explanation blue bibcodes open ADS page with paths to full text
Author name code: vandriel-gesztelyi
ADS astronomy entries on 2022-09-14
author:"van Driel-Gesztelyi, Lidia" OR author:"Gesztelyi, Lidia"
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Title: Stellar FIP effect from the empirical side
Authors: Seli, Bálint; Van Driel-Gesztelyi, Lidia; Baker, Deborah;
Laming, J. Martin; Kovari, Zsolt; Oláh, Katalin; Kriskovics, Levente;
Vida, Krisztián; Balázs, Lajos
2022cosp...44.2585S Altcode:
The difference between the elemental abundances of the corona and the
photosphere is an apparently common feature of stellar atmospheres. The
abundance difference depends on the first ionization potential of the
given element, so the phenomenon is known as the FIP effect. Here we
explore the variation of the strength of the FIP effect for different
types of stars, through the FIP bias parameter. Using a sample of 59
main sequence and evolved stars with known coronal abundances from the
literature, we look for macroscopic, measurable parameters that affect
the stellar FIP bias, and also re-evaluate the simple dependence on
the effective temperature.
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Title: Investigating of the nature of magnetic oscillations associated
with FIP effect
Authors: Murabito, Mariarita; Jafarzadeh, Shahin; Van Driel-Gesztelyi,
Lidia; Ermolli, Ilaria; Baker, Deborah; Brooks, David; Long, David;
Jess, David; Valori, Gherardo; Stangalini, Marco
2022cosp...44.2591M Altcode:
Observations of the photosphere, chromosphere, and corona combined with
magnetic field modeling of one of the biggest sunspots of the 24 solar
cycle, revealed that regions of high FIP bias plasma in the corona
were magnetically linked to the locations of the intrinsic magnetic
oscillations in the solar chromosphere. In order to characterize
the driver of the oscillations, we analyzed the relation between
the spatial distribution of the magnetic wave power and the overall
field geometry and plasma parameters obtained from the multi-height
spectropolarimetric non-local thermodynamic equilibrium (NLTE)
inversions. In correspondence with the locations where the magnetic
wave energy is observed at chromospheric heights, we found evidence
in support of locally excited acoustic waves that, after crossing the
equipartition layer located close to the umbra-penumbra boundary at
photospheric heights, are converted into magnetic-like waves. These
results indicate a direct connection between sunspot chromospheric
activity and observable changes in coronal plasma composition,
demonstrating the power of high resolution, multi-height studies of the
solar atmosphere that will become the gold standard in the era of DKIST.
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Title: Understanding the Correlation between Solar Coronal Abundances
and F10.7 Radio Emission
Authors: To, Andy S. H.; Baker, Deborah; Long, David; James, Alexander;
Brooks, David; van Driel-Gesztelyi, Lidia; Valori, Gherardo; Bastian,
Tim; Lomuscio, Samantha; Stansby, David
2022cosp...44.2592T Altcode:
Solar corona plasma composition, derived from full-Sun spectra, and
the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated
(r = 0.88) during the recent weak solar cycle. However, this correlation
becomes nonlinear at times of increased solar magnetic activity. We used
co-temporal, high spatial resolution, radio (JVLA), and EUV (Hinode/EIS)
images of the Sun taken on the 3 and 7 April 2020 to understand the
underlying causes of the non-linearity of the FIP bias-F10.7 solar
index correlation. We then calculated differential emission measures
from AIA images, and paired them with the observed FIP bias to predict
the bremsstrahlung component of F10.7 radio emission. Results of this
study provide constraints on the amplitude of composition variability
related to solar cycle amplitude, and provide an alternative method
to calculate coronal composition.
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Title: What determines active region coronal plasma composition?
Authors: Mihailescu, Teodora; Baker, Deborah; Long, David; Green,
Lucie; Brooks, David; van Driel-Gesztelyi, Lidia; To, Andy S. H.
2022cosp...44.2580M Altcode:
The chemical composition of the solar corona is different from that
of the solar photosphere, with the strongest variation being observed
in active regions. Using spectral data from the Extreme Ultraviolet
(EUV) Imaging Spectrometer (EIS) on Hinode, we present a survey of
coronal elemental composition as expressed in the FIP bias in 28 active
regions with a wide range of ages and magnetic flux contents, and at
different stages in their evolution. We find no correlation between the
FIP bias of an active region and its magnetic flux or age. However,
there is a dependence of the FIP bias on the evolutionary stage of
the active region. FIP bias shows an increasing trend with average
magnetic flux density up to 200 G but this trend does not continue
at higher values. In contrast to the single values typically used
to characterize the FIP bias in a region, we find that the FIP bias
distribution within active regions has a significant spread. The highest
spread is observed in very dispersed active regions and active regions
that have formed a filament channel along their main polarity inversion
lines, which is an indicator of the wide range of physical processes
that take place in these active regions. These findings indicate that,
while some general trends can be observed, the processes influencing
the composition of an active region are complex and specific to its
evolution, history and magnetic configuration or environment. The
spread of FIP bias values in active regions shows a broad match with
that previously observed in situ in the slow solar wind.
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Title: What have we learned about I-FIP Effect on the Sun from
Hinode/EIS?
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia
2022cosp...44.2572B Altcode:
Plasma composition in stellar coronae can differ from that of their
photospheres, the cause of which is one of the open questions in
astrophysics. Elements with a low first ionization potential (FIP)
are observed to have either enhanced or depleted abundances relative
to that of high FIP elements. The abundance pattern is known as the FIP
effect or inverse FIP (I-FIP) effect, depending on whether the low FIP
elements are over-/under- (FIP/I-FIP) abundant in coronae. Some stellar
coronae are dominated by FIP effect plasma but cooler, more active stars
are dominated by I-FIP effect plasma. Our local laboratory, the Sun,
has a FIP effect dominated corona, however, short-lived I-FIP patches
have occasionally been observed. Analysis of multiple cases of I-FIP
effect revealed certain conditions in the magnetic field and flare
heating to be necessary for the occurrence of I-FIP effect plasma on
the Sun. An overview of what we have learned from sixteen years of
spatially resolved spectroscopic observations from Hinode/EIS will be
presented. We will demonstrate the power of combining spectroscopic,
imaging, and magnetic field observations of our Sun to understand
the physical processes on cooler stars which we only observe as point
sources.
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Title: Evolution of Plasma Composition in an Eruptive Flux Rope
Authors: Baker, Deborah; Demoulin, Pascal; Long, David; Janvier, Miho;
Green, Lucie; Brooks, David; van Driel-Gesztelyi, Lidia; Mihailescu,
Teodora; To, Andy S. H.; Yardley, Stephanie; Valori, Gherardo
2022cosp...44.1361B Altcode:
Magnetic flux ropes are bundles of twisted magnetic field enveloping a
central axis. They harbor free magnetic energy and can be progenitors
of coronal mass ejections (CMEs). However, identifying flux ropes on
the Sun can be challenging. One of the key coronal observables that
has been shown to indicate the presence of a flux rope is a peculiar
bright coronal structure called a sigmoid. In this work, we show Hinode
EUV Imaging Spectrometer observations of sigmoidal active region (AR)
10977. We analyze the coronal plasma composition in the AR and its
evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma
with photospheric composition was observed in coronal loops close to
the main polarity inversion line during episodes of significant flux
cancellation, suggestive of the injection of photospheric plasma into
these loops driven by photospheric flux cancellation. Concurrently,
the increasingly sheared core field contained plasma with coronal
composition. As flux cancellation decreased and a sigmoid/flux
rope formed, the plasma evolved to an intermediate composition in
between photospheric and typical AR coronal compositions. Finally,
the flux rope contained predominantly photospheric plasma during and
after a failed eruption preceding the CME. Hence, plasma composition
observations of AR 10977 strongly support models of flux rope formation
by photospheric flux cancellation forcing magnetic reconnection first
at the photospheric level then at the coronal level.
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Title: What Determines Active Region Coronal Plasma Composition?
Authors: Mihailescu, Teodora; Baker, Deborah; Green, Lucie M.;
van Driel-Gesztelyi, Lidia; Long, David M.; Brooks, David H.; To,
Andy S. H.
2022ApJ...933..245M Altcode: 2022arXiv220505027M
The chemical composition of the solar corona is different from that
of the solar photosphere, with the strongest variation being observed
in active regions (ARs). Using data from the Extreme Ultraviolet
(EUV) Imaging Spectrometer (EIS) on Hinode, we present a survey of
coronal elemental composition as expressed in the first ionization
potential (FIP) bias in 28 ARs of different ages and magnetic flux
content, which are at different stages in their evolution. We find
no correlation between the FIP bias of an AR and its total unsigned
magnetic flux or age. However, there is a weak dependence of FIP
bias on the evolutionary stage, decreasing from 1.9 to 2.2 in ARs
with spots to 1.5-1.6 in ARs that are at more advanced stages of
the decay phase. FIP bias shows an increasing trend with average
magnetic flux density up to 200 G, but this trend does not continue
at higher values. The FIP bias distribution within ARs has a spread
between 0.4 and 1. The largest spread is observed in very dispersed
ARs. We attribute this to a range of physical processes taking place
in these ARs, including processes associated with filament channel
formation. These findings indicate that, while some general trends
can be observed, the processes influencing the composition of an AR
are complex and specific to its evolution, magnetic configuration,
or environment. The spread of FIP bias values in ARs shows a broad
match with that previously observed in situ in the slow solar wind.
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Title: Detection of Stellar-like Abundance Anomalies in the Slow
Solar Wind
Authors: Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia;
Warren, Harry P.; Yardley, Stephanie L.
2022ApJ...930L..10B Altcode: 2022arXiv220409332B
The elemental composition of the Sun's hot atmosphere, the corona,
shows a distinctive pattern that is different from the underlying
surface or photosphere. Elements that are easy to ionize in the
chromosphere are enhanced in abundance in the corona compared to
their photospheric values. A similar pattern of behavior is often
observed in the slow-speed (<500 km s<SUP>-1</SUP>) solar wind
and in solar-like stellar coronae, while a reversed effect is seen
in M dwarfs. Studies of the inverse effect have been hampered in the
past because only unresolved (point-source) spectroscopic data were
available for these stellar targets. Here we report the discovery of
several inverse events observed in situ in the slow solar wind using
particle-counting techniques. These very rare events all occur during
periods of high solar activity that mimic conditions more widespread
on M dwarfs. The detections allow a new way of connecting the slow
wind to its solar source and are broadly consistent with theoretical
models of abundance variations due to chromospheric fast-mode waves
with amplitudes of 8-10 km s<SUP>-1</SUP>, sufficient to accelerate
the solar wind. The results imply that M-dwarf winds are dominated
by plasma depleted in easily ionized elements and lend credence to
previous spectroscopic measurements.
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Title: Extending the FIP bias sample to magnetically active
stars. Challenging the FIP bias paradigm
Authors: Seli, B.; Oláh, K.; Kriskovics, L.; Kővári, Zs.; Vida,
K.; Balázs, L. G.; Laming, J. M.; van Driel-Gesztelyi, L.; Baker, D.
2022A&A...659A...3S Altcode: 2021arXiv211114735S
Context. The different elemental abundances of the photosphere and the
corona are striking features of not only the Sun, but of other stars
as well. This phenomenon is known as the first ionisation potential
(FIP) effect, and its strength can be characterized by the FIP bias,
the logarithmic abundance difference between low- and high-FIP elements
in the corona, compared to the photosphere. The FIP bias was shown to
depend on the surface temperature of the star. <BR /> Aims: We aim to
extend the T<SUB>eff</SUB>−FIP bias relationship to a larger stellar
sample and analyse the effect of other astrophysical parameters on
the relation (e.g. surface gravity, age, activity indicators). <BR
/> Methods: We compiled FIP bias and other parameters for 59 stars
for which coronal composition is available, now including evolved
stars. Using principal component analysis and linear discriminant
analysis, we searched for correlations with other astrophysical
parameters within the sample that may influence the stellar FIP
bias. <BR /> Results: Adding stars to the T<SUB>eff</SUB>−FIP bias
diagram unveiled new features in its structure. In addition to the
previously known relationship, there appears to be a second branch:
a parallel sequence about 0.5 dex above it. While the T<SUB>eff</SUB>
remains the main determinant of the FIP bias, other parameters such as
stellar activity indicators also have influence. We find three clusters
in the FIP bias determinant parameter space. One distinct group is
formed by the evolved stars. Two groups contain main sequence stars
in continuation separated roughly by the sign change of the FIP-bias
value. <BR /> Conclusions: The new branch of the T<SUB>eff</SUB>−FIP
bias diagram contains stars with higher activity level, in terms of
X-ray flux and rotational velocity. The Rossby number also seems
to be important, indicating possible dependence on the type of
dynamo operating in these stars influencing their FIP bias. The two
main-sequence clusters run from the earliest spectral types of A-F with
shallow convection zones through G-K-early-M stars with gradually deeper
convection zones, and they end with the fully convective M dwarf stars,
depicting the change of the dynamo type with the internal differences
of the main sequence stars in connection with the FIP-bias values.
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Title: Evolution of Plasma Composition in an Eruptive Flux Rope
Authors: Baker, D.; Green, L. M.; Brooks, D. H.; Démoulin, P.;
van Driel-Gesztelyi, L.; Mihailescu, T.; To, A. S. H.; Long, D. M.;
Yardley, S. L.; Janvier, M.; Valori, G.
2022ApJ...924...17B Altcode: 2021arXiv211011714B
Magnetic flux ropes are bundles of twisted magnetic field enveloping a
central axis. They harbor free magnetic energy and can be progenitors
of coronal mass ejections (CMEs). However, identifying flux ropes on
the Sun can be challenging. One of the key coronal observables that
has been shown to indicate the presence of a flux rope is a peculiar
bright coronal structure called a sigmoid. In this work, we show Hinode
EUV Imaging Spectrometer observations of sigmoidal active region (AR)
10977. We analyze the coronal plasma composition in the AR and its
evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma
with photospheric composition was observed in coronal loops close to
the main polarity inversion line during episodes of significant flux
cancellation, suggestive of the injection of photospheric plasma into
these loops driven by photospheric flux cancellation. Concurrently,
the increasingly sheared core field contained plasma with coronal
composition. As flux cancellation decreased and a sigmoid/flux
rope formed, the plasma evolved to an intermediate composition in
between photospheric and typical AR coronal compositions. Finally,
the flux rope contained predominantly photospheric plasma during and
after a failed eruption preceding the CME. Hence, plasma composition
observations of AR 10977 strongly support models of flux rope formation
by photospheric flux cancellation forcing magnetic reconnection first
at the photospheric level then at the coronal level.
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Title: Editorial Appreciation
Authors: Arregui, Iñigo; Leibacher, John; Mandrini, Cristina H.;
van Driel-Gesztelyi, Lidia; Wheatland, Michael S.
2022SoPh..297...11A Altcode:
No abstract at ADS
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Title: Investigating the origin of magnetic perturbations associated
with the FIP Effect
Authors: Murabito, M.; Stangalini, M.; Baker, D.; Valori, G.; Jess,
D. B.; Jafarzadeh, S.; Brooks, D. H.; Ermolli, I.; Giorgi, F.; Grant,
S. D. T.; Long, D. M.; van Driel-Gesztelyi, L.
2021A&A...656A..87M Altcode: 2021arXiv210811164M
Recently, magnetic oscillations were detected in the chromosphere
of a large sunspot and found to be linked to the coronal locations
where a first ionization potential (FIP) effect was observed. In
an attempt to shed light on the possible excitation mechanisms
of these localized waves, we further investigate the same data
by focusing on the relation between the spatial distribution of
the magnetic wave power and the overall field geometry and plasma
parameters obtained from multi-height spectropolarimetric non-local
thermodynamic equilibrium (NLTE) inversions of IBIS data. We find,
in correspondence with the locations where the magnetic wave energy
is observed at chromospheric heights, that the magnetic fields have
smaller scale heights, meaning faster expansions of the field lines,
which ultimately results in stronger vertical density stratification
and wave steepening. In addition, the acoustic spectrum of the
oscillations at the locations where magnetic perturbations are
observed is broader than that observed at other locations, which
suggests an additional forcing driver to the p-modes. Analysis of the
photospheric oscillations in the sunspot surroundings also reveals
a broader spectrum between the two opposite polarities of the active
region (the leading spot and the trailing opposite polarity plage),
and on the same side where magnetic perturbations are observed in
the umbra. We suggest that strong photospheric perturbations between
the two polarities are responsible for this broader spectrum of
oscillations, with respect to the p-mode spectrum, resulting in locally
excited acoustic waves that, after crossing the equipartition layer,
located close to the umbra-penumbra boundary at photopheric heights,
are converted into magnetic waves and steepen due to the strong
density gradient. <P />Movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141504/olm">https://www.aanda.org</A>
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Title: Global Contributions of Active Regions to the Solar Wind
Authors: Stansby, David; Green, Lucie; van Driel-Gesztelyi, Lidia;
Horbury, Timothy
2021AGUFMSH24C..04S Altcode:
Both coronal holes and active regions are source regions of the solar
wind. The distribution of these coronal structures across both space
and time within the corona is well known, and is driven by photospheric
magnetic flux evolution across the 11-year solar cycle. In turn these
coronal structures drive variability in the solar wind throughout
the heliosphere. To understand how important active regions are as
solar wind sources, we have used photospheric magnetic field maps from
the past four solar cycles to estimate what fraction of magnetic open
solar flux is rooted in active regions, a proxy for the fraction of all
solar wind originating in active regions. We found that the fractional
contribution of active regions to the solar wind varies between 30%
to 80% at any one time during solar maximum and is negligible at solar
minimum, showing a strong correlation with sunspot number. While active
regions are typically confined to latitudes ±30 in the corona, the
solar wind they produce can reach latitudes up to ±60. These results
quantify the importance of active regions in globally influencing the
whole heliosphere, providing motivation for further studies of active
regions as solar wind sources during Solar Cycle 25.
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Title: Active Region Contributions to the Solar Wind over Multiple
Solar Cycles
Authors: Stansby, David; Green, Lucie M.; van Driel-Gesztelyi, Lidia;
Horbury, Timothy S.
2021SoPh..296..116S Altcode: 2021arXiv210404417S
Both coronal holes and active regions are source regions of the solar
wind. The distribution of these coronal structures across both space and
time is well known, but it is unclear how much each source contributes
to the solar wind. In this study we use photospheric magnetic field maps
observed over the past four solar cycles to estimate what fraction
of magnetic open solar flux is rooted in active regions, a proxy
for the fraction of all solar wind originating in active regions. We
find that the fractional contribution of active regions to the solar
wind varies between 30% to 80% at any one time during solar maximum
and is negligible at solar minimum, showing a strong correlation with
sunspot number. While active regions are typically confined to latitudes
±30<SUP>∘</SUP> in the corona, the solar wind they produce can reach
latitudes up to ±60<SUP>∘</SUP>. Their fractional contribution to
the solar wind also correlates with coronal mass ejection rate, and
is highly variable, changing by ±20% on monthly timescales within
individual solar maxima. We speculate that these variations could
be driven by coronal mass ejections causing reconfigurations of the
coronal magnetic field on sub-monthly timescales.
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Title: Graphical evidence for the solar coronal structure during the
Maunder minimum: comparative study of the total eclipse drawings in
1706 and 1715
Authors: Hayakawa, Hisashi; Lockwood, Mike; Owens, Matthew J.; Sôma,
Mitsuru; Besser, Bruno P.; van Driel-Gesztelyi, Lidia
2021JSWSC..11....1H Altcode:
We discuss the significant implications of three eye-witness drawings
of the total solar eclipse on 1706 May 12 in comparison with two on 1715
May 3, for our understanding of space climate change. These events took
place just after what has been termed the "deep Maunder Minimum" but
fall within the "extended Maunder Minimum" being in an interval when the
sunspot numbers start to recover. Maria Clara Eimmert's image in 1706
is particularly important because she was both a highly accomplished
astronomical observer and an excellent artist: it was thought lost and
was only re-discovered in 2012. Being the earliest coronal drawings of
observational value yet identified, these drawings corroborate verbal
accounts a corona without significant streamers, seen at totality of
this and another eclipse event in 1652 during the Maunder Minimum. The
graphical evidence implies that the coronal solar magnetic field was
not lost but significantly weakened and the lack of coronal structure
means there was little discernable open flux (either polar or at lower
latitudes) even during the recovery phase of the Maunder Minimum. These
observations provide evidence for a different state of oscillation of
the solar dynamo, and hence behaviour of the Sun, in comparison with
that during normal solar cycle minima (when a streamer belt between
two polar coronal holes is visible) or near normal sunspot maxima
(when coronal structure is caused by coronal holes at all latitudes)
even to observers without a telescope.
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Title: Plasma Upflows Induced by Magnetic Reconnection Above an
Eruptive Flux Rope
Authors: Baker, Deborah; Mihailescu, Teodora; Démoulin, Pascal;
Green, Lucie M.; van Driel-Gesztelyi, Lidia; Valori, Gherardo; Brooks,
David H.; Long, David M.; Janvier, Miho
2021SoPh..296..103B Altcode: 2021arXiv210616137B
One of the major discoveries of Hinode's Extreme-ultraviolet
Imaging Spectrometer (EIS) is the presence of upflows at the edges
of active regions. As active regions are magnetically connected
to the large-scale field of the corona, these upflows are a likely
contributor to the global mass cycle in the corona. Here we examine
the driving mechanism(s) of the very strong upflows with velocities
in excess of 70 km s<SUP>−1</SUP>, known as blue-wing asymmetries,
observed during the eruption of a flux rope in AR 10977 (eruptive flare
SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations
combined with magnetic-field modeling to investigate the possible
link between the magnetic topology of the active region and the strong
upflows. A Potential Field Source Surface (PFSS) extrapolation of the
large-scale field shows a quadrupolar configuration with a separator
lying above the flux rope. Field lines formed by induced reconnection
along the separator before and during the flux-rope eruption are
spatially linked to the strongest blue-wing asymmetries in the upflow
regions. The flows are driven by the pressure gradient created when
the dense and hot arcade loops of the active region reconnect with
the extended and tenuous loops overlying it. In view of the fact
that separator reconnection is a specific form of the more general
quasi-separatrix (QSL) reconnection, we conclude that the mechanism
driving the strongest upflows is, in fact, the same as the one driving
the persistent upflows of ≈10 - 20 km s<SUP>−1</SUP> observed in
all active regions.
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Title: The Evolution of Plasma Composition during a Solar Flare
Authors: To, Andy S. H.; Long, David M.; Baker, Deborah; Brooks, David
H.; van Driel-Gesztelyi, Lidia; Laming, J. Martin; Valori, Gherardo
2021ApJ...911...86T Altcode: 2021arXiv210209985T
We analyze the coronal elemental abundances during a small flare using
Hinode/EIS observations. Compared to the preflare elemental abundances,
we observed a strong increase in coronal abundance of Ca XIV 193.84
Å, an emission line with low first ionization potential (FIP <
10 eV), as quantified by the ratio Ca/Ar during the flare. This is in
contrast to the unchanged abundance ratio observed using Si X 258.38
Å/S X 264.23 Å. We propose two different mechanisms to explain
the different composition results. First, the small flare-induced
heating could have ionized S, but not the noble gas Ar, so that the
flare-driven Alfvén waves brought up Si, S, and Ca in tandem via
the ponderomotive force which acts on ions. Second, the location of
the flare in strong magnetic fields between two sunspots may suggest
fractionation occurred in the low chromosphere, where the background
gas is neutral H. In this region, high-FIP S could behave more like a
low-FIP than a high-FIP element. The physical interpretations proposed
generate new insights into the evolution of plasma abundances in the
solar atmosphere during flaring, and suggests that current models must
be updated to reflect dynamic rather than just static scenarios.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Mandrini, Cristina H.; van Driel-Gesztelyi,
Lidia; Wheatland, Michael S.
2021SoPh..296...14L Altcode:
No abstract at ADS
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Title: Alfvénic Perturbations in a Sunspot Chromosphere Linked to
Fractionated Plasma in the Corona
Authors: Baker, Deborah; Stangalini, Marco; Valori, Gherardo; Brooks,
David H.; To, Andy S. H.; van Driel-Gesztelyi, Lidia; Démoulin,
Pascal; Stansby, David; Jess, David B.; Jafarzadeh, Shahin
2021ApJ...907...16B Altcode: 2020arXiv201204308B
In this study, we investigate the spatial distribution of highly
varying plasma composition around one of the largest sunspots of solar
cycle 24. Observations of the photosphere, chromosphere, and corona
are brought together with magnetic field modeling of the sunspot
in order to probe the conditions that regulate the degree of plasma
fractionation within loop populations of differing connectivities. We
find that, in the coronal magnetic field above the sunspot umbra,
the plasma has photospheric composition. Coronal loops rooted in the
penumbra contain fractionated plasma, with the highest levels observed
in the loops that connect within the active region. Tracing field
lines from regions of fractionated plasma in the corona to locations
of Alfvénic fluctuations detected in the chromosphere shows that they
are magnetically linked. These results indicate a connection between
sunspot chromospheric activity and observable changes in coronal
plasma composition.
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Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a
Solar Flare
Authors: French, R.; Judge, P. G.; Matthews, S.; van Driel-Gesztelyi,
L.; Long, D.
2020AGUFMSH045..03F Altcode:
Magnetic reconnection is thought to lie at the heart of energy release
in solar flares, but the process is not yet fully understood. We examine
spectropolarimetric data from the CoMP coronagraph, acquired a few hours
into the evolution of the September 10th 2017 X8.2-class flare. We
find a striking and spatially coherent low polarisation structure,
aligned with the hot plasma sheet observed in EUV. By elimination,
we find the significant depolarisation to be a result of small-scale
sub-pixel magnetic structure along the plasma sheet, consistent with
theory of reconnection instabilities. This interpretation of ongoing
reconnection is supported by further Hinode/EIS observations and AIA
DEMs, from well beyond the impulsive phase of the flare. The plasma
sheet remains visible in CoMP linear polarisation over a day into the
flare's evolution, several hours after its last appearance in EUV. We
conclude that polarisation measurements with new coronagraphs, such
the DKIST CRYO-NIRSP instrument, will further enhance our understanding
of magnetic reconnection during eruptive flares.
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Title: A new trigger mechanism for coronal mass ejections. The role
of confined flares and photospheric motions in the formation of hot
flux ropes
Authors: James, A. W.; Green, L. M.; van Driel-Gesztelyi, L.;
Valori, G.
2020A&A...644A.137J Altcode: 2020arXiv201011204J
Context. Many previous studies have shown that the magnetic precursor of
a coronal mass ejection (CME) takes the form of a magnetic flux rope,
and a subset of them have become known as "hot flux ropes" due to
their emission signatures in ∼10 MK plasma. <BR /> Aims: We seek to
identify the processes by which these hot flux ropes form, with a view
of developing our understanding of CMEs and thereby improving space
weather forecasts. <BR /> Methods: Extreme-ultraviolet observations
were used to identify five pre-eruptive hot flux ropes in the solar
corona and study how they evolved. Confined flares were observed in the
hours and days before each flux rope erupted, and these were used as
indicators of episodic bursts of magnetic reconnection by which each
flux rope formed. The evolution of the photospheric magnetic field
was observed during each formation period to identify the process(es)
that enabled magnetic reconnection to occur in the β < 1 corona and
form the flux ropes. <BR /> Results: The confined flares were found
to be homologous events and suggest flux rope formation times that
range from 18 hours to 5 days. Throughout these periods, fragments of
photospheric magnetic flux were observed to orbit around each other
in sunspots where the flux ropes had a footpoint. Active regions
with right-handed (left-handed) twisted magnetic flux exhibited
clockwise (anticlockwise) orbiting motions, and right-handed
(left-handed) flux ropes formed. <BR /> Conclusions: We infer that
the orbital motions of photospheric magnetic flux fragments about
each other bring magnetic flux tubes together in the corona, enabling
component reconnection that forms a magnetic flux rope above a flaring
arcade. This represents a novel trigger mechanism for solar eruptions
and should be considered when predicting solar magnetic activity. <P
/>Movies associated to Figs. 4, 8, 12, and 14 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038781/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
---------------------------------------------------------
Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
2020A&A...642A...8R Altcode:
Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
sensing instrument package of the ESA/NASA Solar Orbiter mission
that will explore the inner heliosphere and observe the Sun from
vantage points close to the Sun and out of the ecliptic. Solar Orbiter
will advance the "connection science" between solar activity and the
heliosphere. <BR /> Aims: With EUI we aim to improve our understanding
of the structure and dynamics of the solar atmosphere, globally as well
as at high resolution, and from high solar latitude perspectives. <BR />
Methods: The EUI consists of three telescopes, the Full Sun Imager and
two High Resolution Imagers, which are optimised to image in Lyman-α
and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
up to corona. The EUI is designed to cope with the strong constraints
imposed by the Solar Orbiter mission characteristics. Limited telemetry
availability is compensated by state-of-the-art image compression,
onboard image processing, and event selection. The imposed power
limitations and potentially harsh radiation environment necessitate
the use of novel CMOS sensors. As the unobstructed field of view of
the telescopes needs to protrude through the spacecraft's heat shield,
the apertures have been kept as small as possible, without compromising
optical performance. This led to a systematic effort to optimise the
throughput of every optical element and the reduction of noise levels
in the sensor. <BR /> Results: In this paper we review the design
of the two elements of the EUI instrument: the Optical Bench System
and the Common Electronic Box. Particular attention is also given to
the onboard software, the intended operations, the ground software,
and the foreseen data products. <BR /> Conclusions: The EUI will
bring unique science opportunities thanks to its specific design,
its viewpoint, and to the planned synergies with the other Solar
Orbiter instruments. In particular, we highlight science opportunities
brought by the out-of-ecliptic vantage point of the solar poles,
the high-resolution imaging of the high chromosphere and corona,
and the connection to the outer corona as observed by coronagraphs.
---------------------------------------------------------
Title: Dynamics of Late-stage Reconnection in the 2017 September 10
Solar Flare
Authors: French, Ryan J.; Matthews, Sarah A.; van Driel-Gesztelyi,
Lidia; Long, David M.; Judge, Philip G.
2020ApJ...900..192F Altcode: 2020arXiv200713377F
In this multi-instrument paper, we search for evidence of sustained
magnetic reconnection far beyond the impulsive phase of the X8.2-class
solar flare on 2017 September 10. Using Hinode/EIS, CoMP, SDO/AIA,
K-Cor, Hinode/XRT, RHESSI, and IRIS, we study the late-stage evolution
of the flare dynamics and topology, comparing signatures of reconnection
with those expected from the standard solar flare model. Examining
previously unpublished EIS data, we present the evolution of nonthermal
velocity and temperature within the famous plasma sheet structure,
for the first four hours of the flare's duration. On even longer
timescales, we use differential emission measures and polarization data
to study the longevity of the flare's plasma sheet and cusp structure,
discovering that the plasma sheet is still visible in observations
of CoMP linear polarization on 2017 September 11, long after its last
appearance in EUV. We deduce that magnetic reconnection of some form
is still ongoing at this time—27 hr after flare onset.
---------------------------------------------------------
Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a
Solar Flare
Authors: French, R.; Judge, P.; Matthews, S.; van Driel-Gesztelyi,
L.; Long, D.
2020SPD....5121102F Altcode:
Magnetic reconnection is thought to lie at the heart of energy release
in solar flares, but the process is not yet fully understood. We examine
spectropolarimetric data from the CoMP coronagraph, acquired a few hours
into the evolution of the September 10th 2017 X8.2-class flare. We
find a striking and spatially coherent low polarisation structure,
aligned with the hot plasma sheet observed in EUV. By elimination,
we find the significant depolarisation to be a result of small-scale
sub-pixel magnetic structure along the plasma sheet, consistent with
theory of reconnection instabilities. This interpretation of ongoing
reconnection is supported by further Hinode/EIS observations and AIA
DEMs, from well beyond the impulsive phase of the flare. The plasma
sheet remains visible in CoMP linear polarisation over a day into the
flare's evolution, several hours after its last appearance in EUV. We
conclude that polarisation measurements with new coronagraphs, such
the DKIST CRYO-NIRSP instrument, will further enhance our understanding
of magnetic reconnection during eruptive flares.
---------------------------------------------------------
Title: Editorial: Solar Wind at the Dawn of the Parker Solar Probe
and Solar Orbiter Era
Authors: Lapenta, Giovanni; Zhukov, Andrei; van Driel-Gesztelyi, Lidia
2020SoPh..295..103L Altcode:
Solar Wind 15 brought together almost 250 experts from all continents
of the world to discuss the current trends and future perspectives
of the research on the Sun and its solar wind. The present article
collection recaptures some of the highlights of their contributions.
---------------------------------------------------------
Title: Can Subphotospheric Magnetic Reconnection Change the Elemental
Composition in the Solar Corona?
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Brooks, David H.;
Démoulin, Pascal; Valori, Gherardo; Long, David M.; Laming, J. Martin;
To, Andy S. H.; James, Alexander W.
2020ApJ...894...35B Altcode: 2020arXiv200303325B
Within the coronae of stars, abundances of those elements with low
first ionization potential (FIP) often differ from their photospheric
values. The coronae of the Sun and solar-type stars mostly show
enhancements of low-FIP elements (the FIP effect) while more active
stars such as M dwarfs have coronae generally characterized by the
inverse-FIP effect (I-FIP). Here we observe patches of I-FIP effect
solar plasma in AR 12673, a highly complex βγδ active region. We
argue that the umbrae of coalescing sunspots, and more specifically
strong light bridges within the umbrae, are preferential locations for
observing I-FIP effect plasma. Furthermore, the magnetic complexity
of the active region and major episodes of fast flux emergence also
lead to repetitive and intense flares. The induced evaporation of
the chromospheric plasma in flare ribbons crossing umbrae enables
the observation of four localized patches of I-FIP effect plasma in
the corona of AR 12673. These observations can be interpreted in the
context of the ponderomotive force fractionation model which predicts
that plasma with I-FIP effect composition is created by the refraction
of waves coming from below the chromosphere. We propose that the waves
generating the I-FIP effect plasma in solar active regions are generated
by subphotospheric reconnection of coalescing flux systems. Although
we only glimpse signatures of I-FIP effect fractionation produced by
this interaction in patches on the Sun, on highly active M stars it
may be the dominant process.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Mandrini, Cristina H.; van Driel-Gesztelyi,
Lidia; Wheatland, Michael S.
2020SoPh..295....9L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a
Solar Flare
Authors: French, Ryan J.; Judge, Philip G.; Matthews, Sarah A.;
van Driel-Gesztelyi, Lidia
2019ApJ...887L..34F Altcode: 2019arXiv191112666F
We examine spectropolarimetric data from the Coronal Multi-channel
Polarimeter (CoMP) instrument, acquired during the evolution of the 2017
September 10 X8.2 solar flare on the western solar limb. CoMP captured
linearly polarized light from two emission lines of Fe XIII at 1074.7
and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot
plasma sheet lying above the bright flare loops and beneath the ejected
coronal mass ejection. The polarization has a striking and coherent
spatial structure, with unexpectedly small polarization aligned with
the plasma sheet. By elimination, we find that small-scale magnetic
field structure is needed to cause such significant depolarization,
and suggest that plasmoid formation during reconnection (associated
with the tearing-mode instability) creates magnetic structure on scales
below instrument resolution of 6 Mm. We conclude that polarization
measurements with new coronagraphs, such as the upcoming Daniel
K. Inouye Solar Telescope, will further enhance our understanding of
magnetic reconnection and development of turbulence in the solar corona.
---------------------------------------------------------
Title: Understanding the Plasma and Magnetic Field Evolution of a
Filament Using Observations and Nonlinear Force-free Field Modeling
Authors: Yardley, Stephanie L.; Savcheva, Antonia; Green, Lucie M.;
van Driel-Gesztelyi, Lidia; Long, David; Williams, David R.; Mackay,
Duncan H.
2019ApJ...887..240Y Altcode: 2019arXiv191101314Y
We present observations and magnetic field models of an intermediate
filament present on the Sun in 2012 August, associated with a polarity
inversion line that extends from AR 11541 in the east into the quiet
Sun at its western end. A combination of Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly, SDO/Helioseismic and Magnetic
Imager (HMI), and Global Oscillation Network Group Hα data allow
us to analyze the structure and evolution of the filament from 2012
August 4 23:00 UT to 2012 August 6 08:00 UT when the filament was in
equilibrium. By applying the flux rope insertion method, nonlinear
force-free field models of the filament are constructed using SDO/HMI
line-of-sight magnetograms as the boundary condition at the two times
given above. Guided by observed filament barbs, both modeled flux ropes
are split into three sections each with a different value of axial flux
to represent the nonuniform photospheric field distribution. The flux
in the eastern section of the rope increases by 4 × 10<SUP>20</SUP>
Mx between the two models, which is in good agreement with the amount
of flux canceled along the internal PIL of AR 11541, calculated to be
3.2 × 10<SUP>20</SUP> Mx. This suggests that flux cancellation builds
flux into the filament’s magnetic structure. Additionally, the number
of field line dips increases between the two models in the locations
where flux cancellation, the formation of new filament threads, and
growth of the filament is observed. This suggests that flux cancellation
associated with magnetic reconnection forms concave-up magnetic field
that lifts plasma into the filament. During this time, the free magnetic
energy in the models increases by 0.2 × 10<SUP>31</SUP> ergs.
---------------------------------------------------------
Title: Polarized radiative transfer, rotation measure fluctuations,
and large-scale magnetic fields
Authors: On, Alvina Y. L.; Chan, Jennifer Y. H.; Wu, Kinwah; Saxton,
Curtis J.; van Driel-Gesztelyi, Lidia
2019MNRAS.490.1697O Altcode: 2019arXiv190906703O; 2019MNRAS.tmp.2320O
Faraday rotation measure (RM) at radio wavelengths is commonly
used to diagnose large-scale magnetic fields. It is argued that
the length-scales on which magnetic fields vary in large-scale
diffuse astrophysical media can be inferred from correlations in the
observed RM. RM is a variable which can be derived from the polarized
radiative transfer equations in restrictive conditions. This paper
assesses the usage of rotation measure fluctuation (RMF) analyses for
magnetic field diagnostics in the framework of polarized radiative
transfer. We use models of various magnetic field configurations and
electron density distributions to show how density fluctuations could
affect the correlation length of the magnetic fields inferred from the
conventional RMF analyses. We caution against interpretations of RMF
analyses when a characteristic density is ill defined, e.g. in cases
of lognormal-distributed and fractal-like density structures. As the
spatial correlations are generally not the same in the line-of-sight
longitudinal direction and the sky plane direction, one also needs to
clarify the context of RMF when inferring from observational data. In
complex situations, a covariant polarized radiative transfer calculation
is essential to capture all aspects of radiative and transport
processes, which would otherwise ambiguate the interpretations of
magnetism in galaxy clusters and larger scale cosmological structures.
---------------------------------------------------------
Title: Flaring Activity of Proxima Centauri from TESS Observations:
Quasiperiodic Oscillations during Flare Decay and Inferences on the
Habitability of Proxima b
Authors: Vida, Krisztián; Oláh, Katalin; Kővári, Zsolt; van
Driel-Gesztelyi, Lidia; Moór, Attila; Pál, András
2019ApJ...884..160V Altcode: 2019arXiv190712580V
We analyze the light curve of the M5.5 dwarf Proxima Centauri obtained
by the Transiting Exoplanet Survey Satellite (TESS) in Sectors 11 and
12. In the ≈50 day long light curve we identified and analyzed 72
flare events. The flare rate was 1.49 events per day; in total, 7.2%
of the observing time was classified as flaring. The estimated flare
energies were on the order of 10<SUP>30</SUP>-10<SUP>32</SUP> erg in
the TESS passband (≈4.8× higher in bolometric energies, but on the
same order of magnitude). Most of the eruptions appeared in groups. Two
events showed quasiperiodic oscillations during their decay phase with
a timescale of a few hours, which could be caused by quasiperiodic
motions of the emitting plasma or oscillatory reconnection. From the
cumulative flare frequency distribution we estimate that superflares
with energy output of 10<SUP>33</SUP> erg are expected to occur three
times per year, while magnitude larger events (with 10<SUP>34</SUP> erg)
can occur every second year. This reduces the chances of habitability
of Proxima Cen b, although earlier numerical models did not rule out
the existence of liquid water on the planetary surface. We did not
find any obvious signs of planetary transit in the light curve.
---------------------------------------------------------
Title: Spectroscopic Signatures of Plasma-Sheet Dynamics in a
Solar Flare
Authors: French, Ryan J.; Matthews, Sarah A.; van Driel-Gesztelyi,
Lidia; Long, David M.
2019shin.confE.186F Altcode:
According to the standard eruptive flare model, energy is released
in a current sheet formed in the wake of an erupting flux rope. The
current sheet itself is theoretically predicted to be 10m wide,
thus representing a significant challenge for current observational
techniques. However, a handful of observations have reported enhanced
emission from the region surrounding the current sheet, often referred
to as the plasma-sheet. Since this region must respond to processes
occurring in the current sheet itself, the study of its properties
offers the possibility to indirectly probe conditions in the current
sheet related to the reconnection process. Recent observations
(Warren al., (2018), Li et al., 2018) have demonstrated the presence
of enhanced nonthermal velocities in the current sheet observed in the
10th September 2017 X8.2 class flare, consistent with the presence of
turbulence and possible tearing mode instability. In this study, we
combine observations from the Extreme-ultraviolet Imaging Spectrometer
(EIS) and Atmospheric Imaging Assembly (AIA) to explore the relationship
between the Alfven speed calculated for different plasma beta regimes,
observed non-thermal velocity measurements, and the evolution of the
plasma-sheet to test for the presence of the plasmoid instability.
---------------------------------------------------------
Title: Transient Inverse-FIP Plasma Composition Evolution within a
Solar Flare
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Brooks, David
H.; Valori, Gherardo; James, Alexander W.; Laming, J. Martin; Long,
David M.; Démoulin, Pascal; Green, Lucie M.; Matthews, Sarah A.;
Oláh, Katalin; Kővári, Zsolt
2019ApJ...875...35B Altcode: 2019arXiv190206948B
Understanding elemental abundance variations in the solar corona
provides an insight into how matter and energy flow from the
chromosphere into the heliosphere. Observed variations depend on the
first ionization potential (FIP) of the main elements of the Sun’s
atmosphere. High-FIP elements (>10 eV) maintain photospheric
abundances in the corona, whereas low-FIP elements have enhanced
abundances. Conversely, inverse FIP (IFIP) refers to the enhancement of
high-FIP or depletion of low-FIP elements. We use spatially resolved
spectroscopic observations, specifically the Ar XIV/Ca XIV intensity
ratio, from Hinode’s Extreme-ultraviolet Imaging Spectrometer to
investigate the distribution and evolution of plasma composition
within two confined flares in a newly emerging, highly sheared
active region. During the decay phase of the first flare, patches
above the flare ribbons evolve from the FIP to the IFIP effect, while
the flaring loop tops show a stronger FIP effect. The patch and loop
compositions then evolve toward the preflare basal state. We propose
an explanation of how flaring in strands of highly sheared emerging
magnetic fields can lead to flare-modulated IFIP plasma composition
over coalescing umbrae which are crossed by flare ribbons. Subsurface
reconnection between the coalescing umbrae leads to the depletion of
low-FIP elements as a result of an increased wave flux from below. This
material is evaporated when the flare ribbons cross the umbrae. Our
results are consistent with the ponderomotive fractionation model for
the creation of IFIP-biased plasma.
---------------------------------------------------------
Title: Modeling the Effect of Mass-draining on Prominence Eruptions
Authors: Jenkins, Jack M.; Hopwood, Matthew; Démoulin, Pascal; Valori,
Gherardo; Aulanier, Guillaume; Long, David M.; van Driel-Gesztelyi,
Lidia
2019ApJ...873...49J Altcode: 2019arXiv190110970J
Quiescent solar prominences are observed within the solar atmosphere
for up to several solar rotations. Their eruption is commonly preceded
by a slow increase in height that can last from hours to days. This
increase in the prominence height is believed to be due to their host
magnetic flux rope transitioning through a series of neighboring
quasi-equilibria before the main loss of equilibrium that drives
the eruption. Recent work suggests that the removal of prominence
mass from a stable, quiescent flux rope is one possible cause for
this change in height. However, these conclusions are drawn from
observations and are subject to interpretation. Here, we present a
simple model to quantify the effect of “mass-draining” during the
pre-eruptive height evolution of a solar flux rope. The flux rope is
modeled as a line current suspended within a background potential
magnetic field. We first show that the inclusion of mass, up to
10<SUP>12</SUP> kg, can modify the height at which the line current
experiences loss of equilibrium by up to 14%. Next, we show that
the rapid removal of mass prior to the loss of equilibrium can allow
the height of the flux rope to increase sharply and without an upper
bound as it approaches its loss-of-equilibrium point. This indicates
that the critical height for the loss of equilibrium can occur at a
range of heights depending explicitly on the amount and evolution of
mass within the flux rope. Finally, we demonstrate that for the same
amount of drained mass, the effect on the height of the flux rope is
up to two orders of magnitude larger for quiescent prominences than
for active region prominences.
---------------------------------------------------------
Title: The quest for stellar coronal mass ejections in late-type
stars. I. Investigating Balmer-line asymmetries of single stars in
Virtual Observatory data
Authors: Vida, Krisztián; Leitzinger, Martin; Kriskovics, Levente;
Seli, Bálint; Odert, Petra; Kovács, Orsolya Eszter; Korhonen, Heidi;
van Driel-Gesztelyi, Lidia
2019A&A...623A..49V Altcode: 2019arXiv190104229V
Context. Flares and coronal mass ejections (CMEs) can have deleterious
effects on their surroundings: they can erode or completely destroy
atmospheres of orbiting planets over time and also have high importance
in stellar evolution. Most of the CME detections in the literature
are single events found serendipitously sparse for statistical
investigation. <BR /> Aims: We aimed to gather a large amount of
spectral data of M-dwarfs to drastically increase the number of known
events to make statistical analysis possible in order to study the
properties of potential stellar CMEs. <BR /> Methods: Using archival
spectral data we investigated asymmetric features of Balmer-lines,
which could indicate the Doppler-signature of ejected material. <BR
/> Results: Of more than 5500 spectra we find 478 that have line
asymmetries - including nine larger events, in terms of velocity and
mass - on 25 objects, with 1.2-19.6 events per day on objects with
line asymmetries. Most events are connected with enhanced peaks of
Balmer-lines, indicating that these are connected to flares similar
to solar events. In most cases the detected speed does not reach
surface escape velocity: the typical observed maximum velocities are
on the order of 100-300 km s<SUP>-1</SUP>, while the typical masses
of the ejecta were on the order of 10<SUP>15</SUP>-10<SUP>18</SUP>
g. Statistical analysis of the events suggests that these events are
more frequent on cooler stars with stronger chromospheric activity. <BR
/> Conclusions: If the detected events correspond to CMEs, the
detected maximum velocities are lower than those observed on the Sun,
while event rates were somewhat lower than we could expect from the
solar case. If the velocities are not distorted significantly due to
a projection effect, these findings may support the idea that most of
the coronal mass ejections could be suppressed by a strong magnetic
field. Alternatively, it is possible that we can observe only an early
low-coronal phase of the events before being accelerated at higher
altitudes. Our findings could indicate that later-type, active dwarfs
could be a safer environment for exoplanetary systems CME-wise than
previously thought, and atmosphere loss due to radiation effects would
play a stronger role in exoplanetary atmosphere evolution than CMEs.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Mandrini, Cristina H.; van Driel-Gesztelyi,
Lidia; Wheatland, Michael S.
2019SoPh..294....3L Altcode:
We are pleased to acknowledge, with sincere thanks, the following
colleagues who supported the community by reviewing articles for Solar
Physics during 2018.
---------------------------------------------------------
Title: An Observationally Constrained Model of a Flux Rope that
Formed in the Solar Corona
Authors: James, Alexander W.; Valori, Gherardo; Green, Lucie M.; Liu,
Yang; Cheung, Mark C. M.; Guo, Yang; van Driel-Gesztelyi, Lidia
2018csc..confE...9J Altcode:
Coronal mass ejections (CMEs) are large-scale eruptions of plasma
from the coronae of stars, and it is important to study the plasma
processes involved in their initiation. This first requires us to
understand the pre-eruptive configuration of CMEs. To this end, we used
extreme-ultraviolet (EUV) observations from SDO/AIA to conclude that a
magnetic flux rope formed high-up in the solar corona above NOAA Active
Region 11504 before it erupted on 2012 June 14. Then, we used data from
SDO/HMI and our knowledge of the EUV observations to model the coronal
magnetic field of the active region one hour prior to eruption using a
nonlinear force-free field extrapolation. The extrapolation revealed
a flux rope that matches the EUV observations remarkably well, with
its axis 120 Mm above the photosphere. The erupting structure was not
observed to kink, but the decay index near the apex of the axis of
the extrapolated flux rope is comparable to typical critical values
required for the onset of the torus instability. Therefore, we suggest
that the torus instability drove the eruption of the flux rope.
