pre- and main-sequence stars.
---------------------------------------------------------
Title: Multiple Satellite Analysis of the Earth's Thermosphere and
Interplanetary Magnetic Field Variations due to ICME/CIR Events
During 2003-2015
Authors: Krauss, Sandro; Temmer, Manuela; Vennerstrom, Susanne
2019EGUGA..21.4180K Altcode:
We present a refined statistical analysis based on ICMEs as well as
CIRs for the time period 2003-2015 to estimate the impact of different
solar wind types on the geomagnetic activity and the neutral density
in the Earth's thermosphere. For the time-based delimitation of the
events, we rely on the catalog maintained by Richardson and Cane and
the corotating interaction region lists provided by S. Vennerstrom
and L.K. Jian. These archives are based on in situ measurements from
the ACE and/or the Wind spacecraft. On this basis, we will thoroughly
investigate about 400 Earth-directed ICME and CIR events. To verify the
impact on the Earths thermosphere we determine neutral mass densities
by using accelerometer measurements collected by the low-Earth-orbiting
satellites GRACE and CHAMP. Subsequently, the atmospheric densities
will be to characteristic ICME parameters and since increased solar
activity may lead to a decrease of the satellites orbital altitude
we additionally assess the orbital decay for each of the events and
satellites.
---------------------------------------------------------
Title: The in situ Solar Wind and Galactic Cosmic Ray correlation
at Mars and its comparison with Earth observations
Authors: Guo, Jingnan; Temmer, Manuela; Veronig, Astrid; Janvier,
Miho; Hofmeister, Stefan; Wimmer-Schweingruber, Robert; Halekas, Jasper
2019EGUGA..21.9366G Altcode:
The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have
been observing the in situ solar wind properties since its arrival to
Mars at the end of 2014. Together with the Galactic Cosmic Ray (GCR)
observation continuously monitored by the Radiation Assessment Detector
(RAD) on the Martian ground, we are able to analyze the correlation of
the solar wind evolution and the modulated GCR variations at Mars. The
transient variations (mostly observed as short-term decreases) in
these in situ observations are usually related to either the impact
of Coronal Mass Ejections (CMEs) erupted from Solar active regions or
the pass-by of High Speed Streams (HSS) in the solar wind arising from
Coronal Holes (CHs) on the Sun. During the opposition phase in 2016
when Earth and Mars were radially aligned on the same side of the Sun,
we observe the stable evolution of a few CHs on the solar surface over
several solar rotations and analyze the re-current in situ solar wind
and GCR signatures at both Earth and Mars.
---------------------------------------------------------
Title: Unusual plasma and particle signatures at Mars and STEREO-A
related to inhibited expansion caused by CME-CME interaction
Authors: Dumbovic, Mateja; Guo, Jingnan; Temmer, Manuela; Mays, Leila;
Veronig, Astrid; Hofmeister, Stefan; Halekas, Jasper
2019EGUGA..21.6957D Altcode:
On July 25 2017 a multi-step Forbush decrease (FD) with the total
amplitude of more than 15% was observed by MSL/RAD at Mars and this
is one of the biggest FDs ever detected on Mars. We find that these
particle signatures are related to very pronounced plasma and magnetic
field signatures detected in situ by STEREO-A on July 24 2017, with a
higher than average total magnetic field strength reaching more than
60 nT. In the observed time period STEREO-A was longitudinally close
to Mars and both were located at the back side of Sun as viewed from
Earth. Using multi-spacecraft and multi-instrument (both in situ and
remote-sensing) observations, as well as modelling, we find that the
solar sources of these in situ signatures are 2 CMEs which erupted on
July 23 2017 from the same source region on the back side of the Sun as
viewed from Earth and interacted in the interplanetary space, inhibiting
the expansion of one of the CMEs. We present a detailed investigation
on this complex interaction event on its way from Sun to Mars. This
project has received funding from the European Union's Horizon 2020
research and innovation programme under the Marie Skłodowska-Curie
grant agreement No 745782.
---------------------------------------------------------
Title: Multiple EUV wave reflection from a coronal hole
Authors: Podladchikova, Tatiana; Veronig, Astrid M.; Podladchikova,
Olena; Dissauer, Karin; Vršnak, Bojan; Saqri, Jonas; Piantschitsch,
Isabell; Temmer, Manuela
2019EGUGA..21.9793P Altcode:
EUV waves are large-scale propagating disturbances in the solar corona
initiated by coronal mass ejections. We investigate the multiple EUV
wave reflections at a coronal hole boundary, as observed by SDO/AIA on 1
April 2017. The EUV wave originates from Active Region (AR) 12645 close
to the disk center and propagates toward the south polar coronal hole
with an average velocity of 430 km/s. The interaction of the EUV wave
with the coronal hole, which represents a region of high Alfven speed,
is observed as a splitting into two wave components: one continues
propagation inside the coronal hole with an increased velocity of 850
km/s (transmitted wave), while the other one moves back toward the AR,
also with an increased velocity of 600 km/s (reflected wave). The
reflected EUV wave is subsequently reflected again from the AR and
propagates toward the coronal hole with an average velocity of 350
km/s, where it is reflected for the second time at the coronal hole
boundary and propagates again toward the AR with a velocity of 300
km/s. These events are observed over an interval of 40 minutes. The
high cadence SDO imagery allows us to study in detail the kinematics
of the direct and multiple times reflected EUV wave. In addition, its
multi-wavelength EUV imagery allows us to derive the plasma properties
of the corona and the EUV wave pulse via Differential Emission Measure
analysis. These results are used to compare the observed characteristics
of the wave interaction with the coronal hole with simulations.
---------------------------------------------------------
Title: Origin of the two shock waves associated with the September
27/28, 2012 event
Authors: Jebaraj, Immanuel Christopher; Magdalenic, Jasmina; Scolini,
Camilla; Rodriguez, Luciano; Poedts, Stefaan; Kilpua, Emilia; Krupar,
Vratislav; Pomoell, Jens; Temmer, Manuela
2019EGUGA..2116967J Altcode:
Coronal mass ejections and flares are solar eruptive phenomena
responsible for space weather activities near Earth. They can
accelerate particles, and generate shock waves which are a threat to
our technologies at Earth and in space. Therefore, predicting shock
arrival at Earth has been an important goal for space weather. Space
based radio observations provide the unique opportunity to track shock
waves in the inner heliosphere. We present the study of CME/flare event
on September 27/28, 2012. The GOES C3.1 flare that originated from NOAA
AR 1577 was associated with a full-halo CME (first seen in SOHO/LASCO
C2 field of view at 23:47) and white light shock wave observed by all
three spacecraft STEREO A, STEREO B, and SOHO. The associated radio
event shows a group of type III bursts and two somewhat unusual type II
bursts with significantly different starting frequencies. To understand
the origin of the two shock waves we performed multi-wavelength study,
and perform radio triangulation to get their source position in the
3D space. For the radio triangulation study, we used goniopolarimetric
measurements from STEREO/WAVES and WIND/WAVES instruments. We also did
data-driven modelling of the CME propagation using EUHFORIA cone model
(EUropean Heliospheric FORecasting Information Asset) and validate
the results by comparison with in-situ data. Results of this study
indicate that, although temporal association between the shock and
the CME is good, the low frequency type II burst occurs significantly
higher in the solar corona than the associated CME and has therefore
unclear origin. To understand the origin of the low frequency type
II burst we studied preceding event at 10:20 UT (STEREO A/COR2) on
September 27, 2012. The radio triangulation study shows that the type
II source positions are in the southern solar hemisphere and thus may
be associated to the type II emissions in the radio event succeeding
it. We therefore discuss different possibilities for the origin of
two type II bursts.
---------------------------------------------------------
Title: Radial and Tangential Kinematics and Angular Extent of EUV
Coronal Bright Fronts
Authors: Kozarev, Kamen; Veronig, Astrid; Temmer, Manuela; Miteva,
Rositsa; Dissauer, Karin; Koleva, Kostadinka; Dechev, Momchil;
Duchlev, Peter
2019EGUGA..21.9290K Altcode:
Large-scale solar coronal compressive waves are often observed
in extreme UV (EUV) and white light to precede nascent coronal
mass ejections (CMEs), which previous work has shown develop most
dynamically (expansion, acceleration) in the low and middle solar corona
(below 5-8 solar radii). Multiple studies in the last ten years have
suggested that these waves may be manifestations of driven coronal
shock waves, and may accelerate ions to solar energetic particle
(SEP) energies. A commonly invoked condition for the generation of
EUV waves and their capability to produce energetic particles is the
presence of rapid lateral expansion of the front and driver behind
it. As a step to characterizing this capability, we study the radial
and lateral kinematics of a number of EUV off-limb waves in the low
corona, and their departure from spherical expansion. We characterize
their time-dependent angular extent. We compare the results with
the later-stage CME angular sizes and radial kinematics deduced from
SOHO/LASCO observations of the events.
---------------------------------------------------------
Title: Analysis of SDO/EVE Flares in Relation to Solar Energetic
Protons
Authors: Miteva, Rositsa; Koleva, Kostadinka; Dechev, Momchil; Veronig,
Astrid; Dissauer, Karin; Kozarev, Kamen; Temmer, Manuela
2019EGUGA..2115190M Altcode:
Solar energetic proton (SEP) events from SOHO/ERNE instruments
and SDO/EVE solar flares in solar cycle 24 are considered. The
SEP-associated flare emission is analyzed in multiple wavelength
ranges characterizing flare emission. Background subtraction of
the pre-event particle flux and flare emission is performed for
each event. Finally, a Pearson correlation analysis is completed
between the peak values of the SEP events and the UV and EUV flare
intensities. Comparison with the results from flare soft X-ray, hard
X-ray and radio emission is presented. This work is supported by the
Bilateral project Bulgaria-Austria with the National Science Fund of
Bulgaria contract No. NTS/AUSTRIA 01/23 (28.02.2017) and Austria OeAD
Project No. BG 11/2017.
---------------------------------------------------------
Title: Reconstructing coronal holes with EUHFORIA
Authors: Asvestari, Eleanna; Heinemann, Stephan; Pomoell, Jens;
Temmer, Manuela; Kilpua, Emilia; Magdalenic, Jasmina; Poedts, Stefaan
2019EGUGA..21.8085A Altcode:
Modelling accurately the ambient solar wind is important for space
weather forecasting. EUHFORIA (European Heliospheric Forecasting
Information Asset) model employs an empirical solar wind model that is
based on the Wang-Sheeley-Arge model. It combines the Potential Field
Source Surface (PFSS) and the Schatten Current Sheet (SCS) models. In
previous studies it was shown that placing the inner boundary of the
SCS model at a radius, Ri, lower than that of the outer boundary of the
PFSS model, Rii, improves the simulation output. Here, we investigate
the capability of the empirical solar wind model adopted in EUHFORIA
to recreate the geometry and size of coronal holes for a large set of
pairs of PFSS and SCS radii. We vary Rii within the interval [1.4,
3.0]Rs with a step of 0.1Rs, and the Ri within the interval [1.3,
2.8]Rs with the same step size. The study is repeated for 12 coronal
holes of different latitudinal position and geometry. We compare the
modelled coronal holes with boundaries obtained by remote sensing
EUV observations using the CATCH tool (Collection of Analysis Tools
for Coronal Holes). Preliminary results of the study indicate that a
previously defined pair of PFSS and SCS radii results in underestimated
coronal hole sizes. It also indicates that different radii sets give
better results for different types of coronal holes.
---------------------------------------------------------
Title: ICMEs Propagating Towards Mars Observed in Heliospheric
Imagers and their Associated Forbush Decreases at MSL/RAD
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
Robert F.; Temmer, Manuela; Dumbović, Mateja; Veronig, Astrid; Möstl,
Christian; Hassler, Donald M.; Zeitlin, Cary J.; Ehresmann, Bent
2019EGUGA..21.8305V Altcode:
The Radiation Assessment Detector (RAD) onboard the Mars Science
Laboratory (MSL) mission's Curiosity rover has been measuring galactic
cosmic rays (GCR) as well as solar energetic particles (SEP) on the
surface of Mars for more than 6 years since its landing in August
2012 and in interplanetary space during its 8-month cruise to Mars
between 2011 and 2012. The observations include a large number of
Forbush decreases (FD) caused by interplanetary coronal mass ejections
(ICMEs) and their associated shocks passing MSL. Our previous work
(Freiherr von Forstner et al. 2018, JGR: Space Physics) studied 15
ICME events close to oppositions of Mars as seen from Earth or the
STEREO A and B spacecraft, where in situ Forbush decrease observations
at both locations could be used to derive the propagation time of the
ICME from 1 AU to Mars. We found that on average, ICMEs in our sample
continued to decelerate beyond 1 AU. We now investigate a different
constellation where MSL/RAD Forbush decrease measurements are combined
with remote tracking of ICMEs using the STEREO Heliospheric Imager (HI)
telescopes. A large catalog of such remote observations was created
by the HELCATS project (Möstl et al. 2017, Space Weather), not only
including ICMEs propagating towards Earth, but also some that passed
Mars. This allows to enlarge our sample for a statistical study of
ICMEs at Mars. We associate STEREO-HI observations from the catalog with
corresponding FDs at MSL/RAD and study the accuracy when predicting the
arrival of an ICME at Mars using common models applied to HI data. Based
on the catalogue of events built using this method, we also investigate
the properties of the corresponding Forbush decreases at RAD, such
as their magnitude, steepness and duration. We find both correlations
between the parameters themselves as well as possible relations to the
ICME properties (derived from HI data). These data are also compared
to findings from previous studies using Earth-based observations.
---------------------------------------------------------
Title: Benchmarking CME Arrival Time and Impact: Progress on Metadata,
Metrics, and Events
Authors: Verbeke, C.; Mays, M. L.; Temmer, M.; Bingham, S.; Steenburgh,
R.; Dumbović, M.; Núñez, M.; Jian, L. K.; Hess, P.; Wiegand, C.;
Taktakishvili, A.; Andries, J.
2019SpWea..17....6V Altcode: 2018arXiv181110695V
Accurate forecasting of the arrival time and subsequent geomagnetic
impacts of coronal mass ejections (CMEs) at Earth is an important
objective for space weather forecasting agencies. Recently, the CME
Arrival and Impact working team has made significant progress toward
defining community-agreed metrics and validation methods to assess
the current state of CME modeling capabilities. This will allow the
community to quantify our current capabilities and track progress in
models over time. First, it is crucial that the community focuses
on the collection of the necessary metadata for transparency and
reproducibility of results. Concerning CME arrival and impact we have
identified six different metadata types: 3-D CME measurement, model
description, model input, CME (non)arrival observation, model output
data, and metrics and validation methods. Second, the working team
has also identified a validation time period, where all events within
the following two periods will be considered: 1 January 2011 to 31
December 2012 and January 2015 to 31 December 2015. Those two periods
amount to a total of about 100 hit events at Earth and a large amount
of misses. Considering a time period will remove any bias in selecting
events and the event set will represent a sample set that will not be
biased by user selection. Lastly, we have defined the basic metrics and
skill scores that the CME Arrival and Impact working team will focus on.
---------------------------------------------------------
Title: Genesis and Impulsive Evolution of the 2017 September 10
Coronal Mass Ejection
Authors: Veronig, Astrid M.; Podladchikova, Tatiana; Dissauer, Karin;
Temmer, Manuela; Seaton, Daniel B.; Long, David; Guo, Jingnan; Vršnak,
Bojan; Harra, Louise; Kliem, Bernhard
2018ApJ...868..107V Altcode: 2018arXiv181009320V
The X8.2 event of 2017 September 10 provides unique observations
to study the genesis, magnetic morphology, and impulsive dynamics
of a very fast coronal mass ejection (CME). Combining GOES-16/SUVI
and SDO/AIA EUV imagery, we identify a hot (T ≈ 10-15 MK) bright
rim around a quickly expanding cavity, embedded inside a much larger
CME shell (T ≈ 1-2 MK). The CME shell develops from a dense set of
large AR loops (≳0.5R <SUB> s </SUB>) and seamlessly evolves into
the CME front observed in LASCO C2. The strong lateral overexpansion
of the CME shell acts as a piston initiating the fast EUV wave. The
hot cavity rim is demonstrated to be a manifestation of the dominantly
poloidal flux and frozen-in plasma added to the rising flux rope by
magnetic reconnection in the current sheet beneath. The same structure
is later observed as the core of the white-light CME, challenging the
traditional interpretation of the CME three-part morphology. The large
amount of added magnetic flux suggested by these observations explains
the extreme accelerations of the radial and lateral expansion of the CME
shell and cavity, all reaching values of 5-10 km s<SUP>-2</SUP>. The
acceleration peaks occur simultaneously with the first RHESSI 100-300
keV hard X-ray burst of the associated flare, further underlining
the importance of the reconnection process for the impulsive CME
evolution. Finally, the much higher radial propagation speed of the
flux rope in relation to the CME shell causes a distinct deformation
of the white-light CME front and shock.
---------------------------------------------------------
Title: CME-driven Shock and Type II Solar Radio Burst Band Splitting
Authors: Chrysaphi, Nicolina; Kontar, Eduard P.; Holman, Gordon D.;
Temmer, Manuela
2018ApJ...868...79C Altcode: 2018arXiv181008026C
Coronal mass ejections (CMEs) are believed to be effective in
producing shocks in the solar corona and interplanetary space. One of
the important signatures of shocks and shock acceleration are Type II
solar radio bursts that drift with the shock speed and produce bands of
fundamental and higher harmonic plasma radio emission. An intriguing
aspect of Type II radio bursts is the occasional split of a harmonic
band into thinner lanes, known as band splitting. Here we report a
detailed imaging and spectroscopic observation of a CME-driven shock
producing band splitting in a Type II burst. Using LOFAR, we examine the
spatial and temporal relation of the Type II burst to the associated
CME event, use source imaging to calculate the apparent coronal
density, and demonstrate how source imaging can be used to estimate
projection effects. We consider two widely accepted band-splitting
models that make opposing predictions regarding the locations of the
true emission sources with respect to the shock front. Our observations
suggest that the locations of the upper and lower subband sources
are spatially separated by ∼0.2 ± 0.05 R <SUB>⊙</SUB>. However,
we quantitatively show, for the first time, that such separation is
consistent with radio-wave scattering of plasma radio emission from
a single region, implying that the split-band Type II sources could
originate from nearly cospatial locations. Considering the effects
of scattering, the observations provide supporting evidence for the
model that interprets the band splitting as emission originating in
the upstream and downstream regions of the shock front, two virtually
cospatial areas.
---------------------------------------------------------
Title: Coronal holes detection using supervised classification
Authors: Delouille, Veronique; Hofmeister, Stefan; Reiss, Martin;
Mampaey, Benjamin; Temmer, Manuela; Veronig, Astrid
2018csc..confE..93D Altcode:
We demonstrate the use of machine learning algorithms in combination
with segmentation techniques in order to distinguish coronal holes
and filaments in solar EUV images. We used the Spatial Possibilistic
Clustering Algorithm (SPoCA) to prepare data sets of manually labeled
coronal hole and filament channel regions present on the Sun during
the time range 2010-2016. By mapping the extracted regions from EUV
observations onto HMI line-of-sight magnetograms we also include
their magnetic characteristics. We computed average latitude, area,
shape measures from the segmented binary maps as well as first order,
and second order texture statistics from the segmented regions in the
EUV images and magnetograms. These attributes were used for data mining
investigations to identify the most performant rule to differentiate
between coronal holes and filament channels, taking into account the
imbalance in our dataset which contains one filament channel for 15
coronal holes. We tested classifiers such as Support Vector Machine,
Linear Support Vector Machine, Decision Tree, k-Nearest Neighbors, as
well as ensemble classifier based on Decision Trees. Best performance
in terms of True Skill Statistics are obtained with cost-sensitive
learning, Support Vector Machine classifiers, and when HMI attributes
are included in the dataset.
---------------------------------------------------------
Title: The photospheric structure of coronal holes: magnetic elements
Authors: Hofmeister, Stefan; Utz, Dominik; Heinemann, Stephan; Veronig,
Astrid; Temmer, Manuela
2018csc..confE.129H Altcode:
Coronal holes attracted recently more attention by the scientific
community as they represent the source region for the fast solar wind
which is ifself an important ingredient in understanding the space
environment and space weather. Nevertheless, our knowledge about
the detailed magnetic field structure below coronal holes is quite
limited, maybe since such a research would necessarily involve the high
atmospheric and photospheric community. In this contribution we would
like to bridge this gap and investigate in detail the magnetic field
distribution below coronal holes and its relationship to the large-scale
coronal hole topology. To do so, we investigate the distribution and
properties of photospheric magnetic elements below 106 low and medium
latitude coronal holes using SDO/HMI line-of-sight magnetogram data from
2010 to 2016, and relate them to the overall properties of the coronal
holes. Since magnetic elements produce clearly visible photospheric
structures, they can be well observed and give us valuable insights into
the structure of coronal holes. We find that the distribution of the
magnetic flux of magnetic elements follows an exponential function. The
area and flux of magnetic elements are strongly related to each other
by a power law with an exponent of 1.25. The larger magnetic elements
are located at the edges of the magnetic network and seem to be the
"core" structure of coronal holes. They have lifetimes > 4 days,
i.e., longer than the timescale of the supergranulation. Further, they
contain up to 50 magnetic bright points as observed by Hinode/SOT in
the G-Band, meaning that the large magnetic elements are large clusters
of individual magnetic elements. The mean magnetic field density of
the overall coronal holes and thus their unbalanced magnetic flux
is determined by their percentage coverage with magnetic elements
at cc=0.98. Since magnetic elements are the foot points of magnetic
funnels and thus the small-scale source regions of high-speed solar
wind streams, the dependence of the coverage with magnetic elements
on the strength of coronal holes also explains the dependence of the
plasma density of high-speed streams near the Sun to the strength of
its source coronal hole. The rotation rates of the magnetic elements
match the rotation rate of the coronal hole and is surprisingly similar
to the differential rotation rate of active regions at low- and medium
latitudes, suggesting they are rooted at similar deep layers. This
also means that coronal holes do not show an abnormal rotation rate
as suggested by various authors. Finally, by projecting the magnetic
elements to AIA-171 and 193 filtergrams, we surprisingly find that the
magnetic elements are not located in the darkest regions of coronal
holes. Therefore, the vertical plasma outflow from magnetic funnels
is probably not the primary reason why coronal holes appear as dark
patches in EUV images. We conclude that magnetic elements are the
basic building blocks of coronal holes which completely determine
their magnetic properties.
---------------------------------------------------------
Title: Evolution of flux rope, CME and associated EUV wave in the
10-Sep-2018 X8.2 event
Authors: Podladchikova, Tatiana; Veronig, Astrid M.; Dissauer, Karin;
Temmer, Manuela; Seaton, Daniel B.; Long, David; Guo, Jingnan; Vršnak,
Bojan; Harra, Louise; Kliem, Bernhard
2018csc..confE..38P Altcode:
We combine the high-cadence and large field-of-view EUV imagery of
the Atmospheric Imaging Assembly (AIA) onboard SDO and the Solar
Ultraviolet Imager (SUVI) onboard GOES-16 to study the origin and
impulsive evolution of the fast CME that originated in the September
10th 2017 X8.2 event as well as the initiation of the associated EUV
wave. In the LASCO field-of-view, the CME reveals speeds >3000
km/s. In the low-to-mid corona, it shows a distinct bubble in the EUV
imagery that reveals a significant lateral overexpansion. In addition,
is also shows a distinct expanding cavity that is interpreted as
manifestation of the flux rope driving the eruption. We present a method
to automatically identify and segment the CME bubble in SUVI images and
to derive its radial and lateral evolution up to about 2 solar radii,
in terms of velocity and acceleration. These measurements are set into
context with the evolution of the embedded flux rope/cavity observed by
AIA. The observations show clear signatures of new poloidal flux added
to the flux rope by magnetic reconnection in the current sheet beneath
the eruptive structure, which is important for the high accelerations
observed in this event. The radial propagation of the CME shell revealed
a peak value of the acceleration of about 5.3 km/s2, whereas the lateral
expansion reached a peak value of 10.1 km/s2, which is the largest value
reported so far. The flux rope/cavity reveals a radial acceleration of
6.7 km/s2 and lateral acceleration of 5.3 km/s2. We note that at this
early evolution phase, the speed of the cavity/flux rope is higher
than that of the CME bubble (front). The EUV wave associated with
this eruption was observed by AIA, SUVI and STEREO-A EUVI, which had
a separation angle with Earth of 128°, and the common field of view
of the spacecraft was 52°. AIA and SUVI images above the solar limb
reveal the initiation of the EUV wave by the accelerating flanks of
the CME bubble, followed by detachment and propagation of the wave
with a speed of 1100 km/s. The EUV wave shows a global propagation
over the full hemisphere visible to Earth view as well as into the
STEREO-A field-of-view. We study the propagation and kinematics of
the direct as well as the various reflected and refracted EUV wave
components on the solar sphere, finding speeds in the range from 370
to 1010 km/s. Finally, we note that this EUV wave is also distinct as
it reveals propagation and transmission through the polar coronal holes.
---------------------------------------------------------
Title: Studying the dynamics of coronal dimmings and their
relationship to flares and coronal mass ejections
Authors: Dissauer, Karin; Veronig, Astrid M.; Temmer, Manuela;
Podladchikova, Tatiana; Vanninathan, Kamalam
2018csc..confE..26D Altcode:
Coronal dimmings are observed as localized regions of reduced emission
in the EUV and soft X-rays, interpreted as density depletions due to
mass loss during the CME expansion. They contain crucial information on
the evolution and early propagation phase of CMEs low in the corona. For
a set of 62 dimming events, characteristic parameters, describing
their dynamics, morphology, magnetic properties and the brightness
evolution are derived, statistically analyzed and compared with basic
flare and CME quantities. We use optimized multi-point observations,
where the on-disk dimming evolution is studied in high-cadence
SDO/AIA filtergrams and SDO/HMI line-of-sight magnetograms, while
STEREO/EUVI, COR1 and COR2 data is used to measure the associated CME
kinematics close to the limb with low projection effects. For 60% of
the events we identified core dimmings, i.e. potential footpoints of
the erupting CME structure. These regions contain 20% of the magnetic
flux covering only 5% of the total dimming area. The majority of the
total dimming area consists of secondary dimmings mapping overlying
fields that are stretched during the eruption and closed down by
magnetic reconnection, thus adding flux to the erupting structure
via magnetic reconnection. This interpretation is supported by the
high correlation between the magnetic fluxes of secondary dimmings
and flare reconnection fluxes (c=0.63±0.08), the balance between
positive and negative magnetic fluxes (c=0.83±0.04) within the total
dimmings and the fact that for strong flares (>M1.0) the flare
reconnection and secondary dimming fluxes are roughly equal. The area
of the total dimming, i.e. including both core and secondary dimmmings,
its total brightness and the total unsigned magnetic flux show the
highest correlations with the flare fluence (c>0.7) and the CME
mass (c>0.6). Their corresponding time derivatives, describing
the dimming dynamics, strongly correlate with the GOES flare class
(c>0.6). Events where high-cadence observations from STEREO are
available show a moderate correlation between the area growth rate of
the dimming and the maximum speed of the CME.
---------------------------------------------------------
Title: Multiple Satellite Analysis of the Earth's Thermosphere and
Interplanetary Magnetic Field Variations Due to ICME/CIR Events
During 2003-2015
Authors: Krauss, S.; Temmer, M.; Vennerstrom, S.
2018JGRA..123.8884K Altcode: 2018arXiv181102999K
We present a refined statistical analysis based on interplanetary
coronal mass ejections (ICMEs) as well as corotating interaction regions
(CIRs) for the time period 2003-2015 to estimate the impact of different
solar wind types on the geomagnetic activity and the neutral density
in the Earth's thermosphere. For the time-based delimitation of the
events, we rely on the catalog maintained by Richardson and Cane and the
corotating interaction region lists provided by S. Vennerstrom and Jian
et al. (2011, https://doi.org/10.1007/s11207-011-9737-2). These archives
are based on in situ measurements from the Advanced Composition Explorer
and/or the Wind spacecraft. On this basis, we thoroughly investigated
196 Earth-directed ICME and 195 CIR events. To verify the impact
on the Earths thermosphere we determined neutral mass densities by
using accelerometer measurements collected by the low-Earth-orbiting
satellites Gravity Recovery and Climate Experiment and Challenging
Minisatellite Payload. Subsequently, the atmospheric densities
are related to characteristic ICME parameters. In this process a
new calibration method has been examined. Since increased solar
activity may lead to a decrease of the satellites orbital altitude
we additionally assessed the orbital decay for each of the events
and satellites. The influence of CIR events is in the same range of
magnitude as the majority of the ICMEs (186 out of 196). Even though,
the extended investigation period between 2011 and 2015 has a lack
of extreme solar events the combined analysis reveals comparable
correlation coefficients between the neutral densities and the various
ICME and geomagnetic parameters (mostly >0.85). The evaluation of
orbit decay rates at different altitudes revealed a high dependency
on the satellite actual altitude.
---------------------------------------------------------
Title: Hard X-ray Diagnostic of Proton Producing Solar Flares Compared
to Other Emission Signatures
Authors: Miteva, Rositsa; Koleva, Kostadinka; Dechev, Momchil;
Veronig, Astrid; Kozarev, Kamen; Temmer, Manuela; Dissauer, Karin;
Duchlev, Peter
2018PASRB..18..117M Altcode:
We present results on the correlation analysis between the peak
intensity of the in situ proton events from SOHO/ERNE instrument
and the properties of their solar origin, solar flares and coronal
mass ejections (CMEs). Starting at the RHESSI mission launch after
2002, 70 flares well-observed in hard X-rays (HXRs) that are also
accompanied with in situ proton events are selected. In addition
to HXRs, flare emission at several other wavelengths, namely in the
soft X-ray (SXR), ultraviolet (UV) and microwave (MW), is used. We
calculated Pearson correlation coefficients between the proton peak
intensities from one side, and, from another, the peak flare flux at
various wavelengths or the speed of the accompanied CME. We obtain the
highest correlations with the CME speed, with the SXR flare class and
with MWs, lower ones with the SXR derivative, UV and 12-50 keV HXRs
and the lowest correlation coefficients are obtained with the 50-300
keV HXRs. Possible interpretations are discussed.
---------------------------------------------------------
Title: Three-phase Evolution of a Coronal Hole. II. The Magnetic Field
Authors: Heinemann, Stephan G.; Hofmeister, Stefan J.; Veronig,
Astrid M.; Temmer, Manuela
2018ApJ...863...29H Altcode: 2018arXiv180610052H
We investigate the magnetic characteristics of a persistent coronal hole
(CH) extracted from EUV imagery using Heliospheric and Magnetic Imager
filtergrams over the period 2012 February-October. The magnetic field,
its distribution, and the magnetic fine structure in the form of flux
tubes (FTs) are analyzed in different evolutionary states of the CH. We
find a strong linear correlation between the magnetic properties (e.g.,
signed/unsigned magnetic field strength) and the area of the CH. As
such, the evolutionary pattern in the magnetic field clearly follows
a three-phase evolution (growing, maximum, and decaying) as found from
EUV data (Part I). This evolutionary process is most likely driven by
strong FTs with a mean magnetic field strength exceeding 50 G. During
the maximum phase they entail up to 72% of the total signed magnetic
flux of the CH, but only cover up to 3.9% of the total CH area, whereas
during the growing and decaying phases, strong FTs entail 54%-60% of the
signed magnetic flux and cover around 1%-2% of the CH’s total area. We
conclude that small-scale structures of strong unipolar magnetic field
are the fundamental building blocks of a CH and govern its evolution.
---------------------------------------------------------
Title: Filament Eruptions Associated with Flares, Coronal Mass
Ejections and Solar Energetic Particle Events
Authors: Koleva, K.; Duchlev, P.; Dechev, M.; Miteva, R.; Kozarev,
K.; Veronig, A.; Temmer, M.
2018simi.conf...19K Altcode:
We present analysis of three cases of filament eruptions (FEs)
that occurred on 04 Aug 2011, 09 Nov 2011 and 05 Apr 2012 and their
associations with flares as sources of solar energetic particles (SEPs)
and coronal mass ejections. The associated FEs and SEP-related solar
flares were selected by simultaneous observations in X-ray, EUV and
radio wavelengths.
---------------------------------------------------------
Title: Statistics of Coronal Dimmings Associated with Coronal Mass
Ejections. I. Characteristic Dimming Properties and Flare Association
Authors: Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova,
T.; Vanninathan, K.
2018ApJ...863..169D Altcode: 2018arXiv180705056D
Coronal dimmings, localized regions of reduced emission in the
extreme-ultraviolet and soft X-rays (SXRs), are interpreted as density
depletions due to mass loss during the coronal mass ejection (CME)
expansion. They contain crucial information on the early evolution
of CMEs low in the corona. For 62 dimming events, characteristic
parameters are derived, statistically analyzed, and compared with basic
flare quantities. On average, coronal dimmings have a size of 2.15 ×
10<SUP>10</SUP> km<SUP>2</SUP>, contain a total unsigned magnetic flux
of 1.75 × 10<SUP>21</SUP> Mx, and show a total brightness decrease
of -1.91 × 10<SUP>6</SUP> DN, which results in a relative decrease
of ∼60% compared to the pre-eruption intensity level. Their main
evacuation phase lasts for ∼50 minutes. The dimming area, the total
dimming brightness, and the total unsigned magnetic flux show the
highest correlation with the flare SXR fluence (c ≳ 0.7). Their
corresponding time derivatives, describing the dimming dynamics,
strongly correlate with the GOES flare class (c ≳ 0.6). For 60%
of the events we identified core dimmings, i.e., signatures of an
erupting flux rope. They contain 20% of the magnetic flux covering
only 5% of the total dimming area. Secondary dimmings map overlying
fields that are stretched during the eruption and closed down by
magnetic reconnection, thus adding flux to the erupting flux rope
via magnetic reconnection. This interpretation is supported by the
strong correlation between the magnetic fluxes of secondary dimmings
and flare reconnection fluxes (c = 0.63 ± 0.08), the balance between
positive and negative magnetic fluxes (c = 0.83 ± 0.04) within the
total dimmings, and the fact that for strong flares (>M1.0) the
reconnection and secondary dimming fluxes are roughly equal.
---------------------------------------------------------
Title: Dynamcis and magnetic properties in coronal holes using
high-resolution multi-instrument solar observations
Authors: Krikova, K.; Utz, D.; Veronig, A.; Gömöry, P.; Hofmeister,
S.; Temmer, M.
2018simi.conf...31K Altcode:
Using high-resolution solar observations from the Hinode Instruments
SOT/SP, EIS and XRT as well as IRIS from a coronal hole on the 26th of
September 2017, we are investigating the dynamics within the coronal
hole visible on the specified date. Further satellite data support is
given by full disc images from SDO with the AIA and HMI instruments. EIS
and IRIS data provide us with crucial information about the plasma and
energy flow from the Sun's chromosphere into the corona using the EUV
and UV spectra and images. Investigating the magnetic configuration
as well as the dynamics and changes within the coronal hole by using
the SOT/SP data will give us additional crucial insights about the
physical processes leading to the corresponding changes in the higher
atmosphere. We compare the Hinode data with AIA and HMI data to get
a firm comprehensive picture about the connection from high resolved
photospheric fields and its dynamics within the higher layer. Within the
timeframe of the analysed EIS dataset two microflare events associated
with a solar jet were captured, originating inside the coronal hole
under investigation. We believe that it is totally worthwhile to study
these features in full detail as not so much attention was paid to high
energy processes within coronal holes and their basic relationship to
the harboring coronal hole and they show surprisingly high downflows
in the Fe XII iron line (up to 140 km/s). In the current proceeding
we will outline the state of the art of this investigation and give
an overview of the further steps necessary. The mentioned data were
obtained during a recent GREGOR campaign with the joint support of
IRIS and Hinode (HOP 338).
---------------------------------------------------------
Title: Modeling the Evolution and Propagation of 10 September 2017
CMEs and SEPs Arriving at Mars Constrained by Remote Sensing and In
Situ Measurement
Authors: Guo, Jingnan; Dumbović, Mateja; Wimmer-Schweingruber,
Robert F.; Temmer, Manuela; Lohf, Henning; Wang, Yuming; Veronig,
Astrid; Hassler, Donald M.; Mays, Leila M.; Zeitlin, Cary; Ehresmann,
Bent; Witasse, Olivier; Freiherr von Forstner, Johan L.; Heber, Bernd;
Holmström, Mats; Posner, Arik
2018SpWea..16.1156G Altcode: 2018arXiv180300461G
On 10 September 2017, solar energetic particles originating from the
active region 12673 produced a ground level enhancement at Earth. The
ground level enhancement on the surface of Mars, 160 longitudinally
east of Earth, observed by the Radiation Assessment Detector (RAD)
was the largest since the landing of the Curiosity rover in August
2012. Based on multipoint coronagraph images and the Graduated
Cylindrical Shell model, we identify the initial 3-D kinematics of
an extremely fast coronal mass ejection (CME) and its shock front,
as well as another two CMEs launched hours earlier with moderate
speeds. The three CMEs interacted as they propagated outward into the
heliosphere and merged into a complex interplanetary CME (ICME). The
arrival of the shock and ICME at Mars caused a very significant Forbush
decrease seen by RAD only a few hours later than that at Earth, which
was about 0.5 AU closer to the Sun. We investigate the propagation
of the three CMEs and the merged ICME together with the shock, using
the drag-based model and the WSA-ENLIL plus cone model constrained
by the in situ observations. The synergistic study of the ICME and
solar energetic particle arrivals at Earth and Mars suggests that to
better predict potentially hazardous space weather impacts at Earth
and other heliospheric locations for human exploration missions, it is
essential to analyze (1) the eruption of the flare and CME at the Sun,
(2) the CME kinematics, especially during their interactions, and
(3) the spatially and temporally varying heliospheric conditions,
such as the evolution and propagation of the stream interaction regions.
---------------------------------------------------------
Title: What can we learn from coronal dimmings about the early
evolution of Earth-directed CMEs?
Authors: Dissauer, Karin; Podladchikova, Tatiana; Vanninathan, Kamalam;
Veronig, Astrid; Temmer, Manuela
2018cosp...42E.846D Altcode:
Earth-directed coronal mass ejections (CMEs) are the main
drivers for severe space weather events affecting the near-Earth
environment. However, they allow the least accurate measurements of
their properties due to strong projection effects and especially their
early evolution is not well observed with traditional coronagraphs.The
most distinct phenomena associated with CMEs are coronal dimmings,
i.e. localized regions of reduced emission in the extreme-ultraviolet
(EUV) and soft X-rays low in the corona. They are interpreted
as density depletions due to mass loss or rapid expansion of the
overlying corona during the CME lift off.We extract characteristic
parameters describing the dynamics, morphology, magnetic properties
and the brightness evolution of coronal dimming regions in order to
obtain additional information on the initiation and early evolution of
Earth-directed CMEs. To this aim, we developed an automatic dimming
detection algorithm (based on logarithmic base-ratio images) that
allows us also to distinguish between core and secondary dimming
regions. Using this newly developed method, we extract the physical
properties of 76 coronal dimming events in optimized multi-point
observations and compare them with characteristic parameters describing
their corresponding CMEs. The on-disk dimming evolution is studied
using the high-cadence, multi-wavelengths data of SDO/AIA and the
line-of-sight (LOS) magnetograms of SDO/HMI, while STEREO/EUVI, COR1 and
COR2 data is used to measure the associated CME close to the limb with
low projection effects.The impulsive phase of the dimming (i.e. main
expansion phase of its area) starts co-temporal with the onset of the
CME and the associated flare and the overall dimming region expands
around locations that are identified as core dimming regions. On average
this main evacuation phase lasts for about 50 minutes. For the majority
of events, the total unsigned magnetic flux involved in the dimming
regions is balanced and for selected events up to 30% of this flux
results from the localized core dimming regions covering only ∼10% of
the total dimming area. The size of the total dimming region, the total
unsigned magnetic flux, as well as its intensity decrease are strongly
correlated with the CME mass. Events where high-cadence observations
from STEREO are available show in addition also a moderate correlations
between the growth rate of the dimming and the maximum speed of the CME.
---------------------------------------------------------
Title: The September 2017 events and their imprints at Earth, Mars
and STEREO-A
Authors: Guo, Jingnan; Wang, Yuming; Mays, M. Leila; Heber, Bernd;
Holmstroem, Mats; Ehresmann, Bent; Olivier Witasse, .; Zeitlin,
Cary; Taut, Andreas; Veronig, Astrid; Wimmer-Schweingruber, Robert;
Dumbovic, Mateja; Lohf, Henning; Temmer, Manuela; Hassler, Donald M.;
von Forstner, Johan Lauritz Freiherr
2018cosp...42E1321G Altcode:
During the declining phase of the current solar cycle, heliospheric
activity has suddenly and drastically increased starting from a simple
sunspot in Active Region (AR) 2673, which transformed into a complex
region with three X-class flares accompanied by several Earth-directed
Coronal Mass Ejections (CME) from 4th to 6th of September. Only a few
days later, on 10th September, the same AR 2673 produced solar energetic
particles (SEPs) which were registered as a ground level enhancement
(GLE) at Earth and the biggest GLE on the surface of Mars as observed
by the Radiation Assessment Detector (RAD) since the landing of the
Curiosity rover in August 2012. Both Earth and Mars saw an impulsive and
intense enhancement of the accelerated protons with energies larger
than hundreds of MeV whereas STEREO-A, despite being at the back
side of the event, detected gradually increasing fluxes of particles
transported there across the heliospheric magnetic field. These high
energy particles were mainly accelerated by the flares and shocks
which were associated with three consecutive CMEs launched on 9th
and 10th of September. Based on STEREO-A and SOHO coronograph images,
we identified the initial three-dimensional kinematics of the three
CMEs using the Graduated Cylindrical Shell (GCS) model. The first two
CMEs had moderate launch speeds while the last one was extremely fast
(larger than 2500 km/s at 20 solar radii). These three CMEs interacted
as they propagated outwards into the heliosphere and the resulting
complex interplanetary CME (ICME) together with its associated shock
was highly likely related to the effective acceleration of particles
at such high energies causing GLE at both Earth and Mars. The arrival
of the ICME at Mars caused a very significant Forbush decrease seen
by the Radiation Assessment Detector (RAD) on the surface of Mars
and the arrival time is only a few hours later than that at Earth
which is about 0.5 AU closer to the Sun than Mars. We investigated
the interaction of three CMEs and propagation of the consequent ICME
using the Drag Based Model (DBM) as well as the WSA-ENLIL plus cone
model and the simulated results are compared with in-situ measurements
at both Earth and Mars. The comparison shows that in order to better
predict the ICME arrival and its potential space weather impact at
Earth and other heliospheric locations, it is essential to 1) analyze
the evolution of the ICME kinematics, especially during interactions
of different CMEs and 2) better understand the spatially and temporally
varying interplanetary conditions of the heliosphere.
---------------------------------------------------------
Title: Development of adaptive Kalman filter for solar wind forecast
Authors: Podladchikova, Tatiana; Veronig, Astrid; Temmer, Manuela;
Hofmeister, Stefan
2018cosp...42E2698P Altcode:
Accurate solar wind modeling is important for predicting the arrival
and geomagnetic response of high-speed solar wind streams as well as for
modeling the transit of coronal mass ejections in interplanetary space
and their impact at Earth. Data assimilation techniques combining the
strength of models and observations provide a very useful tool for
accurate solar wind forecasts. We develop a method to predict the
solar wind speed at Earth 1-day ahead by using coronal hole areas
derived from SDO AIA images in combination with in situ solar wind
plasma and field data (speed, density, and magnetic field magnitude)
from ACE and Wind spacecraft. To forecast the solar wind speed, we form
a multidimensional linear regression model relating the solar wind speed
one day ahead with the fractional coronal hole area observed three days
before the current moment, as well as proton density, magnetic field
magnitude, and solar wind speed at the current moment. One of the major
concerns with such data assimilation scheme is that the regression
coefficients do not remain constant and are time-varying. To avoid
the fitting of regression coefficients to a particular situation,
that can be changed in future, we develop an adaptive Kalman filter
to create a dynamic linear regression for the 1-day ahead prediction
of the solar wind speed. Testing the developed forecasting technique
for the period 2010-2017, we obtain a correlation coefficient between
the predicted and observed solar wind speed of 0.93, with an RMS error
of prediction of 33 km/s. These results demonstrate that the proposed
adaptive Kalman filter method significantly improves the quality of
the solar wind forecasts and can be applied for reliable real-time
warnings of the space weather conditions in the near-Earth environment.
---------------------------------------------------------
Title: CME acceleration and EUV wave kinematics for September 10th
2017 event
Authors: Podladchikova, Tatiana; Dissauer, Karin; Veronig, Astrid;
Temmer, Manuela; Seaton, Daniel
2018cosp...42E2697P Altcode:
On September 10th 2017 a large solar eruption, accompanied by an X8.2
solar flare, from NOAA active region 12673 was observed on the Sun's
western limb by the new Solar Ultraviolet Imager (SUVI) on the GOES-16
spacecraft. We present a method to identify the CME bubble shape and
to determine its radial and lateral acceleration. The large field of
view of SUVI allows us to study the early impulsive CME acceleration
up to 2 solar radii. The CME bubble reveals a fast evolution and
strong overexpansion. The radial propagation of the CME revealed
a peak value of the acceleration of about 4.8 km/s^{2}, whereas
the lateral expansion reached a peak value of 8.9 km/s^{2}. The EUV
wave associated with this eruption was observed by SUVI and STEREO-A,
which had a separation angle with Earth of 128°, and the common field
of view of both spacecraft was 52°. SUVI images above the solar limb
reveal the initiation of the EUV wave by the accelerating flanks of the
CME bubble, followed by detachment and propagation of the wave with
a speed of 1100 km/s. Above the limb, the wave front can be observed
as high as 0.7 solar radii. The EUV wave shows a global propagation
over the full SUVI disk as well as into the STEREO-A field-of-view,
and can be followed up to distances of about 1727 Mm from the source
region. We study the propagation and kinematics of the direct as well
as the various reflected and refracted EUV wave components on the solar
sphere, finding speeds in the range from 370 to 1010 km/s. Finally,
we note that this EUV wave is also distinct as it reveals propagation
and transmission through a polar coronal hole.
---------------------------------------------------------
Title: Coronal mass ejections and space weather effects
Authors: Temmer, Manuela
2018cosp...42E3354T Altcode:
Earth-directed coronal mass ejections (CMEs), with their embedded
magnetic fields and shocks ahead, compress and reconnect with the
Earth's magnetic field and are the main drivers of strong geomagnetic
storms. The impact of strong events may endanger critical ground-based
infrastructure like power grids or disrupt communication and navigation
systems. Due to such Space Weather effects, CMEs and related phenomena
are an area of intense research interest. Important scientific
knowledge could be achieved by closely monitoring and investigating
the Sun-to-Earth "chain of action" of solar activity (evolution of
surface magnetic fields, flares and CMEs), measurements of near-Earth
space (in-situ plasma and magnetic field, energetic particles) and
geomagnetic activity (response of the magnetosphere and different
atmospheric layers down to ground-induced currents). This overview talk
covers and discusses our recent understanding of the physical processes
about the initiation and propagation of CMEs, their interaction with
the solar wind and other ejecta, and consequences for Space Weather.
---------------------------------------------------------
Title: Three-phase Evolution of a Coronal Hole. I. 360° Remote
Sensing and In Situ Observations
Authors: Heinemann, Stephan G.; Temmer, Manuela; Hofmeister, Stefan
J.; Veronig, Astrid M.; Vennerstrøm, Susanne
2018ApJ...861..151H Altcode: 2018arXiv180609495H
We investigate the evolution of a well-observed, long-lived,
low-latitude coronal hole (CH) over 10 solar rotations in the
year 2012. By combining extreme ultraviolet (EUV) imagery from
the Solar TErrestrial RElations Observatories (STEREO-A/B) and the
Solar Dynamics Observatory (SDO), we are able to track and study the
entire evolution of the CH having a continuous 360° coverage of the
Sun. The remote sensing data are investigated together with in situ
solar wind plasma and magnetic field measurements from STEREO-A/B, the
Advanced Composition Explorer (ACE), and WIND. From this, we obtain
how different evolutionary states of the CH as observed in the solar
atmosphere (changes in EUV intensity and area) affect the properties
of the associated high-speed stream measured at 1 au. Most distinctly
pronounced for the CH area, three development phases are derived:
(a) growing, (b) maximum, and (c) decaying phase. During these phases
the CH area (a) increases over a duration of around three months from
about 1 · 10<SUP>10</SUP> km<SUP>2</SUP> to 6 · 10<SUP>10</SUP>
km<SUP>2</SUP>, (b) keeps a rather constant area for about one month of
>9 · 10<SUP>10</SUP> km<SUP>2</SUP>, and (c) finally decreases in
the following three months below 1 · 10<SUP>10</SUP> km<SUP>2</SUP>
until the CH cannot be identified anymore. The three phases manifest
themselves also in the EUV intensity and in in situ measured solar wind
proton bulk velocity. Interestingly, the three phases are related to
a different range in solar wind speed variations, and we find for the
growing phase a range of 460-600 km s<SUP>-1</SUP>, for the maximum
phase 600-720 km s<SUP>-1</SUP>, and for the decaying phase a more
irregular behavior connected to slow and fast solar wind speeds of
350-550 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Observations of the solar chromosphere with ALMA and comparison
with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
2018csss.confE..37B Altcode: 2018arXiv181207293B
In this work we use solar observations with the ALMA radio telescope
at the wavelength of 1.21 mm. The aim of the analysisis to improve
understanding of the solar chromosphere, a dynamic layer in the
solar atmosphere between the photosphere andcorona. The study has
an observational and a modeling part. In the observational part
full-disc solar images are analyzed.Based on a modied FAL atmospheric
model, radiation models for various observed solar structures are
developed. Finally, theobservational and modeling results are compared
and discussed.
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Title: Ensemble Prediction of a Halo Coronal Mass Ejection Using
Heliospheric Imagers
Authors: Amerstorfer, T.; Möstl, C.; Hess, P.; Temmer, M.; Mays,
M. L.; Reiss, M. A.; Lowrance, P.; Bourdin, P. -A.
2018SpWea..16..784A Altcode: 2017arXiv171200218A
The Solar TErrestrial RElations Observatory (STEREO) and its
heliospheric imagers (HIs) have provided us the possibility to enhance
our understanding of the interplanetary propagation of coronal mass
ejections (CMEs). HI-based methods are able to forecast arrival times
and speeds at any target and use the advantage of tracing a CME's path
of propagation up to 1 AU and beyond. In our study, we use the ELEvoHI
model for CME arrival prediction together with an ensemble approach to
derive uncertainties in the modeled arrival time and impact speed. The
CME from 3 November 2010 is analyzed by performing 339 model runs
that are compared to in situ measurements from lined-up spacecraft
MErcury Surface, Space ENvironment, GEochemistry, and Ranging and
STEREO-B. Remote data from STEREO-B showed the CME as halo event,
which is comparable to an HI observer situated at L1 and observing an
Earth-directed CME. A promising and easy approach is found by using
the frequency distributions of four ELEvoHI output parameters, drag
parameter, background solar wind speed, initial distance, and speed. In
this case study, the most frequent values of these outputs lead to
the predictions with the smallest errors. Restricting the ensemble
to those runs, we are able to reduce the mean absolute arrival time
error from 3.5 ± 2.6 to 1.6 ± 1.1 hr at 1 AU. Our study suggests that
L1 may provide a sufficient vantage point for an Earth-directed CME,
when observed by HI, and that ensemble modeling could be a feasible
approach to use ELEvoHI operationally.
---------------------------------------------------------
Title: Forbush decrease model for expanding CMEs (ForbMod)
Authors: Dumbovic, Mateja; Möstl, Christian; Guo, Jingnan; Heber,
Bernd; Vrsnak, Bojan; Temmer, Manuela
2018cosp...42E.917D Altcode:
Forbush decreases (FDs) can be used as one of the "signatures" of an
ICME passage. An analytical diffusion-expansion FD model (ForbMod) was
developed that is based on the widely used approach of an initially
empty, closed magnetic structure (i.e. flux rope) that fills up
slowly with particles by diffusion perpendicular to the magnetic
field of the flux rope. In our approach the FD amplitude is not only
determined by the diffusion process but also by the expansion of the
flux rope. While the first process leads to a smaller amplitude the
second one leads again to a larger effect. Remote CME observations
and 3D reconstruction is used to constrain initial and boundary
conditions. CME evolutionary properties are taken into account by
incorporating the flux rope expansion. Several options of flux rope
expansion are regarded as competing mechanism to diffusion, which can
lead to different FD characteristics, and forward modelling is used
to analyse flux rope expansion and further constrain the model. In
testing the model, a number of spacecraft and planetary observation is
utilised, including those by the Radiation Assessment Detector aboard
the Mars Rover Curiosity. This project has received funding from the
European Union's Horizon 2020 research and innovation programme under
the Marie Sk_odowska-Curie grant agreement No 745782.
---------------------------------------------------------
Title: Modeling the evolution and propagation of the 2017 September
9th and 10th CMEs and SEPs arriving at Mars constrained by
remote-sensing and in-situ measurement
Authors: Guo, Jingnan; Dumbović, Mateja; Wimmer-Schweingruber,
Robert F.; Temmer, Manuela; Lohf, Henning; Wang, Yuming; Veronig,
Astrid; Hassler, Donald M.; Mays, Leila M.; Zeitlin, Cary; Ehresmann,
Bent; Witasse, Olivier; von Forstner, Johan L. Freiherr; Heber, Bernd;
Holmström, Mats; Posner, Arik
2018shin.confE..84G Altcode:
On 2017-09-10, solar energetic particles (SEPs) originating from the
active region 12673 were registered as a ground level enhancement (GLE)
at Earth and the biggest GLE on the surface of Mars as observed by the
Radiation Assessment Detector (RAD) since the landing of the Curiosity
rover in August 2012. Based on multi-point coronagraph im-
---------------------------------------------------------
Title: Ideas and plans for ISWAT clusters focused on propagation of
transients through evolving ambient heliosphere and input to geospace
Authors: Temmer, Manuela
2018cosp...42E3353T Altcode:
Space Weather is an important issue of global matter, but needs
coordinated efforts. Many international groups perform research
on the propagation of transients and based on that develop Space
Weather forecasting services. In order to avoid duplication and to
efficiently improve the performance of currently available models, they
need to become better visible and to undergo scientific peer-review
qualification. iSWAT is an international, community driven effort
and provides the required platform to challenge propagation models
and to exchange experience with peers. iSWAT is also a network that
fosters collaboration among interdisciplinary group members, like from
geospace, that are potential users of propagation models. Coordinated
international cooperation will offer new perspectives and will make
models more efficient and progress them efficiently towards operational
tools. Operational tools are not only meant to be used by (industrial)
end-users, but particularly by peers in order to get a more complete
understanding of the physical processes underlying CME propagation.