---------------------------------------------------------
Title: Understanding the Role of Mass-Unloading in a Filament Eruption
Authors: Jenkins, Jack; Long, David; van Driel-Gesztelyi, Lidia;
Carlyle, Jack; Hopwood, Matthew
2018csc..confE..17J Altcode:
We combine observations of a partial filament eruption on 11
December 2011 with a simple line-current model to demonstrate
that including mass is an important next step for understanding
solar eruptions. Observations from the Solar Terrestrial Relations
Observatory-Behind (STEREO-B) and the Solar Dynamics Observatory (SDO)
spacecraft were used to remove line-of-sight projection effects in
filament motion and correlate the effect of plasma dynamics with
the evolution of the filament height. The two viewpoints enable
the amount of mass drained to be estimated, and an investigation of
the subsequent radial expansion and eruption of the filament. We use
these observational measurements to constrain a line-current model and
quantitatively demonstrate the important role that the presence and
draining of mass has in the lead-up to solar eruptions. Specifically,
we show that the balance of magnetic and gravitational forces acting
on the line-current is increasingly sensitive to mass perturbations
as it approaches its loss-of-equilibrium. Finally, we conclude that
the eruption of the observed filament was restrained until 70% of the
mass had drained from the structure.
---------------------------------------------------------
Title: The Role of Flux Cancellation in Eruptions from Bipolar ARs
Authors: Yardley, S. L.; Green, L. M.; van Driel-Gesztelyi, L.;
Williams, D. R.; Mackay, D. H.
2018ApJ...866....8Y Altcode: 2018arXiv180810635Y
The physical processes or trigger mechanisms that lead to the eruption
of coronal mass ejections (CMEs), the largest eruptive phenomenon in the
heliosphere, are still undetermined. Low-altitude magnetic reconnection
associated with flux cancellation appears to play an important role in
CME occurrence as it can form an eruptive configuration and reduce the
magnetic flux that contributes to the overlying, stabilizing field. We
conduct the first comprehensive study of 20 small bipolar ARs (ARs)
in order to probe the role of flux cancellation as an eruption trigger
mechanism. We categorize eruptions from the bipolar regions into three
types related to location, and find that the type of eruption produced
depends on the evolutionary stage of the AR. In addition, we find that
ARs that form eruptive structures by flux cancellation (low-altitude
reconnection) had, on average, lower flux cancellation rates than the AR
sample as a whole. Therefore, while flux cancellation plays a key role,
by itself it is insufficient for the production of an eruption. The
results provide supporting evidence that although flux cancellation
in a sheared arcade may be able to build an eruptive configuration,
a successful eruption depends upon the removal of sufficient overlying
and stabilizing field. Convergence of the bipole polarities also appears
to be present in regions that produce an eruption. These findings have
important implications for understanding the physical processes that
occur on our Sun in relation to CMEs and for space weather forecasting.
---------------------------------------------------------
Title: Sequential Eruptions Triggered by Flux Emergence: Observations
and Modeling
Authors: Dacie, S.; Török, T.; Démoulin, P.; Linton, M. G.; Downs,
C.; van Driel-Gesztelyi, L.; Long, D. M.; Leake, J. E.
2018ApJ...862..117D Altcode: 2018arXiv180700020D
We describe and analyze observations by the Solar Dynamics Observatory
of the emergence of a small, bipolar active region within an area of
unipolar magnetic flux that was surrounded by a circular, quiescent
filament. Within only 8 hours from the start of the emergence, a
partial splitting of the filament and two consecutive coronal mass
ejections took place. We argue that all three dynamic events occurred
as a result of particular magnetic-reconnection episodes between
the emerging bipole and the pre-existing coronal magnetic field. To
substantiate our interpretation, we consider 3D magnetohydrodynamic
simulations that model the emergence of magnetic flux in the vicinity of
a large-scale coronal flux rope. The simulations qualitatively reproduce
most of the reconnection episodes suggested by the observations, as
well as the filament splitting, the first eruption, and the formation
of sheared/twisted fields that may have played a role in the second
eruption. Our results suggest that the position of emerging flux with
respect to the background magnetic configuration is a crucial factor for
the resulting evolution, while previous results suggest that parameters
such as the orientation or the amount of emerging flux are important
as well. This poses a challenge for predicting the onset of eruptions
that are triggered by flux emergence, and calls for a detailed survey
of the relevant parameter space by means of numerical simulations.
---------------------------------------------------------
Title: Solar Cycle Observations of the Neon Abundance in the
Sun-as-a-star
Authors: Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia;
Warren, Harry P.
2018ApJ...861...42B Altcode: 2018arXiv180507032B
Properties of the Sun’s interior can be determined accurately
from helioseismological measurements of solar oscillations. These
measurements, however, are in conflict with photospheric elemental
abundances derived using 3D hydrodynamic models of the solar
atmosphere. This divergence of theory and helioseismology is known as
the “solar modeling problem.” One possible solution is that the
photospheric neon abundance, which is deduced indirectly by combining
the coronal Ne/O ratio with the photospheric O abundance, is larger
than generally accepted. There is some support for this idea from
observations of cool stars. The Ne/O abundance ratio has also been
found to vary with the solar cycle in the slowest solar wind streams
and coronal streamers, and the variation from solar maximum to minimum
in streamers (∼0.1-0.25) is large enough to potentially bring some
of the solar models into agreement with the seismic data. Here we use
daily sampled observations from the EUV Variability Experiment on the
Solar Dynamics Observatory taken in 2010-2014, to investigate whether
the coronal Ne/O abundance ratio shows a variation with the solar cycle
when the Sun is viewed as a star. We find only a weak dependence on,
and moderate anti-correlation with, the solar cycle with the ratio
measured around 0.2-0.3 MK falling from 0.17 at solar minimum to
0.11 at solar maximum. The effect is amplified at higher temperatures
(0.3-0.6 MK) with a stronger anti-correlation and the ratio falling
from 0.16 at solar minimum to 0.08 at solar maximum. The values we
find at solar minimum are too low to solve the solar modeling problem.
---------------------------------------------------------
Title: Understanding the Role of Mass-Unloading in a Filament Eruption
Authors: Jenkins, Jack Michael; Long, David; van Driel-Gesztelyi,
Lidia; Carlyle, Jack
2018tess.conf10907J Altcode:
Solar filaments are persistent features on the solar surface,
lasting from days to months before either successfully erupting into
the heliosphere as part of a CME, or collapsing and returning the
suspended plasma to the chromosphere. To date, the consensus has
been that the plasma comprising the filament plays no significant
role in the global evolution of the host flux rope. As a result,
little effort has been made to quantify the impact that mass has on
the evolution of magnetic structures in the solar atmosphere. Here we
present observations and analysis that suggest that the inclusion of
mass is an important next step to fully understand solar eruptions. A
partial filament eruption that occurred on 11 December 2011 was
observed by both the Solar Terrestrial Relations Observatory-Behind
(STEREO-B) and the Solar Dynamics Observatory (SDO) spacecraft. The
combination of multiple perspectives from different locations within
the heliosphere allowed the removal of line-of-sight projection
effects, and the correlation of plasma dynamics to the evolution in
filament height. Our results show that 70\% of the measurable filament
mass drained shortly \textit{prior} to a change in the height--time
expansion profile of the remaining filament material from a shallow
to steeper exponential. A proxy was then formulated to test whether
the observed mass-unloading was responsible for this observed change
in behaviour. This proxy is defined as the ratio between the upward
force supplied to the host flux rope due to this mass-unloading and
the restraining force caused by the tension of the overlying magnetic
field. A ratio range of between 1.8 and 4.1 was found, indicating that
the upward force as a result of the the mass-unloading dominated the
evolution. We conclude that the unloading of filament mass from the
host flux rope was likely responsible for the accelerated expansion.
---------------------------------------------------------
Title: Václav Bumba (1925 - 2018)
Authors: Kotrč, Pavel; Heinzel, Petr; Sobotka, Michal; Ambrož,
Pavel; van Driel-Gesztelyi, Lidia
2018SoPh..293...40K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Observationally Constrained Model of a Flux Rope that
Formed in the Solar Corona
Authors: James, Alexander W.; Valori, Gherardo; Green, Lucie M.; Liu,
Yang; Cheung, Mark C. M.; Guo, Yang; van Driel-Gesztelyi, Lidia
2018ApJ...855L..16J Altcode: 2018arXiv180207965J
Coronal mass ejections (CMEs) are large-scale eruptions of plasma
from the coronae of stars. Understanding the plasma processes involved
in CME initiation has applications for space weather forecasting and
laboratory plasma experiments. James et al. used extreme-ultraviolet
(EUV) observations to conclude that a magnetic flux rope formed in
the solar corona above NOAA Active Region 11504 before it erupted on
2012 June 14 (SOL2012-06-14). In this work, we use data from the Solar
Dynamics Observatory (SDO) to model the coronal magnetic field of the
active region one hour prior to eruption using a nonlinear force-free
field extrapolation, and find a flux rope reaching a maximum height
of 150 Mm above the photosphere. Estimations of the average twist of
the strongly asymmetric extrapolated flux rope are between 1.35 and
1.88 turns, depending on the choice of axis, although the erupting
structure was not observed to kink. The decay index near the apex
of the axis of the extrapolated flux rope is comparable to typical
critical values required for the onset of the torus instability,
so we suggest that the torus instability drove the eruption.
---------------------------------------------------------
Title: Coronal Elemental Abundances in Solar Emerging Flux Regions
Authors: Baker, Deborah; Brooks, David H.; van Driel-Gesztelyi,
Lidia; James, Alexander W.; Démoulin, Pascal; Long, David M.; Warren,
Harry P.; Williams, David R.
2018ApJ...856...71B Altcode: 2018arXiv180108424B
The chemical composition of solar and stellar atmospheres differs from
the composition of their photospheres. Abundances of elements with low
first ionization potential (FIP) are enhanced in the corona relative
to high-FIP elements with respect to the photosphere. This is known as
the FIP effect and it is important for understanding the flow of mass
and energy through solar and stellar atmospheres. We used spectroscopic
observations from the Extreme-ultraviolet Imaging Spectrometer on board
the Hinode observatory to investigate the spatial distribution and
temporal evolution of coronal plasma composition within solar emerging
flux regions inside a coronal hole. Plasma evolved to values exceeding
those of the quiet-Sun corona during the emergence/early-decay phase
at a similar rate for two orders of magnitude in magnetic flux, a rate
comparable to that observed in large active regions (ARs) containing
an order of magnitude more flux. During the late-decay phase, the rate
of change was significantly faster than what is observed in large,
decaying ARs. Our results suggest that the rate of increase during the
emergence/early-decay phase is linked to the fractionation mechanism
that leads to the FIP effect, whereas the rate of decrease during
the later decay phase depends on the rate of reconnection with the
surrounding magnetic field and its plasma composition.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Mandrini, Cristina H.; van Driel-Gesztelyi,
Lidia; Wheatland, Michael S.
2018SoPh..293...14L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Understanding the Role of Mass-Unloading in a Filament Eruption
Authors: Jenkins, J. M.; Long, D. M.; van Driel-Gesztelyi, L.;
Carlyle, J.
2018SoPh..293....7J Altcode: 2017arXiv171102565J
We describe a partial filament eruption on 11 December 2011 that
demonstrates that the inclusion of mass is an important next step for
understanding solar eruptions. Observations from the Solar Terrestrial
Relations Observatory-Behind (STEREO-B) and the Solar Dynamics
Observatory (SDO) spacecraft were used to remove line-of-sight
projection effects in filament motion and correlate the effect
of plasma dynamics with the evolution of the filament height. Flux
cancellation and nearby flux emergence are shown to have played a role
in increasing the height of the filament prior to eruption. The two
viewpoints allow the quantitative estimation of a large mass-unloading,
the subsequent radial expansion, and the eruption of the filament to be
investigated. A 1.8 to 4.1 lower-limit ratio between gravitational and
magnetic-tension forces was found. We therefore conclude that following
the loss-of-equilibrium of the flux-rope, the radial expansion of
the flux-rope was restrained by the filamentary material until 70%
of the mass had evacuated the structure through mass-unloading.
---------------------------------------------------------
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
2018smf..book..317C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-thermal distributions and energy transport in the solar
flares
Authors: Matthews, Sarah; del Zanna, Guilio; Calcines, Ariadna;
Mason, Helen; Mathioudakis, Mihalis; Culhane, Len; Harra, Louise;
van Driel-Gesztelyi, Lidia; Green, Lucie; Long, David; Baker, Deb;
Valori, Gherardo
2017arXiv171200773M Altcode:
Determining the energy transport mechanisms in flares remains a central
goal in solar flares physics that is still not adequately answered
by the 'standard flare model'. In particular, the relative roles of
particles and/or waves as transport mechanisms, the contributions of low
energy protons and ions to the overall flare budget, and the limits of
low energy non-thermal electron distribution are questions that still
cannot be adequately reconciled with current instrumentation. In this
'White Paper' submitted in response to the call for inputs to the Next
Generation Solar Physics Mission review process initiated by JAXA,
NASA and ESA in 2016, we outline the open questions in this area and
possible instrumentation that could provide the required observations
to help answer these and other flare-related questions.
---------------------------------------------------------
Title: Editorial: Last Print Issue of Solar Physics
Authors: Leibacher, John; Mandrini, Cristina H.; van Driel-Gesztelyi,
Lidia; Wheatland, Michael S.
2017SoPh..292..196L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Field distribution of magnetograms from simulations of active
region formation
Authors: Dacie, S.; van Driel-Gesztelyi, L.; Démoulin, P.; Linton,
M. G.; Leake, J. E.; MacTaggart, D.; Cheung, M. C. M.
2017A&A...606A..34D Altcode:
Context. The evolution of the photospheric magnetic field distributions
(probability densities) has previously been derived for a set of active
regions. Photospheric field distributions are a consequence of physical
processes that are difficult to determine from observations alone. <BR
/> Aims: We analyse simulated magnetograms from numerical simulations,
which model the emergence and decay of active regions. These simulations
have different experimental set-ups and include different physical
processes, allowing us to investigate the relative importance of
convection, magnetic buoyancy, magnetic twist, and braiding for flux
emergence. <BR /> Methods: We specifically studied the photospheric
field distributions (probability densities found with a kernel density
estimation analysis) and compared the results with those found from
observations. <BR /> Results: Simulations including convection most
accurately reproduce the observed evolution of the photospheric field
distributions during active region evolution. <BR /> Conclusions: This
indicates that convection may play an important role during the decay
phase and also during the formation of active regions, particularly
for low flux density values.
---------------------------------------------------------
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
2017SSRv..210..317C Altcode: 2016SSRv..tmp...46C
We present a contemporary view of how solar active region
magnetic fields are understood to be generated, transported and
dispersed. Empirical trends of active region properties that guide model
development are discussed. Physical principles considered important
for active region evolution are introduced and advances in modeling
are reviewed.
---------------------------------------------------------
Title: The 2015 St Patrick's Day Storm: Origins
Authors: Carlyle, Jack; van Driel-Gesztelyi, Lidia; Zuccarello,
Francesco; James, Alexander; Williams, David
2017SPD....4840402C Altcode:
The magnetic storm experienced at Earth on St. Patrick's Day 2015 had
been the strongest of cycle 24 (at that time) with a measured DST of
-223 nT, though it was not expected to cause much of a disturbance. In
this work we study the solar source region of several peculiar
eruptions, leading to the formation and destruction of various
structures, in the week leading up to the storm, and determine the
true sequence of events. The evolution of the magnetic flux at the
solar surface is examined in order to place suspected flux-ropes
into context, and the evolution of the magnetic connectivities
is described alongside a PFSS model of the surrounding region. The
balance between positive and negative flux directly before two key
eruptions is investigated in detail, in order to ascertain whether
particular trigger mechanisms are feasible explanations. As well as
these magnetic investigations, the column density of plasma involved
is calculated from extreme ultraviolet images, and this is used to
estimate the total mass of one filament, as well as select other
features relevant to the eruptions. This information is then used to
comment on the energy budgets and requirements of several processes in
order to best understand the underlying drivers of this event.Previous
studies on the St. Patrick's Day Storm are also incorporated into this
work, and an attempt is made to reconcile the disparate conclusions
drawn by the scientific community as to why this storm was not only
so effective, but also a major forecasting failure.
---------------------------------------------------------
Title: A Solar cycle correlation of coronal element abundances in
Sun-as-a-star observations
Authors: Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia;
Warren, Harry P.
2017NatCo...8..183B Altcode: 2018arXiv180200563B
The elemental composition in the coronae of low-activity solar-like
stars appears to be related to fundamental stellar properties such as
rotation, surface gravity, and spectral type. Here we use full-Sun
observations from the Solar Dynamics Observatory, to show that when
the Sun is observed as a star, the variation of coronal composition
is highly correlated with a proxy for solar activity, the F10.7 cm
radio flux, and therefore with the solar cycle phase. Similar cyclic
variations should therefore be detectable spectroscopically in X-ray
observations of solar analogs. The plasma composition in full-disk
observations of the Sun is related to the evolution of coronal magnetic
field activity. Our observations therefore introduce an uncertainty
into the nature of any relationship between coronal composition and
fixed stellar properties. The results highlight the importance of
systematic full-cycle observations for understanding the elemental
composition of solar-like stellar coronae.
---------------------------------------------------------
Title: A study of the long term evolution in active region upflows
Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc;
Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah;
Culhane, J. Leonard; Démoulin, Pascal
2017PASJ...69...47H Altcode:
Since their discovery, upflows at the edges of active regions have
attracted a lot of interest, primarily as they could potentially
contribute to the slow solar wind. One aspect that has not been studied
yet is how the long term evolution of active regions impacts the
upflows. In this work, we analyze one active region that survives three
solar rotations. We track how the flows change with time. We use local
and global modeling of the decaying active region to determine how the
age of the active region will impact the extent of the open magnetic
fields, and then how some of the upflows could become outflows. We
finish with a discussion of how these results, set in a broader context,
can be further developed with the Solar Orbiter mission.
---------------------------------------------------------
Title: On-Disc Observations of Flux Rope Formation Prior to Its
Eruption
Authors: James, A. W.; Green, L. M.; Palmerio, E.; Valori, G.; Reid,
H. A. S.; Baker, D.; Brooks, D. H.; van Driel-Gesztelyi, L.; Kilpua,
E. K. J.
2017SoPh..292...71J Altcode: 2017arXiv170310837J
Coronal mass ejections (CMEs) are one of the primary manifestations of
solar activity and can drive severe space weather effects. Therefore,
it is vital to work towards being able to predict their
occurrence. However, many aspects of CME formation and eruption
remain unclear, including whether magnetic flux ropes are present
before the onset of eruption and the key mechanisms that cause CMEs
to occur. In this work, the pre-eruptive coronal configuration of
an active region that produced an interplanetary CME with a clear
magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid
appears in extreme-ultraviolet (EUV) data two hours before the onset
of the eruption (SOL2012-06-14), which is interpreted as a signature
of a right-handed flux rope that formed prior to the eruption. Flare
ribbons and EUV dimmings are used to infer the locations of the flux
rope footpoints. These locations, together with observations of the
global magnetic flux distribution, indicate that an interaction between
newly emerged magnetic flux and pre-existing sunspot field in the days
prior to the eruption may have enabled the coronal flux rope to form
via tether-cutting-like reconnection. Composition analysis suggests
that the flux rope had a coronal plasma composition, supporting our
interpretation that the flux rope formed via magnetic reconnection in
the corona. Once formed, the flux rope remained stable for two hours
before erupting as a CME.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Mandrini, Cristina H.; van Driel-Gesztelyi,
Lidia; Wheatland, Michael S.
2017SoPh..292...19L Altcode:
We are pleased to acknowledge, with sincere thanks, the following
referees who supported the community by refereeing articles for Solar
Physics during 2016.
---------------------------------------------------------
Title: Evolution of the magnetic field distribution of active regions
Authors: Dacie, S.; Démoulin, P.; van Driel-Gesztelyi, L.; Long,
D. M.; Baker, D.; Janvier, M.; Yardley, S. L.; Pérez-Suárez, D.
2016A&A...596A..69D Altcode: 2016arXiv160903723D
<BR /> Aims: Although the temporal evolution of active regions (ARs)
is relatively well understood, the processes involved continue to be
the subject of investigation. We study how the magnetic field of a
series of ARs evolves with time to better characterise how ARs emerge
and disperse. <BR /> Methods: We examined the temporal variation in
the magnetic field distribution of 37 emerging ARs. A kernel density
estimation plot of the field distribution was created on a log-log
scale for each AR at each time step. We found that the central portion
of the distribution is typically linear, and its slope was used to
characterise the evolution of the magnetic field. <BR /> Results:
The slopes were seen to evolve with time, becoming less steep as the
fragmented emerging flux coalesces. The slopes reached a maximum value
of -1.5 just before the time of maximum flux before becoming steeper
during the decay phase towards the quiet-Sun value of -3. This behaviour
differs significantly from a classical diffusion model, which produces
a slope of -1. These results suggest that simple classical diffusion
is not responsible for the observed changes in field distribution, but
that other processes play a significant role in flux dispersion. <BR />
Conclusions: We propose that the steep negative slope seen during the
late-decay phase is due to magnetic flux reprocessing by (super)granular
convective cells.
---------------------------------------------------------
Title: Editorial: 50 Years of Solar Physics
Authors: Charbonneau, Paul; Leibacher, John; Mandrini, Cristina;
van Driel-Gesztelyi, Lidia; Wheatland, Michael S.
2016SoPh..291.3461C Altcode: 2016SoPh..tmp..189C
No abstract at ADS
---------------------------------------------------------
Title: Preface to Topical Issue: Waves in the Solar Corona: From
Microphysics to Macrophysics
Authors: Nakariakov, V. M.; Pascoe, D. J.; Sych, R.; van
Driel-Gesztelyi, L.
2016SoPh..291.3139N Altcode: 2016SoPh..tmp..187N
No abstract at ADS
---------------------------------------------------------
Title: Flux Cancellation and the Evolution of the Eruptive Filament
of 2011 June 7
Authors: Yardley, S. L.; Green, L. M.; Williams, D. R.; van
Driel-Gesztelyi, L.; Valori, G.; Dacie, S.
2016ApJ...827..151Y Altcode: 2016arXiv160608264Y
We investigate whether flux cancellation is responsible for the
formation of a very massive filament resulting in the spectacular
eruption on 2011 June 7. We analyze and quantify the amount of flux
cancellation that occurs in NOAA AR 11226 and its two neighboring active
regions (ARs 11227 & 11233) using line-of-sight magnetograms from
the Heliospheric Magnetic Imager. During a 3.6 day period building
up to the eruption of the filament, 1.7 × 10<SUP>21</SUP> Mx, 21%
of AR 11226's maximum magnetic flux, was canceled along the polarity
inversion line (PIL) where the filament formed. If the flux cancellation
continued at the same rate up until the eruption then up to 2.8 ×
10<SUP>21</SUP> Mx (34% of the AR flux) may have been built into the
magnetic configuration that contains the filament plasma. The large flux
cancellation rate is due to an unusual motion of the positive-polarity
sunspot, which splits, with the largest section moving rapidly toward
the PIL. This motion compresses the negative polarity and leads to
the formation of an orphan penumbra where one end of the filament is
rooted. Dense plasma threads above the orphan penumbra build into the
filament, extending its length, and presumably injecting material into
it. We conclude that the exceptionally strong flux cancellation in
AR 11226 played a significant role in the formation of its unusually
massive filament. In addition, the presence and coherent evolution of
bald patches in the vector magnetic field along the PIL suggest that
the magnetic field configuration supporting the filament material is
that of a flux rope.
---------------------------------------------------------
Title: An Investigation of the Sources of Earth-directed Solar Wind
during Carrington Rotation 2053
Authors: Fazakerley, A. N.; Harra, L. K.; van Driel-Gesztelyi, L.
2016ApJ...823..145F Altcode:
In this work we analyze multiple sources of solar wind through a full
Carrington Rotation (CR 2053) by analyzing the solar data through
spectroscopic observations of the plasma upflow regions and the in
situ data of the wind itself. Following earlier authors, we link solar
and in situ observations by a combination of ballistic backmapping
and potential-field source-surface modeling. We find three sources
of fast solar wind that are low-latitude coronal holes. The coronal
holes do not produce a steady fast wind, but rather a wind with
rapid fluctuations. The coronal spectroscopic data from Hinode’s
Extreme Ultraviolet Imaging Spectrometer show a mixture of upflow
and downflow regions highlighting the complexity of the coronal
hole, with the upflows being dominant. There is a mix of open and
multi-scale closed magnetic fields in this region whose (interchange)
reconnections are consistent with the up- and downflows they generate
being viewed through an optically thin corona, and with the strahl
directions and freeze-in temperatures found in in situ data. At the
boundary of slow and fast wind streams there are three short periods
of enhanced-velocity solar wind, which we term intermediate based on
their in situ characteristics. These are related to active regions that
are located beside coronal holes. The active regions have different
magnetic configurations, from bipolar through tripolar to quadrupolar,
and we discuss the mechanisms to produce this intermediate wind, and
the important role that the open field of coronal holes adjacent to
closed-field active regions plays in the process.
---------------------------------------------------------
Title: Photospheric Vector Magnetic Field Evolution of NOAA Active
Region 11504 and the Ensuing CME
Authors: James, Alexander; Green, Lucie; Valori, Gherardo; van
Driel-Gesztelyi, Lidia; Baker, Deborah; Brooks, David; Palmerio, Erika
2016SPD....4730305J Altcode:
Coronal mass ejections (CMEs) are eruptions of billions of tonnes of
plasma from the Sun that drive the most severe space weather effects
we observe. In order to be able to produce forecasts of space weather
with lead times of the order of days, accurate predictions of the
occurrence of CMEs must be developed. The eruptive active-region
studied in this work (NOAA 11504) is complex, featuring fragmentation
of penumbral magnetic field in the days prior to eruption, as well as
rotation of the leading sunspot. SDO/HMI vector photospheric magnetic
field measurements are utilised alongside SDO/AIA multi-wavelength
extreme ultra-violet (EUV) observations to study the dynamics of the
photospheric and coronal structures, as well as Hinode/EIS spectroscopic
measurements, including elemental composition data. The EUV data show
flare ribbons as well as coronal dimmings, which are used to infer
the orientation of the erupting flux rope. This flux rope orientation
is then compared to in situ measurements of the flux rope. The vector
magnetic field data is used to determine the possible contributions
the field fragmentation and sunspot rotation may have made to the
formation of the flux rope and the triggering of the CME.
---------------------------------------------------------
Title: Division E Commission 10: Solar Activity
Authors: Schrijver, Carolus J.; Fletcher, Lyndsay; van Driel-Gesztelyi,
Lidia; Asai, Ayumi; Cally, Paul S.; Charbonneau, Paul; Gibson, Sarah
E.; Gomez, Daniel; Hasan, Siraj S.; Veronig, Astrid M.; Yan, Yihua
2016IAUTA..29..245S Altcode: 2015arXiv151003348S
After more than half a century of community support related to the
science of “solar activity”, IAU's Commission 10 was formally
discontinued in 2015, to be succeeded by C.E2 with the same area
of responsibility. On this occasion, we look back at the growth of
the scientific disciplines involved around the world over almost a
full century. Solar activity and fields of research looking into the
related physics of the heliosphere continue to be vibrant and growing,
with currently over 2,000 refereed publications appearing per year from
over 4,000 unique authors, publishing in dozens of distinct journals
and meeting in dozens of workshops and conferences each year. The
size of the rapidly growing community and of the observational and
computational data volumes, along with the multitude of connections
into other branches of astrophysics, pose significant challenges;
aspects of these challenges are beginning to be addressed through,
among others, the development of new systems of literature reviews,
machine-searchable archives for data and publications, and virtual
observatories. As customary in these reports, we highlight some
of the research topics that have seen particular interest over the
most recent triennium, specifically active-region magnetic fields,
coronal thermal structure, coronal seismology, flares and eruptions,
and the variability of solar activity on long time scales. We close
with a collection of developments, discoveries, and surprises that
illustrate the range and dynamics of the discipline.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2016SoPh..291..337L Altcode: 2016SoPh..tmp...10L
No abstract at ADS
---------------------------------------------------------
Title: Erratum to: The Magnetic Helicity Budget of a CME-Prolific
Active Region
Authors: Green, L. M.; López Fuentes, M.; Mandrini, C. H.; Démoulin,
P.; van Driel-Gesztelyi, L.; Culhane, J. L.
2016SoPh..291..335G Altcode: 2015SoPh..tmp..179G
No abstract at ADS
---------------------------------------------------------
Title: Preface
Authors: Fletcher, L.; Heinzel, P.; van Driel-Gesztelyi, L.; Mandrini,
C. H.; Fárník, F.
2015SoPh..290.3379F Altcode: 2015SoPh..tmp..168F
No abstract at ADS
---------------------------------------------------------
Title: Preface: Probing the Sun Inside and Out
Authors: Harra, Louise; Baker, Deborah; Howe, Rachel; Leibacher,
John; van Driel-Gesztelyi, Lidia
2015SoPh..290.3091H Altcode: 2015SoPh..tmp..167H
No abstract at ADS
---------------------------------------------------------
Title: Persistent Near-Surface Flow Structures from Local
Helioseismology
Authors: Howe, Rachel; Komm, R. W.; Baker, D.; Harra, L.; van
Driel-Gesztelyi, L.; Bogart, R. S.
2015SoPh..290.3137H Altcode: 2015arXiv150706525H; 2015SoPh..tmp..115H
Near-surface flows measured by the ring-diagram technique of local
helioseismology show structures that persist over multiple rotations. We
examine these phenomena using data from the Global Oscillation Network
Group (GONG) and the Helioseismic and Magnetic Imager (HMI) and show
that a correlation analysis of the structures can be used to estimate
the rotation rate as a function of latitude, giving a result consistent
with the near-surface rate from global helioseismology and slightly
slower than that obtained from a similar analysis of the surface
magnetic field strength. At latitudes of 60<SUP>∘</SUP> and above,
the HMI flow data reveal a strong signature of a two-sided zonal flow
structure. This signature may be related to recent reports of "giant
cells" in solar convection.
---------------------------------------------------------
Title: A Study of the Coronal Non-thermal Velocity in Polar Regions
During the Rise from Solar Minimum to Solar Maximum in Cycle 24
Authors: Harra, L.; Baker, D.; Edwards, S. J.; Hara, H.; Howe, R.;
van Driel-Gesztelyi, L.
2015SoPh..290.3203H Altcode: 2015SoPh..tmp....8H
We explore the changes in coronal non-thermal velocity (V<SUB>nt</SUB>)
measurements at the poles from solar minimum to solar maximum using
Hinode EUV Imaging Spectrometer data. We find that although the
intensity in the corona at the poles does tend to increase with
the cycle, there are no significant changes in the V<SUB>nt</SUB>
values. The locations of enhanced V<SUB>nt</SUB> values measured do not
always have a counterpart in intensity, and they are sometimes located
in weak emission regions. Unipolar magnetic streams, created through
diffusion of the following polarity of the decaying active regions,
slowly progress towards the poles. These streams are expected to
be related to magnetic nulls as locations that indicate an increased
likelihood for magnetic reconnection to occur. Through global potential
field source-surface modelling, we determine how the number of nulls
varied during the cycle and find that those that lie at < 1.1
solar radii vary significantly. We search for a correlation between
the variation of the magnetic nulls and the V<SUB>nt</SUB> values,
as it may be expected that with an increasing number of nulls, the
V<SUB>nt</SUB> values in the corona increase as well. There is no
correlation with the V<SUB>nt</SUB> values, however. This indicates
that the magnetic structures that create the enhanced V<SUB>nt</SUB>
behaviour are small-scale features and hence not easily measurable at
the poles. Because they do not change during the solar cycle, they are
likely to be created by a local dynamo. The variation of the upper
range of V<SUB>nt</SUB> is reduced, which highlights that strongly
dynamic behaviour is reduced as the solar maximum approaches. This
is likely to be due to the reduced area of the polar coronal hole,
which allows fewer opportunities for reconnection to occur between
open and closed magnetic fields.
---------------------------------------------------------
Title: Source of a Prominent Poleward Surge During Solar Cycle 24
Authors: Yeates, A. R.; Baker, D.; van Driel-Gesztelyi, L.
2015SoPh..290.3189Y Altcode: 2015SoPh..tmp...18Y; 2015arXiv150204854Y
As an observational case study, we consider the origin of a prominent
poleward surge of leading polarity, visible in the magnetic butterfly
diagram during Solar Cycle 24. A new technique is developed for
assimilating individual regions of strong magnetic flux into a
surface-flux transport model. By isolating the contribution of each
of these regions, the model shows the surge to originate primarily in
a single high-latitude activity group consisting of a bipolar active
region present in Carrington Rotations 2104 - 05 (November 2010 -
January 2011) and a multipolar active region in Rotations 2107 - 08
(February - April 2011). This group had a strong axial dipole moment
opposed to Joy's law. On the other hand, the modelling suggests that
the transient influence of this group on the butterfly diagram will
not be matched by a large long-term contribution to the polar field
because it is located at high latitude. This is in accordance with
previous flux-transport models.
---------------------------------------------------------
Title: Evolution of Active Regions
Authors: van Driel-Gesztelyi, Lidia; Green, Lucie May
2015LRSP...12....1V Altcode:
The evolution of active regions (AR) from their emergence through
their long decay process is of fundamental importance in solar
physics. Since large-scale flux is generated by the deep-seated
dynamo, the observed characteristics of flux emergence and that of the
subsequent decay provide vital clues as well as boundary conditions
for dynamo models. Throughout their evolution, ARs are centres of
magnetic activity, with the level and type of activity phenomena being
dependent on the evolutionary stage of the AR. As new flux emerges
into a pre-existing magnetic environment, its evolution leads to
re-configuration of small-and large-scale magnetic connectivities. The
decay process of ARs spreads the once-concentrated magnetic flux over
an ever-increasing area. Though most of the flux disappears through
small-scale cancellation processes, it is the remnant of large-scale AR
fields that is able to reverse the polarity of the poles and build up
new polar fields. In this Living Review the emphasis is put on what
we have learned from observations, which is put in the context of
modelling and simulation efforts when interpreting them. For another,
modelling-focused Living Review on the sub-surface evolution and
emergence of magnetic flux see Fan (2009). In this first version we
focus on the evolution of dominantly bipolar ARs.
---------------------------------------------------------
Title: Parallel Evolution of Quasi-separatrix Layers and Active
Region Upflows
Authors: Mandrini, C. H.; Baker, D.; Démoulin, P.; Cristiani, G. D.;
van Driel-Gesztelyi, L.; Vargas Domínguez, S.; Nuevo, F. A.; Vásquez,
A. M.; Pick, M.
2015ApJ...809...73M Altcode: 2015arXiv150701264M
Persistent plasma upflows were observed with Hinode’s EUV
Imaging Spectrometer (EIS) at the edges of active region (AR)
10978 as it crossed the solar disk. We analyze the evolution of
the photospheric magnetic and velocity fields of the AR, model
its coronal magnetic field, and compute the location of magnetic
null-points and quasi-sepratrix layers (QSLs) searching for the origin
of EIS upflows. Magnetic reconnection at the computed null points
cannot explain all of the observed EIS upflow regions. However, EIS
upflows and QSLs are found to evolve in parallel, both temporarily
and spatially. Sections of two sets of QSLs, called outer and
inner, are found associated to EIS upflow streams having different
characteristics. The reconnection process in the outer QSLs is forced
by a large-scale photospheric flow pattern, which is present in the AR
for several days. We propose a scenario in which upflows are observed,
provided that a large enough asymmetry in plasma pressure exists
between the pre-reconnection loops and lasts as long as a photospheric
forcing is at work. A similar mechanism operates in the inner QSLs; in
this case, it is forced by the emergence and evolution of the bipoles
between the two main AR polarities. Our findings provide strong support
for the results from previous individual case studies investigating the
role of magnetic reconnection at QSLs as the origin of the upflowing
plasma. Furthermore, we propose that persistent reconnection along
QSLs does not only drive the EIS upflows, but is also responsible for
the continuous metric radio noise-storm observed in AR 10978 along
its disk transit by the Nançay Radio Heliograph.
---------------------------------------------------------
Title: Active region plasma outflows as sources of slow/intermediate
solar wind
Authors: van Driel-Gesztelyi, Lidia M.
2015IAUGA..2257850V Altcode:
L. van Driel-Gesztelyi (1,2,3), D. Baker (1), P. Démoulin (2),
Culhane, J.L. (1), M.L. DeRosa (4) C.H. Mandrini (5,6), D.H. Brooks
(7), A.N. Fazakerley (1), L.K. Harra (1), L. Zhao (7), T.H. Zurbuchen
(7), F.A. Nuevo (5,6), A.M. Vásquez (5,6), G.D. Cristiani (5,6)
M. Pick (2)1) UCL/MSSL, UK, (2) Paris Observatory, LESIA, CNRS,
France, (3) Konkoly Observatory, Hungary, (4) Lockheed Martin Solar and
Astrophysics Laboratory, USA, (5) IAFE, CONICET-UBA, Argentina (6) FCEN,
UBA, Argentina (7) Dept. of Atmospheric, Oceanic and Earth Sciences,
Univ. of Michigan, USAWe analyse plasma upflows of tens of km/s from the
edges of solar active regions discovered by Hinode/EIS and investigate
whether or not they become outflows, i.e. find their way into the solar
wind. We analyse two magnetic configurations: bipolar and quadrupolar
and find that the active region plasma may be directly channeled
into the solar wind via interchange reconnection at a high-altitude
null point above the active region especially when active regions are
located besides coronal holes or in a more complex way via multiple
reconnections even from under a closed helmet streamer. We relate the
solar observations to in-situ slow/intermediate solar wind streams.
---------------------------------------------------------
Title: Division II: Commission 10: Solar Activity
Authors: van Driel-Gesztelyi, Lidia; Scrijver, Karel J.; Klimchuk,
James A.; Charbonneau, Paul; Fletcher, Lyndsay; Hasan, S. Sirajul;
Hudson, Hugh S.; Kusano, Kanya; Mandrini, Cristina H.; Peter, Hardi;
Vršnak, Bojan; Yan, Yihua
2015IAUTB..28..106V Altcode:
The Business Meeting of Commission 10 was held as part of the Business
Meeting of Division II (Sun and Heliosphere), chaired by Valentin
Martínez-Pillet, the President of the Division. The President of
Commission 10 (C10; Solar activity), Lidia van Driel-Gesztelyi, took
the chair for the business meeting of C10. She summarised the activities
of C10 over the triennium and the election of the incoming OC.
---------------------------------------------------------
Title: Interaction between CME and surrounding magnetic fields
producing multiple flaring sites
Authors: van Driel-Gesztelyi, Lidia M.
2015IAUGA..2257826V Altcode:
L. van Driel-Gesztelyi (1,2,3), D. Baker (1), T. Török (4), E. Pariat
(2), L.M. Green (1),D.R. Williams (1), J. Carlyle (1,5) G. Valori
(1, 2), P. Démoulin (2), B. Kliem (1,7,8),D. Long (1), S.A. Matthews
(1), J.-M. Malherbe (2)(1) UCL/MSSL, UK, (2) Paris Observatory, LESIA,
CNRS, France, (3) Konkoly Observatory, Hungary, (4) Predictive Science,
Dan Diego, USA, (5) Max Planck Inst., Göttingen, Germany, (6) INAF,
Obs. Roma, Italy, (7) Potsdam Univ., Germany, (8) Yunnan Observatories,
Kunming, ChinaAnalyzing Solar Dynamics Observatory (SDO) observations
of the spectacular Coronal Mass Ejection eruption on 7 June 2011,
we present evidence of coronal magnetic reconnection between the
expanding magnetic structure of the CME and the magnetic fields of an
adjacent active region (AR). The onset of reconnection first became
apparent in the SDO/AIA images when filament plasma, originally
contained within the erupting flux rope, was re-directed towards
remote areas in the neighboring AR, tracing the change of large-scale
magnetic connectivity. The observations are presented jointly with
a topological analysis of the pre-eruption magnetic configuration,
and a data-constrained numerical simulation of the three-AR complex,
demonstrating the formation/intensification of current sheets along
a pre-existing hyperbolic flux tube (HFT) at the interface between
the CME and the neighboring AR, where a secondary flare ribbon was
created. Reconnection across this current sheet resulted in the
formation of new magnetic connections between the erupting magnetic
structure and a neighboring AR about 200 Mm from the eruption site,
in strong qualitative agreement with the observations. In addition,
the CME temporarily created unusually dense plasma conditions around a
reconnection region at high coronal altitudes, enabling us to observe
emission resulting from it. We argue that this exceptional observation
of a coronal brightening was directly observable at SDO/AIA wavelengths
owing to the presence of down-flowing cool and dense (estimated to be
of the order of 10<SUP>10 </SUP>cm<SUP>-3</SUP>) filament plasma in
the vicinity of the reconnection region.
---------------------------------------------------------
Title: FIP Bias Evolution in a Decaying Active Region
Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; Yardley, S. L.;
van Driel-Gesztelyi, L.; Long, D. M.; Green, L. M.
2015ApJ...802..104B Altcode: 2015arXiv150107397B
Solar coronal plasma composition is typically characterized by
first ionization potential (FIP) bias. Using spectra obtained by
Hinode’s EUV Imaging Spectrometer instrument, we present a series
of large-scale, spatially resolved composition maps of active region
(AR)11389. The composition maps show how FIP bias evolves within the
decaying AR during the period 2012 January 4-6. Globally, FIP bias
decreases throughout the AR. We analyzed areas of significant plasma
composition changes within the decaying AR and found that small-scale
evolution in the photospheric magnetic field is closely linked to the
FIP bias evolution observed in the corona. During the AR’s decay
phase, small bipoles emerging within supergranular cells reconnect
with the pre-existing AR field, creating a pathway along which
photospheric and coronal plasmas can mix. The mixing timescales are
shorter than those of plasma enrichment processes. Eruptive activity
also results in shifting the FIP bias closer to photospheric in the
affected areas. Finally, the FIP bias still remains dominantly coronal
only in a part of the AR’s high-flux density core. We conclude that
in the decay phase of an AR’s lifetime, the FIP bias is becoming
increasingly modulated by episodes of small-scale flux emergence,
i.e., decreasing the AR’s overall FIP bias. Our results show that
magnetic field evolution plays an important role in compositional
changes during AR development, revealing a more complex relationship
than expected from previous well-known Skylab results showing that
FIP bias increases almost linearly with age in young ARs.
---------------------------------------------------------
Title: JD3 - 3D Views of the Cycling Sun in Stellar Context: Overview
Authors: van Driel-Gesztelyi, Lidia; Schrijver, Carolus J.
2015HiA....16...81V Altcode:
We summarise the motivations and main results of the joint discussion
“3D Views of the Cycling Sun in Stellar Context”, and give credit
to contributed talks and poster presentations, as due to the limited
number of pages, this proceedings could only include contributions
from the keynote speakers.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2015SoPh..290..657L Altcode: 2015SoPh..tmp...24L
No abstract at ADS
---------------------------------------------------------
Title: Time Evolution of Force-Free Parameter and Free Magnetic
Energy in Active Region NOAA 10365
Authors: Valori, G.; Romano, P.; Malanushenko, A.; Ermolli, I.;
Giorgi, F.; Steed, K.; van Driel-Gesztelyi, L.; Zuccarello, F.;
Malherbe, J. -M.
2015SoPh..290..491V Altcode:
We describe the variation of the accumulated coronal helicity derived
from the magnetic helicity flux through the photosphere in active region
(AR) NOAA 10365, where several large flares and coronal mass ejections
(CMEs) occurred. We used SOHO/MDI full-disk line-of-sight magnetograms
to measure the helicity flux, and the integral of GOES X-ray flux as a
proxy of the coronal energy variations due to flares or CMEs. Using the
linear force-free field model, we transformed the accumulated helicity
flux into a time sequence of the force-free parameter α accounting for
flares or CMEs via the proxy derived from GOES observations. This method
can be used to derive the value of α at different times during the
AR evolution, and is a partial alternative to the commonly used match
of field lines with EUV loops. By combining the accumulated helicity
obtained from the observations with the linear force-free theory, we
describe the main phases of the emergence process of the AR, and relate
them temporally with the occurrence of flares or CMEs. Additionally,
a comparison with the loop-matching method of fixing alpha at each time
independently shows that the proposed method may be helpful in avoiding
unrealistic or undetermined values of alpha that may originate from
an insufficient quality of the image used to identify coronal loops
at a given time. For the relative intensity of the considered events,
the linear force-free field theory implies that there is a direct
correlation between the released energy on the one hand and the product
of the coronal helicity with the variation of α due to the event on
the other. Therefore, the higher the value of the accumulated coronal
helicity, the smaller the force-free parameter variation required to
produce the same decrease in the free energy during the CMEs.
---------------------------------------------------------
Title: Solar Cycle Indices from the Photosphere to the Corona:
Measurements and Underlying Physics
Authors: Ermolli, Ilaria; Shibasaki, Kiyoto; Tlatov, Andrey; van
Driel-Gesztelyi, Lidia
2015sac..book..105E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New Eyes Looking at Solar Activity: Challenges for Theory
and Simulations - Placing It into Context
Authors: Pohjolainen, S.; Karlický, M.; van Driel-Gesztelyi, L.;
Mandrini, C. H.
2015SoPh..290....1P Altcode: 2014SoPh..tmp..190P
Solar Cycle 24 has opened a new era in solar radio physics as we now
have instruments that can probe solar processes from submillimeter to
kilometer waves. New and upgraded instruments provide data that enable
studies of both energetic particles and thermal plasma, enhancing
our knowledge of solar eruptions and acceleration and propagation
of particles, through the solar chromosphere and corona and into
the interplanetary space. In this Topical Issue we highlight the new
observational capabilities and discuss the theoretical issues connected
to solar radio emission and interplanetary radio physics.
---------------------------------------------------------
Title: Magnetic Helicity, Tilt, and Twist
Authors: Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander;
Norton, Aimee A.; van Driel-Gesztelyi, Lidia
2015sac..book..285P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Cycle Indices from the Photosphere to the Corona:
Measurements and Underlying Physics
Authors: Ermolli, Ilaria; Shibasaki, Kiyoto; Tlatov, Andrey; van
Driel-Gesztelyi, Lidia
2014SSRv..186..105E Altcode: 2017arXiv170507054E; 2014SSRv..tmp...48E
A variety of indices have been proposed in order to represent the
many different observables modulated by the solar cycle. Most of these
indices are highly correlated with each other owing to their intrinsic
link with the solar magnetism and the dominant eleven year cycle,
but their variations may differ in fine details, as well as on short-
and long-term trends. In this paper we present an overview of the
indices that are often employed to describe the many features of the
solar cycle, moving from the ones referring to direct observations
of the inner solar atmosphere, the photosphere and chromosphere, to
those deriving from measurements of the transition region and solar
corona. For each index, we summarize existing measurements and typical
use, and for those that quantify physical observables, we describe
the underlying physics.
---------------------------------------------------------
Title: Magnetic Helicity, Tilt, and Twist
Authors: Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander;
Norton, Aimee A.; van Driel-Gesztelyi, Lidia
2014SSRv..186..285P Altcode:
Since its introduction to astro- and solar physics, the concept of
helicity has proven to be useful in providing critical insights into
physics of various processes from astrophysical dynamos, to magnetic
reconnection and eruptive phenomena. Signature of helicity was also
detected in many solar features, including orientation of solar active
regions, or Joy's law. Here we provide a summary of both solar phenomena
and consider mutual relationship and its importance for the evolution
of solar magnetic fields.
---------------------------------------------------------
Title: How Can Active Region Plasma Escape into the Solar Wind from
Below a Closed Helmet Streamer?
Authors: Mandrini, C. H.; Nuevo, F. A.; Vásquez, A. M.; Démoulin,
P.; van Driel-Gesztelyi, L.; Baker, D.; Culhane, J. L.; Cristiani,
G. D.; Pick, M.
2014SoPh..289.4151M Altcode: 2014arXiv1409.7369M; 2014SoPh..tmp..115M
Recent studies show that active-region (AR) upflowing plasma,
observed by the EUV-Imaging Spectrometer (EIS) onboard Hinode, can
gain access to open-field lines and be released into the solar wind
(SW) via magnetic-interchange reconnection at magnetic null-points in
pseudo-streamer configurations. When only one bipolar AR is present
on the Sun and is fully covered by the separatrix of a streamer, such
as AR 10978 in December 2007, it seems unlikely that the upflowing AR
plasma can find its way into the slow SW. However, signatures of plasma
with AR composition have been found at 1 AU by Culhane et al. (Solar
Phys.289, 3799, 2014) that apparently originated west of AR 10978. We
present a detailed topology analysis of AR 10978 and the surrounding
large-scale corona based on a potential-field source-surface (PFSS)
model. Our study shows that it is possible for the AR plasma to move
around the streamer separatrix and be released into the SW via magnetic
reconnection, which occurs in at least two main steps. We analyse data
from the Nançay Radioheliograph (NRH) in a search for evidence of the
chain of magnetic reconnections that we propose. We find a noise storm
above the AR and several varying sources at 150.9 MHz. Their locations
suggest that they might be associated with particles accelerated during
the first-step reconnection process at a null point well outside of
the AR. We find no evidence of the second reconnection step in the
radio data, however. Our results demonstrate that even when it appears
highly improbable for the AR plasma to reach the SW, indirect channels
involving a sequence of reconnections can make it possible.
---------------------------------------------------------
Title: Extreme-ultraviolet Observations of Global Coronal Wave
Rotation
Authors: Attrill, G. D. R.; Long, D. M.; Green, L. M.; Harra, L. K.;
van Driel-Gesztelyi, L.
2014ApJ...796...55A Altcode:
We present evidence of global coronal wave rotation in EUV data from
SOHO/EIT, STEREO/EUVI, and SDO/AIA. The sense of rotation is found
to be consistent with the helicity of the source region (clockwise
for positive helicity, anticlockwise for negative helicity), with the
source regions hosting sigmoidal structures. We also study two coronal
wave events observed by SDO/AIA where no clear rotation (or sigmoid)
is observed. The selected events show supporting evidence that they
all originate with flux rope eruptions. We make comparisons across
this set of observations (both with and without clear sigmoidal
structures). On examining the magnetic configuration of the source
regions, we find that the nonrotation events possess a quadrupolar
magnetic configuration. The coronal waves that do show a rotation
originate from bipolar source regions.