---------------------------------------------------------
Title: Drag-based ensemble model (DBEM)
Authors: Dumbovic, Mateja; Möstl, Christian; Mays, M. Leila; Vrsnak,
Bojan; Veronig, Astrid; Salogovic, Jara; Piantschitsch, Isabell;
Amerstorfer, Tanja; Temmer, Manuela; Sudar, Davor
2018cosp...42E.918D Altcode:
The drag-based model (DBM) for heliospheric propagation of ICMEs is
a widely used simple analytical model which can predict ICME arrival
time and speed at a given heliospheric distance (Vr_nak et al.,
2013, SolPhys). It is based on the assumption that the heliospheric
propagation of ICMEs, is solely under the influence of MHD drag,
where ICME propagation is determined based on CME properties as
well as the properties of the ambient solar wind. The current
version of the DBM is operational as part of ESA's SSA programme
(http://swe.ssa.esa.int/web/guest/graz-dbm-federated). The DBM takes
into account the ICME geometry to track the whole leading edge of an
ICME, it can estimate whether or not an ICME will reach the observer
and calculate the transit time and impact speed. To estimate the
uncertainty for a single event, Drag-Based Ensemble Model (DBEM) was
developed (Dumbovic et al., 2018, ApJ) which utilizes an ensemble of the
observation-based CME input and synthetic values of the ambient solar
wind speed and drag parameter. Using multiple runs with different input
parameters, distributions of predicted arrival times and speeds are
obtained allowing to forecast the confidence in the likelihood of the
ICME arrival. The DBEM was further developed to an on-line application
to provide the real-time CME forecast, which is currently in a test
phase, and will soon be a part of ESA-SSA Heliospheric Weather Expert
Service Group (http://swe.ssa.esa.int/heliospheric-weather). We test
the model and the on-line application using observations and compare
the performance with other CME propagation models.
---------------------------------------------------------
Title: Predicting a CME arrival as observed from L1 by heliospheric
imagers using ELEvoHI
Authors: Amerstorfer, Tanja; Moestl, Christian; Mays, M. Leila; Hess,
Phillip; Temmer, Manuela; Reiss, Martin
2018cosp...42E..85A Altcode:
The Lagrangian point L5 is expected to be an ideal location for
a future operational space weather observatory, already indicated
by The Solar TErrestrial RElations Observatory (STEREO). STEREO has
improved our understanding on the interplanetary (IP) evolution of
coronal mass ejections (CMEs). Especially the wide-angle heliospheric
imagers (HI) facilitated the development of a variety of methods for
analyzing the evolution of CMEs through IP space. In this study,
we present an ensemble forecast based on 339 model runs using the
HI-based CME prediction tool ELEvoHI and test if an HI observer located
at L1 may be an appropriate alternative (or supplement) to an L5 HI
observatory. ELEvoHI, the ELlipse Evolution model (ELEvo) based on HI
observations uses the benefits of different methods and observations. It
provides the possibility to adjust the CME frontal shape (angular width,
ellipse aspect ratio) and the direction of motion for each CME event
individually. This information can be gained from Graduated Cylindrical
Shell (GCS) flux-rope fitting within coronagraph images. Using the
ELlipse Conversion (ELCon) method, the observed HI elongation angle
is converted into a unit of distance, which reveals the kinematics
(including the initial time, distance and speed) of the event. After
fitting the time-distance profile of the CME using the drag-based
equation of motion, where real-time in situ solar wind speed from 1
AU is used as additional input, we obtain all input parameters needed
to run a forecast using the ELEvo model and to predict arrival times
and speeds at any target of interest in IP space. Here, we present a
test on a slow CME event of 3 November 2010, in situ detected by the
lined-up spacecraft MESSENGER and STEREO-B and remotely observed by
STEREO-B/HI, i.e. it was a halo CME for STEREO-B. These conditions
simulate an Earth-directed CME observed by HI located at L1. Our
study suggests that L1 may provide a sufficient vantage point for an
Earth-directed CME, when observed by HI, and that ensemble modeling
could be a feasible approach to use ELEvoHI operationally.
---------------------------------------------------------
Title: An Analytical Diffusion-Expansion Model for Forbush Decreases
Caused by Flux Ropes
Authors: Dumbović, Mateja; Heber, Bernd; Vršnak, Bojan; Temmer,
Manuela; Kirin, Anamarija
2018ApJ...860...71D Altcode: 2018arXiv180500916D
We present an analytical diffusion-expansion Forbush decrease (FD)
model ForbMod, which is based on the widely used approach of an
initially empty, closed magnetic structure (i.e., flux rope) that
fills up slowly with particles by perpendicular diffusion. The model
is restricted to explaining only the depression caused by the magnetic
structure of the interplanetary coronal mass ejection (ICME). We use
remote CME observations and a 3D reconstruction method (the graduated
cylindrical shell method) to constrain initial boundary conditions
of the FD model and take into account CME evolutionary properties by
incorporating flux rope expansion. Several flux rope expansion modes
are considered, which can lead to different FD characteristics. In
general, the model is qualitatively in agreement with observations,
whereas quantitative agreement depends on the diffusion coefficient and
the expansion properties (interplay of the diffusion and expansion). A
case study was performed to explain the FD observed on 2014 May 30. The
observed FD was fitted quite well by ForbMod for all expansion modes
using only the diffusion coefficient as a free parameter, where the
diffusion parameter was found to correspond to an expected range of
values. Our study shows that, in general, the model is able to explain
the global properties of an FD caused by a flux rope and can thus be
used to help understand the underlying physics in case studies.
---------------------------------------------------------
Title: An Event-Based Verification Scheme for the Real-Time Flare
Detection System at Kanzelhöhe Observatory
Authors: Pötzi, W.; Veronig, A. M.; Temmer, M.
2018SoPh..293...94P Altcode:
In the framework of the Space Situational Awareness program of the
European Space Agency (ESA/SSA), an automatic flare detection system
was developed at Kanzelhöhe Observatory (KSO). The system has been in
operation since mid-2013. The event detection algorithm was upgraded
in September 2017. All data back to 2014 was reprocessed using the new
algorithm. In order to evaluate both algorithms, we apply verification
measures that are commonly used for forecast validation. In order to
overcome the problem of rare events, which biases the verification
measures, we introduce a new event-based method. We divide the
timeline of the Hα observations into positive events (flaring period)
and negative events (quiet period), independent of the length of
each event. In total, 329 positive and negative events were detected
between 2014 and 2016. The hit rate for the new algorithm reached 96%
(just five events were missed) and a false-alarm ratio of 17%. This
is a significant improvement of the algorithm, as the original system
had a hit rate of 85% and a false-alarm ratio of 33%. The true skill
score and the Heidke skill score both reach values of 0.8 for the new
algorithm; originally, they were at 0.5. The mean flare positions are
accurate within ±1 heliographic degree for both algorithms, and the
peak times improve from a mean difference of 1.7 ±2.9 minutes to 1.3
±2.3 minutes. The flare start times that had been systematically late
by about 3 minutes as determined by the original algorithm, now match
the visual inspection within −0.47 ±4.10 minutes.
---------------------------------------------------------
Title: "Chapter 15 - Coronal Holes Detection Using Supervised
Classification
Authors: Delouille, Véronique; Hofmeister, Stefan J.; Reiss, Martin
A.; Mampaey, Benjamin; Temmer, Manuela; Veronig, Astrid
2018mlts.book..365D Altcode:
We demonstrate the use of machine learning algorithms in combination
with segmentation techniques in order to distinguish coronal holes and
filaments in solar extreme ultraviolet (EUV) images recorded by the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. We
used the Spatial Possibilistic Clustering Algorithm to prepare datasets
of manually labeled coronal hole and filament channel regions present
on the Sun during the time range 2010-16. By mapping the extracted
regions from EUV observations onto Helioseismic and Magnetic Imager
(HMI) line-of-sight magnetograms, we also include their magnetic
characteristics. We computed average latitude, area, and shape measures
from the segmented binary maps, as well as first-order and second-order
texture statistics from the segmented regions in the EUV images and
magnetograms. These attributes were used for data-mining investigations
to identify the best rule for differentiating between coronal holes
and filame! <P />nt channels, taking into account the imbalance in our
dataset, which contains 1 filament channel for 15 coronal holes. We
tested classifiers such as support vector machine (SVM), linear SVM,
decision tree, k-nearest neighbors, as well as an ensemble classifier
based on decision trees. The best performance in terms of true skill
statistics is obtained with cost-sensitive learning, SVM classifiers,
and when HMI attributes are included in the dataset.
---------------------------------------------------------
Title: A Comparative Study between a Failed and a Successful Eruption
Initiated from the Same Polarity Inversion Line in AR 11387
Authors: Liu, Lijuan; Wang, Yuming; Zhou, Zhenjun; Dissauer, Karin;
Temmer, Manuela; Cui, Jun
2018ApJ...858..121L Altcode: 2018arXiv180400867L
In this paper, we analyzed a failed and a successful eruption that
initiated from the same polarity inversion line within NOAA AR 11387 on
2011 December 25. They both started from a reconnection between sheared
arcades, with distinct pre-eruption conditions and eruption details:
before the failed one, the magnetic fields of the core region had a
weaker non-potentiality; the external fields had a similar critical
height for torus instability, and a similar local torus-stable region,
but a larger magnetic flux ratio (of low corona and near-surface
region) compared to the successful one. During the failed eruption,
a smaller Lorentz force impulse was exerted on the outward ejecta;
the ejecta had a much slower rising speed. Factors that might lead
to the initiation of the failed eruption are identified: (1) a weaker
non-potentiality of the core region, and a smaller Lorentz force impulse
gave the ejecta a small momentum; (2) the large flux ratio, and the
local torus-stable region in the corona provided strong confinements
that made the erupting structure regain an equilibrium state.
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Title: Long-lasting injection of solar energetic electrons into
the heliosphere
Authors: Dresing, N.; Gómez-Herrero, R.; Heber, B.; Klassen, A.;
Temmer, M.; Veronig, A.
2018A&A...613A..21D Altcode: 2018arXiv180204722D
Context. The main sources of solar energetic particle (SEP) events are
solar flares and shocks driven by coronal mass ejections (CMEs). While
it is generally accepted that energetic protons can be accelerated by
shocks, whether or not these shocks can also efficiently accelerate
solar energetic electrons is still debated. In this study we present
observations of the extremely widespread SEP event of 26 Dec 2013
To the knowledge of the authors, this is the widest longitudinal
SEP distribution ever observed together with unusually long-lasting
energetic electron anisotropies at all observer positions. Further
striking features of the event are long-lasting SEP intensity
increases, two distinct SEP components with the second component mainly
consisting of high-energy particles, a complex associated coronal
activity including a pronounced signature of a shock in radio type-II
observations, and the interaction of two CMEs early in the event. <BR
/> Aims: The observations require a prolonged injection scenario not
only for protons but also for electrons. We therefore analyze the data
comprehensively to characterize the possible role of the shock for
the electron event. <BR /> Methods: Remote-sensing observations of
the complex solar activity are combined with in situ measurements of
the particle event. We also apply a graduated cylindrical shell (GCS)
model to the coronagraph observations of the two associated CMEs to
analyze their interaction. <BR /> Results: We find that the shock alone
is likely not responsible for this extremely wide SEP event. Therefore
we propose a scenario of trapped energetic particles inside the CME-CME
interaction region which undergo further acceleration due to the shock
propagating through this region, stochastic acceleration, or ongoing
reconnection processes inside the interaction region. The origin of
the second component of the SEP event is likely caused by a sudden
opening of the particle trap.
---------------------------------------------------------
Title: STEREO-A persistence model for solar wind speed forecasting
and uncertainty assessment from the evolution of coronal holes
Authors: Temmer, Manuela; Hinterreiter, Jürgen; Reiss, Martin
2018EGUGA..20.3996T Altcode:
We present the concept of a persistence model to forecast the solar
wind speed at 1 AU, using the advantage of multi-viewpoint satellite
data. The model is based on STEREO in-situ measurements for satellite
positions eastward of Earth, shifted forward by a variable time
span according to the angle of the STEREO spacecraft with Earth (
2-10 days). The STEREO persistence model is applied on the time range
2008-2012 (STEREO-B) and 2017 (STEREO-A) and compared to a recurrence
model based on ACE data forward shifted by a full rotation. In
addition, the STEREO persistence model is modified by assessing the
speed uncertainties that are caused by the evolution of coronal holes
(CH). We derive the information on CH evolution by comparing CH areas
extracted in EUV data from STEREO and Earth perspective. Compared to
an ACE based persistence model, the performance of the new STEREO+CH
persistence model which takes into account the evolution of coronal
holes, is able to reduce the number of missed high-speed streams by
about 23%, the false alarms by about 19%, and to increase the hit rate
by about 12%.
---------------------------------------------------------
Title: Using Forbush decreases to derive the transit time of ICMEs
propagating from 1 AU to Mars
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
Robert F.; Hassler, Donald M.; Temmer, Manuela; Dumbović, Mateja;
Jian, Lan K.; Appel, Jan K.; Čalogović, Jaša; Ehresmann, Bent;
Heber, Bernd; Lohf, Henning; Posner, Arik; Vršnak, Bojan; Zeitlin,
Cary J.
2018EGUGA..20.9306V Altcode:
The propagation of 15 interplanetary coronal mass ejections (ICMEs) from
Earth's orbit (1 AU) to Mars (∼1.5 AU) has been studied with their
propagation speed estimated from both measurements and simulations. The
enhancement of magnetic fields related to ICMEs and their shock fronts
cause the so-called Forbush decrease, which can be detected as a
reduction of galactic cosmic ray (GCR) intensity measured on-ground
or on a spacecraft. This effect can be used to detect the passage of
ICMEs at various locations in the heliosphere, for example at Earth
(using neutron monitors), the STEREO A and B spacecraft (HET) as well
the on the surface of Mars using the Radiation Assessment Detector
(RAD) instrument on the Mars Science Laboratory (MSL) rover. A set of
ICME events has been selected during the periods when Earth (or STEREO
A or B) and Mars locations were nearly aligned on the same side of the
Sun in the ecliptic plane (so-called opposition phase). Such lineups
allow us to estimate the ICMEs' transit times between 1 and 1.5 AU by
determining the time delay between the corresponding Forbush decreases
measured at each location. We investigate the evolution of the ICME
propagation speeds before and after passing Earth's orbit and find
that their deceleration due to interaction with the ambient solar
wind may continue beyond 1 AU. We also find a substantial variance of
the speed evolution among different events revealing the dynamic and
diverse nature of eruptive solar events. Furthermore, the results are
compared to simulation data obtained from two CME propagation models,
namely the Drag-Based Model and ENLIL plus cone model.
---------------------------------------------------------
Title: Forbush decrease model for expanding CMEs (ForbMod)
Authors: Dumbovic, Mateja; Temmer, Manuela; Guo, Jingnan; Heber,
Bernd; Möstl, Christian; Vrsnak, Bojan
2018EGUGA..2015396D Altcode:
The Project ForbMod aims to unravel how galactic cosmic rays are
influenced by solar storms in the inner solar system (Sun to Mars)
by developing a new model and utilizing a number of spacecraft and
planetary observation, including those by the Radiation Assessment
Detector aboard the Mars Rover Curiosity. The project focuses on
Forbush decreases (FDs) in the galactic cosmic ray flux, which can
be used as one of the "signatures" of an ICME passage. An analytical
diffusion-expansion FD model was developed that is based on the
widely used approach of an initially empty, closed magnetic structure
(i.e. flux rope) that fills up slowly with particles by perpendicular
diffusion. Remote CME observations and 3D reconstruction is used to
constrain initial and boundary conditions. CME evolutionary properties
are taken into account by incorporating the flux rope expansion. Several
options of flux rope expansion are regarded as competing mechanism
to diffusion, which can lead to different FD characteristics. This
project has received funding from the European Union's Horizon 2020
research and innovation programme under the Marie Skłodowska-Curie
grant agreement No 745782.
---------------------------------------------------------
Title: Validation of the background solar wind modeled by EUHFORIA
Authors: Hinterreiter, Jürgen; Temmer, Manuela; Verbeke, Christine;
Poedts, Stefaan; Pomoell, Jens; Magdalenic, Jasmina; Scolini, Camilla;
Rodriguez, Luciano; Kilpua, Emili; Asvestari, Eleanna
2018EGUGA..20.6533H Altcode:
Nowadays, forecasting the arrival time and the geo-effectiveness of CMEs
and the fast solar wind has become of increasing importance. For that
reason, knowledge of the structure and propagation of the background
solar wind is essential. The testing and validation of the performance
of solar wind models is therefore important to assess their reliability
and to further improve the models. This is done for the EUHFORIA
(EUropean Heliospheric FORecasting Information Asset) model within
the CCSOM (Constraining CMEs and Shocks by Observations and Modelling
throughout the inner heliosphere) project [http://sidc.be/ccsom/]. We
validate the modeled background solar wind by comparing the results to
in-situ measurements, in order to make EUHFORIA ready for scientific
exploitation and operational space weather purposes. For this several
established test methods are applied on i) continuous variables of
the solar wind plasma and magnetic field parameters (speed, density,
pressure, Bz), and ii) binary variables based on specific events such
as the arrival time and impact speed of solar wind high speed streams
(HSS). We present first statistical results covering times of low
(2008) and high (2012) solar activity.
---------------------------------------------------------
Title: The 3-Phase evolution of a long-lived low-latitude coronal
hole.
Authors: Heinemann, Stephan; Temmer, Manuela; Hofmeister, Stefan;
Veronig, Astrid; Vennerstrom, Susanne
2018EGUGA..20.6670H Altcode:
High speed solar wind streams (HSS) emanating from coronal holes, and
associated stream interaction regions, may cause geomagnetic storms
and deflect coronal mass ejections propagation in interplanetary
space. By understanding the evolution and the relations between
coronal holes and solar wind parameters, we increase our knowledge
for improving space weather forecasts. We investigate the evolution
of a persistent coronal hole using EUV data from STEREO-A/B and SDO
over the timerange February 2012 -October 2012. Combined STEREO-SDO
data enable a continuous observation of the CH covering 360° degrees
over several rotations. Together with magnetic field measurements from
SDO filtergrams and in-situ solar wind observations, we analyze during
different evolutionary states of the CH, the solar surface properties
of the CH (intensity, area, shape, magnetic flux) and its effects at
1AU (solar wind speed). As a result we find an evolutionary pattern
in most parameters, clearly showing a three-phase evolution (growing,
maximum and decaying phase).
---------------------------------------------------------
Title: Hard X-ray, EUV, and radio signatures in relation to solar
energetic particles
Authors: Koleva, Kostadinka; Miteva, Rositsa; Dechev, Momchil; Kozarev,
Kamen; Veronig, Astrid; Temmer, Manuela
2018EGUGA..20.7408K Altcode:
In this report we present analysis of well-observed electromagnetic
signatures related to solar energetic particles (SEPs). We selected
cases with simultaneous observations in hard X-ray, EUV and radio
wavelengths of the SEP-related solar flares and analyzed the properties
of the emission (light curves, spectrum and temporal evolution). The
non-thermal potential of solar flares is tested in terms of correlation
studies between the particle intensities (protons and electrons) and
the flare flux at various wavelengths. The results are compared with
the outcomes when using GOES soft X-ray flare class. The solar origin
of SEP events in terms of solar flares is discussed.
---------------------------------------------------------
Title: The September 2017 events and their imprints at Earth and Mars
Authors: Guo, Jingnan; Mays, Leila; Dumbovic, Mateja; Temmer, Manuela;
Veronig, Astrid; Wimmer-Schweingruber, Robert; von Forstner, Johan
Freiherr; Hassler, Donald; Heber, Bernd; Zeitlin, Cary; Ehresmann,
Bent; Witasse, Oliver
2018EGUGA..2015655G Altcode:
During the declining phase of the current quiet solar cycle,
heliospheric activity has suddenly and drastically increased starting
from a simple sunspot in Active Region (AR) 2673, which transformed
into a complex region with three X-flares accompanied by several
Earth-directed Coronal Mass Ejections (CME) from 4th to 6th of
September. Four days later, on 10th September, the same AR produced
solar energetic particles (SEPs) which were registered as a ground
level enhancement (GLE) at Earth and the biggest GLE on the surface
of Mars as observed by the Radiation Assessment Detector (RAD) since
the landing of the Curiosity rover in August 2012. Both Earth and Mars
saw an impulsive and intense enhancement of the accelerated protons
with energies larger than hundreds of MeV whereas STEREO-A, despite
being at the back-side of the event, detected gradually increasing
fluxes of particles transported there across the heliospheric magnetic
field. Such high energetic particles were mainly accelerated by shocks
associated with the CMEs also launched on 10th of September. Three CMEs
with similar longitudinal launch directions (between Earth and Mars
with the central axis approximately 100 degrees from Earth and 40-50
degrees from Mars) can be identified based on STEREO-A and SOHO LASCO
chronograph images. The first two had moderate launch speed while the
last one had an extremely fast launch speed ( 2500 km/s). The merging
and interactions of the three CMEs into an interplanetary CME (ICME)
were very complex through the inner heliosphere and caused a very
significant Forbush decrease at Mars three days later, even before the
enhanced particle flux recovered to quiet-time level. The arrival of
the ICME at Mars is only a few hours later than that at Earth, despite
Mars being 0.5 AU further away from the Sun than Earth. This timing
difference between the ICME arrival at Earth and Mars is likely due to
(1) the earlier ICMEs from 4th and 6th which have considerably changed
the interplanetary conditions and (2) the interaction of the ICME with
a High Speed Stream structure passing by Mars. The 3D launch geometry
and direction of the CMEs has been reconstructed based on the Graduated
Cylindrical Shell (GCS) model and the subsequent ICME propagation has
been performed using the WSA-ENLIL plus cone model, as well as the
Drag Based Model (DBM) and CDPP propagation tool. Such modeled ICME
arrivals at Earth and Mars are compared with in-situ measurements and
the comparison shows that it is essential to consider the interactions
of different CMEs as well as the spatially and temporally varying
interplanetary conditions in order to better predict the ICME arrival
at Earth and other planets.
---------------------------------------------------------
Title: Combining remote-sensing image data with in-situ measurements
supported by modeling for Earth-affecting CME events
Authors: Temmer, Manuela; Thalmann, Julia; Dissauer, Karin; Veronig,
Astrid; Tschernitz, Johannes; Hinterreiter, Jürgen; Rodriguez, Luciano
2018EGUGA..20.3999T Altcode:
We analyze the well observed flare-CME event from October 1, 2011
and cover the complete chain of action - from the Sun to Earth. We
study in detail the solar surface and atmosphere (SDO and ground-based
instruments) associated to the flare/CME and also track the off-limb CME
signatures in interplanetary space (STEREO-SoHO). This is complemented
by surface magnetic field information and 3D coronal magnetic field
modeling. From in-situ measurements (Wind), we extract the corresponding
ICME characteristics. Results show that the flare reconnection flux is
most probably a lower limit for estimating the magnetic flux within the
flux rope as 1) magnetic reconnection processes were already ongoing
before the start of the impulsive flare phase and 2) the dimming flux
increased by more than 25% after the end of the flare, indicating that
magnetic flux was still added to the flux rope after eruption. When
comparing this to the in-situ axial magnetic flux of the magnetic cloud,
we find that it is reduced by at least 75%, referring to substantial
erosion in interplanetary space. Careful inspection of on-disk features
associated with CMEs are essential for interpreting such scenarios.
---------------------------------------------------------
Title: Case study of July 2017 CMEs using modelling and
multi-spacecraft observational approach
Authors: Dumbovic, Mateja; Guo, Jingnan; Temmer, Manuela
2018EGUGA..2015713D Altcode:
We present the analysis of several CMEs that erupted mid-July 2017
from the same source region on the back side of the Sun as viewed from
Earth. In our analysis, we use multi-instrument and multi-spacecraft
measurements as well as different modeling approaches. We perform a
3D reconstruction of each CME, to find their respective directions,
geometry and kinematics. We employ WSA/ENLIL simulations and DBM
propagation model to better understand their interplanetary evolution
and associate them to signatures observed at STEREO-A and Mars. At Mars,
a two-step Forbush decrease is observed with MSL/RAD July 24 2017. With
the amplitude of more than 15% this is one of the largest Forbush
decreases detected at Mars. At STEREO-A in situ ICME signatures are
observed July 24/25 2017. This ICME shows a remarkably high magnetic
field strength of 60 nT, probably related to the inability to expand
due to interaction. This project has received funding from the European
Union's Horizon 2020 research and innovation programme under the Marie
Skłodowska-Curie grant agreement No 745782.
---------------------------------------------------------
Title: Tracking and validating ICMEs propagating towards Mars using
STEREO Heliospheric Imagers combined with Forbush decreases detected
by MSL/RAD
Authors: von Forstner, Johan; Guo, Jingnan; Temmer, Manuela; Dumbović,
Mateja; Hassler, Donald M.
2018EGUGA..2014376V Altcode:
The enhancement of magnetic fields related to ICMEs and their shock
fronts cause the so-called Forbush decrease, which can be detected as a
reduction of galactic cosmic ray intensity (GCR) measured on-ground or
on a spacecraft. Forbush decreases observed by the Radiation Assessment
Detector (RAD) instrument onboard Mars Science Laboratory (MSL) on the
surface of Mars as well as during its flight to Mars in 2011-2012 can
be combined with observations at Earth and the two STEREO spacecraft to
study the propagation of ICMEs up to Earth orbit and beyond to Mars. Our
previous work (Freiherr von Forstner et al. 2017, JGR: Space Physics)
considered the case where Earth (or STEREO A or B) and Mars were nearly
forming a straight line with the Sun so that ICMEs can be observed in
situ at both locations. We now also study periods where one or both
of the STEREO spacecraft are positioned suitably to remotely track
ICMEs directed towards Mars continuously with their coronagraph and
heliospheric imaging instruments and compare the arrival signatures with
the in situ detection of the Forbush decrease by MSL/RAD. By studying
additional events in periods with this constellation, we enhance our
investigation of the evolution of ICME propagation speeds through the
inner heliosphere up to Mars.
---------------------------------------------------------
Title: Plasma Diagnostics of Coronal Dimming Events
Authors: Vanninathan, Kamalam; Veronig, Astrid M.; Dissauer, Karin;
Temmer, Manuela
2018ApJ...857...62V Altcode: 2018arXiv180206152V
Coronal mass ejections are often associated with coronal dimmings,
i.e., transient dark regions that are most distinctly observed in
Extreme Ultra-violet wavelengths. Using Atmospheric Imaging Assembly
(AIA) data, we apply Differential Emission Measure diagnostics to
study the plasma characteristics of six coronal dimming events. In
the core dimming region, we find a steep and impulsive decrease of
density with values up to 50%-70%. Five of the events also reveal
an associated drop in temperature of 5%-25%. The secondary dimming
regions also show a distinct decrease in density, but less strong,
decreasing by 10%-45%. In both the core and the secondary dimming the
density changes are much larger than the temperature changes, confirming
that the dimming regions are mainly caused by plasma evacuation. In
the core dimming, the plasma density reduces rapidly within the first
20-30 minutes after the flare start and does not recover for at least
10 hr later, whereas the secondary dimming tends to be more gradual and
starts to replenish after 1-2 hr. The pre-event temperatures are higher
in the core dimming (1.7-2.6 MK) than in the secondary dimming regions
(1.6-2.0 MK). Both core and secondary dimmings are best observed in
the AIA 211 and 193 Å filters. These findings suggest that the core
dimming corresponds to the footpoints of the erupting flux rope rooted
in the AR, while the secondary dimming represents plasma from overlying
coronal structures that expand during the CME eruption.
---------------------------------------------------------
Title: Coronal hole evolution from multi-viewpoint data as input
for a STEREO solar wind speed persistence model
Authors: Temmer, Manuela; Hinterreiter, Jürgen; Reiss, Martin A.
2018JSWSC...8A..18T Altcode: 2018arXiv180110213T
We present a concept study of a solar wind forecasting method for Earth,
based on persistence modeling from STEREO in situ measurements combined
with multi-viewpoint EUV observational data. By comparing the fractional
areas of coronal holes (CHs) extracted from EUV data of STEREO and
SoHO/SDO, we perform an uncertainty assessment derived from changes
in the CHs and apply those changes to the predicted solar wind speed
profile at 1 AU. We evaluate the method for the time period 2008-2012,
and compare the results to a persistence model based on ACE in situ
measurements and to the STEREO persistence model without implementing
the information on CH evolution. Compared to an ACE based persistence
model, the performance of the STEREO persistence model which takes
into account the evolution of CHs, is able to increase the number of
correctly predicted high-speed streams by about 12%, and to decrease the
number of missed streams by about 23%, and the number of false alarms by
about 19%. However, the added information on CH evolution is not able
to deliver more accurate speed values for the forecast than using the
STEREO persistence model without CH information which performs better
than an ACE based persistence model. Investigating the CH evolution
between STEREO and Earth view for varying separation angles over
∼25-140° East of Earth, we derive some relation between expanding
CHs and increasing solar wind speed, but a less clear relation for
decaying CHs and decreasing solar wind speed. This fact most likely
prevents the method from making more precise forecasts. The obtained
results support a future L5 mission and show the importance and valuable
contribution using multi-viewpoint data.
---------------------------------------------------------
Title: The Dependence of the Peak Velocity of High-Speed Solar Wind
Streams as Measured in the Ecliptic by ACE and the STEREO satellites
on the Area and Co-latitude of Their Solar Source Coronal Holes
Authors: Hofmeister, Stefan J.; Veronig, Astrid; Temmer, Manuela;
Vennerstrom, Susanne; Heber, Bernd; Vršnak, Bojan
2018JGRA..123.1738H Altcode: 2018arXiv180409579H
We study the properties of 115 coronal holes in the time range
from August 2010 to March 2017, the peak velocities of the
corresponding high-speed streams as measured in the ecliptic at 1
AU, and the corresponding changes of the Kp index as marker of their
geoeffectiveness. We find that the peak velocities of high-speed streams
depend strongly on both the areas and the co-latitudes of their solar
source coronal holes with regard to the heliospheric latitude of
the satellites. Therefore, the co-latitude of their source coronal
hole is an important parameter for the prediction of the high-speed
stream properties near the Earth. We derive the largest solar wind
peak velocities normalized to the coronal hole areas for coronal holes
located near the solar equator and that they linearly decrease with
increasing latitudes of the coronal holes. For coronal holes located
at latitudes ≳60°, they turn statistically to zero, indicating
that the associated high-speed streams have a high chance to miss the
Earth. Similarly, the Kp index per coronal hole area is highest for the
coronal holes located near the solar equator and strongly decreases
with increasing latitudes of the coronal holes. We interpret these
results as an effect of the three-dimensional propagation of high-speed
streams in the heliosphere; that is, high-speed streams arising from
coronal holes near the solar equator propagate in direction toward and
directly hit the Earth, whereas solar wind streams arising from coronal
holes at higher solar latitudes only graze or even miss the Earth.
---------------------------------------------------------
Title: On the Detection of Coronal Dimmings and the Extraction of
Their Characteristic Properties
Authors: Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova,
T.; Vanninathan, K.
2018ApJ...855..137D Altcode: 2018arXiv180203185D
Coronal dimmings are distinct phenomena associated with coronal mass
ejections (CMEs). The study of coronal dimmings and the extraction
of their characteristic parameters help us to obtain additional
information regarding CMEs, especially on the initiation and early
evolution of Earth-directed CMEs. We present a new approach to detect
coronal dimming regions based on a thresholding technique applied
on logarithmic base-ratio images. Characteristic dimming parameters
describing the dynamics, morphology, magnetic properties, and the
brightness of coronal dimming regions are extracted by cumulatively
summing newly dimmed pixels over time. It is also demonstrated how core
dimming regions are identified as a subset of the overall identified
dimming region. We successfully apply our method to two well-observed
coronal dimming events. For both events, the core dimming regions are
identified and the spatial evolution of the dimming area reveals the
expansion of the dimming region around these footpoints. We also show
that in the early impulsive phase of the dimming expansion the total
unsigned magnetic flux involved in the dimming regions is balanced and
that up to 30% of this flux results from the localized core dimming
regions. Furthermore, the onset in the profile of the area growth rate
is cotemporal with the start of the associated flares and in one case
also with the fast rise of the CME, indicating a strong relationship
of coronal dimmings with both flares and CMEs.
---------------------------------------------------------
Title: The Drag-based Ensemble Model (DBEM) for Coronal Mass Ejection
Propagation
Authors: Dumbović, Mateja; Čalogović, Jaša; Vršnak, Bojan; Temmer,
Manuela; Mays, M. Leila; Veronig, Astrid; Piantschitsch, Isabell
2018ApJ...854..180D Altcode: 2018arXiv180107473D
The drag-based model for heliospheric propagation of coronal mass
ejections (CMEs) is a widely used analytical model that can predict
CME arrival time and speed at a given heliospheric location. It is
based on the assumption that the propagation of CMEs in interplanetary
space is solely under the influence of magnetohydrodynamical drag,
where CME propagation is determined based on CME initial properties
as well as the properties of the ambient solar wind. We present
an upgraded version, the drag-based ensemble model (DBEM), that
covers ensemble modeling to produce a distribution of possible ICME
arrival times and speeds. Multiple runs using uncertainty ranges for
the input values can be performed in almost real-time, within a few
minutes. This allows us to define the most likely ICME arrival times
and speeds, quantify prediction uncertainties, and determine forecast
confidence. The performance of the DBEM is evaluated and compared
to that of ensemble WSA-ENLIL+Cone model (ENLIL) using the same
sample of events. It is found that the mean error is ME = -9.7 hr,
mean absolute error MAE = 14.3 hr, and root mean square error RMSE =
16.7 hr, which is somewhat higher than, but comparable to ENLIL errors
(ME = -6.1 hr, MAE = 12.8 hr and RMSE = 14.4 hr). Overall, DBEM and
ENLIL show a similar performance. Furthermore, we find that in both
models fast CMEs are predicted to arrive earlier than observed, most
likely owing to the physical limitations of models, but possibly also
related to an overestimation of the CME initial speed for fast CMEs.
---------------------------------------------------------
Title: A comparison of solar ALMA observations and model based
predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
2018CEAB...42....1B Altcode:
The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
capable of observing the Sun in the wavelength range from 0.3 mm to 10
mm with an unprecedented spatial, temporal and spectral resolution. The
first aim of the present work is to identify different structures
in the solar atmosphere (quiet Sun, active regions, filaments on the
disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
with full disc solar images from the same day in the Hα line (Cerro
Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
areas, active regions, filaments on the disc, and coronal holes are
identified in the ALMA image. To interpret solar observations with ALMA
it is important to compare the measured and calculated intensities
of various solar structures. So, the second aim of this work is to
calculate the intensity (brightness temperature) for those structures
(quiet Sun, active regions, filaments on the disc, and coronal holes)
for a broad wavelength range (from 0.3 mm to 10 mm), closely related
to that of the ALMA, and to compare the results with available
ALMA observations. Thermal bremsstrahlung is the dominant radiation
mechanism for explanation of the observed phenomena. A procedure for
calculating the brightness temperature for a given wavelength and
model atmosphere, which integrates the radiative transfer equation
for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
active regions appear as bright areas, while filaments on the disc and
coronal holes are not discernible from the quiet Sun background. The
models generally agree with the observed results: Active regions are
bright primarily due to higher densities, filaments can appear bright,
dark or not at all and coronal holes cannot be easily identified.
---------------------------------------------------------
Title: Small-scale dynamcis in a coronal-hole related to microflaring
events
Authors: Krikova, K.; Utz, D.; Veronig, A.; Hofmeister, S.; Temmer,
M.; Gömöry, P.; Holzknecht, L.
2018CEAB...42....8K Altcode:
Using high-resolution solar imagery and spectroscopy from the Hinode
EIS and SDO instruments, we investigate the dynamics within a coronal
hole observed on the 26th September 2017. Further data is given by
full disc images from SDO with the AIA and HMI instruments. EIS
spectra provide us with crucial information about the plasma and
energy flows from the Sun's chromosphere into the corona. Within the
timeframe of the analysed EIS dataset two microflares associated with a
jet-like event were captured, originating inside the coronal hole under
investigation. These two microflare events were analysed in the study at
hand in detail. Such recurring solar transient events could contribute
to the mass and energy input into the solar corona and also to the solar
wind. Our analysis shows that microflare temperatures can reach up to
3 MK with a hot component close to the reconnection site. Moreover an
enhanced density at the microflare region was found. The obtained EIS
ion line ratios suggest a density of up to 2.9 \cdot 10^{10} cm^{-3}.
---------------------------------------------------------
Title: 3D reconstruction and interplanetary expansion of the 2010
April 3^{rd} CME
Authors: Rodari, M.; Dumbović, M.; Temmer, M.; Holzknecht, L.;
Veronig, A.
2018CEAB...42...11R Altcode: 2019arXiv190405611R
We analyse the 2010 April 3^{rd} CME using spacecraft coronagraphic
images at different vantage points (SOHO, STEREO-A and STEREO-B). We
perform a 3D reconstruction of both the flux rope and shock using the
Graduated Cylindrical Shell (GCS) model to calculate CME kinematic
and morphologic parameters (e.g. velocity, acceleration, radius). The
obtained results are fitted with empirical models describing the
expansion of the CME radius in the heliosphere and compared with in
situ measurements from Wind spacecraft: the CME is found to expand
linearly towards Earth. Finally, we relate the event with decreases
in the Galactic Cosmic Ray (GCR) Flux, known as Forbush decreases
(FD), detected by EPHIN instrument onboard SOHO spacecraft. We use the
analytical diffusion-expansion model (ForbMod) to calculate the magnetic
field power law index, obtaining a value of ∼1.6, thus estimating
a starting magnetic field of ∼0.01 G and an axial magnetic flux of
∼5 \cdot 10^{20} Mx at 15.6 R_⊙.
---------------------------------------------------------
Title: Using Forbush Decreases to Derive the Transit Time of ICMEs
Propagating from 1 AU to Mars
Authors: Freiherr von Forstner, Johan L.; Guo, Jingnan;
Wimmer-Schweingruber, Robert F.; Hassler, Donald M.; Temmer, Manuela;
Dumbović, Mateja; Jian, Lan K.; Appel, Jan K.; Čalogović, Jaša.;
Ehresmann, Bent; Heber, Bernd; Lohf, Henning; Posner, Arik; Steigies,
Christian T.; Vršnak, Bojan; Zeitlin, Cary J.
2018JGRA..123...39F Altcode: 2017arXiv171207301V
The propagation of 15 interplanetary coronal mass ejections (ICMEs) from
Earth's orbit (1 AU) to Mars (∼1.5 AU) has been studied with their
propagation speed estimated from both measurements and simulations. The
enhancement of magnetic fields related to ICMEs and their shock fronts
causes the so-called Forbush decrease, which can be detected as a
reduction of galactic cosmic rays measured on ground. We have used
galactic cosmic ray (GCR) data from in situ measurements at Earth, from
both STEREO A and STEREO B as well as GCR measurements by the Radiation
Assessment Detector (RAD) instrument on board Mars Science Laboratory
on the surface of Mars. A set of ICME events has been selected during
the periods when Earth (or STEREO A or STEREO B) and Mars locations
were nearly aligned on the same side of the Sun in the ecliptic plane
(so-called opposition phase). Such lineups allow us to estimate the
ICMEs' transit times between 1 and 1.5 AU by estimating the delay time
of the corresponding Forbush decreases measured at each location. We
investigate the evolution of their propagation speeds before and after
passing Earth's orbit and find that the deceleration of ICMEs due to
their interaction with the ambient solar wind may continue beyond 1
AU. We also find a substantial variance of the speed evolution among
different events revealing the dynamic and diverse nature of eruptive
solar events. Furthermore, the results are compared to simulation data
obtained from two CME propagation models, namely the Drag-Based Model
and ENLIL plus cone model.
---------------------------------------------------------
Title: CME volume calculation from 3D GCS reconstruction
Authors: Holzknecht, L.; Temmer, M.; Dumbović, M.; Wellenzohn, S.;
Krikova, K.; Heinemann, S. G.; Rodari, M.; Vršnak, B.; Veronig, A. M.
2018CEAB...42....3H Altcode: 2019arXiv190411418H
The mass evolution of a coronal mass ejection (CME) is an important
parameter characterizing the drag force acting on a CME as it propagates
through interplanetary space. Spacecraft measure in-situ plasma
densities of CMEs during crossing events, but for investigating the
mass evolution, we also need to know the CME geometry, more specific,
its volume. Having derived the CME volume and mass from remote sensing
data using 3D reconstructed CME geometry, we can calculate the CME
density and compare it with in-situ proton density measurements near
Earth. From that we may draw important conclusions on a possible
mass increase as the CME interacts with the ambient solar wind in the
heliosphere. In this paper we will describe in detail the method for
deriving the CME volume using the graduated cylindrical shell (GCS)
model tep[][see \ref{fig:GCSModel}]{thernisien06,thernisien09}. We show
that, assuming self-similar expansion, one can derive the volume of the
CME from two GCS parameters and that it furthermore can be expressed
as a function of distance.
---------------------------------------------------------
Title: Plasma Diagnostics of Coronal Dimming Regions and Relation
to Characteristic CME Parameters
Authors: Veronig, A.; Vanninathan, K.; Dissauer, K.; Temmer, M.
2017AGUFMSH52B..08V Altcode:
Coronal Mass Ejections (CMEs) are often associated with coronal
dimmings, i.e. transient dark regions in the solar corona that are most
prominently observed at Extreme Ultra-violet (EUV) wavelengths. Coronal
dimmings are thought to be a result of the evacuation of mass related to
the erupting CME structure. Using data from the six EUV channels of the
Atmospheric Imaging Assembly (AIA) onboard SDO, we apply Differential
Emission Measure (DEM) diagnostics, to study the plasma characteristics
of on-disk coronal dimming regions. We analysed in detail seven
coronal dimming events associated with CMEs distributed over a speed
range from 300 to 1250 km/s. We derived the weighted emission measure,
density and temperature as a function of time for both the core and
the secondary dimming regions. In the core dimming regions, the plasma
parameters reached a minimum within about 30 min after the CME onset,
whereas the secondary dimming regions tend to show a more gradual
evolution. For most of the events, the values of these parameters
remained low within the core dimming region for the entire duration
of this study ( 10 hrs after the flare) while the secondary dimming
region showed a gradual increase after 1-2 hrs indicating refilling of
these regions with plasma. The emission measure decrease in the core
dimming region was found to lie in the range from 60-90%, the density
decrease from 35-70% and the temperature decrease from 5-30%. In the
secondary dimming region, the decreases of the plasma parameters derived
are smaller. In addition, we performed a statistical analysis of 76
dimming events during the time range 2010 - 2012, which were observed
on-disk by SDO and close to the limb by at least one of the two STEREO
spacecraft. Characteristic parameters of the early CME dynamics (initial
velocity, peak acceleration, mass and initiation height) are derived
and compared with decisive coronal dimming parameters like the magnetic
flux involved, the area, the area growth rate and the intensity drop
in the dimming region. The findings of our study are discussed with
respect to the different coronal structures involved in the dimming
regions and how they relate to decisive parameters of the CME.
---------------------------------------------------------
Title: Long-lasting solar energetic electron injection during the
26 Dec 2013 widespread SEP event
Authors: Dresing, N.; Klassen, A.; Temmer, M.; Gomez-Herrero, R.;
Heber, B.; Veronig, A.
2017AGUFMSH33C..03D Altcode:
The solar energetic particle (SEP) event on 26 Dec 2013 was detected
all around the Sun by the two STEREO spacecraft and close-to-Earth
observers. While the two STEREOs were separated by 59 degrees and
situated at the front side of the associated large coronal event,
it was a backside-event for Earth. Nevertheless, significant and
long-lasting solar energetic electron anisotropies together with long
rise times were observed at all three viewpoints, pointing to an
extended electron injection. Although the CME-driven shock appears
to account for the SEP event at a first glance a more detailed view
reveals a more complex scenario: A CME-CME interaction takes place
during the very early phase of the SEP event. Furthermore, four hours
after the onset of the event, a second component is measured at all
three viewpoints on top of the first SEP increase, mainly consisting
of high energy particles. We find that the CME-driven shock alone
can hardly account for the observed SEP event in total but a trapping
scenario together with ongoing particle acceleration is more likely.
---------------------------------------------------------
Title: Multi-spacecraft observations of ICMEs propagating beyond
Earth orbit during MSL/RAD flight and surface phases
Authors: von Forstner, J.; Guo, J.; Wimmer-Schweingruber, R. F.;
Hassler, D.; Temmer, M.; Vrsnak, B.; Čalogović, J.; Dumbovic, M.;
Lohf, H.; Appel, J. K.; Heber, B.; Steigies, C. T.; Zeitlin, C.;
Ehresmann, B.; Jian, L. K.; Boehm, E.; Boettcher, S. I.; Burmeister,
S.; Martin-Garcia, C.; Brinza, D. E.; Posner, A.; Reitz, G.; Matthiae,
D.; Rafkin, S. C.; weigle, G., II; Cucinotta, F.
2017AGUFMSH53A2543V Altcode:
The propagation of interplanetary coronal mass ejections (ICMEs)
between Earth's orbit (1 AU) and Mars ( 1.5 AU) has been studied
with their propagation speed estimated from both measurements and
simulations. The enhancement of the magnetic fields related to ICMEs
and their shock fronts cause so-called Forbush decreases, which can
be detected as a reduction of galactic cosmic rays measured on-ground
or on a spacecraft. We have used galactic cosmic ray (GCR) data from
in-situ measurements at Earth, from both STEREO A and B as well
as the GCR measurement by the Radiation Assessment Detector (RAD)
instrument onboard Mars Science Laboratory (MSL) on the surface of
Mars as well as during its flight to Mars in 2011-2012. A set of ICME
events has been selected during the periods when Earth (or STEREO A
or B) and MSL locations were nearly aligned on the same side of the
Sun in the ecliptic plane (so-called opposition phase). Such lineups
allow us to estimate the ICMEs' transit times between 1 AU and the
MSL location by estimating the delay time of the corresponding Forbush
decreases measured at each location. We investigate the evolution of
their propagation speeds after passing Earth's orbit and find that the
deceleration of ICMEs due to their interaction with the ambient solar
wind continues beyond 1 AU. The results are compared to simulation data
obtained from two CME propagation models, namely the Drag-Based Model
(DBM) and the WSA-ENLIL plus cone model.
---------------------------------------------------------
Title: The Analytical Diffusion-Expansion Model for Forbush Decreases
Caused by Flux Ropes
Authors: Dumbovic, M.; Temmer, M.
2017AGUFMSH13C2492D Altcode:
Identification and tracking of interplanetary coronal mass ejections
(ICMEs) throughout the heliosphere is a growingly important aspect
of space weather research. One of the "signatures" of ICME passage
is the corresponding Forbush decrease (FD), a short term decrease
in the galactic cosmic ray flux. These depressions are observed at
the surface of the Earth for over 50 years, by several spacecraft in
interplanetary space in the past couple of decades, and recently also
on Mars' surface with Curiosity rover. In order to use FDs as ICME
signatures efficiently, it is important to model ICME interaction
with energetic particles by taking into account ICME evolution
and constraining the model with observational data. We present an
analytical diffusion-expansion FD model ForbMod which is based on
the widely used approach of the initially empty, closed magnetic
structure (i.e. flux rope) which fills up slowly with particles by
perpendicular diffusion. The model is restricted to explain only
the depression caused by the magnetic structure of the ICME and not
of the associated shock. We use remote CME observations and a 3D
reconstruction method (the Graduated Cylindrical Shell method) to
constrain initial and boundary conditions of the FD model and take
into account CME evolutionary properties by incorporating flux rope
expansion. Several options of flux rope expansion are regarded as
the competing mechanism to diffusion which can lead to different FD
characteristics. This project has received funding from the European
Union's Horizon 2020 research and innovation programme under the Marie
Skłodowska-Curie grant agreement No 745782.
---------------------------------------------------------
Title: Presentation of the project "An investigation of the early
stages of solar eruptions - from remote observations to energetic
particles"
Authors: Kozarev, Kamen; Veronig, Astrid; Duchlev, Peter; Koleva,
Kostadinka; Dechev, Momchil; Miteva, Rositsa; Temmer, Manuela;
Dissauer, Karin
2017ses..conf...63K Altcode:
Coronal mass ejections (CMEs), one of the most energetic manifestations
of solar activity, are complex events, which combine multiple related
phenomena occurring on the solar surface, in the extended solar
atmosphere (corona), as well as in interplanetary space. We present
here an outline of a new collaborative project between scientists
from the Bulgarian Academy of Sciences (BAS), Bulgaria and the
University of Graz, Austria. The goal of the this research project
is to answer the following questions: 1) What are the properties of
erupting filaments, CMEs, and CME-driven shock waves near the Sun, and
of associated solar energetic particle (SEP) fluxes in interplanetary
space? 2) How are these properties related to the coronal acceleration
of SEPs? To achieve the scientific goals of this project, we will use
remote solar observations with high spatial and temporal resolution to
characterize the early stages of coronal eruption events in a systematic
way - studying the pre-eruptive behavior of filaments and flares during
energy build-up, the kinematics and morphology of CMEs and compressive
shock waves, and the signatures of high energy non-thermal particles
in both remote and in situ observations.
---------------------------------------------------------
Title: The Causes of Quasi-homologous CMEs
Authors: Liu, Lijuan; Wang, Yuming; Liu, Rui; Zhou, Zhenjun; Temmer,
M.; Thalmann, J. K.; Liu, Jiajia; Liu, Kai; Shen, Chenglong; Zhang,
Quanhao; Veronig, A. M.
2017ApJ...844..141L Altcode: 2017arXiv170608878L
In this paper, we identified the magnetic source locations of 142
quasi-homologous (QH) coronal mass ejections (CMEs), of which 121
are from solar cycle (SC) 23 and 21 from SC 24. Among those CMEs, 63%
originated from the same source location as their predecessor (defined
as S-type), while 37% originated from a different location within the
same active region as their predecessor (defined as D-type). Their
distinctly different waiting time distributions, peaking around 7.5 and
1.5 hr for S- and D-type CMEs, suggest that they might involve different
physical mechanisms with different characteristic timescales. Through
detailed analysis based on nonlinear force-free coronal magnetic field
modeling of two exemplary cases, we propose that the S-type QH CMES
might involve a recurring energy release process from the same source
location (by magnetic free energy replenishment), whereas the D-type
QH CMEs can happen when a flux tube system is disturbed by a nearby CME.
---------------------------------------------------------
Title: Erratum: “The Confined X-class Flares of Solar Active Region
2192” (<A href="http://doi.org/10.1088/2041-8205/801/2/L23">2015,
ApJL, 801, L23</A>)
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
2017ApJ...844L..27T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Flare-CME Characteristics from Sun to Earth Combining
Remote-Sensing Image Data with In Situ Measurements Supported
by Modeling
Authors: Temmer, Manuela; Thalmann, Julia K.; Dissauer, Karin;
Veronig, Astrid M.; Tschernitz, Johannes; Hinterreiter, Jürgen;
Rodriguez, Luciano
2017SoPh..292...93T Altcode: 2017arXiv170300694T
We analyze the well-observed flare and coronal mass ejection (CME)
from 1 October 2011 (SOL2011-10-01T09:18) covering the complete chain of
effects - from Sun to Earth - to better understand the dynamic evolution
of the CME and its embedded magnetic field. We study in detail the
solar surface and atmosphere associated with the flare and CME using the
Solar Dynamics Observatory (SDO) and ground-based instruments. We also
track the CME signature off-limb with combined extreme ultraviolet
(EUV) and white-light data from the Solar Terrestrial Relations
Observatory (STEREO). By applying the graduated cylindrical shell
(GCS) reconstruction method and total mass to stereoscopic STEREO-SOHO
(Solar and Heliospheric Observatory) coronagraph data, we track
the temporal and spatial evolution of the CME in the interplanetary
space and derive its geometry and 3D mass. We combine the GCS and
Lundquist model results to derive the axial flux and helicity of
the magnetic cloud (MC) from in situ measurements from Wind. This is
compared to nonlinear force-free (NLFF) model results, as well as to
the reconnected magnetic flux derived from the flare ribbons (flare
reconnection flux) and the magnetic flux encompassed by the associated
dimming (dimming flux). We find that magnetic reconnection processes
were already ongoing before the start of the impulsive flare phase,
adding magnetic flux to the flux rope before its final eruption. The
dimming flux increases by more than 25% after the end of the flare,
indicating that magnetic flux is still added to the flux rope after
eruption. Hence, the derived flare reconnection flux is most probably a
lower limit for estimating the magnetic flux within the flux rope. We
find that the magnetic helicity and axial magnetic flux are lower in
the interplanetary space by ∼ 50% and 75%, respectively, possibly
indicating an erosion process. A CME mass increase of 10% is observed
over a range of ∼4 -20 R<SUB>⊙</SUB>. The temporal evolution of
the CME-associated core-dimming regions supports the scenario that
fast outflows might supply additional mass to the rear part of the CME.
---------------------------------------------------------
Title: Sunward-propagating Solar Energetic Electrons inside Multiple
Interplanetary Flux Ropes
Authors: Gómez-Herrero, Raúl; Dresing, Nina; Klassen, Andreas;
Heber, Bernd; Temmer, Manuela; Veronig, Astrid; Bučík, Radoslav;
Hidalgo, Miguel A.; Carcaboso, Fernando; Blanco, Juan J.; Lario, David
2017ApJ...840...85G Altcode:
On 2013 December 2 and 3, the SEPT and STE instruments on board
STEREO-A observed two solar energetic electron events with unusual
sunward-directed fluxes. Both events occurred during a time
interval showing typical signatures of interplanetary coronal mass
ejections (ICMEs). The electron timing and anisotropies, combined with
extreme-ultraviolet solar imaging and radio wave spectral observations,
are used to confirm the solar origin and the injection times of the
energetic electrons. The solar source of the ICME is investigated using
remote-sensing observations and a three-dimensional reconstruction
technique. In situ plasma and magnetic field data combined with
energetic electron observations and a flux-rope model are used to
determine the ICME magnetic topology and the interplanetary electron
propagation path from the Sun to 1 au. Two consecutive flux ropes
crossed the STEREO-A location and each electron event occurred inside
a different flux rope. In both cases, the electrons traveled from the
solar source to 1 au along the longest legs of the flux ropes still
connected to the Sun. During the December 2 event, energetic electrons
propagated along the magnetic field, while during the December 3 event
they were propagating against the field. As found by previous studies,
the energetic electron propagation times are consistent with a low
number of field line rotations N < 5 of the flux rope between the
Sun and 1 au. The flux rope model used in this work suggests an even
lower number of rotations.
---------------------------------------------------------
Title: The February 15 2011 CME-CME interaction and possibly
associated radio emission
Authors: Magdalenic, Jasmina; Temmer, Manuela; Krupar, Vratislav;
Marque, Christophe; Veronig, Astrid; Eastwood, Jonathan
2017EGUGA..19.9850M Altcode:
On February 15, 2011 a particular, continuum-like radio emission was
observed by STEREO WAVES and WIND WAVES spacecraft. The radio event
appeared to be associated with the complex interaction of two coronal
mass ejections (CMEs) successively launched (February 14 and February
15) from the same active region. Although the CME-CME interaction was
widely studied (e.g. Temmer et al., 2014, Maricic et al., 2014, Mishra
& Srivastava, 2014) none of the analyses confirmed an association
with the continuum-like radio emission. The usual method of establishing
temporal coincidence of radio continuum and a CME-CME interaction is not
applicable in this event due to a complex and long-lasting interaction
of the CMEs. Therefore, we performed radio triangulation studies (see
also Magdalenic et al., 2014) which provided us with the 3D source
positions of the radio emission. Comparison of the positions of radio
sources and the reconstructed positions of the interacting CMEs, shows
that the source position of the continuum-like radio emission is about
0.5 AU away from the interacting CMEs. We can therefore concluded that,
in this event, the continuum-like emission is not the radio signature
of the CME-CME interaction.
---------------------------------------------------------
Title: The Interaction of Successive Coronal Mass Ejections: A Review
Authors: Lugaz, Noé; Temmer, Manuela; Wang, Yuming; Farrugia,
Charles J.
2017SoPh..292...64L Altcode: 2016arXiv161202398L
We present a review of the different aspects associated with the
interaction of successive coronal mass ejections (CMEs) in the corona
and inner heliosphere, focusing on the initiation of series of CMEs,
their interaction in the heliosphere, the particle acceleration
associated with successive CMEs, and the effect of compound events
on Earth's magnetosphere. The two main mechanisms resulting in the
eruption of series of CMEs are sympathetic eruptions, when one eruption
triggers another, and homologous eruptions, when a series of similar
eruptions originates from one active region. CME - CME interaction may
also be associated with two unrelated eruptions. The interaction of
successive CMEs has been observed remotely in coronagraphs (with the
Large Angle and Spectrometric Coronagraph Experiment - LASCO - since
the early 2000s) and heliospheric imagers (since the late 2000s), and
inferred from in situ measurements, starting with early measurements
in the 1970s. The interaction of two or more CMEs is associated with
complex phenomena, including magnetic reconnection, momentum exchange,
the propagation of a fast magnetosonic shock through a magnetic ejecta,
and changes in the CME expansion. The presence of a preceding CME a
few hours before a fast eruption has been found to be connected with
higher fluxes of solar energetic particles (SEPs), while CME - CME
interaction occurring in the corona is often associated with unusual
radio bursts, indicating electron acceleration. Higher suprathermal
population, enhanced turbulence and wave activity, stronger shocks,
and shock - shock or shock - CME interaction have been proposed as
potential physical mechanisms to explain the observed associated SEP
events. When measured in situ, CME - CME interaction may be associated
with relatively well organized multiple-magnetic cloud events, instances
of shocks propagating through a previous magnetic ejecta or more complex
ejecta, when the characteristics of the individual eruptions cannot
be easily distinguished. CME - CME interaction is associated with some
of the most intense recorded geomagnetic storms. The compression of a
CME by another and the propagation of a shock inside a magnetic ejecta
can lead to extreme values of the southward magnetic field component,
sometimes associated with high values of the dynamic pressure. This can
result in intense geomagnetic storms, but can also trigger substorms and
large earthward motions of the magnetopause, potentially associated with
changes in the outer radiation belts. Future in situ measurements in
the inner heliosphere by Solar Probe+ and Solar Orbiter may shed light
on the evolution of CMEs as they interact, by providing opportunities
for conjunction and evolutionary studies.
---------------------------------------------------------
Title: Understanding CMEs using plasma diagnostics of the related
dimmings
Authors: Vanninathan, Kamalam; Veronig, Astrid; Gomory, Peter;
Dissauer, Karin; Temmer, Manuela; Hannah, Iain; Kontar, Eduard
2017EGUGA..19.1571V Altcode:
Coronal Mass Ejections (CMEs) are often associated with dimmings that
are well observed in Extreme Ultra-violet (EUV) wavelengths. Such
dimmings are suggested to represent the evacuation of mass that is
carried out by CMEs and are a unique and indirect means to study CME
properties. While Earth-directed CMEs (on-disk CMEs) are difficult to
observe due to the bright background solar disk and projection effects,
their corresponding dimmings are clearly discernible and ideally suited
for analysis. Using data from the 6 EUV channels of Solar Dynamics
Observatory/Atmospheric Imaging Assembly for Differential Emission
Measure (DEM) diagnostics, we determine the plasma characteristics of
the dimming region. These data are well suited for this kind of study
due to the good temperature ranges covered by the multiple passbands
of the instrument. We analyse 7 on-disk and 5 off-limb events and
derive the weighted density and temperature as a function of time,
from the DEMs. From such an analysis we differentiate 2 types of dimming
regions: core and secondary dimmings. Core dimmings often occur in pairs
lying on either sides of the active region and in opposite polarity
regions while the secondary dimming is more extended. In both the
regions the derived plasma parameters reach a minimum within 30-60
min after the flare. For each event the core dimming region shows
a higher decrease in density and temperature than the corresponding
secondary dimming regions. The values of these parameters remains low
within the core dimming region for the entire duration of this study
( 10 hrs after the flare) while the secondary dimming region starts to
show a gradual increase after 1-2 hrs. We also use spectroscopic data
from Hinode/Extreme-Ultraviolet Imaging Spectrometer to differentiate
core and secondary dimming regions. We find that the Fe XIII 202 Å
line shows double component profiles within the core dimming region
with strong blueshifts of 100 km/s while the secondary dimming region
has weak upflows of 10 km/s. We conclude that the core dimming region
corresponds to footpoints of the erupting flux rope from where there
is continuous strong upflowing plasma for at least 10 hrs after the
flare, while the secondary dimming region begins to refill within 1-2
hrs. These measurements can be used to deduce information about the
mass of on-disk CMEs where white light measurements can fail. We also
confirm that the dimmings are mainly caused by density decrease and
not temperature changes. DEM analysis is a strong tool to decipher
CME properties from dimming regions.
---------------------------------------------------------
Title: Statistical analysis on how CME and SIR/CIR events effect
the geomagnetic activity and the Earth's thermosphere
Authors: Krauss, Sandro; Temmer, Manuela; Edl, Martina; Veronig, Astrid
2017EGUGA..1915251K Altcode:
In order to estimate the impact of different types of solar wind
on the geomagnetic activity and the neutral density in the Earth's
thermosphere, we present a comprehensive statistical analysis based on
interplanetary coronal mass ejections (ICME) covering the time range
from July 2003 - 2016 and stream interaction as well as corotating
interaction regions (SIR/CIR) from July 2003 - December 2009. In
general, geomagnetic storms induced by CIR are characterized by lower
energy input compared to ICME induced storms but a significantly longer
duration time due to a long-term negative Bz component in the magnetic
cloud region. Regarding the time of occurrence of ICME events, we rely
on the catalogue maintained by Richardson and Cane. For the period of
investigation more than 250 Earth-directed CME events are listed. All
of them have been measured in situ by plasma and field instruments on
board the ACE spacecraft. The arrival times of SIRs/CIRs are taken from
the catalogue maintained by Lan Jian based on ACE and Wind in-situ
measurements. From this list, we extracted 98 SIR/CIR events, from
which the minimum Bz component is determined within a time window of
36 hours starting at the arrival of the SIR/CIR (same procedure as for
ICMEs). Accordingly, the peak in Earth's neutral density is determined
in the same time window. The densities itself are estimated by using
accelerometer measurements collected by the Gravity Recovery And Climate
Experiment (GRACE) satellites and subsequently related to various
geomagnetic indices (e.g. SYM-H, Polar cap, a-indices, ...) as well
as characteristic CME parameters like the impact speed, the southward
magnetic field strength Bz and resultant derivatives. We find high
correlations (cc=0.9) between the CME characteristic (except the impact
speed) and the thermospheric density enhancements as well as with most
of the geomagnetic indices. However, considering only weaker ICME events
(Bz up to -20nT) a lower correlation must be conceded. The same holds
true for SIR/CIR events, as both cover compressed sheath regions with
turbulent magnetic field. The absolute density increases for SIR/CIR
induced storms is in the order of 1.7E-12kg/m3 for Bz values ranging
from -4 to -19nT, with a related correlation coefficient of -0.41.
---------------------------------------------------------
Title: Quantification of disturbance periods of solar wind speed in
interplanetary space due to coronal mass ejections
Authors: Temmer, Manuela; Reiss, Martin A.; Nikolic, Ljubomir;
Hofmeister, Stefan J.; Veronig, Astrid M.
2017EGUGA..19.1940T Altcode:
Interplanetary space is characteristically structured mainly by
high-speed solar wind streams emanating from coronal holes and transient
disturbances such as coronal mass ejections (CMEs). While high-speed
solar wind streams pose a continuous outflow, CMEs abruptly disrupt
the rather steady structure causing large deviations from the quiet
solar wind conditions. We present a quantification of the duration of
disturbed conditions (preconditioning) for interplanetary space caused
by CMEs by investigating the plasma speed component of the solar wind
and the impact of in situ detected CMEs (ICMEs), compared to different
background solar wind models (ESWF, WSA, persistence model) for the
time range 2011-2015. We obtain for periods within an ICME interval
an increase of 18-32% above the expected quiet Sun background and for
the period of 2 days after the ICME an increase of 9-24%. The total
duration of enhanced deviations is about 3 and up to 6 days after the
ICME start, which is much longer than the average duration of an ICME
disturbance itself (about 1.3 days), concluding that interplanetary
space needs about 2-5 days to recover from the impact of ICMEs. The
obtained results have strong implications for studying CME propagation
behavior and also for space weather forecasting.
---------------------------------------------------------
Title: Testing ElEvoHI on a multi-point in situ detected Coronal
Mass Ejection
Authors: Amerstorfer, Tanja; Möstl, Christian; Hess, Phillip; Mays,
M. Leila; Temmer, Manuela
2017EGUGA..19.7675A Altcode:
The Solar TErrestrial RElations Observatory (STEREO) has provided us
a deep insight into the interplanetary propagation of coronal mass
ejections (CMEs). Especially the wide-angle heliospheric imagers (HI)
enabled the development of a multitude of methods for analyzing the
evolution of CMEs through interplanetary (IP) space. Methods able
to forecast arrival times and speeds at Earth (or other targets)
use the advantage of following a CME's path of propagation up to 1
AU. However, these methods were not able to reduce today's errors
in arrival time forecasts to less than ±6 hours, arrival speeds are
mostly overestimated by some 100 km s-1. One reason for that is the
assumption of constant propagation speed, which is clearly incorrect
for most CMEs—especially for those being faster than the ambient
solar wind. ElEvoHI, the Ellipse Evolution model (ElEvo) based on HI
observations, is a new prediction tool, which uses the benefits of
different methods and observations. It provides the possibility to
adjust the CME frontal shape (angular width, ellipse aspect ratio)
and the direction of motion for each CME event individually. This
information can be gained from Graduated Cylindrical Shell (GCS)
flux-rope fitting within coronagraph images. Using the Ellipse
Conversion (ElCon) method, the observed HI elongation angle is
converted into a unit of distance, which reveals the kinematics of the
event. After fitting the time-distance profile of the CME using the
drag-based equation of motion, where real-time in situ solar wind speed
from 1 AU is used as additional input, we receive all input parameters
needed to run a forecast using the ElEvo model and to predict arrival
times and speeds at any target of interest in IP space. Here, we present
a test on a slow CME event of 3 November 2010, in situ detected by
the lined-up spacecraft MESSENGER and STEREO Behind. We gain the shape
of the CME front from a cut of the 3D GCS CME shape with the ecliptic
plane, resulting in an almost ideal ElEvoHI forecast of arrival time
and speed at 1 AU.
---------------------------------------------------------
Title: Flare-CME characteristics from Sun to Earth combining
observations and modeling
Authors: Temmer, Manuela; Thalmann, Julia K.; Dissauer, Karin;
Veronig, Astrid M.; Tschernitz, Johannes; Hinterreiter, Jürgen;
Rodriguez, Luciano
2017EGUGA..19.1942T Altcode:
We analyze the well observed flare-CME event from October 1, 2011
(SOL2011-10-01T09:18) covering the complete chain of action - from
Sun to Earth - for a better understanding of the dynamic evolution
of the CME and its embedded magnetic field. We study in detail the
solar surface and atmosphere from SDO and ground-based instruments
associated to the flare-CME and also track the CME signature offlimb
from combined EUV and white-light data with STEREO. By applying 3D
reconstruction techniques (GCS, total mass) to stereoscopic STEREO-SoHO
coronagraph data, we track the temporal and spatial evolution of the
CME in interplanetary space and derive its geometry and 3D-mass. We
combine the GCS and Lundquist model results to derive the axial flux
and helicity of the MC from in situ measurements (Wind). This is
compared to nonlinear force-free (NLFF) model results as well as to
the reconnected magnetic flux derived from the flare ribbons (flare
reconnection flux) and the magnetic flux encompassed by the associated
dimming (dimming flux). We find that magnetic reconnection processes
were already ongoing before the start of the impulsive flare phase,
adding magnetic flux to the flux rope before its final eruption. The
dimming flux increases by more than 25% after the end of the flare,
indicating that magnetic flux is still added to the flux rope after
eruption. Hence, the derived flare reconnection flux is most probably a
lower limit for estimating the magnetic flux within the flux rope. We
obtain that the magnetic helicity and axial magnetic flux are reduced
in interplanetary space by ∼50% and 75%, respectively, possibly
indicating to an erosion process. A mass increase of 10% for the CME
is observed over the distance range from about 4-20 Rs. The temporal
evolution of the CME associated core dimming regions supports the
scenario that fast outflows might supply additional mass to the rear
part of the CME.
---------------------------------------------------------
Title: Preconditioning of Interplanetary Space Due to Transient
CME Disturbances
Authors: Temmer, M.; Reiss, M. A.; Nikolic, L.; Hofmeister, S. J.;
Veronig, A. M.
2017ApJ...835..141T Altcode: 2016arXiv161206080T
Interplanetary space is characteristically structured mainly by
high-speed solar wind streams emanating from coronal holes and transient
disturbances such as coronal mass ejections (CMEs). While high-speed
solar wind streams pose a continuous outflow, CMEs abruptly disrupt
the rather steady structure, causing large deviations from the quiet
solar wind conditions. For the first time, we give a quantification
of the duration of disturbed conditions (preconditioning) for
interplanetary space caused by CMEs. To this aim, we investigate
the plasma speed component of the solar wind and the impact of in
situ detected interplanetary CMEs (ICMEs), compared to different
background solar wind models (ESWF, WSA, persistence model) for the
time range 2011-2015. We quantify in terms of standard error measures
the deviations between modeled background solar wind speed and observed
solar wind speed. Using the mean absolute error, we obtain an average
deviation for quiet solar activity within a range of 75.1-83.1 km
s<SUP>-1</SUP>. Compared to this baseline level, periods within
the ICME interval showed an increase of 18%-32% above the expected
background, and the period of two days after the ICME displayed an
increase of 9%-24%. We obtain a total duration of enhanced deviations
over about three and up to six days after the ICME start, which is
much longer than the average duration of an ICME disturbance itself
(∼1.3 days), concluding that interplanetary space needs ∼2-5 days
to recover from the impact of ICMEs. The obtained results have strong
implications for studying CME propagation behavior and also for space
weather forecasting.
---------------------------------------------------------
Title: Characteristics of Low-latitude Coronal Holes near the Maximum
of Solar Cycle 24
Authors: Hofmeister, Stefan J.; Veronig, Astrid; Reiss, Martin A.;
Temmer, Manuela; Vennerstrom, Susanne; Vršnak, Bojan; Heber, Bernd
2017ApJ...835..268H Altcode: 2017arXiv170202050H
We investigate the statistics of 288 low-latitude coronal holes
extracted from SDO/AIA-193 filtergrams over the time range of
2011 January 01-2013 December 31. We analyze the distribution of
characteristic coronal hole properties, such as the areas, mean AIA-193
intensities, and mean magnetic field densities, the local distribution
of the SDO/AIA-193 intensity and the magnetic field within the coronal
holes, and the distribution of magnetic flux tubes in coronal holes. We
find that the mean magnetic field density of all coronal holes under
study is 3.0 ± 1.6 G, and the percentaged unbalanced magnetic flux
is 49 ± 16%. The mean magnetic field density, the mean unsigned
magnetic field density, and the percentaged unbalanced magnetic flux of
coronal holes depend strongly pairwise on each other, with correlation
coefficients cc > 0.92. Furthermore, we find that the unbalanced
magnetic flux of the coronal holes is predominantly concentrated in
magnetic flux tubes: 38% (81%) of the unbalanced magnetic flux of
coronal holes arises from only 1% (10%) of the coronal hole area,
clustered in magnetic flux tubes with field strengths >50 G (10
G). The average magnetic field density and the unbalanced magnetic
flux derived from the magnetic flux tubes correlate with the mean
magnetic field density and the unbalanced magnetic flux of the overall
coronal hole (cc > 0.93). These findings give evidence that the
overall magnetic characteristics of coronal holes are governed by the
characteristics of the magnetic flux tubes.
---------------------------------------------------------
Title: 70 Years of Sunspot Observations at the Kanzelhöhe
Observatory: Systematic Study of Parameters Affecting the Derivation
of the Relative Sunspot Number
Authors: Pötzi, Werner; Veronig, Astrid M.; Temmer, Manuela;
Baumgartner, Dietmar J.; Freislich, Heinrich; Strutzmann, Heinz
2016SoPh..291.3103P Altcode: 2016SoPh..tmp...43P; 2015arXiv151200270P
The Kanzelhöhe Observatory (KSO) was founded during World War II by
the Deutsche Luftwaffe (German Airforce) as one station of a network
of observatories that were set up to provide information on solar
activity in order to better assess the actual conditions of the Earth's
ionosphere in terms of radio-wave propagation. Solar observations
began in 1943 with photographs of the photosphere and drawings of
sunspots, plage regions, and faculae, as well as patrol observations
of the solar corona. At the beginning, all data were sent to Freiburg
(Germany). After WW II, international cooperation was established and
the data were sent to Zurich, Paris, Moscow, and Greenwich. Relative
sunspot numbers have been derived since 1944. The agreement between
relative sunspot numbers derived at KSO and the new International
Sunspot Number (ISN) (SILSO World Data Center in International Sunspot
Number Monthly Bulletin and online catalogue, 1945 - 2015) lies within
≈10 % . However, revisiting the historical data, we also find periods
with larger deviations. The reasons for the deviations were twofold: On
the one hand, a major instrumental change took place during which the
instrument was relocated and modified. On the other hand, a period of
frequent replacements of personnel caused significant deviations; this
clearly shows the importance of experienced observers. In the long term,
the instrumental improvements led to better image quality. Additionally,
we find a long-term trend towards better seeing conditions that began
in 2000.
---------------------------------------------------------
Title: Kinematical properties of coronal mass ejections
Authors: Temmer, M.
2016AN....337.1010T Altcode: 2016arXiv160301398T
Coronal mass ejections (CMEs) are the most dynamic phenomena in our
solar system. They abruptly disrupt the continuous outflow of solar
wind by expelling huge clouds of magnetized plasma into interplanetary
space with velocities enabling to cross the Sun-Earth distance within
a few days. Earth-directed CMEs may cause severe geomagnetic storms
when their embedded magnetic fields and the shocks ahead compress
and reconnect with the Earth's magnetic field. The transit times and
impacts in detail depend on the initial CME velocity, size, and mass,
as well as on the conditions and coupling processes with the ambient
solar wind flow in interplanetary space. The observed CME parameters
may be severely affected by projection effects and the constant changing
environmental conditions are hard to derive. This makes it difficult to
fully understand the physics behind CME evolution, preventing to do a
reliable forecast of Earth-directed events. This short review focusing
on observational data, shows recent methods which were developed to
derive the CME kinematical profile for the entire Sun-Earth distance
range as well as studies which were performed to shed light on the
physical processes that CMEs encounter when propagating from Sun
to Earth.
---------------------------------------------------------
Title: Projection Effects in Coronal Dimmings and Associated EUV
Wave Event
Authors: Dissauer, K.; Temmer, M.; Veronig, A. M.; Vanninathan, K.;
Magdalenić, J.
2016ApJ...830...92D Altcode: 2016arXiv160705961D
We investigate the high-speed (v > 1000 km s<SUP>-1</SUP>)
extreme-ultraviolet (EUV) wave associated with an X1.2 flare and coronal
mass ejection (CME) from NOAA active region 11283 on 2011 September
6 (SOL2011-09-06T22:12). This EUV wave features peculiar on-disk
signatures in particular, we observe an intermittent “disappearance”
of the front for 120 s in Solar Dynamics Observatory (SDO)/AIA 171,
193, 211 Å data, whereas the 335 Å filter, sensitive to hotter
plasmas (T ∼ 2.5 MK), shows a continuous evolution of the wave
front. The eruption was also accompanied by localized coronal dimming
regions. We exploit the multi-point quadrature position of SDO and
STEREO-A, to make a thorough analysis of the EUV wave evolution, with
respect to its kinematics and amplitude evolution and reconstruct
the SDO line-of-sight (LOS) direction of the identified coronal
dimming regions in STEREO-A. We show that the observed intensities
of the dimming regions in SDO/AIA depend on the structures that are
lying along their LOS and are the combination of their individual
intensities, e.g., the expanding CME body, the enhanced EUV wave,
and the CME front. In this context, we conclude that the intermittent
disappearance of the EUV wave in the AIA 171, 193, and 211 Å filters,
which are channels sensitive to plasma with temperatures below ∼2
MK is also caused by such LOS integration effects. These observations
clearly demonstrate that single-view image data provide us with limited
insight to correctly interpret coronal features.
---------------------------------------------------------
Title: A small mission concept to the Sun-Earth Lagrangian L5 point
for innovative solar, heliospheric and space weather science
Authors: Lavraud, B.; Liu, Y.; Segura, K.; He, J.; Qin, G.; Temmer,
M.; Vial, J. -C.; Xiong, M.; Davies, J. A.; Rouillard, A. P.; Pinto,
R.; Auchère, F.; Harrison, R. A.; Eyles, C.; Gan, W.; Lamy, P.;
Xia, L.; Eastwood, J. P.; Kong, L.; Wang, J.; Wimmer-Schweingruber,
R. F.; Zhang, S.; Zong, Q.; Soucek, J.; An, J.; Prech, L.; Zhang,
A.; Rochus, P.; Bothmer, V.; Janvier, M.; Maksimovic, M.; Escoubet,
C. P.; Kilpua, E. K. J.; Tappin, J.; Vainio, R.; Poedts, S.; Dunlop,
M. W.; Savani, N.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard, T.;
DeForest, C.; Webb, D.; Lugaz, N.; Fuselier, S. A.; Dalmasse, K.;
Tallineau, J.; Vranken, D.; Fernández, J. G.
2016JASTP.146..171L Altcode:
We present a concept for a small mission to the Sun-Earth Lagrangian L5
point for innovative solar, heliospheric and space weather science. The
proposed INvestigation of Solar-Terrestrial Activity aNd Transients
(INSTANT) mission is designed to identify how solar coronal magnetic
fields drive eruptions, mass transport and particle acceleration that
impact the Earth and the heliosphere. INSTANT is the first mission
designed to (1) obtain measurements of coronal magnetic fields from
space and (2) determine coronal mass ejection (CME) kinematics with
unparalleled accuracy. Thanks to innovative instrumentation at a vantage
point that provides the most suitable perspective view of the Sun-Earth
system, INSTANT would uniquely track the whole chain of fundamental
processes driving space weather at Earth. We present the science
requirements, payload and mission profile that fulfill ambitious science
objectives within small mission programmatic boundary conditions.
---------------------------------------------------------
Title: Exceptions to the rule: the X-flares of AR 2192 Lacking
Coronal Mass Ejections
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
2016ASPC..504..203T Altcode:
NOAA Active region (AR) 2192, that was present on the Sun in October
2014, was the largest region which occurred since November 1990
(see Figure 1). The huge size accompanied by a very high activity
level, was quite unexpected as it appeared during the unusually weak
solar cycle 24. Nevertheless, the AR turned out to be one of the most
prolific flaring ARs of cycle 24. It produced in total 6 X, 29 M, 79
C flares during its disk passage from October 18-29, 2014 (see Figure
2). Surprisingly, all flares greater than GOES class M5 and X were
confined, i.e. had no coronal mass ejections (CME) associated. All
the flare events had some obvious similarity in morphology, as they
were located in the core of the AR and revealed only minor separation
motion away from the neutral line but a large initial separation of
the conjugate flare ribbons. In the paper by Thalmann et al. (2015)
we describe the series of flares and give details about the confined
X1.6 flare event from October 22, 2014 as well as the single eruptive
M4.0 flare event from October 24, 2014. The study of the X1.6 flare
revealed a large initial separation of flare ribbons together with
recurrent flare brightenings, which were related to two episodes of
enhanced hard X-ray emission as derived from RHESSI observations. This
suggests that magnetic field structures connected to specific regions
were repeatedly involved in the process of reconnection and energy
release. Opposite to the central location of the sequence of confined
events within the AR, a single eruptive (M4.0) event occurred on
the outskirt of the AR in the vicinity of open magnetic fields. Our
investigations revealed a predominantly north-south oriented magnetic
system of arcade fields overlying the AR that could have preserved
the magnetic arcade to erupt, and consequently kept the energy release
trapped in a localized volume of magnetic field high up in the corona
(as supported by the absence of a lateral motion of the flare ribbons
and the recurrent brightenings within them). We conclude that the
background magnetic field configuration is an essential parameter
for deriving the "eruptiveness" of flare events. Sun et al. (2015)
supports this conclusion and derived for this AR a quite slow
decay of the strength of the overlying magnetic field (decay index;
see Török & Kliem 2005). Interestingly, our magnetic field
modellings revealed no flux rope inherent to the AR, indicating that
further investigations are needed. In a recent paper by Veronig $
Polanec (2015), who investigated in more detail the X-flares using
also ground-based observations in Hα from Kanzelhöhe Observatory
(Pötzi et al. 2015), it was shown that such confined events could be
explained by the emerging-flux model, where newly emerging small flux
tubes reconnect with pre-existing large coronal loops.
---------------------------------------------------------
Title: Coimbra Solar Physics Meeting: Ground-based Solar Observations
in the Space Instrumentation Era
Authors: Dorotovic, I.; Fischer, C. E.; Temmer, M.
2016ASPC..504.....D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Projection effects in coronal dimmings and associated EUV
wave event
Authors: Dissauer, Karin; Temmer, Manuela; Veronig, Astrid;
Vanninathan, Kamalam; Magdalenic, Jasmina
2016EGUGA..18.6857D Altcode:
We investigate the high-speed (v > 1000 km s-1) extreme-ultraviolet
(EUV) wave associated with an X1.2 flare and coronal mass ejection (CME)
from NOAA active region 11283. This EUV wave features peculiar on-disk
signatures, in particular we observe an intermittent "disappearance"
of the front for 120 s in SDO/AIA 171, 193, 211 Å data, whereas
the 335 Å filter, sensitive to hotter plasmas (T∼ 2.5 MK), shows
a continuous evolution of the wave front. We exploit the multi-point
quadrature position of SDO and STEREO-A, to make a thorough analysis of
the EUV wave evolution, with respect to its kinematics and amplitude
evolution. We identify on-disk coronal dimming regions in SDO/AIA,
reminiscent of core dimmings, that have no corresponding on-disk dimming
signatures in STEREO-A/EUVI. Reconstructing the SDO line-of-sight (LOS)
direction in STEREO-A clearly shows that the observed SDO on-disk
dimming areas are not the footprints of the erupting fluxrope but
result from decreased emission from the expanding CME body integrated
along the LOS. In this context, we conclude that the intermittent
disappearance of the EUV wave in the AIA 171, 193, 211 Å filters,
which are channels sensitive to plasma with temperatures below ∼ 2
MK is also caused by such LOS integration effects. These observations
clearly demonstrate that single-view image data provide us with limited
insight to correctly interpret coronal features.
---------------------------------------------------------
Title: Chromospheric evaporation flows and density changes deduced
from Hinode/EIS during an M1.6 flare
Authors: Gömöry, P.; Veronig, A. M.; Su, Y.; Temmer, M.; Thalmann,
J. K.
2016A&A...588A...6G Altcode: 2016arXiv160202145G
<BR /> Aims: We study the response of the solar atmosphere during a GOES
M1.6 flare using spectroscopic and imaging observations. In particular,
we examine the evolution of the mass flows and electron density together
with the energy input derived from hard X-ray (HXR) in the context of
chromospheric evaporation. <BR /> Methods: We analyzed high-cadence
sit-and-stare observations acquired with the Hinode/EIS spectrometer
in the Fe xiii 202.044 Å (log T = 6.2) and Fe xvi 262.980 Å (log T =
6.4) spectral lines to derive temporal variations of the line intensity,
Doppler shifts, and electron density during the flare. We combined these
data with HXR measurements acquired with RHESSI to derive the energy
input to the lower atmosphere by flare-accelerated electrons. <BR />
Results: During the flare impulsive phase, we observe no significant
flows in the cooler Fe xiii line but strong upflows, up to 80-150 km
s<SUP>-1</SUP>, in the hotter Fe xvi line. The largest Doppler shifts
observed in the Fe xvi line were co-temporal with the sharp intensity
peak. The electron density obtained from a Fe xiii line pair ratio
exhibited fast increase (within two minutes) from the pre-flare level
of 5.01 × 10<SUP>9</SUP> cm<SUP>-3</SUP> to 3.16 × 10<SUP>10</SUP>
cm<SUP>-3</SUP> during the flare peak. The nonthermal energy flux
density deposited from the coronal acceleration site to the lower
atmospheric layers during the flare peak was found to be 1.34 ×
10<SUP>10</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP> for a low-energy
cut-off that was estimated to be 16 keV. During the decline flare phase,
we found a secondary intensity and density peak of lower amplitude
that was preceded by upflows of ~15 km s<SUP>-1</SUP> that were
detected in both lines. The flare was also accompanied by a filament
eruption that was partly captured by the EIS observations. We derived
Doppler velocities of 250-300 km s<SUP>-1</SUP> for the upflowing
filament material. <BR /> Conclusions: The spectroscopic results
for the flare peak are consistent with the scenario of explosive
chromospheric evaporation, although a comparatively low value of the
nonthermal energy flux density was determined for this phase of the
flare. This outcome is discussed in the context of recent hydrodynamic
simulations. It provides observational evidence that the response
of the atmospheric plasma strongly depends on the properties of the
electron beams responsible for the heating, in particular the steepness
of the energy distribution. The secondary peak of line intensity and
electron density detected during the decline phase is interpreted as a
signature of flare loops being filled by expanding hot material that
is due to chromospheric evaporation. <P />A movie is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527403/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Space Weather and confined CME events
Authors: Thalmann, Julia; Temmer, Manuela; Veronig, Astrid; Su, Yang
2016EGUGA..18.7517T Altcode:
The unusually large NOAA active region (AR) 2192, observed in October
and November 2014, was outstanding in its productivity of major flares
(GOES class M5 and larger). During the time when the AR faced Earth,
major Space Weather events would have been expected. However, none of
the X-flares was associated to a coronal mass ejection. Observational
evidence for the confinement of the flare are large initial separation
of the flare ribbons, together with an almost absent growth in ribbon
separation. The low dynamic of the ribbons also suggests a reconnection
site high up in the corona. From NLFF modeling we show that the
arcade overlying the AR had a predominantly north-south oriented
magnetic system, which served as a strong, also lateral, confinement
for the flares at the core of the active region. From the magnetic
field modeling we derived the decay of the constraining background,
and it was found that the overlying field was only slowly decaying
with height. We conclude that observational data of the solar surface,
especially of flare ribbon dynamics as well as magnetic field models
support Space Weather predictions.
---------------------------------------------------------
Title: ENLIL Global Heliospheric Modeling as a Context For Multipoint
Observations
Authors: Mays, M. Leila; Odstrcil, Dusan; Luhmann, Janet; Bain, Hazel;
Li, Yan; Schwadron, Nathan; Gorby, Matt; Thompson, Barbara; Jian,
Lan; Möstl, Christian; Rouillard, Alexis; Davies, Jackie; Temmer,
Manuela; Rastaetter, Lutz; Taktakishvili, Aleksandre; MacNeice, Peter;
Kuznetsova, Maria
2016EGUGA..1811638M Altcode:
We present heliospheric simulation case studies using recent
enhancements to WSA--ENLIL+Cone (version 2.8) at the Community
Coordinated Modeling Center (CCMC). The global 3D MHD ENLIL model
provides a time-dependent description of the background solar wind
plasma and magnetic field using a sequence of WSA coronal model
maps as input at the inner boundary of 21.5 Rs. A homogeneous,
over-pressured hydrodynamic plasma cloud is launched through the
inner boundary of the heliospheric computational domain and into
the background solar wind. Multipoint observations help constrain
simulations and this modeling system provides global context and
arrival times of the solar wind streams and CMEs at Earth, planets,
and spacecraft. Additionally, one can extract the magnetic topologies
of observer-connected magnetic field lines and all plasma and shock
properties along those field lines. ENLIL "likelihood/all-clear"
forecasting maps provide expected intensity, timing/duration of events
at locations throughout the heliosphere with "possible SEP affected
areas" color-coded based on shock strength. ENLIL simulations are also
useful to drive SEP models such as the Solar Energetic Particle Model
(SEPMOD) (Luhmann et al. 2007, 2010) and Energetic Particle Radiation
Environment Module (EPREM) (Schwadron et al., 2010). SEPMOD injects
protons onto a sequence observer field lines at intensities dependent
on the connected shock source strength which are then integrated at
the observer to approximate the proton flux. EPREM couples with MHD
models such as ENLIL and computes energetic particle distributions
based on the focused transport equation along a Lagrangian grid of
nodes that propagate out with the solar wind. Studies have shown
that accurate descriptions of the heliosphere, and hence modeled CME
arrival times and SEPs, are achieved by ENLIL only when the background
solar wind is well-reproduced and CME parameters are accurate. It is
essential to include all of the relevant CMEs and allow enough time
for the events to propagate and interact. In this presentation we
demonstrate several event case studies of ENLIL simulations compared
with multipoint observations, exploring the background solar wind and
CME pre-conditioning, and including comparisons between ENLIL synthetic
j-maps with observed STEREO/HI j-maps using catalogues from the HELCATS
FP7 project.
---------------------------------------------------------
Title: Forecasting the Arrival of Coronal Mass Ejections: The
Drag-Based Model
Authors: Vršnak, B.; Temmer, M.; Zic, T.; Dumbović, M.; Čalogović,
J.
2016ASPC..504..209V Altcode:
Arrival-time predictions based on the numerical "WSA-ENLIL+Cone model"
and the analytical "Drag-based model" (DBM) are analyzed, employing
a sample of 50 well observed CMEs. The best match between the two
models is obtained if the background solar-wind speed of w = 400 km
s<SUP>-1</SUP> is applied in DBM. It is also demonstrated that both
models show similar prediction accuracy.
---------------------------------------------------------
Title: Impact of coronal mass ejections on the Earth's thermosphere
and geoeffectiveness observed by ACE and GRACE: Statistical results
Authors: Krauss, Sandro; Temmer, Manuela; Veronig, Astrid; Baur, Oliver
2016EGUGA..18.9350K Altcode:
For the period July 2003 to August 2010, the interplanetary coronal
mass ejection (ICME) catalogue maintained by Richardson and Cane
lists 106 Earth-directed events, which have been measured in situ by
plasma and field instruments on board the ACE satellite. We present a
statistical investigation of the Earth's thermospheric neutral density
response by means of accelerometer measurements collected by the
Gravity Recovery And Climate Experiment (GRACE) satellites, which are
available for 104 ICMEs in the data set. We relate the thermospheric
density increase to various geomagnetic indices (e.g. Dst, AE, Kp,
a-indices, ...) and characteristic ICME parameters (impact speed,
southward magnetic field strength Bz). We find high correlations
between the ICME Bz and thermospheric density enhancements as well as
with most of the geomagnetic indices. Separating the response for the
shock-sheath region and the magnetic structure of the ICME, we find
for instance that the Dst and SYM-H indices reveal a tighter relation
to the Bz minimum in the magnetic structure of the ICME, whereas the
polar cap indices show higher correlations with the Bz minimum in the
shock-sheath region. These results are expected to further stimulate
progress in space weather understanding and applications regarding
satellite operations.
---------------------------------------------------------
Title: Injection of solar energetic particles into both loop legs
of a magnetic cloud
Authors: Dresing, N.; Gómez-Herrero, R.; Heber, B.; Hidalgo, M. A.;
Klassen, A.; Temmer, M.; Veronig, A.
2016A&A...586A..55D Altcode: 2016arXiv160100491D
Context. Each of the two Solar TErrestrial RElations Observatory
(STEREO) spacecraft carries a Solar Electron and Proton Telescope
(SEPT) which measures electrons and protons. Anisotropy observations
are provided in four viewing directions: along the nominal magnetic
field Parker spiral in the ecliptic towards the Sun (SUN) and
away from the Sun (Anti-Sun/ASUN), and towards the north (NORTH)
and south (SOUTH). The solar energetic particle (SEP) event on 7
November 2013 was observed by both STEREO spacecraft, which were
longitudinally separated by 68° at that time. While STEREO A observed
the expected characteristics of an SEP event at a well-connected
position, STEREO B detected a very anisotropic bi-directional
distribution of near-relativistic electrons and was situated inside a
magnetic-cloud-like structure during the early phase of the event. <BR
/> Aims: We examine the source of the bi-directional SEP distribution
at STEREO B. On the one hand this distribution could be caused by a
double injection into both loop legs of the magnetic cloud (MC). On the
other hand, a mirroring scenario where the incident beam is reflected in
the opposite loop leg could be the reason. Furthermore, the energetic
electron observations are used to probe the magnetic structure inside
the magnetic cloud. <BR /> Methods: We investigate in situ plasma
and magnetic field observations and show that STEREO B was embedded
in an MC-like structure ejected three days earlier on 4 November from
the same active region. We apply a Graduated Cylindrical Shell (GCS)
model to the coronagraph observations from three viewpoints as well
as the Global Magnetic Cloud (GMC) model to the in situ measurements
at STEREO B to determine the orientation and topology of the MC
close to the Sun and at 1 AU. We also estimate the path lengths of
the electrons propagating through the MC to estimate the amount of
magnetic field line winding inside the structure. <BR /> Results:
The relative intensity and timing of the energetic electron increases
in the different SEPT telescopes at STEREO B strongly suggest that the
bi-directional electron distribution is formed by SEP injections in both
loop legs of the MC separately instead of by mirroring farther away
beyond the STEREO orbit. Observations by the Nançay Radioheliograph
(NRH) of two distinct radio sources during the SEP injection further
support the above scenario. The determined electron path lengths are
around 50% longer than the estimated lengths of the loop legs of the
MC itself (based on the GCS model) suggesting that the amount of field
line winding is moderate.
---------------------------------------------------------
Title: 70 Years of Sunspot Observations at Kanzelhoehe Observatory
Authors: Pötzi, W.; Veronig, A.; Temmer, M.; Baumgartner, D. J.;
Freislich, H.; Strutzmann, H.
2016CEAB...40..143P Altcode:
During World War II the German Airforce established a network of
observatories, among them the Kanzelhöhe Observatory (KSO), which
would provide information on solar activity in order to investigate
the conditions of the Earth's ionosphere in terms of radio-wave
propagation. Solar observations began already in 1943 with photographs
of the photosphere and drawings of sunspots, plage regions and faculae,
as well as patrol observations of the solar corona. Since 1944 relative
sunspot numbers were derived, these relative numbers agree with the new
International Sunspot Number tep[ISN,][]{SIDC,Clette2014} within ≈
10%. However, revisiting the historical data, we also find periods with
larger deviations. There were two main reasons for these deviations. On
the one hand major instrumental changes took place and the instrument
was relocated to another observation tower. On the other hand there
were periods of frequent replacements of personnel. In the long term,
the instrumental improvements led to better image quality, and a trend
towards better seeing conditions since the year 2000 was found.
---------------------------------------------------------
Title: Formation of Coronal Large-Amplitude Waves and the
Chromospheric Response
Authors: Vršnak, B.; Žic, T.; Lulić, S.; Temmer, M.; Veronig, A. M.
2016SoPh..291...89V Altcode: 2015SoPh..tmp..175V
An in-depth analysis of numerical simulations is performed to obtain
a deeper insight into the nature of various phenomena occurring in the
solar atmosphere as a consequence of the eruption of unstable coronal
structures. Although the simulations take into account only the most
basic characteristics of a flux-rope eruption, the simulation analysis
reveals important information on various eruption-related effects. It
quantifies the relation between the eruption dynamics and the evolution
of the large-amplitude coronal magnetohydrodynamic wave and the
associated chromospheric downward-propagating perturbation. We show that
the downward propagation of the chromospheric Moreton-wave disturbance
can be approximated by a constant-amplitude switch-on shock that moves
through a medium of rapidly decreasing Alfvén velocity. The presented
analysis reveals the nature of secondary effects that are observed
as coronal upflows, secondary shocks, various forms of wave-trains,
delayed large-amplitude slow disturbances, transient coronal depletions,
etc. We also show that the eruption can cause an observable Moreton
wave and a secondary coronal front only if it is powerful enough and
is preferably characterized by significant lateral expansion. In weaker
eruptions, only the coronal and transition-region signatures of primary
waves are expected to be observed. In powerful events, the primary
wave moves at an Alfvén Mach number significantly larger than 1 and
steepens into a shock that is due to the nonlinear evolution of the
wavefront. After the eruption-driven phase, the perturbation evolves
as a freely propagating simple wave, characterized by a significant
deceleration, amplitude decrease, and wave-profile broadening. In weak
events the coronal wave does not develop into a shock and propagates
at a speed close to the ambient magnetosonic speed.
---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W Altcode:
This document was created by the Solar Simulations for the Atacama
Large Millimeter Observatory Network (SSALMON) in preparation of
the first regular observations of the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA), which are anticipated to start
in ALMA Cycle 4 in October 2016. The science cases presented here
demonstrate that a large number of scientifically highly interesting
observations could be made already with the still limited solar
observing modes foreseen for Cycle 4 and that ALMA has the potential
to make important contributions to answering long-standing scientific
questions in solar physics. With the proposal deadline for ALMA Cycle
4 in April 2016 and the Commissioning and Science Verification campaign
in December 2015 in sight, several of the SSALMON Expert Teams composed
strategic documents in which they outlined potential solar observations
that could be feasible given the anticipated technical capabilities
in Cycle 4. These documents have been combined and supplemented
with an analysis, resulting in recommendations for solar observing
with ALMA in Cycle 4. In addition, the detailed science cases also
demonstrate the scientific priorities of the solar physics community
and which capabilities are wanted for the next observing cycles. The
work on this White Paper effort was coordinated in close cooperation
with the two international solar ALMA development studies led by
T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
further updated until the beginning of Cycle 4 in October 2016. In
particular, we plan to adjust the technical capabilities of the solar
observing modes once finally decided and to further demonstrate the
feasibility and scientific potential of the included science cases by
means of numerical simulations of the solar atmosphere and corresponding
simulated ALMA observations.
---------------------------------------------------------
Title: The exceptional aspects of the confined X-class flares of
solar active region 2192
Authors: Thalmann, Julia K.; Su, Yang; Temmer, Manuela; Veronig,
Astrid M.
2016IAUS..320...60T Altcode: 2016arXiv160503712T
During late October 2014, active region NOAA 2192 caused an unusual high
level of solar activity, within an otherwise weak solar cycle. While
crossing the solar disk, during a period of 11 days, it was the source
of 114 flares of GOES class C1.0 and larger, including 29 M- and 6
X-flares. Surprisingly, none of the major flares (GOES class M5.0
and larger) was accompanied by a coronal mass ejection, contrary to
statistical tendencies found in the past. From modeling the coronal
magnetic field of NOAA 2192 and its surrounding, we suspect that the
cause of the confined character of the flares is the strong surrounding
and overlying large-scale magnetic field. Furthermore, we find evidence
for multiple magnetic reconnection processes within a single flare,
during which electrons were accelerated to unusual high energies.
---------------------------------------------------------
Title: STEREO Observations of an SEP Event Injected Into Both Loop
Legs of a Magnetic Cloud
Authors: Dresing, N.; Gomez-Herrero, R.; Heber, B.; Hidalgo, M. A. U.;
Klassen, A.; Temmer, M.; Veronig, A.
2015AGUFMSH42A..06D Altcode:
On 7 Nov 2013 STEREO B was embedded in a magnetic-cloud (MC)
like structure when an SEP event occurred reaching both STEREO
spacecraft. The bi-drectional near relativistic electron distribution
observed by STEREO B reveals such timing and relative intensity
characteristics suggesting that the SEPs were injected separately into
both loop legs of the MC. Observations by the Nancay Radioheliograph
(NRH) of two distinct radio sources at the same time further support
the above scenario. In order to derive the 3D morphology and average
speed of the CME close to the Sun, we use the graduated cylindrical
shell model (GCS) which is applied to the white-light coronagraph
observations by the STEREO spacecraft and SOHO. Furthermore, a global
magnetic topology model for magnetic clouds is applied to the in-situ
measurements of the magnetic field. Both models suggest that the MC is
strongly inclined with respect to the ecliptic yielding a north/south
orientation. The energetic electron observations are used to probe the
structure of the magnetic cloud: We determine the electron path lengths
along both loop legs of the structure to infer the amount of field
line twist inside the MC. The resulting path lengths are around 50%
longer than the estimated lengths of the loop legs of the MC itself
suggesting that the amount of field line winding is moderate.
---------------------------------------------------------
Title: Low Solar Wind Density Causing the Fast Coronal Mass Ejection
from 23 July 2012
Authors: Nitta, N.; Temmer, M.
2015AGUFMSH53A2458N Altcode:
The fast coronal mass ejection (CME) from July 23, 2012 raised special
attention due to its short propagation time of less than 21hrs from
Sun to 1 AU. In-situ data from STEREO-A revealed the arrival of a
fast forward shock having a velocity of more than 2200 km/s followed
by a magnetic structure with a speed of almost 1900 km/s. We study the
evolution of the CME in interplanetary (IP) space using the drag based
model to reproduce the short propagation time and high impact speed
as derived from in-situ data. We find that the ambient density must
have been exceptionally low due to which the drag force is reduced
such that the CME experienced almost no deceleration. The density is
found to be rather low due to the weak solar activity and was lowered
even more by a previous CME event.
---------------------------------------------------------
Title: Propagation of the 7 January 2014 CME and Resulting Geomagnetic
Non-event
Authors: Mays, M. L.; Thompson, B. J.; Jian, L. K.; Colaninno, R. C.;
Odstrcil, D.; Möstl, C.; Temmer, M.; Savani, N. P.; Collinson, G.;
Taktakishvili, A.; MacNeice, P. J.; Zheng, Y.
2015ApJ...812..145M Altcode: 2015arXiv150906477M
On 2014 January 7 an X1.2 flare and coronal mass ejection (CME) with a
radial speed ≈2500 km s<SUP>-1</SUP> was observed from near an active
region close to disk center. This led many forecasters to estimate a
rapid arrival at Earth (≈36 hr) and predict a strong geomagnetic
storm. However, only a glancing CME arrival was observed at Earth
with a transit time of ≈49 hr and a K <SUB>P</SUB> geomagnetic
index of only 3-. We study the interplanetary propagation of this
CME using the ensemble Wang-Sheeley-Arge (WSA)-ENLIL+Cone model,
that allows a sampling of CME parameter uncertainties. We explore a
series of simulations to isolate the effects of the background solar
wind solution, CME shape, tilt, location, size, and speed, and the
results are compared with observed in situ arrivals at Venus, Earth,
and Mars. Our results show that a tilted ellipsoid CME shape improves
the initial real-time prediction to better reflect the observed in situ
signatures and the geomagnetic storm strength. CME parameters from the
Graduated Cylindrical Shell model used as input to WSA-ENLIL+Cone, along
with a tilted ellipsoid cloud shape, improve the arrival-time error
by 14.5, 18.7, 23.4 hr for Venus, Earth, and Mars respectively. These
results highlight that CME orientation and directionality with respect
to observatories play an important role in understanding the propagation
of this CME, and for forecasting other glancing CME arrivals. This study
also demonstrates the importance of three-dimensional CME fitting made
possible by multiple viewpoint imaging.
---------------------------------------------------------
Title: Thermospheric and geomagnetic responses to interplanetary
coronal mass ejections observed by ACE and GRACE: Statistical results
Authors: Krauss, S.; Temmer, M.; Veronig, A.; Baur, O.; Lammer, H.
2015JGRA..120.8848K Altcode: 2015arXiv151003549K
For the period July 2003 to August 2010, the interplanetary coronal mass
ejection (ICME) catalogue maintained by Richardson and Cane lists 106
Earth-directed events, which have been measured in situ by plasma and
field instruments on board the ACE satellite. We present a statistical
investigation of the Earth's thermospheric neutral density response by
means of accelerometer measurements collected by the Gravity Recovery
And Climate Experiment (GRACE) satellites, which are available for
104 ICMEs in the data set, and its relation to various geomagnetic
indices and characteristic ICME parameters such as the impact speed
(vmax), southward magnetic field strength (B<SUB>z</SUB>). The majority
of ICMEs causes a distinct density enhancement in the thermosphere,
with up to a factor of 8 compared to the preevent level. We find high
correlations between ICME B<SUB>z</SUB> and thermospheric density
enhancements (≈0.9), while the correlation with the ICME impact speed
is somewhat smaller (≈0.7). The geomagnetic indices revealing the
highest correlations are Dst and SYM-H(≈0.9); the lowest correlations
are obtained for Kp and AE (≈0.7), which show a nonlinear relation
with the thermospheric density enhancements. Separating the response for
the shock-sheath region and the magnetic structure of the ICME, we find
that the Dst and SYM-H reveal a tighter relation to the B<SUB>z</SUB>
minimum in the magnetic structure of the ICME, whereas the polar cap
indices show higher correlations with the B<SUB>z</SUB> minimum in
the shock-sheath region. Since the strength of the B<SUB>z</SUB>
component—either in the sheath or in the magnetic structure of
the ICME—is highly correlated (≈0.9) with the neutral density
enhancement, we discuss the possibility of satellite orbital decay
estimates based on magnetic field measurements at L1, i.e., before
the ICME hits the Earth magnetosphere. These results are expected
to further stimulate progress in space weather understanding and
applications regarding satellite operations.
---------------------------------------------------------
Title: The exceptional aspects of the confined X-Flares of Solar
Active Region 2192
Authors: Thalmann, Julia K.; Su, Yang; Temmer, Manuela; Veronig, Astrid
2015IAUGA..2215645T Altcode:
Active region NOAA 2192 showed an outstanding productivity
of major (GOES class M5 and larger) two-ribbon flares lacking
eruptive events. None of the X-flares was associated to a coronal
mass ejection. The major confined flares on 2014 October 22 and 24
originated from the active-region core and were prohibited to develop
an associated mass ejection due to the confinement of the overlying
strong magnetic field. In contrast, the single eruptive M-flare on
October 24 originated from the outer parts of the active region, in the
neighborhood of open large-scale fields, which allowed for the observed
mass ejection. Analysis of the spacial and temporal characteristics
of the major confined flares revealed exceptional aspects, including a
large initial separation of the confined flares' ribbons and an almost
absent growth in ribbon separation, suggesting a reconnection site
high up in the corona. Furthermore, detailed analysis of a confined
X-flare on October 22 provides evidence that magnetic field structures
were repeatedly involved in magnetic reconnection, that a large number
of electrons was accelerated to non-thermal energies but that only a
small fraction out of these accelerated electrons was accelerated to
high energies. We conclude the latter due to the unusual steepness
of the associated power law spectrum. Finally, we demonstrate that
a considerable portion of the magnetic energy released during the
X-flare was consumed by the non-thermal flare energy.
---------------------------------------------------------
Title: Improvements on coronal hole detection in SDO/AIA images
using supervised classification
Authors: Reiss, Martin A.; Hofmeister, Stefan J.; De Visscher, Ruben;
Temmer, Manuela; Veronig, Astrid M.; Delouille, Véronique; Mampaey,
Benjamin; Ahammer, Helmut
2015JSWSC...5A..23R Altcode: 2015arXiv150606623R
We demonstrate the use of machine learning algorithms in combination
with segmentation techniques in order to distinguish coronal holes
and filaments in SDO/AIA EUV images of the Sun. Based on two coronal
hole detection techniques (intensity-based thresholding, SPoCA), we
prepared datasets of manually labeled coronal hole and filament channel
regions present on the Sun during the time range 2011-2013. By mapping
the extracted regions from EUV observations onto HMI line-of-sight
magnetograms we also include their magnetic characteristics. We computed
shape measures from the segmented binary maps as well as first order
and second order texture statistics from the segmented regions in
the EUV images and magnetograms. These attributes were used for
data mining investigations to identify the most performant rule to
differentiate between coronal holes and filament channels. We applied
several classifiers, namely Support Vector Machine (SVM), Linear Support
Vector Machine, Decision Tree, and Random Forest, and found that all
classification rules achieve good results in general, with linear SVM
providing the best performances (with a true skill statistic of ≈
0.90). Additional information from magnetic field data systematically
improves the performance across all four classifiers for the SPoCA
detection. Since the calculation is inexpensive in computing time,
this approach is well suited for applications on real-time data. This
study demonstrates how a machine learning approach may help improve
upon an unsupervised feature extraction method.
---------------------------------------------------------
Title: Heliospheric Propagation of Coronal Mass Ejections: Drag-based
Model Fitting
Authors: Žic, T.; Vršnak, B.; Temmer, M.
2015ApJS..218...32Z Altcode: 2015arXiv150608582Z
The so-called drag-based model (DBM) simulates analytically the
propagation of coronal mass ejections (CMEs) in interplanetary space
and allows the prediction of their arrival times and impact speeds at
any point in the heliosphere (“target”). The DBM is based on the
assumption that beyond a distance of about 20 solar radii from the
Sun, the dominant force acting on CMEs is the “aerodynamic” drag
force. In the standard form of DBM, the user provisionally chooses
values for the model input parameters, by which the kinematics of the
CME over the entire Sun-“target” distance range is defined. The
choice of model input parameters is usually based on several previously
undertaken statistical studies. In other words, the model is used
by ad hoc implementation of statistics-based values of the input
parameters, which are not necessarily appropriate for the CME under
study. Furthermore, such a procedure lacks quantitative information
on how well the simulation reproduces the coronagraphically observed
kinematics of the CME, and thus does not provide an estimate of the
reliability of the arrival prediction. In this paper we advance the DBM
by adopting it in a form that employs the CME observations over a given
distance range to evaluate the most suitable model input parameters
for a given CME by means of least-squares fitting. Furthermore, the
new version of the model automatically responds to any significant
change of the conditions in the ambient medium (solar wind speed,
density, CME-CME interactions, etc.) by changing the model input
parameters according to changes in the CME kinematics. The advanced
DBM is shaped in a form that can be readily employed in an operational
system for real-time space-weather forecasting by promptly adjusting
to a successively expanding observational data set, thus providing a
successively improving prediction of the CME arrival.