---------------------------------------------------------
Title: Tracking Solar Active Region Outflow Plasma from Its Source
to the Near-Earth Environment
Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.;
Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.;
Zurbuchen, T. H.
2014SoPh..289.3799C Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C
Seeking to establish whether active-region upflow material contributes
to the slow solar wind, we examine in detail the plasma upflows from
Active Region (AR) 10978, which crossed the Sun's disc in the interval 8
to 16 December 2007 during Carrington rotation (CR) 2064. In previous
work, using data from the Hinode/EUV Imaging Spectrometer, upflow
velocity evolution was extensively studied as the region crossed the
disc, while a linear force-free-field magnetic extrapolation was used
to confirm aspects of the velocity evolution and to establish the
presence of quasi-separatrix layers at the upflow source areas. The
plasma properties, temperature, density, and first ionisation potential
bias [FIP-bias] were measured with the spectrometer during the disc
passage of the active region. Global potential-field source-surface
(PFSS) models showed that AR 10978 was completely covered by the
closed field of a helmet streamer that is part of the streamer
belt. Therefore it is not clear how any of the upflowing AR-associated
plasma could reach the source surface at 2.5 R<SUB>⊙</SUB> and
contribute to the slow solar wind. However, a detailed examination of
solar-wind in-situ data obtained by the Advanced Composition Explorer
(ACE) spacecraft at the L<SUB>1</SUB> point shows that increases in
O<SUP>7+</SUP>/O<SUP>6+</SUP>, C<SUP>6+</SUP>/C<SUP>5+</SUP>, and Fe/O -
a FIP-bias proxy - are present before the heliospheric current-sheet
crossing. These increases, along with an accompanying reduction in
proton velocity and an increase in density are characteristic of
both AR and slow-solar-wind plasma. Finally, we describe a two-step
reconnection process by which some of the upflowing plasma from the
AR might reach the heliosphere.
---------------------------------------------------------
Title: The evolution of writhe in kink-unstable flux ropes and
erupting filaments
Authors: Török, T.; Kliem, B.; Berger, M. A.; Linton, M. G.;
Démoulin, P.; van Driel-Gesztelyi, L.
2014PPCF...56f4012T Altcode: 2014arXiv1403.1565T
The helical kink instability of a twisted magnetic flux tube has been
suggested as a trigger mechanism for solar filament eruptions and
coronal mass ejections (CMEs). In order to investigate if estimations
of the pre-emptive twist can be obtained from observations of writhe
in such events, we quantitatively analyze the conversion of twist into
writhe in the course of the instability, using numerical simulations. We
consider the line tied, cylindrically symmetric Gold-Hoyle flux rope
model and measure the writhe using the formulae by Berger and Prior
which express the quantity as a single integral in space. We find that
the amount of twist converted into writhe does not simply scale with
the initial flux rope twist, but depends mainly on the growth rates
of the instability eigenmodes of higher longitudinal order than the
basic mode. The saturation levels of the writhe, as well as the shapes
of the kinked flux ropes, are very similar for considerable ranges of
initial flux rope twists, which essentially precludes estimations of
pre-eruptive twist from measurements of writhe. However, our simulations
suggest an upper twist limit of ∼6π for the majority of filaments
prior to their eruption.
---------------------------------------------------------
Title: Coronal Magnetic Reconnection Driven by CME Expansion—the
2011 June 7 Event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
P.; Kliem, B.; Long, D. M.; Matthews, S. A.; Malherbe, J. -M.
2014ApJ...788...85V Altcode: 2014arXiv1406.3153V
Coronal mass ejections (CMEs) erupt and expand in a magnetically
structured solar corona. Various indirect observational pieces of
evidence have shown that the magnetic field of CMEs reconnects with
surrounding magnetic fields, forming, e.g., dimming regions distant
from the CME source regions. Analyzing Solar Dynamics Observatory
(SDO) observations of the eruption from AR 11226 on 2011 June 7, we
present the first direct evidence of coronal magnetic reconnection
between the fields of two adjacent active regions during a CME. The
observations are presented jointly with a data-constrained numerical
simulation, demonstrating the formation/intensification of current
sheets along a hyperbolic flux tube at the interface between the CME
and the neighboring AR 11227. Reconnection resulted in the formation of
new magnetic connections between the erupting magnetic structure from
AR 11226 and the neighboring active region AR 11227 about 200 Mm from
the eruption site. The onset of reconnection first becomes apparent
in the SDO/AIA images when filament plasma, originally contained
within the erupting flux rope, is redirected toward remote areas in
AR 11227, tracing the change of large-scale magnetic connectivity. The
location of the coronal reconnection region becomes bright and directly
observable at SDO/AIA wavelengths, owing to the presence of down-flowing
cool, dense (10<SUP>10</SUP> cm<SUP>-3</SUP>) filament plasma in its
vicinity. The high-density plasma around the reconnection region is
heated to coronal temperatures, presumably by slow-mode shocks and
Coulomb collisions. These results provide the first direct observational
evidence that CMEs reconnect with surrounding magnetic structures,
leading to a large-scale reconfiguration of the coronal magnetic field.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2014SoPh..289.1455L Altcode: 2014SoPh..tmp....6L
No abstract at ADS
---------------------------------------------------------
Title: Investigating the Dynamics and Density Evolution of Returning
Plasma Blobs from the 2011 June 7 Eruption
Authors: Carlyle, Jack; Williams, David R.; van Driel-Gesztelyi,
Lidia; Innes, Davina; Hillier, Andrew; Matthews, Sarah
2014ApJ...782...87C Altcode: 2014arXiv1401.4824C
This work examines in-falling matter following an enormous coronal mass
ejection on 2011 June 7. The material formed discrete concentrations,
or blobs, in the corona and fell back to the surface, appearing as dark
clouds against the bright corona. In this work we examined the density
and dynamic evolution of these blobs in order to formally assess the
intriguing morphology displayed throughout their descent. The blobs
were studied in five wavelengths (94, 131, 171, 193, and 211 Å)
using the Solar Dynamics Observatory Atmospheric Imaging Assembly,
comparing background emission to attenuated emission as a function
of wavelength to calculate column densities across the descent of
four separate blobs. We found the material to have a column density of
hydrogen of approximately 2 × 10<SUP>19</SUP> cm<SUP>-2</SUP>, which is
comparable with typical pre-eruption filament column densities. Repeated
splitting of the returning material is seen in a manner consistent
with the Rayleigh-Taylor instability. Furthermore, the observed
distribution of density and its evolution is also a signature of this
instability. By approximating the three-dimensional geometry (with data
from STEREO-A), volumetric densities were found to be approximately 2
× 10<SUP>-14</SUP> g cm<SUP>-3</SUP>, and this, along with observed
dominant length scales of the instability, was used to infer a magnetic
field of the order 1 G associated with the descending blobs.
---------------------------------------------------------
Title: Density evolution of in-falling prominence material from the
7th June 2011 CME
Authors: Carlyle, Jack; Williams, David; van Driel-Gesztelyi, Lidia;
Innes, Davina
2014IAUS..300..401C Altcode:
This work investigates the density of in-falling prominence material
following the 7 <SUP>th</SUP> June 2011 eruption. Both the evolution
and the distribution of the density is analysed in five discreet
“blobs” of material. The density appears to be remarkably uniform,
both spatially within the blobs, and temporally over the course of the
descent of each, although a slight concentration of material towards
the leading edge is noted in some cases. Online material is available
at bit.ly/jackblob
---------------------------------------------------------
Title: Spectroscopic measurements of EUV ejecta in a CME: a
high-blueshift trailing thread
Authors: Williams, David; Baker, Deborah; van Driel-Gesztelyi, Lidia;
Green, Lucie
2014IAUS..300..464W Altcode:
The mass of erupting prominence material can be inferred from the
obscuration of emission behind this mass of cool plasma thanks to
the rapid cadence of SDO/AIA images in the short EUV wavelength range
(Carlyle et al. 2013, these proceedings). In comparing this approach
with spectral observations from Hinode/EIS, to monitor contributions
from emission seen around the erupting prominence material, we have
found an intriguing component of blue-shifted emission, trailing
the erupting prominence, with Doppler shifts on the order of 350 km
s<SUP>-1</SUP> in bright lines of both He ii and Fe xii.
---------------------------------------------------------
Title: FIP bias in a sigmoidal active region
Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi,
Lidia; Green, L. M.; Steed, K.; Carlyle, J.
2014IAUS..300..222B Altcode:
We investigate first ionization potential (FIP) bias levels in
an anemone active region (AR) - coronal hole (CH) complex using an
abundance map derived from Hinode/EIS spectra. The detailed, spatially
resolved abundance map has a large field of view covering 359” ×
485”. Plasma with high FIP bias, or coronal abundances, is concentrated
at the footpoints of the AR loops whereas the surrounding CH has a low
FIP bias, ~1, i.e. photospheric abundances. A channel of low FIP bias
is located along the AR's main polarity inversion line containing a
filament where ongoing flux cancellation is observed, indicating a
bald patch magnetic topology characteristic of a sigmoid/flux rope
configuration.
---------------------------------------------------------
Title: Active region upflow plasma: its relation to small activity
and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Cristiani,
Germán; Vásquez, Alberto; Van Driel-Gesztelyi, Lidia; Baker, Deborah;
Pick, Monique; Demoulin, Pascal; Nuevo, Federico
2014cosp...40E1979M Altcode:
Recent studies show that active region (AR) upflowing plasma,
observed by the Hinode EUV Imaging Spectrometer (EIS), can gain
access to open field lines and be released into the solar wind via
magnetic interchange reconnection occurring below the source surface
at magnetic null-points in pseudo-streamer configurations. When only
one simple bipolar AR is present on the Sun and it is fully covered by
the separatrix of a streamer, like AR 10978 on December 2007, it seems
unlikely that the upflowing AR plasma could find its way into the slow
solar wind. However, signatures of plasma with AR composition at 1 AU
that appears to originate from the West of AR 10978 were recently found
by Culhane and coworkers. We present a detailed topology analysis of
AR 10978 based on a linear force-free magnetic field model at the AR
scale, combined with a global PFSS model. This allows us, on one hand,
to explain the variations observed in the upflows to the West of the
AR as the result of magnetic reconnection at quasi-separatrix layers
(QSLs). While at a global scale, we show that reconnection, occurring
in at least two main steps, first at QSLs and later at a high-altitude
coronal null-point, allows the AR plasma to get around the topological
obstacle of the streamer separatrix and be released into the solar wind.
---------------------------------------------------------
Title: Magnetic reconnection driven by filament eruption in the 7
June 2011 event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
P.; Matthews, S. A.; Kliem, B.; Malherbe, J. -M.
2014IAUS..300..502V Altcode:
During an unusually massive filament eruption on 7 June 2011,
SDO/AIA imaged for the first time significant EUV emission around a
magnetic reconnection region in the solar corona. The reconnection
occurred between magnetic fields of the laterally expanding CME
and a neighbouring active region. A pre-existing quasi-separatrix
layer was activated in the process. This scenario is supported by
data-constrained numerical simulations of the eruption. Observations
show that dense cool filament plasma was re-directed and heated in
situ, producing coronal-temperature emission around the reconnection
region. These results provide the first direct observational evidence,
supported by MHD simulations and magnetic modelling, that a large-scale
re-configuration of the coronal magnetic field takes place during
solar eruptions via the process of magnetic reconnection.
---------------------------------------------------------
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: Magnetic Polarity Streams and Subsurface Flows
Authors: Howe, R.; Baker, D.; Harra, L.; van Driel-Gesztelyi, L.;
Komm, R.; Hill, F.; González Hernández, I.
2013ASPC..478..291H Altcode:
An important feature of the solar cycle is the transport of unbalanced
magnetic flux from active regions towards the poles, which eventually
results in polarity reversal. This transport takes the form of distinct
“polarity streams” that are visible in the magnetic butterfly
diagram. We compare the poleward migration rate estimated from such
streams to that derived from the subsurface meridional flows measured
in helioseismic data from the GONG network since 2001, and find that
the results are in reasonable agreement.
---------------------------------------------------------
Title: Plasma Composition in a Sigmoidal Anemone Active Region
Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi,
L.; Green, L. M.; Steed, K.; Carlyle, J.
2013ApJ...778...69B Altcode: 2013arXiv1310.0999B
Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument
onboard Hinode, we present a detailed spatially resolved abundance map
of an active region (AR)-coronal hole (CH) complex that covers an area
of 359” × 485”. The abundance map provides first ionization potential
(FIP) bias levels in various coronal structures within the large EIS
field of view. Overall, FIP bias in the small, relatively young AR
is 2-3. This modest FIP bias is a consequence of the age of the AR,
its weak heating, and its partial reconnection with the surrounding
CH. Plasma with a coronal composition is concentrated at AR loop
footpoints, close to where fractionation is believed to take place in
the chromosphere. In the AR, we found a moderate positive correlation
of FIP bias with nonthermal velocity and magnetic flux density, both
of which are also strongest at the AR loop footpoints. Pathways of
slightly enhanced FIP bias are traced along some of the loops connecting
opposite polarities within the AR. We interpret the traces of enhanced
FIP bias along these loops to be the beginning of fractionated plasma
mixing in the loops. Low FIP bias in a sigmoidal channel above the
AR's main polarity inversion line, where ongoing flux cancellation is
taking place, provides new evidence of a bald patch magnetic topology
of a sigmoid/flux rope configuration.
---------------------------------------------------------
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: Observations and Modelling of the Inner Heliosphere: Preface
and Tribute to the Late Dr. Andy Breen
Authors: Bisi, M. M.; Harrison, R. A.; Lugaz, N.; van Driel-Gesztelyi,
L.; Mandrini, C. H.
2013SoPh..285....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Are subsurface flows and coronal holes related?
Authors: Komm, R.; Howe, R.; González Hernández, I.; Harra, L.;
Baker, D.; van Driel-Gesztelyi, L.
2013JPhCS.440a2022K Altcode:
We study synoptic maps of solar subsurface flows covering six Carrington
rotations (2050 to 2055). The subsurface flows are determined with
a ring-diagram analysis of GONG high-resolution Doppler data. We
identify the locations of coronal holes in synoptic maps of EUV images
at 195Å from the EIT instrument and determine the characteristics
of associated subsurface flows. We study two long-lived coronal holes
that are present during this epoch. We find that large-scale patterns
are present in the subsurface flows but appear to be unrelated to
these coronal holes. The horizontal subsurface flows associated with
the two long-lived coronal holes are weakly divergent (upflows) with
small cyclonic vorticity. These flows are thus similar to subsurface
flows of quiet regions with regard to the vertical flows and similar
to flows of active regions with regard to vorticity.
---------------------------------------------------------
Title: Can we detect local helioseismic parameter shifts in coronal
holes?
Authors: Howe, R.; Haber, D. A.; Bogart, R. S.; Zharkov, S.; Baker,
D.; Harra, L.; van Driel-Gesztelyi, L.
2013JPhCS.440a2019H Altcode:
Changes in helioseismic mode parameters in active regions and across
the solar disk are well documented, but local magnetic activity
and geometric effects may not account for all of the scatter seen
in the results. We use results from the Helioseismic and Magnetic
Imager ring-diagram pipeline for Carrington rotation 2113 to look for
differences in mode amplitude and frequency between coronal holes and
other quiet-Sun regions. While we do not find a systematic difference,
the results do suggest that the correlation between magnetic activity
index and mode parameters shows less scatter in coronal hole regions
than in general quiet Sun.
---------------------------------------------------------
Title: Subsurface flows associated with non-Joy oriented active
regions: a case study
Authors: González Hernández, Irene; Komm, Rudolf; van
Driel-Gesztelyi, Lidia; Baker, Deborah; Harra, Louise; Howe, Rachel
2013JPhCS.440a2050G Altcode:
Non-Joy oriented active regions (ARs) are a challenge for solar magnetic
field modelers. Although significant deviations from Joy's law are
relatively rare for simple bipolar ARs, understanding the causes of
their particularity could be critical for the big picture of the solar
dynamo. We explore the possibility of the sub-surface local dynamics
being responsible for the significant rotation of these ARs. We apply
the ring-diagram technique, a local helioseismology method, to infer
the flows under and surrounding a non-Joy oriented AR and present the
results of a case study in this paper.
---------------------------------------------------------
Title: Preface
Authors: Gopalswamy, N.; Nieves-Chinchilla, T.; Hidalgo, M.; Zhang,
J.; Riley, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.
2013SoPh..284....1G Altcode: 2013arXiv1304.0085G
This Topical Issue of Solar Physics, devoted to the study of flux-rope
structure in coronal mass ejections (CMEs), is based on two Coordinated
Data Analysis Workshops (CDAWs) held in 2010 (20 - 23 September in Dan
Diego, California, USA) and 2011 (September 5-9 in Alcala, Spain). The
primary purpose of the CDAWs was to address the question: Do all CMEs
have flux rope structure? There are 18 papers om this topical issue,
including this preface.
---------------------------------------------------------
Title: On the response of the solar atmosphere to small-scale magnetic
flux emergence
Authors: Vargas Dominguez, Santiago; van Driel-Gesztelyi, Lidia
2013EGUGA..15..925V Altcode:
In this work we analyze data from the Hinode spacecraft targeting
an emerging magnetic flux region. We focus on small-scale events
identified by distinctive dark features in CaII H chromospheric
filtergrams. Energy release at low chromospheric heights is detected
to be boosted by the disappearance of the dark features after they
reached their maximum size. The observed phenomena are explained as
evidencing elementary flux emergence into the solar atmosphere. We
are thus detecting granular-scale arch filament systems, that emerge
and interact with pre-existing fields. The results give new insights
on the resistive flux emergence scenario driving the configuration
and evolution of solar active regions. We compare the results with
emergence of individual magnetic loops seen in quiet sun regions.
---------------------------------------------------------
Title: The 3D Geometry of Active Region Upflows Deduced from Their
Limb-to-Limb Evolution
Authors: Démoulin, P.; Baker, D.; Mandrini, C. H.; van
Driel-Gesztelyi, L.
2013SoPh..283..341D Altcode: 2012arXiv1211.5962D
We analyze the evolution of coronal plasma upflows from the edges of
AR 10978, which has the best limb-to-limb data coverage with Hinode's
EUV Imaging Spectrometer (EIS). We find that the observed evolution is
largely due to the solar rotation progressively changing the viewpoint
of nearly stationary flows. From the systematic changes in the upflow
regions as a function of distance from disc center, we deduce their
3D geometrical properties as inclination and angular spread in three
coronal lines (Si VII, Fe XII, and Fe XV). In agreement with magnetic
extrapolations, we find that the flows are thin, fan-like structures
rooted in quasi separatrix layers (QSLs). The fans are tilted away
from the AR center. The highest plasma velocities in these three
spectral lines have similar magnitudes and their heights increase with
temperature. The spatial location and extent of the upflow regions
in the Si VII, Fe XII, and Fe XV lines are different owing to i)
temperature stratification and ii) line of sight integration of the
spectral profiles with significantly different backgrounds. We conclude
that we sample the same flows at different temperatures. Further,
we find that the evolution of line widths during the disc passage is
compatible with a broad range of velocities in the flows. Everything
considered, our results are compatible with the AR upflows originating
from reconnections along QSLs between over-pressure AR loops and
neighboring under-pressure loops. The flows are driven along magnetic
field lines by a pressure gradient in a stratified atmosphere. Our
interpretation of the above results is that, at any given time, we
observe the superposition of flows created by successive reconnections,
leading to a broad velocity distribution.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2013SoPh..283....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mass Estimates of Rapidly Moving Prominence Material from
High-cadence EUV Images
Authors: Williams, David R.; Baker, Deborah; van Driel-Gesztelyi, Lidia
2013ApJ...764..165W Altcode: 2013arXiv1301.4271W
We present a new method for determining the column density of erupting
filament material using state-of-the-art multi-wavelength imaging
data. Much of the prior work on filament/prominence structure can
be divided between studies that use a polychromatic approach with
targeted campaign observations and those that use synoptic observations,
frequently in only one or two wavelengths. The superior time resolution,
sensitivity, and near-synchronicity of data from the Solar Dynamics
Observatory's Advanced Imaging Assembly allow us to combine these
two techniques using photoionization continuum opacity to determine
the spatial distribution of hydrogen in filament material. We apply
the combined techniques to SDO/AIA observations of a filament that
erupted during the spectacular coronal mass ejection on 2011 June 7. The
resulting "polychromatic opacity imaging" method offers a powerful way
to track partially ionized gas as it erupts through the solar atmosphere
on a regular basis, without the need for coordinated observations,
thereby readily offering regular, realistic mass-distribution estimates
for models of these erupting structures.
---------------------------------------------------------
Title: Tracking Solar Active Region Outflow Plasma from its Source
to the near-Earth Environment
Authors: Culhane, J. L.; Brooks, D.; Zurbuchen, T.; van
Driel-Gesztelyi, L.; Fazakerley, A. N.; DeRosa, M. L.
2012AGUFMSH53A2255C Altcode:
In a recent study of persistent active region outflow from AR 10978 in
the period 10 - 15, December, 2007, Brooks and Warren (2011), using the
Hinode EUV Imaging Spectrometer (EIS) instrument showed the presence
of a strong low-FIP element enhancement in the outflowing plasma that
was replicated three days later in the in-situ solar wind measurements
made by the ACE/SWICS instrument. In the present work, we examine the
outflowing plasma properties (Te, Ne, v, abundances) as a function
of time in greater detail as AR 10978 passes the Earth-Sun line. The
structure of the magnetic field above the two outflow regions - E and
W of the AR, is also examined. Following an assessment of the relevant
magnetic structures between Sun and Earth, the properties of the solar
wind plasma arriving at ACE approximately three days later are measured
and compared with those of the outflowing AR plasma. The relationship
of these measurements to the in-situ magnetic field observed by the
ACE magnetometer is also studied. Finally the role of persistent AR
outflows in contributing to the slow solar wind is assessed.
---------------------------------------------------------
Title: Preface
Authors: Fleck, Bernhard; Heber, Bernd; Vourlidas, Angelos; van
Driel-Gesztelyi, Lidia; Mandrini, Cristina H.; Leibacher, John
2012SoPh..281....1F Altcode: 2012SoPh..tmp..223F
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Topology of Active Regions and Coronal Holes:
Implications for Coronal Outflows and the Solar Wind
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin,
P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.;
Stenborg, G.; Vourlidas, A.; Brooks, D. H.
2012SoPh..281..237V Altcode: 2012SoPh..tmp..228V
During 2 - 18 January 2008 a pair of low-latitude opposite-polarity
coronal holes (CHs) were observed on the Sun with two active regions
(ARs) and the heliospheric plasma sheet located between them. We use
the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows
and measure their velocities. Solar-Terrestrial Relations Observatory
(STEREO) imaging is also employed, as are the Advanced Composition
Explorer (ACE) in-situ observations, to assess the resulting impacts on
the solar wind (SW) properties. Magnetic-field extrapolations of the two
ARs confirm that AR plasma outflows observed with EIS are co-spatial
with quasi-separatrix layer locations, including the separatrix of a
null point. Global potential-field source-surface modeling indicates
that field lines in the vicinity of the null point extend up to the
source surface, enabling a part of the EIS plasma upflows access
to the SW. We find that similar upflow properties are also observed
within closed-field regions that do not reach the source surface. We
conclude that some of plasma upflows observed with EIS remain confined
along closed coronal loops, but that a fraction of the plasma may be
released into the slow SW. This suggests that ARs bordering coronal
holes can contribute to the slow SW. Analyzing the in-situ data, we
propose that the type of slow SW present depends on whether the AR is
fully or partially enclosed by an overlying streamer.
---------------------------------------------------------
Title: Preface
Authors: Nakariakov, V. M.; Georgoulis, M. K.; Poedts, S.; van
Driel-Gesztelyi, L.; Mandrini, C. H.; Leibacher, J.
2012SoPh..280..295N Altcode: 2012SoPh..tmp..226N
No abstract at ADS
---------------------------------------------------------
Title: Identifying the Main Driver of Active Region Outflows
Authors: Baker, D.; van Driel-Gesztelyi, L.; Mandrini, C. H.;
Démoulin, P.; Murray, M. J.
2012ASPC..454..425B Altcode:
Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous
outflows of a few to 50 km s<SUP>-1</SUP> from active regions (ARs). The
characteristics of these outflows are very curious in that they are
most prominent at the AR boundary and appear over monopolar magnetic
areas. They are linked to strong non-thermal line broadening and
are stronger in hotter EUV lines. The outflows persist for at least
several days. Whereas red-shifted down flows observed in AR closed
loops are well understood, to date there is no general consensus
for the mechanism(s) driving blue-shifted AR-related outflows. We
use Hinode EIS and X-Ray Telescope observations of AR 10942 coupled
with magnetic modeling to demonstrate for the first time that the
outflows originate from specific locations of the magnetic topology
where field lines display strong gradients of magnetic connectivity,
namely quasi-separatrix layers (QSLs), or in the limit of infinitely
thin QSLs, separatrices. The strongest AR outflows were found to be
in the vicinity of QSL sections located over areas of strong magnetic
field. We argue that magnetic reconnection at QSLs, separating closed
field lines of the AR and either large-scale externally connected or
‘open’ field lines, is a viable mechanism for driving AR outflows
which are potentially sources of the slow solar wind. In fact, magnetic
reconnection along QSLs (including separatricies) is the first theory
to explain the most puzzling characteristics of the outflows, namely
their occurrence over monopolar areas at the periphery of ARs and
their longevity.
---------------------------------------------------------
Title: Does Magnetic Helicity Affect Active Region Evolution and
Energetics?
Authors: Wallace, A. J.; Green, L. M.; Mandrini, C. H.; Démoulin,
P.; van Driel-Gesztelyi, L.; Matthews, S. A.
2012ASPC..454..281W Altcode:
The purpose of this investigation is to determine whether there is a
difference between the evolution of an active region with additional new
flux emergence if the new flux has either the same or the opposite sign
of magnetic helicity from the active region. Of these two scenarios, the
one that produces the most energetics is still a topic for debate. We
present a study of two active regions following the emergence of a
bipole, one with the same and one with the opposite sign of helicity
from the active region. We discover that while there is less flaring
in the mixed helicity active region the EUV flux normalised to the
magnetic field is three times higher than that of the same helicity
active region. We propose that reconnection is more likely to occur
between opposite helicity structures and thus, the energy can never
build up to the levels required for flaring.
---------------------------------------------------------
Title: The Slow Solar Wind: From Formation on the Sun to the Earth
Authors: Harra, L. K.; Fazakerley, A. N.; van Driel-Gesztelyi, L.
2012ASPC..454..421H Altcode:
Hinode has discovered a potential source of slow solar wind at the
edges of active regions with the X-ray Telescope (XRT) and EUV Imaging
spectrometer (EIS) on board Hinode e.g. Sakao et al. (2007), Harra
et al. (2008), Doschek et al. (2008). These upflows are long-lasting
and exist at the edges of most active regions. In this conference
paper we first discuss the onset of the upflows. This is related to
newly emerged magnetic flux into an active region. Next we discuss
whether the flows that we see on the surface of the Sun actually are
transported to the Earth in the slow solar wind. To do this we looked at
a number of different examples over a Carrington rotation and tracked
the response in the solar wind as measured by the ACE spacecraft at
L1. We found that there is a significant enhancement of the in situ
solar wind speed for active regions located close to a coronal hole.
---------------------------------------------------------
Title: Parallels among the “music scores” of solar cycles, space
weather and Earth's climate
Authors: Kolláth, Zoltán; Oláh, Katalin; van Driel-Gesztelyi, Lidia
2012IAUS..286..423K Altcode:
Solar variability and its effects on the physical variability of our
(space) environment produces complex signals. In the indicators of
solar activity at least four independent cyclic components can be
identified, all of them with temporal variations in their timescales. <P
/>Time-frequency distributions (see Kolláth & Oláh 2009) are
perfect tools to disclose the “music scores” in these complex time
series. Special features in the time-frequency distributions, like
frequency splitting, or modulations on different timescales provide
clues, which can reveal similar trends among different indices like
sunspot numbers, interplanetary magnetic field strength in the Earth's
neighborhood and climate data. <P />On the pseudo-Wigner Distribution
(PWD) the frequency splitting of all the three main components (the
Gleissberg and Schwabe cycles, and an ~5.5 year signal originating from
cycle asymmetry, i.e. the Waldmeier effect) can be identified as a
“bubble” shaped structure after 1950. The same frequency splitting
feature can also be found in the heliospheric magnetic field data and
the microwave radio flux.
---------------------------------------------------------
Title: Modulated stellar and solar cycles: parallels and differences
Authors: Oláh, K.; van Driel-Gesztelyi, L.; Strassmeier, K. G.
2012IAUS..286..279O Altcode:
We present examples of activity cycle timescales on different types
of stars from lowmass dwarfs to more massive giants, with wide-ranging
rotation rates, and compare the observed cyclicities to the irradiance
based solar cycle and its modulations. Using annual spectral solar
irradiance in wavelength bands typical for stellar observations
reconstructed by Shapiro et al. (2011), a direct comparison can be
made between cycle timescales and amplitudes derived for the Sun and
the stars. We show that cycles on multiple timescales, known to be
present in solar activity, also show up on stars when the dataset is
long enough to allow recognition. The cycle lengths are not fixed,
but evolve - gradually during some periods but there are also changes
on short timescales. In case the activity is dominated by spots,
i.e., by cooler surface features, the star is redder when fainter,
whereas other type of activity make the stars bluer when the activity
is higher. We found the Sun to be a member of the former group, based
on reconstructed spectral irradiance data by Shapiro et al. (2011).
---------------------------------------------------------
Title: Magnetic topology, coronal outflows, and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas,
Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea;
Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa,
Marc; Brooks, David
2012cosp...39.1173M Altcode: 2012cosp.meet.1173M
During 2-18 January 2008 a pair of low-latitude opposite polarity
coronal holes were observed on the Sun flanked by two ARs with
the heliospheric plasma sheet between them. Hinode/EUV Imaging
Telescope (EIS) is used to locate AR-related outflows and measure their
velocities. The Advanced Composition Explorer (ACE) in-situ observations
are employed to assess the resulting impacts on the interplanetary solar
wind (SW). Magnetic field extrapolations of the two ARs confirm that AR
plasma outflows observed with EIS are co-spatial with quasi-separatrix
layer locations, including the separatrix of a null point. Global
potential field source-surface modeling indicates that field lines
in the vicinity of the null point extend up to the source-surface,
enabling a part of the EIS plasma upflows access to the SW. Similar
upflow magnitude is also observed within closed field regions. Though
part of the plasma upflows observed with EIS remain confined along
closed coronal loops, a subset of them are indeed able to make their
imprint in the slow SW, making ARs bordering coronal holes a slow
SW contributor.
---------------------------------------------------------
Title: CME-related changes in line-of-sight magnetic field strength
in dimming regions observed by Hinode on 14 December 2006
Authors: Pedram, Ehsan; Matthews, Sarah A.; Van Driel-Gesztelyi, Lidia
2012cosp...39.1479P Altcode: 2012cosp.meet.1479P
No abstract at ADS
---------------------------------------------------------
Title: Are subsurface flows and coronal holes related?
Authors: Komm, Rudolf W.; Howe, R.; González Hernández, I.; Harra,
L.; Baker, D.; van Driel-Gesztelyi, L.
2012shin.confE.120K Altcode:
We study subsurface flows measured with a ring-diagram analysis of GONG
high-resolution Doppler data. In previous studies, we have focused on
the relationship between active regions and subsurface flows associated
with them. Synoptic subsurface flow maps show also large-scale patterns
that are not obviously associated with active regions. It is unknown
whether these flow patterns correlate with any large-scale magnetic
features. Here, we explore whether there is a relationship between
subsurface flows and coronal features. We analyze synoptic maps of
subsurface flows covering 18 Carrington rotations during the years
2006 and 2007 (CR 2038-2055). Long-lived coronal holes are present
during this epoch at low latitudes, which are accessible by ring-diagram
analysis of GONG data. We compare subsurface flow maps with EIT synoptic
maps of EUV images at 195A (http://sun.stanford.edu/synop/EIT/) and
will present the latest results.
---------------------------------------------------------
Title: The Creation of Outflowing Plasma in the Corona at Emerging
Flux Regions: Comparing Observations and Simulations
Authors: Harra, L. K.; Archontis, V.; Pedram, E.; Hood, A. W.; Shelton,
D. L.; van Driel-Gesztelyi, L.
2012SoPh..278...47H Altcode:
In this paper we analyse the flux emergence that occurred in the
following polarity area of an active region on 1 - 2 December
2006. Observations have revealed the existence of fast outflows
at the edge of the emerging flux region. We have performed 3-D
numerical simulations to study the mechanisms responsible for these
flows. The results indicate that these outflows are reconnection jets
or pressure-driven outflows, depending on the relative orientation
of the magnetic fields in contact (i.e. the emerging flux and the
active region's field which is favourable for reconnection on the
west side and nearly parallel with the pre-existing field on the east
side of the emerging flux). In the observations, the flows are larger
on the west side until late in the flux emergence, when the reverse
is true. The simulations show that the flows are faster on the west
side, but do not show the east flows increasing with time. There is an
asymmetry in the expansion of the emerging flux region, which is also
seen in the observations. The west side of the emerging flux region
expands faster into the corona than the other side. In the simulations,
efficient magnetic reconnection occurs on the west side, with new loops
being created containing strong downflows that are clearly seen in the
observations. On the other side, the simulations show strong compression
as the dominant mechanism for the generation of flows. There is evidence
of these flows in the observations, but the flows are stronger than
the simulations predict at the later stages. There could be additional
small-angle reconnection that adds to the flows from the compression,
as well as reconnection occurring in larger loops that lie across the
whole active region.
---------------------------------------------------------
Title: Nonlinear Force-Free Extrapolation of Emerging Flux with a
Global Twist and Serpentine Fine Structures
Authors: Valori, G.; Green, L. M.; Démoulin, P.; Vargas Domínguez,
S.; van Driel-Gesztelyi, L.; Wallace, A.; Baker, D.; Fuhrmann, M.
2012SoPh..278...73V Altcode:
We study the flux emergence process in NOAA active region 11024, between
29 June and 7 July 2009, by means of multi-wavelength observations
and nonlinear force-free extrapolation. The main aim is to extend
previous investigations by combining, as much as possible, high spatial
resolution observations to test our present understanding of small-scale
(undulatory) flux emergence, whilst putting these small-scale events
in the context of the global evolution of the active region. The
combination of these techniques allows us to follow the whole process,
from the first appearance of the bipolar axial field on the east limb,
until the buoyancy instability could set in and raise the main body
of the twisted flux tube through the photosphere, forming magnetic
tongues and signatures of serpentine field, until the simplification
of the magnetic structure into a main bipole by the time the active
region reaches the west limb. At the crucial time of the main emergence
phase high spatial resolution spectropolarimetric measurements of the
photospheric field are employed to reconstruct the three-dimensional
structure of the nonlinear force-free coronal field, which is then
used to test the current understanding of flux emergence processes. In
particular, knowledge of the coronal connectivity confirms the identity
of the magnetic tongues as seen in their photospheric signatures,
and it exemplifies how the twisted flux, which is emerging on small
scales in the form of a sea-serpent, is subsequently rearranged by
reconnection into the large-scale field of the active region. In
this way, the multi-wavelength observations combined with a nonlinear
force-free extrapolation provide a coherent picture of the emergence
process of small-scale magnetic bipoles, which subsequently reconnect
to form a large-scale structure in the corona.
---------------------------------------------------------
Title: Preface
Authors: Green, L. M.; Sakurai, T.; van Driel-Gesztelyi, L.
2012SoPh..278....1G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Granular-Scale Elementary Flux Emergence Episodes in a Solar
Active Region
Authors: Vargas Domínguez, S.; van Driel-Gesztelyi, L.; Bellot Rubio,
L. R.
2012SoPh..278...99V Altcode: 2012SoPh..tmp..259F; 2012arXiv1203.6428V
We analyse data from Hinode spacecraft taken over two 54-minute periods
during the emergence of AR 11024. We focus on small-scale portions
within the observed solar active region and discover the appearance of
very distinctive small-scale and short-lived dark features in Ca II H
chromospheric filtergrams and Stokes I images. The features appear in
regions with close-to-zero longitudinal magnetic field, and are observed
to increase in length before they eventually disappear. Energy release
in the low chromospheric line is detected while the dark features
are fading. Three complete series of these events are detected with
remarkably similar properties, i.e. lifetime of ≈ 12 min, maximum
length and area of 2 - 4 Mm and 1.6 - 4 Mm<SUP>2</SUP>, respectively,
and all with associated brightenings. In time series of magnetograms a
diverging bipolar configuration is observed accompanying the appearance
of the dark features and the brightenings. The observed phenomena
are explained as evidencing elementary flux emergence in the solar
atmosphere, i.e. small-scale arch filament systems rising up from the
photosphere to the lower chromosphere with a length scale of a few
solar granules. Brightenings are explained as being the signatures of
chromospheric heating triggered by reconnection of the rising loops
(once they have reached chromospheric heights) with pre-existing
magnetic fields, as well as being due to reconnection/cancellation
events in U-loop segments of emerging serpentine fields. The
characteristic length scale, area and lifetime of these elementary
flux emergence events agree well with those of the serpentine field
observed in emerging active regions. We study the temporal evolution
and dynamics of the events and compare them with the emergence of
magnetic loops detected in quiet Sun regions and serpentine flux
emergence signatures in active regions. The physical processes of
the emergence of granular-scale magnetic loops seem to be the same
in the quiet Sun and active regions. The difference is the reduced
chromospheric emission in the quiet Sun attributed to the fact that
loops are emerging in a region of lower ambient magnetic field density,
making interactions and reconnection less likely to occur. Incorporating
the novel features of granular-scale flux emergence presented in this
study, we advance the scenario for serpentine flux emergence.
---------------------------------------------------------
Title: On Signatures of Twisted Magnetic Flux Tube Emergence
Authors: Vargas Domínguez, S.; MacTaggart, D.; Green, L.; van
Driel-Gesztelyi, L.; Hood, A. W.
2012SoPh..278...33V Altcode: 2011arXiv1105.0758V
Recent studies of NOAA active region 10953, by Okamoto et
al. (Astrophys. J. Lett.673, 215, 2008; Astrophys. J.697, 913, 2009),
have interpreted photospheric observations of changing widths of the
polarities and reversal of the horizontal magnetic field component as
signatures of the emergence of a twisted flux tube within the active
region and along its internal polarity inversion line (PIL). A filament
is observed along the PIL and the active region is assumed to have an
arcade structure. To investigate this scenario, MacTaggart and Hood
(Astrophys. J. Lett.716, 219, 2010) constructed a dynamic flux emergence
model of a twisted cylinder emerging into an overlying arcade. The
photospheric signatures observed by Okamoto et al. (2008, 2009) are
present in the model although their underlying physical mechanisms
differ. The model also produces two additional signatures that can be
verified by the observations. The first is an increase in the unsigned
magnetic flux in the photosphere at either side of the PIL. The second
is the behaviour of characteristic photospheric flow profiles associated
with twisted flux tube emergence. We look for these two signatures in
AR 10953 and find negative results for the emergence of a twisted flux
tube along the PIL. Instead, we interpret the photospheric behaviour
along the PIL to be indicative of photospheric magnetic cancellation
driven by flows from the dominant sunspot. Although we argue against
flux emergence within this particular region, the work demonstrates
the important relationship between theory and observations for the
successful discovery and interpretation of signatures of flux emergence.
---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Martínez Pillet, Valentín; Klimchuk, James A.; Melrose,
Donald B.; Cauzzi, Gianna; van Driel-Gesztelyi, Lidia; Gopalswamy,
Natchimuthuk; Kosovichev, Alexander; Mann, Ingrid; Schrijver,
Carolus J.
2012IAUTA..28...61M Altcode: 2012IAUTA..28...61P
The solar activity cycle entered a prolonged quiet phase that started
in 2008 and ended in 2010. This minimum lasted for a year longer
than expected and all activity proxies, as measured from Earth and
from Space, reached minimum values never observed before (de Toma,
2012). The number of spotless days from 2006 to 2009 totals 800, the
largest ever recorded in modern times. Solar irradiance was at historic
minimums. The interplanetary magnetic field was measured at values as
low as 2.9 nT and the cosmic rays were observed at records-high. While
rumors spread that the Sun could be entering a grand minimum quiet
phase (such as the Maunder minimum of the XVII century), activity
took over in 2010 and we are now well into Solar Cycle 24 (albeit,
probably, a low intensity cycle), approaching towards a maximum due
by mid 2013. In addition to bringing us the possibility to observe
a quiet state of the Sun and of the Heliosphere that was previously
not recorded with modern instruments, the Sun has also shown us how
little we know about the dynamo mechanism that drives its activity as
all solar cycle predictions failed to see this extended minimum coming.
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: van Driel-Gesztelyi, Lidia; Schrijver, Carolus J.; Klimchuk,
James A.; Charbonneau, Paul; Fletcher, Lyndsay; Hasan, S. Sirajul;
Hudson, Hugh S.; Kusano, Kanya; Mandrini, Cristina H.; Peter, Hardi;
Vršnak, Bojan; Yan, Yihua
2012IAUTA..28...69V Altcode:
Commission 10 of the International Astronomical Union has more than
650 members who study a wide range of activity phenomena produced by
our nearest star, the Sun. Solar activity is intrinsically related
to solar magnetic fields and encompasses events from the smallest
energy releases (nano- or even picoflares) to the largest eruptions
in the Solar System, coronal mass ejections (CMEs), which propagate
into the Heliosphere reaching the Earth and beyond. Solar activity is
manifested in the appearance of sunspot groups or active regions, which
are the principal sources of activity phenomena from the emergence of
their magnetic flux through their dispersion and decay. The period
2008-2009 saw an unanticipated extended solar cycle minimum and
unprecedentedly weak polar-cap and heliospheric field. Associated with
that was the 2009 historical maximum in galactic cosmic rays flux since
measurements begun in the middle of the 20th Century. Since then Cycle
24 has re-started solar activity producing some spectacular eruptions
observed with a fleet of spacecraft and ground-based facilities. In
the last triennium major advances in our knowledge and understanding
of solar activity were due to continuing success of space missions as
SOHO, Hinode, RHESSI and the twin STEREO spacecraft, further enriched
by the breathtaking images of the solar atmosphere produced by the
Solar Dynamic Observatory (SDO) launched on 11 February 2010 in the
framework of NASA's Living with a Star program. In August 2012, at the
time of the IAU General Assembly in Beijing when the mandate of this
Commission ends, we will be in the unique position to have for the
first time a full 3-D view of the Sun and solar activity phenomena
provided by the twin STEREO missions about 120 degrees behind and
ahead of Earth and other spacecraft around the Earth and ground-based
observatories. These new observational insights are continuously
posing new questions, inspiring and advancing theoretical analysis
and modelling, improving our understanding of the physics underlying
magnetic activity phenomena. Commission 10 reports on a vigorously
evolving field of research produced by a large community. The number
of refereed publications containing `Sun', `heliosphere', or a synonym
in their abstracts continued the steady growth seen over the preceding
decades, reaching about 2000 in the years 2008-2010, with a total of
close to 4000 unique authors. This report, however, has its limitations
and it is inherently incomplete, as it was prepared jointly by the
members of the Organising Committee of Commission 10 (see the names
of the primary contributors to the sections indicated in parentheses)
reflecting their fields of expertise and interest. Nevertheless, we
believe that it is a representative sample of significant new results
obtained during the last triennium in the field of solar activity.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2012SoPh..276....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Forecasting a CME by Spectroscopic Precursor?
Authors: Baker, D.; van Driel-Gesztelyi, L.; Green, L. M.
2012SoPh..276..219B Altcode:
Multi-temperature plasma flows resulting from the interaction between
a mature active region (AR) inside an equatorial coronal hole (CH) are
investigated. Outflow velocities observed by Hinode EIS ranged from a
few to 13 km s<SUP>−1</SUP> for three days at the AR's eastern and
western edges. However, on the fourth day, velocities intensified up to
20 km s<SUP>−1</SUP> at the AR's western footpoint about six hours
prior to a CME. 3D MHD numerical simulations of the observed magnetic
configuration of the AR-CH complex showed that the expansion of the
mature AR's loops drives persistent outflows along the neighboring CH
field (Murray et al. in Solar Phys.261, 253, 2010). Based on these
simulations, intensification of outflows observed pre-eruption on
the AR's western side where same-polarity AR and CH field interface,
is interpreted to be the result of the expansion of a sigmoidal
AR, in particular, a flux rope containing a filament that provides
stronger compression of the neighboring CH field on this side of the
AR. Intensification of outflows in the AR is proposed as a new type
of CME precursor.
---------------------------------------------------------
Title: Preface
Authors: Marqué, C.; Nindos, A.; van Driel-Gesztelyi, L.; Mandrini,
C. H.
2012esrs.book....1M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Sun-Earth Connection near Solar Minimum: Placing it
into Context
Authors: Bisi, Mario M.; Thompson, Barbara J.; Emery, Barbara A.;
Gibson, Sarah E.; Leibacher, John; van Driel-Gesztelyi, Lidia
2011SoPh..274....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Preface
Authors: Marqué, C.; Nindos, A.; van Driel-Gesztelyi, L.; Mandrini,
C. H.
2011SoPh..273..307M Altcode: 2011SoPh..tmp..385M
No abstract at ADS
---------------------------------------------------------
Title: Coronal Jets, Magnetic Topologies, and the Production of
Interplanetary Electron Streams
Authors: Li, C.; Matthews, S. A.; van Driel-Gesztelyi, L.; Sun, J.;
Owen, C. J.
2011ApJ...735...43L Altcode: 2013arXiv1305.5602L
We investigate the acceleration source of the impulsive solar
energetic particle (SEP) events on 2007 January 24. Combining the in
situ electron measurements and remote-sensing solar observations, as
well as the calculated magnetic fields obtained from a potential-field
source-surface model, we demonstrate that the jets associated with
the hard X-ray flares and type-III radio bursts, rather than the
slow and partial coronal mass ejections, are closely related to the
production of interplanetary electron streams. The jets, originated
from the well-connected active region (AR 10939) whose magnetic
polarity structure favors the eruption, are observed to be forming
in a coronal site, extending to a few solar radii, and having a good
temporal correlation with the electron solar release. The open-field
lines near the jet site are rooted in a negative polarity, along which
energetic particles escape from the flaring AR to the near-Earth space,
consistent with the in situ electron pitch angle distribution. The
analysis enables us to propose a coronal magnetic topology relating
the impulsive SEP events to their solar source.
---------------------------------------------------------
Title: Twisted Flux Tube Emergence Evidenced in Longitudinal
Magnetograms: Magnetic Tongues
Authors: Luoni, M. L.; Démoulin, P.; Mandrini, C. H.; van
Driel-Gesztelyi, L.
2011SoPh..270...45L Altcode: 2011SoPh..tmp...66L
Bipolar active regions (ARs) are thought to be formed by twisted flux
tubes, as the presence of such twist is theoretically required for a
cohesive rise through the whole convective zone. We use longitudinal
magnetograms to demonstrate that a clear signature of a global magnetic
twist is present, particularly, during the emergence phase when the AR
is forming in a much weaker pre-existing magnetic field environment. The
twist is characterised by the presence of elongated polarities, called
"magnetic tongues", which originate from the azimuthal magnetic field
component. The tongues first extend in size before retracting when the
maximum magnetic flux is reached. This implies an apparent rotation of
the magnetic bipole. Using a simple half-torus model of an emerging
twisted flux tube having a uniform twist profile, we derive how the
direction of the polarity inversion line and the elongation of the
tongues depend on the global twist in the flux rope. Using a sample of
40 ARs, we verify that the helicity sign, determined from the magnetic
polarity distribution pattern, is consistent with the sign derived from
the photospheric helicity flux computed from magnetogram time series,
as well as from other proxies such as sheared coronal loops, sigmoids,
flare ribbons and/or the associated magnetic cloud observed in situ
at 1 AU. The evolution of the tongues observed in emerging ARs is
also closely similar to the evolution found in recent MHD numerical
simulations. We also found that the elongation of the tongue formed
by the leading magnetic polarity is significantly larger than that of
the following polarity. This newly discovered asymmetry is consistent
with an asymmetric Ω-loop emergence, trailing the solar rotation,
which was proposed earlier to explain other asymmetries in bipolar ARs.
---------------------------------------------------------
Title: Pulsed Flows Along a Cusp Structure Observed with SDO/AIA
Authors: Thompson, Barbara; Démoulin, P.; Mandrini, C.; Mays, M.;
Ofman, L.; Van Driel-Gesztelyi, L.; Viall, N.
2011SPD....42.2117T Altcode: 2011BAAS..43S.2117T
We present observations of a cusp-shaped structure that formed after
a flare and coronal mass ejection on 14 February 2011. Throughout
the evolution of the cusp structure, blob features up to a few Mm in
size were observed flowing along the legs and stalk of the cusp at
projected speeds ranging from 50 to 150 km/sec. Around two dozen blob
features, on order of 1 - 3 minutes apart, were tracked in multiple
AIA EUV wavelengths. The blobs flowed outward (away from the Sun)
along the cusp stalk, and most of the observed speeds were either
constant or decelerating. We attempt to reconstruct the 3-D magnetic
field of the evolving structure, discuss the possible drivers of the
flows (including pulsed reconnection and tearing mode instability),
and compare the observations to studies of pulsed reconnection and
blob flows in the solar wind and the Earth's magnetosphere.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2011SoPh..269....1L Altcode: 2011SoPh..tmp...21L
No abstract at ADS
---------------------------------------------------------
Title: Pre-Flare Flows in the Corona
Authors: Wallace, A. J.; Harra, L. K.; van Driel-Gesztelyi, L.; Green,
L. M.; Matthews, S. A.
2010SoPh..267..361W Altcode: 2010SoPh..tmp..223W; 2010SoPh..tmp..199W
Solar flares take place in regions of strong magnetic fields and
are generally accepted to be the result of a resistive instability
leading to magnetic reconnection. When new flux emerges into a
pre-existing active region it can act as a flare and coronal mass
ejection trigger. In this study we observed active region 10955 after
the emergence of small-scale additional flux at the magnetic inversion
line. We found that flaring began when additional positive flux levels
exceeded 1.38×10<SUP>20</SUP> Mx (maxwell), approximately 7 h after
the initial flux emergence. We focussed on the pre-flare activity of
one B-class flare that occurred on the following day. The earliest
indication of activity was a rise in the non-thermal velocity one
hour before the flare. 40 min before flaring began, brightenings and
pre-flare flows were observed along two loop systems in the corona,
involving the new flux and the pre-existing active region loops. We
discuss the possibility that reconnection between the new flux
and pre-existing loops before the flare drives the flows by either
generating slow mode magnetoacoustic waves or a pressure gradient
between the newly reconnected loops. The subsequent B-class flare
originated from fast reconnection of the same loop systems as the
pre-flare flows.
---------------------------------------------------------
Title: Temporal evolution and spatial variation of the solar wind
from multi-spacecraft measurements
Authors: Opitz, A.; Wurz, P.; Fedorov, A.; Sauvaud, J.; Luhmann, J. G.;
Riley, P.; Szego, K.; Russell, C. T.; Galvin, A. B.; Rouillard, A. P.;
Vourlidas, A.; van Driel-Gesztelyi, L.
2010AGUFMSH33C..07O Altcode:
We study the temporal evolution and the spatial variation of the solar
wind on different scales. The analyzed multi-spacecraft (STEREO, VEX,
SOHO, MEX, and other spacecraft) measurements were obtained between 2007
and 2010 during solar minimum in the inner heliosphere. We derived
the temporal and spatial variability of the different solar wind
parameters (proton bulk velocity, electron core density, etc). These
results support prediction of the solar wind parameters for different
heliospheric positions and help to derive its validity range. In order
to explain occasional deviations from the nominal solar wind evolution
we use imaging data and modeling results.
---------------------------------------------------------
Title: Solar Physics Memoir Series Reinstituted
Authors: Cliver, Ed; van Driel-Gesztelyi, Lidia
2010SoPh..267..233C Altcode: 2010SoPh..tmp..194C
No abstract at ADS
---------------------------------------------------------
Title: Observational and numerical study of the 25 July 2004 event
Authors: Soenen, A.; Jacobs, C.; Poedts, S.; van Driel-Gesztelyi,
L.; Torok, T.; Lapenta, G.
2010AGUFMSH23B1843S Altcode:
We study the 25 July 2004 event. By analyzing SOHO EIT images we
establish a basic understanding of the large-scale interaction going
on during this event. Magnetic reconnection between the expanding
CME and the Southern hemispheric active regions (AR) will connect the
leading polarities of the two ARs, lead to brightening in the ARs and
transport CME field line foot points to distant ARs (observable as
dimming at the foot points).We reproduce the large scale interactions
during this event using three-dimensional magneto-hydrodynamic (MHD)
simulations. We superimpose a magnetic source region that resembles
the SOHO MDI images on a basic wind model. By emerging new flux at the
centre of this region we initiate a Coronal Mass Ejection (CME). We
monitor the evolution of this CME and study its interaction with the
source region.
---------------------------------------------------------
Title: Preface
Authors: Bisi, M. M.; Breen, A. R.; van Driel-Gesztelyi, L.; Mandrini,
C. H.
2010SoPh..265....1B Altcode: 2010SoPh..tmp..143B
No abstract at ADS
---------------------------------------------------------
Title: Revealing the Fine Structure of Coronal Dimmings and Associated
Flows with Hinode/EIS. Implications for Understanding the Source
Regions of Sustained Outflow Following CMEs
Authors: Attrill, G. D. R.; Harra, L. K.; van Driel-Gesztelyi, L.;
Wills-Davey, M. J.
2010SoPh..264..119A Altcode: 2010SoPh..tmp...80A
We study two CME events on 13 and 14 December 2006 that were associated
with large-scale dimmings. We study the eruptions from pre-event on
11 December through the recovery on 15 December, using a combination
of Hinode/EIS, SOHO/EIT, SOHO/MDI, and MLSO Hα data. The GOES
X-class flares obscured the core dimmings, but secondary dimmings
developed remote from the active region (AR) in both events. The
secondary dimmings are found to be formed by a removal of bright
coronal material from loops in the plage region to the East of the
AR. Using Hinode/EIS data, we find that the outflows associated with
the coronal-dimming regions are highly structured. The concentrated
outflows are located at the footpoints of coronal loops (which exist
before, and are re-established after, the eruptions), and these are
correlated with regions of positive magnetic elements. Comparative
study of the Hinode/EIS and SOHO/EIT data shows that the reduction in
outflow velocity is consistent with the recovery in intensity of the
studied regions. We find that concentrated downflows develop during the
recovery phase of the dimmings and are also correlated with the same
positive magnetic elements that were previously related to outflows.
---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Melrose, Donald B.; Martinez Pillet, Valentin; Webb, David
F.; Bougeret, Jean-Louis; Klimchuk, James A.; Kosovichev, Alexander;
van Driel-Gesztelyi, Lidia; von Steiger, Rudolf
2010IAUTB..27..146M Altcode:
This report is on activities of the Division at the General Assembly
in Rio de Janeiro. Summaries of scientific activities over the past
triennium have been published in Transactions A, see Melrose et
al. (2008), Klimchuk et al. (2008), Martinez Pillet et al. (2008) and
Bougeret et al. (2008). The business meeting of the three Commissions
were incorporated into the business meeting of the Division. This
report is based in part on minutes of the business meeting, provided
by the Secretary of the Division, Lidia van Driel-Gesztelyi, and it
also includes reports provided by the Presidents of the Commissions
(C10, C12, C49) and of the Working Groups (WGs) in the Division.
---------------------------------------------------------
Title: Solar Observation Target Identification Convention for use
in Solar Physics
Authors: Leibacher, John; Sakurai, Takashi; Schrijver, Carolus J.;
van Driel-Gesztelyi, Lidia
2010SoPh..263....1L Altcode: 2010SoPh..263....1.; 2010SoPh..tmp...71.
We strongly encourage the use of a standardized target identification
to be included in pub- lications on solar events. The primary purpose
is to enable the automated identification of publications on the same
event, or on other related events, in the on-line literature by search
engines such as the Astrophysics Data System (ADS). The convention does
not aim to categorize or classify events, but is limited specifically
to the identification of regions in space and intervals in time within
which events occur.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2010SoPh..262....1L Altcode: 2010SoPh..tmp...18L
No abstract at ADS
---------------------------------------------------------
Title: Outflows at the Edges of an Active Region in a Coronal Hole:
A Signature of Active Region Expansion?
Authors: Murray, M. J.; Baker, D.; van Driel-Gesztelyi, L.; Sun, J.
2010SoPh..261..253M Altcode: 2009arXiv0912.1246M
Outflows of plasma at the edges of active regions surrounded by quiet
Sun are now a common observation with the Hinode satellite. While there
is observational evidence to suggest that the outflows are originating
in the magnetic field surrounding the active regions, there is no
conclusive evidence that reveals how they are driven. Motivated
by observations of outflows at the periphery of a mature active
region embedded in a coronal hole, we have used a three-dimensional
simulation to emulate the active region's development in order to
investigate the origin and driver of these outflows. We find that
outflows are accelerated from a site in the coronal hole magnetic
field immediately surrounding the active region and are channelled
along the coronal hole field as they rise through the atmosphere. The
plasma is accelerated simply as a result of the active region
expanding horizontally as it develops. Many of the characteristics
of the outflows generated in the simulation are consistent with
those of observed outflows: velocities up to 45 km s<SUP>−1</SUP>,
properties akin to the coronal hole, proximity to the active region's
draining loops, expansion with height, and projection over monopolar
photospheric magnetic concentrations. Although the horizontal expansion
occurs as a consequence of the active region's development in the
simulation, expansion is also a general feature of established active
regions. Hence, it is entirely possible and plausible that the expansion
acceleration mechanism displayed in the simulation is occurring in
active regions on the Sun and, in addition to reconnection, is driving
the outflows observed at their edges.
---------------------------------------------------------
Title: EIT/Coronal waves and coronal dimming: a holistic approach
Authors: van Driel-Gesztelyi, Lidia
2010cosp...38.1793V Altcode: 2010cosp.meet.1793V
If EIT waves were simple, they would not be such interesting and
divisive a subject. I will argue that one of the main reasons for the
persistent elusiveness of their interpretation is that they are due to
a composite of causes, which include MHD waves, compression of coronal
plasma by the expanding CME as well as magnetic reconnection between the
CME and surrounding magnetic structures. There is not one single cause
which on itself could explain all the observed characteristics. I will
show that magnetic reconnection between the CME and other magnetic
structures is responsible for some of the transient brightenings
which show up along the diffuse bright EIT wave front, as evidenced by
long-lived (¿ 1 h) dimming regions which form in their wake. CME-driven
dynamic reconnection provides a natural explanation for the formation
of widespread secondary dimming regions, indicating that large portions
of the Sun become constituents of the CME. This implies that the extent
of the secondary dimming matches the final angular width of the CME,
as observed. I will review observations and MHD simulations supporting
the composite nature of the causes of EIT waves, and will argue in
favour of a holistic approach, which will not diminish their interest,
but rather bring us closer to understanding them.
---------------------------------------------------------
Title: Magnetic reconnection along QSLs -a major driver of active
region outflows
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Mandrini,
Cristina H.; Demoulin, Pascal
2010cosp...38.2926B Altcode: 2010cosp.meet.2926B
The relationship between quasi-separatrix layers (QSLs), or in the limit
of infinitely thin QSLs, separatrices, and various activity phenomena
has been explored in many different solar magnetic configurations
across all scales in recent years. In the absence of magnetic nulls,
fast reconnec-tion along QSLs, which are specific locations in the
magnetic topology where field lines display strong gradients of
magnetic connectivity, was identified as the main physical process
at the origin of flares. Recently, it was shown that fast (tens of
km/s) persistent hot plasma upflows in active regions (ARs) can also
be linked to locations of QSLs. It is likely that these upflows that
occur at the edges of ARs over unipolar magnetic field concentrations
are accelerated by magnetic reconnection along QSLs. We will show
multi-temperature spectral scan observations from Hinode's EIS combined
with magnetic modeling of QSLs in two ARs observed on 20-21 February
2007 and 11 January 2008. The latter AR is observed and modeled when
it is in the vicinity of the solar central meridian where there are no
projection effects, thereby eliminating ambiguity linking the origin
of multi-temperature observations of AR upflows to QSLs. We use the
Potential Source Surface Model to look for open field lines in the
vicinity of upflows and QSL locations in order to demonstrate whether
these upflows become outflows and can contribute to the solar wind.
---------------------------------------------------------
Title: Interacting active regions and coronal holes: implications
for coronal outflows and solar wind structure
Authors: Culhane, J. Leonard; Baker, Deborah; Rouillard, Alexis;
van Driel-Gesztelyi, Lidia
2010cosp...38.1863C Altcode: 2010cosp.meet.1863C
When active regions are adjacent to coronal holes a variety of magnetic
field interactions can result. These may include the interchange
reconnection between the closed active region (AR) fields and the
open field of the coronal hole (CH), leading to fast and significant
evolution of coronal hole boundaries. Outcomes may include variability
of -or changes in, active region-associated hot plasma outflows seen
with Hinode/EIS and the modulation of the solar wind flows on open
field lines. Depending on their relative positions on the Sun, the
AR-CH interactions may have their signatures embedded in co-rotating
interaction regions (CIRs) or rarefaction regions. During two intervals
-8/11 January, 2008 and 7/9 December, 2008, we have made observations
with Hinode of two oppositely configured situations on the Sun. For
8/11 January, the coronal hole leads the active region while for
7/9 December the order is reversed. The Hinode EIS instrument is
used to locate outflows and measure their velocities while the XRT
is used to image the source regions, including the variable nature
of the outflows. SOHO EIT imaging is used to follow the longer-term
evolution of the coronal hole boundaries while MDI is used to observe
changes in the magnetic field. STEREO imaging and in-situ data are also
employed -as are ACE observations, to assess the resulting impacts on
interplanetary solar wind structures. The contrasting behaviour that
results from magnetic interactions in the two different configurations
is described and assessed.
---------------------------------------------------------
Title: Coronal magnetic topology and the solar source of beam-like
electron events
Authors: Li, Chuan; van Driel-Gesztelyi, Lidia; Matthews, Sarah A.;
Sun, Jian; Mandrini, Cristina H.; Owen, Christopher
2010cosp...38.2986L Altcode: 2010cosp.meet.2986L
More and more evidence indicates a strong correlation between impulsive
solar energetic particle (SEP) events and the magnetic reconnections in
the vicinity of flaring active regions (ARs). However, it is still not
clear how they are related to each other. We present the investigation
of the AR 10939, which produced two B-class flares, accompanied by
narrow coronal mass ejections (CMEs)and successive beam-like electron
events on 24 January 2007. Using in situ electron observations from
ACE/EPAM and WIND/3DP, and imaging data from Hinode/EIS, RHESSI,
and TRACE, coupled with magnetic modeling, we could establish the
correlations of the coronal magnetic topologies, jet activities,
and the accelerations of impulsive electrons.
---------------------------------------------------------
Title: Characteristics of the Nonthermal Velocity Signature Observed
in the Impulsive Phase of the 2007 May 19 Flare
Authors: Hara, H.; Watanabe, T.; Bone, L. A.; Culhane, J. L.; van
Driel-Gesztelyi, L.; Young, P. R.
2009ASPC..415..459H Altcode:
The Hinode EUV Imaging Spectrometer (EIS) observed a long duration
flare with a weak impulsive phase that appears to conform to the
standard two-ribbon flare reconnection model. EIS scanned the flare
site during the impulsive phase and observed Fe XXIII and Fe XXIV line
emission that closely followed the flare hard X-ray emission while the
line profiles showed significant non-thermal broadening. We suggest
that a shock originating at the reconnection site which sweeps up and
heats the coronal plasma can account for our observations.
---------------------------------------------------------
Title: Intensification of Plasma Upflows in an Active Region---Coronal
Hole Complex: A CME Precursor
Authors: Baker, D.; van Driel-Gesztelyi, L.; Murray, M. J.; Green,
L. M.; Török, T.; Sun, J.
2009ASPC..415...75B Altcode:
We investigate the plasma flows resulting from the interaction between
a mature active region (AR) and a surrounding equatorial coronal hole
(CH) observed by Hinode's EIS and XRT from 15 to 18 October 2007. For 3
days, EIS velocity maps showed upflows at the AR's eastern and western
edges that were consistently between 5 and 10 km s<SUP>-1</SUP>, whereas
downflows of up to 30 km s<SUP>-1</SUP> were seen in AR loops. However,
on 18 October, velocity profiles of hotter coronal lines revealed
intensification in upflow velocities of up to 18 km s<SUP>-1</SUP>
at the AR's western footpoints 4.5 hours prior to a CME. We compare
the AR's plasma flows with 2.5D MHD numerical simulations of the
magnetic configuration, which show that expansion of the mature AR's
loops drives upflows along the neighboring CH field. Further, the
intensification of upflows observed on the AR's western side prior to
a CME is interpreted to be the result of the expansion of a flux rope
containing a filament further compressing the neighboring CH field.
---------------------------------------------------------
Title: Solar Physics Publication Ethics Policies
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2009SoPh..260....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Reconnection along Quasi-separatrix Layers as a
Driver of Ubiquitous Active Region Outflows
Authors: Baker, D.; van Driel-Gesztelyi, L.; Mandrini, C. H.;
Démoulin, P.; Murray, M. J.
2009ApJ...705..926B Altcode: 2009arXiv0909.4738B
Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous
outflows of a few to 50 km s<SUP>-1</SUP> from active regions
(ARs). These outflows are most prominent at the AR boundary and
appear over monopolar magnetic areas. They are linked to strong
non-thermal line broadening and are stronger in hotter EUV lines. The
outflows persist for at least several days. Using Hinode EIS and X-Ray
Telescope observations of AR 10942 coupled with magnetic modeling,
we demonstrate that the outflows originate from specific locations
of the magnetic topology where field lines display strong gradients
of magnetic connectivity, namely quasi-separatrix layers (QSLs),
or in the limit of infinitely thin QSLs, separatrices. We found the
strongest AR outflows to be in the vicinity of QSL sections located over
areas of strong magnetic field. We argue that magnetic reconnection at
QSLs separating closed field lines of the AR and either large-scale
externally connected or "open" field lines is a viable mechanism for
driving AR outflows which are likely sources of the slow solar wind.
---------------------------------------------------------
Title: Signatures of interchange reconnection: STEREO, ACE and Hinode
observations combined
Authors: Baker, D.; Rouillard, A. P.; van Driel-Gesztelyi, L.;
Démoulin, P.; Harra, L. K.; Lavraud, B.; Davies, J. A.; Opitz, A.;
Luhmann, J. G.; Sauvaud, J. -A.; Galvin, A. B.
2009AnGeo..27.3883B Altcode: 2009arXiv0909.5624B
Combining STEREO, ACE and Hinode observations has presented an
opportunity to follow a filament eruption and coronal mass ejection
(CME) on 17 October 2007 from an active region (AR) inside a coronal
hole (CH) into the heliosphere. This particular combination of
"open" and closed magnetic topologies provides an ideal scenario for
interchange reconnection to take place. With Hinode and STEREO data
we were able to identify the emergence time and type of structure
seen in the in-situ data four days later. On the 21st, ACE observed
in-situ the passage of an ICME with "open" magnetic topology. The
magnetic field configuration of the source, a mature AR located
inside an equatorial CH, has important implications for the solar and
interplanetary signatures of the eruption. We interpret the formation of
an "anemone" structure of the erupting AR and the passage in-situ of the
ICME being disconnected at one leg, as manifested by uni-directional
suprathermal electron flux in the ICME, to be a direct result of
interchange reconnection between closed loops of the CME originating
from the AR and "open" field lines of the surrounding CH.
---------------------------------------------------------
Title: Formation, Interaction and Merger of an Active Region and a
Quiescent Filament Prior to Their Eruption on 19 May 2007
Authors: Bone, L. A.; van Driel-Gesztelyi, L.; Culhane, J. L.;
Aulanier, G.; Liewer, P.
2009SoPh..259...31B Altcode:
We report observations of the formation of two filaments - one
active and one quiescent, and their subsequent interactions prior to
eruption. The active region filament appeared on 17 May 2007, followed
by the quiescent filament about 24 hours later. In the 26 hour interval
preceding the eruption, which occurred at around 12:50 UT on 19 May
2007, we see the two filaments attempting to merge and filament material
is repeatedly heated suggesting magnetic reconnection. The filament
structure is observed to become increasingly dynamic preceding the
eruption with two small hard X-ray sources seen close to the active
part of the filament at around 01:38 UT on 19 May 2007 during one of
the activity episodes. The final eruption on 19 May at about 12:51 UT
involves a complex CME structure, a flare and a coronal wave. A magnetic
cloud is observed near Earth by the STEREO-B and WIND spacecraft about
2.7 days later. Here we describe the behaviour of the two filaments
in the period prior to the eruption and assess the nature of their
dynamic interactions.
---------------------------------------------------------
Title: Preface
Authors: Christian, Eric R.; Kaiser, Michael L.; Kucera, Therese A.;
St. Cyr, O. C.; van Driel-Gesztelyi, Lidia; Mandrini, Cristina H.
2009SoPh..256....1C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stereoscopic Analysis of the 19 May 2007 Erupting Filament
Authors: Liewer, P. C.; De Jong, E. M.; Hall, J. R.; Howard, R. A.;
Thompson, W. T.; Culhane, J. L.; Bone, L.; van Driel-Gesztelyi, L.
2009SoPh..256...57L Altcode: 2009arXiv0904.1055L
A filament eruption, accompanied by a B9.5 flare, coronal dimming,
and an EUV wave, was observed by the Solar TERrestrial Relations
Observatory (STEREO) on 19 May 2007, beginning at about 13:00 UT. Here,
we use observations from the SECCHI/EUVI telescopes and other solar
observations to analyze the behavior and geometry of the filament before
and during the eruption. At this time, STEREO A and B were separated by
about 8.5°, sufficient to determine the three-dimensional structure
of the filament using stereoscopy. The filament could be followed in
SECCHI/EUVI 304 Å stereoscopic data from about 12 hours before to about
2 hours after the eruption, allowing us to determine the 3D trajectory
of the erupting filament. From the 3D reconstructions of the filament
and the chromospheric ribbons in the early stage of the eruption,
simultaneous heating of both the rising filamentary material and the
chromosphere directly below is observed, consistent with an eruption
resulting from magnetic reconnection below the filament. Comparisons
of the filament during eruption in 304 Å and Hα show that when it
becomes emissive in He II, it tends to disappear in Hα , indicating
that the disappearance probably results from heating or motion, not
loss, of filamentary material.
---------------------------------------------------------
Title: Magnetic reconnection and energy release on the Sun and
solar-like stars
Authors: van Driel-Gesztelyi, Lidia
2009IAUS..259..191V Altcode:
Magnetic reconnection is thought to play an important role in liberating
free energy stored in stressed magnetic fields. The consequences vary
from undetectable nanoflares to huge flares, which have signatures
over a wide wavelength range, depending on e.g. magnetic topology,
free energy content, total flux, and magnetic flux density of the
structures involved. Events of small energy release, which are thought
to be the most numerous, are one of the key factors in the existence
of a hot corona in the Sun and solar-like stars. The majority of large
flares are ejective, i.e. involve the expulsion of large quantities of
mass and magnetic field from the star. Since magnetic reconnection
requires small length-scales, which are well below the spatial
resolution limits of even the solar observations, we cannot directly
observe magnetic reconnection happening. However, there is a plethora
of indirect evidences from X-rays to radio observations of magnetic
reconnection. I discuss key observational signatures of flares on the
Sun and solar-paradigm stellar flares and describe models emphasizing
synergy between observations and theory.
---------------------------------------------------------
Title: Magnetic Flux Emergence, Activity, Eruptions and Magnetic
Clouds: Following Magnetic Field from the Sun to the Heliosphere
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.
2009SSRv..144..351V Altcode: 2008SSRv..tmp..185V
We present an overview of how the principal physical properties of
magnetic flux which emerges from the toroidal fields in the tachocline
through the turbulent convection zone to the solar surface are linked
to solar activity events, emphasizing the effects of magnetic field
evolution and interaction with other magnetic structures on the
latter. We compare the results of different approaches using various
magnetic observables to evaluate the probability of flare and coronal
mass ejection (CME) activity and forecast eruptive activity on the
short term (i.e. days). Then, after a brief overview of the observed
properties of CMEs and their theoretical models, we discuss the
ejecta properties and describe some typical magnetic and composition
characteristics of magnetic clouds (MCs) and interplanetary CMEs
(ICMEs). We review some individual examples to clarify the link between
eruptions from the Sun and the properties of the resulting ejecta. The
importance of a synthetic approach to solar and interplanetary magnetic
fields and activity is emphasized.
---------------------------------------------------------
Title: The link between CME-associated dimmings and interplanetary
magnetic clouds
Authors: Mandrini, Cristina H.; Nakwacki, María S.; Attrill, Gemma;
van Driel-Gesztelyi, Lidia; Dasso, Sergio; Démoulin, Pascal
2009IAUS..257..265M Altcode:
Coronal dimmings often develop in the vicinity of erupting magnetic
configurations. It has been suggested that they mark the location of
the footpoints of ejected flux ropes and, thus, their magnetic flux can
be used as a proxy for the ejected flux. If so, this quantity can be
compared to the flux in the associated interplanetary magnetic cloud
(MC) to find clues about the origin of the ejected flux rope. In the
context of this interpretation, we present several events for which
we have done a comparative solar-interplanetary analysis. We combine
SOHO/Extreme Ultraviolet Imaging Telescope (EIT) data and Michelson
Doppler Imager (MDI) magnetic maps to identify and measure the flux
in the dimmed regions. We model the associated MCs and compute their
magnetic flux using in situ observations. We find that the magnetic
fluxes in the dimmings and MCs are compatible in some events; though
this is not the case for large-scale and intense eruptions that occur in
regions that are not isolated from others. We conclude that, in these
particular cases, a fraction of the dimmed regions can be formed by
reconnection between the erupting field and the surrounding magnetic
structures, via a stepping process that can also explain other CME
associated events.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2009SoPh..255....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Melrose, Donald B.; Martínez Pillet, Valentin; Webb, David
F.; van Driel-Gesztelyi, Lidia; Bougeret, Jean-Louis; Klimchuk,
James A.; Kosovichev, Alexander; von Steiger, Rudolf
2009IAUTA..27...73M Altcode:
Division II of the IAU provides a forum for astronomers and
astrophysicists studying a wide range of phenomena related to the
structure, radiation and activity of the Sun, and its interaction with
the Earth and the rest of the solar system. Division II encompasses
three Commissions, 10, 12 and 49, and four Working Groups.
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Klimchuk, James A.; van Driel-Gesztelyi, Lidia; Schrijver,
Carolus J.; Melrose, Donald B.; Fletcher, Lyndsay; Gopalswamy,
Natchimuthuk; Harrison, Richard A.; Mandrini, Cristina H.; Peter,
Hardi; Tsuneta, Saku; Vršnak, Bojan; Wang, Jing-Xiu
2009IAUTA..27...79K Altcode: 2008arXiv0809.1444K
Commission 10 deals with solar activity in all of its forms,
ranging from the smallest nanoflares to the largest coronal mass
ejections. This report reviews scientific progress over the roughly
two-year period ending in the middle of 2008. This has been an exciting
time in solar physics, highlighted by the launches of the Hinode and
STEREO missions late in 2006. The report is reasonably comprehensive,
though it is far from exhaustive. Limited space prevents the inclusion
of many significant results. The report is divided into the following
sections: Photosphere and chromosphere; Transition region; Corona and
coronal heating; Coronal jets; flares; Coronal mass ejection initiation;
Global coronal waves and shocks; Coronal dimming; The link between low
coronal CME signatures and magnetic clouds; Coronal mass ejections in
the heliosphere; and Coronal mass ejections and space weather. Primary
authorship is indicated at the beginning of each section.
---------------------------------------------------------
Title: Simulations of emerging flux in a coronal hole: oscillatory
reconnection
Authors: Murray, M. J.; van Driel-Gesztelyi, L.; Baker, D.
2009A&A...494..329M Altcode:
Context: Observations and simulations show that reconnection will
take place when a flux tube emerges into a coronal hole, which is
characterised by magnetic fieldlines “open” towards interplanetary
space. Although the mechanism by which reconnection is initiated has
been thoroughly studied, the long-term evolution of this reconnecting
magnetic system remains unreported. <BR />Aims: We aim to understand
the long-term evolution of the reconnecting flux tube and coronal
hole system and, in particular, to ascertain whether it can reach an
equilibrium state in which all reconnection has ceased. By determining
the evolution in this particular scenario, we aim to be able to
select a subset from the broad spectrum of reconnecting systems,
which will undergo the same progression to equilibrium. <BR />Methods:
Using a 2.5-dimensional numerical magnetohydrodynamic (MHD) code, we
evolve a simple stratified atmospheric domain, which is endowed with a
vertical magnetic field, representing the interior of a coronal hole,
and a horizontal buoyant flux tube that is placed near the bottom
of the domain. To investigate the long-term evolution of the system,
we continue to study the domain long after the flux tube has emerged
and reconnection has commenced between the magnetic fields of the
flux tube and coronal hole. <BR />Results: We find that a series of
reconnection reversals (or oscillatory reconnection) takes place,
whereby reconnection occurs in distinct bursts and the inflow and
outflow magnetic fields of one burst of reconnection become the
outflow and inflow fields in the following burst of reconnection,
respectively. During each burst of reconnection the gas pressure in the
bounded outflow regions increases above the level of that in the inflow
regions and, eventually, gives rise to a reconnection reversal. In
consecutive bursts of reconnection, the contrast in the gas pressure
across the boundaries of the inflow and outflow regions decreases and,
over time, the system settles towards equilibrium. Once the equilibrium
state is reached, all reconnection ceases. This is the first reported
instance of oscillatory reconnection initiated in a self-consistent
manner, and the signatures of the mechanism compare favourably with
observations of select flux emergence events and with solar and stellar
flares. <BR />Conclusions: Across the broader spectrum of reconnecting
systems, oscillatory reconnection will only occur if the outflow regions
are quasi-bounded during each burst of reconnection. The swaying outflow
jet and periodic heating signatures of oscillatory reconnection are
exceedingly similar to those exhibited by MHD modes and, in many
observations, distinction between the two mechanisms may be impossible.
---------------------------------------------------------
Title: Magnetic Flux Emergence, Activity, Eruptions and Magnetic
Clouds: Following Magnetic Field from the Sun to the Heliosphere
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.
2009odsm.book..351V Altcode:
We present an overview of how the principal physical properties of
magnetic flux which emerges from the toroidal fields in the tachocline
through the turbulent convection zone to the solar surface are linked
to solar activity events, emphasizing the effects of magnetic field
evolution and interaction with other magnetic structures on the
latter. We compare the results of different approaches using various
magnetic observables to evaluate the probability of flare and coronal
mass ejection (CME) activity and forecast eruptive activity on the
short term (i.e. days). Then, after a brief overview of the observed
properties of CMEs and their theoretical models, we discuss the
ejecta properties and describe some typical magnetic and composition
characteristics of magnetic clouds (MCs) and interplanetary CMEs
(ICMEs). We review some individual examples to clarify the link between
eruptions from the Sun and the properties of the resulting ejecta. The
importance of a synthetic approach to solar and interplanetary magnetic
fields and activity is emphasized.
---------------------------------------------------------
Title: Flux Rope Eruption From the Sun to the Earth: What do Reversals
in the Azimuthal Magnetic Field Gradient Tell us About the Evolution
of the Magnetic Structure?
Authors: Steed, K.; Owen, C. J.; Harra, L. K.; Green, L. M.; Dasso,
S.; Walsh, A. P.; Démoulin, P.; van Driel-Gesztelyi, L.
2008AGUFMSH23B1638S Altcode:
Using ACE in situ data we identify and describe an interplanetary
magnetic cloud (MC) observed near Earth on 13 April 2006. We also use
multi-instrument and multi-wavelength observations from SOHO, TRACE and
ground-based solar observatories to determine the solar source of this
magnetic cloud. A launch window for the MC between 9 and 11 April 2006
was estimated from the propagation time of the ejecta observed near
Earth. A number of large active regions were present on the Sun during
this period, which were initially considered to be the most likely
candidate source regions of the MC. However, it was determined that
the solar source of the MC was a small, spotless active region observed
in the Northern Hemisphere. Following an eruption from this region on
11 April 2006, the ACE spacecraft detected, 59 h later, the passage of
the MC, preceded by the arrival of a weak, forward fast shock. The link
between the eruption in this active region and the interplanetary MC is
supported by several pieces of evidence, including the location of the
solar source near to the disk centre and to the east of the central
meridian (in agreement with the spacecraft trajectory through the
western leg of the magnetic cloud), the propagation time of the ejecta,
the agreement between the amount of flux in the magnetic cloud and in
the active region, and the agreement between the signs of helicity of
the magnetic cloud and the active region (which differs from the sign
of helicity of each of the other active regions on the Sun at this
time). In addition, the active region is located on the boundary of
a coronal hole, and a high speed solar wind stream originating from
this region is observed near Earth shortly after the passage of the
magnetic cloud. This event highlights the complexities associated
with locating the solar source of an ICME observed near Earth, and
serves to emphasise that it is the combination of a number of physical
characteristics and signatures that is important for successfully
tying together the Earth-end and the Sun-end of an event. Further
investigation of this MC has revealed some sub-structure towards its
centre, observed as a small scale reversal of the azimuthal magnetic
field of the MC, similar to that reported by Dasso et al., 2007. We
explore several possible explanations for this signature, including
the occurrence of multiple flux ropes and/or warping of the magnetic
cloud. We also consider whether magnetic reconnection plays a role in
creating the geometry that would explain these observations.
---------------------------------------------------------
Title: Preface
Authors: Klein, Karl-Ludwig; Pohjolainen, Silja; van Driel-Gesztelyi,
Lidia
2008SoPh..253....1K Altcode: 2008SoPh..tmp..191K
No abstract at ADS
---------------------------------------------------------
Title: The Recovery of CME-Related Dimmings and the ICME's Enduring
Magnetic Connection to the Sun
Authors: Attrill, G. D. R.; van Driel-Gesztelyi, L.; Démoulin, P.;
Zhukov, A. N.; Steed, K.; Harra, L. K.; Mandrini, C. H.; Linker, J.
2008SoPh..252..349A Altcode: 2008SoPh..tmp..158A
It is generally accepted that transient coronal holes (TCHs, dimmings)
correspond to the magnetic footpoints of CMEs that remain rooted in
the Sun as the CME expands out into the interplanetary space. However,
the observation that the average intensity of the 12 May 1997 dimmings
recover to their pre-eruption intensity in SOHO/EIT data within 48
hours, whilst suprathermal unidirectional electron heat fluxes are
observed at 1 AU in the related ICME more than 70 hours after the
eruption, leads us to question why and how the dimmings disappear
whilst the magnetic connectivity is maintained. We also examine two
other CME-related dimming events: 13 May 2005 and 6 July 2006. We study
the morphology of the dimmings and how they recover. We find that, far
from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data
have a deep central core and a more shallow extended dimming area. The
dimmings recover not only by shrinking of their outer boundaries but
also by internal brightenings. We quantitatively demonstrate that the
model developed by Fisk and Schwadron (Astrophys. J.560, 425, 2001)
of interchange reconnections between "open" magnetic field and small
coronal loops is a strong candidate for the mechanism facilitating the
recovery of the dimmings. This process disperses the concentration of
"open" magnetic field (forming the dimming) out into the surrounding
quiet Sun, thus recovering the intensity of the dimmings whilst still
maintaining the magnetic connectivity to the Sun.
---------------------------------------------------------
Title: Why are CMEs large-scale coronal events: nature or nurture?
Authors: van Driel-Gesztelyi, L.; Attrill, G. D. R.; Démoulin, P.;
Mandrini, C. H.; Harra, L. K.
2008AnGeo..26.3077V Altcode:
The apparent contradiction between small-scale source regions of,
and large-scale coronal response to, coronal mass ejections (CMEs)
has been a long-standing puzzle. For some, CMEs are considered to
be inherently large-scale events eruptions in which a number of flux
systems participate in an unspecified manner, while others consider
magnetic reconnection in special global topologies to be responsible
for the large-scale response of the lower corona to CME events. Some
of these ideas may indeed be correct in specific cases. However,
what is the key element which makes CMEs large-scale? Observations
show that the extent of the coronal disturbance matches the angular
width of the CME an important clue, which does not feature strongly
in any of the above suggestions. We review observational evidence
for the large-scale nature of CME source regions and find them
lacking. Then we compare different ideas regarding how CMEs evolve
to become large-scale. The large-scale magnetic topology plays an
important role in this process. There is amounting evidence, however,
that the key process is magnetic reconnection between the CME and other
magnetic structures. We outline a CME evolution model, which is able
to account for all the key observational signatures of large-scale
CMEs and presents a clear picture how large portions of the Sun become
constituents of the CME. In this model reconnection is driven by the
expansion of the CME core resulting from an over-pressure relative to
the pressure in the CME's surroundings. This implies that the extent of
the lower coronal signatures match the final angular width of the CME.
---------------------------------------------------------
Title: Locating the solar source of 13 April 2006 magnetic cloud
Authors: Steed, K.; Owen, C. J.; Harra, L. K.; Green, L. M.; Dasso,
S.; Walsh, A. P.; Démoulin, P.; van Driel-Gesztelyi, L.
2008AnGeo..26.3159S Altcode:
Using Advanced Composition Explorer (ACE) in situ data we identify and
describe an interplanetary magnetic cloud (MC) observed near Earth
on 13 April 2006. We also use multi-instrument and multi-wavelength
observations from the Solar and Heliospheric Observatory (SOHO), the
Transition Region and Coronal Explorer (TRACE) and ground-based solar
observatories to determine the solar source of this magnetic cloud. A
launch window for the MC between 9 and 11 April 2006 was estimated from
the propagation time of the ejecta observed near Earth. A number of
large active regions (ARs) were present on the Sun during this period,
which were initially considered to be the most likely candidate source
regions of the MC. However, it was determined that the solar source
of the MC was a small, spotless active region observed in the Northern
Hemisphere. Following an eruption from this region on 11 April 2006, the
ACE spacecraft detected, 59 h later, the passage of the MC, preceded by
the arrival of a weak, forward fast shock. The link between the eruption
in this active region and the interplanetary MC is supported by several
pieces of evidence, including the location of the solar source near to
the disk centre and to the east of the central meridian (in agreement
with the spacecraft trajectory through the western leg of the magnetic
cloud), the propagation time of the ejecta, the agreement between
the amount of flux in the magnetic cloud and in the active region,
and the agreement between the signs of helicity of the magnetic cloud
and the active region (which differs from the sign of helicity of each
of the other active regions on the Sun at this time). In addition,
the active region is located on the boundary of a coronal hole, and a
high speed solar wind stream originating from this region is observed
near Earth shortly after the passage of the magnetic cloud.
---------------------------------------------------------
Title: Multi-scale reconnections in a complex CME
Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Démoulin, P.; Culhane,
J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. -L.;
Kurokawa, H.
2008AdSpR..42..858V Altcode:
A series of three flares of GOES class M, M and C, and a CME were
observed on 20 January 2004 occurring in close succession in NOAA
10540. Types II, III, and N radio bursts were associated. We use
the combined observations from TRACE, EIT, Hα images from Kwasan
Observatory, MDI magnetograms, GOES, and radio observations from
Culgoora and Wind/ WAVES to understand the complex development of this
event. We reach three main conclusions. First, we link the first two
impulsive flares to tether-cutting reconnections and the launch of
the CME. This complex observation shows that impulsive quadrupolar
flares can be eruptive. Second, we relate the last of the flares, an
LDE, to the relaxation phase following forced reconnections between
the erupting flux rope and neighbouring magnetic field lines, when
reconnection reverses and restores some of the pre-eruption magnetic
connectivities. Finally, we show that reconnection with the magnetic
structure of a previous CME launched about 8 h earlier injects electrons
into open field lines having a local dip and apex (located at about six
solar radii height). This is observed as an N-burst at decametre radio
wavelengths. The dipped shape of these field lines is due to large-scale
magnetic reconnection between expanding magnetic loops and open field
lines of a neighbouring streamer. This particular situation explains
why this is the first N-burst ever observed at long radio wavelengths.
---------------------------------------------------------
Title: Study of the Physical Properties of Coronal “Waves” and
Associated Dimmings
Authors: Attrill, G. D. R.; Harra, L. K.; van Driel-Gesztelyi, L.;
Williams, D.; Alexeev, I. V.
2008ASPC..397..126A Altcode:
We present results from our study run by Hinode, designed to obtain
information on the physical properties of the diffuse bright fronts
known as “EIT coronal waves” and their associated dimmings. We
analyse data obtained during a frustrated eruption event on 5th May
2007. The event produces a bright front as well as deep and shallow
dimmings. We show that the dimmings of this frustrated eruption
show similar physical properties to those observed in textbook “EIT
coronal wave” events. The Hinode/EIS data show that both the deep
and shallow dimmings associated with this frustrated eruption show
blue-shifted velocities. It is therefore consistent that, like the
deep core dimmings, the widespread shallow dimmings observed with many
textbook coronal “wave” events may also be due to plasma outflows.
---------------------------------------------------------
Title: Long Duration Thermal Hard X-ray Sources Observed in Two
Eruptive Flares
Authors: Bone, L. A.; Culhane, J. L.; van Driel-Gesztelyi, L.; Hara, H.
2008ASPC..397..160B Altcode:
We present observations of two eruptive flares on 17 of December
2006 (C1.9) and 19 of May 2007 (B9.7) which had good coverage with
both Hinode and RHESSI. In these flares we see a long lived, gradual
thermal hard X-ray source of low emission measure and, relative to
the loops observed with GOES and XRT, high temperature. The lack of a
non-thermal hard X-ray component and impulsive behaviour is inconsistent
with electron beam driven chromospheric evaporation.
---------------------------------------------------------
Title: Hinode EIS and XRT Observations of Hot Jets in Coronal Holes -
Does the Plasma Escape?
Authors: Baker, D.; van Driel-Gesztelyi, L.; Kamio, S.; Culhane,
J. L.; Harra, L. K.; Sun, J.; Young, P. R.; Matthews, S. A.
2008ASPC..397...23B Altcode:
X-ray jets have been detected in the extreme ultraviolet (EUV) and
soft X-ray observations of Hinode's EIS and XRT instruments. Both
instruments were used to observe the jets in polar and on-disk coronal
holes (CHs). Here, we present a multi-wavelength study of an X-ray
jet and its associated bright point found in an equatorial CH on 19
June 2007. Light curves (LCs) in 22 different emission lines were
compared to that of Hinode/XRT. As we found in a previous study of
two polar X-ray jets, this jet shows a post-jet increase in its EUV
LCs. The post-jet enhancement appears cooler than the jet. We suggest
this feature arises because the hot plasma of the jet, having failed to
reach escape speeds, cools and falls back along the near vertical paths
expected to be created by reconnection with open field lines of CHs. In
addition to the increase in post-jet EUV intensity, we found tentative
evidence of impact heating possibly caused by the fall-back of plasma.
---------------------------------------------------------
Title: Twist, Writhe and Rotation of Magnetic Flux Ropes in Filament
Eruptions and Coronal Mass Ejections
Authors: Török, T.; Berger, M. A.; Kliem, B.; Démoulin, P.; Linton,
M.; van Driel-Gesztelyi, L.
2008ESPM...12.3.54T Altcode:
We present the first quantitative analysis of the conversion of twist
into writhe in the course of ideal MHD instabilities in erupting coronal
magnetic flux ropes. For our analysis, we consider numerical simulations
of two instabilities which have been suggested as trigger and initial
driving mechanisms in filament eruptions and coronal mass ejections,
namely the helical kink instability and the torus instability. We
use two different coronal flux rope models as initial conditions
in the simulations, namely the cylindrical Gold-Hoyle equilibrium
and the toroidal Titov-Demoulin equilibrium. <P />For each model, we
perform a series of simulations with different amounts of initial flux
rope twist. In order to study both confined and ejective eruptions,
we additionally use different initial potential fields overlying
the flux rope in the simulations of the Titov-Demoulin model. <P
/>In all simulations, we measure the writhe of the flux rope and the
corresponding rotation of its axis in vertical projection by making use
of recently developed expressions which permit us to calculate writhe as
a single integral in space. We discuss the implications of our results
for filament eruptions, coronal mass ejections and magnetic clouds.
---------------------------------------------------------
Title: Outflows at the Edges of Active Regions: Contribution to
Solar Wind Formation?
Authors: Harra, L. K.; Sakao, T.; Mandrini, C. H.; Hara, H.; Imada,
S.; Young, P. R.; van Driel-Gesztelyi, L.; Baker, D.
2008ApJ...676L.147H Altcode:
The formation of the slow solar wind has been debated for many years. In
this Letter we show evidence of persistent outflow at the edges of
an active region as measured by the EUV Imaging Spectrometer on board
Hinode. The Doppler velocity ranged between 20 and 50 km s<SUP>-1</SUP>
and was consistent with a steady flow seen in the X-Ray Telescope. The
latter showed steady, pulsing outflowing material and some transverse
motions of the loops. We analyze the magnetic field around the active
region and produce a coronal magnetic field model. We determine from
the latter that the outflow speeds adjusted for line-of-sight effects
can reach over 100 km s<SUP>-1</SUP>. We can interpret this outflow as
expansion of loops that lie over the active region, which may either
reconnect with neighboring large-scale loops or are likely to open to
the interplanetary space. This material constitutes at least part of
the slow solar wind.
---------------------------------------------------------
Title: Erratum: "Outflows at the Edges of Active Regions: Contribution
to Solar Wind Formation?" (ApJ, 676, L147 [2008])
Authors: Harra, L. K.; Sakao, T.; Mandrini, C. H.; Hara, H.; Imada,
S.; Young, P. R.; van Driel-Gesztelyi, L.; Baker, D.
2008ApJ...677L.159H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: CME-related dimmings as a signature of interplanetary magnetic
cloud footpoints
Authors: Mandrini, Cristina H.; Soledad Nakwacki, Ms Maria; Attrill,
Gemma; van Driel-Gesztelyi, Lidia; Dasso, Sergio; Demoulin, Pascal
2008cosp...37.1900M Altcode: 2008cosp.meet.1900M
Coronal dimmings are often present on both sides of erupting magnetic
configurations. It has been suggested that dimmings mark the location
of the footpoints of ejected flux ropes and, thus, their magnetic
flux can be used as a proxy for the flux involved in the ejection. If
so, this quantity can be compared to the flux in the associated
interplanetary magnetic cloud to find clues about the origin of the
ejected flux rope. In the context of this physical interpretation,
we analyse several events, flares and coronal mass ejections (CMEs),
for which we can find their interplanetary counterpart. We combine
SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler
Imager magnetic maps to identify and measure the flux in the dimming
regions. We model the associated clouds and compute their magnetic
flux using in situ observations. We find that the magnetic fluxes of
the dimmings and magnetic clouds are compatible in some cases; though
this is not the case for large-scale events and eruptions that occur
in regions that are not isolated from other flux concentrations. We
conclude that the interpretation of dimmings requires a deeper analysis
of the global magnetic field configuration, since at least a fraction
of the dimmed regions could be formed by reconnection between the
erupting field and the surrounding magnetic structures.
---------------------------------------------------------
Title: Interaction between emerging flux and coronal hole -
observations and simulations
Authors: van Driel-Gesztelyi, Lidia; Baker, Deborah; Murray, Michelle;
Demoulin, Pascal; Attrill, Gemma; Matthews, Sarah A.; Mandrini,
Cristina H.; Toeroek, Tibor
2008cosp...37.3288V Altcode: 2008cosp.meet.3288V
Flux emergence in the vicinity of or inside a coronal hole (CH) is
expected to induce magnetic reconnection between the closed emerging
and open CH magnetic field lines, resulting in an evolution of the
CH as formerly closed field lines become topologically open, while at
the same time, open field lines close down. Through two case studies
we show observational signatures of this (interchange) reconnection
process and discuss its implications. First, using SOHO EIT and MDI
data, we study a small active region (AR10869) emerging in the close
vicinity of a low-latitude coronal hole in April 2006. The interfacing
magnetic polarities between the AR and the CH were opposite, favourable
for magnetic reconnection. We indeed observe the coupled formation of
bright closed loops between the CH and the AR and coronal dimming on
the far side of the AR, which we interpret as evidence of interchange
reconnection. This process effectively modifies the CH boundary
(making it retreat), while simultaneously displacing open field lines
to the far side of the AR. In order to study this process in detail,
we perform 2.5D MHD simulations, which qualitatively reproduce important
aspects of the observations. We expect to find upflows of plasma at the
location where previously closed field lines are opening up as well as
on the reconnecting side, but since we had no spectroscopic data for
this event, we can not verify this. Therefore we analyze Hinode/EIS
line-of-sight velocity maps of another low-latitude CH with a small AR
in its midst observed on 18 Oct. 2007. We find that while closed loops
of the bipole are dominated by downflows in the Fe XII, Fe XIII and
Fe XV lines, the strongest coronal plasma upflows are indeed located
around and particularly at the "far side" of the bipolar AR, i.e. having
the same polarity as the dominant polarity of the CH. The emerging
biplole and the series of interchange reconnections it induces create
a significant additional plasma upflow in the CH, thus we identify
this outflow must contribute to the acceleration of the fast solar wind.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2008SoPh..247....1L Altcode: 2008SoPh..tmp....5L
No abstract at ADS
---------------------------------------------------------
Title: Breaking or maintaining magnetic connection of CMEs to the
Sun - solar vs. interplanetary signatures tested
Authors: van Driel-Gesztelyi, Lidia; Attrill, Gemma; Demoulin, Pascal;
Mandrini, Cristina H.; Harra, Louise K.