---------------------------------------------------------
Title: Strong coronal channelling and interplanetary evolution of
a solar storm up to Earth and Mars
Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu,
Ying D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.;
Temmer, Manuela; Farrugia, Charles J.; Posner, Arik; Dumbović,
Mateja; Janvier, Miho; Démoulin, Pascal; Boakes, Peter; Devos, Andy;
Kraaikamp, Emil; Mays, Mona L.; Vršnak, Bojan
2015NatCo...6.7135M Altcode: 2015arXiv150602842M; 2015NatCo...6E7135M
The severe geomagnetic effects of solar storms or coronal mass
ejections (CMEs) are to a large degree determined by their propagation
direction with respect to Earth. There is a lack of understanding of
the processes that determine their non-radial propagation. Here we
present a synthesis of data from seven different space missions of a
fast CME, which originated in an active region near the disk centre
and, hence, a significant geomagnetic impact was forecasted. However,
the CME is demonstrated to be channelled during eruption into a
direction +37+/-10° (longitude) away from its source region, leading
only to minimal geomagnetic effects. In situ observations near Earth
and Mars confirm the channelled CME motion, and are consistent with
an ellipse shape of the CME-driven shock provided by the new Ellipse
Evolution model, presented here. The results enhance our understanding
of CME propagation and shape, which can help to improve space weather
forecasts.
---------------------------------------------------------
Title: Real-Time Solar Wind Prediction Based on SDO/AIA Coronal
Hole Data
Authors: Rotter, T.; Veronig, A. M.; Temmer, M.; Vršnak, B.
2015SoPh..290.1355R Altcode: 2015arXiv150106697R; 2015SoPh..tmp...37R
We present an empirical model based on the visible area covered by
coronal holes close to the central meridian with the aim to predict
the solar wind speed at 1 AU with a lead time of up to four days in
advance with a time resolution of one hour. Linear prediction functions
are used to relate coronal hole areas to solar wind speed. The function
parameters are automatically adapted by using the information from the
previous three Carrington Rotations. Thus the algorithm automatically
reacts to the changes of the solar wind speed during different phases
of the solar cycle. The adaptive algorithm was applied to and tested
on SDO/AIA-193 Å observations and ACE measurements during the years
2011 - 2013, covering 41 Carrington Rotations. The solar wind needs
on average 4.02±0.5 days to reach Earth. The algorithm produces good
predictions for the 156 solar wind high-speed streams peak amplitudes
with correlation coefficients of cc≈0.60. For 80 % of the peaks,
the predicted arrival matches the ACE in situ measurements within a
time window of 0.5 days. The same algorithm, using linear predictions,
was also applied to predict the magnetic field strength in wind streams
originating from coronal hole areas, but it did not give reliable
predictions (cc≈0.15).
---------------------------------------------------------
Title: Strong coronal deflection of a CME and its interplanetary
evolution to Earth and Mars
Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu, Ying
D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.; Temmer,
Manuela; Farrugia, Charles J.; Posner, Arik; Dumbovic, Mateja; Janvier,
Miho; Demoulin, Pascal; Boakes, Peter; Devos, Andy; Kraaikamp, Emil;
Mays, Mona L.; Vrsnak, Bojan
2015EGUGA..17.1366M Altcode:
We discuss multipoint imaging and in situ observations of the coronal
mass ejection (CME) on January 7 2014 which resulted in a major false
alarm. While the source region was almost at disk center facing Earth,
the eruption was strongly deflected in the corona, and in conjunction
with its particular orientation this CME missed Earth almost entirely,
leading to no significant geomagnetic effects. We demonstrate this
by a synthesis of data from 7 different heliospheric and planetary
space missions (STEREO-A/B, SOHO, SDO, Wind, Mars Express, Mars
Science Laboratory). The CMEs ecliptic part was deflected by 37
± 10° in heliospheric longitude, a value larger than previously
thought. Multipoint in situ observations at Earth and Mars confirm
the deflection, and are consistent with an elliptical interplanetary
shock shape of aspect ratio 1.4 ± 0.4. We also discuss our new method,
the Ellipse Evolution (ElEvo) model, which allows us to optimize the
global shape of the CME shock with multipoint in situ observations of
the interplanetary CME arrival. ElEvo, which is an extension to the
Drag-Based-Model by Vrsnak et al., may also be used for real time space
weather forecasting. The presented results enhance our understanding
of CME deflection and shape, which are fundamental ingredients for
improving space weather forecasts.
---------------------------------------------------------
Title: The Confined X-class Flares of Solar Active Region 2192
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
2015ApJ...801L..23T Altcode: 2015arXiv150205157T
The unusually large active region (AR) NOAA 2192, observed in 2014
October, was outstanding in its productivity of major two-ribbon flares
without coronal mass ejections. On a large scale, a predominantly
north-south oriented magnetic system of arcade fields served as a strong
top and lateral confinement for a series of large two-ribbon flares
originating from the core of the AR. The large initial separation of
the flare ribbons, together with an almost absent growth in ribbon
separation, suggests a confined reconnection site high up in the
corona. Based on a detailed analysis of the confined X1.6 flare on
October 22, we show how exceptional the flaring of this AR was. We
provide evidence for repeated energy release, indicating that the
same magnetic field structures were repeatedly involved in magnetic
reconnection. We find that a large number of electrons was accelerated
to non-thermal energies, revealing a steep power-law spectrum, but
that only a small fraction was accelerated to high energies. The total
non-thermal energy in electrons derived (on the order of 10<SUP>25</SUP>
J) is considerably higher than that in eruptive flares of class X1,
and corresponds to about 10% of the excess magnetic energy present in
the active-region corona.
---------------------------------------------------------
Title: Interplanetary Propagation Behavior of the Fast Coronal Mass
Ejection on 23 July 2012
Authors: Temmer, M.; Nitta, N. V.
2015SoPh..290..919T Altcode: 2015SoPh..tmp....2T; 2014arXiv1411.6559T
The fast coronal mass ejection (CME) on 23 July 2012 caused attention
because of its extremely short transit time from the Sun to 1 AU,
which was shorter than 21 h. In situ data from STEREO-A revealed the
arrival of a fast forward shock with a speed of more than 2200 km
s<SUP>−1</SUP> followed by a magnetic structure moving with almost
1900 km s<SUP>−1</SUP>. We investigate the propagation behavior of the
CME shock and magnetic structure with the aim to reproduce the short
transit time and high impact speed as derived from in situ data. We
carefully measured the 3D kinematics of the CME using the graduated
cylindrical shell model and obtained a maximum speed of 2580±280 km
s<SUP>−1</SUP> for the CME shock and 2270±420 km s<SUP>−1</SUP>
for its magnetic structure. Based on the 3D kinematics, the drag-based
model (DBM) reproduces the observational data reasonably well. To
successfully simulate the CME shock, the ambient flow speed needs
to have an average value close to the slow solar wind speed (450
km s<SUP>−1</SUP>), and the initial shock speed at a distance of
30 R<SUB>⊙</SUB> should not exceed ≈ 2300 km s<SUP>−1</SUP>,
otherwise it would arrive much too early at STEREO-A. The model results
indicate that an extremely small aerodynamic drag force is exerted
on the shock, smaller by one order of magnitude than average. As
a consequence, the CME hardly decelerates in interplanetary space
and maintains its high initial speed. The low aerodynamic drag can
only be reproduced when the density of the ambient solar wind flow,
in which the fast CME propagates, is decreased to ρ<SUB>sw</SUB>=1 -
2 cm<SUP>−3</SUP> at the distance of 1 AU. This result is consistent
with the preconditioning of interplanetary space by a previous CME.
---------------------------------------------------------
Title: Real-time Flare Detection in Ground-Based Hα Imaging at
Kanzelhöhe Observatory
Authors: Pötzi, W.; Veronig, A. M.; Riegler, G.; Amerstorfer, U.;
Pock, T.; Temmer, M.; Polanec, W.; Baumgartner, D. J.
2015SoPh..290..951P Altcode: 2014arXiv1411.3896P; 2014SoPh..tmp..193P
Kanzelhöhe Observatory (KSO) regularly performs high-cadence full-disk
imaging of the solar chromosphere in the Hα and Ca II K spectral
lines as well as in the solar photosphere in white light. In the frame
of ESA's (European Space Agency) Space Situational Awareness (SSA)
program, a new system for real-time Hα data provision and automatic
flare detection was developed at KSO. The data and events detected
are published in near real-time at ESA's SSA Space Weather portal
(http://swe.ssa.esa.int/web/guest/kso-federated). In this article,
we describe the Hα instrument, the image-recognition algorithms we
developed, and the implementation into the KSO Hα observing system. We
also present the evaluation results of the real-time data provision
and flare detection for a period of five months. The Hα data provision
worked in 99.96 % of the images, with a mean time lag of four seconds
between image recording and online provision. Within the given criteria
for the automatic image-recognition system (at least three Hα images
are needed for a positive detection), all flares with an area ≥ 50
micro-hemispheres that were located within 60° of the solar center
and occurred during the KSO observing times were detected, a number of
87 events in total. The automatically determined flare importance and
brightness classes were correct in ∼ 85 %. The mean flare positions in
heliographic longitude and latitude were correct to within ∼ 1°. The
median of the absolute differences for the flare start and peak times
from the automatic detections in comparison with the official NOAA
(and KSO) visual flare reports were 3 min (1 min).
---------------------------------------------------------
Title: Initiation and Evolution of Global Coronal Waves
Authors: Vršnak, B.; Muhr, N.; Žic, T.; Lulić, S.; Kienreich,
I. W.; Temmer, M.; Veronig, A. M.
2015CEAB...39...65V Altcode:
Some essential outcomes of a detailed analysis of the formation and
evolution of the coronal EUV wave of 15 February 2011 are presented,
focused on the relationship between the source region expansion, wave
kinematics, and the evolution of the wave amplitude. The observations
are explained in terms of the results of the numerical MHD simulations,
providing new insights into the physical background of coronal waves,
especially considering the nature of the relationship of the wave
amplitude and propagation velocity in different phases of the wave
evolution.
---------------------------------------------------------
Title: The real-time flare detection system at Kanzelhöhe Observatory
Authors: Pötzi, W.; Veronig, A.; Riegler, G.; Amerstorfer, U.; Pock,
TH.; Temmer, M.; Polanec, W.; Baumgartner, D. J.
2015CEAB...39..125P Altcode:
Kanzelhöhe Observatory performs regular high-cadence full-disk
observations of the solar chromosphere in the Hα and Ca II K spectral
lines as well as the solar photosphere in white-light. In the frame
of ESA's Space Situational Awareness (SSA) activities, a system for
near real-time H-alpha image provision through the SSA Space Weather
(SWE) portal (swe.ssa.esa.int) and for automatic alerting of flares
and erupting filaments was developed. Image segmentation algorithms,
for the automatic detection of solar filaments in real time H-alpha
images have been developed and implemented at the Kanzelhöhe observing
system. We present results of this system with respect to the automatic
recognition and segmentation of flares on the Sun.
---------------------------------------------------------
Title: Forbush decreases associated to Stealth Coronal Mass Ejections
Authors: Heber, B.; Wallmann, C.; Galsdorf, D.; Herbst K.; Kühl,
P.; Dumbovic, M.; Vršnak, B.; Veronig, A.; Temmer, M.; Möstl, C.;
Dalla, S.
2015CEAB...39...75H Altcode:
Interplanetary coronal mass ejections (ICMEs) are structures in the
solar wind that are the counterparts of coronal mass ejections (CMEs)
at the Sun. It is commonly believed that enhanced magnetic fields
in interplanetary shocks and solar ejecta as well as the increased
turbulence in the solar wind sheath region are the cause of Forbush
decreases (FDs) representing decreases of galactic cosmic ray (GCR)
intensities. Recently, stealth CMEs i.e.~CMEs with no apparent solar
surface association have become a subject in recent studies of solar
activity. Whether all of such stealth CMEs can drive a FD is difficult
to investigate on the basis of neutron monitor NM measurements because
these measurements not only reflect the GCR intensity variation in
interplanetary space but also the variation of the geomagnetic field as
well as the conditions in the Earth atmosphere. Single detector counter
from spacecraft instrumentation, here SOHO and Chandra EPHIN, exceed
counting statistic of NMs allowing to determine intensity variation of
less than 1 permil in interplanetary space on the basis of 30 minute
count rate averages. Here we present the ongoing analysis of eleven
stealth CMEs.
---------------------------------------------------------
Title: Instant: An Innovative L5 Small Mission Concept for Coordinated
Science with Solar Orbiter and Solar Probe Plus
Authors: Lavraud, B.; Liu, Y. D.; Harrison, R. A.; Liu, W.;
Auchere, F.; Gan, W.; Lamy, P. L.; Xia, L.; Eastwood, J. P.;
Wimmer-Schweingruber, R. F.; Zong, Q.; Rochus, P.; Maksimovic, M.;
Temmer, M.; Escoubet, C. P.; Kilpua, E.; Rouillard, A. P.; Davies,
J. A.; Vial, J. C.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard,
T. A.; DeForest, C. E.
2014AGUFMSH21B4109L Altcode:
We will present both the science objectives and related instrumentation
of a small solar and heliospheric mission concept, INSTANT:
INvestigation of Solar-Terrestrial Activity aNd Transients. It will be
submitted as an opportunity to the upcoming ESA-China S-class mission
call later this year. This concept was conceived to allow innovative
measurements and unprecedented, early determination of key properties
of Earthbound CMEs from the L5 vantage point. Innovative measurements
will include magnetic field determination in the corona thanks to
Hanle measurement in Lyman-α and polarized heliospheric imaging
for accurate determination of CME trajectories. With complementary
in situ measurements, it will uniquely permit solar storm science,
solar storm surveillance, and synergy with Solar Orbiter and Solar
Probe Plus (the ESA-China S2 mission launch is planned in 2021).
---------------------------------------------------------
Title: Statistical Analysis of Large-Scale EUV Waves Observed by
STEREO/EUVI
Authors: Muhr, N.; Veronig, A. M.; Kienreich, I. W.; Vršnak, B.;
Temmer, M.; Bein, B. M.
2014SoPh..289.4563M Altcode: 2014arXiv1408.2513M; 2014SoPh..tmp..126M
We statistically analyzed the kinematical evolution and wave pulse
characteristics of 60 strong large-scale EUV wave events that
occurred during January 2007 to February 2011 with the STEREO
twin spacecraft. For the start velocity, the arithmetic mean
is 312±115 km s<SUP>−1</SUP> (within a range of 100 - 630 km
s<SUP>−1</SUP>). For the mean (linear) velocity, the arithmetic
mean is 254±76 km s<SUP>−1</SUP> (within a range of 130 - 470
km s<SUP>−1</SUP>). 52 % of all waves under study show a distinct
deceleration during their propagation (a≤−50 m s<SUP>−2</SUP>),
the other 48 % are consistent with a constant speed within the
uncertainties (−50≤a≤50 m s<SUP>−2</SUP>). The start velocity
and the acceleration are strongly anticorrelated with c≈−0.8,
i.e. initially faster events undergo stronger deceleration than
slower events. The (smooth) transition between constant propagation
for slow events and deceleration in faster events occurs at an EUV wave
start-velocity of v≈230 km s<SUP>−1</SUP>, which corresponds well to
the fast-mode speed in the quiet corona. These findings provide strong
evidence that the EUV waves under study are indeed large-amplitude
fast-mode MHD waves. This interpretation is also supported by the
correlations obtained between the peak velocity and the peak amplitude,
impulsiveness, and build-up time of the disturbance. We obtained
the following association rates of EUV wave events with other solar
phenomena: 95 % are associated with a coronal mass ejection (CME),
74 % to a solar flare, 15 % to interplanetary type II bursts, and 22
% to coronal type II bursts. These findings are consistent with the
interpretation that the associated CMEs are the driving agents of the
EUV waves.
---------------------------------------------------------
Title: Heliospheric Propagation of Coronal Mass Ejections: Comparison
of Numerical WSA-ENLIL+Cone Model and Analytical Drag-based Model
Authors: Vršnak, B.; Temmer, M.; Žic, T.; Taktakishvili, A.;
Dumbović, M.; Möstl, C.; Veronig, A. M.; Mays, M. L.; Odstrčil, D.
2014ApJS..213...21V Altcode:
Real-time forecasting of the arrival of coronal mass ejections (CMEs) at
Earth, based on remote solar observations, is one of the central issues
of space-weather research. In this paper, we compare arrival-time
predictions calculated applying the numerical "WSA-ENLIL+Cone
model" and the analytical "drag-based model" (DBM). Both models use
coronagraphic observations of CMEs as input data, thus providing an
early space-weather forecast two to four days before the arrival of
the disturbance at the Earth, depending on the CME speed. It is shown
that both methods give very similar results if the drag parameter Γ =
0.1 is used in DBM in combination with a background solar-wind speed
of w = 400 km s<SUP>-1</SUP>. For this combination, the mean value
of the difference between arrival times calculated by ENLIL and DBM
is \overline{Δ }=0.09+/- 9.0 hr with an average of the absolute-value
differences of \overline{\vert Δ \vert }=7.1 hr. Comparing the observed
arrivals (O) with the calculated ones (C) for ENLIL gives O - C = -0.3
± 16.9 hr and, analogously, O - C = +1.1 ± 19.1 hr for DBM. Applying
Γ = 0.2 with w = 450 km s<SUP>-1</SUP> in DBM, one finds O - C =
-1.7 ± 18.3 hr, with an average of the absolute-value differences
of 14.8 hr, which is similar to that for ENLIL, 14.1 hr. Finally,
we demonstrate that the prediction accuracy significantly degrades
with increasing solar activity.
---------------------------------------------------------
Title: Combined Multipoint Remote and in situ Observations of the
Asymmetric Evolution of a Fast Solar Coronal Mass Ejection
Authors: Rollett, T.; Möstl, C.; Temmer, M.; Frahm, R. A.; Davies,
J. A.; Veronig, A. M.; Vršnak, B.; Amerstorfer, U. V.; Farrugia,
C. J.; Žic, T.; Zhang, T. L.
2014ApJ...790L...6R Altcode: 2014arXiv1407.4687R
We present an analysis of the fast coronal mass ejection (CME) of 2012
March 7, which was imaged by both STEREO spacecraft and observed in
situ by MESSENGER, Venus Express, Wind, and Mars Express. Based on
detected arrivals at four different positions in interplanetary space,
it was possible to strongly constrain the kinematics and the shape of
the ejection. Using the white-light heliospheric imagery from STEREO-A
and B, we derived two different kinematical profiles for the CME
by applying the novel constrained self-similar expansion method. In
addition, we used a drag-based model to investigate the influence of
the ambient solar wind on the CME's propagation. We found that two
preceding CMEs heading in different directions disturbed the overall
shape of the CME and influenced its propagation behavior. While the
Venus-directed segment underwent a gradual deceleration (from ~2700 km
s<SUP>-1</SUP> at 15 R <SUB>⊙</SUB> to ~1500 km s<SUP>-1</SUP> at 154
R <SUB>⊙</SUB>), the Earth-directed part showed an abrupt retardation
below 35 R <SUB>⊙</SUB> (from ~1700 to ~900 km s<SUP>-1</SUP>). After
that, it was propagating with a quasi-constant speed in the wake of
a preceding event. Our results highlight the importance of studies
concerning the unequal evolution of CMEs. Forecasting can only be
improved if conditions in the solar wind are properly taken into
account and if attention is also paid to large events preceding the
one being studied.
---------------------------------------------------------
Title: Solar Energetic Particles and Associated EIT Disturbances in
Solar Cycle 23
Authors: Miteva, R.; Klein, K. -L.; Kienreich, I.; Temmer, M.; Veronig,
A.; Malandraki, O. E.
2014SoPh..289.2601M Altcode: 2014arXiv1402.1676M; 2014SoPh..tmp...37M
We explore the link between solar energetic particles (SEPs) observed
at 1 AU and large-scale disturbances propagating in the solar corona,
named after the Extreme ultraviolet Imaging Telescope (EIT) as EIT
waves, which trace the lateral expansion of a coronal mass ejection
(CME). A comprehensive search for SOHO/EIT waves was carried out for
179 SEP events during Solar Cycle 23 (1997 - 2006). 87 % of the SEP
events were found to be accompanied by EIT waves. In order to test if
the EIT waves play a role in the SEP acceleration, we compared their
extrapolated arrival time at the footpoint of the Parker spiral with
the particle onset in the 26 eastern SEP events that had no direct
magnetic connection to the Earth. We find that the onset of proton
events was generally consistent with this scenario. However, in a
number of cases the first near-relativistic electrons were detected too
early. Furthermore, the electrons had in general only weakly anisotropic
pitch-angle distributions. This poses a problem for the idea that the
SEPs were accelerated by the EIT wave or in any other spatially confined
region in the low corona. The presence of weak electron anisotropies in
SEP events from the eastern hemisphere suggests that transport processes
in interplanetary space, including cross-field diffusion, play a role
in giving the SEPs access to a broad range of helio-longitudes.
---------------------------------------------------------
Title: ISEST Program: International Stud of Earth-affecting Solar
Transients
Authors: Zhang, Jie; Temmer, Manuela; Gopalswamy, Nat
2014shin.confE...7Z Altcode:
A new international program: International Study of Earth-affecting
Solar Transients (IEST), is introduced. This program is one of
the four scientific elements supported by the VarSITI (Variability
of the Sun and Its Terrestrial Impact) project, a five-year long
international-cross-discipline-collaboration project from 2014-2018,
sponsored by the SCOSTEP (Scientific Committee of Solar-Terrestrial
Physics). The aim of ISEST is to understand the origin, propagation and
evolution of solar transients, including CMEs, CIRs and SEPs, through
the space between the Sun and the Earth, and improve the prediction
capability for space weather. Particular emphasis will be placed on the
weak solar activity prevailing in Solar Cycle 24 (MiniMax24). The ISEST
program consists of six working groups, encompassing data analysis,
theoretical interpretation, numerical modeling, B-south challenge,
event campaign study, and long-term MiniMax24 campaign studies. It
is anticipated that the ISEST will create a comprehensive online
database of Earth-affecting solar transients contributed by both
observers and modelers. By the end of the program It is expected that
the space weather prediction using solar observations will be improved
significantly.
---------------------------------------------------------
Title: Future mmVLBI Research with ALMA: A European vision
Authors: Tilanus, R. P. J.; Krichbaum, T. P.; Zensus, J. A.; Baudry,
A.; Bremer, M.; Falcke, H.; Giovannini, G.; Laing, R.; van Langevelde,
H. J.; Vlemmings, W.; Abraham, Z.; Afonso, J.; Agudo, I.; Alberdi,
A.; Alcolea, J.; Altamirano, D.; Asadi, S.; Assaf, K.; Augusto, P.;
Baczko, A-K.; Boeck, M.; Boller, T.; Bondi, M.; Boone, F.; Bourda,
G.; Brajsa, R.; Brand, J.; Britzen, S.; Bujarrabal, V.; Cales, S.;
Casadio, C.; Casasola, V.; Castangia, P.; Cernicharo, J.; Charlot,
P.; Chemin, L.; Clenet, Y.; Colomer, F.; Combes, F.; Cordes, J.;
Coriat, M.; Cross, N.; D'Ammando, F.; Dallacasa, D.; Desmurs, J-F.;
Eatough, R.; Eckart, A.; Eisenacher, D.; Etoka, S.; Felix, M.; Fender,
R.; Ferreira, M.; Freeland, E.; Frey, S.; Fromm, C.; Fuhrmann, L.;
Gabanyi, K.; Galvan-Madrid, R.; Giroletti, M.; Goddi, C.; Gomez, J.;
Gourgoulhon, E.; Gray, M.; di Gregorio, I.; Greimel, R.; Grosso, N.;
Guirado, J.; Hada, K.; Hanslmeier, A.; Henkel, C.; Herpin, F.; Hess,
P.; Hodgson, J.; Horns, D.; Humphreys, E.; Hutawarakorn Kramer, B.;
Ilyushin, V.; Impellizzeri, V.; Ivanov, V.; Julião, M.; Kadler, M.;
Kerins, E.; Klaassen, P.; van 't Klooster, K.; Kording, E.; Kozlov,
M.; Kramer, M.; Kreikenbohm, A.; Kurtanidze, O.; Lazio, J.; Leite,
A.; Leitzinger, M.; Lepine, J.; Levshakov, S.; Lico, R.; Lindqvist,
M.; Liuzzo, E.; Lobanov, A.; Lucas, P.; Mannheim, K.; Marcaide, J.;
Markoff, S.; Martí-Vidal, I.; Martins, C.; Masetti, N.; Massardi,
M.; Menten, K.; Messias, H.; Migliari, S.; Mignano, A.; Miller-Jones,
J.; Minniti, D.; Molaro, P.; Molina, S.; Monteiro, A.; Moscadelli,
L.; Mueller, C.; Müller, A.; Muller, S.; Niederhofer, F.; Odert,
P.; Olofsson, H.; Orienti, M.; Paladino, R.; Panessa, F.; Paragi,
Z.; Paumard, T.; Pedrosa, P.; Pérez-Torres, M.; Perrin, G.; Perucho,
M.; Porquet, D.; Prandoni, I.; Ransom, S.; Reimers, D.; Rejkuba, M.;
Rezzolla, L.; Richards, A.; Ros, E.; Roy, A.; Rushton, A.; Savolainen,
T.; Schulz, R.; Silva, M.; Sivakoff, G.; Soria-Ruiz, R.; Soria, R.;
Spaans, M.; Spencer, R.; Stappers, B.; Surcis, G.; Tarchi, A.; Temmer,
M.; Thompson, M.; Torrelles, J.; Truestedt, J.; Tudose, V.; Venturi,
T.; Verbiest, J.; Vieira, J.; Vielzeuf, P.; Vincent, F.; Wex, N.;
Wiik, K.; Wiklind, T.; Wilms, J.; Zackrisson, E.; Zechlin, H.
2014arXiv1406.4650T Altcode:
Very long baseline interferometry at millimetre/submillimetre
wavelengths (mmVLBI) offers the highest achievable spatial
resolution at any wavelength in astronomy. The anticipated inclusion
of ALMA as a phased array into a global VLBI network will bring
unprecedented sensitivity and a transformational leap in capabilities
for mmVLBI. Building on years of pioneering efforts in the US and
Europe the ongoing ALMA Phasing Project (APP), a US-led international
collaboration with MPIfR-led European contributions, is expected to
deliver a beamformer and VLBI capability to ALMA by the end of 2014
(APP: Fish et al. 2013, arXiv:1309.3519). This report focuses on
the future use of mmVLBI by the international users community from
a European viewpoint. Firstly, it highlights the intense science
interest in Europe in future mmVLBI observations as compiled from
the responses to a general call to the European community for future
research projects. A wide range of research is presented that includes,
amongst others: - Imaging the event horizon of the black hole at the
centre of the Galaxy - Testing the theory of General Relativity an/or
searching for alternative theories - Studying the origin of AGN jets
and jet formation - Cosmological evolution of galaxies and BHs, AGN
feedback - Masers in the Milky Way (in stars and star-forming regions) -
Extragalactic emission lines and astro-chemistry - Redshifted absorption
lines in distant galaxies and study of the ISM and circumnuclear gas -
Pulsars, neutron stars, X-ray binaries - Testing cosmology - Testing
fundamental physical constants
---------------------------------------------------------
Title: Connecting Speeds, Directions and Arrival Times of 22 Coronal
Mass Ejections from the Sun to 1 AU
Authors: Möstl, C.; Amla, K.; Hall, J. R.; Liewer, P. C.; De Jong,
E. M.; Colaninno, R. C.; Veronig, A. M.; Rollett, T.; Temmer, M.;
Peinhart, V.; Davies, J. A.; Lugaz, N.; Liu, Y. D.; Farrugia, C. J.;
Luhmann, J. G.; Vršnak, B.; Harrison, R. A.; Galvin, A. B.
2014ApJ...787..119M Altcode: 2014arXiv1404.3579M
Forecasting the in situ properties of coronal mass ejections (CMEs)
from remote images is expected to strongly enhance predictions of
space weather and is of general interest for studying the interaction
of CMEs with planetary environments. We study the feasibility of using
a single heliospheric imager (HI) instrument, imaging the solar wind
density from the Sun to 1 AU, for connecting remote images to in situ
observations of CMEs. We compare the predictions of speed and arrival
time for 22 CMEs (in 2008-2012) to the corresponding interplanetary
coronal mass ejection (ICME) parameters at in situ observatories
(STEREO PLASTIC/IMPACT, Wind SWE/MFI). The list consists of front-
and backsided, slow and fast CMEs (up to 2700 km s<SUP>-1</SUP>). We
track the CMEs to 34.9 ± 7.1 deg elongation from the Sun with J maps
constructed using the SATPLOT tool, resulting in prediction lead times
of -26.4 ± 15.3 hr. The geometrical models we use assume different
CME front shapes (fixed-Φ, harmonic mean, self-similar expansion) and
constant CME speed and direction. We find no significant superiority
in the predictive capability of any of the three methods. The absolute
difference between predicted and observed ICME arrival times is 8.1 ±
6.3 hr (rms value of 10.9 hr). Speeds are consistent to within 284 ±
288 km s<SUP>-1</SUP>. Empirical corrections to the predictions enhance
their performance for the arrival times to 6.1 ± 5.0 hr (rms value
of 7.9 hr), and for the speeds to 53 ± 50 km s<SUP>-1</SUP>. These
results are important for Solar Orbiter and a space weather mission
positioned away from the Sun-Earth line.
---------------------------------------------------------
Title: Morphology of an ICME-event derived by Multi-point in Situ
and Heliospheric Imaging Data
Authors: Rollett, Tanja; Möstl, Christian; Temmer, Manuela; Veronig,
Astrid M.; Frahm, Rudy A.; Davies, Jackie A.; Vrsnak, Bojan; Farrugia,
Charles J.; Amerstorfer, Ute V.
2014EGUGA..1610892R Altcode:
We show the analysis of an outstanding fast interplanetary coronal
mass ejection (ICME) of 07 March 2012, which has been observed
stereoscopically from both STEREO spacecraft. Assuming self-similar
expansion and constant direction of motion we derive the kinematical
profiles for the eastern and the western part of the roughly
Earth-directed ICME. As additional constraints we use the huge
advantage of in situ measurements at various locations during the
ICME's propagation, namely from Venus Express, Messenger, Wind and
Mars Express. We found that the eastern part of the ICME had a much
higher propagation speed than its western part. Using the drag-based
model, a model for the propagation of ICMEs in the inner heliosphere,
we analyzed the influence of the drag on both sides of the ICME due
to the surrounding solar wind conditions. These different solar wind
conditions could have been the reason for the differing velocities
and therefore for a distortion of the ICME front. These studies are
fundamental in order to deepen the understanding of ICME evolution
and to enhance existing forecasting methods.
---------------------------------------------------------
Title: Connecting speeds, directions and arrival times of 22 coronal
mass ejections from the Sun to 1 AU
Authors: Möstl, Christian; Amla, Keshav; Hall, Jeff R.; Liewer,
Paulett C.; DeJong, Eric M.; Colaninno, Robin C.; Veronig, Astrid M.;
Rollett, Tanja; Temmer, Manuela; Peinhart, Vanessa; Davies, Jackie
A.; Lugaz, Noé; Liu, Ying; Farrugia, Charles J.; Luhmann, Janet G.;
Vrsnak, Bojan; Harrison, Richard A.; Galvin, Antoinette B.
2014EGUGA..16.1755M Altcode:
Forecasting in situ properties of coronal mass ejections (CMEs) from
remote images is expected to strongly enhance predictions of space
weather, and is of general interest for studying the interaction of
the solar wind with planetary environments. We study the feasibility of
using a heliospheric imager (HI) instrument, which is able to image the
solar wind density along the full Sun to 1 AU distance, for connecting
remote images to in situ observations of CMEs. Such an instrument
is currently in operation on each of the two STEREO spacecraft. We
compare the predictions for speed and arrival time for 22 different
CME events (between 2008-2012), each observed remotely by one STEREO
spacecraft, to the interplanetary coronal mass ejection (ICME) speed and
arrival time observed at in situ observatories (STEREO PLASTIC/IMPACT,
Wind SWE/MFI). We use croissant modeling for STEREO/COR2, and with a
single-spacecraft STEREO/HI instrument, we track each CME to 34.9 ± 7.1
degree elongation from the Sun with J-maps constructed with the SATPLOT
tool. We then fit geometrical models to each track, assuming different
CME front shapes (Fixed-Φ, Harmonic Mean, Self-Similar Expansion),
and constant CME speed and direction. We find no significant preference
in the predictive capability for any of the three geometrical modeling
methods used on the full event list, consisting of front- and backsided,
slow and fast CMEs (up to 2700 km s-1). The absolute difference between
predicted and observed ICME arrival times is 8.1 ± 6.4 hours (rms
value of 10.9h), and speeds are consistent within 284 ± 291 km s-1,
including the geometric effects of CME apex or flank encounters. We
derive new empirical corrections to the imaging results, enhancing
the performance of the arrival time predictions to 6.1 ± 5.0 hours
(rms value of 7.9h), and the speed predictions to 53 ± 50 km s-1,
for this particular set of events. The prediction lead time is around
1 day (-26.4 ± 15.3h). CME directions given by the HI methods differ
considerably, and biases are found on the order of 30-50 degree in
heliospheric longitude, consistent with theoretical expectations. These
results are of interest concerning future missions such as Solar Orbiter
or a dedicated space weather mission positioned remotely from the Earth.
---------------------------------------------------------
Title: Comparative Study of MHD Modeling of the Background Solar Wind
Authors: Gressl, C.; Veronig, A. M.; Temmer, M.; Odstrčil, D.;
Linker, J. A.; Mikić, Z.; Riley, P.
2014SoPh..289.1783G Altcode: 2013arXiv1312.1220G
Knowledge about the background solar wind plays a crucial role in
the framework of space-weather forecasting. In-situ measurements
of the background solar wind are only available for a few points in
the heliosphere where spacecraft are located, therefore we have to
rely on heliospheric models to derive the distribution of solar-wind
parameters in interplanetary space. We test the performance of different
solar-wind models, namely Magnetohydrodynamic Algorithm outside
a Sphere/ENLIL (MAS/ENLIL), Wang-Sheeley-Arge/ENLIL (WSA/ENLIL),
and MAS/MAS, by comparing model results with in-situ measurements
from spacecraft located at 1 AU distance to the Sun (ACE, Wind). To
exclude the influence of interplanetary coronal mass ejections
(ICMEs), we chose the year 2007 as a time period with low solar
activity for our comparison. We found that the general structure of the
background solar wind is well reproduced by all models. The best model
results were obtained for the parameter solar-wind speed. However,
the predicted arrival times of high-speed solar-wind streams have
typical uncertainties of the order of about one day. Comparison of
model runs with synoptic magnetic maps from different observatories
revealed that the choice of the synoptic map significantly affects
the model performance.
---------------------------------------------------------
Title: Response of the Earth's thermosphere to interplanetary coronal
mass ejections
Authors: Krauss, S.; Temmer, M.; Lammer, H.; Veronig, A.; Baur, O.;
Pfleger, M.; Boudjada, M. Y.; Leitzinger, M.; Besser, B. P.
2014EPSC....9..724K Altcode:
In this contribution we address the Earth's thermospheric response to
interplanetary coronal mass ejections. We investigate several ICME
events by means of neutral density measurements from the low-Earth
orbiting satellites GRACE. Furthermore we correlate these observations
with data from the ACE satellite located at L1 upstream of the Earth. By
analyzing the data, high correlations between the neutral density and
various combinations of ICME parameters can be found.
---------------------------------------------------------
Title: Asymmetry in the CME-CME Interaction Process for the Events
from 2011 February 14-15
Authors: Temmer, M.; Veronig, A. M.; Peinhart, V.; Vršnak, B.
2014ApJ...785...85T Altcode: 2014arXiv1402.6891T
We present a detailed study of the interaction process of two coronal
mass ejections (CMEs) successively launched on 2011 February 14 (CME1)
and 2011 February 15 (CME2). Reconstructing the three-dimensional
shape and evolution of the flux ropes, we verify that the two CMEs
interact. The frontal structure of both CMEs, measured along different
position angles (PAs) over the entire latitudinal extent, reveals
differences in the kinematics for the interacting flanks and the
apexes. The interaction process is strongly PA-dependent in terms of
timing as well as kinematical evolution. The central interaction occurs
along PA-100°, which shows the strongest changes in kinematics. During
interaction, CME1 accelerates from ~400 km s<SUP>-1</SUP> to ~700 km
s<SUP>-1</SUP> and CME2 decelerates from ~1300 km s<SUP>-1</SUP> to ~600
km s<SUP>-1</SUP>. Our results indicate that a simplified scenario such
as inelastic collision may not be sufficient to describe the CME-CME
interaction. The magnetic field structures of the intertwining flux
ropes and the momentum transfer due to shocks each play an important
role in the interaction process.
---------------------------------------------------------
Title: Solar Magnetized Tornadoes: Rotational Motion in a Tornado-like
Prominence
Authors: Su, Yang; Gömöry, Peter; Veronig, Astrid; Temmer, Manuela;
Wang, Tongjiang; Vanninathan, Kamalam; Gan, Weiqun; Li, YouPing
2014ApJ...785L...2S Altcode: 2013arXiv1312.5226S
Su et al. proposed a new explanation for filament formation and
eruption, where filament barbs are rotating magnetic structures driven
by underlying vortices on the surface. Such structures have been noticed
as tornado-like prominences when they appear above the limb. They may
play a key role as the source of plasma and twist in filaments. However,
no observations have successfully distinguished rotational motion of
the magnetic structures in tornado-like prominences from other motions
such as oscillation and counter-streaming plasma flows. Here we report
evidence of rotational motions in a tornado-like prominence. The
spectroscopic observations in two coronal lines were obtained from a
specifically designed Hinode/EIS observing program. The data revealed
the existence of both cold and million-degree-hot plasma in the
prominence leg, supporting the so-called prominence-corona transition
region. The opposite velocities at the two sides of the prominence and
their persistent time evolution, together with the periodic motions
evident in SDO/AIA dark structures, indicate a rotational motion of
both cold and hot plasma with a speed of ~5 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: A Challenging Solar Eruptive Event of 18 November 2003 and
the Causes of the 20 November Geomagnetic Superstorm. II. CMEs,
Shock Waves, and Drifting Radio Bursts
Authors: Grechnev, V. V.; Uralov, A. M.; Chertok, I. M.; Slemzin,
V. A.; Filippov, B. P.; Egorov, Y. I.; Fainshtein, V. G.; Afanasyev,
A. N.; Prestage, N. P.; Temmer, M.
2014SoPh..289.1279G Altcode: 2013arXiv1308.3010G
We continue our study (Grechnev et al., 2013,
doi:10.1007/s11207-013-0316-6; Paper I) on the 18 November 2003
geoffective event. To understand possible impact on geospace of coronal
transients observed on that day, we investigated their properties
from solar near-surface manifestations in extreme ultraviolet, LASCO
white-light images, and dynamic radio spectra. We reconcile near-surface
activity with the expansion of coronal mass ejections (CMEs) and
determine their orientation relative to the earthward direction. The
kinematic measurements, dynamic radio spectra, and microwave and X-ray
light curves all contribute to the overall picture of the complex event
and confirm an additional eruption at 08:07 - 08:20 UT close to the
solar disk center presumed in Paper I. Unusual characteristics of the
ejection appear to match those expected for a source of the 20 November
superstorm but make its detection in LASCO images hopeless. On the
other hand, none of the CMEs observed by LASCO seem to be a promising
candidate for a source of the superstorm being able to produce, at most,
a glancing blow on the Earth's magnetosphere. Our analysis confirms free
propagation of shock waves revealed in the event and reconciles their
kinematics with "EUV waves" and dynamic radio spectra up to decameters.
---------------------------------------------------------
Title: A Challenging Solar Eruptive Event of 18 November 2003 and
the Causes of the 20 November Geomagnetic Superstorm. I. Unusual
History of an Eruptive Filament
Authors: Grechnev, V. V.; Uralov, A. M.; Slemzin, V. A.; Chertok,
I. M.; Filippov, B. P.; Rudenko, G. V.; Temmer, M.
2014SoPh..289..289G Altcode: 2013arXiv1304.7950G
This is the first of four companion papers, which comprehensively
analyze a complex eruptive event of 18 November 2003 in active region
(AR) 10501 and the causes of the largest Solar Cycle 23 geomagnetic
storm on 20 November 2003. Analysis of a complete data set, not
considered before, reveals a chain of eruptions to which hard X-ray and
microwave bursts responded. A filament in AR 10501 was not a passive
part of a larger flux rope, as usually considered. The filament erupted
and gave origin to a coronal mass ejection (CME). The chain of events
was as follows: i) a presumable eruption at 07:29 UT accompanied by
a not reported M1.2 class flare probably associated with the onset of
a first southeastern CME (CME1), which most likely is not responsible
for the superstorm; ii) a confined eruption (without a CME) at 07:41 UT
(M3.2 flare) that destabilized the large filament; iii) the filament
acceleration around 07:56 UT; iv) the bifurcation of the eruptive
filament that transformed into a large "cloud"; v) an M3.9 flare in
AR 10501 associated to this transformation. The transformation of the
filament could be due to the interaction of the eruptive filament with
the magnetic field in the neighborhood of a null point, located at a
height of about 100 Mm above the complex formed by ARs 10501, 10503,
and their environment. The CORONAS-F/SPIRIT telescope observed the
cloud in 304 Å as a large Y-shaped darkening, which moved from the
bifurcation region across the solar disk to the limb. The masses and
kinematics of the cloud and the filament were similar. Remnants of
the filament were not clearly observed in the second southwestern CME
(CME2), previously regarded as a source of the 20 November geomagnetic
storm. These facts do not support a simple scenario, in which the
interplanetary magnetic cloud is considered as a flux rope formed from
a structure initially associated with the pre-eruption filament in AR
10501. Observations suggest a possible additional eruption above the
bifurcation region close to solar disk center between 08:07 and 08:17
UT, which could be the source of the 20 November superstorm.
---------------------------------------------------------
Title: Kinematics of Interacting ICMEs and Related Forbush Decrease:
Case Study
Authors: Maričić, D.; Vršnak, B.; Dumbović, M.; Žic, T.; Roša,
D.; Hržina, D.; Lulić, S.; Romštajn, I.; Bušić, I.; Salamon, K.;
Temmer, M.; Rollett, T.; Veronig, A.; Bostanjyan, N.; Chilingarian,
A.; Mailyan, B.; Arakelyan, K.; Hovhannisyan, A.; Mujić, N.
2014SoPh..289..351M Altcode:
We study heliospheric propagation and some space weather aspects of
three Earth-directed interplanetary coronal mass ejections (ICMEs),
successively launched from the active region AR 11158 in the period
13 - 15 February 2011. From the analysis of the ICME kinematics,
morphological evolution, and in situ observations, we infer that the
three ICMEs interacted on their way to Earth, arriving together at 1
AU as a single interplanetary disturbance. Detailed analysis of the
in situ data reveals complex internal structure of the disturbance,
where signatures of the three initially independent ICMEs could be
recognized. The analysis also reveals compression and heating of the
middle ICME, as well as ongoing magnetic reconnection between the
leading and the middle ICME. We present evidence showing that the
propagation of these two, initially slower ICMEs, was boosted by the
fastest, third ICME. Finally, we employ the ground-based cosmic ray
observations, to show that this complex disturbance produced a single
cosmic ray event, i.e., a simple Forbush decrease (FD). The results
presented provide a better understanding of the ICME interactions and
reveal effects that should be taken into account in forecasting of
the arrival of such compound structures.
---------------------------------------------------------
Title: Identification of coronal holes and filament channels in
SDO/AIA 193Å images via geometrical classification methods
Authors: Reiss, M.; Temmer, M.; Rotter, T.; Hofmeister, S. J.; Veronig,
A. M.
2014CEAB...38...95R Altcode: 2014arXiv1408.2777R
In this study, we describe and evaluate shape measures for
distinguishing between coronal holes and filament channels as
observed in Extreme Ultraviolet (EUV) images of the Sun. For a set
of well-observed coronal hole and filament channel regions extracted
from SDO/AIA 193Å images we analyze their intrinsic morphology during
the period 2011 to 2013, by using well known shape measures from the
literature and newly developed geometrical classification methods. The
results suggest an asymmetry in the morphology of filament channels
giving support for the sheared arcade or weakly twisted flux rope model
for filaments. We find that the proposed shape descriptors have the
potential to reduce coronal hole classification errors and are eligible
for screening techniques in order to improve the forecasting of solar
wind high-speed streams from CH observations in solar EUV images.
---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections by Sunspot Rotation
Authors: Valori, G.; Török, T.; Temmer, M.; Veronig, A. M.; van
Driel-Gesztelyi, L.; Vršnak, B.
2014IAUS..300..201V Altcode:
We report observations of a filament eruption, two-ribbon flare, and
coronal mass ejection (CME) that occurred in Active Region NOAA 10898
on 6 July 2006. The filament was located South of a strong sunspot that
dominated the region. In the evolution leading up to the eruption, and
for some time after it, a counter-clockwise rotation of the sunspot of
about 30 degrees was observed. We suggest that the rotation triggered
the eruption by progressively expanding the magnetic field above the
filament. To test this scenario, we study the effect of twisting
the initially potential field overlying a pre-existing flux rope,
using three-dimensional zero-β MHD simulations. We consider a magnetic
configuration whose photospheric flux distribution and coronal structure
is guided by the observations and a potential field extrapolation. We
find that the twisting leads to the expansion of the overlying field. As
a consequence of the progressively reduced magnetic tension, the flux
rope quasi-statically adapts to the changed environmental field, rising
slowly. Once the tension is sufficiently reduced, a distinct second
phase of evolution occurs where the flux rope enters an unstable regime
characterized by a strong acceleration. Our simulation thus suggests
a new mechanism for the triggering of eruptions in the vicinity of
rotating sunspots.
---------------------------------------------------------
Title: The Wave-Driver System of the Off-Disk Coronal Wave of 17
January 2010
Authors: Temmer, M.; Vrsnak, B.; Veronig, A. M.
2013SoPh..287..441T Altcode: 2012arXiv1207.2857T; 2012SoPh..tmp..194T
We study the 17 January 2010 flare-CME-wave event by using
STEREO/SECCHI-EUVI and -COR1 data. The observational study is combined
with an analytic model that simulates the evolution of the coronal wave
phenomenon associated with the event. From EUV observations, the wave
signature appears to be dome shaped having a component propagating
on the solar surface (\overline{v}≈280~km s^{-1}) as well as one
off-disk (\overline{v}≈ 600~km s^{-1}) away from the Sun. The off-disk
dome of the wave consists of two enhancements in intensity, which
conjointly develop and can be followed up to white-light coronagraph
images. Applying an analytic model, we derive that these intensity
variations belong to a wave-driver system with a weakly shocked wave,
initially driven by expanding loops, which are indicative of the early
evolution phase of the accompanying CME. We obtain the shock standoff
distance between wave and driver from observations as well as from
model results. The shock standoff distance close to the Sun (< 0.3
R<SUB>⊙</SUB> above the solar surface) is found to rapidly increase
with values of ≈ 0.03 - 0.09 R<SUB>⊙</SUB>, which gives evidence
of an initial lateral (over)expansion of the CME. The kinematical
evolution of the on-disk wave could be modeled using input parameters
that require a more impulsive driver (duration t=90 s, acceleration
a=1.7 km s<SUP>−2</SUP>) compared to the off-disk component (duration
t=340 s, acceleration a=1.5 km s<SUP>−2</SUP>).
---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections by Sunspot Rotation
Authors: Török, T.; Temmer, M.; Valori, G.; Veronig, A. M.; van
Driel-Gesztelyi, L.; Vršnak, B.
2013SoPh..286..453T Altcode: 2014arXiv1401.2922T
We study a filament eruption, two-ribbon flare, and coronal mass
ejection (CME) that occurred in NOAA Active Region 10898 on 6 July
2006. The filament was located South of a strong sunspot that dominated
the region. In the evolution leading up to the eruption, and for some
time after it, a counter-clockwise rotation of the sunspot of about
30 degrees was observed. We suggest that the rotation triggered the
eruption by progressively expanding the magnetic field above the
filament. To test this scenario, we study the effect of twisting
the initially potential field overlying a pre-existing flux-rope,
using three-dimensional zero-β MHD simulations. We first consider
a relatively simple and symmetric system, and then study a more
complex and asymmetric magnetic configuration, whose photospheric-flux
distribution and coronal structure are guided by the observations and a
potential field extrapolation. In both cases, we find that the twisting
leads to the expansion of the overlying field. As a consequence of the
progressively reduced magnetic tension, the flux-rope quasi-statically
adapts to the changed environmental field, rising slowly. Once the
tension is sufficiently reduced, a distinct second phase of evolution
occurs where the flux-rope enters an unstable regime characterised by
a strong acceleration. Our simulations thus suggest a new mechanism
for the triggering of eruptions in the vicinity of rotating sunspots.
---------------------------------------------------------
Title: Formation of Coronal Shock Waves
Authors: Lulić, S.; Vršnak, B.; Žic, T.; Kienreich, I. W.; Muhr,
N.; Temmer, M.; Veronig, A. M.
2013SoPh..286..509L Altcode: 2013arXiv1303.2786L
Magnetosonic wave formation driven by an expanding cylindrical
piston is numerically simulated to obtain better physical insight
into the initiation and evolution of large-scale coronal waves caused
by coronal eruptions. Several very basic initial configurations are
employed to analyze intrinsic characteristics of MHD wave formation
that do not depend on specific properties of the environment. It turns
out that these simple initial configurations result in piston/wave
morphologies and kinematics that reproduce common characteristics of
coronal waves. In the initial stage, the wave and the expanding source
region cannot be clearly resolved; i.e. a certain time is needed before
the wave detaches from the piston. Thereafter, it continues to travel
as what is called a "simple wave." During the acceleration stage of the
source region inflation, the wave is driven by the piston expansion, so
its amplitude and phase-speed increase, whereas the wavefront profile
steepens. At a given point, a discontinuity forms in the wavefront
profile; i.e. the leading edge of the wave becomes shocked. The
time/distance required for the shock formation is shorter for a more
impulsive source-region expansion. After the piston stops, the wave
amplitude and phase speed start to decrease. During the expansion,
most of the source region becomes strongly rarefied, which reproduces
the coronal dimming left behind the eruption. However, the density
increases at the source-region boundary, and stays enhanced even after
the expansion stops, which might explain stationary brightenings
that are sometimes observed at the edges of the erupted coronal
structure. Also, in the rear of the wave a weak density depletion
develops, trailing the wave, which is sometimes observed as weak
transient coronal dimming. Finally, we find a well-defined relationship
between the impulsiveness of the source-region expansion and the wave
amplitude and phase speed. The results for the cylindrical piston are
also compared with the outcome for a planar wave that is formed by a
one-dimensional piston, to find out how different geometries affect
the evolution of the wave.
---------------------------------------------------------
Title: Imaging coronal magnetic-field reconnection in a solar flare
Authors: Su, Yang; Veronig, Astrid M.; Holman, Gordon D.; Dennis,
Brian R.; Wang, Tongjiang; Temmer, Manuela; Gan, Weiqun
2013NatPh...9..489S Altcode: 2013arXiv1307.4527S
Magnetic-field reconnection is believed to play a fundamental role
in magnetized plasma systems throughout the Universe, including
planetary magnetospheres, magnetars and accretion disks around black
holes. This letter presents extreme ultraviolet and X-ray observations
of a solar flare showing magnetic reconnection with a level of clarity
not previously achieved. The multi-wavelength extreme ultraviolet
observations from SDO/AIA show inflowing cool loops and newly formed,
outflowing hot loops, as predicted. RHESSI X-ray spectra and images
simultaneously show the appearance of plasma heated to >10MK at
the expected locations. These two data sets provide solid visual
evidence of magnetic reconnection producing a solar flare, validating
the basic physical mechanism of popular flare models. However, new
features are also observed that need to be included in reconnection
and flare studies, such as three-dimensional non-uniform, non-steady
and asymmetric evolution.
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Title: Solar TErrestrial Relations Observatory-A (STEREO-A) and
PRoject for On-Board Autonomy 2 (PROBA2) Quadrature Observations of
Reflections of Three EUV Waves from a Coronal Hole
Authors: Kienreich, I. W.; Muhr, N.; Veronig, A. M.; Berghmans, D.;
De Groof, A.; Temmer, M.; Vršnak, B.; Seaton, D. B.
2013SoPh..286..201K Altcode: 2012SoPh..tmp..138K
We investigate the interaction of three consecutive large-scale coronal
waves with a polar coronal hole, simultaneously observed on-disk by the
Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on
the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on
27 January 2011. All three extreme ultraviolet (EUV) waves originate
from the same active region, NOAA 11149, positioned at N30E15 in the
STEREO-A field of view and on the limb in PROBA2. For the three primary
EUV waves, we derive starting velocities in the range of ≈ 310 km
s<SUP>−1</SUP> for the weakest up to ≈ 500 km s<SUP>−1</SUP>
for the strongest event. Each large-scale wave is reflected at the
border of the extended coronal hole at the southern polar region. The
average velocities of the reflected waves are found to be smaller than
the mean velocities of their associated direct waves. However, the
kinematical study also reveals that in each case the ending velocity
of the primary wave matches the initial velocity of the reflected
wave. In all three events, the primary and reflected waves obey the
Huygens-Fresnel principle, as the incident angle with ≈ 10° to
the normal is of the same magnitude as the angle of reflection. The
correlation between the speed and the strength of the primary EUV waves,
the homologous appearance of both the primary and the reflected waves,
and in particular the EUV wave reflections themselves suggest that the
observed EUV transients are indeed nonlinear large-amplitude MHD waves.
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Title: Propagation of Interplanetary Coronal Mass Ejections: The
Drag-Based Model
Authors: Vršnak, B.; Žic, T.; Vrbanec, D.; Temmer, M.; Rollett, T.;
Möstl, C.; Veronig, A.; Čalogović, J.; Dumbović, M.; Lulić, S.;
Moon, Y. -J.; Shanmugaraju, A.
2013SoPh..285..295V Altcode: 2012SoPh..tmp..124V
We present the "Drag-Based Model" (DBM) of heliospheric propagation
of interplanetary coronal mass ejections (ICMEs). The DBM is based on
the hypothesis that the driving Lorentz force, which launches a CME,
ceases in the upper corona and that beyond a certain distance the
dynamics becomes governed solely by the interaction of the ICME and
the ambient solar wind. In particular, we consider the option where
the drag acceleration has a quadratic dependence on the ICME relative
speed, which is expected in a collisionless environment, where the
drag is caused primarily by emission of magnetohydrodynamic (MHD)
waves. In this paper we present the simplest version of DBM, where
the equation of motion can be solved analytically, providing explicit
solutions for the Sun-Earth ICME transit time and impact speed. This
offers easy handling and straightforward application to real-time
space-weather forecasting. Beside presenting the model itself, we
perform an analysis of DBM performances, applying a statistical and
case-study approach, which provides insight into the advantages and
drawbacks of DBM. Finally, we present a public, DBM-based, online
forecast tool.
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Title: Heliospheric Imaging of 3D Density Structures During the
Multiple Coronal Mass Ejections of Late July to Early August 2010
Authors: Webb, D. F.; Möstl, C.; Jackson, B. V.; Bisi, M. M.; Howard,
T. A.; Mulligan, T.; Jensen, E. A.; Jian, L. K.; Davies, J. A.; de
Koning, C. A.; Liu, Y.; Temmer, M.; Clover, J. M.; Farrugia, C. J.;
Harrison, R. A.; Nitta, N.; Odstrcil, D.; Tappin, S. J.; Yu, H. -S.