2008cosp...37.3287V Altcode: 2008cosp.meet.3287V
Though their relationship is complex, the presence of suprathermal
unior bi-directional electron streams in ICMEs are treated as
signatures of magnetic field lines with one or both ends being
connected to the Sun, respectively, while their absence is
interpreted as disconnection. However, do we have any reliable
signature in the solar corona distinguishing between maintained
connection and disconnection? We test two solar signatures against
interplanetary suprathermal electron signatures in order to establish
their relevance. We test the hypothesis that the recovery of Transient
Coronal Holes (TCHs, dimming regions corresponding to the footpoints of
CMEs) is a signature of magnetic disconnection from the Sun. Through
three case studies we quantitatively demonstrate that magnetic
reconnections between field lines of the expanded CME magnetic field
and small coronal loops can act to disperse the concentration of
CME footpoints (forming the dimming region) out into the surrounding
quiet Sun, thus recovering the intensity of the dimming region whilst
still maintaining the magnetic connectivity to the Sun. This analysis
provides evidence that the recovery of coronal dimming regions can,
in fact, be simply reconciled with maintained magnetic connectivity
to the Sun. However, disconnection can occur when open field lines are
involved in reconnection with CMEs. We show through two well-observed
case studies that magnetic reconnection between the expanding CME and
a nearby coronal hole (CH) is indeed able to disconnect one leg of
the expanding CME magnetic structure, as indicated by uni-directional
electron streams in their respective ICMEs. Therefore we suggest that
brightenings (signatures of reconnection) appearing along a coronal
hole boundary in the wake of a CME can be treated as a signature of
(at least partial) disconnection of one of the CME legs from the Sun.
---------------------------------------------------------
Title: Flare and Erupting Filament of 19th May, 2007 - Sources of
a Magnetic Cloud Observed by Stereo
Authors: Culhane, J. Leonard; Bone, Laura; Hara, Hirohisa; Farrugia,
Charles; Galvin, Antoinette; van Driel-Gesztelyi, Lidia; Popecki,
Mark; Luhmann, Janet G.; Veronig, Astrid
2008cosp...37..609C Altcode: 2008cosp.meet..609C
A GOES Class B9.5 flare was observed on the Sun starting 19-May-2007
at 12:51 UT. Data obtained by the Hinode, TRACE, RHESSI, STEREO and
SOHO spacecraft will be discussed. The evolution and eventual eruption
of a related Halpha filament were monitored by patrol observations at
Kanzelhoehe. These observations and associated detection of EUV-emitting
filament material will also be presented. The flare energetics and
the possible role of the flare in the filament eruption will be
examined. Finally the relationship of the magnetic configuration
of the solar eruption along with the temperature and composition of
erupting material will be assessed in relation to the properties of
a magnetic cloud later detected by STEREO in-situ instruments near
Earth on 22-May-2007.
---------------------------------------------------------
Title: What kinking filament eruptions tell us about the physical
nature of transient coronal sigmoids ?
Authors: van Driel-Gesztelyi, Lidia; Green, Lucie M.; Kliem, Bernhard;
Toeroek, Tibor; Attrill, Gemma
2008cosp...37.3289V Altcode: 2008cosp.meet.3289V
Soft X-ray images of the Sun have shown that some active regions contain
loops, or collections of loops, which appear forward or reverse 'S'
in shape. These features have been termed sigmoids. These structures
are of interest because their presence in an active region has been
linked to eruptive activity and the sense of sigmoid orientation is
taken to indicate the sense of shear and twist (or helicity) in the
magnetic field. Differing models have been put forward in order to
explain the physical nature of sigmoids and the role they play in an
eruption. We use multiwavelength observations (Yohkoh/SXT, TRACE,
SOHO/EIT and MDI, H-alpha) to investigate how transient sigmoids
are formed. We also investigate filament eruptions from these active
regions, which show a clear sign of rotation of their apex. We find
that for positive (negative) helicity the filament apex rotates
clockwise (counterclockwise), consistent with the flux rope taking on
a reverse (forward) S shape, which is opposite to that observed for
the sigmoid. These observations put constraints on sigmoid models,
excluding some of them. We conclude that transient sigmoids are
associated with the formation of current sheets and heating along
field lines under a dynamic flux rope.
---------------------------------------------------------
Title: Transient Coronal Sigmoids and Rotating Erupting Flux Ropes
Authors: Green, L. M.; Kliem, B.; Török, T.; van Driel-Gesztelyi,
L.; Attrill, G. D. R.
2007SoPh..246..365G Altcode:
To determine the relationship between transient coronal (soft X-ray
or EUV) sigmoids and erupting flux ropes, we analyse four events
in which a transient sigmoid could be associated with a filament
whose apex rotates upon eruption and two further events in which
the two phenomena were spatially but not temporally coincident. We
find the helicity sign of the erupting field and the direction of
filament rotation to be consistent with the conversion of twist
into writhe under the ideal MHD constraint of helicity conservation,
thus supporting our assumption of flux rope topology for the rising
filament. For positive (negative) helicity the filament apex rotates
clockwise (counterclockwise), consistent with the flux rope taking on
a reverse (forward) S shape, which is opposite to that observed for
the sigmoid. This result is incompatible with two models for sigmoid
formation: one identifying sigmoids with upward arching kink-unstable
flux ropes and one identifying sigmoids with a current layer between
two oppositely sheared arcades. We find instead that the observations
agree well with the model by Titov and Démoulin (Astron. Astrophys.351,
707, 1999), which identifies transient sigmoids with steepened current
layers below rising flux ropes.
---------------------------------------------------------
Title: Hinode EUV Study of Jets in the Sun's South Polar Corona
Authors: Culhane, Len; Harra, Louise K.; Baker, Deborah; van
Driel-Gesztelyi, Lidia; Sun, Jian; Doschek, George A.; Brooks, David
H.; Lundquist, Loraine L.; Kamio, Suguru; Young, Peter R.; Hansteen,
Viggo H.
2007PASJ...59S.751C Altcode:
A number of coronal bright points and associated plasma jet features
were seen in an observation of the South polar coronal hole during
2007 January. The 40" wide slot was used at the focus of the Hinode
EUV Imaging Spectrometer to provide spectral images for two of these
events. Light curves are plotted for a number of emission lines that
include He II 256Å (0.079MK) and cover the temperature interval from
0.4MK to 5.0MK. Jet speed measurements indicate values less than the
escape velocity. The light curves show a post-jet enhancement in a
number of the cooler coronal lines indicating that after a few minutes
cooling, the plasma fell back to its original acceleration site. This
behavior has not been previously observed by e.g., the Yohkoh Soft
X-ray Telescope due to the comparatively high temperature cut-off
in its response. The observations are consistent with the existing
models that involve magnetic reconnection between emerging flux and the
ambient open field lines in the polar coronal hole. However we do not
have sufficient coverage of lines from lower temperature ion species
to register the Hα-emitting surge material that is associated with
some of these models.
---------------------------------------------------------
Title: Optical flares from the faint mid-dM star 2MASS
J00453912+4140395
Authors: Kovári, Zs.; Vilardell, F.; Ribas, I.; Vida, K.; van
Driel-Gesztelyi, L.; Jordi, C.; Oláh, K.
2007AN....328..904K Altcode: 2007arXiv0711.0742K
We present B and V light curves of a large stellar flare obtained
with the Wide Field Camera at the Isaac Newton 2.5-m telescope (La
Palma). The source object is a faint (m_V=21.38) foreground star in
the field of the Andromeda galaxy, with its most probable spectral
type being dM4. We provide an estimate of the total flare energy in
the optical range and find it to be of the order of 10<SUP>35</SUP>
erg. The cooling phase of the large flare shows three additional
weak flare-like events, which we interpret as results of a triggering
mechanism also observed on the Sun during large coronal mass ejections.
---------------------------------------------------------
Title: Editors' note
Authors: Forgács-Dajka, E.; Ballai, I.; van Driel-Gesztelyi, L.
2007AN....328..725F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for interchange reconnection between a coronal hole
and an adjacent emerging flux region
Authors: Baker, D.; van Driel-Gesztelyi, L.; Attrill, G. D. R.
2007AN....328..773B Altcode:
Coronal holes are regions of dominantly monopolar magnetic field on the
Sun where the field is considered to be `open' towards interplanetary
space. Magnetic bipoles emerging in proximity to a coronal hole
boundary naturally interact with this surrounding "open" magnetic
field. In the case of oppositely aligned polarities between the active
region and the coronal hole, we expect interchange reconnection to
take place, driven by the coronal expansion of the emerging bipole as
well as occasional eruptive events. Using SOHO/EIT and SOHO/MDI data,
we present observational evidence of such interchange reconnection
by studying AR 10869 which emerged close to a coronal hole. We find
closed loops forming between the active region and the coronal hole
leading to the retreat of the hole. At the same time, on the far side
of the active region, we see dimming of the corona which we interpret
as a signature of field line `opening' there, as a consequence of a
topological displacement of the `open' field lines of the coronal hole.
---------------------------------------------------------
Title: Coronal “wave”: A signature of the mechanism making CMEs
large-scale in the low corona?
Authors: Attrill, G. D. R.; Harra, L. K.; van Driel-Gesztelyi, L.;
Démoulin, P.; Wülser, J. -P.
2007AN....328..760A Altcode:
We analyse one of the first coronal waves observed by STEREO/EUVI
associated with a source region just behind the limb, NOAA 10940. We
apply the coronal “wave” model proposed by Attrill et al. (2007) to
explain the evolution of the observed bright fronts, thereby arguing
that the bright fronts and dimmings are due to magnetic reconnections
between the expanding CME core and surrounding magnetic structures. We
offer a discussion showing that this model provides a mechanism via
which CMEs, expanding from a small source region can naturally become
large-scale in the low corona.
---------------------------------------------------------
Title: How Does Large Flaring Activity from the Same Active Region
Produce Oppositely Directed Magnetic Clouds?
Authors: Harra, Louise K.; Crooker, Nancy U.; Mandrini, Cristina H.;
van Driel-Gesztelyi, Lidia; Dasso, Sergio; Wang, Jingxiu; Elliott,
Heather; Attrill, Gemma; Jackson, Bernard V.; Bisi, Mario M.
2007SoPh..244...95H Altcode:
We describe the interplanetary coronal mass ejections (ICMEs) that
occurred as a result of a series of solar flares and eruptions from
4 to 8 November 2004. Two ICMEs/magnetic clouds occurring from these
events had opposite magnetic orientations. This was despite the fact
that the major flares related to these events occurred within the same
active region that maintained the same magnetic configuration. The solar
events include a wide array of activities: flares, trans-equatorial
coronal loop disappearance and reformation, trans-equatorial filament
eruption, and coronal hole interaction. The first major ICME/magnetic
cloud was predominantly related to the active region 10696 eruption. The
second major ICME/magnetic cloud was found to be consistent with the
magnetic orientation of an erupting trans-equatorial filament or else
a rotation of 160° of a flux rope in the active region. We discuss
these possibilities and emphasize the importance of understanding the
magnetic evolution of the solar source region before we can begin to
predict geoeffective events with any accuracy.
---------------------------------------------------------
Title: CME Propagation Characteristics from Radio Observations
Authors: Pohjolainen, S.; van Driel-Gesztelyi, L.; Culhane, J. L.;
Manoharan, P. K.; Elliott, H. A.
2007SoPh..244..167P Altcode: 2007arXiv0711.3168P
We explore the relationship among three coronal mass ejections (CMEs),
observed on 28 October 2003, 7 November 2004, and 20 January 2005,
the type II burst-associated shock waves in the corona and solar wind,
as well as the arrival of their related shock waves and magnetic clouds
at 1 AU. Using six different coronal/interplanetary density models,
we calculate the speeds of shocks from the frequency drifts observed
in metric and decametric radio wave data. We compare these speeds
with the velocity of the CMEs as observed in the plane-of-the-sky
white-light observations and calculated with a cone model for the 7
November 2004 event. We then follow the propagation of the ejecta using
Interplanetary Scintillation measurements, which were available for the
7 November 2004 and 20 January 2005 events. Finally, we calculate the
travel time of the interplanetary shocks between the Sun and Earth and
discuss the velocities obtained from the different data. This study
highlights the difficulties in making velocity estimates that cover
the full CME propagation time.
---------------------------------------------------------
Title: Are CME-Related Dimmings Always a Simple Signature of
Interplanetary Magnetic Cloud Footpoints?
Authors: Mandrini, C. H.; Nakwacki, M. S.; Attrill, G.; van
Driel-Gesztelyi, L.; Démoulin, P.; Dasso, S.; Elliott, H.
2007SoPh..244...25M Altcode:
Coronal dimmings are often present on both sides of erupting magnetic
configurations. It has been suggested that dimmings mark the location
of the footpoints of ejected flux ropes and, thus, their magnetic
flux can be used as a proxy for the flux involved in the ejection. If
so, this quantity can be compared to the flux in the associated
interplanetary magnetic cloud to find clues about the origin of the
ejected flux rope. In the context of this physical interpretation,
we analyze the event, flare, and coronal mass ejection (CME) that
occurred in active region 10486 on 28 October 2003. The CME on this
day is associated with large-scale dimmings, located on either side of
the main flaring region. We combine SOHO/Extreme Ultraviolet Imaging
Telescope data and Michelson Doppler Imager magnetic maps to identify
and measure the flux in the dimming regions. We model the associated
cloud and compute its magnetic flux using in situ observations from
the Magnetometer Instrument and the Solar Wind Electron Proton Alpha
Monitor aboard the Advance Composition Explorer. We find that the
magnetic fluxes of the dimmings and magnetic cloud are incompatible, in
contrast to what has been found in previous studies. We conclude that,
in certain cases, especially in large-scale events and eruptions that
occur in regions that are not isolated from other flux concentrations,
the interpretation of dimmings requires a deeper analysis of the global
magnetic configuration, since at least a fraction of the dimmed regions
is formed by reconnection between the erupting field and the surrounding
magnetic structures.
---------------------------------------------------------
Title: Hinode Euv Study Of Jets In The Sun’s South Polar Corona
Authors: Culhane, J. L.; Brooks, D. H.; Doschek, G. A.; Harra, L. K.;
van Driel-Gesztelyi, L.; Baker, D.; Lundquist, L. L.; Hansteen, V. H.;
Kamio, S.
2007AAS...210.7201C Altcode: 2007BAAS...39..178C
Using the Hinode EUV Imaging Spectrometer coronal jets were observed
on 20-JAN-2007 over a range of emission lines and corresponding plasma
temperatures using the 40 arc sec wide slot images. In this preliminary
analysis, jet plasma temperature and emissivity have been estimated
while, based on assumptions about the jet morphology, electron density
estimates are given and jet velocity measured. The evolution of the
jets will be followed in a number of different EUV emission lines and
jet energy input as a function of time will be assessed with reference
to the magnetic field topologies involved.
---------------------------------------------------------
Title: Coronal "wave": Magnetic Footprint Of A Cme?
Authors: Attrill, Gemma; Harra, L. K.; van Driel-Gesztelyi, L.;
Demoulin, P.; Wuelser, J.
2007AAS...210.2921A Altcode: 2007BAAS...39..141A
We propose a new mechanism for the generation of "EUV coronal
waves". This work is based on new analysis of data from SOHO/EIT,
SOHO/MDI & STEREO/EUVI. Although first observed in 1997, the
interpretation of coronal waves as flare-induced or CME-driven remains
a debated topic. We investigate the properties of two "classical"
SOHO/EIT coronal waves in detail. The source regions of the associated
CMEs possess opposite helicities & the coronal waves display
rotations in opposite senses. We observe deep dimmings near the
flare site & also widespread diffuse dimming, accompanying the
expansion of the EIT wave. We report a new property of these EIT
waves, namely, that they display dual brightenings: persistent ones
at the outermost edge of the core dimming regions & simultaneously
diffuse brightenings constituting the leading edge of the coronal wave,
surrounding the expanding diffuse dimmings. We show that such behaviour
is consistent with a diffuse EIT wave being the magnetic footprint of
a CME. We propose a new mechanism where driven magnetic reconnections
between the skirt of the expanding CME & quiet-Sun magnetic loops
generate the observed bright diffuse front. The dual brightenings &
widespread diffuse dimming are identified as innate characteristics
of this process. In addition we present some of the first analysis
of a STEREO/EUVI limb coronal wave. We show how the evolution of the
diffuse bright front & dimmings can be understood in terms of the
model described above. We show that an apparently stationary part of
the bright front can be understood in terms of magnetic interchange
reconnections between the expanding CME & the "open" magnetic
field of a low-latitude coronal hole. We use both the SOHO/EIT &
STEREO/EUVI events to demonstrate that through successive reconnections,
this new model provides a natural mechanism via which CMEs can become
large-scale in the lower corona.
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Melrose, Donald B.; Klimchuk, James A.; Benz, A. O.; Craig,
I. J. D.; Gopalswamy, N.; Harrison, R. A.; Kozlovsky, B. Z.; Poletto,
G.; Schrijver, K. J.; van Driel-Gesztelyi, L.; Wang, J. -X.
2007IAUTA..26...75M Altcode:
Commission 10 aims at the study of various forms of solar activity,
including networks, plages, pores, spots, fibrils, surges, jets,
filaments/prominences, coronal loops, flares, coronal mass ejections
(CMEs), solar cycle, microflares, nanoflares, coronal heating etc.,
which are all manifestation of the interplay of magnetic fields and
solar plasma. Increasingly important is the study of solar activities
as sources of various disturbances in the interplanetary space
and near-Earth "space weather".Over the past three years a major
component of research on the active Sun has involved data from the
RHESSI spacecraft. This review starts with an update on current and
planned solar observations from spacecraft. The discussion of solar
flares gives emphasis to new results from RHESSI, along with updates on
other aspects of flares. Recent progress on two theoretical concepts,
magnetic reconnection and magnetic helicity is then summarized, followed
by discussions of coronal loops and heating, the magnetic carpet
and filaments. The final topic discussed is coronal mass ejections
and space weather.The discussions on each topic is relatively brief,
and intended as an outline to put the extensive list of references
in context.The review was prepared jointly by the members of the
Organizing Committee, and the names of the primary contributors to
the various sections are indicated in parentheses.
---------------------------------------------------------
Title: A Multiple Flare Scenario where the Classic Long-Duration
Flare Was Not the Source of a CME
Authors: Goff, C. P.; van Driel-Gesztelyi, L.; Démoulin, P.; Culhane,
J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.;
Kurokawa, H.
2007SoPh..240..283G Altcode:
A series of flares (GOES class M, M and C) and a CME were observed in
close succession on 20 January 2004 in NOAA 10540. Radio observations,
which took the form of types II, III and N bursts, were associated with
these events. We use the combined observations from TRACE, EIT, Hα
images from Kwasan, MDI magnetograms and GOES to understand the complex
development of this event. Contrary to a standard interpretation,
we conclude that the first two impulsive flares are part of the CME
launch process while the following long-duration event flare represents
simply the recovery phase. Observations show that the flare ribbons
not only separate but also shift along the magnetic inversion line
so that magnetic reconnection progresses stepwise to neighboring flux
tubes. We conclude that "tether cutting" reconnection in the sheared
arcade progressively transforms it to a twisted flux tube, which
becomes unstable, leading to a CME. We interpret the third flare,
a long-duration event, as a combination of the classical two-ribbon
flare with the relaxation process following forced reconnection between
the expanding CME structure and neighboring magnetic fields.
---------------------------------------------------------
Title: Decametric N Burst: A Consequence of the Interaction of Two
Coronal Mass Ejections
Authors: Démoulin, P.; Klein, K. -L.; Goff, C. P.; van
Driel-Gesztelyi, L.; Culhane, J. L.; Mandrini, C. H.; Matthews, S. A.;
Harra, L. K.
2007SoPh..240..301D Altcode:
Radio emissions of electron beams in the solar corona and interplanetary
space are tracers of the underlying magnetic configuration and of
its evolution. We analyse radio observations from the Culgoora and
WIND/WAVES spectrographs, in combination with SOHO/LASCO and SOHO/MDI
data, to understand the origin of a type N burst originating from NOAA
AR 10540 on January 20, 2004, and its relationship with type II and
type III emissions. All bursts are related to the flares and the CME
analysed in a previous paper (Goff et al., 2007). A very unusual feature
of this event was a decametric type N burst, where a type III-like
burst, drifting towards low frequencies (negative drift), changes drift
first to positive, then again to negative. At metre wavelengths, i.e.,
heliocentric distances ≲1.5R<SUB>⊙</SUB>, these bursts are ascribed
to electron beams bouncing in a closed loop. Neither U nor N bursts are
expected at decametric wavelengths because closed quasi-static loops
are not thought to extend to distances ≫1.5R<SUB>⊙</SUB>. We take
the opportunity of the good multi-instrument coverage of this event to
analyse the origin of type N bursts in the high corona. Reconnection
of the expanding ejecta with the magnetic structure of a previous CME,
launched about 8 hours earlier, injects electrons in the same manner as
with type III bursts but into open field lines having a local dip and
apex. The latter shape was created by magnetic reconnection between
the expanding CME and neighbouring (open) streamer field lines. This
particular flux tube shape in the high corona, between 5R<SUB>⊙</SUB>
and 10R<SUB>⊙</SUB>, explains the observed type N burst. Since the
required magnetic configuration is only a transient phenomenon formed
by reconnection, severe timing and topological constraints are present
to form the observed decametric N burst. They are therefore expected
to be rare features.
---------------------------------------------------------
Title: Coronal “Wave”: Magnetic Footprint of a Coronal Mass
Ejection?
Authors: Attrill, Gemma D. R.; Harra, Louise K.; van Driel-Gesztelyi,
Lidia; Démoulin, Pascal
2007ApJ...656L.101A Altcode:
We investigate the properties of two “classical” EUV Imaging Telescope
(EIT) coronal waves. The two source regions of the associated coronal
mass ejections (CMEs) possess opposite helicities, and the coronal waves
display rotations in opposite senses. We observe deep core dimmings
near the flare site and also widespread diffuse dimming, accompanying
the expansion of the EIT wave. We also report a new property of these
EIT waves, namely, that they display dual brightenings: persistent ones
at the outermost edge of the core dimming regions and simultaneously
diffuse brightenings constituting the leading edge of the coronal wave,
surrounding the expanding diffuse dimmings. We show that such behavior
is consistent with a diffuse EIT wave being the magnetic footprint of
a CME. We propose a new mechanism where driven magnetic reconnections
between the skirt of the expanding CME magnetic field and quiet-Sun
magnetic loops generate the observed bright diffuse front. The dual
brightenings and the widespread diffuse dimming are identified as
innate characteristics of this process.
---------------------------------------------------------
Title: From The Photosphere to the Interplanetary Medium: The Magnetic
Helicity Sign from Observations
Authors: Luoni, M. L.; Mandrini, C. H.; Dasso, S.; Démoulin, P.;
Van Driel-Gesztelyi, L.
2007BAAA...50...43L Altcode:
The helicity sign of the solar magnetic field exhibits a hemispheric
preference. On a certain statistical base, it is negative (positive)
in the northern (southern) hemisphere. In this work we study a set of
active regions, observed from 1997 to 2001, for which we can determine
the magnetic helicity sign from the evolution of their polarities during
flux emergence. We confirm this sign analyzing the coronal field of
the studied regions. Then, we combine this analysis with “in situ”
observations of the magnetic clouds associated with the coronal mass
ejections that occurred in those regions. Finally, we find that the
helicity sign predicted by the distribution of the photospheric flux
agrees with the one observed at coronal and interplanetary level.
---------------------------------------------------------
Title: Study of CME transit speeds for the event of 07-NOV-2004
Authors: Culhane, J. L.; Pohjolainen, S.; van Driel-Gesztelyi, L.;
Manoharan, P. K.; Elliott, H. A.
2007AdSpR..40.1807C Altcode:
Several methods for CME speed estimation are discussed. These include
velocity derivation based on the frequency drifts observed in metric
and decametric radio wave data using a range of coronal density
models. Coronagraph height-time plots allow measurement of plane-of-sky
and expansion speeds. These in turn can enable propagation speeds to
be derived from a range of empirical relations. Simple geometric e.g.,
cone, models can provide propagation velocity estimates for suitable
halo or partial halo events. Interplanetary scintillation observations
allow speed estimates at large distances from the Sun detecting in
particular the deceleration of the faster CMEs. Related interplanetary
shocks and the arrival times and speeds of the associated magnetic
clouds at Earth can also be considered. We discuss the application of
some of these methods to the transit to Earth of a complex CME that
originated earlier than 16:54 U.T. on 07-NOV-2004. The difficulties
in making velocity estimates from radio observations, particularly
under disturbed coronal conditions, are highlighted.
---------------------------------------------------------
Title: Using the Evolution of Coronal Dimming Regions to Probe the
Global Magnetic Field Topology
Authors: Attrill, G.; Nakwacki, M. S.; Harra, L. K.; Van
Driel-Gesztelyi, L.; Mandrini, C. H.; Dasso, S.; Wang, J.
2006SoPh..238..117A Altcode: 2006SoPh..tmp...31A
We demonstrate that study of the evolving magnetic nature of coronal
dimming regions can be used to probe the large-scale magnetic structure
involved in the eruption of a coronal mass ejection (CME). We analyse
the intensity evolution of coronal dimming regions using 195 Å data
from the Extreme ultraviolet Imaging Telescope (EIT) on board the Solar
and Heliospheric Observatory (SOHO). We measure the magnetic flux, using
data from the SOHO/Michelson Doppler Imager (MDI), in the regions that
seem most likely to be related to plasma removal. Then, we compare these
magnetic flux measurements to the flux in the associated magnetic cloud
(MC). Here, we present our analysis of the well-studied event on 12
May 1997 that took place just after solar minimum in a simple magnetic
configuration. We present a synthesis of results already published and
propose that driven "interchange reconnection" between the expanding
CME structure with “open” field lines of the northern coronal hole
region led to the asymmetric temporal and spatial evolution of the
two main dimming regions, associated with this event. As a result of
this reconnection process, we find the southern-most dimming region
to be the principal foot-point of the MC. The magnetic flux from this
dimming region and that of the MC are found to be in close agreement
within the same order of magnitude, 10<SUP>21</SUP> Mx.
---------------------------------------------------------
Title: Build-up of a CME and its Interaction with Large-Scale
Magnetic Structures
Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Demoulin, P.; Culhane,
J. L.; Klein, K. L.; Mandrini, C. H.; Matthews, S. A.; Harra, K. L.;
Kurokawa, H.
2006IAUJD...3E..86V Altcode:
Introduction: A series of flares (GOES class M, M and C) and a
CME were observed on 20-JAN-2004 occurring in close succession in
NOAA 10540. Types II, III and a N radio bursts were associated. We
investigate the link between the flares (two impulsive flares followed
by an LDE) and the CME as well as the origin of the rare decametric
N-burst. Methods: We use the combined observations from TRACE, SOHO/EIT,
H-alpha images from Kwasan Observatory, SOHO/MDI magnetograms, GOES
and radio observations from Culgoora and Wind/WAVES as well as magnetic
modelling to understand the complex development of this event. Results:
We link the first two impulsive flares to tether-cutting reconnections
and the launch of the CME, while the last of the flares, an LDE,
to the relaxation phase following forced reconnections between the
erupting flux rope and neighbouring magnetic field lines. We show
that reconnection with the magnetic structure of a previous CME,
launched about 8 hours earlier, injects electrons into open field
lines having a local dip and apex of about 6 solar radii height. The
dipped shape of these field lines was due to large-scale magnetic
reconnection between expanding magnetic loops and open field lines of a
neighbouring streamer. This particular situation explains the observed
decametric N burst. Discussion: This complex observation shows that
impulsive quadrupolar flares can be eruptive, while an LDE may remain
a confined event. We find that reconnection forced by the expanding CME
structure is followed by a relaxation phase, when reconnection reverses
and restores some of the pre-eruption magnetic connectivities. The
observed decametric N-burst was caused by the interaction of two CMEs
and reconnection of their expanding magnetic field with neighbouring
streamer field lines - a very particular interplay, which explains
why N-bursts are so rare.
---------------------------------------------------------
Title: Magnetic Fields and Large-Scale SXR and EUV Coronal Structures
Authors: van Driel-Gesztelyi, Lidia
2006IAUS..233..205V Altcode:
An overview is presented of large-scale coronal structures as observed
in soft X-rays (SXR) and extreme ultraviolet (EUV) wavelengths in
the context of their magnetic properties. These structures include
large-scale interconnecting and trans-equatorial loops, coronal
streamers, coronal holes, filaments and filament channels. Since the
general appearance of the corona and its structures change with evolving
underlying fields, evolutionary trends and solar cycle dependence of
these coronal structures are discussed as well.
---------------------------------------------------------
Title: Editorial Appreciation
Authors: Engvold, Oddbjørn; Harvey, Jack; Leibacher, John; Sakurai,
Takashi; Švestka, Zdeněk; van Driel-Gesztelyi, Lidia; Solar Physics
editors
2006SoPh..233....1E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Combined analysis of the 15-16 May, 1997, magnetic cloud and
of its solar source region
Authors: Nakwacki, M. S.; Atrill, G.; Dasso, S.; Mandrini, C. H.;
van Driel-Gesztelyi, L.; Harra, L.; Wang, J.
2006BAAA...49...46N Altcode:
In this work we analise the structure of the magnetic cloud (MC)
observed by Wind between 15-16 May 1997, and the related solar
event, a long duration C1.3 flare which ocurred on 12 May 1997. This
event presented two dark regions in EUV (dimmings) with asymmetric
evolution. The magnetic structure of the MC was modeled using three
cylindrical helicoidal models, considering the asymmetry between its
front and its final part. We calculate the magnetic flux in the dimmings
and their evolution, and the flux through the surface perpendicular to
the cloud axis and to the azimuthal direction. Finally, we compare the
total flux of both, MC and dimmings, and propose a topological model
for the solar event. FULL TEXT IN SPANISH
---------------------------------------------------------
Title: A combined analysis of the magnetic cloud on 15-16 May 1997
and its solar source region
Authors: Nakwacki, M. S.; Attrill, G.; Dasso, S.; Mandrini, C. H.;
van Driel-Gesztelyi, L.; Harra, L. K.; Wang, J.
2006cosp...36.2479N Altcode: 2006cosp.meet.2479N
Coronal Mass Ejections CMEs are the most important short-lived agents
that transport magnetic flux from the Sun to the interplanetary medium
Thus detailed studies of the solar sources of CMEs and the associated
magnetic clouds MCs are an important key to understand and constrain
solar and interplanetary models We analyze the magnetic structure of the
MC observed on 15-16 May 1997 by the spacecraft Wind and its associated
solar event a C1 3 long duration event that occurred on 12 May 1997 in
AR8038 Two main dimming regions that exhibit an asymmetric temporal
and spatial evolution were observed in association with this event
We compute the magnetic flux in the dimmings and follow its evolution
using magnetograms from the Michelson Doppler Imager SoHO MDI The MC
structure is inferred using three different helical cylindrical models
with a significantly different radial twist distribution We also take
into account the asymmetry observed between the front and the rear
part of the cloud We fit the free parameters of each model comparing
models with in situ observations Then we estimate the flux across the
surface perpendicular to the axis of the cylinder and the flux across
the surface formed by this axis and the cloud radial direction Finally
we compare the MC total flux with that corresponding to both observed
dimmings By combining our interplanetary measurements and the dimmings
flux evolution we propose a topological model for the 12 May eruptive
event We discuss the constrains set by solar observations on
---------------------------------------------------------
Title: Multi-scale reconnections in a complex CME
Authors: van Driel-Gesztelyi, L.; Goff, C.; Demoulin, P.; Culhane,
J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.;
Kurokawa, H.
2006cosp...36.2371V Altcode: 2006cosp.meet.2371V
A series of flares GOES class M M and C and a CME were observed on
20-JAN-2004 occurring in close succession in NOAA 10540 Types II III
and an N radio bursts were associated We use the combined observations
from TRACE EIT H-alpha images from Kwasan Observatory MDI magnetograms
GOES and radio observations from Culgoora and Wind WAVES to understand
the complex development of this event We link the first two impulsive
flares to tether-cutting reconnections and the launch of the CME while
the last of the flares an LDE to the relaxation phase following forced
reconnections between the erupting flux rope and neighbouring magnetic
field lines We show that reconnection with the magnetic structure of
a previous CME launched about 8 hours earlier injects electrons into
open field lines having a local dip and apex of about 6 solar radii
height The dipped shape of these field lines was due to large-scale
magnetic reconnection between expanding magnetic loops and open field
lines of a neighbouring streamer This particular situation explains
the observed decametric N burst and why N-bursts are so rare
---------------------------------------------------------
Title: Sun-to-earth propagation speeds for three CMEs
Authors: Culhane, L.; Pohjolainen, S.; van Driel-Gesztelyi, L.;
Elliott, H.
2006cosp...36.2544C Altcode: 2006cosp.meet.2544C
Several methods for CME speed estimation are discussed for events
that occurred on 28-OCT-2003 7-NOV-2004 and 20-JAN-2005 These include
velocity derivation based on the frequency drifts observed in metric
and decametric radio wave data using a range of coronal density models
These estimated speeds are compared with plane of the sky values and
with estimates made from the application of a cone model The related
interplanetary shocks and the arrival times of the associated magnetic
clouds at Earth are also considered The range of speeds and Sun-Earth
transit times obtained from these studies is assessed The difficulties
in making velocity estimates from radio observations particularly
under disturbed coronal conditions will be highlighted
---------------------------------------------------------
Title: The MOSES spectral imager for KuaFu-A
Authors: Harra, L. K.; van Driel-Gesztelyi, L.; Cole, R.; Sun, J.;
Winter, B.; Hancock, B.
2006cosp...36.3670H Altcode: 2006cosp.meet.3670H
We will describe the instrument design for a spectral imager on the
KuaFu mission KuaFu s science goals are aimed at understanding space
weather with a spacecraft located at L1 and 2 spacecraft in a polar
orbit around the Earth The spectral imager will provide crucial
information on the source region of coronal mass ejections It will
achieve this by measuring the Doppler velocities and intensity over
the field of view of the solar activity zone which is geoeffective
This allows us to determine whether activity on the Sun does actually
releases material into the interplanetary medium BEFORE we observe
it in coronagraphs We will summarise the instrument design and the
scientific drivers for it
---------------------------------------------------------
Title: Tracing magnetic helicity from the solar corona to the
interplanetary space
Authors: Luoni, M. L.; Mandrini, C. H.; Dasso, Sergio; van
Driel-Gesztelyi, L.; Démoulin, P.
2005JASTP..67.1734L Altcode: 2005JATP...67.1734L
On October 14, 1995, a C1.6 long duration event (LDE) started in active
region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about
15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic
Field Instrument (MFI) on board the Wind spacecraft registered a
magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic
storm. We identify the solar source of this phenomenon as AR 7912. We
use magnetograms obtained by the Imaging Vector Magnetograph at Mees
Solar Observatory, as boundary conditions to the linear force-free
model of the coronal field, and, we determine the model in which the
field lines best fit the loops observed by the Soft X-ray Telescope on
board Yohkoh. The computations are done before and after the ejection
accompanying the LDE. We deduce the loss of magnetic helicity from AR
7912. We also estimate the magnetic helicity of the MC from in situ
observations and force-free models. We find the same sign of magnetic
helicity in the MC and in its solar source. Furthermore, the helicity
values turn out to be quite similar considering the large errors that
could be present. Our results are a first step towards a quantitative
confirmation of the link between solar and interplanetary phenomena
through the study of magnetic helicity.
---------------------------------------------------------
Title: Erupting Flux Rope, Rising X-Ray Source and a Slow CME on 16
April 2002
Authors: Goff, C. P.; van Driel-Gesztelyi, L.; Harra, L. K.; Matthews,
S. A.; Mandrini, C. H.
2005ESASP.600E..46G Altcode: 2005ESPM...11...46G; 2005dysu.confE..46G
No abstract at ADS
---------------------------------------------------------
Title: Relating Near-Earth Observations of AN Interplanetary Coronal
Mass Ejection to the Conditions at its Site of Origin in the Solar
Corona
Authors: Fazakerley, A. N.; Harra, L. K.; Culhane, J. L.; van
Driel-Gesztelyi, L.; Lucek, E.; Matthews, S. A.; Owen, C. J.; Mazelle,
C.; Balogh, A.; Réme, H.
2005ESASP.600E..47F Altcode: 2005dysu.confE..47F; 2005ESPM...11...47F
No abstract at ADS
---------------------------------------------------------
Title: Quantitative Link Between Solar Ejecta and Interplanetary
Magnetic Clouds: Magnetic Helicity
Authors: Mandrini, C. H.; Dasso, S.; Luoni, M. L.; Pohjolainen, S.;
Démoulin, P.; van Driel-Gesztelyi, L.
2005ESASP.596E..29M Altcode: 2005ccmf.confE..29M
No abstract at ADS
---------------------------------------------------------
Title: Linking Coronal to Heliospheric Magnetic Helicity: A New
Model-Independent Technique to Compute Helicity in Magnetic Clouds
Authors: Dasso, Sergio; Mandrini, Cristina H.; Luoni, Maria L.;
Gulisano, Adriana M.; Nakwacki, Maria S.; Pohjolainen, Silja; van
Driel-Gesztelyi, Lidia; Démoulin, Pascal
2005ESASP.592..605D Altcode: 2005soho...16E.117D; 2005ESASP.592E.117D
No abstract at ADS
---------------------------------------------------------
Title: Flows in the solar atmosphere due to the eruptions on the
15th July, 2002
Authors: Harra, L. K.; Démoulin, P.; Mandrini, C. H.; Matthews,
S. A.; van Driel-Gesztelyi, L.; Culhane, J. L.; Fletcher, L.
2005A&A...438.1099H Altcode:
Which kind of flows are present during flares? Are they compatible
with the present understanding of energy release and which model
best describes the observations? We analyze successive flare events
in order to answer these questions. The flares were observed in the
magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One
of them is of GOES X-class. The description of these flares and how
they relate to the break-out model is presented in Gary & Moore
(2004). The Coronal Diagnostic Spectrometer on board SOHO observed
this active region for around 14 h. The observed emission lines
provided data from the transition region to the corona with a field
of view covering more than half of the active region. In this paper
we analyse the spatially resolved flows seen in the atmosphere from
the preflare to the flare stages. We find evidence for evaporation
occurring before the impulsive phase. During the main phase, the
ongoing magnetic reconnection is demonstrated by upflows located at
the edges of the flare loops (while downflows are found in the flare
loops themselves). We also report the impact of a filament eruption
on the atmosphere, with flows up to 300 km s<SUP>-1</SUP> observed at
transition-region temperatures in regions well away from the location
of the pre-eruptive filament. Our results are consistent with the
predictions of the break out model before the impulsive phase of the
flare; while, as the flare progresses, the directions of the flows are
consistent with flare models invoking evaporation followed by cooling
and downward plasma motions in the flare loops.
---------------------------------------------------------
Title: Eruption of a Kink-unstable Filament in NOAA Active Region
10696
Authors: Williams, David R.; Török, Tibor; Démoulin, Pascal;
van Driel-Gesztelyi, Lidia; Kliem, Bernhard
2005ApJ...628L.163W Altcode: 2005astro.ph..7661W
We present rapid-cadence Transition Region and Coronal Explorer (TRACE)
observations that show evidence of a filament eruption from NOAA active
region 10696, accompanied by an X2.5 flare, on 2004 November 10. The
eruptive filament, which manifests as a fast coronal mass ejection
some minutes later, rises as a kinking structure with an apparently
exponential growth of height within TRACE's field of view. We compare
the characteristics of this filament eruption with MHD numerical
simulations of a kink-unstable magnetic flux rope, finding excellent
qualitative agreement. We suggest that while tether weakening by
breakout-like quadrupolar reconnection may be the release mechanism
for the previously confined flux rope, the driver of the expansion is
most likely the MHD helical kink instability.
---------------------------------------------------------
Title: Relating near-Earth observations of an interplanetary coronal
mass ejection to the conditions at its site of origin in the solar
corona
Authors: Fazakerley, A. N.; Harra, L. K.; Culhane, J. L.; van
Driel-Gesztelyi, L.; Lucek, E.; Matthews, S. A.; Owen, C. J.; Mazelle,
C.; Balogh, A.; Rème, H.
2005GeoRL..3213105F Altcode:
A halo coronal mass ejection (CME) was detected on January 20, 2004. We
use solar remote sensing data (SOHO, Culgoora) and near-Earth in situ
data (Cluster) to identify the CME source event and show that it was a
long duration flare in which a magnetic flux rope was ejected, carrying
overlying coronal arcade material along with it. We demonstrate that
signatures of both the arcade material and the flux rope material are
clearly identifiable in the Cluster and ACE data, indicating that the
magnetic field orientations changed little as the material traveled
to the Earth, and that the methods we used to infer coronal magnetic
field configurations are effective.
---------------------------------------------------------
Title: Editorial
Authors: Leibacher, John; Sakurai, Takashi; van Driel-Gesztelyi, Lidia
2005SoPh..229....3L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A slow coronal mass ejection with rising X-ray source
Authors: Goff, C. P.; van Driel-Gesztelyi, L.; Harra, L. K.; Matthews,
S. A.; Mandrini, C. H.
2005A&A...434..761G Altcode:
An eruptive event, which occurred on 16th April 2002, is
discussed. Using images from the Transition Region and Coronal Explorer
(TRACE) at 195 Å, we observe a lifting flux rope which gives rise
to a slow coronal mass ejection (CME). There are supporting velocity
observations from the Coronal Diagnostic Spectrometer (CDS) on the Solar
and Heliospheric Observatory (SOHO), which illustrate the helical nature
of the structure. Additionally a rising coronal hard X-ray source,
which is observed with the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), is shown to follow the flux rope with a speed of ~60
km s<SUP>-1</SUP>. It is also sampled by the CDS slit, although it has
no signature in the Fe XIX band. Following the passage of this source,
there is evidence from the CDS for down-flowing (cooling) material
along newly reconnected loops through Doppler velocity observations,
combined with magnetic field modeling. Later, a slow CME is observed
with the Large Angle and Spectroscopic Coronagraph (LASCO). We combine
a height-time profile of the flux rope at lower altitudes with the slow
CME. The rising flux rope speeds up by a factor of 1.7 at the start
of the impulsive energy release and goes through further acceleration
before reaching 1.5 solar radii. These observations support classical
CME scenarios in which the eruption of a filament precedes flaring
activity. Cusped flare loops are observed following the erupting
flux rope and their altitude increases with time. In addition we
find RHESSI sources both below and above the probable location of the
reconnection region.
---------------------------------------------------------
Title: Interplanetary flux rope ejected from an X-ray bright
point. The smallest magnetic cloud source-region ever observed
Authors: Mandrini, C. H.; Pohjolainen, S.; Dasso, S.; Green, L. M.;
Démoulin, P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C.
2005A&A...434..725M Altcode:
Using multi-instrument and multi-wavelength observations (SOHO/MDI and
EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic
field of a tiny bipole combined with modelling of Wind in situ data,
we provide evidences for the smallest event ever observed which links
a sigmoid eruption to an interplanetary magnetic cloud (MC). The
tiny bipole, which was observed very close to the solar disc centre,
had a factor one hundred less flux than a classical active region
(AR). In the corona it had a sigmoidal structure, observed mainly
in EUV, and we found a very high level of non-potentiality in the
modelled magnetic field, 10 times higher than we have ever found in
any AR. From May 11, 1998, and until its disappearance, the sigmoid
underwent three intense impulsive events. The largest of these events
had extended EUV dimmings and a cusp. The Wind spacecraft detected 4.5
days later one of the smallest MC ever identified (about a factor one
hundred times less magnetic flux in the axial component than that of an
average MC). The link between this last eruption and the interplanetary
magnetic cloud is supported by several pieces of evidence: good timing,
same coronal loop and MC orientation, same magnetic field direction
and magnetic helicity sign in the coronal loops and in the MC. We
further quantify this link by estimating the magnetic flux (measured
in the dimming regions and in the MC) and the magnetic helicity (pre-
to post-event change in the solar corona and helicity content of the
MC). Within the uncertainties, both magnetic fluxes and helicities
are in reasonable agreement, which brings further evidences of their
link. These observations show that the ejections of tiny magnetic flux
ropes are indeed possible and put new constraints on CME models.
---------------------------------------------------------
Title: Relationship between X-ray and ultraviolet emission of flares
from dMe stars observed by XMM-Newton
Authors: Mitra-Kraev, U.; Harra, L. K.; Güdel, M.; Audard, M.;
Branduardi-Raymont, G.; Kay, H. R. M.; Mewe, R.; Raassen, A. J. J.;
van Driel-Gesztelyi, L.
2005A&A...431..679M Altcode: 2004astro.ph.10592M
We present simultaneous ultraviolet and X-ray observations of
the dMe-type flaring stars <ASTROBJ>AT Mic</ASTROBJ>, <ASTROBJ>AU
Mic</ASTROBJ>, <ASTROBJ>EV Lac</ASTROBJ>, <ASTROBJ>UV Cet</ASTROBJ>
and <ASTROBJ>YZ CMi</ASTROBJ> obtained with the XMM-Newton
observatory. During 40 h of simultaneous observation we identify
13 flares which occurred in both wave bands. For the first time,
a correlation between X-ray and ultraviolet flux for stellar flares
has been observed. We find power-law relationships between these two
wavelength bands for the flare luminosity increase, as well as for
flare energies, with power-law exponents between 1 and 2. We also
observe a correlation between the ultraviolet flare energy and the
X-ray luminosity increase, which is in agreement with the Neupert
effect and demonstrates that chromospheric evaporation is taking place.
---------------------------------------------------------
Title: Coronal Mass Ejections and Magnetic Helicity
Authors: Van Driel-Gesztelyi, L.
2005ASSL..320...57V Altcode: 2005smp..conf...57V
No abstract at ADS
---------------------------------------------------------
Title: The smallest source region of an interplanetary magnetic cloud:
A mini-sigmoid
Authors: Mandrini, C. H.; Pohjolainen, S.; Dasso, S.; Green, L. M.;
Démoulin, P.; van Driel-Gesztelyi, L.; Foley, C.; Copperwheat, C.
2005AdSpR..36.1579M Altcode:
We provide evidence for the smallest sigmoid eruption - CME -
interplanetary magnetic cloud event ever observed by combining
multi-wavelength remote sensing and in situ observations, as well as
computing the coronal and interplanetary magnetic fields. The tiny
bipole had 100 times less flux than an average active region (AR). It
had a sigmoidal structure in the corona and we detected a very high
level of twist in its magnetic field. On 11 May 1998, at about 8 UT, the
sigmoid underwent eruption evidenced by expanding elongated EUV loops,
dimmings and formation of a cusp. The Wind spacecraft, 4.5 days later,
detected one of the smallest magnetic clouds (MC) ever identified
(100 times less magnetic flux than an average MC). The link between
the EUV bright point eruption and the interplanetary MC is supported by
several pieces of evidence: timing, same coronal loop and MC orientation
relative to the ecliptic, same magnetic field direction and magnetic
helicity sign in the coronal loops and in the MC, comparable magnetic
flux measured in the dimming regions and in the interplanetary MC and,
most importantly, the pre- to post-event change of magnetic helicity
in the solar corona is found to be comparable to the helicity content
of the cloud.
---------------------------------------------------------
Title: Source Regions of Coronal Mass Ejections
Authors: Schmieder, Brigitte; van Driel-Gesztelyi, L.
2005IAUS..226..149S Altcode:
The majority of flare activity arises in active regions which
contain sunspots, while CME activity can also originate from decaying
active regions and even so-called quiet solar regions which contain a
filament. Two classes of CME, namely flare-related CME events and CMEs
associated with filament eruption are well reflected in the evolution
of active regions, flare related CMEs mainly occur in young active
regions containing sunspots and as the magnetic flux of active region
is getting dispersed, the filament-eruption related CMEs will become
dominant. This is confirmed by statistical analyses.</p>All the
CMEs are, nevertheless, caused by loss of equilibrium of the magnetic
structure. With observational examples we show that the association
of CME, flare and filament eruption depends on the characteristics
of the source regions: (i) the strength of the magnetic field, the
amount of possible free energy storage, (ii) the small- and large-scale
magnetic topology of the source region as well as its evolution (new
flux emergence, photospheric motions, canceling flux), and (iii) the
mass loading of the configuration (effect of gravity). These examples
are discussed in the framework of theoretical models.
---------------------------------------------------------
Title: Linking Coronal to Interplanetary Magnetic Helicity
Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; Van Driel-Gesztelyi,
L.; Démoulin, P.
2005ASSL..320..243L Altcode: 2005smp..conf..243L
No abstract at ADS
---------------------------------------------------------
Title: Solar and Interplanetary Magnetic Helicity Balance of Active
Regions
Authors: Mandrini, Cristina H.; Démoulin, Pascal; van Driel-Gesztelyi,
Lidia; Dasso, Sergio; Green, Lucinda M.; López Fuentes, Marcelo
2005HiA....13..122M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Relating magnetic field strengths to hard X-ray emission in
solar flares
Authors: Goff, C. P.; Matthews, S. A.; van Driel-Gesztelyi, L.; Harra,
L. K.
2004A&A...423..363G Altcode:
The observation of hard X-ray (HXR) emission in solar flares provides
important diagnostic information about the acceleration and subsequent
transport of energetic electrons in the flare process. However,
while hard X-rays are thought to be emitted from the flare footpoints
through thick-target bremsstrahlung interactions, the details of the
transport of accelerated electrons through the solar atmosphere still
remains unclear. <P />Trapping of the electrons is one particular
effect that is expected to occur as a result of the convergence of the
magnetic field between the corona and the chromosphere. In this case
the brightness of the HXR footpoints should be related to the strength
of the magnetic field present and we would expect greater precipitation
and higher HXR intensities at the footpoints with lower magnetic field
strength. This relationship has been observed to hold in many flares
(see \citealt{Sakaothesis}) but interestingly the opposite relationship,
where the stronger HXR source is found at the stronger magnetic field
region, has also been observed in an event studied by \citet{Asai}. <P
/>Using Data from Yohkoh's Hard X-Ray Telescope (HXT) and SOHO's
Michelson Doppler Imager (MDI) we have studied the magnetic field
strengths at the footpoints of a sample of 32 flares and have compared
them to the hard X-ray brightness to determine whether the expected
ratios are seen. We find that contrary to the expected relationship
the brighter HXR footpoint is found in the region of stronger magnetic
field in approximately one third of our sample of events. We discuss
the implications of these results in terms of the transport mechanisms.