2013SoPh..285..317W Altcode:
It is usually difficult to gain a consistent global understanding
of a coronal mass ejection (CME) eruption and its propagation
when only near-Sun imagery and the local measurements derived from
single-spacecraft observations are available. Three-dimensional (3D)
density reconstructions based on heliospheric imaging allow us to
"fill in" the temporal and spatial gaps between the near-Sun and in
situ data to provide a truly global picture of the propagation and
interactions of the CME as it moves through the inner heliosphere. In
recent years the heliospheric propagation of dense structures has been
observed and measured by the heliospheric imagers of the Solar Mass
Ejection Imager (SMEI) and on the twin Solar TErrestrial RElations
Observatory (STEREO) spacecraft. We describe the use of several 3D
reconstruction techniques based on these heliospheric imaging data sets
to distinguish and track the propagation of multiple CMEs in the inner
heliosphere during the very active period of solar activity in late July
- early August 2010. We employ 3D reconstruction techniques used at the
University of California, San Diego (UCSD) based on a kinematic solar
wind model, and also the empirical Tappin-Howard model. We compare
our results with those from other studies of this active period,
in particular the heliospheric simulations made with the ENLIL model
by Odstrcil et al. (J. Geophys. Res., 2013) and the in situ results
from multiple spacecraft provided by Möstl et al. (Astrophys. J.758,
10 - 28, 2012). We find that the SMEI results in particular provide
an overall context for the multiple-density flows associated with
these CMEs. For the first time we are able to intercompare the 3D
reconstructed densities with the timing and magnitude of in situ
density structures at five spacecraft spread over 150° in ecliptic
longitude and from 0.4 to 1 AU in radial distance. We also model the
magnetic flux-rope structures at three spacecraft using both force-free
and non-force-free modelling, and compare their timing and spatial
structure with the reconstructed density flows.
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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.
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Title: 2.5D MHD Simulations of the Kelvin-Helmholtz Instability at
CME-Boundaries in the Solar Corona
Authors: Möstl, Ute; Temmer, Manuela; Veronig, Astrid
2013EGUGA..15.4171M Altcode:
We discuss the observation of a coronal mass ejection (CME) by the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory from
2011 February 24. This CME with an embedded filament shows periodic
vortex-like structures at the northern side of the filament boundary
with a wavelength of approximately 14.4 Mm and a propagation speed of
about 310 ± 20 km/s. The morphological analysis hints at structures
produced by the Kelvin-Helmholtz (KH) instability on the boundary of the
filament. We conduct 2.5D numerical simulations of the KH instability,
whose results yield qualitative as well as quantitative agreements with
the observations. Furthermore, we study the absence of KH vortex-like
structures on the southern side of the filament boundary and find that
a magnetic field component parallel to the boundary with a strength
of about 20% of the total magnetic field has stabilizing effects
resulting in an asymmetric development of the instability. This work
receives funding from the Austrian Science Fund (FWF): P21051-N16,
V195-N16 and P24092-N16.
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Title: The Kanzelhöhe Observatory
Authors: Pötzi, Werner; Temmer, Manuela; Veronig, Astrid;
Hirtenfellner-Polanec, Wolfgang; Baumgartner, Dietmar
2013EGUGA..15.1459P Altcode:
Kanzelhöhe Observatory (KSO; kso.ac.at) located in the South of
Austria is part of the Institute of Physics of the University of
Graz. Since the early 1940s, the Sun has been observed in various
layers and wavelengths. Currently, KSO provides high-cadence full-disk
observations of the solar disk in three wavelengths: H-alpha line,
Ca II K line, white light. Real-time images are published online. For
scientific use, the data is processed, and immediately available to
the scientific community after each observing day via the Kanzelhöhe
Online Data Archive archive (KODA; kanzelhohe.uni-graz.at). KSO is part
of the Global H-Alpha Network and is also one of the contributing
stations for the international sunspot number. In the frame of
ESA's Space Situational Awareness program, methods are currently
under development for near-real image recognition with respect to
solar flares and filaments. These data products will give valuable
complementary information for the solar sources of space weather.
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Title: Assessing the Constrained Harmonic Mean Method for Deriving
the Kinematics of ICMEs with a Numerical Simulation
Authors: Rollett, T.; Temmer, M.; Möstl, C.; Lugaz, N.; Veronig,
A. M.; Möstl, U. V.
2013SoPh..283..541R Altcode: 2013arXiv1301.6945R
In this study we use a numerical simulation of an artificial coronal
mass ejection (CME) to validate a method for calculating propagation
directions and kinematical profiles of interplanetary CMEs (ICMEs). In
this method observations from heliospheric images are constrained
with in-situ plasma and field data at 1 AU. These data are used
to convert measured ICME elongations into distance by applying the
harmonic mean approach, which assumes a spherical shape of the ICME
front. We used synthetic white-light images, similar to those observed
by STEREO-A/HI, for three different separation angles between remote
and in-situ spacecraft of 30<SUP>∘</SUP>, 60<SUP>∘</SUP>, and
90<SUP>∘</SUP>. To validate the results of the method, the images were
compared to the apex speed profile of the modeled ICME, as obtained
from a top view. This profile reflects the "true" apex kinematics
because it is not affected by scattering or projection effects. In
this way it is possible to determine the accuracy of the method for
revealing ICME propagation directions and kinematics. We found that
the direction obtained by the constrained harmonic mean method is not
very sensitive to the separation angle (30<SUP>∘</SUP> sep: ϕ=W7;
60<SUP>∘</SUP> sep: ϕ=W12; 90<SUP>∘</SUP> sep: ϕ=W15; true dir.:
E0/W0). For all three cases the derived kinematics agree relatively
well with the real kinematics. The best consistency is obtained for the
30<SUP>∘</SUP> case, while with growing separation angle the ICME
speed at 1 AU is increasingly overestimated (30<SUP>∘</SUP> sep:
ΔV<SUB>arr</SUB>≈− 50 km s<SUP>−1</SUP>, 60<SUP>∘</SUP> sep:
ΔV<SUB>arr</SUB>≈+ 75 km s<SUP>−1</SUP>, 90<SUP>∘</SUP> sep:
ΔV<SUB>arr</SUB>≈+ 125 km s<SUP>−1</SUP>). Especially for future
L<SUB>4</SUB>/L<SUB>5</SUB> missions, the 60<SUP>∘</SUP> separation
case is highly interesting in order to improve space-weather forecasts.
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Title: Evolution of CMEs in the inner heliosphere - observations
versus models
Authors: Temmer, Manuela; Vrsnak, Bojan; Möstl, Christian; Veronig,
Astrid; Rollett, Tanja; Bein, Bianca
2013EGUGA..15.1328T Altcode:
With the SECCHI instrument suite aboard STEREO, coronal mass ejections
(CMEs) can be observed from multiple vantage points during their entire
propagation all the way from the Sun to 1 AU. The propagation behavior
of CMEs in the interplanetary space is mainly influenced by the ambient
solar wind flow. CMEs that are faster than the ambient solar wind get
decelerated, whereas slower ones are accelerated until the CME speed
is finally adjusted to the solar wind speed. On a statistical basis,
empirical models taking into account the drag force acting on CMEs,
are able to describe the observed kinematical behaviors. For several
well observed events, we will present a comparative study showing
the kinematical evolution of CMEs derived from remote sensing and
in situ data, as well as from empirical models using 2D and 3D input
parameters. From this we aim to obtain the distance regime at which
the solar wind drag force is dominating the CME propagation.
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Title: Forecasting coronal mass ejections at 1 AU using Heliospheric
Imagers
Authors: Möstl, Christian; Amla, Keshav; Hall, Jeffrey R.; Liewer,
Paulett C.; De Jong, Eric; Temmer, Manuela; Davies, Jackie A.; Lugaz,
Noé; Rollett, Tanja; Veronig, Astrid M.; Farrugia, Charles J.; Liu,
Ying; Luhmann, Janet G.; Galvin, Antoinette B.; Zhang, Tielong
2013EGUGA..15.1311M Altcode:
We study the feasibility of using a Heliospheric Imager (HI) instrument,
such as STEREO/HI, for operational space weather forecasting of
interplanetary coronal mass ejections (ICMEs) at 1 AU. We compare the
predictions for speed and arrival time for about 20 ICME events, each
observed remotely by one STEREO spacecraft, to the speed and arrival
time observed at various in situ observatories. We use geometrical
modeling, which means we approximate the ICME fronts with various shapes
(Fixed-Phi, Harmonic Mean, Self-Similar Expansion). These models are
applied to the time-elongation functions extracted from STEREO/SECCHI
images with the SolarSoft SATPLOT package. We use these techniques for
a single-spacecraft HI observer, and consequently assume constant ICME
speed and direction. Partly, the configuration mimics the situation of
a single HI observatory parked at the L4 or L5 point in the Sun-Earth
system. For assessing the accuracy of these predictions we look at
plasma and magnetic field in situ data by Wind (MFI, SWE instruments)
and STEREO-A/B (IMPACT, PLASTIC) around 1 AU. Wherever possible we
include ICME arrivals in the inner heliosphere (< 1 AU), from the
magnetic field data by Venus Express and MESSENGER. We also look at
the ratio of prediction lead time to its accuracy, and see if there
is a preferred value for the ICME width.
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Title: Radial evolution of magnetic cloud properties
Authors: Rollett, Tanja; Veronig, Astrid M.; Leitner, Martin; Vrsnak,
Bojan; Möstl, Christian; Farrugia, Charles J.; Temmer, Manuela
2013EGUGA..15.2710R Altcode:
Magnetic clouds (MCs) are characterized as intervals of enhanced,
smoothly rotating interplanetary magnetic field, low plasma beta and
temperature in spacecraft in situ data and can be part of ICMEs. In
this study we analyze the radial evolution of MCs using a sample of
events detected by radial aligned spacecrafts at different heliocentric
distances. The data-sets are fitted with a force-free, constant-alpha
flux rope model. Using the outcome of this fitting model we calculate
the estimated cross section diameter (assuming a cylindrical flux tube),
the poloidal and the axial magnetic field, the current, the magnetic
flux and the inductance. All these parameter are further studied as a
function of heliocentric distance. Strong variations of the current or
the magnetic flux could be a hint for magnetic reconnection between
the MC and the solar wind. This work has received funding from the
European Commission FP7 Project COMESEP (263252).
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Title: The Kelvin-Helmholtz Instability at Coronal Mass Ejection
Boundaries in the Solar Corona: Observations and 2.5D MHD Simulations
Authors: Möstl, U. V.; Temmer, M.; Veronig, A. M.
2013ApJ...766L..12M Altcode: 2013arXiv1304.5884M
The Atmospheric Imaging Assembly on board the Solar Dynamics Observatory
observed a coronal mass ejection with an embedded filament on 2011
February 24, revealing quasi-periodic vortex-like structures at
the northern side of the filament boundary with a wavelength of
approximately 14.4 Mm and a propagation speed of about 310 ± 20 km
s<SUP>-1</SUP>. These structures could result from the Kelvin-Helmholtz
instability occurring on the boundary. We perform 2.5D numerical
simulations of the Kelvin-Helmholtz instability and compare the
simulated characteristic properties of the instability with the
observations, where we obtain qualitative as well as quantitative
accordance. We study the absence of Kelvin-Helmholtz vortex-like
structures on the southern side of the filament boundary and find that
a magnetic field component parallel to the boundary with a strength of
about 20% of the total magnetic field has stabilizing effects resulting
in an asymmetric development of the instability.
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Title: The role of solar "tornadoes" and vortices in filament
fromation and eruption
Authors: Su, Yang; Wang, Tongjiang; Veronig, Astrid; Temmer, Manuela;
Gan, Weiqun
2013enss.confE..51S Altcode:
Solar magnetized "tornadoes" are rotating vertical magnetic
structures in the corona probably driven by underlying vortex flows
in the photosphere. They usually exist as a group and are related
to filaments/prominences. Detailed case studies show that these
tornadoes may play a distinct role in the supply of mass and twists
to filaments. The findings could lead to a new explanation of filament
formation and eruption.
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Title: Direct Observations of Coronal Magnetic Reconnection
Authors: Su, Yang; Veronig, Astrid; Dennis, Brian R.; Holman, Gordon
D.; Wang, Tongjiang; Temmer, Manuela; Gan, Weiqun
2013enss.confE..53S Altcode:
Magnetic field reconnection is believed to play a fundamental role in
magnetized plasma systems throughout the universe, but never before
has it been so clearly demonstrated as in the EUV and X-ray movies
of a GOES-C-class solar flare presented here. The multiwavelength EUV
observations from SDO/AIA show the predicted inflowing cool loops and
newly formed outflowing hot loops while simultaneous RHESSI X-ray
spectra and images show the appearance of plasma heated to >10
MK at the expected locations. These two data sets provide solid
visual evidence of magnetic reconnection producing a solar flare. The
non-uniform, nonsteady, and asymmetric nature of the observed process,
together with the measured reconnection rates, supports the so called
flux-pile-up reconnection. These new features of plasma inflows should
be included in reconnection and flare studies.
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Title: The Kanzelhöhe Online Data Archive
Authors: Pötzi, W.; Hirtenfellner-Polanec, W.; Temmer, M.
2013CEAB...37..655P Altcode:
The Kanzelhöhe Observatory provides high-cadence full-disk observations
of solar activity phenomena like sunspots, flares and prominence
eruptions on a regular basis. The data are available for download
from the KODA (Kanzelhöhe Observatory Data Archive) which is freely
accessible. The archive offers sunspot drawings back to 1950 and
high cadence H-α data back to 1973. Images from other instruments,
like white-light and CaIIK, are available since 2007 and 2010,
respectively. In the following we describe how to access the archive
and the format of the data.
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Title: Relation Between Coronal Hole Areas on the Sun and the Solar
Wind Parameters at 1 AU
Authors: Rotter, T.; Veronig, A. M.; Temmer, M.; Vršnak, B.
2012SoPh..281..793R Altcode: 2012SoPh..tmp..202R
We analyze the relationship between the coronal hole (CH)
characteristics on the Sun (area, position, and intensity levels)
and the corresponding solar wind parameters (solar wind speed v,
proton temperature T, proton density n, and magnetic field strength B)
measured in situ at 1 AU with a 6-h time resolution. We developed a
histogram-based intensity thresholding method to obtain fractional CH
areas from SOHO/EIT 195 Å images. The algorithm was applied to 6-h
cadence EIT 195 Å images for the year 2005, which were characterized
by a low solar activity. In calculating well-defined peaks of the solar
wind parameters corresponding to the peaks in CH area, we found that the
solar wind speed v shows a high correlation with correlation coefficient
cc=0.78, medium correlation for T and B with cc=0.41 and cc=0.41. No
significant correlation was found with the proton density n. Applying
an intensity-weighted CH area did not improve the relations, since
the size and the mean intensity of the CH areas are not independent
parameters but strongly correlated (cc=− 0.72). Comparison of the
fractional CH areas derived from GOES/SXI and SOHO/EIT and the related
solar wind predictions shows no systematic differences (cc=0.79).
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Title: Forecasting coronal mass ejections at 1 AU using Heliospheric
Imagers
Authors: Moestl, C.; Amla, K.; Temmer, M.; Hall, J. R.; Liewer, P. C.;
De Jong, E. M.; Davies, J.; Lugaz, N.; Rollett, T.; Veronig, A.; Liu,
Y.; Farrugia, C. J.; Luhmann, J. G.; Galvin, A. B.; Zhang, T.
2012AGUFMSH31A2208M Altcode:
We study the feasibility of using a Heliospheric Imager (HI) instrument,
such as STEREO/HI, for space weather forecasting of interplanetary
coronal mass ejections (ICMEs) at 1 AU. We compare the predictions for
speed and arrival time for ~15 ICME events, each observed remotely by
one STEREO spacecraft, to the speed and arrival time observed at in
situ observatories. We use three different models with varying ICME
geometry, from point-like (Fixed-Phi) to a circle with a given width
(Self-Similar-Expansion) to a very wide circle (Harmonic Mean). The
models are fitted to density tracks on HI Jmaps with the SolarSoft
SATPLOT tool. All these techniques assume constant ICME speed and
direction. Partly, the configuration mimics the situation of a
single HI observatory parked at the L4 or L5 point in the Sun-Earth
system. We discuss problems associated with this study, such as CME-CME
interactions leading to complicated Jmaps. For assessing the accuracy
of these predictions we look at in situ data by Wind/ACE, STEREO-A/B,
and Venus Express and MESSENGER. We also look at the ratio of prediction
lead time to its accuracy, and see if there is a preferred value for
the ICME width.
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Title: CMEs - interaction with the background solar wind and
other CMEs
Authors: Temmer, M.
2012AGUFMSH21C..01T Altcode:
The propagation behavior of coronal mass ejections (CMEs) in the
interplanetary space is mainly influenced by the ambient solar
wind flow and can be expressed as drag force. CMEs that are faster
than the ambient solar wind get decelerated, whereas slower ones are
accelerated until the CME speed is finally adjusted to the solar wind
speed. As solar activity is rising, active regions will emerge hosting
enough energy to erupt in quick succession. CMEs heading into similar
directions are expected to interact, which means (dramatic) changes in
their kinematical behavior. With the SECCHI instrument suite aboard
STEREO, CMEs can be observed during their entire propagation all
the way from the Sun to 1 AU. Various 3D reconstruction techniques,
developed over the recent years, are used to derive the propagation
direction of CMEs which is essential to interpret the interaction/drag
processes. The talk will summarize observations in EUV and white light,
from the corona to the heliosphere, concerning the interaction of CMEs
with the background solar wind and other CMEs.
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Title: Relation between the impulsive CME acceleration and the
nonthermal flare characteristics
Authors: Veronig, A. M.; Berkebile-Stoiser, S.; Bein, B. M.; Temmer, M.
2012AGUFMSH54A..03V Altcode:
We investigate the relationship between the main acceleration phase of
CMEs and the particle acceleration in the associated flares observed
by RHESSI for a set of 37 impulsive flare-CME events. Both the CME peak
velocity and peak acceleration yield distinct correlations with various
parameters characterizing the flare-accelerated electron spectra. The
highest correlation coefficient is obtained for the relation of the
CME peak velocity and the total energy in accelerated electrons (c =
0.85), supporting the idea that the acceleration of the CME and the
particle acceleration in the associated flare draw their energy from
a common source, probably magnetic reconnection in the current sheet
behind the erupting structure. In general, the CME peak velocity shows
somewhat higher correlations with the non-thermal flare parameters
than the CME peak acceleration, except for the spectral index of the
accelerated electron spectrum, which yields a higher correlation with
the CME peak acceleration (c = -0.6), indicating that the hardness
of the flare-accelerated electron spectrum is tightly coupled to
the impulsive acceleration process of the rising CME structure. We
also obtained high correlations between the CME initiation height h0
and the non-thermal flare parameters, with the highest correlation
of h0 to the spectral index δ of flare-accelerated electrons (c =
0.8). This means that CMEs erupting at low coronal heights, i.e., in
regions of stronger magnetic fields, are accompanied by flares that are
more efficient at accelerating electrons to high energies. In 80% of the
events, the non-thermal flare emission starts after the CME acceleration
(on average 6 min), which corresponds to a mean current sheet length
at the onset of magnetic reconnection of 21 ± 7 Mm. The flare hard
X-ray peaks are well synchronized with the peak of the CME acceleration
profile, and in 75% of the cases they occur within ±5 minutes. Our
findings provide strong evidence for the tight coupling between the
CME dynamics and the particle acceleration in the associated flare
in impulsive events, with the total energy in accelerated electrons
being closely correlated with the peak velocity (and thus the kinetic
energy) of the CME, whereas the number of electrons accelerated to
high energies is decisively related to the CME peak acceleration and
the height of the pre-eruptive structure.
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Title: Deep Solar Activity Minimum 2007-2009: Solar Wind Properties
and Major Effects on the Terrestrial Magnetosphere
Authors: Farrugia, C. J.; Harris, B. S.; Leitner, M.; Moestl, C.;
Galvin, A. B.; Simunac, K.; Torbert, R. B.; Temmer, M.; Veronig, A.;
Erkaev, N.; Szabo, A.; Ogilvie, K. W.; Luhmann, J. G.; Osherovich, V.
2012AGUFMSM41C2226F Altcode:
We discuss the temporal variations and frequency distributions of
solar wind and IMF parameters during the solar minimum of 2007-2009
from measurements returned by the IMPACT and PLASTIC instruments on
STEREO-A. We find that the density and total field strength were
significantly weaker than in the previous minimum. The Alfvén
Mach number was higher than typical.This reflects the weakness of
magnetohydrodynamic (MHD) forces, and has a direct effect on the
solar wind-magnetosphere interactions. We then discuss two major
aspects that this weak solar activity had on the magnetosphere,
using data from textit{Wind} and ground-based observations: (a) the
dayside contribution to the cross-polar cap potential (CPCP), and (b)
the shapes of the magnetopause and bow shock. For (a) we find a low
interplanetary electric field of 1.3 ± 0.9 mV m<SUP>-1</SUP> and a
CPCP of 37.3 ± 20.2 kV. The auroral activity is closely correlated to
the prevalent stream-stream interactions. We suggest that the Alfvén
wave trains in the fast streams and Kelvin-Helmholtz instability were
the predominant agents mediating the transfer of solar wind momentum
and energy to the magnetosphere during this three-year period. For
(b) we determine 328 magnetopause and 271 bow shock crossings made by
textit{Geotail, Cluster 1}, and the THEMIS B and C spacecraft during
a three-month interval when the daily averages of the magnetic and
kinetic energy densities attained their lowest value during the three
years under survey. We use the same numerical approach as in Fairfield's
(textit{J. Geophys. Res.} 76, 7600, 1971) empirical model and compare
our findings with three magnetopause models. The stand-off distance
of the subsolar magnetopause and bow shock were 11.8 R<SUB>E</SUB>
and 14.35 R<SUB>E</SUB>, respectively. When comparing with Fairfield's
(1971) classic result, we find that the subsolar magnetosheath is
thinner by ∼1 R<SUB>E</SUB>. This is mainly due to the low dynamic
pressure which results in a sunward shift of the magnetopause The
magnetopause is more flared than in Fairfield's model. By contrast
the bow shock is less flared, and the latter is the result of weaker
MHD forces.
---------------------------------------------------------
Title: Validating a new method for deriving the kinematics of ICMEs
with a numerical simulation
Authors: Rollett, T.; Temmer, M.; Moestl, C.; Lugaz, N.; Veronig,
A.; Moestl, U. V.
2012AGUFMSH31A2209R Altcode:
Using a numerical simulation of a very wide coronal mass ejection
(CME) we validate a method for calculating propagation directions
and kinematical profiles of interplanetary CMEs (ICMEs). In this
method observations from heliospheric images are constrained with the
in-situ arrival time at 1 AU. This additional boundary condition is
used to calculate the propagation direction and to convert measured
ICME elongations into distance by applying the Harmonic Mean approach
that assumes a spherical shape of the ICME front. We use synthetic
white light images, similar as observed by STEREO-A/HI, for three
different separation angles between remote and in-situ spacecraft,
of 30°, 60° and 90°. For validation, the results of the method are
compared to the "true" speed profile of the modeled ICME, as obtained
from top view density images, for every separation case. In this way
it is possible to determine the accuracy of the method for revealing
ICME propagation directions and kinematics. We found that the direction
yield by the constrained Harmonic Mean method is not very sensitive
on the separation angle. For all three cases the derived kinematics
are in a relatively good agreement with the real kinematics. The best
consistency is obtained for the 30° case, while with growing separation
the ICME speed at 1 AU is increasingly overestimated. Especially for
future L4/L5 missions the 60° separation case is highly interesting
in order to improve space weather forecasts.
---------------------------------------------------------
Title: The Deflection of CMEs During Instances of CME-CME Interactions
Authors: Lugaz, N.; Farrugia, C. J.; Davies, J.; Moestl, C.; Temmer,
M.; Davis, C. J.; Roussev, I. I.
2012AGUFMSH31A2211L Altcode:
The interaction of successive coronal mass ejections (CMEs) can
be directly imaged by remote-sensing instruments such as the HIs
onboard STEREO and the resulting transients can be measured in situ by
spacecraft such as STEREO-A, STEREO-B, ACE and Wind. Here, we present
the analysis of two successive CMEs from May 2010, observed to interact
within HI1 field-of-view. During the interaction, the second CME
(CME2) is found to decelerate and the first CME (CME1) is found to get
compressed. At 1 AU, Wind observed a single, typical magnetic cloud-like
ejecta. By combining the different observations, we determine that this
event shows a clear instance of the deflection of two CMEs due to their
collision in the heliosphere, and we estimate the deflection of CME1
to be about 10 degrees in the longitudinal direction. The resulting
ejecta at 1 AU has a duration in agreement with the previously proposed
hypothesis that compressed CMEs may over-expand after the end of the
interaction. We also discuss additional events of CME-CME interaction
and relate the findings to previous simulation efforts.
---------------------------------------------------------
Title: The Deflection of the Two Interacting Coronal Mass Ejections
of 2010 May 23-24 as Revealed by Combined in Situ Measurements and
Heliospheric Imaging
Authors: Lugaz, N.; Farrugia, C. J.; Davies, J. A.; Möstl, C.; Davis,
C. J.; Roussev, I. I.; Temmer, M.
2012ApJ...759...68L Altcode: 2012arXiv1209.2359L
In 2010 May 23-24, Solar Dynamics Observatory (SDO) observed the launch
of two successive coronal mass ejections (CMEs), which were subsequently
tracked by the SECCHI suite on board STEREO. Using the COR2 coronagraphs
and the heliospheric imagers (HIs), the initial direction of both CMEs
is determined to be slightly west of the Sun-Earth line. We derive the
CME kinematics, including the evolution of the CME expansion until 0.4
AU. We find that, during the interaction, the second CME decelerates
from a speed above 500 km s<SUP>-1</SUP> to 380 km s<SUP>-1</SUP>, the
speed of the leading edge of the first CME. STEREO observes a complex
structure composed of two different bright tracks in HI2-A but only one
bright track in HI2-B. In situ measurements from Wind show an "isolated"
interplanetary CME, with the geometry of a flux rope preceded by a
shock. Measurements in the sheath are consistent with draping around
the transient. By combining remote-sensing and in situ measurements,
we determine that this event shows a clear instance of deflection of
two CMEs after their collision, and we estimate the deflection of the
first CME to be about 10° toward the Sun-Earth line. The arrival time,
arrival speed, and radius at Earth of the first CME are best predicted
from remote-sensing observations taken before the collision of the
CMEs. Due to the over-expansion of the CME after the collision, there
are few, if any, signs of interaction in in situ measurements. This
study illustrates that complex interactions during the Sun-to-Earth
propagation may not be revealed by in situ measurements alone.
---------------------------------------------------------
Title: Deep Solar Activity Minimum 2007 - 2009: Solar Wind Properties
and Major Effects on the Terrestrial Magnetosphere
Authors: Farrugia, C. J.; Harris, B.; Leitner, M.; Möstl, C.; Galvin,
A. B.; Simunac, K. D. C.; Torbert, R. B.; Temmer, M. B.; Veronig,
A. M.; Erkaev, N. V.; Szabo, A.; Ogilvie, K. W.; Luhmann, J. G.;
Osherovich, V. A.
2012SoPh..281..461F Altcode: 2012SoPh..tmp..222F
We discuss the temporal variations and frequency distributions of
solar wind and interplanetary magnetic field parameters during the
solar minimum of 2007 - 2009 from measurements returned by the IMPACT
and PLASTIC instruments on STEREO-A. We find that the density and
total field strength were significantly weaker than in the previous
minimum. The Alfvén Mach number was higher than typical. This
reflects the weakness of magnetohydrodynamic (MHD) forces, and has a
direct effect on the solar wind-magnetosphere interactions. We then
discuss two major aspects that this weak solar activity had on the
magnetosphere, using data from Wind and ground-based observations:
i) the dayside contribution to the cross-polar cap potential (CPCP),
and ii) the shapes of the magnetopause and bow shock. For i) we find a
low interplanetary electric field of 1.3±0.9 mV m<SUP>−1</SUP> and
a CPCP of 37.3±20.2 kV. The auroral activity is closely correlated to
the prevalent stream-stream interactions. We suggest that the Alfvén
wave trains in the fast streams and Kelvin-Helmholtz instability were
the predominant agents mediating the transfer of solar wind momentum
and energy to the magnetosphere during this three-year period. For
ii) we determine 328 magnetopause and 271 bow shock crossings made
by Geotail, Cluster 1, and the THEMIS B and C spacecraft during a
three-month interval when the daily averages of the magnetic and kinetic
energy densities attained their lowest value during the three years
under survey. We use the same numerical approach as in Fairfield's
(J. Geophys. Res.76, 7600, 1971) empirical model and compare our
findings with three magnetopause models. The stand-off distance of the
subsolar magnetopause and bow shock were 11.8 R<SUB>E</SUB> and 14.35
R<SUB>E</SUB>, respectively. When comparing with Fairfield's (1971)
classic result, we find that the subsolar magnetosheath is thinner
by ∼1 R<SUB>E</SUB>. This is mainly due to the low dynamic pressure
which results in a sunward shift of the magnetopause. The magnetopause
is more flared than in Fairfield's model. By contrast the bow shock
is less flared, and the latter is the result of weaker MHD forces.
---------------------------------------------------------
Title: Multi-point Shock and Flux Rope Analysis of Multiple
Interplanetary Coronal Mass Ejections around 2010 August 1 in the
Inner Heliosphere
Authors: Möstl, C.; Farrugia, C. J.; Kilpua, E. K. J.; Jian, L. K.;
Liu, Y.; Eastwood, J. P.; Harrison, R. A.; Webb, D. F.; Temmer, M.;
Odstrcil, D.; Davies, J. A.; Rollett, T.; Luhmann, J. G.; Nitta, N.;
Mulligan, T.; Jensen, E. A.; Forsyth, R.; Lavraud, B.; de Koning,
C. A.; Veronig, A. M.; Galvin, A. B.; Zhang, T. L.; Anderson, B. J.
2012ApJ...758...10M Altcode: 2012arXiv1209.2866M
We present multi-point in situ observations of a complex
sequence of coronal mass ejections (CMEs) which may serve as
a benchmark event for numerical and empirical space weather
prediction models. On 2010 August 1, instruments on various
space missions, Solar Dynamics Observatory/Solar and Heliospheric
Observatory/Solar-TErrestrial-RElations-Observatory (SDO/SOHO/STEREO),
monitored several CMEs originating within tens of degrees from the
solar disk center. We compare their imprints on four widely separated
locations, spanning 120° in heliospheric longitude, with radial
distances from the Sun ranging from MESSENGER (0.38 AU) to Venus
Express (VEX, at 0.72 AU) to Wind, ACE, and ARTEMIS near Earth and
STEREO-B close to 1 AU. Calculating shock and flux rope parameters at
each location points to a non-spherical shape of the shock, and shows
the global configuration of the interplanetary coronal mass ejections
(ICMEs), which have interacted, but do not seem to have merged. VEX
and STEREO-B observed similar magnetic flux ropes (MFRs), in contrast
to structures at Wind. The geomagnetic storm was intense, reaching
two minima in the Dst index (≈ - 100 nT), and was caused by the
sheath region behind the shock and one of two observed MFRs. MESSENGER
received a glancing blow of the ICMEs, and the events missed STEREO-A
entirely. The observations demonstrate how sympathetic solar eruptions
may immerse at least 1/3 of the heliosphere in the ecliptic with their
distinct plasma and magnetic field signatures. We also emphasize the
difficulties in linking the local views derived from single-spacecraft
observations to a consistent global picture, pointing to possible
alterations from the classical picture of ICMEs.
---------------------------------------------------------
Title: Solar Magnetized "Tornadoes:" Relation to Filaments
Authors: Su, Yang; Wang, Tongjiang; Veronig, Astrid; Temmer, Manuela;
Gan, Weiqun
2012ApJ...756L..41S Altcode: 2012arXiv1208.0138S
Solar magnetized "tornadoes," a phenomenon discovered in the solar
atmosphere, appear as tornado-like structures in the corona but are
rooted in the photosphere. Like other solar phenomena, solar tornadoes
are a feature of magnetized plasma and therefore differ distinctly
from terrestrial tornadoes. Here we report the first analysis of solar
"tornadoes" (two papers which focused on different aspects of solar
tornadoes were published in the Astrophysical Journal Letters and
Nature, respectively, during the revision of this Letter). A detailed
case study of two events indicates that they are rotating vertical
magnetic structures probably driven by underlying vortex flows
in the photosphere. They usually exist as a group and are related
to filaments/prominences, another important solar phenomenon whose
formation and eruption are still mysteries. Solar tornadoes may play
a distinct role in the supply of mass and twists to filaments. These
findings could lead to a new explanation of filament formation and
eruption.
---------------------------------------------------------
Title: Impulsive Acceleration of Coronal Mass Ejections. II. Relation
to Soft X-Ray Flares and Filament Eruptions
Authors: Bein, B. M.; Berkebile-Stoiser, S.; Veronig, A. M.; Temmer,
M.; Vršnak, B.
2012ApJ...755...44B Altcode: 2012arXiv1206.2144B
Using high time cadence images from the STEREO EUVI, COR1, and COR2
instruments, we derived detailed kinematics of the main acceleration
stage for a sample of 95 coronal mass ejections (CMEs) in comparison
with associated flares and filament eruptions. We found that CMEs
associated with flares reveal on average significantly higher peak
accelerations and lower acceleration phase durations, initiation
heights, and heights, at which they reach their peak velocities and peak
accelerations. This means that CMEs that are associated with flares are
characterized by higher and more impulsive accelerations and originate
from lower in the corona where the magnetic field is stronger. For CMEs
that are associated with filament eruptions we found only for the CME
peak acceleration significantly lower values than for events that were
not associated with filament eruptions. The flare rise time was found
to be positively correlated with the CME acceleration duration and
negatively correlated with the CME peak acceleration. For the majority
of the events the CME acceleration starts before the flare onset (for
75% of the events) and the CME acceleration ends after the soft X-ray
(SXR) peak time (for 77% of the events). In ~60% of the events, the
time difference between the peak time of the flare SXR flux derivative
and the peak time of the CME acceleration is smaller than ±5 minutes,
which hints at a feedback relationship between the CME acceleration and
the energy release in the associated flare due to magnetic reconnection.
---------------------------------------------------------
Title: Relation between the Coronal Mass Ejection Acceleration and
the Non-thermal Flare Characteristics
Authors: Berkebile-Stoiser, S.; Veronig, A. M.; Bein, B. M.; Temmer, M.
2012ApJ...753...88B Altcode:
We investigate the relationship between the main acceleration phase
of coronal mass ejections (CMEs) and the particle acceleration in
the associated flares as evidenced in Reuven Ramaty High Energy
Solar Spectroscopic Imager non-thermal X-rays for a set of 37
impulsive flare-CME events. Both the CME peak velocity and peak
acceleration yield distinct correlations with various parameters
characterizing the flare-accelerated electron spectra. The highest
correlation coefficient is obtained for the relation of the CME peak
velocity and the total energy in accelerated electrons (c = 0.85),
supporting the idea that the acceleration of the CME and the particle
acceleration in the associated flare draw their energy from a common
source, probably magnetic reconnection in the current sheet behind the
erupting structure. In general, the CME peak velocity shows somewhat
higher correlations with the non-thermal flare parameters than the CME
peak acceleration, except for the spectral index of the accelerated
electron spectrum, which yields a higher correlation with the CME
peak acceleration (c ≈ -0.6), indicating that the hardness of the
flare-accelerated electron spectrum is tightly coupled to the impulsive
acceleration process of the rising CME structure. We also obtained
high correlations between the CME initiation height h <SUB>0</SUB>
and the non-thermal flare parameters, with the highest correlation of
h <SUB>0</SUB> to the spectral index δ of flare-accelerated electrons
(c ≈ 0.8). This means that CMEs erupting at low coronal heights,
i.e., in regions of stronger magnetic fields, are accompanied by flares
that are more efficient at accelerating electrons to high energies. In
the majority of events (~80%), the non-thermal flare emission starts
after the CME acceleration, on average delayed by ≈6 minutes, in line
with the standard flare model where the rising flux rope stretches the
field lines underneath until magnetic reconnection sets in. We find
that the current sheet length at the onset of magnetic reconnection
is 21 ± 7 Mm. The flare hard X-ray peaks are well synchronized with
the peak of the CME acceleration profile, and in 75% of the cases they
occur within ±5 minutes. Our findings provide strong evidence for the
tight coupling between the CME dynamics and the particle acceleration
in the associated flare in impulsive events, with the total energy in
accelerated electrons being closely correlated with the peak velocity
(and thus the kinetic energy) of the CME, whereas the number of
electrons accelerated to high energies is decisively related to the
CME peak acceleration and the height of the pre-eruptive structure.
---------------------------------------------------------
Title: The Kelvin-Helmholtz Instability at CME-Boundaries in the
Solar Corona: Observations and Preliminary 2.5D MHD Simulations
Authors: Moestl, Ute Verena; Temmer, M.; Veronig, A. M.
2012shin.confE..85M Altcode:
Just recently, the Solar Dynamics Observatory (SDO) observedfor the
first time Kelvin-Helmholtz vortices at the boundary of acoronal mass
ejection (CME). The importance of the Kelvin-Helmholtz instability might
lie in its effect on the CME kinematics due to exerting a drag force
via anomalous viscosity.We discuss the observation of a CME by SDO from
February 24th2011. This event shows periodic vortex-like structures
on the boundary to the filament. First analysis of these structures
reveals a periodic appearance with a wavelength of approximately 14 Mm
and a height of 3-4 Mm.Another striking feature of this observation
is an apparent asymmetric evolution of the periodic structures on
only one side of the boundary layer. This asymmetry is also seen in
other observations. Such observed asymmetry could be due to different
magnetic field directions, for example. We test this hypothesis and
present results of preliminary 2.5D magnetohydrodynamic simulations
of the February 24th 2011event using different input parameters for
the plasma background. Our aim is to check if the observed structures
can be produced by the Kelvin-Helmholtz instability and to investigate
the effect of different magnetic field directions on the evolution of
the instability.
---------------------------------------------------------
Title: Kinematics of Coronal Mass Ejections in the Inner Heliosphere
Constrained with In Situ Signatures
Authors: Rollett, Tanja; Möstl, Christian; Temmer, Manuela; Veronig,
Astrid; Farrugia, Charles J.
2012shin.confE..80R Altcode:
On the basis of the Harmonic Mean and Fixed-Phi methods we developed
a new approach to derive kinematics and propagation directions of
interplanetary coronal mass ejections (ICMEs). By combining remote
observations performed by STEREO/HI with in situ measurements of the
Wind and STEREO-B spacecraft at 1 AU, we make the derived kinematical
ICME profiles as consistent as possible with in situ data. Within the
limitations of the geometrical assumptions that are used for the shape
of the ICME, the improved methods aim to isolate the kinematics from
that part of the CME which is most probably directed towards the in
situ spacecraft. The methods are applied and tested on observational
data from well observed ICME events (1-6 June 2008, 13-18 February
2009). This work has received funding from the European Commission
FP7 Project COMESEP (263252).
---------------------------------------------------------
Title: Multi-point shock and flux rope analysis of multiple ICMEs
around 2010 August 1 in the inner heliosphere
Authors: Moestl, Christian; Farrugia, C. J.; Kilpua, E. K. J.; Jian,
L.; Liu, Y.; Jensen, L.; Mulligan, T.; Eastwood, J.; Rollett, T.;
Temmer, M.; Luhmann, J. G.; Harrison, R.; Davies, J. A.; Webb, D.;
Forsyth, R.; Lavraud, B.; Odstrcil, D.; de Koning, C. A.; Nitta, N.;
Veronig, A. M.; Galvin, A. B.; Zhang, T. L.
2012shin.confE..77M Altcode:
We present multi-point in situ observations of a complex sequence
of coronal mass ejections which may serve as a benchmark event for
numerical and empirical space weather prediction models. On 2010 August
1, instruments on various space missions (SDO/SOHO/STEREO) monitored
repeated coronal mass ejections originating within tens of degrees from
solar disk center. We compare their imprints on four widely separated
locations, covering 120 degree in heliospheric longitude, with radial
distances from the Sun ranging from MESSENGER (0.38 AU) to Venus Express
(VEX, at 0.72 AU) to Wind, ACE and ARTEMIS near Earth and STEREO-B close
to 1 AU. Calculating shock and flux rope parameters at each location
points to a non-spherical shape of the shock, and shows the global
configuration of the interplanetary coronal mass ejections (ICMEs),
which have interacted but not merged, making individual identifications
still possible. VEX and STEREO-B observed similar magnetic flux ropes,
in contrast to the structures at Wind. The geomagnetic storm was
moderate to major, reaching two minima in the Dst index, caused by the
sheath region behind the shock and one of two observed magnetic flux
ropes. MESSENGER received a glancing blow of the ICMEs, and the events
missed STEREO-A entirely. The observations demonstrate how sympathetic
solar eruptions may immerse at least 1/3 of the heliosphere in the
ecliptic with their distinct plasma and magnetic field signatures
and emphasize the difficulties in linking the local views derived
from single-spacecraft observations to a consistent global picture,
pointing to possible alterations from the classical picture of ICMEs.
---------------------------------------------------------
Title: Comparison of MHD Simulations of the Solar Wind with In-Situ
Measurements
Authors: Gressl, Corinna; Veronig, A. M.; Temmer, M.; Odstrcil, D.
2012shin.confE..31G Altcode:
ENLIL is a time-dependent 3D MHD model to simulate the structure
and evolution of the solar wind parameters in the inner and
mid heliosphere. ENLIL can be coupled to the coronal models
"Magnetohydrodynamics Around Sphere" (MAS) and "Wang-Sheeley-Arge"
(WSA) which use synoptic magnetograms of the solar photosphere as input
parameter. We tested the performance of the coupled models ENLIL/MAS and
ENLIL/WSA by comparing the modeled solar wind speed, proton density,
temperature, and radial and total magnetic field strength to in-situ
measurements from Wind and ACE at 1 AU. For the comparison we chose the
year 2005 as a time period with low solar activity. We requested model
runs with the aim to produce a stationary solution of the background
solar wind. All simulations were carried out by CCMC/NASA. For the
analysis of the model results we extracted the data at the exact
position of the spacecraft. We calculated correlation coefficients to
quantify the agreement between model predictions and measurements. The
accuracy of the predicted arrival times of solar wind structures was
quantified by carrying out cross-correlations. The results show that
ENLIL/MAS and ENLIL/WSA are able to simulate the general features of
the background solar wind and to reproduce recurring structures in the
heliosphere. The best results were obtained for the parameter solar
wind speed. However, the predicted arrival times of high speed solar
wind streams have typical uncertainties of the order of 1 - 1.5 days,
and the absolute values of the magnetic field were systematically too
low. The sector structure of the interplanetary magnetic field was
well reproduced by both models.
---------------------------------------------------------
Title: CME acceleration and non-thermal flare characteristics
Authors: Berkebile-Stoiser, S.; Veronig, A. M.; Bein, B. M.; Temmer, M.
2012arXiv1205.2539B Altcode:
We investigate the relationship between the main acceleration phase
of coronal mass ejections (CMEs) and the particle acceleration in
the associated flares as evidenced in RHESSI non-thermal X-rays for
a set of 37 impulsive flare-CME events. CME peak velocity and peak
acceleration yield distinct correlations with various parameters
characterizing the flare-accelerated electron spectra. The highest
correlation coefficient is obtained for the relation of the CME peak
velocity and the total energy in accelerated electrons (c = 0.85),
supporting the idea that the acceleration of the CME and the particle
acceleration in the associated flare draw their energy from a common
source, probably magnetic reconnection in the current sheet behind
the erupting structure. In general, the CME peak velocity shows
somewhat higher correlations with the non-thermal flare parameters
than the CME peak acceleration, except for the spectral index of the
accelerated electron spectrum which yields a higher correlation with
the CME peak acceleration (c = -0.6), indicating that the hardness
of the flare-accelerated electron spectrum is tightly coupled to the
impulsive acceleration process of the rising CME structure. We also
obtained high correlations between the CME initiation height $h_0$
and the non-thermal flare parameters, with the highest correlation
of $h_0$ to the spectral index of flare-accelerated electrons (c =
0.8). This means that CMEs erupting at low coronal heights, i.e.\
in regions of stronger magnetic fields, are accompanied with flares
which are more efficient to accelerate electrons to high energies. In
the majority of events (80%), the non-thermal flare emission starts
after the CME acceleration (6 min), giving a current sheet length at
the onset of magnetic reconnection of 21 \pm 7 Mm. The flare HXR peaks
are well synchronized with the peak of the CME acceleration profile.
---------------------------------------------------------
Title: An Analysis of the Origin and Propagation of the Multiple
Coronal Mass Ejections of 2010 August 1
Authors: Harrison, R. A.; Davies, J. A.; Möstl, C.; Liu, Y.; Temmer,
M.; Bisi, M. M.; Eastwood, J. P.; de Koning, C. A.; Nitta, N.; Rollett,
T.; Farrugia, C. J.; Forsyth, R. J.; Jackson, B. V.; Jensen, E. A.;
Kilpua, E. K. J.; Odstrcil, D.; Webb, D. F.
2012ApJ...750...45H Altcode:
On 2010 August 1, the northern solar hemisphere underwent significant
activity that involved a complex set of active regions near central
meridian with, nearby, two large prominences and other more distant
active regions. This activity culminated in the eruption of four major
coronal mass ejections (CMEs), effects of which were detected at Earth
and other solar system bodies. Recognizing the unprecedented wealth of
data from the wide range of spacecraft that were available—providing
the potential for us to explore methods for CME identification and
tracking, and to assess issues regarding onset and planetary impact—we
present a comprehensive analysis of this sequence of CMEs. We show that,
for three of the four major CMEs, onset is associated with prominence
eruption, while the remaining CME appears to be closely associated
with a flare. Using instrumentation on board the Solar Terrestrial
Relations Observatory spacecraft, three of the CMEs could be tracked
out to elongations beyond 50° their directions and speeds have been
determined by various methods, not least to assess their potential for
Earth impact. The analysis techniques that can be applied to the other
CME, the first to erupt, are more limited since that CME was obscured
by the subsequent, much faster event before it had propagated far from
the Sun; we discuss the speculation that these two CMEs interact. The
consistency of the results, derived from the wide variety of methods
applied to such an extraordinarily complete data set, has allowed
us to converge on robust interpretations of the CME onsets and their
arrivals at 1 AU.
---------------------------------------------------------
Title: A Self-similar Expansion Model for Use in Solar Wind Transient
Propagation Studies
Authors: Davies, J. A.; Harrison, R. A.; Perry, C. H.; Möstl, C.;
Lugaz, N.; Rollett, T.; Davis, C. J.; Crothers, S. R.; Temmer, M.;
Eyles, C. J.; Savani, N. P.
2012ApJ...750...23D Altcode:
Since the advent of wide-angle imaging of the inner heliosphere,
a plethora of techniques have been developed to investigate the
three-dimensional structure and kinematics of solar wind transients,
such as coronal mass ejections, from their signatures in single-
and multi-spacecraft imaging observations. These techniques, which
range from the highly complex and computationally intensive to methods
based on simple curve fitting, all have their inherent advantages and
limitations. In the analysis of single-spacecraft imaging observations,
much use has been made of the fixed phi fitting (FPF) and harmonic
mean fitting (HMF) techniques, in which the solar wind transient is
considered to be a radially propagating point source (fixed phi,
FP, model) and a radially expanding circle anchored at Sun centre
(harmonic mean, HM, model), respectively. Initially, we compare the
radial speeds and propagation directions derived from application of
the FPF and HMF techniques to a large set of STEREO/Heliospheric Imager
(HI) observations. As the geometries on which these two techniques
are founded constitute extreme descriptions of solar wind transients
in terms of their extent along the line of sight, we describe a
single-spacecraft fitting technique based on a more generalized model
for which the FP and HM geometries form the limiting cases. In addition
to providing estimates of a transient's speed and propagation direction,
the self-similar expansion fitting (SSEF) technique provides, in theory,
the capability to estimate the transient's angular extent in the plane
orthogonal to the field of view. Using the HI observations, and also
by performing a Monte Carlo simulation, we assess the potential of
the SSEF technique.
---------------------------------------------------------
Title: STEREO-A and PROBA2 Quadrature Observations of Reflections
of three EUV Waves from a Coronal Hole
Authors: Kienreich, Ines Waltraud; Muhr, Nicole; Veronig, Astrid;
Berghmans, David; de Groof, Anik; Temmer, Manuela; Vršnak, Bojan;
Seaton, Dan
2012arXiv1204.6472K Altcode: 2012arXiv1204.6472W
We investigate the interaction of three consecutive large-scale coronal
waves with a polar coronal hole, simultaneously observed on-disk by the
Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on
the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on
January 27, 2011. All three extreme-ultraviolet(EUV) waves originate
from the same active region NOAA 11149 positioned at N30E15 in the
STEREO-A field-of-view and on the limb in PROBA2. We derive for the
three primary EUV waves start velocities in the range of ~310 km/s for
the weakest up to ~500 km/s for the strongest event. Each large-scale
wave is reflected at the border of the extended coronal hole at the
southern polar region. The average velocities of the reflected waves
are found to be smaller than the mean velocities of their associated
direct waves. However, the kinematical study also reveals that in each
case the end velocity of the primary wave matches the initial velocity
of the reflected wave. In all three events the primary and reflected
waves obey the Huygens-Fresnel principle, as the incident angle with
~10° to the normal is of the same size as the angle of reflection. The
correlation between the speed and the strength of the primary EUV waves,
the homologous appearance of both the primary and the reflected waves,
and in particular the EUV wave reflections themselves implicate that the
observed EUV transients are indeed nonlinear large-amplitude MHD waves.
---------------------------------------------------------
Title: The first STEREO multi-event: Numerical simulation of coronal
mass ejections (CMEs) launched on August 1, 2010
Authors: Odstrcil, D.; de Koning, C. A.; Xie, H.; Moestl, C.;
Temmer, M.; Jian, L.; Rouillard, A. P.; Davies, J. A.; Davis, C. J.;
Harrison, R.
2012EGUGA..1414429O Altcode:
On 2010-08-01 at least four coronal mass ejections (CMEs) were observed
by the Heliospheric Imagers (HIs) onboard STEREO spacecraft. These
events originated at different parts of the solar corona and generated
complex scenario of four mutually interacting CMEs. Real-time
prediction of the arrival times to Earth failed and it is difficult
to associate features observed by HIs with their solar sources and
impacts at spacecraft. We use the heliospheric code ENLIL to show the
global solution for various scenarios using fitted CME parameters
from coronagraph observations by different techniques. We present
the temporal profiles and synthetic white-light images that enables
direct comparison with in-situ and remote observations. These results
show that in addition to multi-perspective coronagraph observations,
heliospheric imagers and numerical simulations are needed to understand
and predict the impact of complex heliospheric disturbances.
---------------------------------------------------------
Title: CME-CME interaction during the 2010 August 1 events
Authors: Temmer, M.; Vrsnak, B.; Rollett, T.; Bein, B.; deKoning,
C. A.; Liu, Y.; Bosman, E.; Davies, J. A.; Möstl, C.; Zic, T.;
Veronig, A. M.; Bothmer, V.; Harrison, R.; Nitta, N.; Bisi, M.; Flor,
O.; Eastwood, J.; Odstrcil, D.; Forsyth, R.
2012EGUGA..14.1677T Altcode:
We study a CME-CME interaction that occurred during the 2010 August 1
events using STEREO/SECCHI data (COR and HI). The CMEs were Earth
directed where clear signatures of magnetic flux ropes could be
measured from in situ Wind data. To give evidence of the actual
interaction we derive the direction of motion for both CMEs applying
several independent methods. From this we obtain that both CMEs head
into similar directions enabling us to actually observe the merging
in the HI1 field-of-view (and rule out the possibility that this is
just a line of sight effect). The full de-projected kinematics of the
faster CME from Sun to Earth is derived when combining data points from
remote observations with in situ parameters of the ICME measured at
1 AU. We study the evolution of the kinematical profile of the faster
CME by applying a drag based model.
---------------------------------------------------------
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: Deep Solar Activity Minimum 2007-2009: Solar Wind Properties
and Major Effects on the Terrestrial Magnetosphere
Authors: Farrugia, C. J.; Harris, B.; Leitner, M.; Möstl, C.; Galvin,
A. B.; Simunac, K. D. C.; Torbert, R. B.; Temmer, M. B.; Veronig,
A. M.; Erkaev, N. V.; Szabo, A.; Ogilvie, K. W.; Luhmann, J. G.;
Osherovich, V. A.
2012EGUGA..14.6381F Altcode:
We discuss the temporal variations and frequency distributions of
solar wind and interplanetary magnetic field parameters during the
solar minimum of 2007- 2009 from measurements returned by the IMPACT
and PLASTIC instruments on STEREO-A. We find that the density and
total field strength were considerably weaker than in the previous
minimum. The Alfvén Mach number was higher than typical. This reflects
the weakness of magnetohydrodynamic (MHD) forces, and has a direct
effect on the solar wind-magnetosphere interactions. We then discuss two
major aspects that this weak solar activity had on the magnetosphere
using data from Wind and ground-based observations: (a) the level
of solar wind driving and the associated dayside contribution to the
crosspolar cap potential (CPCP), and (b) the shapes of the magnetopause
and bow shock. For (a) we find very weak interplanetary electric
field (V xBz = -0.05 ± 0.83 mV/m) and a CPCP of 36.6 ± 18.2 kV. The
auroral activity is closely correlated to the prevalent stream-stream
interactions.We argue that the Alfvén waves in the fast streams and
Kelvin-Helmholtz instability were the predominant agents mediating the
transfer of solar wind momentum and energy to the magnetosphere during
this 3-year period. For (b) we determine 328 magnetopause and 271 bow
shock crossings made by the Cluster 1, Themis B and C spacecraft during
a 3-month interval when the daily averages of the magnetic and kinetic
energy densities attained their lowest value during the 3 years under
survey. We use the same numerical approach as in Fairfield's (1971)
empirical model and compare our findings with his classic result. The
stand-off distance of the subsolar magnetopause and bow shock were
11.8 RE and 14.35 RE, respectively, making the subsolar magnetosheath
thinner by ≈ 1RE. This is mainly due to the low dynamic pressure
which result in a sunward shift of the magnetopause The magnetopause
is more flared than Fairfield's result. By contrast the bow shock is
less flared, and the latter is the result of weaker MHD forces.
---------------------------------------------------------
Title: Characteristics of Kinematics of a Coronal Mass Ejection
during the 2010 August 1 CME-CME Interaction Event
Authors: Temmer, Manuela; Vršnak, Bojan; Rollett, Tanja; Bein, Bianca;
de Koning, Curt A.; Liu, Ying; Bosman, Eckhard; Davies, Jackie A.;
Möstl, Christian; Žic, Tomislav; Veronig, Astrid M.; Bothmer, Volker;
Harrison, Richard; Nitta, Nariaki; Bisi, Mario; Flor, Olga; Eastwood,
Jonathan; Odstrcil, Dusan; Forsyth, Robert
2012ApJ...749...57T Altcode: 2012arXiv1202.0629T
We study the interaction of two successive coronal mass ejections (CMEs)
during the 2010 August 1 events using STEREO/SECCHI COR and heliospheric
imager (HI) data. We obtain the direction of motion for both CMEs by
applying several independent reconstruction methods and find that the
CMEs head in similar directions. This provides evidence that a full
interaction takes place between the two CMEs that can be observed in the
HI1 field of view. The full de-projected kinematics of the faster CME
from Sun to Earth is derived by combining remote observations with in
situ measurements of the CME at 1 AU. The speed profile of the faster
CME (CME2; ~1200 km s<SUP>-1</SUP>) shows a strong deceleration over
the distance range at which it reaches the slower, preceding CME (CME1;
~700 km s<SUP>-1</SUP>). By applying a drag-based model we are able
to reproduce the kinematical profile of CME2, suggesting that CME1
represents a magnetohydrodynamic obstacle for CME2 and that, after
the interaction, the merged entity propagates as a single structure
in an ambient flow of speed and density typical for quiet solar wind
conditions. Observational facts show that magnetic forces may contribute
to the enhanced deceleration of CME2. We speculate that the increase
in magnetic tension and pressure, when CME2 bends and compresses the
magnetic field lines of CME1, increases the efficiency of drag.
---------------------------------------------------------
Title: Calculation of CME kinematics and propagation directions by
constraining STEREO HI-images with in situ signatures at 1 AU
Authors: Rollett, T.; Möstl, C.; Temmer, M.; Veronig, A. M.; Farrugia,
C. J.; Biernat, H. K.
2012EGUGA..14.4778R Altcode:
We present a new approach to combine remote observations and in
situ measurements by STEREO/HI and Wind, respectively, to derive the
kinematics and propagation directions of interplanetary coronal mass
ejections (ICMEs). We use two methods, Fixed-Phi and Harmonic Mean,
to convert ICME elongations into distance. The ICME direction is
constrained such that the ICME distance-time and speed-time profiles
are most consistent with in situ measurements of the arrival time and
speed at 1 AU. These methods are applied to two ICME events of 02 - 06
June 2008 and 13 - 18 February 2009. Due to the geometrical assumptions
HM delivers the propagation direction further away from the observing
spacecraft with a mean difference of 25°. This work has received
funding from the European Commission FP7 Project COMESEP (263252).
---------------------------------------------------------
Title: Constraining the Kinematics of Coronal Mass Ejections in the
Inner Heliosphere with In-Situ Signatures
Authors: Rollett, T.; Möstl, C.; Temmer, M.; Veronig, A. M.; Farrugia,
C. J.; Biernat, H. K.
2012SoPh..276..293R Altcode: 2011SoPh..tmp..414R; 2011SoPh..tmp..412R; 2011arXiv1110.0300R
We present a new approach to combine remote observations and in-situ
data by STEREO/HI and Wind, respectively, to derive the kinematics
and propagation directions of interplanetary coronal mass ejections
(ICMEs). We use two methods, Fixed-ϕ (Fϕ) and Harmonic Mean (HM),
to convert ICME elongations into distance, and constrain the ICME
direction such that the ICME distance-time and velocity-time profiles
are most consistent with in-situ measurements of the arrival time and
velocity. The derived velocity-time functions from the Sun to 1 AU for
the three events under study (1 - 6 June 2008, 13 - 18 February 2009,
3 - 5 April 2010) do not show strong differences for the two extreme
geometrical assumptions of a wide ICME with a circular front (HM)
or an ICME of small spatial extent in the ecliptic (Fϕ). Due to the
geometrical assumptions, HM delivers the propagation direction further
away from the observing spacecraft with a mean difference of ≈ 25°.
---------------------------------------------------------
Title: Interactions between Coronal Mass Ejections Viewed in
Coordinated Imaging and in situ Observations
Authors: Liu, Ying D.; Luhmann, Janet G.; Möstl, Christian;
Martinez-Oliveros, Juan C.; Bale, Stuart D.; Lin, Robert P.; Harrison,
Richard A.; Temmer, Manuela; Webb, David F.; Odstrcil, Dusan
2012ApJ...746L..15L Altcode: 2012arXiv1201.2968L
The successive coronal mass ejections (CMEs) from 2010 July 30 to
August 1 present us the first opportunity to study CME-CME interactions
with unprecedented heliospheric imaging and in situ observations from
multiple vantage points. We describe two cases of CME interactions:
merging of two CMEs launched close in time and overtaking of a preceding
CME by a shock wave. The first two CMEs on August 1 interact close to
the Sun and form a merged front, which then overtakes the July 30 CME
near 1 AU, as revealed by wide-angle imaging observations. Connections
between imaging observations and in situ signatures at 1 AU suggest
that the merged front is a shock wave, followed by two ejecta observed
at Wind which seem to have already merged. In situ measurements show
that the CME from July 30 is being overtaken by the shock at 1 AU and
is significantly compressed, accelerated, and heated. The interaction
between the preceding ejecta and shock also results in variations
in the shock strength and structure on a global scale, as shown by
widely separated in situ measurements from Wind and STEREO B. These
results indicate important implications of CME-CME interactions for
shock propagation, particle acceleration, and space weather forecasting.
---------------------------------------------------------
Title: Relation Between the 3D-Geometry of the Coronal Wave and
Associated CME During the 26 April 2008 Event
Authors: Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.
2012esrs.book..115T Altcode:
We study the kinematical characteristics and 3D geometry of
a large-scale coronal wave that occurred in association with the
26 April 2008 flare-CME event. The wave was observed with the EUVI
instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B)
with a mean speed of ∼ 240 km s<SUP>-1</SUP>. The wave is more
pronounced in the eastern propagation direction, and is thus, better
observable in STEREO-B images. From STEREO-B observations we derive
two separate initiation centers for the wave, and their locations fit
with the coronal dimming regions. Assuming a simple geometry of the
wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B
observations. We find that the wave structure is asymmetric with an
inclination toward East. The associated CME has a deprojected speed
of ∼ 750±50 km s<SUP>-1</SUP>, and it shows a non-radial outward
motion toward the East with respect to the underlying source region
location. Applying the forward fitting model developed by Thernisien,
Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the
CME flux rope position on the solar surface to be close to the dimming
regions. We conclude that the expanding flanks of the CME most likely
drive and shape the coronal wave.
---------------------------------------------------------
Title: Plasma Diagnostics of an EIT Wave Observed by Hinode/EIS
and SDO/AIA
Authors: Veronig, A. M.; Gömöry, P.; Kienreich, I. W.; Muhr, N.;
Vršnak, B.; Temmer, M.; Warren, H. P.
2011ApJ...743L..10V Altcode: 2011arXiv1111.3505V
We present plasma diagnostics of an Extreme-Ultraviolet
Imaging Telescope (EIT) wave observed with high cadence in
Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) sit-and-stare
spectroscopy and Solar Dynamics Observatory/Atmospheric Imaging
Assembly imagery obtained during the HOP-180 observing campaign on 2011
February 16. At the propagating EIT wave front, we observe downward
plasma flows in the EIS Fe XII, Fe XIII, and Fe XVI spectral lines
(log T ≈ 6.1-6.4) with line-of-sight (LOS) velocities up to 20
km s<SUP>-1</SUP>. These redshifts are followed by blueshifts with
upward velocities up to -5 km s<SUP>-1</SUP> indicating relaxation
of the plasma behind the wave front. During the wave evolution, the
downward velocity pulse steepens from a few km s<SUP>-1</SUP> up to 20
km s<SUP>-1</SUP> and subsequently decays, correlated with the relative
changes of the line intensities. The expected increase of the plasma
densities at the EIT wave front estimated from the observed intensity
increase lies within the noise level of our density diagnostics from
EIS Fe XIII 202/203 Å line ratios. No significant LOS plasma motions
are observed in the He II line, suggesting that the wave pulse was not
strong enough to perturb the underlying chromosphere. This is consistent
with the finding that no Hα Moreton wave was associated with the
event. The EIT wave propagating along the EIS slit reveals a strong
deceleration of a ≈ -540 m s<SUP>-2</SUP> and a start velocity of v
<SUB>0</SUB> ≈ 590 km s<SUP>-1</SUP>. These findings are consistent
with the passage of a coronal fast-mode MHD wave, pushing the plasma
downward and compressing it at the coronal base.
---------------------------------------------------------
Title: Influence of the Ambient Solar Wind Flow on the Propagation
Behavior of Interplanetary Coronal Mass Ejections
Authors: Temmer, Manuela; Rollett, Tanja; Möstl, Christian; Veronig,
Astrid M.; Vršnak, Bojan; Odstrčil, Dusan
2011ApJ...743..101T Altcode: 2011arXiv1110.0827T
We study three coronal mass ejection (CME)/interplanetary coronal mass
ejection (ICME) events (2008 June 1-6, 2009 February 13-18, and 2010
April 3-5) tracked from Sun to 1 AU in remote-sensing observations
of Solar Terrestrial Relations Observatory Heliospheric Imagers and
in situ plasma and magnetic field measurements. We focus on the ICME
propagation in interplanetary (IP) space that is governed by two
forces: the propelling Lorentz force and the drag force. We address
the question: which heliospheric distance range does the drag become
dominant and the CME adjust to the solar wind flow. To this end,
we analyze speed differences between ICMEs and the ambient solar
wind flow as a function of distance. The evolution of the ambient
solar wind flow is derived from ENLIL three-dimensional MHD model
runs using different solar wind models, namely, Wang-Sheeley-Arge and
MHD-Around-A-Sphere. Comparing the measured CME kinematics with the
solar wind models, we find that the CME speed becomes adjusted to the
solar wind speed at very different heliospheric distances in the three
events under study: from below 30 R <SUB>⊙</SUB>, to beyond 1 AU,
depending on the CME and ambient solar wind characteristics. ENLIL can
be used to derive important information about the overall structure of
the background solar wind, providing more reliable results during times
of low solar activity than during times of high solar activity. The
results from this study enable us to obtain greater insight into the
forces acting on CMEs over the IP space distance range, which is an
important prerequisite for predicting their 1 AU transit times.
---------------------------------------------------------
Title: Elliptical approximation for the fronts of ICMEs and
application to STEREO events in August 2010 and February 2011
Authors: Moestl, C.; Davies, J. A.; Rollett, T.; Temmer, M.; Lugaz,
N.; Farrugia, C. J.; Liu, Y.; Veronig, A. M.
2011AGUFMSH23C1971M Altcode:
Geo-effective solar eruptions can now be followed continuously
from the Sun to 1 AU from a viewpoint far away from the Sun-Earth
line (with STEREO/SECCHI), thus making it possible to link solar,
heliospheric and in situ observations unambiguously. A very basic
problem is that only the elongation of the interplanetary coronal mass
ejection's (ICME) density enhancements, and not the radial distances,
are measured by an observer when the ICME is propagating at large
angles to the Sun. Additionally, this is complicated by the effects
of Thomson scattering. Nevertheless, the community has worked so far
with increasingly realistic geometrical approximations to convert the
observed elongations to radial distance, such as Point-P (a circle
around the Sun), Fixed-Phi (a point), Harmonic Mean (a circle always
attached to the Sun at one end), and Self-Similar Expansion (a circle
with a given angular width). We add to this an analytical formula
which is based on an elliptical geometry (abbreviated EL), with the
assumption, similar to HM and SSE, that the observer looks along the
tangent of the ellipse which approximates the ICME front. In this way
we still ignore Thomson-scattering, but otherwise the free parameters
direction, angular width and aspect ratio allow more freedom to derive
ICME radial distances and speeds from heliospheric imager observations,
which should improve the consistency with in situ ICME observations
and the CME directions and speeds in coronagraphs. An application to
combined STEREO heliospheric imager and multi-point in situ observations
of the multiple ICME events on 1-4 August 2010 and 15-17 February 2011
is presented, and the possibility of using EL for real-time forecasts
by means of inverse fitting and triangulation is discussed.
---------------------------------------------------------
Title: Propagation behavior of interplanetary CMEs: driving versus
drag force
Authors: Temmer, M.; Rollett, T.; Moestl, C.; Veronig, A. M.;
Vrsnak, B.
2011AGUFMSH23C1968T Altcode:
The evolution of coronal mass ejections (CMEs) is governed by the
Lorentz and the drag force. Initially, the CME is launched and driven
by the Lorentz force, whereas the drag force owing to the ambient solar
wind controls the CME kinematics as it propagates into interplanetary
(IP) space. The subject of the current study is to infer a heliospheric
distance at which the drag force starts to prevail over the driving
force. With the SECCHI instrument suite aboard STEREO, CMEs can be
observed during their entire propagation all the way from Sun to 1
AU. In combination with in-situ measurements at 1 AU we are able to
derive the direction and speed of a CME. This information is used as
input to derive the kinematical behavior of well observed CME events
in the IP distance regime, which is subsequently compared to the output
from ENLIL (NASA/CCMC) MHD model runs for the ambient solar wind flow.
---------------------------------------------------------
Title: Interaction between Coronal Mass Ejections Viewed in
Coordinated Imaging and In Situ Observations
Authors: Liu, Y.; Luhmann, J. G.; Moestl, C.; Martinez Oliveros,
J. C.; Harrison, R.; Temmer, M.; Bale, S.; Lin, R. P.
2011AGUFMSH23C1973L Altcode:
Interaction between coronal mass ejections (CMEs), which is expected
to be a frequent phenomenon, has important implications for both
space weather and basic plasma physics. First, the interaction alters
the global heliospheric configuration, which may lead to favorable
conditions for geomagnetic storm generation. Second, the interaction
implies significant energy and momentum transfer between the interacting
CMEs where magnetic reconnection may take place. Third, in case a
shock is driven by the trailing CME, interesting physical processes
may occur when the shock is propagating through the preceding one,
such as modifications in the shock strength, particle intensity and
transport. There are successive CMEs on July 30 - August 1, 2011,
which presents us the first opportunity to study CME-CME interaction
with unprecedented heliospheric imaging and in situ observations from
a fleet of spacecraft. The first two CMEs on August 1 interact close
to the Sun and form a merged front, which then overtakes the July
30 CME near 1 AU, as revealed by wide-angle imaging observations. In
situ measurements indicate that the first two CMEs on August 1 seem
to have already merged at 0.7 and 1 AU, and at 1 AU their shock is
propagating into the CME from July 30. We will report and discuss the
CME-CME interaction signatures from the coordinated imaging and in
situ observations in this presentation.
---------------------------------------------------------
Title: Validation of a New Method to Derive Sun-to-1 AU Kinematics
of ICMEs with a Numerical Simulation
Authors: Rollett, T.; Moestl, C.; Lugaz, N.; Temmer, M.; Veronig, A. M.
2011AGUFMSH23C1970R Altcode:
The Heliospheric Imagers (HI) aboard the NASA STEREO mission offer the
possibility to follow coronal mass ejections (CMEs) continuously on
their way from close to the Sun up to ~ 1 AU. The interpretation of
these images is challenging because line-of-sight as well as Thomson
scattering effects influence the white-light signal. There are different
methods to derive the velocity profiles and propagation directions of
CMEs in the interplanetary space, e.g. Fixed-Φ (Kahler and Webb, 2007)
and Harmonic Mean (Lugaz, Vourlidas and Roussev, 2009), which make the
assumptions of a point like structure and a circle shaped front of the
CME, respectively. These two approaches can be constrained using in situ
measurements at 1 AU as shown in Rollett et al. (2011). To validate the
applied methods, we perform the same procedures for a simulated CME as
modeled in the space weather modeling framework (SWMF, Toth, et al.,
2005). The measurements are outlined for synthetic HI images (Lugaz et
al., 2005) at different observing points. The research leading to these
results has received funding from the European Union Seventh Framework
Programme (FP7/2007-2013) under grant agreement no. 263252 [COMESEP].
---------------------------------------------------------
Title: The first STEREO multi-event: Numerical simulation of coronal
mass ejections (CMEs) launched on August 1, 2010
Authors: Odstrcil, D.; de Koning, C. A.; Xie, H.; Moestl, C.;
Temmer, M.; Jian, L.; Rouillard, A. P.; Davies, J. A.; Davis, C. J.;
Harrison, R.
2011AGUFMSH32A..03O Altcode:
On 2010-08-01 at least four coronal mass ejections (CMEs) were observed
by the Heliospheric Imagers (HIs) onboard STEREO spacecraft. These
events originated at different parts of the solar corona and generated
complex scenario of four mutually interacting CMEs. Real-time
prediction of the arrival times to Earth failed and it is difficult
to associate features observed by HIs with their solar sources and
impacts at spacecraft. We use the heliospheric code ENLIL to show
the global solution for two scenarios using fitted CME parameters
from coronagraph observations by two different techniques. We present
the temporal profiles and synthetic white-light images that enables
direct comparison with in-situ and remote observations. These results
show that in addition to multi-perspective coronagraph observations,
heliospheric imagers and numerical simulations are needed to understand
and predict the impact of complex heliospheric disturbances.
---------------------------------------------------------
Title: Comparison between MHD modeled and in situ measured solar
wind parameters
Authors: Gressl, C.; Veronig, A. M.; Temmer, M.; Moestl, C.
2011AGUFMSH23C1977G Altcode:
The numerical MHD model ENLIL enables us to simulate the solar wind
conditions from Sun to 1 AU based on synoptic magnetograms over an
entire Carrington rotation (runs are performed at the NASA/CCMC and
are available on request under http://ccmc.gsfc.nasa.gov/). We use
ENLIL for the inner-heliosphere coupled with the coronal model MAS
(MHD-Around-A-Sphere) and the combined empirical and physics-based
model WSA (Wang-Sheeley-Arge), respectively, to extract solar wind
parameters at the distance of 1AU. The results from the simulation are
compared to measured solar wind parameters at 1AU from ACE and Wind
spacecraft. The study aims to test the accuracy and reliability for
forecasting solar wind parameters like density, speed, temperature, and
magnetic field from numerical models on time scales smaller than 1 day.
---------------------------------------------------------
Title: Arrival Time Calculation for Interplanetary Coronal Mass
Ejections with Circular Fronts and Application to STEREO Observations
of the 2009 February 13 Eruption
Authors: Möstl, C.; Rollett, T.; Lugaz, N.; Farrugia, C. J.; Davies,
J. A.; Temmer, M.; Veronig, A. M.; Harrison, R. A.; Crothers, S.;
Luhmann, J. G.; Galvin, A. B.; Zhang, T. L.; Baumjohann, W.; Biernat,
H. K.
2011ApJ...741...34M Altcode: 2011arXiv1108.0515M
One of the goals of the NASA Solar TErestrial RElations Observatory
(STEREO) mission is to study the feasibility of forecasting the
direction, arrival time, and internal structure of solar coronal
mass ejections (CMEs) from a vantage point outside the Sun-Earth
line. Through a case study, we discuss the arrival time calculation
of interplanetary CMEs (ICMEs) in the ecliptic plane using data from
STEREO/SECCHI at large elongations from the Sun in combination with
different geometric assumptions about the ICME front shape [fixed-Φ
(FP): a point and harmonic mean (HM): a circle]. These forecasting
techniques use single-spacecraft imaging data and are based on the
assumption of constant velocity and direction. We show that for the
slow (350 km s<SUP>-1</SUP>) ICME on 2009 February 13-18, observed at
quadrature by the two STEREO spacecraft, the results for the arrival
time given by the HM approximation are more accurate by 12 hr than
those for FP in comparison to in situ observations of solar wind
plasma and magnetic field parameters by STEREO/IMPACT/PLASTIC, and by
6 hr for the arrival time at Venus Express (MAG). We propose that the
improvement is directly related to the ICME front shape being more
accurately described by HM for an ICME with a low inclination of its
symmetry axis to the ecliptic. In this case, the ICME has to be tracked
to >30° elongation to obtain arrival time errors < ± 5 hr. A
newly derived formula for calculating arrival times with the HM method
is also useful for a triangulation technique assuming the same geometry.
---------------------------------------------------------
Title: Relation Between the 3D-Geometry of the Coronal Wave and
Associated CME During the 26 April 2008 Event
Authors: Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.
2011SoPh..273..421T Altcode: 2011SoPh..tmp...75T; 2011arXiv1103.0196T; 2011SoPh..tmp..227T;
2011SoPh..tmp..158T
We study the kinematical characteristics and 3D geometry of a
large-scale coronal wave that occurred in association with the 26
April 2008 flare-CME event. The wave was observed with the EUVI
instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B)
with a mean speed of ∼ 240 km s<SUP>−1</SUP>. The wave is more
pronounced in the eastern propagation direction, and is thus, better
observable in STEREO-B images. From STEREO-B observations we derive
two separate initiation centers for the wave, and their locations fit
with the coronal dimming regions. Assuming a simple geometry of the
wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B
observations. We find that the wave structure is asymmetric with an
inclination toward East. The associated CME has a deprojected speed
of ∼ 750±50 km s<SUP>−1</SUP>, and it shows a non-radial outward
motion toward the East with respect to the underlying source region
location. Applying the forward fitting model developed by Thernisien,
Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the
CME flux rope position on the solar surface to be close to the dimming
regions. We conclude that the expanding flanks of the CME most likely
drive and shape the coronal wave.
---------------------------------------------------------
Title: Coronal Dimmings and the Early Phase of a CME Observed with
STEREO and Hinode/EIS
Authors: Miklenic, C.; Veronig, A. M.; Temmer, M.; Möstl, C.; Biernat,
H. K.
2011SoPh..273..125M Altcode: 2011arXiv1110.0362M; 2011SoPh..tmp..350M
We investigate the early phase of the 13 February 2009 coronal
mass ejection (CME). Observations with the twin STEREO spacecraft
in quadrature allow us to compare for the first time in one and the
same event the temporal evolution of coronal EUV dimmings, observed
simultaneously on-disk and above-the-limb. We find that these dimmings
are synchronized and appear during the impulsive acceleration phase of
the CME, with the highest EUV intensity drop occurring a few minutes
after the maximum CME acceleration. During the propagation phase two
confined, bipolar dimming regions, appearing near the footpoints of a
pre-flare sigmoid structure, show an apparent migration away from the
site of the CME-associated flare. Additionally, they rotate around the
`center' of the flare site, i.e., the configuration of the dimmings
exhibits the same `sheared-to-potential' evolution as the postflare
loops. We conclude that the motion pattern of the twin dimmings reflects
not only the eruption of the flux rope, but also the ensuing stretching
of the overlying arcade. Finally, we find that: i) the global-scale
dimmings, expanding from the source region of the eruption, propagate
with a speed similar to that of the leaving CME front; ii) the mass
loss occurs mainly during the period of strongest CME acceleration. Two
hours after the eruption Hinode/EIS observations show no substantial
plasma outflow, originating from the `open' field twin dimming regions.
---------------------------------------------------------
Title: The LSO/KSO Hα prominence catalogue: cross-calibration of data
Authors: Rybák, J.; Gömöry, P.; Mačura, R.; Kučera, A.; Rušin,
V.; Pötzi, W.; Baumgartner, D.; Hanslmeier, A.; Veronig, A.;
Temmer, M.
2011CoSka..41..133R Altcode:
We present work on the extension of the homogeneous prominence
catalogue created for the epoch 1967 — 2009 at the Lomnicky Peak
Observatory (LSO) by incorporating new data acquired at the Kanzelhöhe
Observatory for Solar and Environmental Research (KSO). We use data of
20 Hα prominences observed almost simultaneously at both observatories
during four days in August/September 2009 to analyze the significance
of differences of the determined parameters used in the Hα prominence
catalogue. A reduction of the data from KSO and adaptation of the
resulting parameters to fit the parameters of the LSO catalogue confirm
that no special homogenization is needed to create a common catalogue
data set. Thus, we justified that the LSO catalogue could be extended
onward in the future using a more comprehensive database of observations
from KSO.
---------------------------------------------------------
Title: Analysis of Characteristic Parameters of Large-scale Coronal
Waves Observed by the Solar-Terrestrial Relations Observatory/Extreme
Ultraviolet Imager
Authors: Muhr, N.; Veronig, A. M.; Kienreich, I. W.; Temmer, M.;
Vršnak, B.
2011ApJ...739...89M Altcode:
The kinematical evolution of four extreme ultraviolet waves,
well observed by the Extreme Ultraviolet Imager on board the
Solar-Terrestrial Relations Observatory (STEREO), is studied by visually
tracking wave fronts as well as by a semi-automatized perturbation
profile method, which leads to results matching each other within
the error limits. The derived mean velocities of the events under
study lie in the range of 220-350 km s<SUP>-1</SUP>. The fastest of
the events (2007 May 19) reveals a significant deceleration of ≈ -
190 m s<SUP>-2</SUP>, while the others are consistent with a constant
velocity during wave propagation. The evolution of maximum-intensity
values reveals initial intensification of 20%-70% and decays to original
levels within 40-60 minutes, while the widths at half-maximum and
full-maximum of the perturbation profiles broaden by a factor of two
to four. The integral below the perturbation profile remains basically
constant in two cases, while it shows a decrease by a factor of three
to four in the other two cases. From the peak perturbation amplitudes,
we estimate the corresponding magnetosonic Mach numbers M <SUB>ms</SUB>,
which range from 1.08-1.21. The perturbation profiles reveal three
distinct features behind the propagating wave fronts: coronal dimmings,
stationary brightenings, and rarefaction regions. All features appear
after the wave passage and only slowly fade away. Our findings indicate
that the events under study are weak-shock fast-mode magnetohydrodynamic
waves initiated by the CME lateral expansion.
---------------------------------------------------------
Title: Propagation and impact of multiple coronal mass ejections
events on August 1 2010 in the heliosphere
Authors: Möstl, Christian; Farrugia, Charles J.; Harrison, Richard
A.; Davies, J. A.; Kilpua, Emilia K. J.; Odstrcil, Dusan; Rollett,
Tanja; Temmer, Manuela; Veronig, Astrid; Jian, Lan; Liu, Ying;
Eastwood, Jonathan; Forsyth, Robert; Webb, David; Bisi, Mario M.;
Jackson, Bernard V.; Mulligan, Tamitha; Jensen, Liz; Lavraud, Benoit;
de Koning, Curt A.; Nitta, Nariaki; Luhmann, Janet; Galvin, Antoinette
B.; Zhang, Tielong
2011sdmi.confE..69M Altcode:
On August 1 2010 a large region of the solar northern hemisphere
displayed major activity involving a complex set of central meridian and
remote active regions, and two large prominence channels (Schrijver
and Title, JGR, 2011). We witnessed the eruption of four coronal
mass ejections (CMEs) which partly impacted Earth and lead to one
of the first geomagnetic storms of the new solar cycle. We present an
overview of the results of several analyses exploiting the extraordinary
completeness of the imaging data (SDO/STEREO/SOHO) in combination with
numerical simulations (ENLIL) and in situ observations. The imprints of
the CMEs, including a prior event on July 30, were observed in situ in
an almost laboratory-like configuration at 4 widely separated locations
spanning over 120 degrees of heliospheric longitude (STEREO-B, Venus
Express, ACE/Wind, ARTEMIS, and MESSENGER). The CME density enhancements
could be followed with the STEREO-A/HI and Coriolis/SMEI instruments
continuously from the Sun to 1 AU. Evidences of CME-CME interactions
and resulting overlapping tracks in Jmaps make the analysis complex,
but nevertheless we find robust interpretations for linking two magnetic
flux ropes at Earth, one of them geo-effective and including elevated
alpha particles related to possible filament material, to their solar
counterparts. Additionally, we discuss the relationship between the
in situ observations and the global picture given by the ENLIL model.
---------------------------------------------------------
Title: Solar wind high-speed streams and related geomagnetic activity
in the declining phase of solar cycle 23
Authors: Verbanac, G.; Vršnak, B.; Živković, S.; Hojsak, T.;
Veronig, A. M.; Temmer, M.
2011A&A...533A..49V Altcode:
Context. Coronal holes (CHs) are the source of high-speed streams
(HSSs) in the solar wind, whose interaction with the slow solar wind
creates corotating interaction regions (CIRs) in the heliosphere. <BR
/> Aims: We investigate the magnetospheric activity caused by CIR/HSS
structures, focusing on the declining phase of the solar cycle 23
(years 2005 and 2006), when the occurrence rate of coronal mass
ejections (CMEs) was low. We aim to (i) perform a systematic analysis
of the relationship between the CH characteristics, basic parameters of
HSS/CIRs, and the geomagnetic indices Dst, Ap and AE; (ii) study how the
magnetospheric/ionospheric current systems behave when influenced by
HSS/CIR; (iii) investigate if and how the evolution of the background
solar wind from 2005 to 2006 affected the correlations between CH,
CIR, and geomagnetic parameters. <BR /> Methods: The cross-correlation
analysis was applied to the fractional CH area (CH) measured in the
central meridian distance interval ± 10°, the solar wind velocity (V),
the interplanetary magnetic field (B), and the geomagnetic indices Dst,
Ap, and AE. <BR /> Results: The performed analysis shows that Ap and
AE are better correlated with CH and solar wind parameters than Dst,
and quantitatively demonstrates that the combination of solar wind
parameters BV<SUP>2</SUP> and BV plays the central role in the process
of energy transfer from the solar wind to the magnetosphere. <BR />
Conclusions: We provide reliable relationships between CH properties,
HSS/CIR parameters, and geomagnetic indices, which can be used in
forecasting the geomagnetic activity in periods of low CME activity.
---------------------------------------------------------
Title: An Observational Overview of Solar Flares
Authors: Fletcher, L.; Dennis, B. R.; Hudson, H. S.; Krucker, S.;
Phillips, K.; Veronig, A.; Battaglia, M.; Bone, L.; Caspi, A.; Chen,
Q.; Gallagher, P.; Grigis, P. T.; Ji, H.; Liu, W.; Milligan, R. O.;
Temmer, M.
2011SSRv..159...19F Altcode: 2011SSRv..tmp..261F; 2011arXiv1109.5932F
We present an overview of solar flares and associated phenomena,
drawing upon a wide range of observational data primarily from the
RHESSI era. Following an introductory discussion and overview of
the status of observational capabilities, the article is split into
topical sections which deal with different areas of flare phenomena
(footpoints and ribbons, coronal sources, relationship to coronal mass
ejections) and their interconnections. We also discuss flare soft X-ray
spectroscopy and the energetics of the process. The emphasis is to
describe the observations from multiple points of view, while bearing
in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is
far from complete, so we conclude with a brief discussion of models,
and a list of missing but important observations.
---------------------------------------------------------
Title: Impulsive Acceleration of Coronal Mass Ejections. I. Statistics
and Coronal Mass Ejection Source Region Characteristics
Authors: Bein, B. M.; Berkebile-Stoiser, S.; Veronig, A. M.; Temmer,
M.; Muhr, N.; Kienreich, I.; Utz, D.; Vršnak, B.
2011ApJ...738..191B Altcode: 2011arXiv1108.0561B
We use high time cadence images acquired by the STEREO EUVI and
COR instruments to study the evolution of coronal mass ejections
(CMEs) from their initiation through impulsive acceleration to the
propagation phase. For a set of 95 CMEs we derived detailed height,
velocity, and acceleration profiles and statistically analyzed
characteristic CME parameters: peak acceleration, peak velocity,
acceleration duration, initiation height, height at peak velocity,
height at peak acceleration, and size of the CME source region. The CME
peak accelerations we derived range from 20 to 6800 m s<SUP>-2</SUP>
and are inversely correlated with the acceleration duration and the
height at peak acceleration. Seventy-four percent of the events reach
their peak acceleration at heights below 0.5 R <SUB>sun</SUB>. CMEs that
originate from compact sources low in the corona are more impulsive and
reach higher peak accelerations at smaller heights. These findings can
be explained by the Lorentz force, which drives the CME accelerations
and decreases with height and CME size.
---------------------------------------------------------
Title: Analysis of characteristic parameters of large-scale coronal
waves observed by STEREO/EUVI
Authors: Muhr, N.; Veronig, A. M.; Kienreich, I. W.; Temmer, M.;
Vrsnak, B.
2011arXiv1107.0921M Altcode:
The kinematical evolution of four EUV waves, well observed by the
Extreme UltraViolet Imager (EUVI) onboard the Solar-Terrestrial
Relations Observatory (STEREO), is studied by visually tracking the
wave fronts as well as by a semiautomatized perturbation profile
method leading to results matching each other within the error
limits. The derived mean velocities of the events under study lie
in the range of 220-350 km/s. The fastest of the events (May 19,
2007) reveals a significant deceleration of \approx -190 m s-2 while
the others are consistent with a constant velocity during the wave
propagation. The evolution of the maximum intensity values reveals
initial intensification by 20 up to 70%, and decays to original
levels within 40-60 min, while the width at half maximum and full
maximum of the perturbation profiles are broadening by a factor of
2 - 4. The integral below the perturbation profile remains basically
constant in two cases, while it shows a decrease by a factor of 3 -
4 in the other two cases. From the peak perturbation amplitudes we
estimate the corresponding magnetosonic Mach numbers Mms which are
in the range of 1.08-1.21. The perturbation profiles reveal three
distinct features behind the propagating wave fronts: coronal dimmings,
stationary brightenings and rarefaction regions. All of them appear
after the wave passage and are only slowly fading away. Our findings
indicate that the events under study are weak shock fast-mode MHD
waves initiated by the CME lateral expansion.
---------------------------------------------------------
Title: The Drag Based Model of ICME Propagation
Authors: Dumbović, M.; Vršnak, B.; Žic, T.; Vrbanec, D.; Veronig,
A.; Temmer, M.; Rollett, T.; Moestl, C.; Moon, Y. -J.
2011simi.confR...2D Altcode:
One of central issues of space weather is the propagation of
interplanetary coronal mass ejections (ICMEs). At the heliospheric
distances beyond R=20 solar radii the "aerodynamic" drag is presumably
the dominant force governing ICME propagation; therefore, a drag based
model (DBM) was established, which can be used to forecast the ICME
arrival at the Earth. <P />First, the model was tested on a sample
of CMEs by combining remote observations of the CME take-off gained
by the LASCO onboard SOHO, and in situ measurements from ACE and Wind
satellites. The results of the DBM were compared to observational data
and a fairly good agreement of the two was found. The model was then
tested against STEREO observations. The ICME kinematics was inferred
from STEREO observations by applying the Harmonic Mean method and
compared to the DBM results. In this way we were able to reproduce
the propagation of both slow and fast ICMEs, as well as to identify
ICME-ICME interactions and a transition from fast-to-slow solar wind
regimes. Finally, a statistical study was performed, where parameters
were varied within a model in order to obtain optimal values, for
which the average difference in the observed and calculated TT is zero
(O-C=0) and the O-C scatter gets minimum. The source of the scatter
in O–C values was investigated. <P />The research leading to the
results presented in this paper has received funding from European
Community's Seventh Framework Programme (FP7/2007-2013) under grant
agreement No. 218816.
---------------------------------------------------------
Title: Multiple, distant (40°) in situ observations of a magnetic
cloud and a corotating interaction region complex
Authors: Farrugia, C. J.; Berdichevsky, D. B.; Möstl, C.; Galvin,
A. B.; Leitner, M.; Popecki, M. A.; Simunac, K. D. C.; Opitz, A.;
Lavraud, B.; Ogilvie, K. W.; Veronig, A. M.; Temmer, M.; Luhmann,
J. G.; Sauvaud, J. A.
2011JASTP..73.1254F Altcode:
We report a comprehensive analysis of in situ observations made
by Wind and the STEREO probes (STA, STB) of a complex interaction
between a magnetic cloud (MC) and a corotating interaction region (CIR)
occurring near the heliospheric current sheet (HCS) on November 19-21,
2007. The probes were separated by 0.7 AU (∼40<SUP>∘</SUP>) with
a spread in heliographic latitudes (4.8,° 2.2,° and -0.4,° for STB,
Wind and STA, respectively). We employ data from the MFI, SWE and 3DP
instruments on Wind, and the PLASTIC and IMPACT suites on STEREO. STB,
located east of Earth, observed a forward shock followed by signatures
of a MC. The MC took the role of the HCS in that the polarity of the
interplanetary magnetic field (IMF) on exit was the reverse of that
on entry. A passage through a plasma sheet was observed. Along the
Sun-Earth line Wind observed a stream interface (SI) between a forward
and a reverse shock. A MC, compressed by the CIR, was entrained in
this. STA, located 20° to the west of Earth, saw a MC which was not
preceded by a shock. A SI trailed the transient. The shocks are examined
using various methods and from this it is concluded that the forward
shock at Wind—but not at STB—was driven by the MC. Examining the MC
by Grad-Shafranov reconstruction, we find evidence of a double-flux rope
structure at Wind and STA and possibly also at STB. The orientations are
at variance with the notion of a large-scale flux tube being observed at
the three spacecraft. We find consistency of this with the directional
properties of the solar wind "strahl" electrons. We examine aspects of
the geomagnetic response and find a double-dip storm corresponding to
the two interplanetary triggers. The minimum Dst phase was prolonged
and the geoeffects were intensified due to the interaction. We conclude
that while the formation of compound streams is a common feature of
interplanetary space, understanding their components when CIRs are
involved is a complicated matter needing numerical simulations and/or
more in situ observations for its complete elucidation.
---------------------------------------------------------
Title: Equatorial coronal holes, solar wind high-speed streams,
and their geoeffectiveness
Authors: Verbanac, G.; Vršnak, B.; Veronig, A.; Temmer, M.
2011A&A...526A..20V Altcode:
Context. Solar wind high-speed streams (HSSs), originating in equatorial
coronal holes (CHs), are the main driver of the geomagnetic activity in
the late-declining phase of the solar cycle. <BR /> Aims: We analyze
correlations between CH characteristics, HSSs parameters, and the
geomagnetic activity indices, to establish empirical relationships
that would provide forecasting of the solar wind characteristics,
as well as the effect of HSSs on the geomagnetic activity in periods
when the effect of coronal mass ejections is low. <BR /> Methods:
We apply the cross-correlation analysis to the fractional CH area
(CH) measured between central meridian distances ±10°, solar wind
parameters (flow velocity V, proton density n, temperature T, and
the magnetic field B), and the geomagnetic indices Dst and Ap. <BR
/> Results: The cross-correlation analysis reveals a high degree
of correlation between all studied parameters. In particular, we
show that the Ap index is considerably more sensitive to HSS and CH
characteristics than Dst. The Ap and Dst indices are most tightly
correlated with the solar wind parameter BV<SUP>2</SUP>. <BR />
Conclusions: From the point of view of space weather, the most
important result is that the established empirical relationships
provide a few-days-in-advance forecasting of the HSS characteristics
and the related geomagnetic activity at the six-hour resolution. <P
/>Appendices, Figs. 9-14, and table 4 are only available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Case Study of Four Homologous Large-scale Coronal Waves
Observed on 2010 April 28 and 29
Authors: Kienreich, I. W.; Veronig, A. M.; Muhr, N.; Temmer, M.;
Vršnak, B.; Nitta, N.
2011ApJ...727L..43K Altcode: 2011arXiv1101.5232K
On 2010 April 28 and 29, the Solar TErrestrial Relations Observatory
B/Extreme Ultraviolet Imager observed four homologous large-scale
coronal waves, the so-called EIT-waves, within 8 hr. All waves emerged
from the same source active region, were accompanied by weak flares and
faint coronal mass ejections, and propagated into the same direction
at constant velocities in the range of ~220-340 km s<SUP>-1</SUP>. The
last of these four coronal wave events was the strongest and fastest,
with a velocity of 337 ± 31 km s<SUP>-1</SUP> and a peak perturbation
amplitude of ~1.24, corresponding to a magnetosonic Mach number of M
<SUB>ms</SUB> ~ 1.09. The magnetosonic Mach numbers and velocities of
the four waves are distinctly correlated, suggestive of the nonlinear
fast-mode magnetosonic wave nature of the events. We also found a
correlation between the magnetic energy buildup times and the velocity
and magnetosonic Mach number.
---------------------------------------------------------
Title: Implementation of a Calcium telescope at Kanzelhöhe
Observatory (KSO)
Authors: Hirtenfellner-Polanec, W.; Temmer, M.; Pötzi, W.; Freislich,
H.; Veronig, A. M.; Hanslmeier, A.
2011CEAB...35..205H Altcode:
A new telescope is implemented at Kanzelhöhe Observatory in order to
observe the chromosphere in the Ca II K line at 393.4 nm (FWHM 0.3
nm). The design of the new Ca camera system is very similar to the
well established Kanzelhöhe Photosphere Digital Camera and the Hα
system and allows obtaining automatically full disc Ca~II~K 2k×2k
images time series with a cadence of a few seconds. The main purpose
of this new instrument is a high precision full disc imaging of the
chromosphere in order to observe flares, plages and the chromospheric
network. The Ca emission is also an indicator for magnetic activity
on the sun. Therefore the Ca data will be taken for analysing the
variations in the structures of the magnetic field.
---------------------------------------------------------
Title: STEREO and Wind observations of a fast ICME flank triggering
a prolonged geomagnetic storm on 5-7 April 2010
Authors: Möstl, C.; Temmer, M.; Rollett, T.; Farrugia, C. J.; Liu,
Y.; Veronig, A. M.; Leitner, M.; Galvin, A. B.; Biernat, H. K.
2010GeoRL..3724103M Altcode: 2010arXiv1010.4150M
On 5 April 2010 an interplanetary (IP) shock was detected by the
Wind spacecraft ahead of Earth, followed by a fast (average speed
650 km/s) IP coronal mass ejection (ICME). During the subsequent
moderate geomagnetic storm (minimum D<SUB>st</SUB> = -72 nT,
maximum K<SUB>p</SUB> = 8<SUP>-</SUP>), communication with the
Galaxy 15 satellite was lost. We link images from STEREO/ SECCHI to
the near-Earth in situ observations and show that the ICME did not
decelerate much between Sun and Earth. The ICME flank was responsible
for a long storm growth phase. This type of glancing collision was
for the first time directly observed with the STEREO Heliospheric
Imagers. The magnetic cloud (MC) inside the ICME cannot be modeled with
approaches assuming an invariant direction. These observations confirm
the hypotheses that parts of ICMEs classified as (1) long-duration
MCs or (2) magnetic-cloud-like (MCL) structures can be a consequence
of a spacecraft trajectory through the ICME flank.
---------------------------------------------------------
Title: Application of data assimilation to solar wind forecasting
models
Authors: Innocenti, M.; Lapenta, G.; Vrsnak, B.; Temmer, M.; Veronig,
A.; Bettarini, L.; Lee, E.; Markidis, S.; Skender, M.; Crespon, F.;
Skandrani, C.; Soteria Space-Weather Forecast; Data Assimilation Team
2010AGUFMSM54A..08I Altcode:
Data Assimilation through Kalman filtering [1,2] is a powerful
statistical tool which allows to combine modeling and observations
to increase the degree of knowledge of a given system. We apply this
technique to the forecast of solar wind parameters (proton speed, proton
temperature, absolute value of the magnetic field and proton density) at
1 AU, using the model described in [3] and ACE data as observations. The
model, which relies on GOES 12 observations of the percentage of the
meridional slice of the sun covered by coronal holes, grants 1-day and
6-hours in advance forecasts of the aforementioned quantities in quiet
times (CMEs are not taken into account) during the declining phase
of the solar cycle and is tailored for specific time intervals. We
show that the application of data assimilation generally improves
the quality of the forecasts during quiet times and, more notably,
extends the periods of applicability of the model, which can now provide
reliable forecasts also in presence of CMEs and for periods other than
the ones it was designed for. Acknowledgement: The research leading
to these results has received funding from the European Commission’s
Seventh Framework Programme (FP7/2007-2013) under the grant agreement
N. 218816 (SOTERIA project: http://www.soteria-space.eu). References:
[1] R. Kalman, J. Basic Eng. 82, 35 (1960); [2] G. Welch and G. Bishop,
Technical Report TR 95-041, University of North Carolina, Department
of Computer Science (2001); [3] B. Vrsnak, M. Temmer, and A. Veronig,
Solar Phys. 240, 315 (2007).
---------------------------------------------------------
Title: Multiple, Distant (40 deg) in situ Observations of a Magnetic
Cloud and a Corotating Interaction Region Complex
Authors: Farrugia, C. J.; Berdichevsky, D. B.; Moestl, C.; Galvin,
A. B.; Leitner, M.; Popecki, M.; Simunac, K. D.; Opitz, A.; Lavraud,
B.; Ogilvie, K.; Veronig, A.; Temmer, M.; Luhmann, J. G.; Sauvaud, J.
2010AGUFMSH51C1689F Altcode:
We report a comprehensive analysis of in situ observations made
by Wind and the STEREO probes (STA, STB) of a complex interaction
between a magnetic cloud (MC) and a corotating interaction region (CIR)
occurring near the heliospheric current sheet (HCS) on November 19-21,
2007. The probes were separated by 0.7 AU (~40 deg) with a spread in
heliographic latitudes (4.8, 2.2, and -0.4 deg for STB, Wind and STA,
respectively). We employ data from the MFI, SWE and 3DP instruments
on Wind, and the PLASTIC and IMPACT suites on STEREO. STB, located
east of Earth, observed a forward shock followed by signatures of
a MC. The MC took the role of the HCS in that the polarity of the
interplanetary magnetic field (IMF) on exit was the reverse of that on
entry. A passage through a plasma sheet is observed. Along the Sun-Earth
line Wind observed a stream interface (SI) between a forward and a
reverse shock. A MC, compressed by the CIR, was entrained in this. STA,
located 20 deg to the west of Earth, saw a MC which was not preceded
by a shock. A SI trailed the transient. The shocks are examined using
various methods and from this it is concluded that the forward shock
at Wind - but not at STB - was driven by the MC. Examining the MC by
Grad-Shafranov reconstruction, we find evidence of a double-flux rope
structure at Wind and STA and possibly also at STB. The orientations are
at variance with the notion of a large-scale flux tube being observed at
the three spacecraft. We find consistency of this with the directional
properties of the solar wind "strahl" electrons. We examine aspects of
the geomagnetic response and find a double-dip storm corresponding to
the two interplanetary triggers. The minimum Dst phase was prolonged
and the geoffects were intensified due to the interaction. We conclude
that while the formation of compound streams is a common feature of
interplanetary space, understanding their components when CIRs are
involved is a complicated matter needing numerical simulations and/or
morein situ observations for its complete elucidation.
---------------------------------------------------------
Title: Propagation Directions and Kinematics of STEREO CME/ICMEs
Events
Authors: Rollett, T.; Moestl, C.; Temmer, M.; Veronig, A.; Lugaz,
N.; Biernat, H. K.
2010AGUFMSH41A1775R Altcode:
The Heliospheric Imagers on board the two STEREO twin satellites give
us the possibilities to track Coronal Mass Ejections up to a distance
of 1 AU. For events of our interest, remote sensing data as well as
in situ measurements from the other STEREO spacecraft or Wind are
available. The combination of both allows us to calculate a constant
propagation direction in the ecliptic plane by using different methods
(Fixed-Phi and the Harmonic Mean). These methods convert the measured
elongation into distance by making different assumptions on the
shape of the CME. With the combined data sets we can also derive the
kinematics (distance-velocity plots) and try to crosscheck the results
by taking care of the ambient solar wind. Moreover, we use inverse
fitting methods for both the Fixed-Phi and Harmonic Mean approaches
(which assume constant velocity) to fit our measurements and compare
it to the results calculated by our combined method.
---------------------------------------------------------
Title: The CME/ICME relationship for the 3-5 April 2010 and Aug 1-4
2010 events
Authors: Moestl, C.; Temmer, M.; Rollett, T.; Kilpua, E. K.; Farrugia,
C. J.; Veronig, A.; Galvin, A. B.; Biernat, H. K.
2010AGUFMSH43C..07M Altcode:
For two coronal mass ejections (CMEs) associated with interplanetary
CMEs (ICMEs) causing moderate geomagnetic storms in 2010, we discuss
properties such as interplanetary propagation, orientation and
arrival time calculation. We study heliospheric images of the CMEs
provided by STEREO / HI in combination with in situ observations by
the Wind spacecraft near Earth. The 3-5 April 2010 event was the
first fast (800 km/s) ICME including a magnetic cloud observed by
both the STEREO/HI instruments and a near Earth spacecraft. During
the subsequent geomagnetic storm (minimum Dst = -72 nT, maximum Kp =
8-), communication with the Galaxy 15 satellite was lost. Using forward
modeling in combination with HI techniques and the in situ velocity, we
show that the ICME did not decelerate much between Sun and Earth. Earth
was not hit directly, but the ICME flank was responsible for a long
storm growth phase. The magnetic cloud (MC) inside the ICME cannot
be modeled with approaches assuming an invariant direction. These
observations confirm the hypotheses that parts of ICMEs classified as
(1) long-duration MCs or (2) magnetic-cloud-like (MCL) structures
can be a consequence of a spacecraft trajectory through the ICME
flank. The 1-4 Aug 2010 events consisted of several CMEs accompanied
by multiple ICME signatures near Earth, responsible for a two-step
geomagnetic storm. We discuss which of the ICMEs correspond to the
flare/filaments/CMEs observed by STEREO/COR/HI and SDO HMI/AIA observed
closer to the Sun. We apply reconstruction methods to estimate the
local flux rope orientation and other properties. The ICME signatures
are linked to HI observations of the CME fronts, which yields full
CME kinematics between the Sun and Earth. STEREO Ahead HI1/2 images
of the 3-5 April 2010 Earth-directed coronal mass ejection.
---------------------------------------------------------
Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
B.; White, S. M.
2010ApJ...723..587B Altcode:
We analyzed ground- and space-based observations of the eruptive flare
(3B/X6.5) and associated Moreton wave (~850 km s<SUP>-1</SUP> ~270°
azimuthal span) of 2006 December 6 to determine the wave driver—either
flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
analysis favors a CME driver of the wave, despite key gaps in coronal
data. The CME scenario has a less constrained/smoother velocity versus
time profile than is the case for the flare hypothesis and requires an
acceleration rate more in accord with observations. The CME picture is
based, in part, on the assumption that a strong and impulsive magnetic
field change observed by a GONG magnetograph during the rapid rise phase
of the flare corresponds to the main acceleration phase of the CME. The
Moreton wave evolution tracks the inferred eruption of an extended
coronal arcade, overlying a region of weak magnetic field to the west
of the principal flare in NOAA active region 10930. Observations of
Hα foot point brightenings, disturbance contours in off-band Hα
images, and He I 10830 Å flare ribbons trace the eruption from 18:42
to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
observations show strong blueshifts at foot points of this arcade
during the post-eruption phase, indicating mass outflow. At 18:45
UT, the Moreton wave exhibited two separate arcs (one off each flank
of the tip of the arcade) that merged and coalesced by 18:47 UT to
form a single smooth wave front, having its maximum amplitude in
the southwest direction. We suggest that the erupting arcade (i.e.,
CME) expanded laterally to drive a coronal shock responsible for the
Moreton wave. We attribute a darkening in Hα from a region underlying
the arcade to absorption by faint unresolved post-eruption loops.
---------------------------------------------------------
Title: Multiwavelength Imaging and Spectroscopy of Chromospheric
Evaporation in an M-class Solar Flare
Authors: Veronig, A. M.; Rybák, J.; Gömöry, P.; Berkebile-Stoiser,
S.; Temmer, M.; Otruba, W.; Vršnak, B.; Pötzi, W.; Baumgartner, D.
2010ApJ...719..655V Altcode: 2010arXiv1007.0930V
We study spectroscopic observations of chromospheric evaporation mass
flows in comparison with the energy input by electron beams derived
from hard X-ray (HXR) data for the white-light M2.5 flare of 2006 July
6. The event was captured in high-cadence spectroscopic observing mode
by SOHO/CDS combined with high-cadence imaging at various wavelengths
in the visible, extreme ultraviolet, and X-ray domain during the joint
observing campaign JOP171. During the flare peak, we observe downflows
in the He I and O V lines formed in the chromosphere and transition
region, respectively, and simultaneous upflows in the hot coronal
Si XII line. The energy deposition rate by electron beams derived
from RHESSI HXR observations is suggestive of explosive chromospheric
evaporation, consistent with the observed plasma motions. However, for
a later distinct X-ray burst, where the site of the strongest energy
deposition is exactly located on the Coronal Diagnostics Spectrometer
(CDS) slit, the situation is intriguing. The O V transition region
line spectra show the evolution of double components, indicative of
the superposition of a stationary plasma volume and upflowing plasma
elements with high velocities (up to 280 km s<SUP>-1</SUP>) in single
CDS pixels on the flare ribbon. However, the energy input by electrons
during this period is too small to drive explosive chromospheric
evaporation. These unexpected findings indicate that the flaring
transition region is much more dynamic, complex, and fine structured
than is captured in single-loop hydrodynamic simulations.
---------------------------------------------------------
Title: Statistical Properties of Flares and Sunspots over the
Solar Cycle
Authors: Temmer, M.
2010ASPC..428..161T Altcode: 2010arXiv1002.0413T
The present paper reviews results derived from statistical studies of
solar activity indices. The prolonged minimum phase of cycle 23 raised
the question of peculiarities inherent in cycle 23. The most important
solar activity index is the relative sunspot number and though most
of the other indices are closely related, shifts are obtained between
their peak activities of the order of 1-2 years. These shifts reveal
a 22-year pattern which can be attributed to solar interior or dynamo
related processes. The minimum phase of cycle 23 is not found to be
exceptional. Investigating the relative sunspot numbers over the past
150 years, solar cycles of more prolonged minima are observed. Since
1920, solar activity has been quite high ("modern maximum") and cycle
23 might be the herald of the end of this phase.
---------------------------------------------------------
Title: First Observations of a Dome-shaped Large-scale Coronal
Extreme-ultraviolet Wave
Authors: Veronig, A. M.; Muhr, N.; Kienreich, I. W.; Temmer, M.;
Vršnak, B.
2010ApJ...716L..57V Altcode: 2010arXiv1005.2060V
We present first observations of a dome-shaped large-scale
extreme-ultraviolet coronal wave, recorded by the Extreme Ultraviolet
Imager instrument on board STEREO-B on 2010 January 17. The main
arguments that the observed structure is the wave dome (and not the
coronal mass ejection, CME) are (1) the spherical form and sharpness of
the dome's outer edge and the erupting CME loops observed inside the
dome; (2) the low-coronal wave signatures above the limb perfectly
connecting to the on-disk signatures of the wave; (3) the lateral
extent of the expanding dome which is much larger than that of the
coronal dimming; and (4) the associated high-frequency type II burst
indicating shock formation low in the corona. The velocity of the upward
expansion of the wave dome (v ~ 650 km s<SUP>-1</SUP>) is larger than
that of the lateral expansion of the wave (v ~ 280 km s<SUP>-1</SUP>),
indicating that the upward dome expansion is driven all the time,
and thus depends on the CME speed, whereas in the lateral direction it
is freely propagating after the CME lateral expansion stops. We also
examine the evolution of the perturbation characteristics: first the
perturbation profile steepens and the amplitude increases. Thereafter,
the amplitude decreases with r <SUP>-2.5 ± 0.3</SUP>, the width
broadens, and the integral below the perturbation remains constant. Our
findings are consistent with the spherical expansion and decay of a
weakly shocked fast-mode MHD wave.