---------------------------------------------------------
Title: Intensity variations in EIT shutterless mode: Waves or flows?
Authors: De Groof, A.; Berghmans, D.; van Driel-Gesztelyi, L.;
Poedts, S.
2004A&A...415.1141D Altcode:
On 11 July 2001 an EIT shutterless campaign was conducted which provided
120 high-cadence (68 s) 304 Å images of the north eastern quarter of
the Sun. The most interesting feature seen in the data is an off-limb
half loop structure along which systematic intensity variations are
seen which appear to propagate from the top of the loop towards its
footpoint. We investigate the underlying cause of these propagating
disturbances, i.e. whether they are caused by waves or by plasma
flows. First we identify 7 blobs with the highest intensities and
follow them along the loop. By means of a location-time plot, bulk
velocities can be measured at several locations along the loop. The
velocity curve found this way is then compared with characteristic
wave speeds and with the free-fall speed in order to deduce the nature
of the intensity variations. Additional information on density and
temperature is derived by measuring the relative intensity enhancements
and comparing the EIT 304 Å sequence with Big Bear data and 171 Å
data (TRACE/EIT). The combination of all these constraints gives us an
insight on the nature and origin of these intensity variations. The
idea of slow magneto-acoustic waves is rejected, and we find several
arguments supporting that these intensity variations are due to
flowing/falling plasma blobs.
---------------------------------------------------------
Title: Magnetic Helicity Budget of Solar-Active Regions from the
Photosphere to Magnetic Clouds
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
van Driel-Gesztelyi, L.; van Driel-Gesztelyi, L.; van Driel-Gesztelyi,
L. L. M.; López Fuentes, M. C.
2004Ap&SS.290..319M Altcode:
We have analyzed the long-term evolution of two active regions (ARs)
from their emergence through their decay using observations from several
instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We
have computed the evolution of the relative coronal magnetic helicity
combining data from MDI and SXT with a linear force-free model of
the coronal magnetic field. Next, we have computed the injection of
helicity by surface differential rotation using MDI magnetic maps. To
estimate the depletion of helicity we have counted all the CMEs of which
these ARs have been the source, and we have evaluated their magnetic
helicity assuming a one to one correspondence with magnetic clouds
with an average helicity contain. When these three values (variation
of coronal magnetic helicity, injection by differential rotation and
ejection via CMEs) are compared, we find that surface differential
rotation is a minor contributor to the helicity budget since CMEs carry
away at least 10 times more helicity than the one differential rotation
can provide. Therefore, the magnetic helicity flux needed in the global
balance should come from localized photospheric motions that, at least
partially, reflect the emergence of twisted flux tubes. We estimate
that the total helicity carried away in CMEs can be provided by the
end-to-end helicity of the flux tubes forming these ARs. Therefore,
we conclude that most of the helicity ejected in CMEs is generated
below the photosphere and emerges with the magnetic flux.
---------------------------------------------------------
Title: Evidence of Magnetic Reconnection along Coronal Hole Boundaries
Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L.
2004ApJ...603L..57M Altcode:
The present study reveals for the first time the existence of
bidirectional jets, which are a signature of magnetic reconnection,
occurring along coronal hole boundaries. The Solar Ultraviolet
Measurement of Emitted Radiation spectrometer observations obtained
in the N IV 765.15 Å (1.3×10<SUP>5</SUP> K) and Ne VIII 770.42
Å (6×10<SUP>5</SUP> K) emission lines in an equatorial extension
of a polar coronal hole, known as the “Elephant's Trunk” coronal
hole, show small regions of a few arcseconds size with strong blue-
and redshifted emission reaching Doppler shifts of up to 150 km
s<SUP>-1</SUP>, i.e., bidirectional jets. The jets' number density
along coronal hole boundaries was found to be about 4-5 times higher
with respect to the quiet Sun.
---------------------------------------------------------
Title: An Observational Test for Coronal Heating Models
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
Harra, L. K.; Klimchuk, J. A.
2004IAUS..219..473V Altcode: 2003IAUS..219E..97V
We correlate the evolution of the mean X-ray flux emission measure
and temperature (Yohkoh SXT & BCS) with the magnetic flux density
(SOHO/MDI) in active region NOAA 7978 from its birth throughout its
decay for five solar rotations. We show that these plasma parameters
together with other quantities deduced from them such as the density
and the pressure follow power-law relationships with the mean magnetic
flux density (bar{B}). We derive the dependence of the mean coronal
heating rate on the magnetic flux density. We use the obtained scaling
laws of coronal loops in thermal equilibrium to derive observational
estimates of the scaling of the coronal heating with bar{B}. These
results are used to test the validity of coronal heating models. We
find that models invoking stochastic buildup of energy current layers
and MHD turbulence are in best agreement with the observations. This
narrows down the range of possible models retained by previous results
obtained for individual coronal loops as well as for the global coronal
emission of the Sun and cool stars.
---------------------------------------------------------
Title: Bi-Directional Jets at Coronal Hole Boundaries
Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L.
2004ESASP.547..397M Altcode: 2004soho...13..397M
Our study reveals, for the first time, the presence of bi-directional
jets which are considered to be signatures of magnetic reconnection
occurring along coronal hole boundaries. The SUMER observations obtained
in Ne VIII 770.42 Å (6 10 K) and N IV 765.15 Å (1.3 10 K) show small
regions of a few arcsec size with strong blueand red-shifted emission
reaching Doppler shifts up to 150 km s which appear along the coronal
hole boundaries where evolving loop systems are present.
---------------------------------------------------------
Title: Intensity Variations in EIT Shutterless Mode: Waves or Flows?
Authors: de Groof, A.; Berghmans, D.; van Driel-Gesztelyi, L.;
Poedts, S.
2004ESASP.547..245D Altcode: 2004soho...13..245D
On 11 July 2001 an EIT shutterless campaign was conducted which provided
120 high-cadence (68s) 304 Å images of the north eastern quarter of the
Sun. The most interesting feature seen in the data is an off-limb half
loop structure along which systematic intensity variations appear to
propagate from the top of the loop towards its footpoint. We investigate
the underlying cause of these propagating disturbances, i.e. whether
they are caused by waves or by plasma flows. First we identify 7 blobs
with the highest intensities and follow them along the loop. By means
of a location-time plot, bulk velocities can be measured at several
locations along the loop. The velocity curve found this way is then
compared with characteristic wave speeds and with the free-fall speed
in order to deduce the nature of the intensity variations. Additional
information is derived by measuring the relative intensity enhancements
and comparing the EIT 304 Å sequence with Big Bear and 171 Å data. The
idea of slow magneto-acoustic waves is rejected, and we find several
arguments supporting that these intensity variations are due to
flowing/falling plasma blobs.
---------------------------------------------------------
Title: Linking coronal observations of a `mini´active region with
its interplanetary manifestation
Authors: Dasso, S.; Mandrini, C. H.; Pohjolainen, S.; Green, L. M.;
Démoulin, P.; van Driel-Gesztelyi, L.; Foley, C.; Copperwheat, C.
2004BAAA...47...18D Altcode:
We analyze the smallest 'sigmoidal eruption - CME - interplanetary
magnetic cloud' event even observed before. We find: (a) the same
magnetic helicity sign and (b) similar magnetic flux values in the
coronal source region and associated cloud, and (c) that the magnetic
helicity changes, before and after the ejection, in approximately the
same amount as the helicity content in the interplanetary cloud. These
results stress the importance of complementary solar and interplanetary
studies, to achieve a better understanding of the origin of eruptive
phenomena.
---------------------------------------------------------
Title: Flux Cancellation in a Decaying Active Region
Authors: Martinez Pillet, V.; Sainz Dalda, A.; van Driel-Gesztelyi, L.
2004cosp...35.1133M Altcode: 2004cosp.meet.1133M
Flux Cancellation in a Decaying Active Region Flux cancellation
is observed in many regions on the Sun as internetwork, network
and active regions fields. It clearly plays a crucial role in the
constant flux processing observed in the solar surface. During the
decay of an active region, we have observed the in-situ dissapearance
of 70 % of its flux (from SOHO/MDI). Active region flux decay is a
global, large-scale, process crucial to the solar cycle. But the
flux cancellations, where the flux actually disappears, do take
place in very small scale regions. There opposite polarities meet and
vanish. The process needs of observations with sufficient sensitivity
and angular resolution. In the example presented here, we show how
up to 4 of these cancellations are associated with outward moving
material in the Corona (as observed by TRACE), including a major
active region filament eruption. Solar Orbiter, profiting from the
advantage observing position and near-corotation can follow these
subtle, but crucial, processes with the necessary set of instruments:
Magnetographs, Coronal imagers and spectrographs. For those events
occurring in the spacecraft solar vertical, one should not exclude
the detection of the phenomena in the in-situ instruments.
---------------------------------------------------------
Title: The smallest source region of an interplanetary magnetic cloud:
a mini-sigmoid
Authors: Mandrini, C.; Pohjolainen, S.; Dasso, S.; Green, L.; Demoulin,
P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C.
2004cosp...35..290M Altcode: 2004cosp.meet..290M
Using multi-instrument and multi-wavelength observations (SOHO/MDI
and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal
magnetic field of a tiny bipole combined with modelling of WIND in situ
data, we provide evidence for the smallest sigmoid eruption - CME -
interplanetary magnetic cloud event ever observed. The tiny bipole,
which was observed very close to the solar disc centre, had 100 times
less flux than an average active region (AR). In the corona it had a
sigmoidal structure and we detected a very high level of twist. On 11
May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by
expanding elongated EUV loops, dimmings and formation of a cusp. The
WIND spacecraft detected 4.5 days later one of the smallest magnetic
clouds (MC) ever identified (100 times less flux and radius than an
average MC). The link between the sigmoidal EUV bright point eruption
and the interplanetary magnetic cloud is supported by several pieces of
evidence: good timing, same coronal loop and MC orientation relative
to the ecliptic, same magnetic field direction and magnetic helicity
sign in the coronal loops and in the MC, comparable magnetic flux
measured in the dimming regions and in the interplanetary MC and,
most importantly, the pre- to post-event change of magnetic helicity
in the solar corona is found to be similar to the helicity content of
the cloud, when assuming a length compatible with the fact that the
cloud can be detached from the Sun one day after its ejection. These
observations are a challenge to present theoretical CME models, and show
us the need of missions such us Solar B and Stereo to contribute to our
understanding of the broad spectrum covered by solar eruptive phenomena.
---------------------------------------------------------
Title: How small can an interplanetary magnetic cloud source-region
be?
Authors: Mandrini, C.; Pohjolainen, S.; Dasso, S.; Green, L.; Demoulin,
P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C.
2004cosp...35..282M Altcode: 2004cosp.meet..282M
Using multi-instrument and multi-wavelength observations (SOHO/MDI
and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal
magnetic field of a tiny bipole combined with modelling of WIND in situ
data, we provide evidence for the smallest sigmoid eruption - CME -
interplanetary magnetic cloud event ever observed. The tiny bipole,
which was observed very close to the solar disc centre, had 100 times
less flux than an average active region (AR). In the corona it had a
sigmoidal structure and we detected a very high level of twist. On 11
May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by
expanding elongated EUV loops, dimmings and formation of a cusp. The
WIND spacecraft detected 4.5 days later one of the smallest magnetic
clouds (MC) ever identified (100 times less flux and radius than an
average MC). The link between the sigmoidal EUV bright point eruption
and the interplanetary magnetic cloud is supported by several pieces of
evidence: good timing, same coronal loop and MC orientation relative
to the ecliptic, same magnetic field direction and magnetic helicity
sign in the coronal loops and in the MC, comparable magnetic flux
measured in the dimming regions and in the interplanetary MC and,
most importantly, the pre- to post-event change of magnetic helicity
in the solar corona is found to be similar to the helicity content
of the cloud, when assuming a length compatible with the fact that
thecloud can be dettached from the Sun one day after its ejection. These
observations are a challenge to present theoretical CME models, and show
us the need of missions such us Solar B and Stereo to contribute to our
understandig of the broad spectrum covered by solar eruptive phenomena.
---------------------------------------------------------
Title: An Introduction to Magnetohydrodynamics
Authors: van Driel-Gesztelyi, Lidia
2004spsc.book..279V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The possible back-rotation of sunspots
Authors: Williams, D. R.; van Driel-Gesztelyi, L.; Nakariakov, V. M.
2004cosp...35.4391W Altcode: 2004cosp.meet.4391W
The curious case of sunspot rotation in two senses, presented by
Kucera (1982), provided an interesting challenge to the idea of sunspot
rotation being due simply to the differential rotation of the Sun above
the tachocline. As the rotation rate and direction, in that case, are
seen to vary as a damped sinusoid, this presents the possibility that
such motion is the result of torsional waves trapped in the sunspot's
sub-photospheric flux tube. We therefore analyse the rotation of a
number of sunspots using SoHO/MDI and track their rotation, presenting
evidence of 'back-rotation' -- rotational motion which reverses --
in a several of these spots. Intuitively, this raises the possibility
of extending the field of 'Coronal Seismology' back down to beneath
the photosphere (where helioseismology already exists).
---------------------------------------------------------
Title: Evidence of Flaring in a Transequatorial Loop on the Sun
Authors: Harra, Louise K.; Matthews, Sarah A.; van Driel-Gesztelyi,
Lidia
2003ApJ...598L..59H Altcode:
We present evidence of flaring behavior in a transequatorial loop (TEL)
that lights up in soft X-rays on 2000 July 13. The large loop structure
connects NOAA Active Regions 9070/9066 in the northern hemisphere and
AR 9069/9068 in the southern hemisphere. We follow the loop systems for
2 days and observe several pieces of evidence strongly suggesting flare
behavior of the form seen in standard flaring in active regions. These
include brightenings of the loop structure, cooling of plasma that is
seen both in soft X-rays and in the transition region temperatures,
morphological evidence of reconnection inflow, and blueshifts around
the footpoint of the TEL suggestive of chromospheric evaporation. We
present, to our knowledge for the first time, observations of TEL in
the O V emission line.
---------------------------------------------------------
Title: A catalogue of white-light flares observed by Yohkoh
Authors: Matthews, S. A.; van Driel-Gesztelyi, L.; Hudson, H. S.;
Nitta, N. V.
2003A&A...409.1107M Altcode:
The aspect camera of the Soft X-ray Telescope (SXT) on Yohkoh provided
the first systematic survey of white-light flares from an observatory in
space. The observations were made in the Fraunhofer g-band at a pixel
size of 2.46 arcsec and a typical sample interval on the order of ten
seconds. A total of 28 flares with clear white-light signatures were
detected, corresponding to GOES events down to the C7.8 level in one
case. Above the X-class threshold, all 5 events observed by SXT were
observed in white light, and the maximum average contrast observed
was 30% relative to the pre-flare continuum brightness of the flare
location. We have made comprehensive comparisons of Yohkoh soft X-ray
and hard X-ray data for this list of flares. In addition we compare
the properties of the WLF sample to a sample of 31 flares that showed
no white-light emission. These comparisons show that while white-light
continuum emission has a strong association with hard X-ray emission
it is also strongly related to coronal overpressure, as determined
from the soft X-ray spectrum, indicating a component with a thermal,
rather than non-thermal origin. <P />Appendices are only available in
electronic form at http://www.edpsciences.org
---------------------------------------------------------
Title: How are Emerging Flux, Flares and CMEs Related to Magnetic
Polarity Imbalance in Midi Data?
Authors: Green, L. M.; Démoulin, P.; Mandrini, C. H.; Van
Driel-Gesztelyi, L.
2003SoPh..215..307G Altcode: 2003astro.ph..4092G
In order to understand whether major flares or coronal mass ejections
(CMEs) can be related to changes in the longitudinal photospheric
magnetic field, we study 4 young active regions during seven days of
their disk passage. This time period precludes any biases which may
be introduced in studies that look at the field evolution during the
short-term flare or CME period only. Data from the Michelson Doppler
Imager (MDI) with a time cadence of 96 min are used. Corrections are
made to the data to account for area foreshortening and angle between
line of sight and field direction, and also the underestimation of
the flux densities. We make a systematic study of the evolution of the
longitudinal magnetic field, and analyze flare and CME occurrence in
the magnetic evolution. We find that the majority of CMEs and flares
occur during or after new flux emergence. The flux in all four active
regions is observed to have deviations from polarity balance both on
the long term (solar rotation) and on the short term (few hours). The
long-term imbalance is not due to linkage outside the active region; it
is primarily related to the east-west distance from central meridian,
with the sign of polarity closer to the limb dominating. The sequence
of short-term imbalances are not closely linked to CMEs and flares and
no permanent imbalance remains after them. We propose that both kinds
of imbalance are due to the presence of a horizontal field component
(parallel to the photospheric surface) in the emerging flux.
---------------------------------------------------------
Title: The Long-Term Evolution of AR 7978: The Scalings of the
Coronal Plasma Parameters with the Mean Photospheric Magnetic Field
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
Harra, L.; Klimchuk, J. A.
2003ApJ...586..579V Altcode:
We analyze the evolution of the fluxes observed in X-rays and correlate
them with the magnetic flux density in active region (AR) NOAA 7978
from its birth throughout its decay, for five solar rotations. We
use Solar and Heliospheric Observatory Michelson Doppler Imager
(MDI) data, together with Yohkoh Soft X-Ray Telescope (SXT) and
Yohkoh Bragg Crystal Spectrometer (BCS) data, to determine the global
evolution of the temperature and the emission measure of the coronal
plasma at times when no significant brightenings were observed. We
show that the mean X-ray flux and derived parameters, temperature
and emission measure (together with other quantities deduced from
them, such as the density and the pressure), of the plasma in the AR
follow power-law relationships with the mean magnetic flux density
(B). The exponents (b) of these power-law functions (aB<SUP>b</SUP>)
are derived using two different statistical methods, a classical
least-squares method in log-log plots and a nonparametric method,
which takes into account the fact that errors in the data may not be
normally distributed. Both methods give similar exponents, within
error bars, for the mean temperature and for both instruments (SXT
and BCS); in particular, b stays in the range [0.27, 0.31] and [0.24,
0.57] for full-resolution SXT images and BCS data, respectively. For
the emission measure, the exponent b lies in the range [0.85, 1.35]
and [0.45, 1.96] for SXT and BCS, respectively. The determination of
such power-law relations, when combined with the results from coronal
heating models, can provide us with powerful tools for determining the
mechanism responsible for the existence of the high-temperature corona.
---------------------------------------------------------
Title: The Long-Term Evolution of AR 7978: Testing Coronal Heating
Models
Authors: Démoulin, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.;
Klimchuk, J. A.; Harra, L.
2003ApJ...586..592D Altcode:
We derive the dependence of the mean coronal heating rate on the
magnetic flux density. Our results are based on a previous study of
the plasma parameters and the magnetic flux density (B) in the active
region NOAA 7978 from its birth to its decay, throughout five solar
rotations using the Solar and Heliospheric Observatory Michelson
Doppler Imager, Yohkoh Soft X-Ray Telescope (SXT), and Yohkoh Bragg
Crystal Spectrometer (BCS). We use the scaling laws of coronal loops
in thermal equilibrium to derive four observational estimates of the
scaling of the coronal heating with B (two from SXT and two from
BCS observations). These results are used to test the validity of
coronal heating models. We find that models based on the dissipation
of stressed, current-carrying magnetic fields are in better agreement
with the observations than models that attribute coronal heating to
the dissipation of MHD waves injected at the base of the corona. This
confirms, with smaller error bars, previous results obtained for
individual coronal loops, as well as for the global coronal emission
of the Sun and cool stars. Taking into account that the photospheric
field is concentrated in thin magnetic flux tubes, both SXT and BCS
data are in best agreement with models invoking a stochastic buildup
of energy, current layers, and MHD turbulence.
---------------------------------------------------------
Title: How to test coronal heating models?
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
Klimchuk, J. A.; Harra, L. K.
2003BAAA...46....5M Altcode:
We have tested coronal heating models following two different
approaches. In the first case, we compared the dependence of the
coronal heating rate predicted by theoretical models with the
observed one, deriving the scalings of parameters, such as: the
density, temperature and intensity of the coronal magnetic field,
with the length of magnetic field lines. To do so, we combined density
and temperature measurements for 47 coronal loops with magnetic field
models for 14 active regions. In the second case, we analyzed the long
term evolution of an active region observed during seven rotations
on the solar disk and we determined the dependence of the observed
heating rate with the magnetic field density (bar{B}), after finding
the scalings of plasma parameters with bar{B}. In both cases, we found
that models based on the dissipation of stressed, current-carrying
magnetic fields (called direct current models) are in better agreement
with observations than models that attribute coronal heating to the
dissipation of MHD waves injected at the base of the corona (called
alternate current models). Taking into account that the photospheric
field is concentrated in thin magnetic flux tubes, observations are
in best agreement with models invoking a stochastic buildup of energy,
current layers and MHD turbulence, within direct current models.
---------------------------------------------------------
Title: Active region helicity evolution and related coronal mass
ejection activity
Authors: Green, L. M.; López Fuentes, M. C.; Mandrini, C. H.; van
Driel-Gesztelyi, L.; Démoulin, P.
2003AdSpR..32.1959G Altcode:
The computation of magnetic helicity has become increasingly important
in the studies of solar activity. Observations of helical structures
in the solar atmosphere, and their subsequent ejection into the
interplanetary medium, have resulted in considerable interest to find
the link between the amount of helicity in the coronal magnetic field
and the origin of coronal mass ejections (CMEs), which provide a natural
method to remove helicity from the corona. Recent works have endeavored
to find the source of helicity to explain the observed CME activity
in specific cases. The main candidates being differential rotation,
shear motions or a transfer of helicity from below the photosphere
into the corona. We study an active region for several rotations
during 1997 and 1998 to investigate the relative importance of these
mechanisms. We find that photospheric differential rotation cannot
provide the required magnetic helicity to the corona and the ejected
CMEs. Localized photospheric motions can provide a larger helicity flux,
though still not sufficient.
---------------------------------------------------------
Title: Magnetic twist and writhe of active regions. On the origin
of deformed flux tubes
Authors: López Fuentes, M. C.; Démoulin, P.; Mandrini, C. H.;
Pevtsov, A. A.; van Driel-Gesztelyi, L.
2003A&A...397..305L Altcode: 2014arXiv1411.5626L
We study the long term evolution of a set of 22 bipolar active regions
(ARs) in which the main photospheric polarities are seen to rotate one
around the other during several solar rotations. We first show that
differential rotation is not at the origin of this large change in
the tilt angle. A possible origin of this distortion is the nonlinear
development of a kink-instability at the base of the convective zone;
this would imply the formation of a non-planar flux tube which,
while emerging across the photosphere, would show a rotation of its
photospheric polarities as observed. A characteristic of the flux tubes
deformed by this mechanism is that their magnetic twist and writhe
should have the same sign. From the observed evolution of the tilt of
the bipoles, we derive the sign of the writhe of the flux tube forming
each AR; while we compute the sign of the twist from transverse field
measurements. Comparing the handedness of the magnetic twist and writhe,
we find that the presence of kink-unstable flux tubes is coherent with
no more than 35% of the 20 cases for which the sign of the twist can
be unambiguously determined. Since at most only a fraction of the tilt
evolution can be explained by this process, we discuss the role that
other mechanisms may play in the inferred deformation. We find that
36% of the 22 cases may result from the action of the Coriolis force
as the flux tube travels through the convection zone. Furthermore,
because several bipoles overpass in their rotation the mean toroidal
(East-West) direction or rotate away from it, we propose that a
possible explanation for the deformation of all these flux tubes
may lie in the interaction with large-scale vortical motions of the
plasma in the convection zone, including also photospheric or shallow
sub-photospheric large scale flows.
---------------------------------------------------------
Title: Observations of magnetic helicity
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.
2003AdSpR..32.1855V Altcode:
The first observational signature of magnetic helicity in the solar
atmosphere (sunspot whirls) was discovered 77 years ago. Since then,
the existence of a cycle-invariant hemispheric helicity pattern has
been firmly established through current helicity and morphological
studies. During the last years, attempts were made to estimate/ measure
magnetic helicity from solar and interplanetary observations. Magnetic
helicity (unlike current helicity) is one of the few global quantities
that is conserved even in resistive magnetohydrodynamics (MHD) on a
timescale less than the global diffusion timescale, thus magnetic
helicity studies make it possible to trace helicity as it emerges
from the sub-photospheric layers to the corona and then is ejected via
coronal mass ejections (CMEs) into the interplanetary space reaching
the Earth in a magnetic cloud. We give an overview of observational
studies on the relative importance of different sources of magnetic
helicity, i.e. whether photospheric plasma motions (photospheric
differential rotation and localized shearing motions) or the twist
of the emerging flux tubes created under the photosphere (presumably
by the radial shear in the differential rotation in the tachocline)
is the dominant helicity source. We examine the sources of errors
present in these early results and try to judge how realistic they are.
---------------------------------------------------------
Title: Why to determine the magnetic helicity in corona and
interplanetary medium?
Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; van Driel-Gesztelyi,
L.; Démoulin, P.
2003BAAA...46....8L Altcode:
Magnetic clouds are huge objects that travel in the interplanetary
medium, transporting magnetic helicity (MH) produced by the Sun. Since
the dissipation time of MH is much larger than the typical time
associated with the dynamical processes in the solar corona and the
heliosphere, MH is the natural magnetohydrodinamic (MHD) magnitude
to compare interplanetary manifestations with the associated solar
processes. In this work we study an active region that produced a
coronal mass ejection (CME). We model the coronal magnetic field
using a linear force free approach, and we calculate the magnetic
flux and the variation of MH, before and after the ejection of
the CME. We model also the magnetic field configuration of the
associated interplanetary cloud, using several cylindrical models,
and estimate the flux and the content of MH. Finally, we compare the
coronal and the interplanetary values for the flux and the MH, and we
find a very good agreement. The coronal flux is 10<SUP>22</SUP>Mx,
while the magnetic flux for the cloud is around 10<SUP>21</SUP>Mx
(∼ 10% of the coronal flux, as typically observed). The variation
of the coronal MH turns out to be 3x10<SUP>42</SUP>Mx<SUP>2</SUP>,
while we obtain that the MH contained in the magnetic cloud is in the
range (2-8)x10<SUP>42</SUP>Mx<SUP>2</SUP>. Our results indicate that
MH is a very useful tool to link phenomena in very different regimes
and can be used to constrain both coronal and interplanetary models.
---------------------------------------------------------
Title: CME shock warps coronal streamer - observation and MHD
simulation
Authors: van der Holst, B.; van Driel-Gesztelyi, L.; Poedts, S.
2002ESASP.506...71V Altcode: 2002svco.conf...71V; 2002ESPM...10...71V
A fast (v ≥ 1000 km s<SUP>-1</SUP>) CME was observed on 14 January
2002, which was linked to an M4.4 long-duration flare event and
a post-eruption loop system visible on, but partially occulted by,
the SW limb. The fast expanding CME collided with a North-hemispheric
helmet streamer, which was located above NOAA AR 9773 and was in 60°
distance from the CME source region. An interaction with the CME (I)
pushed the streamer aside and (II) created a deflection, setting off an
outward propagating wavelike deformation along it. At the same time,
a decametric-hectometric type-II radio burst was observed with the
WAVES RAD2 instrument onboard the WIND spacecraft. Type-II bursts
are indicative of shock waves. At about the time of the CME-streamer
interaction a splitting was seen in the type-II emission, which
indicated a shock continuing to propagate away from the Sun (thus
getting into lower and lower density domains) and another branch,
which indicated a shock propagating into denser plasma domain. We
interpret this fine-structure of the type-II bursts as a result of the
CME-streamer interaction. We suggest that the shock wave, which was
associated with this fast CME, penetrated into the helmet streamer
and then died away in the denser plasma (the splitting lasted for
about 30 minutes). With our 2-D MHD code we simulate this CME-streamer
interaction, using the observed configuration and magnetic topology. The
simulation results confirm our hypothesis.
---------------------------------------------------------
Title: Global budget for an eruptive active region . I. Equilibrium
reconstruction approach
Authors: Bleybel, A.; Amari, T.; van Driel-Gesztelyi, L.; Leka, K. D.
2002A&A...395..685B Altcode:
We present results on the magnetic structure of NOAA Active Region
#7912 which was involved in a long duration flare on 14 October 1995,
and was the source region for a magnetic cloud observed by the WIND
spacecraft from October 18-20. Using vector magnetograms from the
Imaging Vector Magnetograph (“IVM”), we reconstruct the magnetic
field above this active region, assuming it is in a non-linear
force-free state. This reconstruction is used to determine global
properties of the active region magnetic field including topology,
magnetic energy, and relative magnetic helicity. A comparison of some
global quantities before and after the eruptive event is discussed. We
show that the magnetic energy and relative helicity of the active
region decreased after the eruption, consistent with the ejection
of a large amount of helicity (in the magnetic cloud). We also show
that the relaxed post-flare state still contains nonlinearities and is
not consistent with a linear force-free state as predicted by Taylor's
theory of relaxation. These results agree with those of recent numerical
simulations concerning plasmoid ejection and helicity redistribution in
the disruption of magnetic configurations. We propose as an explanation
that the anchoring of field lines in the photosphere prevents a full
cascade to the Taylor state, and that a variational formulation in which
the action functional would describe this constraint should be derived.
---------------------------------------------------------
Title: On the origin of peculiar active regions
Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.;
van Driel-Gesztelyi, L.; Pevtsov, A. A.
2002ESASP.505..121M Altcode: 2002solm.conf..121M; 2002IAUCo.188..121M
We study the long term evolution of a set of bipolar active regions
(ARs) in which the main photospheric polarities are seen to rotate one
around the other during several solar rotations. After showing that
differential rotation cannot produce this large change in the tilt
angle, we interpret this peculiar evolution as being the result of the
emergence of magnetic flux tubes that are distorted with respect to
the classical Ω-loop shape. A possible origin of this distortion is
the nonlinear development of a kink-instability. Flux tubes deformed
by this mechanism must have the same sign of twist and writhe. From
the observed evolution of the tilt of the bipoles, we derive the
sign of the writhe of the tube forming each AR; while we compute
the sign of the twist from transverse field measurements. Comparing
the handedness of the magnetic twist and writhe, we find that the
presence of kink-unstable flux tubes is coherent with no more than 32%
of the studied cases; so, a small fraction of these peculiar ARs can
be explained by this process. Then we discuss the role that other
mechanisms may play inducing the inferred deformation, such as the
Coriolis force or external rotational motions of the plasma as the
tube ascends in the convection zone.
---------------------------------------------------------
Title: Dedication (SOLMAG 2002): Karen L. Harvey 1942 - 2002
Authors: Schrijver, Karel; van Driel-Gesztelyi, Lidia
2002ESASP.505D..15S Altcode: 2002IAUCo.188D..15S; 2002solm.confD..15S
No abstract at ADS
---------------------------------------------------------
Title: Emergence and loss of magnetic flux on the solar surface
Authors: van Driel-Gesztelyi, Lidia
2002ESASP.505..113V Altcode: 2002solm.conf..113V; 2002IAUCo.188..113V
This review is focused on observations and theoretical advances
on large-scale flux emergence and decay, which forms and dominates
the magnetic field patterns on the Sun. The basic characteristics
of emerging flux (asymmetry, inclination to the vertical, twist,
sea-serpent-like appearance in the early stage of flux emergence in the
photosphere) are described together with the results of relevant MHD
simulations, which help us to interpret these observations. Magnetic
flux emergence is far from being a random process in the active belt:
it has a grouping (nesting) tendency, which has important implications
for the operation of the solar dynamo. As soon as active regions are
fully formed, they start decaying. Their magnetic flux gradually speads
over an ever-increasing area and gets removed from the photosphere via
small scale processes (e.g. Ohmic dissipation and flux cancellation,
including flux submergence). Emergence of U-loops may play an important
role in the removal of large-scale flux from the photopshere.
---------------------------------------------------------
Title: The Magnetic Helicity Budget of a cme-Prolific Active Region
Authors: Green, L. M.; López fuentes, M. C.; Mandrini, C. H.;
Démoulin, P.; Van Driel-Gesztelyi, L.; Culhane, J. L.
2002SoPh..208...43G Altcode:
Coronal mass ejections (CMEs) are thought to be the way by which the
solar corona expels accumulated magnetic helicity which is injected
into the corona via several methods. DeVore (2000) suggests that a
significant quantity is injected by the action of differential rotation,
however Démoulin et al. (2002b), based on the study of a simple bipolar
active region, show that this may not be the case. This paper studies
the magnetic helicity evolution in an active region (NOAA 8100) in
which the main photospheric polarities rotate around each other during
five Carrington rotations. As a result of this changing orientation of
the bipole, the helicity injection by differential rotation is not a
monotonic function of time. Instead, it experiences a maximum and even
a change of sign. In this particular active region, both differential
rotation and localized shearing motions are actually depleting the
coronal helicity instead of building it. During this period of five
solar rotations, a high number of CMEs (35 observed, 65 estimated)
erupted from the active region and the helicity carried away has
been calculated, assuming that each can be modeled by a twisted flux
rope. It is found that the helicity injected by differential rotation
(≈−7×10<SUP>42</SUP> Mx<SUP>2</SUP>) into the active region cannot
provide the amount of helicity ejected via CMEs, which is a factor 5
to 46 larger and of the opposite sign. Instead, it is proposed that
the ejected helicity is provided by the twist in the sub-photospheric
part of the magnetic flux tube forming the active region.
---------------------------------------------------------
Title: The Magnetic Helicity Injected by Shearing Motions
Authors: Démoulin, P.; Mandrini, C. H.; Van Driel-Gesztelyi, L.;
Lopez Fuentes, M. C.; Aulanier, G.
2002SoPh..207...87D Altcode:
Photospheric shearing motions are one of the possible ways to inject
magnetic helicity into the corona. We explore their efficiency as
a function of their particular properties and those of the magnetic
field configuration. Based on the work of M. A. Berger, we separate
the helicity injection into two terms: twist and writhe. For shearing
motions concentrated between the centers of two magnetic polarities
the helicity injected by twist and writhe add up, while for spatially
more extended shearing motions, such as differential rotation, twist
and writhe helicity have opposite signs and partially cancel. This
implies that the amount of injected helicity can change in sign with
time even if the shear velocity is time independent. We confirm the
amount of helicity injected by differential rotation in a bipole
in the two particular cases studied by DeVore (2000), and further
explore the parameter space on which this injection depends. For a
given latitude, tilt and magnetic flux, the generation of helicity is
slightly more efficient in young active regions than in decayed ones
(up to a factor 2). The helicity injection is mostly affected by the
tilt of the AR with respect to the solar equator. The total helicity
injected by shearing motions, with both spatial and temporal coherence,
is at most equivalent to that of a twisted flux tube having the same
magnetic flux and a number of turns of 0.3. In the solar case, where
the motions have not such global coherence, the injection of helicity
is expected to be much smaller, while for differential rotation this
maximum value reduces to 0.2 turns. We conclude that shearing motions
are a relatively inefficient way to bring magnetic helicity into the
corona (compared to the helicity carried by a significantly twisted
flux tube).
---------------------------------------------------------
Title: Long-term helicity evolution in NOAA active region 8100
Authors: Green, L. M.; López Fuentes, M. C.; Mandrini, C. H.; van
Driel-Gesztelyi, L.; Démoulin, P.
2002ESASP.477...43G Altcode: 2002scsw.conf...43G
Magnetic helicity is the topological parameter used to describe
the structure in the magnetic field and has become increasingly
important in coronal studies. Helicity is well preserved in the
corona even under non-ideal MHD conditions (see Biskamp 1993), and
the Sun can avoid endless accumulation of helicity by ejecting it
via the launch of coronal mass ejections (eg. Rust 1994; Low 1996;
Devore 2000). Computations are made for NOAA active region 8100 to
determine the coronal helicity and helicity injected into the region
by differential rotation. These values are then compared to the total
amount of helicity lost via coronal mass ejections to test whether
differential rotation can inject a significant amount of helicity into
the corona. It is found that differential rotation cannot inject a
significant amount of helicity to be a viable source for the coronal
mass ejection activity. Instead, helicity is likely to be brought into
the corona by the emergence of twisted and distorted flux tubes.
---------------------------------------------------------
Title: Numerical modeling of CME initiation and propagation
Authors: Poedts, S.; van der Holst, B.; de Sterck, H.; van
Driel-Gesztelyi, L.; Csík, A.; Milesi, A.; Deconinck, H.
2002ESASP.477..263P Altcode: 2002scsw.conf..263P
The shocks in the solar corona caused by fast Coronal Mass Ejections
(CMEs) and the shock at the Earth's magnetosphere caused by the
corresponding magnetic clouds (superposed on the solar wind) are studied
in the framework of computational magnetohydrodynamics (MHD). Due to the
presence of three characteristic velocities and the anisotropy induced
by the magnetic field, MHD shocks can have a complicated structure
including secondary shock fronts, overcompressive and compound shocks,
etc. Numerical simulations show that CME shocks (in the lower corona)
and the shock at the Earth's magnetosphere (at times of the impact of
a magnetic cloud) have such a complex structure. The CME shocks are
important for 'space weather' because they can easily be observed in
radio wavelengths. This makes it possible to track the position of the
CMEs/magnetic clouds and, hence, to follow their propagation through
the corona. The collision of two such shocks is discussed. Also,
the possibility of locating the magnetic cloud from the passage of
a satellite through the leading shock front is discussed. Moreover,
the topology of the shock at the Earth's magnetosphere at the impact
of a magnetic cloud is important for the 'geo-effectiveness' of the
magnetic storms. Hence, a detailed study of the MHD shocks generated
by CMEs may reveal some of the key properties space weather.
---------------------------------------------------------
Title: The distribution of peculiar active regions along two solar
cycles
Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.;
van Driel-Gesztelyi, L.
2002ESASP.477...27M Altcode: 2002scsw.conf...27M
We perform a statistical study of the spatial and temporal distribution
of "peculiar" active regions (ARs) along solar cycles 21 and 22. ARs
usually appear in the photosphere in the form of bipolar concentrations
of magnetic flux, by "peculiar" we mean regions in which the the
main polarities rotate one around the other along several solar
rotations. Our results show that these regions are spatially distributed
as usual ARs when no selection on their magnetic flux is applied. When
classified according to their flux, the latitudinal distribution of
ARs above 10<SUP>22</SUP> Mx closely follow the butterfly diagram;
while those with lower flux are more randomly distributed. The number
of rotating ARs follow the activity cycle, with a tendency to dual-peak
maxima.
---------------------------------------------------------
Title: Magnetic build-up and precursors of CMEs
Authors: van Driel-Gesztelyi, Lidia; Schmieder, Brigitte; Poedts,
Stefaan
2002ESASP.477...47V Altcode: 2002scsw.conf...47V
CMEs are fundamentally magnetic phenomena, thus to improve CME forecast
we have to find out more about the characteristics of the small and
large-scale magnetic field in and around their source region prior
to CME occurrence. In this paper we show examples of the magnetic
evolution of CME-prolific active regions using SOHO/MDI data. It
appears that CMEs are preceded by magnetic evolution during which
the helicity of the source region is increasing due to twisted flux
emergence, shearing motions between opposite polarity footpoints
of subsequently emerging bipoles and, in a smaller extend, by the
differential rotation acting on the emerged flux. Furthermore, we find
short-term magnetic precursors of CME events, typically a combination of
major flux emergence, cancellation and fast shearing motions in active
regions with strong concentrated magnetic fields prior to flare-related
CMEs and small-scale cancellation events along the magnetic inversion
line in decayed active regions with low magnetic flux density prior to
filament eruption-related CMEs. We make an overview of recent studies
on magnetic helicity and suggest that such analyses will be able to
provide a key to unlock the secrets of CME buildup and initiation.
---------------------------------------------------------
Title: Multi-wavelength observations of an X-class flare without a
coronal mass ejection.
Authors: Green, L. M.; Matthews, S. A.; van Driel-Gesztelyi, L.;
Harra, L. K.; Culhane, J. L.
2002SoPh..205..325G Altcode:
Developments in our knowledge of coronal mass ejections (CMEs) have
shown that many of these transients occur in association with solar
flares. On the occasions when there is a common occurrence of the
eruption and the flare, it is most likely that the flare is of high
intensity and/or long-duration (Burkepile, Hundhausen, and Webb,
1994; Munro et al., 1979; Webb and Hundhausen, 1987). A model for
the relationship between the long-duration event and eruption has
been developed (Carmichael, 1964; Sturrock, 1966; Hirayama, 1974;
Kopp and Pneuman, 1976), but not so for the high-intensity flares and
eruptions. This work investigates the magnetic topology changes that
occur for a X1.2 GOES classification flare which has no associated
CME. It is found that the flare is likely to result from the interaction
between two pre-existing loops low in the corona, producing a confined
flare. Slightly higher in the corona, a loop is observed which
exhibits an outward motion as a result of the reconfiguration during
reconnection. The objective of this work is to gain insight on the
magnetic topology of the event which is critical in order to determine
whether a high-intensity flare is likely to be related to a CME or not.
---------------------------------------------------------
Title: What is the source of the magnetic helicity shed by CMEs? The
long-term helicity budget of AR 7978
Authors: Démoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L.;
Thompson, B. J.; Plunkett, S.; Kovári, Zs.; Aulanier, G.; Young, A.
2002A&A...382..650D Altcode:
An isolated active region (AR) was observed on the Sun during seven
rotations, starting from its birth in July 1996 to its full dispersion
in December 1996. We analyse the long-term budget of the AR relative
magnetic helicity. Firstly, we calculate the helicity injected
by differential rotation at the photospheric level using MDI/SoHO
magnetograms. Secondly, we compute the coronal magnetic field and
its helicity selecting the model which best fits the soft X-ray loops
observed with SXT/Yohkoh. Finally, we identify all the coronal mass
ejections (CMEs) that originated from the AR during its lifetime using
LASCO and EIT/SoHO. Assuming a one to one correspondence between CMEs
and magnetic clouds, we estimate the magnetic helicity which could be
shed via CMEs. We find that differential rotation can neither provide
the required magnetic helicity to the coronal field (at least a factor
2.5 to 4 larger), nor to the field ejected to the interplanetary
space (a factor 4 to 20 larger), even in the case of this AR for
which the total helicity injected by differential rotation is close
to the maximum possible value. However, the total helicity ejected is
equivalent to that of a twisted flux tube having the same magnetic flux
as the studied AR and a number of turns in the interval [0.5,2.0]. We
suggest that the main source of helicity is the inherent twist of the
magnetic flux tube forming the active region. This magnetic helicity
is transferred to the corona either by the continuous emergence of the
flux tube for several solar rotations (i.e. on a time scale much longer
than the classical emergence phase), or by torsional Alfvén waves.
---------------------------------------------------------
Title: Relation between the coronal magnetic helicity to the helicity
in interplanetary magnetic clouds
Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P.; van
Driel-Gesztelyi, L.; López Fuentes, M. C.
2002BAAA...45...20L Altcode:
On October 18, 1995, the Solar Wind Experiment and the Magnetic
Field Instrument on board the WIND spacecraft registered a magnetic
cloud at 1 AU, which was followed by a strong geomagnetic storm. The
solar source of this phenomenon was located in active region (AR) NOAA
7912. On October 14, 1995, a C1.6 long duration event (LDE) started at
approximately 5:00 UT and lasted for around 15 hours. In this work, we
compute the variation of the coronal magnetic helicity using a linear
force-free model of the field. We use magnetograms obtained at Kitt
Peak National Solar Observatory as boundary conditions to extrapolate
the photospheric magnetic field to the corona. The magnetic helicity
is calculated at three different times, changing the parameters of the
magnetic field model to fit the loops observed in soft X-rays by the
Soft X-ray Telescope on board of Yohkoh (SXT/Yohkoh). The computations
are done before the LDE, during its maximun and its decay phase. The
variation of the coronal magnetic helicity is compared to the helicity
of the interplanetary magnetic cloud observed by WIND. These values
turn out to be quite similar, considering the errors involved. Our
results confirm quantitatively the link between solar and interplanetary
phenomena.
---------------------------------------------------------
Title: Active region helicity evolution and related coronal mass
ejection activity.
Authors: Green, L.; Mandrini, C.; van Driel-Gesztelyi, L.; Demoulin, P.
2002cosp...34E1213G Altcode: 2002cosp.meetE1213G
The computation of magnetic helicity has become increasingly important
in the studies of solar activity. Observations of helical structures
in the solar atmosphere, and their subsequent ejection into the
interplanetary medium, have resulted in considerable interest to find
the link between the amount of helicity in the coronal magnetic field
and the origin of coronal mass ejections (CMEs). This is reinforced by
theory which shows magnetic helicity to be a well preserved quantity
(Berger, 1984), and so with a continued injection into the corona an
endless accumulation will occur. CMEs therefore provide a natural
method to remove helicity from the corona. Recent works (DeVore,
2000, Chae, 2001, Chae et al., 2001, Demoulin et al., 2002, Green et
al., 2002) have endeavoured to find the source of helicity in the
corona to explain the observed CME activity in specific cases. The
main candidates being differential rotation, shear motions or a
transfer of helicity from below the photosphere into the corona. In
order to establish a confident relation between CMEs and helicity,
these works needs to be expanded to include CME source regions with
different characteristics. A study of a very different active region
will be presented and the relationship between helicity content and
CME activity will be discussed in the framework of the previous studies.
---------------------------------------------------------
Title: Helicity Loading and Dissipation: The Helicity Budget of AR
7978 from the Cradle to the Grave
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
Plunkett, S.; Thompson, B.; Kövári, Zs.; Aulanier, G.; Young, A.;
López Fuentes, M.; Poedts, S.
2002mwoc.conf..143V Altcode:
An isolated active region was observed on the Sun during seven
rotations, starting in July 1996. I will present a study of its magnetic
field, concentrating on its helicity budget. The photospheric field
is extrapolated into the corona in a linear force-free approach,
using SOHO/MDI magnetograms and Yohkoh/SXT images, allowing us to
compute, in a crude way, the relative coronal magnetic helicity of
the active region. Using the observed magnetic field distribution
(SOHO/MDI magnetograms) we also calculate the helicity injected by
the differential rotation during seven solar rotations. Finally, using
SOHO/LASCO and EIT as well as Yohkoh/SXT observations, we identify all
the 26 CMEs which originated from this active region during its lifetime
and using average values of the field and radius of magnetic clouds,
we estimate the helicity which should be shed via CMEs. We compare
these three values to evaluate the importance of the differential
rotation relative to twisted flux emergence as a source of magnetic
helicity. We find that the differential rotation can neither provide
enough helicity to account for the diagnosed coronal heicity values,
nor for the helicity carried away by CMEs. We suggest that the main
source of the magnetic helicity must be the inherent twist of the
magnetic flux tube forming the active region. This magnetic helicity is
transferred to the corona either by a slow continuous emergence of the
flux tube or by torsional Alfven waves, during several solar rotations.
---------------------------------------------------------
Title: Multi-Wavelength Observations of Yohkoh White-Light Flares
Authors: Matthews, S. A.; van Driel-Gesztelyi, L.; Hudson, H. S.;
Nitta, N. V.
2002mwoc.conf..289M Altcode:
The problem of accounting for the continuum emission that is observed
in solar flares is still one which is largely unresolved. These
white-light flares place severe constraints on the energy requirements
and transport mechanisms operating in the flare, raising the question
of whether partial or total in-situ heating is required to account for
this deep atmospheric heating. Since it is widely believed that the
energy release in solar flares occurs in the corona and that energy is
then transported to the low chromosphere where the optical emission is
produced, most attempts to explain the origin of white-light flares
have centred on canonical mechanisms. However, it has become clear
that the spatial and temporal correspondence between white-light and
HXR is not one-to one. In order to further our understanding of these
events we study the temporal and spatial relationships between emission
in the visible, SXR and HXR regimes in all of the white-light flares
observed by Yohkoh prior to the failure of the Soft X-ray Telescope
(SXT) Aspect Camera in 1992; a total of approximately 30 events.
---------------------------------------------------------
Title: Observations of emerging flux tubes
Authors: van Driel-Gesztelyi, Lidia
2002ocnd.confE...6V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Inferring the Writhe of Emerging Flux Tubes from the Evolution
of the Orientation of Bipole Axes
Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.;
van Driel-Gesztelyi, L.; Pevtsov, A.
2002RMxAC..14..108L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of helicity
Authors: van Driel-Gesztelyi, L.
2002cosp...34E1455V Altcode: 2002cosp.meetE1455V
I will review attempts made during the last decade to evaluate
and measure current helicity and magnetic helicity from solar and
interplanetary observations. I will show the main results of the current
helicity studies, which led to important discoveries like e.g. the
hemispheric helicity pattern. Then I give an overview of multiwavelength
observational studies on magnetic helicity. Magnetic helicity (unlike
current helicity) is one of the few global quantities, which is
conserved even in resistive MHD on a timescale less than the global
diffusion timescale, thus magnetic helicity studies make it possible
to trace helicity as it emerges from the sub-photospheric layers
to the corona and then is ejected via CMEs into the interplanetary
space reaching the Earth in a magnetic cloud. I will give an overview
of observational studies on the relative importance of different
sources of magnetic helicity, i.e. whether photospheric plasma motions
(differential rotation and localised shearing motions) generate the bulk
of helicity ejected in CMEs or the twist of the emerging flux tubes
created under the photosphere (presumably by differential rotation in
the tachocline) is the dominant helicity source.
---------------------------------------------------------
Title: Peculiar Active Regions during the Last Two Solar Cycles
Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.;
van Driel-Gesztelyi, L.