---------------------------------------------------------
Title: Four decades of geomagnetic and solar activity: 1960-2001
Authors: Verbanac, Giuli; Vršnak, Bojan; Temmer, Manuela; Mandea,
Mioara; Korte, Monika
2010JASTP..72..607V Altcode:
We analyze the relationship between some space weather indices (Dst,
Ap, F10.7) and geomagnetic effects on the regional (European) scale,
over the period 1960-2001. The remaining external field signal (RES)
detected in the Northward magnetic component of the European observatory
annual means are used as an indicator of the regional geomagnetic
activity. Relationship RES-F10.7 suggests correction factors for getting
the geomagnetic annual means of the Northern component less affected by
the external sources. We have found some time lags among investigated
parameters. These delays may suggest that the Ap responds to the solar
activity in a differently than Dst and RES, Ap being more sensitive
to the high-speed streams (HSS) and the Alfvenic waves present in HSS,
while Dst and RES being more influenced by the coronal mass ejections
activity (CME).
---------------------------------------------------------
Title: Calculating the propagation direction of coronal mass ejections
by connecting in situ observations with heliospheric images
Authors: Rollett, Tanja; Möstl, Christian; Temmer, Manuela; Veronig,
Astrid; Biernat, Helfried K.
2010EGUGA..12.3468R Altcode:
We determined the propagation direction of two coronal mass ejections
by using data provided by the Heliospheric Imagers (HI) and the PLASTIC
and IMPACT instruments onboard the two STEREO satellites. To facilitate
the tracking of the CME's leading edge we made time-elongation plots
(J-plots) for the investigated events and tracked the apparent leading
edge therein several times in order to estimate the measurement
error. For converting elongation to distance we compared several
methods (Point-P, Fixed-Phi and their harmonic mean). To determine the
direction of the CME's propagation in the ecliptic we connected the
CME-track derived from HI J-plots with the measured in situ arrival
time by modifying the propagation direction within the used model
equations. The resulting directions and their errors are discussed
with respect to the different assumptions used for each technique.
---------------------------------------------------------
Title: Combined STEREO/RHESSI Study of Coronal Mass Ejection
Acceleration and Particle Acceleration in Solar Flares
Authors: Temmer, M.; Veronig, A. M.; Kontar, E. P.; Krucker, S.;
Vršnak, B.
2010ApJ...712.1410T Altcode: 2010arXiv1002.3080T
Using the potential of two unprecedented missions, Solar Terrestrial
Relations Observatory (STEREO) and Reuven Ramaty High-Energy Solar
Spectroscopic Imager (RHESSI), we study three well-observed fast coronal
mass ejections (CMEs) that occurred close to the limb together with
their associated high-energy flare emissions in terms of RHESSI hard
X-ray (HXR) spectra and flux evolution. From STEREO/EUVI and STEREO/COR1
data, the full CME kinematics of the impulsive acceleration phase up to
~4 R <SUB>sun</SUB> is measured with a high time cadence of <=2.5
minutes. For deriving CME velocity and acceleration, we apply and
test a new algorithm based on regularization methods. The CME maximum
acceleration is achieved at heights h <= 0.4 R <SUB>sun</SUB>,
and the peak velocity at h <= 2.1 R <SUB>sun</SUB> (in one case,
as small as 0.5 R <SUB>sun</SUB>). We find that the CME acceleration
profile and the flare energy release as evidenced in the RHESSI HXR flux
evolve in a synchronized manner. These results support the "standard"
flare/CME model which is characterized by a feedback relationship
between the large-scale CME acceleration process and the energy release
in the associated flare.
---------------------------------------------------------
Title: STEREO quadrature observations of the large-scale EUV wave
of Feb 13th, 2009
Authors: Ines Kienreich, Mag.; Veronig, Astrid; Temmer, Manuela
2010cosp...38.1841I Altcode: 2010cosp.meet.1841I
The event on Feb 13th, 2009 was the first case of a global coronal
wave observed by the STEREO twin satellites in quadrature. The wave's
initiation site was at the disk center in EUVI STEREO-B and precisely at
the limb in STEREO-A. Therefore it was possible to determine the wave's
on-disk as well as edge-on kinematics and to study its three-dimensional
structure. From the two STEREO observations we derive the height of
propagation of the wave, which was found to be in the range between
80-100 Mm above the photosphere. Comparison of the early phases of
the contemporaneous CME and the wave's kinematics suggest that the
wave is set off by the CME lateral expansion. The wave propagates
globally over the whole hemisphere with a constant velocity 263 16 km
s-1, which is close to the fast magnetosonic speed in the quiet solar
corona. Thus we conclude that the observed EUV wave is consistent with
a MHD fast-mode wave.
---------------------------------------------------------
Title: Analysis of a Global Moreton Wave Observed on 2003 October 28
Authors: Muhr, N.; Vršnak, B.; Temmer, M.; Veronig, A. M.;
Magdalenić, J.
2010ApJ...708.1639M Altcode: 2009arXiv0911.4405M
We study the well-pronounced Moreton wave that occurred in association
with the X17.2 flare/CME event of 2003 October 28. This Moreton wave is
striking for its global propagation and two separate wave centers, which
implies that two waves were launched simultaneously. The mean velocity
of the Moreton wave, tracked within different sectors of propagation
direction, lies in the range of v ≈ 900-1100 km s<SUP>-1</SUP> with
two sectors showing wave deceleration. The perturbation profile analysis
of the wave indicates amplitude growth followed by amplitude weakening
and broadening of the perturbation profile, which is consistent with
a disturbance first driven and then evolving into a freely propagating
wave. The Extreme-Ultraviolet Imaging Telescope wave front is found to
lie on the same kinematical curve as the Moreton wave fronts indicating
that both are different signatures of the same physical process. Bipolar
coronal dimmings are observed on the same opposite east-west edges of
the active region as the Moreton wave ignition centers. The radio type
II source, which is cospatially located with the first wave front,
indicates that the wave was launched from an extended source region
(gsim60 Mm). These findings suggest that the Moreton wave is initiated
by the coronal mass ejection expanding flanks.
---------------------------------------------------------
Title: Automated detection of coronal hole areas
Authors: Rotter, Mag. Thomas; Veronig, Astrid; Temmer, Manuela
2010cosp...38.1890R Altcode: 2010cosp.meet.1890R
Coronal holes, as regions of low-density plasma on the sun, have
magnetic fields that open freely into interplanetary space and thus
shape our heliosphere. Along these open magnetic fields, charged
particles leave the Sun to form the high speed component of the solar
wind. SOHO EIT (Extreme ultraviolet Imaging Telescope) provides for the
first time continuous observations of coronal holes over a full solar
cycle (no.23). These data enable us to study the solar cycle evolution
of coronal holes and their relation to in-situ solar wind magnetic
field and plasma parameters at 1 AU. In the poster we will present
first results of an automated coronal hole detection algorithm that
is currently under development. The algorithm uses a histogram-based
intensity treshholding technique to determine coronal hole areas and
their positions.
---------------------------------------------------------
Title: Calculation of CME kinematics and propagation directions by
connecting STEREO HI-images with in situ data
Authors: Rollett, Tanja; Moestl, Christian; Temmer, Manuela; Veronig,
Astrid; Biernat, Helfried K.
2010cosp...38.1894R Altcode: 2010cosp.meet.1894R
On a sample of selected events we determined the propagation directions
and the kinematics of several coronal mass ejections by using data
provided by the Heliospheric Imagers (HI) and the PLASTIC and IMPACT
instruments onboard the two STEREO satellites and the Wind spacecraft
near Earth. We tracked for each CME the leading edge and core within
time-elongation plots (Jplots) and converted the measured elongation
angle into distance by using different methods (Point-P, Fixed-Phi
and their harmonic mean). Furthermore, we used the Sheeley-method to
fit our measurements and calculate the propagation angles and arrival
times at the other spacecraft assuming that the CMEs propagate with
constant velocity. Finally we discuss our results by comparing the
kinematics derived from the different techniques.
---------------------------------------------------------
Title: Evolution of solar wind energy densities during solar minimum
2007-2009, and features of its effects on the Earth's magnetopause
and magnetosheath
Authors: Farrugia, Charles; Harris, B.; Leitner, Mag. Martin; Moestl,
Christian; Simunac, Kristin; Galvin, Antoinette; Veronig, Astrid;
Temmer, Manuela; Luhmann, Janet G.; Szabo, Adam; Biernat, Helfried K.;
Lucek, Elizabeth A.
2010cosp...38.1898F Altcode: 2010cosp.meet.1898F
We quantify the distribution of magnetic and kinetic energies densities
of the solar wind at 1 AU as the deep solar activity minimum 2007-2009
progressed. For this we use near -Earth spacecraft Wind and the STEREO-A
and B probes, the latter giving us a more comprehensive description
by extending the longitudinal coverage. We relate general trends in
interplanetary data to observations on the Sun. We then pick out a
4-month period, characterized by minima in both the kinetic and magnetic
energy densities, and examine the profiles of the plasma and magnetic
field parameters. They show slow-slower solar wind interactions with
pronounced compressions, and low field strengths in slow solar wind
streams. These are compared with the general plasma and field properties
of the slow solar wind and differences are noted. Using Cluster data,
we determine the average shapes of the bow shock and magnetopause for
this period. We compare these with gas dynamic and MHD predictions for
the average Alfven Mach number realized. Major features of observations
in the Earth's magnetosheath are discussed. This work is meant as a
contribution to Sun-Earth connection studies.
---------------------------------------------------------
Title: Relation between the dynamics of coronal mass ejections and
solar flare energetics derived from STEREO and RHESSI observations
Authors: Bein, Bianca; Veronig, Astrid; Berkebile-Stoiser, Sigrid;
Temmer, Manuela
2010cosp...38.3019B Altcode: 2010cosp.meet.3019B
We aim to explore the relation of the energy release in solar flares
to the dynamical evolution of their associated coronal mass ejections
for a statistically representative sample of events. For our study,
we use EUV (171˚, 195˚) and white light coronographic observations
from A A the STEREO (Solar Terrestial Relations Observatory) SECCHI
instrument suite. Due to the high time cadence of the STEREO EUVI
and COR images, the detailed CME kinematics from the initiation
through the impulsive acceleration to the propagation phase can
be derived. Information on the energy release in the flares under
study comes from hard X-ray observations of the RHESSI instrument
(Ramaty High Energy Solar Spectroscopic Imager). RHESSI non-thermal
lightcurves as well as the derivative of the GOES soft X-ray flux are
compared with the acceleration curve of the associated CME.
---------------------------------------------------------
Title: Coronal mass ejections in the STEREO era
Authors: Temmer, Manuela
2010cosp...38.2967T Altcode: 2010cosp.meet.2967T
The present paper reviews recent results derived from studies of
coronal mass ejections (CMEs) and associated flares. CMEs are the most
violent activity signatures from our Sun. Discov-ered in the 70's,
extensive studies were carried out particularly in the SOHO era, but
still, our understanding of the physical characteristics of CMEs is
limited. Mainly this is due to single coronagraph observations, which
image CMEs in projection against the plane of sky, hence, missing their
3D structure and evolution. The Solar Terrestrial Relations Observatory
-STEREO, launched on October 25th, 2006, is composed of two nearly
identical spacecrafts, one ahead of Earth in its orbit (STEREO-A), the
other trailing behind (STEREO-B). This unprecedented mission observes
CMEs simultaneously from two different vantage points, from which new
insights into the 3D aspects of CMEs are derived. In addition, with the
Heliospheric Imager instruments aboard STEREO, events can be tracked
seamlessly from Sun to Earth where they can be related to in-situ plasma
and magnetic field measurements. High spatial and temporal resolution
images of the low corona in EUV and from coronagraphs in white light
give information on CME initiation and its early propagation phase. In
com-bination with observations of the associated flare, those enable us
to examine in detail the CME-flare relationship, from both observational
and theoretical points of view. Recent studies give evidence that the
energy release process in flares (HXR emission) and the acceleration of
CMEs are closely related. Complementary multi-wavelength observations
of eruptive events are therefore needed to understand the "big picture"
including both phenomena CMEs and flares.
---------------------------------------------------------
Title: Study of the kinematics and driver of the global Moreton wave
observed on 2003 October 28
Authors: Muhr, Mmag. Nicole; Vrsnak, Bojan; Temmer, Manuela; Veronig,
Astrid; Magdalenic, Jasmina
2010cosp...38.1844M Altcode: 2010cosp.meet.1844M
We analyze the evolution and kinematics of the fast, globally
propagating Moreton wave of 2003 October 28 associated with the extreme
X17.2 solar flare/CME event. This Moreton wave is distinct due to its
strengths and azimuthal span of span 360. We study the wave kinematics
in different propagation directions, and compare it with the following
associated phenomena: EIT wave, coronal dimmings, fast halo CME, flare,
and type II burst. The sectoral analysis yield mean velocity values
in the range 900-1000 km/s; two sectors show wave deceleration. The
perturbation profile evolution indicates an amplitude growth followed
by amplitude weakening and broadening, which is consistent with a
disturbance first driven and then evolving into a freely propagating
wave. We find two `'radiant points" for the Moreton wave fronts on
opposite east-west edges of the source region, roughly co-spatial with
the bipolar coronal dimming. The co-spatiality of the associated radio
type II burst source and the first Moreton wave fronts indicate that
the wave was launched from an extended region. These findings indicate
that the wave is initiated by the CME expanding flanks.
---------------------------------------------------------
Title: Direction and orientation of CME/ICME events observed by STEREO
Authors: Moestl, Christian; Rollett, Tanja; Temmer, Manuela; Farrugia,
Charles; Veronig, Astrid; Galvin, Antoinette; Biernat, Helfried K.
2010cosp...38.1881M Altcode: 2010cosp.meet.1881M
The two NASA STEREO spacecraft are now approaching a quadrature
configuration with respect to the Earth. In conjunction with the rising
solar activity this represents a great opportunity to study coronal
mass ejections (CMEs) during their journey from the Sun to 1 AU. We
are in particular concerned with those events which were observed by
the STEREO/SECCHI imaging instrument in the inner heliosphere and which
were also detected in situ at 1 AU with STEREO (IMPACT/PLASTIC) or WIND
(SWE/MFI). This allows for example to check (1) if the direction of
propagation given by various direction-finding techniques is indeed
correlated with the signatures which are later observed in situ and (2)
if the orientation of the magnetic flux rope inside the ICME, which we
model using the Grad-Shafranov technique, is reflected in properties of
the CME. Also, the classic three-part structure of CMEs can be related
to the in situ data. The results are discussed regarding the possibility
to forecast ICME properties from observations closer to the Sun.
---------------------------------------------------------
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: Linking remote imagery of two coronal mass ejections to their
in situ signatures at 1 AU
Authors: Moestl, C.; Farrugia, C. J.; Temmer, M.; Miklenic, C.;
Veronig, A.; Galvin, A. B.; Leitner, M.; Biernat, H. K.
2009AGUFMSH41A1629M Altcode:
We report on how the internal structure of two coronal mass ejections
at 1 AU might be deduced from white-light images of the heliosphere
taken from a remote observation point. On June 6-7 2008 the STEREO-B
spacecraft encountered typical signatures of a magnetic flux rope inside
an interplanetary coronal mass ejection (ICME). Its axis was inclined
at 45° to the solar equatorial plane, crossing it at approximately
30° east of Earth. This direction matches well with various CME
direction-finding techniques to within 15°, and a possible westward
deflection of 10° took place between the Sun and 1 AU. Further, we use
remote images from STEREO-A to show that (1) the CME is unambiguously
connected to the ICME which swept over STEREO B and can be tracked all
the way to the 1 AU event, (2) the particular arc-like morphology of the
CME pointing to an inclined axis, and (3) the three-part structure of
the CME may be plausibly related to the in situ data with clear density
variations. The CME event on Feb 13 2009 followed by a magnetic cloud
on Feb 18 2009 is discussed from the same viewpoint, though the in-situ
signatures are more complex than for the simple event discussed above.
---------------------------------------------------------
Title: Linking Remote Imagery of a Coronal Mass Ejection to Its In
Situ Signatures at 1 AU
Authors: Möstl, C.; Farrugia, C. J.; Temmer, M.; Miklenic, C.;
Veronig, A. M.; Galvin, A. B.; Leitner, M.; Biernat, H. K.
2009ApJ...705L.180M Altcode: 2009arXiv0910.1188M
In a case study (2008 June 6-7) we report on how the internal structure
of a coronal mass ejection (CME) at 1 AU can be anticipated from
remote observations of white-light images of the heliosphere. Favorable
circumstances are the absence of fast equatorial solar wind streams and
a low CME velocity which allow us to relate the imaging and in situ
data in a straightforward way. The STEREO-B spacecraft encountered
typical signatures of a magnetic flux rope inside an interplanetary
CME (ICME) whose axis was inclined at 45° to the solar equatorial
plane. Various CME direction-finding techniques yield consistent
results to within 15°. Further, remote images from STEREO-A show that
(1) the CME is unambiguously connected to the ICME and can be tracked
all the way to 1 AU, (2) the particular arc-like morphology of the CME
points to an inclined axis, and (3) the three-part structure of the CME
may be plausibly related to the in situ data. This is a first step in
predicting both the direction of travel and the internal structure of
CMEs from complete remote observations between the Sun and 1 AU, which
is one of the main requirements for forecasting the geo-effectiveness
of CMEs.
---------------------------------------------------------
Title: STEREO Quadrature Observations of the Three-Dimensional
Structure and Driver of a Global Coronal Wave
Authors: Kienreich, I. W.; Temmer, M.; Veronig, A. M.
2009ApJ...703L.118K Altcode: 2009arXiv0908.3571K
We present the first observations of a global coronal wave ("EIT wave")
from the two STEREO satellites in quadrature. The wave's initiation
site was at the disk center in STEREO-B and precisely on the limb in
STEREO-A. These unprecedented observations from the STEREO Extreme
Ultraviolet Imaging (EUVI) instruments enable us to gain insight into
the wave's kinematics, initiation, and three-dimensional structure. The
wave propagates globally over the whole solar hemisphere visible to
STEREO-B with a constant velocity of ~263 ± 16 km s<SUP>-1</SUP>. From
the two STEREO observations, we derive a height of the wave in the
range of ~80-100 Mm. Comparison of the wave kinematics with the early
phase of the erupting coronal mass ejection (CME) structure indicates
that the wave is initiated by the CME lateral expansion, and then
propagates freely with a velocity close to the fast magnetosonic speed
in the quiet solar corona.
---------------------------------------------------------
Title: Analytic Modeling of the Moreton Wave Kinematics
Authors: Temmer, M.; Vršnak, B.; Žic, T.; Veronig, A. M.
2009ApJ...702.1343T Altcode: 2009arXiv0908.3746T
The issue whether Moreton waves are flare-ignited or coronal mass
ejection (CME)-driven, or a combination of both, is still a matter of
debate. We develop an analytical model describing the evolution of a
large-amplitude coronal wave emitted by the expansion of a circular
source surface in order to mimic the evolution of a Moreton wave. The
model results are confronted with observations of a strong Moreton
wave observed in association with the X3.8/3B flare/CME event from
2005 January 17. Using different input parameters for the expansion
of the source region, either derived from the real CME observations
(assuming that the upward moving CME drives the wave), or synthetically
generated scenarios (expanding flare region, lateral expansion of the
CME flanks), we calculate the kinematics of the associated Moreton
wave signature. Those model input parameters are determined which
fit the observed Moreton wave kinematics best. Using the measured
kinematics of the upward moving CME as the model input, we are not able
to reproduce the observed Moreton wave kinematics. The observations
of the Moreton wave can be reproduced only by applying a strong and
impulsive acceleration for the source region expansion acting in a
piston mechanism scenario. Based on these results we propose that the
expansion of the flaring region or the lateral expansion of the CME
flanks is more likely the driver of the Moreton wave than the upward
moving CME front.
---------------------------------------------------------
Title: CME Projection Effects Studied with STEREO/COR and SOHO/LASCO
Authors: Temmer, M.; Preiss, S.; Veronig, A. M.
2009SoPh..256..183T Altcode:
Based on a set of 11 CME events we study the impact of projection
effects by tracking CME leading edge features in the plane of sky
(traditional CME tracking) from combined STEREO-SECCHI and SOHO-LASCO
observations up to 20R<SUB>⊙</SUB>. By using CME observations from two
vantage points and applying triangulation techniques, the source region
location of the CME on the solar surface was determined (heliospheric
longitude and latitude) to correct for projection effects. With
this information, the directivity and "true" speed of a CME can be
estimated in a simple way. The comparison of the results obtained from
the spacecraft pairs SOHO-LASCO/STEREO-A and SOHO-LASCO/STEREO-B allows
us to study the reliability of the method. The determined CME source
region is generally coincident within ≲10°.
---------------------------------------------------------
Title: Multispacecraft recovery of a magnetic cloud and its origin
from magnetic reconnection on the Sun
Authors: Möstl, C.; Farrugia, C. J.; Miklenic, C.; Temmer, M.;
Galvin, A. B.; Luhmann, J. G.; Kilpua, E. K. J.; Leitner, M.;
Nieves-Chinchilla, T.; Veronig, A.; Biernat, H. K.
2009JGRA..114.4102M Altcode: 2009JGRA..11404102M
Multipoint spacecraft observations of a magnetic cloud on 22 May 2007
have given us the opportunity to apply a multispacecraft technique
to infer the structure of this large-scale magnetic flux rope in
the solar wind. Combining WIND and STEREO-B magnetic field and
plasma measurements, we construct a combined magnetic field map by
integrating the Grad-Shafranov equation, this being one of the very
first applications of this technique in the interplanetary context. From
this we obtain robust results on the shape of the cross section,
the orientation and magnetic fluxes of the cloud. The only slightly
“flattened” shape is discussed with respect to its heliospheric
environment and theoretical expectations. We also relate these results
to observations of the solar source region and its associated two-ribbon
flare on 19 May 2007, using Hα images from the Kanzelhöhe observatory,
SOHO/MDI magnetograms and SECCHI/EUVI 171 Å images. We find a close
correspondence between the magnetic flux reconnected in the flare and
the poloidal flux of the magnetic cloud. The axial flux of the cloud
agrees with the prediction of a recent 3-D finite sheared arcade
model to within a factor of 2, which is evidence for formation of
at least half of the magnetic flux of the ejected flux rope during
the eruption. We outline the relevance of this result to models of
coronal mass ejection initiation, and find that to explain the solar
and interplanetary observations elements from sheared arcade as well
as erupting-flux-rope models are needed.
---------------------------------------------------------
Title: Multi-spacecraft STEREO observations of magnetic clouds
Authors: Möstl, C.; Farrugia, C. J.; Miklenic, C.; Temmer, M.;
Veronig, A.; Biernat, H. K.; Kilpua, E. K. J.; Galvin, A. B.; Luhmann,
J. G.; Ogilvie, K. W.
2009EGUGA..11.4987M Altcode:
In addition to 3D imaging capabilities, the two STEREO spacecraft
also provide unprecedented in-situ observations of the local solar
wind plasma and magnetic field at 1 AU at increasing longitudinal
separation from Earth. This presents a very good opportunity to
model interplanetary coronal mass ejections with a clearly rotating
magnetic field (magnetic clouds) using more than one spacecraft
to probe their full spatial extent and flux content. This is
important not only for space weather prediction purposes but also
for understanding CME initiation processes. To this end, we employ
the Grad-Shafranov reconstruction technique suitably extended for
the use of multi-spacecraft data. We present a summary of results on
some magnetic clouds seen by STEREO and WIND where this approach was
feasible. Furthermore, we search for the solar sources of these events
and, wherever possible, also discuss comparisons with CME triangulation
techniques.
---------------------------------------------------------
Title: Cosmic ray modulation by corotating interaction regions
Authors: Čalogović, Jaša; Vršnak, Bojan; Temmer, Manuela; Veronig,
Astrid M.
2009IAUS..257..425C Altcode:
We analyzed the relationship between the ground-based modulation of
cosmic rays (CR) and corotating interaction regions (CIRs). Daily
averaged data from 8 different neutron monitor (NM) stations were
used, covering rigidities from R<SUB>c</SUB> = 0 - 12.91 GeV. The in
situ solar wind data were taken from the Advanced Composition Explorer
(ACE) database, whereas the coronal hole (CH) areas were derived from
the Solar X-Ray Imager onboard GOES-12. For the analysis we have
chosen a period in the declining phase of solar cycle 23, covering
the period 25 January-5 May 2005. During the CIR periods CR decreased
typically from 0.5% to 2%. A cross-correlation analysis showed a
distinct anti-correlation between the magnetic field and CR, with the
correlation coefficient (r) ranging from -0.31 to -0.38 (mean: -0.36)
and with the CR time delay of 2 to 3 days. Similar anti-correlations
were found for the solar wind density and velocity characterized by
the CR time lag of 4 and 1 day, respectively. The relationship was also
established between the CR modulation and the area of the CIR-related CH
with the CR time lag of 5 days after the central-meridian passage of CH.
---------------------------------------------------------
Title: EUV Wave Reflection from a Coronal Hole
Authors: Gopalswamy, N.; Yashiro, S.; Temmer, M.; Davila, J.; Thompson,
W. T.; Jones, S.; McAteer, R. T. J.; Wuelser, J. -P.; Freeland, S.;
Howard, R. A.
2009ApJ...691L.123G Altcode:
We report on the detection of EUV wave reflection from a coronal
hole, as observed by the Solar Terrestrial Relations Observatory
mission. The EUV wave was associated with a coronal mass ejection
(CME) erupting near the disk center. It was possible to measure the
kinematics of the reflected waves for the first time. The reflected
waves were generally slower than the direct wave. One of the important
implications of the wave reflection is that the EUV transients are
truly a wave phenomenon. The EUV wave reflection has implications for
CME propagation, especially during the declining phase of the solar
cycle when there are many low-latitude coronal holes.
---------------------------------------------------------
Title: Solar Differential Rotation Determined by Tracing Low and
High Brightness Temperature Regions at 8 mm
Authors: Romštajn, I.; Brajša, R.; Wöhl, H.; Benz, A. O.; Temmer,
M.; Roša, D.; Ruždjak, V.
2009CEAB...33...79R Altcode:
At the wavelength of 8 mm absorption features (Low brightness
Temperature Regions, LTRs) and emission features (High brightness
Temperature Regions, HTRs) can be traced for determination of solar
rotation. From earlier studies it is known that about two thirds of LTRs
are associated with Hα filaments. The goal of the present analysis is
to determine the heights of these solar structures and their rotational
velocities. We used the method for the simultaneous determination of
the solar synodic rotation velocity and the height of tracers. The
rotation velocities were determined by the linear least-square fit of
their central meridian distances as a function of time. The mean value
of the low brightness temperature regions' heights is about 45 600
km. The results of solar rotation determined by tracing LTRs and HTRs
are mutually compared and also compared with the results using other
tracers and methods. The method for the simultaneous determination
of the solar synodic rotation velocity and the height of the tracers
could be applied properly only on LTRs, since a wide distribution
over latitudes and central meridian distances of a large data set is
necessary, which was not available for HTRs. Observational findings that
HTRs rotate systematically faster than LTRs and the possibility that
they can be observed at and outside the solar limb are consistent with
relatively high altitudes of HTRs. It was concluded that the radiation
mechanism of HTRs is thermal bremsstrahlung, probably associated with
flaring active regions.
---------------------------------------------------------
Title: Triangulation of CME Source Region Locations on the Sun and
Dependence on Spacecraft Observation Angles
Authors: Preiss, S.; Temmer, M.; Hanslmeier, A.
2009CEAB...33..125P Altcode:
STEREO-A, STEREO-B, and LASCO/SOHO observe coronal mass ejections
(CMEs) from three different vantage points. On the basis of the radial
plane-of-sky (POS) measurements of a CME in these three projection
planes, the CME source region (SR) location was determined using the
triangulation method of Temmeretal2009. As this triangulation method
needs distance-time measurements in one POS as reference input, the
determined SR varies with the change of the reference system. In the
present study we vary the reference system, which shows the dependence
of the resulting SR location of a CME on the spacecraft observation
angles, and also reveals the limitation of the radial POS measurements.
---------------------------------------------------------
Title: Heights of solar tracers observed at 8 mm and an interpretation
of their radiation
Authors: Brajša, R.; Romštajn, I.; Wöhl, H.; Benz, A. O.; Temmer,
M.; Roša, D.
2009A&A...493..613B Altcode:
Context: At the wavelength of 8 mm, emissive features (high
brightness-temperatrue regions, HTRs) and absorptive features
(low brightness-temperature regions, LTRs) can be traced for the
determining the solar rotation. From earlier studies it is known
that about two thirds of LTRs are associated with Hα filaments. <BR
/>Aims: Thermal bremsstrahlung and gyromagnetic (cyclotron) radiation
mechanism can be important for explaining the observed phenomena,
so we determine the heights of solar structures and interpret their
radiation mechanism(s). <BR />Methods: We use the method of simultaneous
determination of the solar synodic rotation velocity and the height
of tracers. The rotation velocities were determined by the linear
least-square fit of their central meridian distance as a function of
time. We used a procedure for calculating the brightness temperature for
a given wavelength and model atmosphere, which integrates the radiative
transfer equation for the thermal bremsstrahlung. <BR />Results:
The mean value of the low brightness-temperature regions' heights
is about 45 600 km. This height was used as input for constructing
prominence and coronal condensation models, which, when assuming thermal
bremsstrahlung as the radiation mechanism, yield a decrease in the
brightness temperature of 2-14%, in agreement with observations. If the
same radiation mechanism is considered, the models of the solar corona
above active regions give an increase in the brightness temperature of
5-19%, also in agreement with observations. In this case an indirect
indication (from the rotational analysis) that the HTRs are located
higher in the solar atmosphere than the LTRs was taken into account. <BR
/>Conclusions: The method for simultaneously determining the solar
synodic rotation velocity and the height of tracers could have only
been properly applied on LTRs, since a homogeneous distribution over
latitudes and central meridian distances of a large enough data set is
necessary. Thermal bremsstrahlung can explain both the LTR (prominences
and coronal condensations) and HTR (ordinary active regions) phenomena
observed at 8 mm. At this wavelength, thermal gyromagnetic emission
is almost surely excluded as a possible radiation mechanism.
---------------------------------------------------------
Title: Cylindrical and Spherical Pistons as Drivers of MHD Shocks
Authors: Žic, Tomislav; Vršnak, Bojan; Temmer, Manuela; Jacobs, Carla
2008SoPh..253..237Z Altcode: 2008SoPh..tmp..153Z
We consider an expanding three-dimensional (3-D) piston as a driver
of an MHD shock wave. It is assumed that the source-region surface
accelerates over a certain time interval to achieve a particular maximum
velocity. Such an expansion creates a large-amplitude wave in the
ambient plasma. Owing to the nonlinear evolution of the wavefront, its
profile steepens and after a certain time and distance a discontinuity
forms, marking the onset of the shock formation. We investigate
how the formation time and distance depend on the acceleration phase
duration, the maximum expansion velocity (defining also acceleration),
the Alfvén velocity (defining also Mach number), and the initial size
of the piston. The model differs from the 1-D case, since in the 3-D
evolution, a decrease of the wave amplitude with distance must be taken
into account. We present basic results, focusing on the timing of the
shock formation in the low- and high-plasma-beta environment. We find
that the shock-formation time and the shock-formation distance are
(1) approximately proportional to the acceleration phase duration;
(2) shorter for a higher expansion velocity; (3) larger in a higher
Alfvén speed environment; (4) only weakly dependent on the initial
source size; (5) shorter for a stronger acceleration; and (6) shorter
for a larger Alfvén Mach number of the source surface expansion. To
create a shock causing a high-frequency type II burst and the Moreton
wave, the source region expansion should, according to our results,
achieve a velocity on the order of 1000 km s<SUP>−1</SUP> within a
few minutes, in a low Alfvén velocity environment.
---------------------------------------------------------
Title: Multi-spacecraft Recovery of a Magnetic Cloud and its Origin
From Magnetic Reconnection on the Sun
Authors: Möstl, C.; Farrugia, C. J.; Miklenic, C.; Temmer, M.; Galvin,
A. B.; Luhmann, J. G.; Biernat, H. K.; Huttunen, K. E.; Leitner, M.;
Nieves-Chinchilla, T.; Veronig, A.
2008AGUFMSH23B1634M Altcode:
Multi-point spacecraft observations of a magnetic cloud on May 22, 2007
has given us the opportunity to apply a multi-spacecraft technique
to infer the structure of this large-scale magnetic flux rope in
the solar wind. Combining WIND and STEREO-B magnetic field and plasma
measurements, since these spacecraft entered the ejecta, we construct a
combined magnetic field map by integrating the Grad-Shafranov equation,
this being one of the very first applications of this technique in
the interplanetary context. From this we obtain robust results on the
shape of the cross-section, the orientation and magnetic fluxes of the
cloud. The only slightly "flattened" shape is discussed with respect
to its heliospheric environment and theoretical expectations. We also
relate these results to observations of the Solar source region and
its associated two- ribbon flare on May 19, 2007 using Hα images from
the Kanzelhöhe observatory, SOHO/MDI magnetograms and SECCHI/EUVI
171~Å~images. We find a close correspondence between the magnetic
flux reconnected in the flare and the poloidal flux of the magnetic
cloud. The axial flux of the cloud agrees with the prediction of a
recent 3D finite sheared arcade model to within a factor of 2, which
is evidence for formation of at least half of the magnetic flux of the
ejected flux rope during the eruption. We outline the relevance of
this result to models of coronal mass ejection initiation, and find
that to explain the solar and interplanetary observations elements
from sheared-arcade as well as erupting-flux-rope models are needed.
---------------------------------------------------------
Title: A Flare-Generated Shock during a Coronal Mass Ejection on 24
December 1996
Authors: Magdalenić, J.; Vršnak, B.; Pohjolainen, S.; Temmer, M.;
Aurass, H.; Lehtinen, N. J.
2008SoPh..253..305M Altcode: 2008SoPh..tmp..120M
We present a multiwavelength study of the large-scale coronal
disturbances associated with the CME - flare event recorded on 24
December 1996. The kinematics of the shock wave signature, the type
II radio burst, is analyzed and compared with the flare evolution
and the CME kinematics. We employ radio dynamic spectra, position
of the Nançay Radioheliograph sources, and LASCO-C1 observations,
providing detailed study of this limb event. The obtained velocity of
the shock wave is significantly higher than the contemporaneous CME
velocity (1000 and 235 km s<SUP>−1</SUP>, respectively). Moreover,
since the main acceleration phase of the CME took place 10 - 20 min
after the shock wave was launched, we conclude that the shock wave
on 24 December 1996 was probably not driven by the CME. However,
the shock wave was closely associated with the flare impulsive phase,
indicating that it was ignited by the energy release in the flare.
---------------------------------------------------------
Title: Investigation of geomagnetic and solar activity over time
span 1960-2001
Authors: Verbanac, G.; Vrsnak, B.; Korte, M.; Mandea, M.; Temmer, M.
2008AGUFMSH13A1502V Altcode:
The solar-terrestrial relationship has been widely studied by means
of space weather indices and various solar wind parameters. In this
study we perform such an investigation over four decades (1960--2001)
on the global scale, and for the first time on the regional scale as
well. The variations regarded as the remaining external field signal
(thereafter RES) and present in the European observatory annual means
of the Northward, X, magnetic component is used as an indicator of
the regional geomagnetic activity and are investigated regarding
different processes occurring on the Sun. In order to understand how
various geomagnetic activity indices respond to the interplanetary
disturbances during different periods of the solar cycle, the annual
means of the solar activity index, F10.7, and geomagnetic Ap and Dst
indices, are studied. The indices are inherently complex since they
include contributions from different solar phenomena. By studying
the cross-correlations we aim to distinguish between different
generation mechanisms. The relationships between the solar parameter
F10.7 and RES, Dst, Ap, characterized by high cross-correlation
coefficients, suggest the possibility to evaluate the behaviour of
these geomagnetic parameters on short timescale. We found finite
time lags among the investigated parameters. Our study suggests a
one year delay of both RES and Dst after F10.7. The Ap is clearly
delayed for about two years with respect to F10.7 and about one year
with respect to Dst and RES. This indicate that the Ap responds to
the solar activity in a different manner than Dst and RES, which are
dominated by the coronal mass ejections activity. On the other hand,
it seems that Ap is more sensitive to the high--speed streams (HSS)
and Alfvenic waves present in HSS. The existence of time lags gives
us the possibility to forecast different parameters. Importantly, the
proposed forecasting procedure offers the possibility to reconstruct
the F10.7 from the inferred geomagnetic activity for the epochs prior
to solar activity monitoring. This study contributes to understanding
some physical processes on the Sun that cause the perturbations in the
near-Earth interplanetary space and consequently in the Earth's magnetic
field. Moreover such investigations may provide a better insight into
the time evolution of the open and closed solar magnetic field, and into
long term changes in the solar activity with related physical processes.
---------------------------------------------------------
Title: Global thermospheric density variations caused by high-speed
solar wind streams during the declining phase of solar cycle 23
Authors: Lei, Jiuhou; Thayer, Jeffrey P.; Forbes, Jeffrey M.; Sutton,
Eric K.; Nerem, R. Steven; Temmer, Manuela; Veronig, Astrid M.
2008JGRA..11311303L Altcode:
Thermosphere densities at 400 km altitude from accelerometer
measurements on the CHAMP satellite are used to investigate oscillations
at periods of less than 13 days during the declining phase of solar
cycle 23 (2002-2007). The periodic oscillations around 7 and 9 days in
neutral density tend to occur during the latter part of the declining
solar cycle when periodically recurrent fast streams in the solar
wind modulate the level of geomagnetic activity in the geospace
environment. It is interesting that the periodic oscillations in
neutral density are felt globally and are proportional to the periodic
Kp perturbations at the same frequency. Moreover, the periods of 7
and 9 days apparently reflect subharmonics of the 27-day rotation
and may be related to the longitudinal distribution of coronal holes;
however the comparison of the temporal evolution of the periodicities
between the coronal holes area and solar wind in 2005 indicates that
their relationships are rather complex.
---------------------------------------------------------
Title: Two-spacecraft reconstruction of a magnetic cloud and
comparison to its solar source
Authors: Möstl, C.; Miklenic, C.; Farrugia, C. J.; Temmer, M.;
Veronig, A.; Galvin, A. B.; Vršnak, B.; Biernat, H. K.
2008AnGeo..26.3139M Altcode:
This paper compares properties of the source region with those inferred
from satellite observations near Earth of the magnetic cloud which
reached 1 AU on 20 November 2003. We use observations from space
missions SOHO and TRACE together with ground-based data to study
the magnetic structure of the active region NOAA 10501 containing
a highly curved filament, and determine the reconnection rates and
fluxes in an M4 flare on 18 November 2003 which is associated with
a fast halo CME. This event has been linked before to the magnetic
cloud on 20 November 2003. We model the near-Earth observations with
the Grad-Shafranov reconstruction technique using a novel approach in
which we optimize the results with two-spacecraft measurements of the
solar wind plasma and magnetic field made by ACE and WIND. The two
probes were separated by hundreds of Earth radii. They pass through
the axis of the cloud which is inclined -50 degree to the ecliptic. The
magnetic cloud orientation at 1 AU is consistent with an encounter with
the heliospheric current sheet. We estimate that 50% of its poloidal
flux has been lost through reconnection in interplanetary space. By
comparing the flare ribbon flux with the original cloud fluxes we infer
a flux rope formation during the eruption, though uncertainties are
still significant. The multi-spacecraft Grad-Shafranov method opens
new vistas in probing of the spatial structure of magnetic clouds in
STEREO-WIND/ACE coordinated studies.
---------------------------------------------------------
Title: Large-scale Coronal Waves Observed with EUVI/STEREO
Authors: Veronig, A.; Temmer, M.; Vrsnak, B.
2008ESPM...12.2.97V Altcode:
We report first observations and analysis of flare/CME associated
large-scale coronal waves (so-called "EIT waves") observed with
high time cadence by the EUVI instruments onboard the recent STEREO
mission. The EIT instrument onboard SOHO for the first time directly
imaged global disturbances in the solar corona, but the observations
are severely hampered by the low cadence of EIT (12-15 min). Thus,
the nature and origin of these large-scale disturbances are still
not sufficiently constraint by observations, and it is an intense
matter of debate whether EIT waves: a) are the coronal counterparts of
Moreton waves observed in the chromosphere; b) are caused by the flare
explosive energy release or by the erupting CME; c) are waves at all or
rather propagating disturbances related to magnetic field line opening
and restructuring associated with the CME lift-off. The high cadence
full-disk coronal imaging by the EUVI instruments on the twin STEREO
spacecraft provide us with the unprecedented opportunity to study the
dynamics and origin of flare/CME associated coronal waves. We present
first studies of global coronal waves observed with EUVI finding wave
deceleration, indicative of an MHD blast wave (Veronig et al. 2008,
ApJ Lett., in press).
---------------------------------------------------------
Title: Relation between CME SchmiederAcceleration Profile and Flare
Energy Release derived from Combined STEREO and RHESSI Observations
Authors: Temmer, M.; Veronig, A. M.; Vrsnak, B.
2008ESPM...12.2.96T Altcode:
In the standard flare/CME picture magnetic reconnection occurs in
a current sheet formed behind the CME, which may provide a feedback
relationship between both phenomena. To study the relationship of the
large-scale CME acceleration and the energy release in the associated
flare we analyze three well observed events. The observations cover
the early (low corona) evolution of the CMEs with the EUVI instruments
aboard the twin STEREO spacecraft and the RHESSI hard X-ray emission
of the associated flare. Since the flare hard X-rays are due to fast
electrons, they provide the most direct indicator of the evolution of
the flare energy release in the flare. The results are compared to case
studies for halo-CMEs where a close synchronization between the CME
acceleration and the flare energy release was found (Temmer et al.,
ApJ, 2008, 673, L95).
---------------------------------------------------------
Title: High-Cadence Observations of a Global Coronal Wave by
STEREO EUVI
Authors: Veronig, Astrid M.; Temmer, Manuela; Vršnak, Bojan
2008ApJ...681L.113V Altcode: 2008arXiv0806.0710V
We report a large-scale coronal wave (so-called EIT wave) observed
with high cadence by EUVI on board STEREO in association with the GOES
B9.5 flare and double CME event on 2007 May 19. The EUVI instruments
provide us with the unprecedented opportunity to study the dynamics of
flare/CME associated coronal waves. The coronal wave under study reveals
deceleration, indicative of a freely propagating MHD wave. Complementary
analysis of the associated flare and erupting filament/CME hint at wave
initiation by the CME expanding flanks, which drive the wave only over
a limited distance. The associated flare is very weak and occurs too
late to account for the wave initiation.
---------------------------------------------------------
Title: Analysis of a Moreton Wave Associated with the X17.2/4B
Flare/CME of 28-10-2003
Authors: Muhr, M.; Temmer, M.; Veronig, A.; Vršnak, B.; Hanslmeier, A.
2008CEAB...32...79M Altcode:
The fast Moreton wave of 28-Oct-2003 associated with the extreme X17.2
solar flare/CME event is studied. It can be followed in four sectors,
spanning almost over 360° on the visible solar disc. The mean wave
velocity lies in the range of v∼900-1000 km s^{-1}. We find two
wave ignition centres on opposite edges of the source region, which
may indicate that the wave is driven by the CME expanding flanks.
---------------------------------------------------------
Title: Acceleration in Fast Halo CMEs and Synchronized Flare HXR
Bursts
Authors: Temmer, M.; Veronig, A. M.; Vršnak, B.; Rybák, J.; Gömöry,
P.; Stoiser, S.; Maričić, D.
2008ApJ...673L..95T Altcode:
We study two well-observed, fast halo CMEs, covering the full CME
kinematics including the initiation and impulsive acceleration phase,
and their associated flares. We find a close synchronization between the
CME acceleration profile and the flare energy release as indicated by
the RHESSI hard X-ray flux onsets, as well as peaks occur simultaneously
within 5 minutes. These findings indicate a close physical connection
between both phenomena and are interpreted in terms of a feedback
relationship between the CME dynamics and the reconnection process in
the current sheet beneath the CME.
---------------------------------------------------------
Title: Large-scale coronal waves observed with STEREO/EUVI
Authors: Veronig, Astrid; Temmer, Manuela; Vrsnak, Bojan
2008cosp...37.3328V Altcode: 2008cosp.meet.3328V
The EUVI instruments onboard the twin STEREO spacecraft provide
high-cadence full-disk imaging of the solar atmosphere with four
different filters at EUV wavelengths. These observations are highly
suitable to study the kinematics and dynamics of flare/CME associated
coronal waves, so-called "EIT waves". We present a detailed analysis
of one coronal wave captured by the EUVI instruments, with particular
emphasis on the wave dynamics and its connection to the associated
flare (RHESSI hard X-rays) and CME (STEREO COR1) in terms of blast
wave versus driven wave scenario.
---------------------------------------------------------
Title: Synchronization between the CME acceleration and the energy
release in the associated flare
Authors: Temmer, Manuela; Veronig, Astrid; Vrsnak, Bojan
2008cosp...37.3167T Altcode: 2008cosp.meet.3167T
In the standard flare/CME picture magnetic reconnection occurs in a
current sheet formed behind the CME, which is indicative of a feedback
relationship between both phenomena. We analyze two X-class flare/CME
events which were well covered by RHESSI hard X-ray observations,
and the early evolution of the CMEs could be observed in TRACE and
GOES/SXI images. Since the flare hard X-rays are due to fast electrons,
they provide the most direct indicator of the evolution of the energy
release in the flare. This data set enables us to study in detail
the relationship of the large-scale CME acceleration and the energy
release in the associated flare.
---------------------------------------------------------
Title: On the relation between in situ observations of a magnetic
cloud and its solar source
Authors: Christiane, Miklenic; Möstl, Christian; Temmer, Manuela;
Veronig, Astrid; Farrugia, Charles; Biernat, Helfried K.
2008cosp...37..543C Altcode: 2008cosp.meet..543C
During flare/CME events, fast plasma clouds and shocks may be generated,
which propagate through interplanetary space. Interplanetary coronal
mass ejections, which contain a magnetic cloud, can induce, if
Earth-directed, geomagnetic storms, which can cause deleterious effects
on space-borne and ground-based installations. Since our dependency
on space-borne technical equipment is increasing, the importance of
reliable space weather forecasts is indisputable. To achieve better
space weather forecasts, it is essential to understand the relation
between solar source observations and in situ observations of the
magnetic cloud. For the CME/flare event on July 6, 2006, we present
a detailed analysis of the magnetic field configuration of the solar
source and the reconnection flux of the flare, which is related to the
associated magnetic cloud properties observed at the Earth. The event is
well covered by multi-wavelength observations from SoHO, TRACE, RHESSI,
as well as ground-based Hα observations. The magnetic field geometry
of the magnetic cloud at 1 AU is modeled with the Grad-Shafranov
reconstruction technique, applying observations from two satellites,
namely WIND and ACE.
---------------------------------------------------------
Title: Projection effects in coronal mass ejections studied with
STEREO and SoHO
Authors: Temmer, Manuela; Preiss, Stefanie; Veronig, Astrid; Vrsnak,
Bojan
2008cosp...37.3168T Altcode: 2008cosp.meet.3168T
The STEREO mission consists of two identical satellites, positioned
ahead (A) and behind (B) the Earth, which observe the Sun from viewing
angles different from that of LASCO aboard SoHO (positioned at L1). The
kinematics (speed) and width of a coronal mass ejection (CME) is derived
by measuring distinct CME features observed in projection against the
plane of sky. As STEREO-A, STEREO-B, and LASCO/SoHO, observe a CME
from three different viewing angles, the resulting CME kinematics and
widths differ. By combining the observations from the three satellites
we study for several well observed CMEs the importance of projection
effects for the CME kinematics and expansion.
---------------------------------------------------------
Title: Two-spacecraft Reconstruction of a Magnetic Cloud and
Comparison to its Solar Source
Authors: Moestl, C.; Miklenic, C.; Farrugia, C.; Temmer, M.; Veronig,
A.; Galvin, A.; Biernat, H.
2007AGUFMSH32A0781M Altcode:
Relating observations of coronal mass ejections (CMEs) and their
interplanetary counterpart (ICMEs) is a centerpoint of Sun-Earth
connection studies and our ability to forecast space weather. Here we
focus on the ICME containing a magnetic cloud which reached Earth on
November 20, 2003 and gave rise to the strongest storm of solar cycle
23, with a minimum Dst of -472 nT. Its strong geoeffective impact
came about two weeks after the massive eruptions known as "Halloween"
events resulted in comparable geo-effects. The aims of this study
are threefold. We first apply an advanced methodology to analyze with
diverse observations the event on the solar disk, which occurred on
Nov 18, 2003, and was associated with an M4 flare and a halo CME. We
then employ a Grad-Shafranov reconstruction technique to model the
magnetic field geometry at 1 AU. To this end, we use measurements
acquired by spacecraft WIND and ACE, ~400 RE apart. We show how these
twin-spacecraft observations allow us to optimize the reconstructed
map. Finally, we relate the solar to the interplanetary observations,
paying special attention to the orientations and the magnetic fluxes
involved at the two locales. By comparing the flare with the original
cloud fluxes we infer a possible in-situ flux rope formation during
the eruption, though uncertainties are still significant. The error
margins in the comparisons are also carefully assessed.
---------------------------------------------------------
Title: An Interpretation of the Coronal Holes' Visibility in the
Millimeter Wavelength Range
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
Šaina, B.; Wöhl, H.
2007SoPh..245..167B Altcode:
Various observations indicate that coronal holes generally appear as low
brightness temperature regions (LTRs) in the centimeter and millimeter
wavelength ranges. However, within their borders local enhancements of
radiation, that is, high brightness temperature regions (HTRs), often
occur. The theory behind the described behavior is not fully understood
and therefore we analyze full-disk solar images obtained at a wavelength
of 8 mm at Metsähovi Radio Observatory and compare them with data
simultaneously taken in other wavelength ranges. The observational
finding that the average brightness temperature of coronal holes is
not much different from the quiet-Sun level (with localized deviations
toward higher and lower intensities on the order of a few percent)
is compared with theoretical models of the thermal bremsstrahlung
radiation originating in the solar chromosphere, transition region,
and corona. Special attention is devoted to the interpretation of the
localized enhancements of radiation observed inside coronal holes at
millimeter wavelengths. The main conclusion is that the most important
contribution to the brightness temperature comes from an increased
density in the transition region and low corona (i.e., at the heights
where the temperature is below 10<SUP>6</SUP> K). This can explain
both the LTRs and HTRs associated with coronal holes.
---------------------------------------------------------
Title: Periodic Appearance of Coronal Holes and the Related Variation
of Solar Wind Parameters
Authors: Temmer, Manuela; Vršnak, Bojan; Veronig, Astrid M.
2007SoPh..241..371T Altcode:
We compared the variability of coronal hole (CH) areas (determined
from daily GOES/SXI images) with solar wind (daily ACE data) and
geomagnetic parameters for the time span 25 January 2005 until 11
September 2005 (late declining phase of solar cycle 23). Applying
wavelet spectral analysis, a clear 9-day period is found in the
CH time series. The GOES/SXI image sequence suggests that this
periodic variation is caused by a mutual triangular distribution of
CHs ∼120° apart in longitude. From solar wind parameters a 9-day
periodicity was obtained as well, simultaneously with the 9-day period
in the CH area time series. These findings provide strong evidence
that the 9-day period in solar wind parameters, showing up as higher
harmonic of the solar rotation frequency, is caused by the "periodic"
longitudinal distribution of CHs on the Sun recurring for several
solar rotations. The shape of the wavelet spectrum from the Dst index
matches only weakly with that from the CH areas and is more similar to
the wavelet spectrum of the solar wind magnetic field magnitude. The
distinct 9-day period does not show up in sunspot group areas which
gives further evidence that the solar wind modulation is strongly
related to CH areas but not to active region complexes. The wavelet
power spectra for the whole ACE data range (∼1998 - 2006) suggest that
the 9-day period is not a singular phenomenon occurring only during
a specific time range close to solar minimum but is occasionally also
present during the maximum and decay phase of solar cycle 23. The main
periods correspond to the solar rotation (27<SUP>d</SUP>) as well as
to the second (13.5<SUP>d</SUP>) and third (9<SUP>d</SUP>) harmonic.
---------------------------------------------------------
Title: Acceleration Phase of Coronal Mass Ejections: I. Temporal
and Spatial Scales
Authors: Vršnak, Bojan; Maričić, Darije; Stanger, Andrew L.;
Veronig, Astrid M.; Temmer, Manuela; Roša, Dragan
2007SoPh..241...85V Altcode:
We study kinematics of 22 coronal mass ejections (CMEs) whose
motion was traced from the gradual pre-acceleration phase up to
the post-acceleration stage. The peak accelerations in the studied
sample range from 40, up to 7000 m s<SUP>−2</SUP>, and are inversely
proportional to the acceleration phase duration and the height range
involved. Accelerations and velocities are, on average, larger in CMEs
launched from a compact source region. The acceleration phase duration
is proportional to the source region dimensions; i.e., compact CMEs
are accelerated more impulsively. Such behavior is interpreted as
a consequence of stronger Lorentz force and shorter Alfvén time
scales involved in compact CMEs (with stronger magnetic field and
larger Alfvén speed being involved at lower heights). CMEs with
larger accelerations and velocities are on average wider, whereas the
widths are not related to the source region dimensions. Such behavior is
explained in terms of the field pile-up ahead of the erupting structure,
which is more effective in the case of a strongly accelerated structure.
---------------------------------------------------------
Title: Acceleration Phase of Coronal Mass Ejections:
II. Synchronization of the Energy Release in the Associated Flare
Authors: Maričić, Darije; Vršnak, Bojan; Stanger, Andrew L.;
Veronig, Astrid M.; Temmer, Manuela; Roša, Dragan
2007SoPh..241...99M Altcode:
We analyze the relationship between the acceleration of coronal mass
ejections (CMEs) and the energy release in associated flares, employing
a sample of 22 events in which the CME kinematics were measured from
the pre-eruption stage up to the post-acceleration phase. The data
show a distinct correlation between the duration of the acceleration
phase and the duration of the associated soft X-ray (SXR) burst rise,
whereas the CME peak acceleration and velocity are related to the
SXR peak flux. In the majority of events the acceleration started
earlier than the SXR burst, and it is usually prolonged after the
SXR burst maximum. In about one half of the events the acceleration
phase is very closely synchronized with the fastest growth of the SXR
burst. An additional one quarter of the events may be still considered
as relatively well-synchronized, whereas in the remaining quarter of the
events there is a considerable mismatch. The results are interpreted
in terms of the feedback relationship between the CME dynamics and
the reconnection process in the wake of the CME.
---------------------------------------------------------
Title: Coronal Holes and Solar Wind High-Speed Streams:
II. Forecasting the Geomagnetic Effects
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid M.