2002RMxAC..14R.107L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evolution of the source region of the interplanetary magnetic
cloud of 18-20 Oct. 1995
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Baranyi, T.
2002AdSpR..29.1489V Altcode:
We follow the evolution and activity of the reversed polarity AR
7912 using multi-wavelength observations. We find that the presence
of high shear increased by flux emergence led to the occurrence
of a long-duration eruptive flare on 14 October 1995, which was
manifested in the SXR corona by an arcade of expanding sigmoidal
loops. A twisted magnetic cloud was observed at 1 AU between October
18-20. We propose that it was ejected from this reversed polarity AR,
and it was associated with the expanding sigmoids.
---------------------------------------------------------
Title: Relationships between CME's and prominences
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Aulanier, G.;
Démoulin, P.; Thompson, B.; De Forest, C.; Wiik, J. E.; Saint Cyr,
C.; Vial, J. C.
2002AdSpR..29.1451S Altcode:
We have studied the erupting prominences which were associated with
coronal mass ejections during a series of campaigns involving both
spacecraft and ground-based observatories. The evolution of the
physical conditions within the prominences was established from Hα
and magnetic field observations. Particular attention ahs been paid
to the presence of mixed amgnetic polarity in the filament channel,
the evolution of the shear of the large-scale magnetic field, and
the existence of multiple magnetic inversion lines. We conclude that
reconnection of large-scale coronal magnetic fields is responsible
for both the CME and filament eruption.
---------------------------------------------------------
Title: Long-Term Evolution of Active Regions
Authors: López Fuentes, M.; Mandrini, C. H.; Démoulin, P.; van
Driel-Gesztelyi, L.
2001ASPC..248..131L Altcode: 2001mfah.conf..131L
No abstract at ADS
---------------------------------------------------------
Title: An Observational Test for Solar Atmospheric Heating
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Ireland, J.; Thompson,
B.; Fludra, A.; Oláh, K.; Kövári, Zs.; Harra, L. K.; Mandrini,
C. H.; Bocchialini, K.; Orlando, S.
2001IAUS..203..514V Altcode:
We study the evolution of the emissivity and heating correlated with
magnetic observables of an active region from its birth throughout
its decay during seven solar rotations (July-Dec. 1996). Taking one
"snapshot" per g:wq: Command not found. time of flares, we analyse
multi-wavelength and multi-instrument data obtained from SOHO (MDI,
EIT, CDS and SUMER), Yohkoh (SXT), GOES, SOLSTICE and 10.7 cm radio
data from DRAO, Canada. We utilise our results to test the validity
of coronal heating models. We find that models which are based on
the dissipation of stressed, current-carrying magnetic fields are in
better agreement with the observations than the models which attribute
coronal heating to the dissipation of MHD waves.
---------------------------------------------------------
Title: The Relationship between CMEs and Prominence Eruptions
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Delannée, C.;
Simnett, G. M.; Wiik, J. E.
2001IAUS..203..310S Altcode:
From multi-wavelength studies of eruptions of prominences observed by
Yohkoh, SoHO and ground-based observatories, we find a good correlation
between prominence eruptions and CMEs (i.e. May 1 1996, Sept 25 1996,
May 31 1997). Focusing our interest on their temporal relationship,
we observe that it is not clear that filament eruption is prior to
the CME. Nevertheless they are both signatures of destabilization of
the global coronal magnetic field. The magnetic configuration in the
corona should involve the initial presence of a twisted flux tube. The
eruption could be driven by a fast increase of the poloidal field in
the flux tube or by photospheric shearing motions of the flux tube.
---------------------------------------------------------
Title: Magnetic Evolution of a Long-Lived Active Region: The Sources
of Magnetic Helicity
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
Aulanier, G.; Thompson, B.; Plunkett, S.; Kövári, Zs.
2001ASPC..248..139M Altcode: 2001mfah.conf..139M
No abstract at ADS
---------------------------------------------------------
Title: Flux Ratios of Solar and Stellar Active Regions (CD-ROM
Directory: contribs/olah2)
Authors: Oláh, K.; van Driel-Gesztelyi, L.
2001ASPC..223..709O Altcode: 2001csss...11..709O
No abstract at ADS
---------------------------------------------------------
Title: Emergence of a U-loop - sub-photospheric link between solar
active regions
Authors: van Driel-Gesztelyi, L.; Malherbe, J. -M.; Démoulin, P.
2000A&A...364..845V Altcode:
Using SOHO/MDI magnetic maps we present the first direct observational
evidence for the emergence of a U-loop in the solar photosphere. We
show that two active regions (ARs), i.e. two adjacent Omega -loops,
which were emerging at the same time at the same solar latitude,
about 150000 km distance in longitude from each other, emerged from
at least partially the same toroidal flux strand, and we bring five
independent arguments to prove this assertion. The opposite polarity
legs of the two Omega -loops were connected below the photosphere by a
U-shaped loop. Following the emergence of the Omega -loops, the U-loop
started emerging, manifested by the fast proper motion of the leading
spots of the eastern (smaller) active region, which, after forming an
elongated channel, collided with the following spots of the westerly
AR and started cancelling with them. The full cancellation could not be
followed because the ARs rotated out of sight. The total magnetic flux
of the two ARs was unequal, the flux in the smaller AR was a quarter of
that of the larger one. We propose scenarios for the formation of such
a U-loop and discuss the implications of the confirmed existence of
U-loops for the solution of such puzzles as the in-situ disappearance
of magnetic flux from active regions, active nests and the formation
of inter-AR filaments.
---------------------------------------------------------
Title: Initiation of CMEs: the role of magnetic twist
Authors: van Driel-Gesztelyi, L.; Manoharan, P. K.; Démoulin, P.;
Aulanier, G.; Mandrini, C. H.; Lopez-Fuentes, M.; Schmieder, B.;
Orlando, S.; Thompson, B.; Plunkett, S.
2000JASTP..62.1437V Altcode: 2000JATP...62.1437V
Recent multiwavelength observations, modelling results and
theoretical developments indicate the importance of twisted magnetic
configurations in solar active regions (ARs) in the initiation of
coronal mass ejections (CMEs). Through multiwavelength analysis of a
few representative events we make an attempt to provide constraints
for CME models. The two events presented here in detail start with
the expansion of sigmoids (S- or inverse S-shaped loops) observed in
soft X-rays. Both events (on 25 October /1994 and 14 October /1995)
occurred before the launch of the SOHO spacecraft, but indirect
evidences (i.e. signatures of an outward propagation traced up to /~20
solar radii and an associated magnetic cloud) suggest that both of them
were related to CMEs. We show evidence that sigmoids are the coronal
manifestations of twisted magnetic flux tubes, which start expanding
presumably due to a loss of equilibrium. It is noteworthy that the
analysed CMEs occurred in a complex (not simply bipolar) magnetic
environment and in all cases we found evidences of the interaction
(magnetic reconnection) with the surrounding fields. We propose a
scenario for sigmoid expansion related CME events and suggest that
twisted magnetic configurations are good candidates for being source
regions of CMEs.
---------------------------------------------------------
Title: The Counterkink Rotation of a Non-Hale Active Region
Authors: López Fuentes, M. C.; Demoulin, P.; Mandrini, C. H.; van
Driel-Gesztelyi, L.
2000ApJ...544..540L Altcode: 2014arXiv1412.1456L
We describe the long-term evolution of a bipolar non-Hale active region
that was observed from 1995 October to 1996 January. During these
four solar rotations the sunspots and subsequent flux concentrations,
during the decay phase of the region, were observed to move in such a
way that by December their orientation conformed to the Hale-Nicholson
polarity law. The sigmoidal shape of the observed soft X-ray coronal
loops allows us to determine the sense of the twist in the magnetic
configuration. This sense is confirmed by extrapolating the observed
photospheric magnetic field, using a linear force-free approach,
and comparing the shape of computed field lines with the observed
coronal loops. This sense of twist agrees with that of the dominant
helicity in the solar hemisphere where the region lies, as well as
with the evolution observed in the longitudinal magnetogram during
the first rotation. At first sight the relative motions of the
spots may be misinterpreted as the rising of an Ω loop deformed by
a kink instability, but we deduce from the sense of their relative
displacements a handedness for the flux-tube axis (writhe) that is
opposite to that of the twist in the coronal loops and, therefore,
to what is expected for a kink-unstable flux tube. After excluding
the kink instability, we interpret our observations in terms of a
magnetic flux tube deformed by external motions while rising through
the convective zone. We compare our results with those of other related
studies, and we discuss, in particular, whether the kink instability
is relevant to explain the peculiar evolution of some active regions.
---------------------------------------------------------
Title: Magnetic Activity Associated With Radio Noise Storms
Authors: Bentley, R. D.; Klein, K. -L.; van Driel-Gesztelyi, L.;
Démoulin, P.; Trottet, G.; Tassetto, P.; Marty, G.
2000SoPh..193..227B Altcode:
As it crossed the solar disk in May and June 1998, AR 8227 was tracked
by TRACE, Yohkoh, SOHO, and many ground-based observatories. We have
studied how the evolution of the magnetic field resulted in changes in
activity in the corona. In particular, we examine how the evolving field
may have led to the acceleration of electrons which emit noise storms
observed by the Nançay Radio Heliograph between 30 May and 1 June
1998, in the absence of any flare. The magnetic changes were related
to moving magnetic features (MMFs) in the vicinity of the leading
spot and are related to the decay of this spot. Within the limits of
the instrumental capabilities, the location in time and space of the
radio emissions followed the changes observed in the photospheric
magnetograms. We have extrapolated the photospheric magnetic field
with a linear force-free approximation and find that the active region
magnetic field was very close to being potential. These computations
show a complex magnetic topology associated to the MMFs. The observed
photospheric evolution is expected to drive magnetic reconnection in
such complex magnetic topology. We therefore propose that the MMFs
are at the origin of the observed metric noise-storms.
---------------------------------------------------------
Title: Large-Scale Evolution of the Active Region NOAA 7978, 7981,
7986 Observed by Goes, Soho, and Yohkoh
Authors: Orlando, S.; Khan, J.; van Driel-Gesztelyi, L.; Thompson,
B.; Fludra, A.; Foing, B.
2000AdSpR..25.1913O Altcode:
We took part in a joint project aimed to study the large-scale
evolution of an active region from its emergence throughout its decay
for several solar rotations. Our interest focuses on the understanding
of how energy is generated, released, deposited, and transformed in
active regions. To this end, we determined physical parameters like
intensity, temperature, and emission measure of the whole active region
as a function of time for the entire period selected. We present the
preliminary results of the analysis of GOES (Geosynchronous Operational
Environmental Satellite), SOHO (Solar and Heliospheric Observatory)
and Yohkoh data of the active region named NOAA 7978, 7981, and 7986
observed between July and October 1996
---------------------------------------------------------
Title: Yohkoh Observations of White-Light Flares
Authors: Matthews, S.; van Driel-Gesztelyi, L.; Hudson, H.; Nitta, N.
2000ASPC..206..239M Altcode: 2000hesp.conf..239M
No abstract at ADS
---------------------------------------------------------
Title: Long-term evolution of an AR
Authors: van Driel-Gesztelyi, L.
2000ssls.work...95V Altcode:
I summarize the results of a complex and comprehensive analysis of
the evolution of an isolated active region (AR) in the period of
July-November 1996. Using SOHO/MDI full-disc magnetic maps, we follow
the magnetic evolution of the AR for several months. We extrapolate the
photospheric magnetic fields in the linear force-free approximation and
match the modelled field lines with the soft X-ray loops observed with
the Yohkoh/SXT in order to diagnose the coronal magnetic shear. We find
that while the turbulent motions diffuse the flux, the differential
rotation, and possibly twisted flux emergence, increase the magnetic
shear. Flares are observed during the first three rotations, while CME
events (observed by SOHO/EIT and LASCO) originate from this AR from its
emergence throughout its decay. Several early CMEs, while none of the
late CMEs, are related to flare events above the GOES B1 level. We find
that the late CMEs occur when the magnetic shear, after accumulating
for four rotations, reaches a high level and saturates. We propose that
CME activity serves as a valve through which the AR could get rid of
excess shear and helicity. Furthermore, we study the evolution of the
emissivity and heating correlated with magnetic observables of the AR
from its birth throughout its decay. Taking one "snapshot" per rotation
at each consecutive central meridian passage (CMP) of the AR, outside
the time of flares, we analyse multi-wavelength and multi-instrument
data obtained from SOHO (MDI and SUMER), Yohkoh (SXT), GOES and 10.7 cm
radio data from DRAO, Canada. We find that the magnetic flux density -
emitted radiation relations follow a power-law with exponents which
appear to depend on the formation temperature (height) of the emission.
---------------------------------------------------------
Title: 3-D Magnetic Configurations for Filaments and Flares: The
Role of “Magnetic Dips” and “Bald Patches”
Authors: Aulanier, G.; Schmieder, B.; van Driel-Gesztelyi, L.; Kucera,
T.; Démoulin, P.; Fang, C.; Mein, N.; Vial, J. -C.; Mein, P.; Tang,
Y. H.; Deforest, C.
2000AdSpR..26..485A Altcode:
The 3-D magnetic configuration of a filament and of a low energy
flare is reconstructed, using linear mag- netohydrostatic (lmhs)
extrapolations. In both cases, we find observational signatures
of energy release at the locations of computed “bald patches”
separatrices, characterised by field lines which are tangent to
the photosphere.The filament was observed on Sept. 25, 1996, in Hα
with the MSDP on the German VTT, Tenerife, as well as in Si IV with
SOHO/SUMER. It is modeled as a twisted flux-tube deformed by the
magnetic polarities observed with SOHO/MDI. The shape and location of
the computed dipped field lines are in good agreement with the shape of
the filament and its feet observed in Hα. Some “bald patches” (BPs)
are present where the distribution of dips reaches the photosphere. We
show that some of the large scale field lines rooted in BPs can be
related to bright fine structures in Si IV. We propose that the plasma
there is heated by ohmic dissipation from the currents expected to be
present along the BP separatrices.The flare was observed on May 18,
1994, in soft X-rays with Yohkoh/SXT, and in Hα at Mitaka (Japan). The
magnetic field is directly extrapolated from a photospheric magnetogram
from Kitt Peak Observatory. The intersections with the photosphere of
the computed separatrices match well the bright Hα ribbons. The later
are associated to three BPs, with overlaying dipped field lines. We
show that enhanced densities are present in these dips, which can be
correlated with dark Hα fibrils.Both cases show the importance of
dipped field lines and BPs in the solar atmosphere. Energy release
via ohmic dissipation as well as reconnection along BP separatrices
is proposed to provide heating observed as UV brightenings in filament
channels and even as small flares
---------------------------------------------------------
Title: Flares and Large Scale Evolution of a Solar Active Region
Observed in 1996 by GOES, SOHO and YOHKOH: Implications for X-Ray
stellar Variability
Authors: Orlando, S.; van Driel-Gesztelyi, L.; Thomson, B.; Khan,
J.; Foing, B. H.
2000ASIC..544..783O Altcode: 2000vsea.conf..783O
No abstract at ADS
---------------------------------------------------------
Title: What Can we Learn Studying Long-Term Magnetic Evolution of
Solar Active Regions?
Authors: van Driel-Gesztelyi, L.; Kovari, Zs.; Lopez-Fuentes, M.;
Mandrini, C. H.; Demoulin, P.
2000ESASP.463..451V Altcode: 2000sctc.proc..451V
No abstract at ADS
---------------------------------------------------------
Title: Non Linear Force-Free Reconstruction of a Flaring Active Region
Authors: Bleybel, A.; Amari, T.; van Driel-Gesztelyi, L.; Leka, K. D.
1999ESASP.448..709B Altcode: 1999ESPM....9..709B; 1999mfsp.conf..709B
No abstract at ADS
---------------------------------------------------------
Title: The Total Eclipse Experience in Hungary
Authors: van Driel-Gesztelyi, L.; Jankovics, I.; Kovács, J.;
Schmieder, B.; Vincze, I. J.
1999ESASP.448.1297V Altcode: 1999ESPM....9.1297V; 1999mfsp.conf.1297V
No abstract at ADS
---------------------------------------------------------
Title: On the Topology of Magnetic Reconnection in Flares -
Constraints from Multiwavelength Observations
Authors: van Driel-Gesztelyi, L.
1999ESASP.448..901V Altcode: 1999mfsp.conf..901V; 1999ESPM....9..901V
No abstract at ADS
---------------------------------------------------------
Title: Flare loop geometry
Authors: Nitta, N.; Van Driel-Gesztelyi, L.; Harra-Murnion, L. K.
1999SoPh..189..181N Altcode:
In selected flares that occurred in AR 7260, we have studied
the geometry of the brightest soft X-ray loop by tracing it on
an image. Even under the assumption that the loop is contained
in a plane, it is clear that a single image does not permit us to
determine the full geometry. It only provides possible loop shapes as
a function of the inclination angle of the loop plane with respect
to the vertical. However, all the loops that reproduce the observed
appearance give the same direction of increasing height as projected
on to the image plane. This direction is compared with two relevant
observations. Based on 2-D reconnection models that involve a cusp
configuration, it is expected that the soft X-ray loop top source moves
upward with time and that a higher temperature region exists above the
loop top. Several flares are found to contradict these predictions,
presumably implying the inadequacy of the models. Lastly we discuss
a possibility of constraining the inclination angle (and hence the
loop shape) with spatially-unresolved soft X-ray line spectra which
are Doppler-shifted due to plasma upflows.
---------------------------------------------------------
Title: Working Group 1: Magnetic Field Structuring
Authors: van Driel-Gesztelyi, L.; Martinez Pillet, V.
1999ESASP.446...71V Altcode: 1999soho....8...71V
No abstract at ADS
---------------------------------------------------------
Title: Long-Term Evolution Of Emissivity And Heating In A Solar
Active Region
Authors: van Driel-Gesztelyi, L.; Thompson, B.; Démoulin, P.; Orlando,
S.; Bocchialini, K.; Oláh, K.; Kövári, Z.; Deforest, C.; Khan,
J.; Fludra, A.; Mandrini, C.
1999ESASP.446..663V Altcode: 1999soho....8..663V
We study the evolution of the heating and emissivity of an active
region from its birth throughout its decay during six solar rotations
(July-Nov. 1996). We analyse multi-wavelength and multi-instrument
data obtained from SOHO (EIT, SUMER, CDS, MDI), Yohkoh (SXT), GOES
and 10.7cm radio data from DRAO, Canada. We take one "snapshot" per
rotation at the time of the central meridian passage (CMP) of the
AR, outside of time of flares, which appears to be representative
enough to allow us to make some general conclusions about the
long-term evolution. Deriving physical parameters like intensity
(flux), temperature and emission measure of the entire AR vs. time,
we formulate mathematically the change in radiation emitted by the
decaying AR at several wavelengths. Combining the emissivity data with
the evolution of magnetic flux density as the flux is being dispersed
by small- and larger-scale convective motions, we make an attempt to
understand the physics behind the emission and heating. We also analyse
the effects of flaring on the heating of the AR, and study whether and
how the flare properties evolve during the life of the active region.
---------------------------------------------------------
Title: Analysis of evolution of NOAA 7912 active region on 19
October 1995
Authors: Rudawy, P.; van Driel-Gesztelyi, L.; Cader-Sroka, B.; Mein,
P.; Mein, N.; Schmieder, B.; Malherbe, J. -M.; Rompolt, B.
1999A&AS..139...89R Altcode:
An analysis of a minor (B3.2) flare related to an X-ray jet in the
reversed polarity NOAA 7912 active region is presented, focusing
on various kinds of activity observed in the Hα line with the MSDP
instrument. Using complementary Yohkoh soft X-ray observations and a
Kitt Peak magnetic field map we study the influence of a rather low
and graduate energy release on filaments, fibrils and chromospheric
brightenings and their relevant coronal features. We find that this
small flare affected the entire AR and was associated with strong up-
and downflows along remote fibrils and filaments, which appear to be
connected by large-scale loops. It is shown that at least one of the
observed brightenings was caused by downflow of the matter, thus, by
the kinematic heating of the material. The filament in the vicinity
of the flare footpoints changed the most: it broke into two parts,
temporarily rose to higher altitudes inside the AR and even erupted
outside of the AR, re-forming only three hours later. We show that
even a minor flare can lead to important morphological and dynamical
changes in an active region.
---------------------------------------------------------
Title: The Role of "Magnetic Dips" and "Bald Patches" for a Filament
Observed by SOHO and GBO
Authors: Aulanier, G.; Schmieder, B.; Kucera, T.; van Driel-Gesztelyi,
L.; Démoulin, P.; Mein, N.; Vial, J. -C.; Mein, P.
1999ASPC..184..291A Altcode:
The studied filament was observed on Sept. 25, 1996, in Hα with
the MSDP on the German VTT, Tenerife, as well as in Si IV with
SOHO/SUMER. The 3-D magnetic configuration of the filament channel is
reconstructed, using linear magnetohydrostatic (lmhs) extrapolations
from a SOHO/MDI magnetogram, which is modified by a background magnetic
component constraining a twisted flux-tube. This flux-tube is deformed
by the magnetic polarities observed with SOHO/MDI. The shape and
location of the computed "dipped field lines" are in good agreement
with the shape of the filament and its feet observed in Hα. Some "bald
patches" (BPs) are present where the distribution of dips reaches the
photosphere. We find observational signatures in Si IV brightenings of
energy release at the locations of computed "bald patch separatrices",
defined by field lines which are tangent to the photosphere. We propose
that the plasma is there heated by ohmic dissipation from the expected
currents in the BP separatrices. The results show the importance of
"dipped field lines" and "bald patches" in filament channels.
---------------------------------------------------------
Title: Making sense of sunspot decay - II. Deviations from the Mean
Law and Plage Effects
Authors: Petrovay, K.; Martínez Pillet, V.; van Driel-Gesztelyi, L.
1999SoPh..188..315P Altcode: 1999astro.ph..6258P
In a statistical analysis of Debrecen Photoheliographic Results sunspot
area data we find that the logarithmic deviation (log D)' of the area
decay rate D from the parabolic mean decay law (derived in the first
paper in this series) follows a Gaussian probability distribution. As
a consequence, the actual decay rate D and the time-averaged decay
rate are also characterized by approximately lognormal distributions,
as found in an earlier work. The correlation time of (log D)' is about
3 days. We find a significant physical anticorrelation between (log
D)' and the amount of plage magnetic flux of the same polarity in an
annulus around the spot on Kitt Peak magnetograms. The anticorrelation
is interpreted in terms of a generalization of the turbulent erosion
model of sunspot decay to the case when the flux tube is embedded in
a preexisting homogeneous `plage' field. The decay rate is found to
depend inversely on the value of this plage field, the relation being
very close to logarithmic, i.e., the plage field acts as multiplicative
noise in the decay process. A Gaussian probability distribution of
the field strength in the surrounding plage will then naturally lead
to a lognormal distribution of the decay rates, as observed. It is
thus suggested that, beside other multiplicative noise sources, the
environmental effect of surrounding plage fields is a major factor
in the origin of lognormally distributed large random deviations from
the mean law in the sunspot decay rates.
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Title: Long-Term Magnetic Evolution of an AR and its CME Activity
Authors: van Driel-Gesztelyi, L.; Mandrini, C. H.; Thompson, B.;
Plunkett, S.; Aulanier, G.; Démoulin, P.; Schmieder, B.; de Forest, C.
1999ASPC..184..302V Altcode:
Using SOHO/MDI full-disc magnetic maps, we follow the magnetic
evolution of a solar active region for several months in the period of
July-November 1996. We extrapolate the photospheric magnetic fields in
the linear force-free approximation and match the modelled field lines
with the soft X-ray loops observed with the Yohkoh/SXT in order to
diagnose the coronal magnetic shear. We find that while the turbulent
motions diffuse the flux, the differential rotation, and possibly
twisted flux emergence, increase the magnetic shear. Flares are observed
during the first three rotations, while CME events (observed by SOHO/EIT
and LASCO) originate from this AR from its emergence throughout its
decay. Several early CMEs, while none of the late CMEs, are related to
flare events above the GOES B1 level. We find that the late CMEs occur
when the magnetic shear, after accumulating for four rotations, reaches
a high level and saturates. We propose that CME activity serves as a
valve through which the AR could get rid of excess shear and helicity.
---------------------------------------------------------
Title: Modelling the Sun as an active star. I. A diagnosis of
photometric starspot models
Authors: Oláh, K.; van Driel-Gesztelyi, L.; Kővári, Zs.; Bartus, J.
1999A&A...344..163O Altcode:
We provide a diagnosis of photometric starspot models through modelling
active areas on the Sun using softwares originally written for starspot
modelling. The data we used were one-dimensional measurements of
the Sun in radio (10.7 cm, DRAO, Canada) and in soft X-rays (GOES
satellites). In these wavelengths the response to magnetic activity
results in similar amplitude variability on the Sun to those we
attribute to starspots in visual wavelengths. The modelling results
were compared with contemporaneous direct images (obtained at Nobeyama,
Japan and with the Yohkoh and SOHO spacecraft). We found that: a)
knowing well the basic physical parameters of a star, the resulting
total spotted area is a fairly good approximation of the reality, thus
making sense of photometric starspot modelling; b) long-term variability
coupled with the rotational modulation may result in artificially high
latitude spots; c) in two- or multi-spot models a resulting small spot
can account for short living spots; d) systematic change in spot size
could be partially due to flux ratio changes. The contrast between
the studied bright active region and the undisturbed area on the Sun
decreased in time following roughly a power law. At the same time,
the emission measure of the active region's core similarly decreased.
---------------------------------------------------------
Title: 3-D magnetic configurations supporting
prominences. III. Evolution of fine structures observed in a filament
channel
Authors: Aulanier, G.; Démoulin, P.; Mein, N.; van Driel-Gesztelyi,
L.; Mein, P.; Schmieder, B.
1999A&A...342..867A Altcode:
On September 25() th 1996, a quiescent filament located near the
center disc (S2, E5) was observed on the German VTT (Tenerife)
with the MSDP instrument, in the Hα line center and wings. SOHO/MDI
line-of-sight magnetograms were co-aligned with the MSDP images, showing
the position and evolution of the lateral feet of the filament in the
vicinity of the parasitic magnetic polarities observed in the filament
channel. Using the assumptions developed in the previous papers of this
series related to the reconstruction of the 3-D magnetic configuration
of filaments, we perform “linear magnetohydrostatic” extrapolations
(taking into account the effects of plasma pressure and gravity) on the
SOHO/MDI magnetograms. The main hypothesis is the presence of a twisted
flux-tube located above the photospheric inversion line. Assuming that
the parameters of the model do not need to be significantly modified
during the evolution of the configuration for a duration of 1 day,
we have shown that the 3-D distribution of dipped field lines is well
correlated with Hα dark absorbing features in the filament channel:
the filament itself, its lateral feet and some of the surrounding dark
fibrils. In this way we confirm what was suggested in our earlier
papers, i.e. that the feet are composed of the dipped portions of
some field lines, which form a continuous pattern from the corona
to the photosphere. We propose the same explanation for the magnetic
configuration of some of the dark Hα fibrils in the channel. We show
that the plasma effects are not responsible for the existence of most
of the magnetic dips, however their inclusion helps to get a better
correspondence between the model and the observations. We find that the
average Hα Doppler velocities associated with the filament and with
the chromospheric fibrils is of the order of a few hundred m s(-1)
(though it can go locally up to 3 km s(-1) in the filament). These
upward velocities are consistent with a quasi-static evolution of
the magnetic configuration and with the support of dense plasma in
magnetic dips.
---------------------------------------------------------
Title: What can we learn from Modelling the Sun as a Star?
Authors: Oláh, K.; van Driel-Gesztelyi, L.; Kővári, Zs.; Bartus, J.
1999ASPC..158..170O Altcode: 1999ssa..conf..170O
No abstract at ADS
---------------------------------------------------------
Title: The NOAA AR 6718 magnetic field extrapolation with localized
current filaments.
Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van
Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K.
1999joso.proc...97K Altcode:
The 3-D extrapolation of magnetic field lines of the July 11, 1991
Kitt Peak magnetogram shows a differential magnetic field shear in
the NOAA 6718 active region. A new combined extrapolation technique,
which includes localized current filaments is suggested and applied in
modelling of this shear. First, the potential field extrapolation is
made and then force-free current paths for several current filaments
in specific positions are computed. It is shown that with the electric
current increase the localized magnetic field shear is increasing. The
total electric current in 16 current filaments is considered up to
1.2×10<SUP>12</SUP>A.
---------------------------------------------------------
Title: On the role of beam driven return current instabilities in
white-light flares
Authors: Matthews, S. A.; Brown, J. C.; van Driel-Gesztelyi, L.
1998A&A...340..277M Altcode:
It has been shown previously that the low ionization levels in the
deep chromosphere of solar flares can cause the return current driven
by a thick target electron beam to be unstable to ion aoustic wave
generation, contrary to conventional wisdom. We investigate, using
Yohkoh data, the possibility that anomalous heating as a result of
this instability is capable of producing sufficient heating, in the
right places at the right times, to account for the enhanced continuum
emission actually observed in white-light flares. The Soft X-ray
Telescope (SXT) onboard \it Yohkoh incorporates an aspect camera which,
prior to its failure in 1992, provided white-light images at 431 nm with
a bandpass of 3 nm. A number of white-light flares were observed during
its operational lifetime for which there was coincident hard X-ray data
from the Hard X-ray Telescope (HXT), providing suitable candidates for
study. Four such events are discussed, and the model found to be viable.
---------------------------------------------------------
Title: Multi-wavelength observations of POST flare loops in two long
duration solar flares
Authors: Harra-Murnion, L. K.; Schmieder, B.; van Driel-Gesztelyi,
L.; Sato, J.; Plunkett, S. P.; Rudawy, P.; Rompolt, B.; Akioka, M.;
Sakao, T.; Ichimoto, K.
1998A&A...337..911H Altcode:
We have analysed two Long Duration solar Events (LDEs) which produced
large systems of Post Flare Loops (PFLs) and which have been observed by
Yohkoh and ground-based observatories. Using the Maximum Entropy Method
(MEM) image synthesis technique with new modulation patterns we were
able to make hard X-ray (HXR) images of the post flare loops recorded
in the L Channel (13.9-22.7 keV) of the Yohkoh Hard X-ray Telescope. We
obtained co-aligned 2-D maps in Hα (10(4) K), in soft X-rays (5x 10(6)
K) and in hard X-rays (20x 10(6) K). We conclude that the soft X-ray
(SXR) loops lie higher than the Hα loops and the former are overlaid
by HXR emission. This is suggestive of the magnetic reconnection
process. However some details are not consistent with the standard
models. Firstly the separation between the HXR source and the SXR
loop increases with time, with the HXR source being approximately
a factor of five larger than the equivalent source in impulsive
flares. Secondly the cooling times deduced from observations are longer
than the theoretically expected ones and the discrepancy increases
with time. We review the current models in view of these results.
---------------------------------------------------------
Title: 3-D magnetic configurations supporting prominences. II. The
lateral feet as a perturbation of a twisted flux-tube
Authors: Aulanier, G.; Demoulin, P.; van Driel-Gesztelyi, L.; Mein,
P.; Deforest, C.
1998A&A...335..309A Altcode:
In a previous paper we have shown that a twisted flux-tube is the
most probable magnetic configuration supporting prominences. The
model interprets many observations in a natural way (in particular
the magnetic measurements in prominences and the chirality
properties). Moreover, prominence feet appear as a direct consequence
of the parasitic polarities present in the filament channel. Here we
investigate further the link between feet and parasitic polarities
by modelling explicitly these polarities. We show that the prominence
lateral feet appear naturally, above secondary photospheric inversion
lines and we describe the morphological change of feet as parasitic
polarities evolve. This approach is applied to an observed filament
in Hα with the MSDP on the German VTT (Tenerife) where SOHO/MDI
magnetograms are available. We show that the shape of the prominence
is defined by the distribution of the dips in the computed magnetic
configuration. Then we analyse the topology of the magnetic field using
the quasi-separatrix layers (QSLs) method. We describe the basic changes
in the topology as the parasitic polarities evolve, in particular
how the configuration pass from an OX to an OF topology. We find a
correspondance between the computed QSLs and some of the chromospheric
brightenings, observed around the feet of filaments in the y line (Ca
II, 8542 Angstroms). It confirms the deduced magnetic configuration
and shows that energy release is present at a low level in the complex
topology of the filament configuration.
---------------------------------------------------------
Title: The Postflare Loops and the Nearby Active Chromosphere of
1992 June 26: Addendum
Authors: Malherbe, J. -M.; Tarbell, T.; Wiik, J. E.; Schmieder, B.;
Frank, Z.; Shine, R. A.; van Driel-Gesztelyi, L.
1998ApJ...495..502M Altcode:
Video segments are presented that were processed from a quantitative
study of the dynamics of the evolution of Hα postflare loops developed
after a large solar flare. The high spatial resolution of the Swedish
Vacuum Solar Telescope (SVST) at La Palma provided a unique set of
data for such an event.
---------------------------------------------------------
Title: Asymmetric Magnetic Field Distribution in Active Regions
Authors: Cauzzi, Gianna; van Driel-Gesztelyi, Lidia
1998ASPC..140..105C Altcode: 1998ssp..conf..105C
No abstract at ADS
---------------------------------------------------------
Title: Evolution of the Magnetic Field and Chromospheric Fine
Structure in a Filament Channel
Authors: van Driel-Gesztelyi, L.; Mein, P.; Mein, N.; Schmieder,
B.; Malherbe, J. -M.; Aulanier, G.; Démoulin, P.; Deforest, C.;
Staiger, J.
1998ASPC..155..321V Altcode: 1998sasp.conf..321V
No abstract at ADS
---------------------------------------------------------
Title: Evolution and Decay of Active Regions (Invited review)
Authors: van Driel-Gesztelyi, L.
1998ASPC..155..202V Altcode: 1998sasp.conf..202V
No abstract at ADS
---------------------------------------------------------
Title: Reorganization of solar magnetic field by a flare event
Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.;
Démoulin, P.
1998BASI...26..319M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non potentiality of coronal loops above active regions
Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; van
Driel-Gesztelyi, L.; Deforest, C.
1998ASPC..155..105A Altcode: 1998sasp.conf..105A
No abstract at ADS
---------------------------------------------------------
Title: Filament Disparition Brusque and CME - September 25-26,
1996 Event
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Aulanier, G.;
Demoulin, P.; Martens, P. C. H.; Zarro, D.; Deforest, C.; Thompson,
B.; St. Cyr, C.; Kucera, T.; Burkepile, J. T.; White, O. R.; Hanaoka,
Y.; Nitta, N.
1998ASPC..150..366V Altcode: 1998IAUCo.167..366V; 1998npsp.conf..366V
No abstract at ADS
---------------------------------------------------------
Title: 3-D Modelling of a Filament Observed in Hα and with SOHO
Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; Mein, N.; van
Driel-Gesztelyi, L.; Mein, P.; Vial, J. C.; Deforest, C.
1998ESASP.417..217A Altcode: 1998cesh.conf..217A
No abstract at ADS
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Title: A study of activity in interacting sunspot groups
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Hénoux, J. -C.
1998PAICz..88...13S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: 3-D Modelling of a Filament Observed in Hα and with SOHO/MDI
Authors: Aulanier, G.; Démoulin, P.; van Driel-Gesztelyi, L.; Mein,
P.; Deforest, C.
1998ASPC..155..326A Altcode: 1998sasp.conf..326A
No abstract at ADS
---------------------------------------------------------
Title: Evolution of a reversed polarity active region NOAA 7912 in
the photosphere, the chromosphere and the corona.
Authors: van Driel-Gesztelyi, L.; Baranyi, T.; Mein, N.; Cader-Sroka,
B.; Rudawy, P.; Mein, P.; Rompolt, B.; Schmieder, B.; Malherbe,
J. -M.; Willson, R.; Kile, J. N.; Raoult, A.
1998joso.proc..103V Altcode:
The authors follow the evolution and activity of NOAA 7912, a reversed
polarity region, in the photosphere (Kitt Peak magnetograms and Debrecen
white-light photoheliograms), chromosphere (MSDP instrument mounted
on the German VTT at Tenerife), and the corona (Yohkoh/SXT, Nançay
radioheliograph and the VLA) between October 12-20, 1995. They find
that in spite of the high shear and creation of several mixed-polarity
regions through flux emergence, the flares in the group did not
exceed the M-class level. This might be due to the fact that the
highly inclined bipolar fields emerging in the following part of the
primary reversed dipole were relatively small and quickly "consumed"
by cancellation enhanced by sunspot motions. On the other hand, the
presence of high shear and minor fast-moving parasitic polarities in
NOAA 7912 was sufficient to produce eruptive events like X-ray jets
with important coronal and interplanetary effects.
---------------------------------------------------------
Title: X-Ray Jets and Their Radio Signatures at Metric and Centimeter
Wavelenths
Authors: van Driel-Gesztelyi, L.; Willson, R. F.; Kile, J. N.; Raoult,
A.; Klein, L.; Mein, N.; Rudawy, P.; Cader, B.; Rompolt, B.; Schmieder,
B.; Mein, P.; Malherbe, J. M.
1998ASPC..154..707V Altcode: 1998csss...10..707V
On October 19, 1995 at 10:30 UT and 17:00 UT, two semi-homologous X-ray
jets were observed with the Yohkoh/SXT from AR 7912, a region having a
reversed polarity group with vortex-like Hα fibril pattern and X-ray
loops. The jets appeared over a mixed magnetic polarity region in
the vicinity of the leading spot. The first event was also observed
with the Nancay radio heliograph at 167, 236, and 327 MHz. Type III
activity, indicating the presence of electron beams, superimposed on
a noise-storm was clearly visible. Type III activity first appeared
at 10:25 UT, coincident with the onset of the X-ray jet, at 164 MHz
and 236 MHz close to the storm position, and in the direction of the
X-ray jet. At 10:28:40 UT a new group of sources appeared eastward
of the former activity, which may correspond to another jet branch
along a more easterly path seen in the ohkoh} images. The second X-ray
jet event was also observed with the Very Large Array (VLA) at 6.2,
20.7, and 91.6 cm. For this event, VLA snapshot maps at 6.2 and 20.7
cm reveal low-brightness temperature changes in source structure at
the site of the X-ray jet during the preburst, impulsive, and decay
phases. The VLA 91.6 cm observations also show noise storm emission
above the active region but there is no clear temporal correlation
between this later X-ray jet and the impulsive decimetric bursts that
were observed during this period. Although the X-ray observations
show that the two jets had similar temperatures, emission measures,
speeds and trajectories they appear to have had dissimilar metric
responses to these events. This surprising result may question our
understanding of the process of electron beam acceleration in jets.
---------------------------------------------------------
Title: Making Sense of Sunspot Decay. I. Parabolic Decay Law and
Gnevyshev-Waldmeier Relation
Authors: Petrovay, K.; van Driel-Gesztelyi, L.
1997SoPh..176..249P Altcode: 1997astro.ph..6029P
In a statistical study of the decay of individual sunspots based on
DPR data we find that the mean instantaneous area decay rate is related
to the spot radius r<SUB>o</SUB> and the maximum radius r<SUB>o</SUB>
as D = C<SUB>D</SUB> r/r<SUB>o</SUB>, C<SUB>D</SUB> = 32.0±0.26 MSH
day <SUP>-1</SUP>. This implies that sunspots on the mean follow a
parabolic decay law; the traditional linear decay law is excluded
by the data. The validity of the Gnevyshev-Waldmeier relationship
between the maximum area A <SUB>0</SUB> and lifetime T of a spot group,
A<SUB>0</SUB>/T ≃10 MSH day<SUP>-1</SUP>, is also demonstrated for
individual sunspots. No evidence is found for a supposed supergranular
`quantization' of sunspot areas. Our results strongly support the
recent turbulent erosion model of sunspot decay while all other models
are excluded.
---------------------------------------------------------
Title: Magnetic reconnection driven by emergence of sheared magnetic
field.
Authors: Schmieder, B.; Aulanier, G.; Demoulin, P.; van
Driel-Gesztelyi, L.; Roudier, T.; Nitta, N.; Cauzzi, G.
1997A&A...325.1213S Altcode:
Recurrent subflares (Class C) were observed in the NOAA 7608 active
region on 27 October 1993. From multi-wavelength observations
(white-light, magnetic field, H-alpha, X-ray), obtained during a
coordinated campaign between Pic du Midi and Yohkoh, it appears that
these flares were double ribbon flares caused by new flux emergence. As
the flare begins, the X-ray emission observed with Yohkoh/SXT is
loop-shaped with the axis almost parallel to the magnetic inversion
line, while during the flare development, X-ray loops appear at the
location of the emerging flux. The extrapolation of the photospheric
magnetic field in a linear force-free field configuration allows
identification of the magnetic configuration given by the flares. The
Hα flare ribbons are located at the intersections of the computed
quasi-separatrice layers (QSLs) with the chromosphere. We show that
the initial loop-shaped X-ray emission region is in fact formed by
several smaller loops directed in a nearly orthogonal direction with
their feet anchored close to or in the Hα ribbons. During the flare
development there are X-ray loops which represent only one foot of
open or largescale magnetic loops. For the studied flares the puzzling
soft X-rays observations could only be understood with the help of Hα
and magnetic data combined with a modeling of the coronal magnetic
field. Further, from the deduced magnetic field topology, the width
of the QSLs and our present knowledge of 3-D magnetic reconnection,
we conclude that the flare was due to magnetic reconnection driven
by emergence of sheared magnetic field impacting in the pre-existing
coronal field.
---------------------------------------------------------
Title: Evidence of Magnetic Reconnection from Hα, Soft X-Ray and
Photospheric Magnetic Field Observations
Authors: Mandrini, C. H.; DÉmoulin, P.; BagalÁ, L. G.; Van
Driel-Gesztelyi, L.; HÉnoux, J. C.; Schmieder, B.; Rovira, M. G.
1997SoPh..174..229M Altcode:
A conventional view of magnetic reconnection is mainly based on
the 2-D picture of an X-type neutral point, or on the extension of
it to 3-D, and it is thought to be accompanied by flux transport
across separatrices (places where the field-line mapping is
discontinuous). This view is too restrictive when we realize the variety
of configurations that are seen flaring. We designed an algorithm,
called Source Method (SM), to determine the magnetic topology of
active regions (ARs). The observed photospheric field was extrapolated
to the corona using subphotospheric sources and the topology was
defined by the link between these sources. Hα flare brightenings
were found to be located at the intersection with the chromosphere
of the separatrices so defined. These results and the knowledge we
gained on the properties of magnetic field-line linkage, led us to
generalize the concept of separatrices to `quasi-separatrix layers'
(QSLs) and to design a new method (`quasi-separatrix layers method',
QSLM) to determine the magnetic topology of ARs. QSLs are regions where
the magnetic field-line linkage changes drastically (discontinuously
when they behave like separatrices) and the QSLM can be applied to ARs
where the photospheric field has been extrapolated using any kind of
technique. In this paper we apply the QSLM to observed flaring regions
presenting very different configurations and also to a decaying AR where
a minor phenomenon, like an X-ray bright point (XBP), is observed. We
find that the locations of flare and XBP brightenings are related to the
properties of the field-line linkage of the underlying magnetic region,
as expected from recent developments of 3-D magnetic reconnection. The
extrapolated coronal field lines representing the structures involved
in the analyzed events have their photospheric footpoints located
at both sides of QSLs. Our results strongly support the hypothesis
that magnetic reconnection is at work in various coronal phenomena,
ranging from the less energetic ones to large-scale eruptions.
---------------------------------------------------------
Title: Post-Flare Loops of 26 June 1992 - IV. Formation and Expansion
of Hot and Cool Loops
Authors: Van Driel-Gesztelyi, L.; Wiik, J. E.; Schmieder, B.; Tarbell,
T.; Kitai, R.; Funakoshi, Y.; Anwar, B.
1997SoPh..174..151V Altcode:
Observations of the post-flare loops after the X3.9 flare which occurred
on 25 June, 1992 at 20:11 UT by the Yohkoh/SXT in X-rays, as well as
in Hα obtained at 5 different observatories, have provided a unique,
longest ever, set of data for a study of the relationship between the
hot and cool post-flare loops as they evolve. At any given time, the
altitude difference between the hot X-ray loops of 6-7× 10<SUP>6</SUP>
K and the cool Hα loops of 1.5× 10<SUP>4</SUP> K is related to the
expansion rate of the loop systems and their cooling time. Therefore,
measurements of the expansion rate and relative height of hot and
cool loops can provide direct observational values for their cooling
times. We measured the altitude of hot and cool loops for 15 and 19
hours, respectively, and found that the cooling time increased as the
density of the loops decreased. We found a reasonably good agreement
between the observed cooling times and those obtained from model
calculations, although the observed values were always somewhat longer
than the theoretical ones. Taking into account evolutionary effects,
we also found similar shapes and configurations of hot and cool loops
during the entire observing period and confirmed that, at any time,
hot loops are at higher altitude than cool loops, suggesting that cool
loops indeed evolve from hot loops. These results were used to check
the validity of the reconnection model.
---------------------------------------------------------
Title: The Postflare Loops and the Nearby Active Chromosphere of
1992 June 26
Authors: Malherbe, J. -M.; Tarbell, T.; Wiik, J. E.; Schmieder, B.;
Frank, Z.; Shine, R. A.; van Driel-Gesztelyi, L.
1997ApJ...482..535M Altcode:
The main objective of this paper is to present a quantitative study
of the dynamics of the evolution of Hα postflare loops developed
after a large solar flare and the processed videos produced from the
observations. The high spatial resolution of the Swedish Vacuum Solar
Telescope (SVST) at La Palma has provided a unique set of data for such
an event. A Gaussian fitting method is proposed to derive intensities
and Doppler shifts from observations taken at three wavelengths (Hα
center and Hα +/- 0.07 nm). Moving condensations or “blobs” of cold
material provide transverse velocities, which, together with the radial
component, enable us to derive their velocity vector magnitude. Plasma
velocities are around free-fall velocities near the top of the loops
but are significantly smaller close to their footpoints, suggesting
a deceleration mechanism. The loops are anchored in the chromosphere,
which shows tremendous activity in the active region and in the nearby
“quiet Sun.” Spicules and ejection of plasmoids are also observed
at the limb.
---------------------------------------------------------
Title: Solar Magnetic Field Events related to CMEs observed with SOHO
(MDI, EIT, SUMER, LASCO)
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Wiik, J. E.; Thompson,
B.; de Forest, C.; Saint Cyr, C.; Vial, J. -C.; Nitta, N.; Simnett, G.
1997IAUJD..19E..42S Altcode:
We shall present two CMEs observed by LASCO during the minimum of
activity of the Sun. These are associated with filament disparitions
brusques (DB). CME and DB definitively seem to be consequences of global
magnetic field instability, which causes reconnection of pre-existing
field lines in the corona. We shall demonstrate how cancelling flux
and converging magnetic field in photosphere may destabilize coronal
streamers overlying one or two filament channels.
---------------------------------------------------------
Title: 3-D reconnection related to new emerging flux
Authors: Schmeider, B.; Démoulin, P.; Aulanier, G.; Malherbe, J. M.;
van Driel-Gesztelyi, L.; Mandrini, C. H.; Roudier, T.; Nitta, N.;
Harra-Murnion, L. K.
1997AdSpR..19.1871S Altcode:
We present evidences that emergence of new flux in the lower
atmosphere leads to magnetic reconnection of field lines. In a
first phase the phenomenon is observed in the chromosphere by the
formation of dark filaments (arch filament system) which are overlaid
by bright loops visible in soft X-rays. Different types of event appear
according to the magnetic field configuration and the amount of energy
involved. 3-D modelling of the photospheric magnetic field provides a
new tool for understanding reconnection in real configurations. The
observed chromospheric and coronal loops are good diagnostics for
the modelling. We document our statement by examples obtained during
coordinated campaigns with the Hα Multichannel Subtractive Double
Pass spectrographs-MSDP (Pic du Midi and Tenerife) and the Yohkoh
instruments.
---------------------------------------------------------
Title: Prominence Activity Related to CME Observed by SOHO, YOHKOH
and Ground-Based Observatories
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Wiik, J. E.; Kucera,
T.; Thompson, B.; de Forest, C.; Saint Cyr, C.; Simnett, G. M.
1997ESASP.404..663S Altcode: 1997cswn.conf..663S
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Decay as Turbulent Erosion of a Magnetic Flux Tube
Authors: Petrovay, K.; van Driel-Gesztelyi, L.
1997ASPC..118..145P Altcode: 1997fasp.conf..145P
Decisive evidence is presented against the validity of the conventional
linear decay law for sunspots. Preliminary results from a statistical
analysis of Debrecen Photoheliographic Results data show that the decay
rate of sunspots is significantly slower in late phases of the decay
than in earlier phases. Our findings are compatible with the predictions
of a recently developed turbulent erosion model for sunspot decay.
---------------------------------------------------------
Title: East-West inclination of field lines in active regions
Authors: Cauzzi, G.; van Driel-Gesztelyi, L.
1997MmSAI..68..487C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic reconnection driven by an emerging flux.
Authors: Aulanier, G.; Démoulin, P.; Schmieder, B.; Malherbe, J. M.;
van Driel-Gesztelyi, L.; Roudier, T.
1997joso.proc...51A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis of long duration flares
Authors: Harra-Murnion, L. K.; Plunkett, S. P.; Helsdon, S. F.;
Phillips, K. J. H.; van Driel-Gesztelyi, L.; Schmieder, B.; Rompolt,
B.; Akioka, M.