2007SoPh..240..331V Altcode:
We present a simple method of forecasting the geomagnetic storms caused
by high-speed streams (HSSs) in the solar wind. The method is based
on the empirical correlation between the coronal hole area/position
and the value of the Dst index, which is established in a period of
low interplanetary coronal mass ejection (ICME) activity. On average,
the highest geomagnetic activity, i.e., the minimum in Dst, occurs
four days after a low-latitude coronal hole (CH) crosses the central
meridian. The amplitude of the Dst dip is correlated with the CH area
and depends on the magnetic polarity of the CH due to the Russell -
McPherron effect. The Dst variation may be predicted by employing the
expression Dst(t)=(−65±25×cos λ)[A(t<SUP>*</SUP>)]<SUP>0.5</SUP>,
where A(t<SUP>*</SUP>) is the fractional CH area measured in the
central-meridian slice [−10°,10°] of the solar disc, λ is the
ecliptic longitude of the Earth, ± stands for positive/negative CH
polarity, and t−t<SUP>*</SUP>=4 days. In periods of low ICME activity,
the proposed expression provides forecasting of the amplitude of the
HSS-associated Dst dip to an accuracy of ≈30%. However, the time of
occurrence of the Dst minimum cannot be predicted to better than ±2
days, and consequently, the overall mean relative difference between
the observed and calculated daily values of Dst ranges around 50%.
---------------------------------------------------------
Title: Coronal Holes and Solar Wind High-Speed Streams: I. Forecasting
the Solar Wind Parameters
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid M.
2007SoPh..240..315V Altcode:
We analyze the relationship between the coronal hole (CH) area/position
and physical characteristics of the associated corotating high-speed
stream (HSS) in the solar wind at 1 AU. For the analysis we utilize the
data in the period DOY 25 - 125 of 2005, characterized by a very low
coronal mass ejection (CME) activity. Distinct correlations between
the daily averaged CH parameters and the solar wind characteristics
are found, which allows us to forecast the solar wind velocity v,
proton temperature T, proton density n, and magnetic field strength B,
several days in advance in periods of low CME activity. The forecast
is based on monitoring fractional areas A, covered by CHs in the
meridional slices embracing the central meridian distance ranges
[−40°,−20°], [−10°,10°], and [20°,40°]. On average, the
peaks in the daily values of n, B, T, and v appear delayed by 1, 2,
3, and 4 days, respectively, after the area A attains its maximum
in the central-meridian slice. The peak values of the solar wind
parameters are correlated to the peak values of A, which provides
also forecasting of the peak values of n, B, T, and v. The most
accurate prediction can be obtained for the solar wind velocity, for
which the average relative difference between the calculated and the
observed peak values amounts to \overline{\vertδ\vert}≈10 %. The
forecast reliability is somewhat lower in the case of T, B, and n (
\overline{\vertδ\vert}≈20 , 30, and 40%, respectively). The space
weather implications are discussed, including the perspectives for
advancing the real-time calculation of the Sun - Earth transit times
of coronal mass ejections and interplanetary shocks, by including more
realistic real-time estimates of the solar wind characteristics.
---------------------------------------------------------
Title: Analysis of the Flare Wave Associated with the 3B/X3.8 Flare
of January 17, 2005
Authors: Thalmann, J. K.; Veronig, A. M.; Temmer, M.; Vršnak, B.;
Hanslmeier, A.
2007CEAB...31..187T Altcode:
The flare wave associated with the 3B/X3.8 flare and coronal mass
ejection (CME) of January 17, 2005 are studied using imaging data
in the Hα and EUV spectral channels. Due to the high-cadence Hα
observations from Kanzelhöhe Solar Observatory (KSO), a distinct
Moreton wave can be identified in ∼40 Hα frames over a period
of ∼7 minutes. The associated coronal EIT wave is identifiable in
only one EUV frame and appears close to the simultaneously observed
Moreton wave front, indicating that they are closely associated
phenomena. Beside the morphology of the wave across the solar disc
(covering an angular extend of ∼130°), the evolution in different
directions is studied to analyse the influence of a coronal hole (CH)
on the wave propagation. The Moreton wave shows a decelerating character
which can be interpreted in terms of a freely propagating fast-mode MHD
shock. The parts of the wave front moving towards the CH show a lower
initial and mean speed, and a greater amount of deceleration than the
segments moving into the undisturbed direction. This is interpreted
as the tendency of high Alfvén velocity regions to influence the
propagation of wave packets.
---------------------------------------------------------
Title: On the Visibility of Coronal Holes in Microwaves
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
Šaina, B.; Wöhl, H.; Ruždjak, V.
2007CEAB...31..219B Altcode:
Previous observations indicate that coronal holes generally appear as
low brightness temperature regions in microwaves. However, within their
borders local enhancements of radiation often occur. This is confirmed
by comparing a full-disc solar image obtained at 37 GHz on 27 May 1993
with full-disc solar images obtained at various wavelengths. Microwave
brightness temperatures of three coronal holes are determined and
interpreted.
---------------------------------------------------------
Title: Spatial Restriction to HXR Footpoint Locations by Reconnection
Site Geometries
Authors: Temmer, M.; Vršnak, B.; Veronig, A.; Miklenic, M.
2007CEAB...31...49T Altcode: 2007astro.ph..1203T
It is assumed that HXR sources map to the primary energy release site in
flares where particle acceleration occurs. Strong HXR sources are mostly
observed at confined regions along the reconnecting magnetic arcade. We
make a general approach on how the geometry of the reconnecting current
sheet (CS) may influence the strength and localization of observed HXR
sources. For this we use results from an analysis on the 3B/X3.8 flare
on January 17, 2005 (Temmer et al., 2007), as well as measurements from
the associated CME. Due to the close match of the CME acceleration
profile and the flare HXR flux, we suppose that the CME might play a
certain role in modifying the geometry of the CS (“symmetric” versus
“asymmetric” vertically stretched CS). This could be the driver for
“guiding” the accelerated particles to confined areas along the
flaring arcade and might explain the spatially limited occurrence of
strong HXR sources in comparison to elongated ribbons as seen in Hα
and UV.
---------------------------------------------------------
Title: Energy Release Rates along Hα Flare Ribbons and the Location
of Hard X-Ray Sources
Authors: Temmer, M.; Veronig, A. M.; Vršnak, B.; Miklenic, C.
2007ApJ...654..665T Altcode:
Local reconnection and energy release rates for an X3.8 flare that
occurred on 2005 January 17 are derived. In particular, we distinguish
between Hα flare ribbon segments that were accompanied by RHESSI
hard X-ray (HXR) footpoints and those without HXRs. We find that the
reconnection and energy release rates are not uniform along the flare
ribbons but much larger at the locations where the HXR footpoints are
observed. The difference is about 2 orders of magnitude in the case of
the energy release rates and 1 order of magnitude for the reconnection
rates (with peak values up to 8 kV m<SUP>-1</SUP>). These differences
are enough to explain the different flare morphologies typically
observed in HXRs (compact footpoints) and Hα/UV (extended ribbons)
by the limited dynamic range of present HXR instruments. Our results
are consistent with a scenario in which the electrons are accelerated
primarily along a certain subsystem of magnetic loops as outlined by
the HXR footpoints, and only a minor fraction (for the 2005 January
17 flare estimated to be about 1/15) go into the large flare arcade
outlined by the Hα ribbons and EUV postflare loops.
---------------------------------------------------------
Title: Interaction of a Moreton/EIT Wave and a Coronal Hole
Authors: Veronig, Astrid M.; Temmer, Manuela; Vršnak, Bojan; Thalmann,
Julia K.
2006ApJ...647.1466V Altcode: 2006astro.ph..4613V
We report high-cadence Hα observations of a distinct Moreton wave
observed at Kanzelhöhe Solar Observatory associated with the 3B/X3.8
flare and coronal mass ejection (CME) event of 2005 January 17. The
Moreton wave can be identified in about 40 Hα frames over a period of
7 minutes. The EIT wave is observed in only one frame, but the derived
propagation distance is close to that of the simultaneously measured
Moreton wave fronts, indicating that they are closely associated
phenomena. The large angular extent of the Moreton wave allows us to
study the wave kinematics in different propagation directions with
respect to the location of a polar coronal hole (CH). In particular, we
find that the wave segment whose propagation direction is perpendicular
to the CH boundary (“frontal encounter”) is stopped by the CH, which
is in accordance with observations reported from EIT waves. However,
we also find that at a tongue-shaped edge of the coronal hole, where
the front orientation is perpendicular to the CH boundary (the wave
“slides along” the boundary), the wave signatures can be found up
to 100 Mm inside the CH. These findings are briefly discussed in the
frame of recent modeling results.
---------------------------------------------------------
Title: Shrinking and Cooling of Flare Loops in a Two-Ribbon Flare
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid; Karlický,
Marian; Lin, Jun
2006SoPh..234..273V Altcode:
We analyze the evolution of the flare/postflare-loop system in the
two-ribbon flare of November 3, 2003, utilizing multi-wavelength
observations that cover the temperature range from several tens of
MK down to 10<SUP>4</SUP> K. A non-uniform growth of the loop system
enables us to identify analogous patterns in the height-time, h(t),
curves measured at different temperatures. The "knees," "plateaus,"
and "bends" in a higher-temperature curve appear after a certain time
delay at lower heights in a lower-temperature curve. We interpret such
a shifted replication as a track of a given set of loops (reconnected
field lines) while shrinking and cooling after being released from the
reconnection site. Measurements of the height/time shifts between h(t)
curves of different temperatures provide a simultaneous estimate of
the shrinkage speed and cooling rate in a given temperature domain,
for a period of almost ten hours after the flare impulsive phase. From
the analysis we find the following: (a) Loop shrinkage is faster at
higher temperatures - in the first hour of the loop-system growth,
the shrinkage velocity at 5 MK is 20 - 30 km s<SUP>−1</SUP>, whereas
at 1 MK it amounts to 5 km s<SUP>−1</SUP>; (b) Shrinking becomes
slower as the flare decays - ten hours after the impulsive phase,
the shrinkage velocity at 5 MK becomes 5 km s<SUP>−1</SUP>; (c) The
cooling rate decreases as the flare decays - in the 5 MK range it is
1 MK min<SUP>−1</SUP> in the first hour of the loop-system growth,
whereas ten hours later it decreases to 0.2 MK min<SUP>−1</SUP>;
(d) During the initial phase of the loop-system growth, the cooling
rate is larger at higher temperatures, whereas in the late phases
the cooling rate apparently does not depend on the temperature; (e)
A more detailed analysis of shrinking/cooling around one hour after
the impulsive phase reveals a deceleration of the loop shrinkage,
amounting to ā ≈ 10 m s<SUP>−2</SUP> in the T < 5 MK range;
(f) In the same interval, conductive cooling dominates down to T ≈
3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few
hours after the impulsive phase, radiation becomes dominant across the
whole T < 5 MK range. These findings are compared with results of
previous studies and discussed in the framework of relevant models.
---------------------------------------------------------
Title: Multi-wavelength study of coronal waves associated with the
CME-flare event of 3 November 2003
Authors: Vršnak, B.; Warmuth, A.; Temmer, M.; Veronig, A.;
Magdalenić, J.; Hillaris, A.; Karlický, M.
2006A&A...448..739V Altcode:
The large flare/CME event that occurred close to the west solar limb on
3 November 2003 launched a large-amplitude large-scale coronal wave that
was observed in Hα and Fe xii 195 Å spectral lines, as well as in the
soft X-ray and radio wavelength ranges. The wave also excited a complex
decimeter-to-hectometer type II radio burst, revealing the formation of
coronal shock(s). The back-extrapolation of the motion of coronal wave
signatures and the type II burst sources distinctly marks the impulsive
phase of the flare (the hard X-ray peak, drifting microwave burst,
and the highest type III burst activity), favoring a flare-ignited
wave scenario. On the other hand, comparison of the kinematics of
the CME expansion with the propagation of the optical wave signatures
and type II burst sources shows a severe discrepancy in the CME-driven
scenario. However, the CME is quite likely associated with the formation
of an upper-coronal shock revealed by the decameter-hectometer type II
burst. Finally, some six minutes after the launch of the first coronal
wave, another coronal disturbance was launched, exciting an independent
(weak) decimeter-meter range type II burst. The back-extrapolation
of this radio emission marks the revival of the hard X-ray burst,
and since there was no CME counterpart, it was clearly ignited by the
new energy release in the flare.
---------------------------------------------------------
Title: Hemispheric sunspot numbers {R<SUB>n</SUB>} and {R<SUB>s</SUB>}
from 1945-2004: catalogue and N-S asymmetry analysis for solar
cycles 18-23
Authors: Temmer, M.; Rybák, J.; Bendík, P.; Veronig, A.; Vogler,
F.; Otruba, W.; Pötzi, W.; Hanslmeier, A.
2006A&A...447..735T Altcode:
From sunspot drawings provided by the Kanzelhöhe Solar Observatory,
Austria, and the Skalnaté Pleso Observatory, Slovak Republic, we
extracted a data catalogue of hemispheric Sunspot Numbers covering
the time span 1945-2004. The validated catalogue includes daily,
monthly-mean, and smoothed-monthly relative sunspot numbers
for the northern and southern hemispheres separately and is
available for scientific use. These data we then investigated with
respect to north-south asymmetries for almost 6 entire solar cycles
(Nos. 18-23). For all the cycles studied, we found that the asymmetry
based on the absolute asymmetry index is enhanced near the cycle
maximum, which contradicts to previous results that are based on the
normalized asymmetry index. Moreover, the weak magnetic interdependence
between the two solar hemispheres is confirmed by their self-contained
evolution during a cycle. For the time span 1945-2004, we found that
the cycle maxima and also the declining and increasing phases are
clearly shifted, whereas the minima seem to be in phase for both
hemispheres. The asymmetric behavior reveals no obvious connection
to either the sunspot cycle period of ~11- or the magnetic cycle of
~22-years. The most striking excess of activity is observed for the
northern hemisphere in cycles 19 and 20.
---------------------------------------------------------
Title: X-ray sources and magnetic reconnection in the X3.9 flare of
2003 November 3
Authors: Veronig, A. M.; Karlický, M.; Vršnak, B.; Temmer, M.;
Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2006A&A...446..675V Altcode:
Context: .Recent RHESSI observations indicate an apparent altitude
decrease of flare X-ray loop-top (LT) sources before changing to the
commonly observed upward growth of the flare loop system.<BR /> Aims:
.We performed a detailed study of the LT altitude decrease for one well
observed flare in order to find further hints on the physics of this
phenomenon and how it is related to the magnetic reconnection process in
solar flares.<BR /> Methods: .RHESSI X-ray source motions in the 2003
November 3, X3.9 flare are studied together with complementary data
from SXI, EIT, and Kanzelhöhe Hα. We particularly concentrate on the
apparent altitude decrease of the RHESSI X-ray LT source early in the
flare and combine kinematical and X-ray spectral analysis. Furthermore,
we present simulations from a magnetic collapsing trap model embedded
in a standard 2-D magnetic reconnection model of solar flares.<BR />
Results: .We find that at higher photon energies the LT source is
located at higher altitudes and shows higher downward velocities
than at lower energies. The mean downward velocities range from
14 km s<SUP>-1</SUP> in the RHESSI 10-15 keV energy band to 45 km
s<SUP>-1</SUP> in the 25-30 keV band. For this flare, the LT altitude
decrease was also observed by the SXI instrument with a mean speed of
12 km s<SUP>-1</SUP>. RHESSI spectra indicate that during the time
of LT altitude decrease the emission of the LT source is thermal
bremsstrahlung from a "superhot" plasma with temperatures increasing
from 35 MK to 45 MK and densities of the order of 10<SUP>10</SUP>
cm<SUP>-3</SUP>. The temperature does not significantly increase
after this early (pre-impulsive superhot LT) phase, whereas the
LT densities increase to a peak value of (3-4) × 10<SUP>11</SUP>
cm<SUP>-3</SUP>.<BR /> Conclusions: .Modeling of a collapsing magnetic
trap embedded in a standard 2D magnetic reconnection model can reproduce
the key observational findings in case that the observed emission is
thermal bremsstrahlung from the hot LT plasma. This agrees with the
evaluated RHESSI spectra for this flare.
---------------------------------------------------------
Title: Hemispheric Sunspot Numbers 1945--2004: data merging from
two observatories
Authors: Temmer, M.; Rybák, J.; Bendík, P.; Veronig, A.; Vogler,
F.; Pötzi, W.; Otruba, W.; Hanslmeier, A.
2006CEAB...30...65T Altcode:
For the time span 1945--2004 from daily sunspot drawings northern
and southern relative sunspot numbers are extracted using drawings
provided by Kanzelhöhe Solar Observatory, Austria, and Skalnaté Pleso
Observatory, Slovak Republic. The derived data will be used to improve
and extend an already existing catalogue of hemispheric sunspot numbers
(Temmer et al., 2002). Since northern and southern solar hemispheres
do not evolve in phase during the cycle, hemispheric data are very
important for activity studies. In the present paper the compilation
of the data for the period 1945--2004 is described. Furthermore as a
quality check of the derived hemispheric data a regression analysis and
the comparison to the international hemispheric sunspot numbers from
the Sunspot Index Data Center for the time span 1992--2004 is presented.
---------------------------------------------------------
Title: Periodical patterns in major flare occurrence and their
relation to magnetically complex active regions
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
A.
2006AdSpR..38..886T Altcode:
A periodical occurrence rate of major solar flares (observed in hard
X-rays) of ∼24 days (synodic) was first reported by Bai (1987)
[Bai, T. Distribution of flares on the sun superactive regions and
active zones of 1980 1985. ApJ 314, 795 807, 1987] for the years 1980
1985. Here, we report a significant relation between the appearance of
the 24-day period in major Hα flares and magnetically complex sunspot
groups (i.e., including a γ and/or δ configuration). From synoptic
maps of magnetograms (NSO/KP) patterns in the magnetic flux evolution
are traced which might be the cause of the 24-day period observed in
flare activity.
---------------------------------------------------------
Title: X-Ray Sources and Magnetic Reconnection in AN X-Class Flare
Authors: Veronig, A. M.; Vršnak, B.; Karlický, M.; Temmer, M.;
Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2005ESASP.600E..32V Altcode: 2005ESPM...11...32V; 2005dysu.confE..32V
No abstract at ADS
---------------------------------------------------------
Title: Hemispheric Sunspot Numbers RN and RS from 1945-2004: Extended
and Improved Catalogue
Authors: Temmer, M.; Rybák, J.; Veronig, A.; Bendík, P.; Vogler,
F.; Pötzi, W.; Otruba, W.; Hanslmeier, A.
2005ESASP.600E..52T Altcode: 2005ESPM...11...52T; 2005dysu.confE..52T
No abstract at ADS
---------------------------------------------------------
Title: Wave Phenomena Associated with the X3.8 Flare/cme of
17-JAN-2005
Authors: Temmer, M.; Veronig, A.; Vršnak, B.; Thalmann, J.;
Hanslmeier, A.
2005ESASP.600E.144T Altcode: 2005ESPM...11..144T; 2005dysu.confE.144T
No abstract at ADS
---------------------------------------------------------
Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers
1945-2004 (Temmer+, 2006)
Authors: Temmer, M.; Rybak, J.; Bendik, P.; Veronig, A.; Vogler, F.;
Otruba, W.; Poetzi, W.; Hanslmeier, A.
2005yCat..34470735T Altcode:
From sunspot drawings provided by the Kanzelhoehe Solar Observatory,
Austria, and the Skalnate Pleso Observatory, Slovak Republic,
a data catalogue of hemispheric Sunspot Numbers covering the time
span 1945-2004 is extracted. The validated catalogue includes daily,
monthly-mean and smoothed-monthly relative sunspot numbers for the
northern and southern hemispheres separately and is available for
scientific use. Based on this data set an analysis concerning the
North-South asymmetry is made within this paper. <P />(2 data files).
---------------------------------------------------------
Title: Spatial Distribution and North-South Asymmetry of Coronal
Bright Points from Mid-1998 to Mid-1999
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Rušdjak, V.; Clette,
F.; Hochedez, J. -F.; Verbanac, G.; Temmer, M.
2005SoPh..231...29B Altcode:
Full-disc full-resolution (FDFR) solar images obtained with the Extreme
Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric
Observatory (SOHO) were used to analyse the centre-to-limb function and
latitudinal distribution of coronal bright points. The results obtained
with the interactive and the automatic method, as well as for three
subtypes of coronal bright points for the time period 4 June 1998 to 22
May 1999 are presented and compared. An indication of a two-component
latitudinal distribution of coronal bright points was found. The
central latitude of coronal bright points traced with the interactive
method lies between 10<SUP>∘</SUP> and 20<SUP>∘</SUP>. This is
closer to the equator than the average latitude of sunspots in the
same period. Possible implications for the interpretation of the
solar differential rotation are discussed. In the appendix, possible
differences between the two solar hemispheres are analysed. More coronal
bright points were present in the southern solar hemisphere than in
the northern one. This asymmetry is statistically significant for the
interactive method and not for the automatic method. The visibility
function is symmetrical around the central meridian.
---------------------------------------------------------
Title: Broadband Metric-Range Radio Emission Associated with a
Moreton/EIT Wave
Authors: Vršnak, B.; Magdalenić, J.; Temmer, M.; Veronig, A.;
Warmuth, A.; Mann, G.; Aurass, H.; Otruba, W.
2005ApJ...625L..67V Altcode:
We present the evolution and kinematics of a broadband radio source
that propagated collaterally with an Hα/EIT wave, linking it with the
type II burst that was excited higher up in the corona. The NRH wave
emission extended from the frequency f~327 to f<151 MHz and was
considerably weaker than the flare-related type IV burst. The emission
centroid propagated at a height of 0-200 Mm above the solar limb and
was intensified when the disturbance passed over enhanced coronal
structures. We put forward the ad hoc hypothesis that the NRH wave
signature is optically thin gyrosynchrotron emission excited by the
passage of the coronal MHD fast-mode shock. The identification of radio
emission associated with the coronal wave front is important since it
offers us new diagnostic information that could provide us with better
insight into the physical conditions in the disturbance itself.
---------------------------------------------------------
Title: What causes the 24-day period observed in solar flares?
Authors: Temmer, M.; Rybák, J.; Veronig, A.; Hanslmeier, A.
2005A&A...433..707T Altcode:
Previous studies report a 24-day (synodic) period in the occurrence
rate of solar flares for each of the solar cycles studied, Nos. 19-22
(Bai 1987, ApJ, 314, 795; Temmer et al. 2004, Sol. Phys. 221,
325). Here we study the 24-day period in the solar flare occurrence
for solar cycles 21 and 22 by means of wavelet power spectra together
with the solar flare locations in synoptic magnetic maps. We find
that the 24-day peak revealed in the power spectra is just the
result of a particular statistical clumping of data points, most
probably caused by a characteristic longitudinal separation of about
+40<SUP>circ</SUP> to +50<SUP>circ</SUP> of activity complexes in
successive Carrington rotations. These complexes appear as parallel,
diverging or converging branches in the synoptic magnetic maps and
are particularly flare-productive.
---------------------------------------------------------
Title: The Two Complexes of Activity Observed in the Northern
Hemisphere during 1982 and the 24-Day Periodicity of Flare Occurrence
Authors: Ruždjak, V.; Ruždjak, D.; Brajša, R.; Temmer, M.;
Hanslmeier, A.
2005HvaOB..29..117R Altcode:
Daily numbers of solar Hα flares of importance classes ≥ 1 for
the northern solar hemisphere in 1982 are studied applying wavelet
power spectra (WPS). Special attention is paid to the occurrence of a
24-day period in the WPS. The wavelet power spectra method is combined
with synoptic maps of the magnetic fields. Separately, flare indices
of two activity complexes mainly contributing to flare occrrence in
this period are examined. It is found that the detected 24-day signal
in the WPS is mainly a consequence of the presence of the two flare
activity complexes separated by about 45° in longitude during several
succesive Carrington rotations.
---------------------------------------------------------
Title: Properties of Type IV Radio Bursts with Periodical Fine
Structures
Authors: Magdalenić, J.; Vršnak, B.; Zlobec, P.; Messerotti, M.;
Temmer, M.
2005ASSL..320..259M Altcode: 2005smp..conf..259M
No abstract at ADS
---------------------------------------------------------
Title: On the Relation Between the Coronal Free Energy and Solar
Flare Occurrence
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2005HvaOB..29..109T Altcode:
A significant delay with a 22-year modulation in solar flare occurrence
was found by te{temmer03solph} with respect to the solar cycle defined
on the basis of the relative sunspot number. These observational results
were modelled by te{litvi03} through a time-dependent balance of the
magnetic free energy in the solar corona. The free magnetic energy is
assumed to be depleted mainly by flares and lags behind the variation
of the energy supply (emerging magnetic flux - proxy: relative sunspot
numbers) to this system. For solar cycles 21 and 23, in accordance with
the delay obtained for flare rates, the rate of sunspot group numbers
lags behind the solar cycle maximum. Theses findings suggest that
the energy supply itself is delayed, most prominent in odd numbered
solar cycles which subsequently causes the delay observed for flare
and sunspot group occurrences.
---------------------------------------------------------
Title: Loop-Top Altitude Decrease in an X-Class Flare
Authors: Veronig, A.; Vršnak, B.; Karlický, M.; Temmer, M.;
Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2005HvaOB..29..127V Altcode:
We study RHESSI X-ray source motions in the X3.9 flare of 2003 November
3. Particular attention is drawn to the apparent altitude decrease
of a distinct loop-top (LT) source at the early flare phase before
then changing to the commonly observed upward expansion of the flare
loop system. We obtain that the downward motion is more pronounced
at higher X-ray energies (peak values up to 50 km s^{-1}) consistent
with recent findings by Sui et al. (2004). RHESSI spectra indicate
that the emission process in the LT source is thermal bremsstrahlung
from a super hot plasma (∼40 MK) with high densities increasing from
∼10^{10} cm^{-3} early in the flare to several times 10^{11} cm^{-3}
at the end of RHESSI observations.
---------------------------------------------------------
Title: On the 24- and 155-Day Periodicity Observed in Solar Hα Flares
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2005ASSL..320..211T Altcode: 2005smp..conf..211T
No abstract at ADS
---------------------------------------------------------
Title: On the 24-day period observed in solar flare occurrence
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
A.
2004SoPh..221..325T Altcode:
Time series of daily numbers of solar Hα flares from 1955 to
1997 are studied by means of wavelet power spectra with regard to
predominant periods in the range of ∼ 24 days (synodic). A 24-day
period was first reported by Bai (1987) for the occurrence rate of
hard X-ray flares during 1980-1985. Considering the northern and
southern hemisphere separately, we find that the 24-day period is not
an isolated phenomenon but occurs in each of the four solar cycles
investigated (No. 19-22). The 24-day period can be established also
in the occurrence rate of subflares but occurs more prominently in
major flares (importance classes ≥ 1). A comparative analysis of
magnetically classified active regions subdivided into magnetically
complex (i.e., including a γ and/or δ configuration) and non-complex
(α, β) reveals a significant relation between the appearance of
the 24-day period in Hα flares and magnetically complex sunspot
groups, whereas it cannot be established for non-complex groups. It is
suggested that the 24-day period in solar flare occurrence is related
to a periodic emergence of new magnetic flux rather than to the surface
rotation of sunspots.
---------------------------------------------------------
Title: Merging two data sets of hemispheric Sunspot Numbers
Authors: Rybák, J.; Bendík, P.; Temmer, M.; Veronig, A.; Hanslmeier,
A.
2004HvaOB..28...63R Altcode:
First results on merging two data sets of hemispheric sunspot numbers
-- from the Kanzelhöhe Solar Observatory and the Skalnaté Pleso
Observatory -- for the time span 1977 -- 1978 are presented. A total
coverage of 86% was reached for the merged data set. In order to have
a homogeneous time series, the daily sunspot numbers for the full disk
from both observing stations were normalized to the international
relative sunspot number of the day. The derived hemispheric sunspot
numbers from Kanzelhöhe and Skalnaté Pleso Observatory %compared
for 290 common observing show very high correlations (r ≳ 0.95), and
the estimated data noise yields significant differences only for small
values of sunspot numbers. These outcomes demonstrate the high potential
of the applied merging procedure, and are the basis for an ongoing
project to derive hemispheric sunspot numbers back to the year 1945
using sunspot drawings from Kanzelhöhe and Skalnaté Pleso Observatory.
---------------------------------------------------------
Title: Importance of magnetically complex active regions on solar
flare occurrence
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
A.
2004HvaOB..28...95T Altcode:
Daily numbers of solar Hα flares from 1955 to 1997 and daily numbers
of magnetically classified active regions for the time span 1964--1997
are studied applying wavelet power spectra. The occurrence of dominant
periods in the range of ∼24 days (synodic) is investigated considering
the northern and southern hemisphere separately. From the flare events
it is revealed that the 24-day period occurs in each of the four solar
cycles investigated (no. 19--22). The 24-day period can be established
also in the occurrence rate of subflares but occurs more prominently
in major flares (importance classes ≥1). Magnetically complex active
regions, i.e. including a γ and/or δ configuration, show the 24-day
period closely related to those found for major Hα flares, whereas
it cannot be established for non-complex α, β groups.
---------------------------------------------------------
Title: Periodical patterns in major flare occurrence and their
relation to magnetically complex active regions
Authors: Temmer, M.; Veronig, A.; Rybak, J.; Brajsa, R.; Hanslmeier, A.
2004cosp...35.1395T Altcode: 2004cosp.meet.1395T
A periodical occurrence rate of solar major flares (observed in
hard X-rays) of about 24 days (synodic) was first reported by Bai
(1987) for the years 1980--1985. Its origin is still far from being
understood. Applying wavelet analyses for daily numbers of Hα flare
events covering almost four entire solar cycles (no. 19--22) reveals a
24-day period in each of the cycles studied. This can be established
primarily in the occurrence rate of major flares but is also seen
in subflares. Since large flares occur preferentially in association
with active regions of complex magnetic configuration a comparative
study of magnetically classified active regions, subdivided into
magnetically complex (i.e. including a γ and/or δ configuration)
and non-complex (α, β) was performed. A significant relation
between the appearance of the 24-day period in major Hα flares and
magnetically complex sunspot groups is found, whereas it cannot be
established for non-complex groups. From solar rotation studies based
on tracing sunspots practically no siderial rotation velocities as high
as 16 deg/day (which corresponds to a synodic period of ∼24 days)
are reported. Thus the cause of the 24-day period is very likely not
related to solar surface rotation. Alternatively it might be due to
periodical patterns in magnetic flux emergence which is an important
driver of flare eruptions. We test this hypothesis by investigating
synoptic maps of magnetograms (National Solar Observatory/Kitt Peak)
for selected time ranges in which the 24-day period is revealed for
both flares and magnetically complex active regions.
---------------------------------------------------------
Title: The solar soft X-ray background flux and its relation to
flare occurrence
Authors: Veronig, Astrid M.; Temmer, Manuela; Hanslmeier, Arnold
2004SoPh..219..125V Altcode:
The soft X-ray background flux (XBF) based on GOES 1-8 Å measurements
for the period 1975-2003 is studied. There is strong evidence that
in the XBF the flare contribution is not eliminated but the XBF is
dominated by flare and post-flare emission of intense events. The
significant delay (∼ 2 years) of the peak of the X-ray background
flux with regard to sunspot numbers reported for cycle 21 recurs in
the present cycle 23. The relation between monthly XBF and sunspot
numbers can be well represented by a power law. For cycles 21 and 23
the derived fit values are the same within the uncertainties, whereas
the values for cycle 22 are significantly different. It is suggested
that the lag of the XBF in cycles 21 and 23 is a secondary effect
related to the substantial contribution of energetic flares which is
not fully subtracted out by the actual XBF definition.
---------------------------------------------------------
Title: On rotational patterns of the solar magnetic field
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Hanslmeier, A.
2003ESASP.535..157T Altcode: 2003iscs.symp..157T
Solar magnetic field variations (NSO/Kitt Peak data) through solar cycle
23 with respect to rotational modulations are analyzed. A comparative
study to solar cycles 21 and 22 is performed. The results are compared
to the rotational behavior of activity tracers like sunspots and solar
Hα flares. Periodical occurrences of flares often match the 27-day
solar rotation due to recurrent stable sunspot groups and complexes
of activity which likely produce more flare events than short-living
small sunspots. However, periods with strong deviations from the 27-day
period are obtained for higher energetic flares. The solar magnetic
field is found to vary on similar time scales, which suggests a close
relation to the occurrence of strong flare events.
---------------------------------------------------------
Title: Solar cycle variations of the soft X-ray background flux and
its relation to flare occurrence
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.
2003ESASP.535..259V Altcode: 2003iscs.symp..259V
The X-ray background flux (XBF) based on GOES 1-8 Å measurements for
the period 1975-2000 is studied. We come to the conclusion that in the
XBF the flare contribution is not eliminated but the XBF is dominated
by flare and post-flare emission of intense events. Furthermore, we
suggest that the characteristic lag of the X-ray background flux with
regard to Sunspot Numbers reported for cycle 21 is a secondary effect
related to the substantial contribution of large flares to the XBF.
---------------------------------------------------------
Title: Radio signatures of fast oscillatory phenomena in the solar
corona
Authors: Magdalenic, Jasmina; Zlobec, P.; Vršnak, B.; Messerotti,
M.; Aurass, H.; Temmer, M.
2003ESASP.535..619M Altcode: 2003iscs.symp..619M
During type IV solar radio bursts different types of periodic fine
structures (PFSs) are frequently observed, which can be interpreted
as radio signatures of fast oscillatory phenomena in the coronal
plasma. We analyze a large set of type IV bursts containing PFSs,
recorded with high time resolution at single frequencies in the
metric and decimetric bands. Focusing on the association with flares
and flare-like phenomena we found: PFSs can be found in about 50% of
type IV bursts characterized by fine structures; 10% of PFS-containing
events are weak/short type IV-like radio bursts that occur in absence
of any flare-like activity. In the weakest events the whole radio
burst was in fact just one short PFS-episode recorded at only one
observing frequency; In flare associated events we found two distinct
classes of PFSs - impulsive phase and decay phase related PFSs; yet,
no statistically significant difference in the characteristic periods
and amplitudes is found between the two classes; PFS-rich radio events
are characterized by large SXR and radio peak fluxes - neither one
of the weak type IV bursts was PFS-rich. The opposite is not true:
mainly powerful bursts are PFS-poor.
---------------------------------------------------------
Title: Does solar flare activity lag behind sunspot activity?
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2003SoPh..215..111T Altcode:
Recently, Wheatland and Litvinenko (2001) have suggested that over the
solar cycle both the flaring rate and the magnetic free energy in the
corona lag behind the energy supply to the system. To test this model
result, we analyzed the evolution of solar flare occurrence with regard
to sunspot numbers (as well as sunspot areas), using Hα flare data
available for the period 1955-2002, and soft X-ray flare data (GOES
1-8 Å) for the period 1976-2002. For solar cycles 19, 21, and 23,
we find a characteristic time lag between flare activity and sunspot
activity in the range 10≲τ≲15 months, consistent with the model
predictions by Wheatland and Litvinenko (2001). The phenomenon turns
out to be more prominent for highly energetic flares. The investigation
of solar activity separately for the northern and southern hemisphere
allows us to exclude any bias due to overlapping effects from the
activity of both hemispheres and confirms the dynamic relevance of the
delay phenomenon. Yet, no characteristic time lag τ>0 is found for
solar cycles 20 and 22. The finding that in odd-numbered cycles flare
activity is statistically delayed with respect to sunspot activity,
while in even-numbered cycles it is not, suggests a connection to the
22-year magnetic cycle of the Sun. Further insight into the connection
to the 22-year magnetic cycle could possibly be gained when a 22-year
variation in the energy supply rate is taken into account in the
Wheatland and Litvinenko (2001) model. The existence of a 22-year
modulation in the energy supply rate is suggested by the empirical
Gnevyshev - Ohl rule, and might be caused by a relic solar field.
---------------------------------------------------------
Title: Rotational modulation of northern and southern activity tracers
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Hanslmeier, A.
2003HvaOB..27...59T Altcode:
We study solar activity phenomena, Hα flares and sunspots, with respect
to their periodical occurrence related to the solar rotation. The
analysis is carried out separately for the northern and the southern
hemisphere. Furthermore, flare occurrences are studied with respect
to different importance classes, and the results are compared to
the predominant periods derived from Sunspot Numbers. Significant
asymmetries are obtained between the northern and southern activity for
both Sunspot Numbers and flare occurrences. Differences between Sunspot
Numbers and flares result particularly when only higher energetic
flares are considered. A 24-day period is found for large flare events
in both hemispheres which is not detected in Sunspot Numbers.
---------------------------------------------------------
Title: Catalogue of hemispheric sunspot numbers R<SUB>N</SUB> and
R<SUB>S</SUB>: 1975 - 2000
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002ESASP.506..855T Altcode: 2002svco.conf..855T; 2002ESPM...10..855T
Sunspot drawings are provided on a regular basis at the Kanzelhöhe
Solar Obseratory, Austria, and the derived relative sunspot numbers
are reported to the Sunspot Index Data Center in Brussels. From the
daily sunspot drawings, we derived the northern, R<SUB>n</SUB>,
and southern, R<SUB>s</SUB>, relative sunspot numbers for the
time span 1975-2000. In order to accord with the International
Sunspot Numbers R<SUB>i</SUB>, the R<SUB>n</SUB> and R<SUB>s</SUB>
have been normalized to the R<SUB>i</SUB>, which ensures that the
relation R<SUB>n</SUB>+R<SUB>s</SUB> = R<SUB>i</SUB> is complied. For
validation, the derived R<SUB>n</SUB> and R<SUB>s</SUB> are compared
to the international northern and southern relative sunspot numbers,
which are available since 1992. The regression analysis performed for
the period 1992-2000 reveals good agreement with the International
hemispheric Sunspot Numbers. The monthly mean and the smoothed monthly
mean hemispheric Sunspot Numbers are compiled to a catalogue. In
addition, the daily hemispheric Sunspot Numbers are made available
via Internet.
---------------------------------------------------------
Title: Cycle dependence of hemispheric activity
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Hanslmeier, A.
2002ESASP.506..859T Altcode: 2002ESPM...10..859T; 2002svco.conf..859T
Data of daily hemispheric Sunspot Numbers are analyzed including the
time span 1975-2001. The study of north-south asymmetries concerning
solar activity and rotational behaviors is in particular relevant,
as it is related to the solar dynamo and the generation of magnetic
fields. As diagnostic tools we use wavelets and autocorrelation
functions in combination with statistical significance tests that are
applied separately to the northern and southern hemisphere. Pronounced
differences between the northern and southern rotational periods
are obtained. The northern hemisphere shows a rigid rotation of ~27
days which can be followed up to ~15 periods in the autocorrelation
function. The signal of the southern hemisphere is strongly attenuated
after 3 recurrences showing variable periods in the range ~26-28.5
days. The presence of these periods is not permanent during a cycle
suggesting activity pulses in each hemisphere. For the northern
hemisphere strong relations to the motions of deeper lying convective
structures building up long-living 'active zones' are suggested.
---------------------------------------------------------
Title: The Neupert effect and the electron-beam-driven evaporation
model
Authors: Veronig, A.; Vršnak, B.; Dennis, B. R.; Temmer, M.;
Hanslmeier, A.; Magdalenić, J.
2002ESASP.506..367V Altcode: 2002svco.conf..367V; 2002ESPM...10..367V
Based on a sample of ~1100 solar flares observed simultaneously in
hard and soft X-rays, we performed a statistical analysis of the
Neupert effect. For a subset of ~500 events, supplementary Hα flare
data were considered. The timing behavior of >50% of the events
is consistent with the Neupert effect. A high correlation between
the soft X-ray peak flux and the hard X-ray fluence is obtained,
being indicative of electron-beam-driven evaporation. However, about
one fourth of the events (predominantly weak flares) reveal strong
deviations from the predicted timing, with a prolonged increase of
the thermal emission beyond the end of the hard X-rays. These findings
suggest that electron-beam-driven evaporation plays an important role
in solar flares. Yet, in a significant fraction of events there is also
evidence for an additional energy transport mechanism from the energy
release site other than electron beams, presumably thermal conduction.
---------------------------------------------------------
Title: The Neupert effect in solar flares and implications for
coronal heating
Authors: Veronig, A.; Vrsnak, B.; Dennis, B. R.; Temmer, M.;
Hanslmeier, A.; Magdalenić, J.
2002ESASP.505..599V Altcode: 2002solm.conf..599V; 2002IAUCo.188..599V; 2002astro.ph..8089V
Based on simultaneous observations of solar flares in hard and soft
X-rays we studied several aspects of the Neupert effect. About half of
1114 analyzed events show a timing behavior consistent with the Neupert
effect. For these events, a high correlation between the soft X-ray
peak flux and the hard X-ray fluence is obtained, being indicative of
electron-beam-driven evaporation. However, for about one fourth of the
events there is strong evidence for an additional heating agent other
than electron beams. We discuss the relevance of these findings with
respect to Parker's idea of coronal heating by nanoflares.
---------------------------------------------------------
Title: Hemispheric asymmetry of solar activity phenomena: north-south
excesses rotational periods and their links to the magnetic field
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002ESASP.505..587T Altcode: 2002solm.conf..587T; 2002IAUCo.188..587T
We present a cycle dependent analysis of various solar activity
phenomena, namely Sunspot Numbers and Hα flares, including the
time range 1975-2000. The data are studied on a statistical basis
with relation to their spatial distribution, significance of the
north-south asymmetry and rotational periods. For the considered time
span we obtain significant values of north-south asymmetries. For the
northern hemisphere the significant excesses are revealed during the
increasing and maximum phase of a solar cycle whereas a southern excess
dominates near the end of a cycle. Furthermore, we obtain differences
in rotational periods and activity gaps between both hemispheres that
suggest an independent evolution in hemispheric activity for these
indices. Hence, a weak interdependence of the magnetic field system
originating in the two hemispheres is suggested. Additionally we find
differences in the dominant rotational periods of photospheric and
chromospheric tracers.
---------------------------------------------------------
Title: Investigation of the Neupert effect in solar
flares. I. Statistical properties and the evaporation model
Authors: Veronig, A.; Vršnak, B.; Dennis, B. R.; Temmer, M.;
Hanslmeier, A.; Magdalenić, J.
2002A&A...392..699V Altcode: 2002astro.ph..7217V
Based on a sample of 1114 flares observed simultaneously in hard X-rays
(HXR) by the BATSE instrument and in soft X-rays (SXR) by GOES, we
studied several aspects of the Neupert effect and its interpretation
in the frame of the electron-beam-driven evaporation model. In
particular, we investigated the time differences (Delta t) between
the maximum of the SXR emission and the end of the HXR emission,
which are expected to occur at almost the same time. Furthermore,
we performed a detailed analysis of the SXR peak flux - HXR fluence
relationship for the complete set of events, as well as separately for
subsets of events which are likely compatible/incompatible with the
timing expectations of the Neupert effect. The distribution of the time
differences reveals a pronounced peak at Delta t = 0. About half of the
events show a timing behavior which can be considered to be consistent
with the expectations from the Neupert effect. For these events, a high
correlation between the SXR peak flux and the HXR fluence is obtained,
indicative of electron-beam-driven evaporation. However, there is also
a significant fraction of flares (about one fourth), which show strong
deviations from Delta t = 0, with a prolonged increase of the SXR
emission distinctly beyond the end of the HXR emission. These results
suggest that electron-beam-driven evaporation plays an important role
in solar flares. Yet, in a significant fraction of events, there is
also clear evidence for the presence of an additional energy transport
mechanism other than nonthermal electron beams, where the relative
contribution is found to vary with the flare importance.
---------------------------------------------------------
Title: Hemispheric Sunspot Numbers R<SUB>n</SUB> and R<SUB>s</SUB>:
Catalogue and N-S asymmetry analysis
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002A&A...390..707T Altcode: 2002astro.ph..8436T
Sunspot drawings are provided on a regular basis at the Kanzelhöhe
Solar Observatory, Austria, and the derived relative sunspot numbers
are reported to the Sunspot Index Data Center in Brussels. From the
daily sunspot drawings, we derived the northern, R<SUB>n</SUB>,
and southern, R<SUB>s</SUB>, relative sunspot numbers for the
time span 1975-2000. In order to accord with the International
Sunspot Numbers R<SUB>i</SUB>, the R<SUB>n</SUB> and R<SUB>s</SUB>
have been normalized to the R<SUB>i</SUB>, which ensures that the
relation R<SUB>n</SUB>+R<SUB>s</SUB>=R<SUB>i</SUB> is fulfilled. For
validation, the derived R<SUB>n</SUB> and R<SUB>s</SUB> are compared
to the international northern and southern relative sunspot numbers,
which are available from 1992. The regression analysis performed for
the period 1992-2000 reveals good agreement with the International
hemispheric Sunspot Numbers. The monthly mean and the smoothed
monthly mean hemispheric Sunspot Numbers are compiled into a
catalogue. Based on the derived hemispheric Sunspot Numbers,
we study the significance of N-S asymmetries and the rotational
behavior separately for both hemispheres. We obtain that ~ 60% of the
monthly N-S asymmetries are significant at a 95% level, whereas the
relative contributions of the northern and southern hemisphere are
different for different cycles. From the analysis of power spectra
and autocorrelation functions, we derive a rigid rotation with ~
27 days for the northern hemisphere, which can be followed for up
to 15 periods. Contrary to that, the southern hemisphere reveals a
dominant period of ~ 28 days, whereas the autocorrelation is strongly
attenuated after 3 periods. These findings suggest that the activity
of the northern hemisphere is dominated by an active zone, whereas
the southern activity is mainly dominated by individual long-lived
sunspot groups. The catalogue is available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/707
---------------------------------------------------------
Title: Relative timing of solar flares observed at different
wavelengths
Authors: Veronig, A.; Vršnak, B.; Temmer, M.; Hanslmeier, A.
2002SoPh..208..297V Altcode: 2002astro.ph..8088V
The timing of 503 solar flares observed simultaneously in hard X-rays,
soft X-rays and Hα is analyzed. We investigated the start and the peak
time differences in different wavelengths, as well as the differences
between the end of the hard X-ray emission and the maximum of the
soft X-ray and Hα emission. In more than 90% of the analyzed events,
a thermal pre-heating seen in soft X-rays is present prior to the
impulsive flare phase. On average, the soft X-ray emission starts 3 min
before the hard X-ray and the Hα emission. No correlation between the
duration of the pre-heating phase and the importance of the subsequent
flare is found. Furthermore, the duration of the pre-heating phase
does not differ for impulsive and gradual flares. For at least half of
the events, the end of the non-thermal emission coincides well with
the maximum of the thermal emission, consistent with the beam-driven
evaporation model. On the other hand, for ∼ 25% of the events there
is strong evidence for prolonged evaporation beyond the end of the
hard X-rays. For these events, the presence of an additional energy
transport mechanism, most probably thermal conduction, seems to play
an important role.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers
1975-2000 (Temmer+, 2002)
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002yCat..33900707T Altcode:
Hemispheric sunspot numbers including the time span from 1975-2000 are
presented. The Sunspot Numbers are calculated from sunspot drawings
made at the Kanzelhoehe Solar Observatory (KSO), Austria. The counted
northern and southern Sunspot Numbers are normalized and multiplied
with the International Sunspot Numbers taken from SIDC for matching
days in order to provide the data within an international usage. Days
without observation by KSO (about 27 percent) were reconstructed
applying a linear interpolation method. As validation of the data,
regression methods and a cross-correlation analysis are made with
hemispheric Sunspot Numbers from SIDC for the available time span
1992-2000 obtaining very good agreements. The results are given in
monthly mean and smoothed monthly mean Sunspot Numbers. Based on this
data set an analysis concerning the North-South asymmetry is made in
the paper. (1 data file).
---------------------------------------------------------
Title: Soft X-ray flares for the period 1975-2000
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.; Otruba, W.;
Messerotti, M.
2002ESASP.477..175T Altcode: 2002scsw.conf..175T
Statistical aspects of solar soft X-ray (SXR) flares for the period
September 1975 to December 2000 are investigated. In particular,
we analyzed the spatial distribution of SXR flares with regard to
the solar hemispheres, i.e. N-S and E-W asymmetries, as well as the
occurrence of SXR flares in the course of the solar cycle. We obtain
that the occurrence rate of SXR flares is delayed in relation to the
Sunspot Numbers which can be interpreted as an interaction between
the northern and southern hemisphere activity.
---------------------------------------------------------
Title: Temporal characteristics of solar soft X-ray and Hα flares
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.; Messerotti, M.;
Otruba, W.; Moretti, P. F.
2002ESASP.477..187V Altcode: 2002scsw.conf..187V
Temporal aspects of solar soft X-ray and Hα flares for the period
1997-2000 are investigated. For the considered time span about 8400
SXR and 11400 Hα flares are reported in the SGD. Related flares
observed in Hα as well as in SXR are identified amounting to about
2100 events. Correlations among corresponding SXR and Hα events are
analyzed and their relative timing is investigated. From the timing
analysis we infer that for most of the events (84%) the start of the
Hα emission is delayed with respect to the SXR emission. On average,
the Hα flare starts 3 minutes after the SXR flare. The peaks occur
preferentially simultaneously with a slight tendency that the Hα peak
precedes the SXR peak.
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Title: Temporal aspects and frequency distributions of solar soft
X-ray flares
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.; Otruba, W.;
Messerotti, M.
2002A&A...382.1070V Altcode: 2002astro.ph..7234V
A statistical analysis of almost 50 000 soft X-ray (SXR) flares observed
by GOES during the period 1976-2000 is presented. On the basis of
this extensive data set, statistics on temporal properties of soft
X-ray flares, such as duration, rise and decay times with regard to
the SXR flare classes is presented. Correlations among distinct flare
parameters, i.e. SXR peak flux, fluence and characteristic times,
and frequency distributions of flare occurrence as function of the
peak flux, the fluence and the duration are derived. We discuss the
results of the analysis with respect to statistical flare models, the
idea of coronal heating by nanoflares, and elaborate on implications
of the obtained results on the Neupert effect in solar flares.
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Title: Frequency Distributions of solar Flares
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.
2002HvaOB..26....7V Altcode:
Flare frequency distributions as function of the soft X-ray peak flux
and fluence are investigated. We analyse GOES 1--8 Å data for the
period 1986--2000. The results are discussed with respect to avalanche
flare models and the hypothesis of coronal heating by nanoflares.
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Title: Statistical analysis of solar Hα flares
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.; Otruba, W.;
Messerotti, M.
2001A&A...375.1049T Altcode: 2002astro.ph..7239T
A statistical analysis of a large data set of Hα flares comprising
almost 100 000 single events that occurred during the period
January 1975 to December 1999 is presented. We analyzed the flares
evolution steps, i.e. duration, rise times, decay times and event
asymmetries. Moreover, these parameters characterizing the temporal
behavior of flares, as well as the spatial distribution on the solar
disk, i.e. N-S and E-W asymmetries, are analyzed in terms of their
dependency on the solar cycle. The main results are: 1) The duration,
rise and decay times increase with increasing importance class. The
increase is more pronounced for the decay times than for the rise
times. The same relation is valid with regard to the brightness
classes but in a weaker manner. 2) The event asymmetry indices,
which characterize the proportion of the decay to the rise time of
an event, are predominantly positive (~90%). For about 50% of the
events the decay time is even more than 4 times as long as the rise
time. 3) The event asymmetries increase with the importance class. 4)
The flare duration and decay times vary in phase with the solar cycle;
the rise times do not. 5) The event asymmetries do not reveal a distinct
correlation with the solar cycle. However, they drop during times of
solar minima, which can be explained by the shorter decay times found
during minimum activity. 6) There exists a significant N-S asymmetry
over longer periods, and the dominance of one hemisphere over the
other can persist for more than one cycle. 7) For certain cycles there
may be evidence that the N-S asymmetry evolves with the solar cycle,
but in general this is not the case. 8) There exists a slight but
significant E-W asymmetry with a prolonged eastern excess.
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Title: Statistical Study of Solar Flares Observed in Soft X-Ray,
Hard X-Ray and Hα Emission
Authors: Veronig, A.; Vršnak, B.; Temmer, M.; Magdalenić, J.;
Hanslmeier, A.
2001HvaOB..25...39V Altcode:
Correlations among statistical properties of solar flares observed
in soft X-rays, hard X-rays and Hα are studied. We investigate
corresponding HXR flares measured by BATSE, SXR flares observed by GOES
and Hα flares reported in the SGD for the period 1997--2000. Distinct
correlations are found among the SXR peak flux and Hα area, as well
as between the SXR peak flux and HXR fluence. This can be comprehended
in the frame of the chromospheric evaporation model of flares.
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Title: Automatic Image Processing in the Frame of a Solar Flare
Alerting System
Authors: Veronig, A.; Steinegger, M.; Otruba, W.; Hanslmeier, A.;
Messerotti, M.; Temmer, M.; Gonzi, S.; Brunner, G.
2000HvaOB..24..195V Altcode:
In the present paper we describe image processing techniques applied
to solar H-alpha full-disk images, with the objective of automatic
and quasi real-time detection of the onset of H-alpha flares and
describing their evolution. For this purpose we utilize a combination
of region-based and edge-based image segmentation methods.
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Title: Automatic Image Segmentation and Feature Detection in Solar
Full-Disk Images
Authors: Veronig, A.; Steinegger, M.; Otruba, W.; Hanslmeier, A.;
Messerotti, M.; Temmer, M.; Brunner, G.; Gonzi, S.
2000ESASP.463..455V Altcode: 2000sctc.proc..455V
At Kanzelhoehe Solar Observatory, Austria, a solar activity monitoring
and flare alerting system is under development, which will be based
on the parametrization of solar flare activity using photometric and
magnetic full-disk images of the Sun obtained simultaneously with high
time cadence. An important step in this project is the automatic image
segmentation and feature detection of solar activity phenomena related
to the occurrence of solar flares. In a first step we have developed
a procedure for automatically detecting the onset and describing the
evolution of flares in H-alpha full-disk images.
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Title: Statistical Properties Relevant to Solar Flare Prediction
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.; Steinegger, M.;
Brunner, G.; Gonzi, S.; Otruba, W.; Messerotti, M.
2000HvaOB..24..185T Altcode:
We statistically analyzed the characteristic temporal properties of
H-alpha flares, such as duration, rising and setting times, with the aim
to determine a proper acquisition rate for H-alpha patrol observations,
which will be the basis for the automatic flare alerting and prediction
system at the Kanzelhoehe Solar Observatory, Austria. Furthermore,
the comparison of absolute and normalized values reveals interesting
aspects on how flares of different importance classes behave with
respect to the rising and decay phase.
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Title: Solar Activity Monitoring - a New Approach Using Combined
Datasets, Pattern Recognition and Neural Networks
Authors: Hanslmeier, A.; Veronig, M.; Steinegger, M.; Brunner, G.;
Gonzi, S.; Temmer, M.; Otruba, W.; Messerotti, M.
1999HvaOB..23...31H Altcode:
In this paper we give an overview of the activities of the recently
established solar activity monitoring and flare alerting working group
at the University of Graz and its planned activities. Solar flares
can trigger events at the earth environment that can be dangerous to
technological systems as well as to human life. Therefore, it is an
important target in solar physics to predict such events, providing
an essential contribution to space weather forecasts.