1997AdSpR..20.2333H Altcode:
Yohkoh has observed many long duration events permitting a statistical
study of the properties of these interesting events. We have selected
ten flares for analysis which have durations between 5 and 20 hours, and
size ranging from C to X GOES class. Employing the Soft X-ray Telescope,
the Bragg Crystal Spectrometer, GOES spacecraft, and ground-based
H_alpha data, we examine the morphology, temperature, emission measure,
location of the hard X-ray source, non-thermal velocities and upflows
of the plasma at different stages in the flare development. Our results
are used to address the question of the energy source that maintains the
hot plasma at temperatures of several million degrees for many hours.
---------------------------------------------------------
Title: Post-flare loops in the chromosphere and corona.
Authors: van Driel-Gesztelyi, L.; Wiik, J. E.; Schmieder, B.
1997ASIC..494...85V Altcode: 1997topr.conf...85V
Post-flare loops, which may last for several hours during the gradual
phase of powerful flares, can provide spectacular limb events during
solar eclipses. According to models, on-going magnetic reconnection
keeps creating new loops at an ever-increasing altitude. The newly
formed hot loops can cool down to chromospheric temperatures quickly,
in a few minutes, or slowly, over a few hours, depending on their
density. A good test of the model is to measure the altitude difference
between loops observed at different wavelengths which show the loops
at different stages of the cooling process.
---------------------------------------------------------
Title: Reorganization of the solar corona following a C4.7 flare
Authors: van Driel-Gesztelyi, L.; Manoharan, P. K.; Pick, M.;
Démoulin, P. P.
1997AdSpR..19.1883V Altcode:
Yohkoh X-ray images, multifrequency two-dimensional observations of
the Nancay Radioheliograph, Kitt Peak and Mees magnetograms provide
a unique set of data with which to study a C4.7 long-duration flare
that was observed close to the equator (S07, W11) on 25 Oct. 1994
at 09:49 UT. Linear force-free field extrapolations indicate a
very high degree of non-potentiality in the active region. The
X-ray flare started with the expansion of spectacular twisted
loops. Fifteen minutes after the flare onset sporadic radio (type
III) bursts were observed spreading over an area of almost <FR
SHAPE="SOL">1<DE>3</DE></FR> of the solar disc
and two remote X-ray brightenings appeared over quiet regions of
opposite magnetic polarity located in on opposite hemispheres of the
Sun. In the close vicinity of these remote brightenings two coronal
holes formed. The timing and location of these events combined with
the overall magnetic configuration provide evidence for a large-scale
magnetic reconnection occurring between the expanding twisted loops
and the overlying huge loops which inter-connect quiet solar regions.
---------------------------------------------------------
Title: Emerging Flux Tube Geometry and Sunspot Proper Motions
Authors: van Driel-Gesztelyi, Lidia
1997ASPC..118...81V Altcode: 1997fasp.conf...81V
As sunspots appear at the intersection of rising flux tubes with
the photosphere, the observed proper motions of a bipolar sunspot
pair is a good indicator of the geometry of the underlying emerging
flux tube. An emerging bipole caused by a simple symmetric potential
flux tube should display a symmetric divergence of the two spots in
diametrically opposite directions, while the proper motions of bipolar
spot-pairs belonging to tilted or/and twisted (non-potential) emerging
flux tubes are more complicated: asymmetric, not diametrically opposite
and may follow a curved pattern. Observation of such motions may help
to prove that emerging flux tubes are tilted and frequently twisted,
in good agreement with predictions by recent simulation studies.
---------------------------------------------------------
Title: Evidence for Large-Scale Solar Magnetic Reconnection from
Radio and X-Ray Measurements
Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.;
Demoulin, P.
1996ApJ...468L..73M Altcode:
Utilizing Yohkoh Soft X-ray Telescope and Nancay radioheliograph data,
we present, for the first time, observations of expanding twisted
X-ray loops and a series of nonthermal radio bursts that follow the
loop expansion in time and space up to ~12' distance. The loops were
produced during a long-duration C4.7 flare close to disk center on 1994
October 25 at 1049 UT. The series of radio bursts were observed on the
southern hemisphere above a weak positive-polarity region. The Kitt
Peak magnetogram shows the existence of a weak negative-polarity region
on the northern hemisphere at the same heliolongitude. Simultaneously
with the nonthermal radio bursts, we observed the appearance of two
remote X-ray brightenings and subsequent formation of two coronal
holes above these weak (quiet) magnetic regions of opposite polarity,
which strongly suggest the involvement of these remote regions in the
event. During the 6 hr--long gradual phase of the flare, new X-ray
loop connections developed among the active region and the remote
quiet regions. A nonthermal radio continuum emission originating
from the active region was also observed. We propose that the series
of radio bursts, two remote X-ray brightenings, and new coronal loop
connections were all signatures of a large-scale reconnection process
between the expanding twisted flare loops and overlying transequatorial
loops connecting quiet-Sun regions. The reconnection was only partial;
the external part of the overlying large-scale fields were pushed out in
the solar wind by the expanding twisted loops, leading to the formation
of the coronal holes. The interaction between the active region and
the large-scale fields seemed to be active during the entire gradual
phase of the flare. This scenario may also explain the measurement of
high-energy electrons in the interplanetary medium from 74 deg south
heliolatitude as observed by Ulysses.
---------------------------------------------------------
Title: 3D Magnetic Reconnection at an X-Ray Bright Point
Authors: Mandrini, C. H.; Démoulin, P.; Van Driel-Gesztelyi, L.;
Schmieder, B.; Cauzzi, G.; Hofmann, A.
1996SoPh..168..115M Altcode:
On May 1, 1993, a flaring X-ray bright point (XBP) was observed for
about 16 hours in the old, disintegrating, bipolar active region (AR)
NOAA 7493. During this period, a minor magnetic bipole (10<SUP>20</SUP>
Mx) emerged in the region. We have found observational evidence showing
that the XBP brightenings were due to magnetic reconnection between
the new bipole and pre-existing plage fields. The aim of the present
work is to substantiate with magnetic modelling what has been shown
by the observations. For this purpose we extrapolate the observed
photospheric magnetic fields in the linear force-free approximation
and follow its evolution during the lifetime of the XBP. From the
computed coronal field lines we determine the location of regions of
drastic change in field-line linkage, called `quasi-separatrix layers'
or QSLs. QSLs are open layers that behave physically like separatrices:
the break down of ideal magnetohydrodynamics and the release of free
magnetic energy may occur at these locations when their thickness
is small enough. The extrapolated field lines, with photospheric
footpoints on both sides of QSLs, match the observed chromospheric and
coronal structures (arch filament system, XBP and faint X-ray loops
(FXL)). We study also the evolution of the width of the QSL located
over the new negative polarity pore: the calculated QSL is very thin
(typically less than 100 m) during the lifetime of the XBP, but becomes
much thicker (≥ 10<SUP>4</SUP> m) after the XBP has faded. Furthermore
we show that peaks in X-ray brightness propagate along the FXL with a
velocity of ≈ 670 km s<SUP>-1</SUP>, starting from the XBP location,
implying that the energy is released where the emerging bipole impacts
against pre-existing coronal loops. We discuss the possible mechanism
of energy transport and conclude that the energy is conducted to the
remote footpoints of the FXL by a thermal front. These results strongly
support the supposition that the XBP brightness and flaring are due
to the interaction of different flux systems, through 3D magnetic
reconnection, at QSLs.
---------------------------------------------------------
Title: Post-Flare Loops of 26 June 1992, II
Authors: Schmieder, B.; Heinzel, P.; Van Driel-Gesztelyi, L.; Lemen,
J. R.
1996SoPh..165..303S Altcode:
We observed the large post-flare loop system, which developed after the
X 3.9 flare of 25 June 1992 at 20∶11 UT, in Hα with the Multichannel
Subtractive Double Pass Spectrograph at Pic-du-Midi and in X-rays with
the it Yohkoh/SXT instrument. Following the long-term development of
cool and hot plasmas, we have determined the emission measure of the
cool plasma and, for the first time, the temporal evolution of the
hot-loop emission measure and temperature during the entire gradual
phase. Thus, it was possible to infer the temporal variation of electron
densities, leading to estimates of cooling times. A gradual decrease of
the hot-loop emission measure was observed, from 4 × 10<SUP>30</SUP>
cm<SUP>−5</SUP> at 23∶00 UT on 25 June 1992 to 3 × 10<SUP>28</SUP>
cm<SUP>−5</SUP> at 13∶10 UT on 26 June 1992. During the same period,
the temperature decreased only slowly from 7.2 to 6.0 × 10<SUP>6</SUP>
K. Using recent results of NLTE modeling of prominence-like plasmas,
we also derive the emission measure of cool Hα loops and discuss
their temperature and ionisation degree. During two hours of Hα
observations (11-13 hours after the flare) the averaged emission
measure does not show any significant change, though the amount
of visible cool material decreases and the volume of the loops
increases. The emission measure in Hα, after correction for the
Doppler-brightening effect, is slightly lower than in soft X-rays. Since
the hot plasma seems to be more spatially extended, we arrive at
electron densities in the range n<SUB>infe</SUB><SUP>supho</SUP>≤
n<SUB>infe</SUB><SUP>supcool</SUP>∼ 2 × 10<SUP>10</SUP>
cm<SUP>−3</SUP> at the time of the Hα observations.
---------------------------------------------------------
Title: Evidence for Current-carrying Emerging Flux
Authors: Leka, K. D.; Canfield, R. C.; McClymont, A. N.; van
Driel-Gesztelyi, L.
1996ApJ...462..547L Altcode:
To determine the relationship between electric currents and magnetic
flux in emerging sunspots, we use observations of the morphology,
proper motion, magnetic flux, and currents associated with several
well-observed growing bipoles. Our target was NOAA Active Region 7260,
which included a preexisting large spot and a fast-growing area of new
magnetic flux. Magnetic bipoles in this region are well documented
by X-ray images from the Yohkoh spacecraft and optical images and
vector magnetograms from several ground-based observatories. <P />In
this paper we show that (1) the Hα and X-ray structures associated
with these bipoles do not agree with potential-field extrapolations
of magnetograms; (2) proper motions imply that the flux bundles that
make up these new bipoles are twisted before they emerge; (3) these
new bipoles are cospatial with significant vertical electric currents;
(4) the morphology, proper motion, and measured currents of these
bipoles all imply the same sense of twist; (5) this sense of twist
is the same as the large-scale twist of the preexisting large spot;
and (6) the increase of these currents, as new flux emerges, is not
consistent with their generation by photospheric motions. <P />We
conclude that the new magnetic flux that emerged in this active region
carried currents generated below the photosphere.
---------------------------------------------------------
Title: Flare Activity Associated with Large-Scale Loops in AR 7260
Authors: Nitta, N.; van Driel-Gesztelyi, L.
1996AAS...188.1901N Altcode: 1996BAAS...28..849N
Active region NOAA AR 7260 (August 1992) is marked as one of the fastest
growing regions in solar cycle 22 and has extensively been studied by
several workers. We have learned from the Yohkoh SXT data that flares in
this region were generally confined rather than eruptive. In addition
to the flares, we notice the formation of large-scale X-ray loops
connecting the large preceding spot and the emerging flux region as
the latter became complexed. One of them produced a LDE after a cusp
structure formed on top it. These loops were occasionally observed to
erupt, perhaps responsible for coronal mass ejections. Even some of
the apparently localized flares may have been due to interactions of
compact loops with such large-scale loops. It is possible that they
also caused sympathetic flares. We try to understand how such loops
formed in the context of evolution of the region, which is known to
have consisted of intrinsically twisted magnetic field.
---------------------------------------------------------
Title: Chromospheric ejections and their signatures in X-ray observed
by YOHKOH
Authors: Schmieder, B.; Mein, N.; Shibata, K.; van Driel-Gesztelyi,
L.; Kurokawa, H.
1996AdSpR..17d.193S Altcode: 1996AdSpR..17..193S
Surges, or condensations of chromospheric material, are commonly
observed in active regions when new emerging magnetic flux (EMF)
occurs. In order to study EMF-related phenomena in the corona, observing
campaigns were organized with the Yohkoh X-ray satellite and ground
based observatories. EMFs could be detected in magnetograms made in
Potsdam and Hawaii, surge and arch filament system (AFS) events (on
Oct 7 1991, May 1 1993, respectively) with the Multichannel Subtractive
Double Pass instruments operating at Meudon and on the Canary Islands
and with the Hida telescope at Kyoto University. Bright X-ray loops
coincident with chromospheric surge activity were detected in the high
resolution Yohkoh SXT images. We also found coincident brightness
variations between an X-ray bright point (XBP) and the underlying
chromospheric plage related to EMF. We interpret the appearance of
AFS as condensation of material among magnetic field lines, the X-ray
bright points as the result of a magnetic reconnection process, and
surges as ejection of cold plasma bubbles squeezed between field lines
as a result of reconnection.
---------------------------------------------------------
Title: Emerging flux and flares in NOAA 7260
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Shibata, K.
1996AdSpR..17d.201N Altcode: 1996AdSpR..17..201N
We have studied the relation between flux emergence and flare
activity in the active region NOAA 7260, using images from the Soft
X-ray Telescope aboard the Yohkoh spacecraft and other supporting
ground-based data. It is found that microflares start around the time
of flux emergence as recorded in white-light data, which generally
precedes a major flare by several hours. We interpret the microflares as
due to fast reconnection that takes place intermittently in the slow
reconnection stage while more energy is accumulated in preparation
for a larger flare.
---------------------------------------------------------
Title: Flare Associated Large-Scale Magnetic Reconnection
Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.;
Demoulin, P.
1996ASPC..111..398M Altcode: 1997ASPC..111..398M
Reports a unique set of observations, for a low heliolatitude flare,
obtained with the Yohkoh satellite and the Nançay radioheliograph. This
flare starts with the expansion of spectacularly twisted loops,
followed by sporadic radio bursts (some of them are detected at high
heliolatitude, ≡65°S), appearance of two remote X-ray brightenings
and formation of two coronal holes on opposite hemispheres of the
Sun. The timing and location of these events provide evidence for
a large-scale magnetic reconnection between the expanding twisted
flare loops and overlying huge loops inter-connecting quiet regions
on the Sun.
---------------------------------------------------------
Title: Asymmetries in solar active regions and flux emergence models
Authors: Cauzzi, G.; Moreno-Insertis, F.; van Driel-Gesztelyi, L.
1996ASPC..109..121C Altcode: 1996csss....9..121C
No abstract at ADS
---------------------------------------------------------
Title: Beam Driven Return Current Instabilities and White-Light Flares
Authors: Matthews, S. A.; Brown, J. C.; van Driel-Gesztelyi, L.
1996ASPC..111..304M Altcode: 1997ASPC..111..304M
It has been shown that the low ionization levels in the deep
chromosphere of solar flares can cause the return current driven by a
thick target flare beam to be unstable to ion acoustic wave generation,
contrary to previous conventional wisdom. The authors investigate the
possibility that anomalous heating as a result of this instability
may produce sufficient heating to power the white-light flare. Four
white-light flares observed by Yohkoh are examined: 1991 Oct 27,
1991 Nov 15, 1992 Jan 26, and 1992 Feb 14.
---------------------------------------------------------
Title: X-Ray Bright Point Flares Due to Magnetic Reconnection
Authors: Van Driel-Gesztelyi, L.; Schmieder, B.; Cauzzi, G.; Mein,
N.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein, P.; Staiger, J.
1996SoPh..163..145V Altcode:
Ground-based optical observations coordinated with Yohkoh/SXT X-ray
observations of an old, disintegrating bipolar active region AR NOAA
7493 (May 1, 1993) provided a multiwavelength data base to study
a flaring `active region' X-ray bright point (XBP) of about 16 hr
lifetime, and the activity related to it in different layers of the
solar atmosphere. The XBP appeared to be related to a new minor bipole
of about 10<SUP>20</SUP> Mx. Superposed on a global evolution of soft
X-ray brightness, the XBP displayed changes of brightness, lasting for
1-10 min. During the brightenings the XBP apparently had a spatial
structure, which was (tiny) loop-like rather than point-like. The
X-ray brightenings were correlated with chromospheric activity: (i)
brightenings of underlying chromospheric faculae, and (ii) appearance
of strong turbulent velocities in the arch filament system. We propose
that the XBP brightenings were due to reconnection of the magnetic
field lines (sketched in 3D) between the new bipole and a pre-existing
plage field induced by the motion of one of the new pores (v = 0.2
km s<SUP>−1</SUP>) towards the plage, and that the XBP itself was
a reconnected hot loop between them.
---------------------------------------------------------
Title: Hot and Cool Post-Flare Loops: Formation and Dynamics
Authors: Schmieder, B.; Heinzel, P.; van Driel-Gesztelyi, L.; Wiik,
J. E.; Lemen, J.
1996mpsa.conf..211S Altcode: 1996IAUCo.153..211S
No abstract at ADS
---------------------------------------------------------
Title: Reconexión magnética en una región activa en decaimiento
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
Schmieder, B.; Bagalá, L. G.; Rovira, M. G.
1996BAAA...40....5M Altcode:
Se han obtenido observaciones desde Tierra (Hα y magnetogramas)
coordinadas con el Soft X-ray Telescope (SXT), a bordo del satélite
japonés Yohkoh, de una región activa bipolar en decaimiento. Estos
datos constituyen la base para el estudio de un punto brillante en rayos
X (PBX) y de la actividad relacionada con el mismo en distintas capas
de la atmósfera solar. Las observaciones muestran que el PBX está
relacionado con la aparición de un bipolo menor (~ 10<SUP>20</SUP> Mx)
y que su abrillantamiento continuo, así como sus aumentos de brillo
esporádicos (“fulguraciones"), son el resultado de la reconexión
entre el pequeño arco emergente (visto en Hα como un sistema de
filamentos arqueados, SFA) y arcos mayores asociados al campo facular
preexistente. Se ha extrapolado el campo magnético observado en la
aproximación libre de fuerzas lineal y se ha seguido su evolución
a lo largo de la vida del PBX. Se ha calculado la posición de las
cuasiseparatrices (CSs) a partir del campo modelado. Las líneas de
campo extrapoladas, cuyas bases fotosféricas se encuentran a ambos
lados de las CSs, están de acuerdo con las estructuras cromosféricas
y coronales observadas. Se ha calculado el espesor de la CD ubicada
a lo largo de la polaridad negativa emergente, encontrándose que su
variación está de acuerdo con la evolución de la intensidad del PBX;
la CS es muy delgada durante la vida del PBX (~ 100 m), mientras que
su espesor aumenta considerablemente (>= 10^4 m) cuando el PBX
desaparece de las imágenes del SXT. Estos resultados señalan que
el abrillantamiento y las “fulguraciones" de este PBX se deben al
proceso de reconexión en 3D que tiene lugar en las CSs.
---------------------------------------------------------
Title: Relative Altitude of Hot and Cool Post-Flare Loops
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Wiik, J. E.; Tarbell,
T.; Heinzel, P.; Kitai, R.; Funakoshi, Y.; Anwar, B.
1996ASPC..111..359V Altcode: 1997ASPC..111..359V
The authors collected a unique set of data obtained simultaneously at
4 different ground based observatories and with the Yohkoh satellite
to study the relationship between hot X-ray and cool Hα post-flare
loops as they evolved during the long gradual phase of the X3.9 flare
which occurred on 25 June 1992. They found reasonably good agreement
between the computed 'theoretical' cooling times and the 'observed'
cooling times derived from the relative altitudes of hot and cool
loops. Taking into account evolutionary effects, the authors also found
similar shape and configuration of hot and cool loops during the entire
observing period and confirmed that at any time hot loops are at higher
altitude than cool loops, suggesting that cool loops indeed descend
from hot loops. The results provide support for the reconnection model.
---------------------------------------------------------
Title: Signatures of New Emerging Flux in the Solar Atmosphere
Authors: Schmieder, B.; Malherbe, J. M.; Mein, P.; Mein, N.; van
Driel-Gesztelyi, L.; Roudier, T.; Nitta, N.; Harra-Murnion, L. K.
1996ASPC..111...43S Altcode: 1997ASPC..111...43S
The emergence of new flux in the low atmosphere leads to magnetic
reconnection of field lines. In a stable phase the phenomenon is
observed in the chromosphere by the formation of dark filaments (arch
filament system, AFS). The authors show how bright loops visible in soft
X-rays are co-aligned with the AFS. Different types of events appear
as the released energy increases. With less energetic phenomena than
flares one observes surges, jets or X-ray bright points, according
to the configuration of the field lines (open/closed). A low-level
reconnection process is detectable as an X-ray bright point. If
the energy is ≡10<SUP>28</SUP>ergs cm<SUP>-3</SUP>, one observes
subflares. The authors document their statement by showing examples
observed in coordinated observations obtained with the MSDP (Pic du
Midi and Tenerife) and Yohkoh/SXT and BCS for the events occurring on
Oct 5, 1994, Oct 27, 1993, and May 1, 1993.
---------------------------------------------------------
Title: 3D Magnetic Reconnection: Example of an X-Ray Bright Point
Authors: Demoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L.;
Priest, E. R.; Henoux, J. C.; Schmieder, B.
1996ASPC..111...49D Altcode: 1997ASPC..111...49D
In the classical view magnetic reconnection occurs at neutral points
and implies transport of magnetic field-lines across separatrices. The
authors show that reconnection may also occur in the absence of neutral
points at so-called "quasi-separatrix layers" (QSLs), where there is a
steep gradient in field-line linkage at the boundaries. Reconnection
occurs in QSLs where the field-line velocity becomes larger than the
allowed maximal plasma velocity or where the electric-current density
becomes too great. The authors describe both a theoretical and an
observed configuration. In the case of a simple sheared X-field they
show that even a smooth continuous shear flow, imposed at the boundary,
gives strong plasma jetting inside and parallel to the QSLs. Applying
the QSL method to an X-ray bright point observed by Yohkoh, they find
field lines in the extrapolated field which are on both sides of QSLs
and which are in good agreement with loops observed in Hα and X-rays
related to emerging flux. The evolution of the QSL width may explain
the brightness evolution of the XBP.
---------------------------------------------------------
Title: Emerging Flux, Reconnection, and XBP
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Demoulin, P.;
Mandrini, C.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein,
N.; Mein, P.
1996mpsa.conf..459V Altcode: 1996IAUCo.153..459V
No abstract at ADS
---------------------------------------------------------
Title: Emerging flux seen by Yohkoh.
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Mandrini, C.;
Démoulin, P.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.;
Mein, N.; Mein, P.
1996joso.proc..124V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Active Region Evolution and Flare Activity
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Hudson, H. S.
1996mpsa.conf..515N Altcode: 1996IAUCo.153..515N
No abstract at ADS
---------------------------------------------------------
Title: Hα surges and associated Soft X-ray loops
Authors: Schmieder, B.; Shibata, K.; van Driel-Gesztelyi, L.;
Freeland, S.
1995SoPh..156..245S Altcode:
A recurrent Hα surge was observed on 7 October, 1991 on the western
solar limb with the Meudon MSDP spectrograph. The GOES satellite
recorded X-ray subflares coincident with all three events. During
two of the surges high-resolutionYohkoh Soft X-ray Telescope (SXT)
images have been taken. Low X-ray loops overlying the active region
where the surges occurred were continuously restructuring. A flare
loop appeared at the onset of each surge event and somewhat separated
from the footpoint of the surge. The loops are interpreted as causally
related to the surges. It is suggested that surges are due to magnetic
reconnection between a twisted cool loop and open field lines. Cold
plasma bubbles or jets squeezed among untwisting magnetic field
lines could correspond to the surge material. No detection was made
of either X-ray emission along the path of the surges or X-ray jets,
possibly because of the finite detection threshold of theYohkoh SXT.
---------------------------------------------------------
Title: The Magnetic Evolution of the Activity Complex AR:7260 -
a Roadmap
Authors: Leka, K. D.; Canfield, R. C.; Mickey, D. L.; van
Driel-Gesztelyi, L.; Nitta, N.; Sakurai, T.; Ichimoto, K.
1994SoPh..155..301L Altcode:
The active region NOAA 7260 rotated onto the north solar hemisphere
as a mature bipole: a dominant negative-polarity sunspot with trailing
plage and scattered small spots in attendance. The dominantp spot itself
had strong magnetic fields and covered almost 400 × 10<SUP>−6</SUP>
of a solar hemisphere. For a period of seven days beginning 14 August,
1992 this active region displayed rapid and drastic evolution: no fewer
than 50 magnetic bipoles emerged in the area trailing the large sunspot,
increasing the region's magnetic flux by more than 10<SUP>22</SUP>
Mx. This new group of sunspots formed a complexβγδ configuration
with twoδ spots and a high degree of magnetic shear.
---------------------------------------------------------
Title: A Yohkoh search for “black-light flares”
Authors: van Driel-Gesztelyi, Lidia; Hudson, Hugh S.; Anwar, Bachtiar;
Hiei, Eijiro
1994SoPh..152..145V Altcode: 1994svs..coll..145V; 1994IAUCo.143..145V
Calculations which predict that a phenomenon analogous to stellar
negative pre-flares could also exist on the Sun were published by
Hénouxet al. (1990), and Aboudarhamet al., (1990), who showed that
at the beginning of a solar white-light flare (WLF) event an electron
beam can cause a transient darkening before the WLF emission starts,
under certain conditions. They named this event a "black light flare"
(BLF). Such a BLF event should appear as diffuse dark patches lasting
for about 20 seconds preceding the WLF emission, which would coincide
with intense and impulsive hard X-ray bursts. The BLF location would
be at (or in the vicinity of) the forthcoming bright patches. Their
predicted contrast depends on the position of the flare on the solar
disc and on the wavelength band of the observation.
---------------------------------------------------------
Title: Erratum: A study of surges and flares within an active region
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Gerlei, O.; Simnett,
G. M.
1994SoPh..151..399S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Relationship between electric currents, photospheric motions,
chromospheric activity, and magnetic field topology
Authors: van Driel-Gesztelyi, L.; Hofmann, A.; Demoulin, P.; Schmieder,
B.; Csepura, G.
1994SoPh..149..309V Altcode:
Through coordinated observations made during the Max'91 campaign in June
1989 in Potsdam (magnetograms), Debrecen (white light and Hα), and
Meudon (MSDP), we follow the evolution of the sunspot group in active
region NOAA 5555 for 6 days. The topology of the coronal magnetic field
is investigated by using a method based on the concept of separatrices -
applied previously (Mandriniet al., 1991) to a magnetic region slightly
distorted by field-aligned currents. The present active region differs
by having significant magnetic shear. We find that the Hα flare
kernels and the main photospheric electric current cells are located
close to the intersection of the separatrices with the chromosphere,
in a linear force-free field configuration adapted to the observed
shear. Sunspot motions, strong currents, isolated polarities, or
intersecting separatrices are not in themselves sufficient to produce a
flare. A combination of them all is required. This supports the idea
that flares are due to magnetic reconnection, when flux tubes with
field-aligned currents move towards the separatrix locations.
---------------------------------------------------------
Title: Evidence for Twisted Emerging Flux in NOAA AR 7260
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C.
1994ASPC...68..145L Altcode: 1994sare.conf..145L
No abstract at ADS
---------------------------------------------------------
Title: Diagnostics of Twisted Flux Emergence (noaa AR7260)
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Anwar, B.; Canfield,
R. C.; Hudson, H. S.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.;
Kurokawa, H.
1994xspy.conf...25L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flares in Active Region NOAA 7260
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Sakurai,
T.; Shibata, K.; Ichimoto, K.; Canfield, R. C.; Wülser, J. -P.;
Metcalf, T. R.; Mickey, D. L.
1994xspy.conf..111N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Emerging Flux Tube Geometry and Sunspot Proper Motions
Authors: van Driel-Gesztelyi, L.; Leka, K. D.
1994ASPC...68..138V Altcode: 1994sare.conf..138V
No abstract at ADS
---------------------------------------------------------
Title: Twisted Flux Tubes and Sunspot Motions in AR 5555
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Schmieder, B.;
Hofmann, A.; Csepura, G.
1994emsp.conf..115V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Study of Surges and Flares Within an Active Region
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Gerlei, O.; Simnett,
G. M.
1993SoPh..146..163S Altcode:
Active region 2684 was observed by the Solar Maximum Mission and
ground-based observatories simultaneously for over 12 hours on September
23, 1980. During these observations, recurrent surges were detected
above an area with complex parasitic magnetic polarity located at the
periphery of the active region. The time evolution of the Hα surges,
CIV brightenings and X-ray spikes leads to the conclusion that the
energy source is in the corona, from magnetic reconnection. The energy
is transported by energetic charged particles along the loops, thereby
heating the chromosphere as the particles lose their energy. The
divergent motion of the spots corresponding to small dipoles at
the base of the surge indicates that there is important magnetic
reorganisation. According to the magnetic field-line configuration
(large loop or open structures), X-rays can (or cannot) be associated
with surges.
---------------------------------------------------------
Title: Evidence for Twisted Emerging Flux: NOAA AR 7260
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C.; Anwar,
B.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.
1993BAAS...25R1187L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Common Evolution of Adjacent Sunspot Groups
Authors: van Driel-Gesztelyi, L.; Csepura, G.; Nagy, I.; Gerlei, O.;
Schmieder, B.; Rayrole, J.; Demoulin, P.
1993SoPh..145...77V Altcode:
The evolution of two adjacent bipolar sunspot groups is studied using
Debrecen full-disc, white-light photoheliograms and Hα filtergrams
as well as Meudon magnetograms. The proper motions of the principal
preceding spots of both groups show quite similar patterns; the
spots move along almost parallel tracks and change the direction
of their motion on the same day at almost the same heliographic
longitude. Also, three simultaneous emergences of magnetic flux were
observed in both groups. These observations support the idea that
these adjacent sunspot groups were magnetically linked below the
photosphere. Matching the extrapolated magnetic field lines with the
chromospheric fibril structure appears to be different in the two groups
since they indicate quite different model solutions for each group,
i.e., a near-potential magnetic field configuration in the older group
(1) and a twisted force-free field configuration in the younger group
(2). The latter configuration could be created by a considerable twist
of the main bunch of flux tubes in Group 2, which is reflected in the
relative sunspot motions. It is also showed how this twist contributed
to the formation of a filament between the two groups.
---------------------------------------------------------
Title: Evidence for magnetic reconnection in solar flares
Authors: Demoulin, P.; van Driel-Gesztelyi, L.; Schmieder, B.; Hemoux,
J. C.; Csepura, G.; Hagyard, M. J.
1993A&A...271..292D Altcode:
From a study of the magnetic field topology in an active region,
evidence is derived that solar flares are produced by magnetic
reconnection. We study a complex group with two active regions (AR
25 t 1 and AR 2512) for three consecutive days, June 13-15 1980. The
observed longitudinal magnetic field is used to model the coronal
magnetic field by the potential field created by a series of magnetic
charges. This computed field matches satisfactorily the Ho fibrils
and the observed transverse field direction. A set of flares occurs
principally in the northern group (AR 2511). During these three days,
two different magnetic configurations in succession are responsible
for the occurrence of these flares: first the intrusion of a new
opposite flux in the following polarity, secondly the emergence of new
flux between the main polarities. In this last case flares occurred,
although the emerging bipole is almost parallel to the main bipole. We
show that even in this bipolar configuration a separator is present
and that observed H flare ribbons are located near the intersection of
the computed separatrices with the photosphere. This provides strong
support to a model where reconnection releases the stored magnetic
energy. The induced evolution of the magnetic field forces reconnection
along others separators. They are connected by magnetic field lines
to fainter kernels.
---------------------------------------------------------
Title: Book reviews
Authors: van Driel-Gesztelyi, L.; Meynet, G.; Gaizauskas, V.; Cook,
J. W.; McKenna-Lawlor, S. M. P.; Garmany, C. D.; Jugaku, Jun; Lamers,
Henny J. G. L. M.; Achterberg, A.; De Greve, J. P.; Dommanget, J.;
van der Kruit, P. C.
1993SSRv...64..165V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotation Rates of Active Nests on the Sun
Authors: van Driel-Gesztelyi, L.; van der Zalm, E. B. J.; Zwaan, C.
1993ASPC...46..504V Altcode: 1993mvfs.conf..504V; 1993IAUCo.141..504V
No abstract at ADS
---------------------------------------------------------
Title: Book Review: Solar observations: techniques and interpretation
/ Cambridge U Press, 1991
Authors: van Driel Gesztelyi, L.
1993SSRv...64..167V Altcode: 1993SSRv...64..167S; 1993SSRv...64..167G
No abstract at ADS
---------------------------------------------------------
Title: Book Review: Opening the frontiers in solar research /
Pergamon, 1991
Authors: van Driel-Gesztelyi, Lidia; Bumba, V.; van Driel Gesztelyi, L.
1992SoPh..141..203V Altcode: 1992SoPh..141..203F
No abstract at ADS
---------------------------------------------------------
Title: Active Nests on the Sun
Authors: van Driel-Gesztelyi, Lidia; van der Zalm, Ed B. J.; Zwaan,
Cornelis
1992ASPC...27...89V Altcode: 1992socy.work...89V
No abstract at ADS
---------------------------------------------------------
Title: Conditions for flare and filament formation in interacting
solar active regions
Authors: Schmieder, B.; Henoux, J. -C.; van Driel-Gesztelyi, L.;
Simnett, G. M.
1991A&A...244..533S Altcode:
The evolution of two interacting sunspot groups of different ages is
traced over a period of three days. The photospheric velocity field is
obtained and compared with the general evolution of the region in an
attempt to better understand the conditions that lead to flare activity
and filament formation. It is shown that the observed photospheric
motions can generate dc electric currents, which, in effect, could
lead to energy storage.
---------------------------------------------------------
Title: Flares and filament formation due to the interaction between
two active regions
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Hénoux, J. C.;
Simnett, G.
1991AdSpR..11e..95S Altcode: 1991AdSpR..11...95S
We follow the evolution (flare activity, filament formation) of two
interacting active regions of different ages over three days, through
observations at white-light, Hα, UV, and X-ray wavelengths. We show
that the observed photospheric motions could generate DC electric
currents and that they could lead to free energy storage. Flares
were observed more-or-less simultaneously in remote locations of the
sunspot group. This suggests that the same perturbation affected an
ensemble of lines of force. Filament formation took place due to DC
current generation by photospheric shearing motions with a velocity
up to 350 m s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Effect of Electron Beams during Solar Flares
Authors: Aboudarham, J.; Henoux, J. C.; Brown, J. C.; van den Oord,
G. H. J.; van Driel-Gesztelyi, L.; Gerlei, O.
1990SoPh..130..243A Altcode:
Electron bombardment of the solar atmosphere has two effects: one is
to enhance hydrogen recombination emission, the other is to increase
the opacity via an increase of H<SUP>−</SUP> population. The first
effect is the most important in the upper part of the atmosphere and
the second in the lower part. We predict that, when enhanced absorption
dominates in the part of the atmosphere where radiation originates,
there will be a decrease in the white-light emission, leading to a
`negative flare', or what we call a `Black-Light Flare'. This phenomenon
occurs only for a short duration, not more than ∼ 20 s. `Black-Light
Flares' have already been observed in the case of flare stars and we
suggest here that they could also be present on the Sun, just prior
to a White-Light Flare.
---------------------------------------------------------
Title: Homologous and Homologous like Microwave Solar Radio Bursts
Authors: Trevisan, R. H.; Sawant, H. S.; Kalman, B.; Gesztelyi, L.
1990RMxAA..21..557T Altcode:
ABSTRACT. Solar radio observations at 1.6 GHz were carried out in the
month of July, 1985 by using 13.7 m diameter Itapetinga antenna with
time resolution of 3 ms. Homologous Bursts, with total duration of
about couple of seconds and repeated by some seconds were observed
associated with Homologous H- flares. These H- flares were having
periodicities of about 40 min. Observed long periodicities were
attributed to oscillation of prominences, and small periods were
attributed to removal of plasma from the field interaction zone. Also
observed are "Homologous-Like" bursts. These bursts are double peak
bursts with same time profile repeating in time. In addition to this,
the ratio of the total duration of the bursts to time difference in
the peaks of bursts remain constant. Morphological studies of these
bursts have been presented. Keq tuoit : SUN-BURSTS - SUN-FLARE
---------------------------------------------------------
Title: Black and white flares?
Authors: Henoux, J. -C.; Aboudarham, J.; Brown, J. C.; van den Oord,
G. H. J.; van Driel-Gesztelyi, L.
1990A&A...233..577H Altcode:
It is shown that the nonthermal ionization of a solar flare atmosphere
by beam bombardment can result, in the initial stages of a flare, in
dimunitions in the continuum solar flare brightness (termed 'black
light flares'). The most favorable conditions for observing this
diagnostic phenomenon are investigated in terms of flare location and
wavelength. In terms of bombarding beam parameters, electron beams
of large peak flux are shown to be the most favorable as are target
atmospheres with minimal preheating.
---------------------------------------------------------
Title: Asymmetric Flux Loops in Active Regions - Part Two
Authors: Petrovay, K.; Brown, J. C.; van Driel-Gesztelyi, L.; Fletcher,
L.; Marik, M.; Stewart, G.
1990SoPh..127...51P Altcode:
We propose that magnetic flux loops in the subphotospheric layers
of the Sun are seriously asymmetrical as a consequence of the drag
force exerted on them because of the different rotational rate of the
surrounding plasma. In numerical models of stationary slender flux
loops in the plane parallel approximation we show that a serious
tilt is both possible and probable. Observational facts (see van
Driel-Gesztelyi and Petrovay, 1989; Paper I) strongly support the case
for high asymmetry. The different stability of p and f spots may also
be related to such an asymmetry.
---------------------------------------------------------
Title: Asymmetric flux loops in active regions, I
Authors: van Driel-Gesztelyi, L.; Petrovay, K.
1990SoPh..126..285V Altcode: 1990SoPh..126..285G
We investigate asymmetries of bipolar sunspot groups. We find that
the magnetic field distribution of simple bipolar sunspot groups is
significantly asymmetrical: the polarity inversion line is usually
nearer to the main following polarity spot than to the main preceding
one. This asymmetry grows with the age of the sunspot group. We suggest
that this asymmetry has a causal link with two long-established
asymmetries- the one in the proper motions of young sunspots, the
other in the relative stability of p and f spots.
---------------------------------------------------------
Title: Negative Flares on the Sun
Authors: van Driel-Gesztelyi, L.; Brown, J. C.; Hénoux, J. -C.;
Aboudarham, J.; van den Oord, G. H. J.; Gerlei, O.; Fárnik, F.
1990PDHO....7..202V Altcode: 1990dysu.conf..202V; 1990ESPM....6..202V
The authors showed that under certain conditions at the beginning
of a solar white-light flare (WLF) event an electron beam can cause
a transient darkening before the WLF emission starts. They propose
optimal conditions for possible observation of solar negative flares and
present an observation, which may be the first identified observation
of such events.
---------------------------------------------------------
Title: Interaction between Bipolar Sunspot Groups
Authors: Csepura, G.; van Driel-Gesztelyi, L.; Nagy, I.; Gerlei, O.;
Schmieder, B.; Rayrole, J.
1990PDHO....7...88C Altcode: 1990ESPM....6...88C; 1990dysu.conf...88C
The authors find some evidence for the interaction of two close-by
developing sunspot groups.
---------------------------------------------------------
Title: Photospheric-induced destabilization and ejection of prominence
material
Authors: Raadu, M. A.; Schmieder, B.; Mein, N.; Gesztelyi, L.
1988A&A...197..289R Altcode:
The sequence of events leading up to prominence activation in two
different cases is studied. In one case, observed on September 3, 1980,
strong velocity shears were produced indicating filament twisting. In
the other case, observed on June 22, 1980, activation results in the
ejection of prominence material. The paper presents new evidence for a
common initial triggering mechanism, the birth or motion of pores at one
end of the activated filament sections. This is taken as an indication
of emerging magnetic flux and current induction in the filaments. The
difference in the final results is partly due to the different ambient
magnetic field structures. In particular in the case leading to material
ejection there is a subsequent associated flare occurred indicating
the storage of magnetic energy in the region. Models are proposed for
the two sequences of events, clarifying the underlying similarities
and interpreting the distinct features of the two sets of observations.
---------------------------------------------------------
Title: Solar Global Background Magnetic Field Changes Accompanying the
Development of the White-Light Flare Region of April 1984 (NOAA 4474)
Authors: Bumba, V.; Gesztelyi, L.
1988BAICz..39....1B Altcode:
In investigating the large-scale distribution changes of solar
background magnetic field during a wide time interval around the
formation of this very complex region, it is demonstrated that this
development must be taken as part of a global process in the solar
atmosphere. Complete reorganizations are seen in the magnetic active
longitude patterns and the solar magnetic-field sector structure,
clearly related to its maximum stage. It is also shown that, at
the same time, restructuralization of coronal holes took place. The
relation of large-scale cellularlike structures to this development
is also studied. It is concluded that the formation of this strong
white-light flare region was casually related to the rebuilding of
the global solar magnetic field.
---------------------------------------------------------
Title: Rotation of Individual Background Magnetic Field Components
During the Formation of the White-Light Flare Region of April 1984
(NOAA 4474)
Authors: Bumba, V.; Gesztelyi, L.
1987BAICz..38..351B Altcode:
In the present continuation of their study of processes related to the
development of the white-light flare region of April 1984, the authors
pay greater attention to the problem of rotation rates of certain
components of the background magnetic field, constituting the main
patterns of the weak as well as strong fields, from three points of
view: as they are demonstrated by the distribution of chromospheric
filaments, from point of view of the existence of so-called "pivot
points" (Mouradian et al., 1987) and of the rotation of the strongest
magnetic flux sources.
---------------------------------------------------------
Title: Local rigid rotation and the emergence of active centres
Authors: Mouradian, Z.; Martres, M. J.; Soru-Escaut, I.; Gesztelyi, L.
1987A&A...183..129M Altcode:
Deviations from the mean solar rotation rule of filaments are
frequent. They correspond to real physical behaviour. Using filaments as
tracers, limited solar areas of rigid rotation are observed: these are
"pivot points" around which the filaments rotate during two or more
successive rotations. It is shown that a relation exists between the
pivot points and Active Centres: many Active Centres appear close to a
pivot point whatever their latitude, whereas filaments which reveal the
classical differential rotation do not generate any Active Centres. The
magnetic flux emergence is associated in time with apparent reduced
speed of the filament tilt about the pivot point. Some examples show
that the relation exists using a reduced time scale of several days
as well. The new Active Centre may destroy or displace the associated
pivot point.
---------------------------------------------------------
Title: Photospheric Induced Destabilization and Ejection of Prominence
Material
Authors: Raadu, M. A.; Schmieder, B.; Mein, N.; Gesztelyi, L.
1987HvaOB..11..105R Altcode:
The cause of the sudden activation of solar prominences is not
clear. The authors present observations of two cases which were preceded
by the emergence and motion of pores (new flux) in the near vicinity
of the filaments, which seem to be closely related to the process which
triggered the filament destabilization. These observations may be well
described by a theoretical model in which the new flux interacts with
the older "stable" magnetic field.
---------------------------------------------------------
Title: High flare activity and redistribution of solar global
magnetic fields.
Authors: Bumba, V.; Hejna, L.; Gesztelyi, L.
1987PAICz..66..129B Altcode: 1987eram....1..129B
The authors demonstrate that both in the global scale and in the
scale of large and complex active regions the high flare activity
is closely related to the changes in the whole background magnetic
field distribution.
---------------------------------------------------------
Title: Starspot proper motion in HK Lac.
Authors: Oláh, K.; Gesztelyi, L.; Holl, A.
1987PAICz..70...95O Altcode: 1987eram....5...95O
HK Lac is a long period RS CVn system with complex behaviour due to
spots on the surface of the primary. Significant spot changes occur on
long time scales (years), sometimes changes are seen over a few stellar
rotation (months). The authors try to interpret these occasional events
as spot proper motions on the primary star of the system.
---------------------------------------------------------
Title: Sunspot groups as tracers of radial differential rotation.
Authors: Gesztelyi, L.; Pap, J.
1987PAICz..66...77G Altcode: 1987eram....1...77G
Measurements of the proper motions of young bipolar sunspot groups show
that these groups rotate faster than the surrounding photosphere. The
faster proper motion of the young sunspot groups as well as the 24
days periodicity of the young active spot areas might indicate that
the young sunspots are connected to the deeper regions of the Sun
which rotate faster than the photosphere. Thus, the sunspot groups
in the early stage of their life would be an indicator of rotation of
the deeper layers of the Sun.
---------------------------------------------------------
Title: Filament eruption connected to photospheric activity.
Authors: Simon, G.; Gesztelyi, L.; Schmieder, B.; Mein, N.
1986NASCP2442..229S Altcode: 1986copp.nasa..229S
Two cases of activation of filaments that occured in regions of
intense magnetic activity was studied. The simultaneous observations
from Debrecen Observatory (white light and H alpha filtergram), and
from Meudon Observatory (magnetogram, MSDP dopplergram and intensity
maps in H alpha) gave a complementary set of data from which can be
produced evidence of the influence of the photospheric magnetic field
on the destabilization process of the filaments. On June 22, 1980,
the eruption of the filament is associated with the motion of pores,
which are manifestations of emerging flux knots. On September 3, 1980,
the twisting motions in the filament are associated to the birth of
a pore in its neighborhood. These observations are discussed.
---------------------------------------------------------
Title: White light flares and atmospheric modeling (Working Group
report).
Authors: Machado, M. E.; Avrett, E. H.; Falciani, R.; Fang, C.;
Gesztelyi, L.; Henoux, J. -C.; Hiei, E.; Neidig, D. F.; Rust, D. M.;
Sotirovski, P.; Svestka, Z.; Zirin, H.
1986lasf.conf..483M Altcode:
The authors give a short summary of their discussions, and a set
of recommendations which may help in the study of white light flare
emission processes.
---------------------------------------------------------
Title: Motion of small sunspots in a channel
Authors: Gesztelyi, L.
1986CoSka..15..251G Altcode:
In the old bipolar sunspot group in Hale region 17117 new fluxes
emerged. Numerous small spots became settled to a curved shape channel
around the old leader spot. During 5 days (11 - 15 Sept. 1980) the
spots were emerging and moving along this channel or joined it,
irrespective of their polarities. This channel of sunspot motion
might be in connection with large-scale flows of photospheric or
sub-photospheric layers, perhaps with supergranular flows.
---------------------------------------------------------
Title: Sunspot proper motions in connection with the white-light
flare of 25 April 1984
Authors: Gesztelyi, L.; Kalman, B.
1986AdSpR...6f..21G Altcode: 1986AdSpR...6...21G
During the descending phase of the present cycle of solar activity
one of the largest events was the 3B/X13.0 white-light flare in
NOAA Active Region No. 4474 near the eastern limb on 24/25 April
1984. We present a study of the evolution of the very complex and
extended active region 4474, the proper motion of the sunspots and
the changes in the magnetic field in connection with the large flare,
with special emphasis on the magnetic shear and other possible types
of motion leading to flare build-up, and following the flare.
---------------------------------------------------------
Title: White-light flare of 26 July 1981.
Authors: Gesztelyi, L.; Karlicky, M.; Farnik, F.; Gerlei, O.;
Valnicek, B.
1986lasf.conf..163G Altcode: 1986lasf.symp..163G
Making use of series of white light heliograms the authors studied
the development of a flare-active sunspot group in Hale region 17760,
where a white-light flare (WLF) was observed on 26 July 1981. The
WLF appeared in a disintegrating delta-configuration, where rapid
motion of newly emerged spots and of separating fragments of older
umbrae was shearing and distorting the magnetic field. On the basis
of optical, X-ray and radio observations the authors analysed the WLF
event. Some observational indications exist supporting the hypothesis
that the WLF knots are situated in the places of concentrated electric
current which electrically couples sub-photospheric, photospheric
and higher layers. Provided this is true the WL emission has been
interpreted as the response of deep layers of the solar atmosphere to
the dissipation-spreading process propagating along the electric current
system. Intensity of the WLF knots relatively to the photosphere has
been deduced and the power emitted between 545 and 555 nm estimated. The
total energy emitted by the WLF knots is roughly estimated.
---------------------------------------------------------
Title: Preflare Activity of Solar Prominences
Authors: Simon, G.; Mein, N.; Mein, P.; Gesztelyi, L.
1984SoPh...93..325S Altcode:
The preflare activity of a plage filament is analysed from Hα
observations made with the Multichannel Subtractive Double Pass
Spectrograph (MSDP) of the Meudon Solar Tower. The June 22, 1980
event is studied and interpreted in terms of preflare heating of a
filament, connected to the rise of emerging flux, and the relative
approach of pores of different magnetic polarity, prior to the onset
of a two-ribbon flare.
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Title: Relationships of a growing magnetic flux region to flares
Authors: Martin, S. F.; Bentley, R. D.; Schadee, A.; Antalova, A.;
Kucera, A.; Dezső, L.; Gesztelyi, L.; Harvey, K. L.; Jones, H.;
Livi, S. H. B.; Wang, J.
1984AdSpR...4g..61M Altcode: 1984AdSpR...4...61M
Some sites for solar flares are known to develop where new magnetic
flux emerges and becomes abutted against opposite polarity pre-existing
magnetic flux (review by Galzauskas/1/). We have identified and analyzed
the evolution of such flare sites at the boundaries of a major new and
growing magnetic flux region within a complex of active regions, Hale
No. 16918. This analysis was done as a part of a continuing study of the
circumstances associated with flares in Hale Region 16918, which was
designated as an FBS target during the interval 18 - 23 June 1980. We
studied the initiation and development of both major and minor flares in
Hα images in relation to the identified potential flare sites at the
boundaries of the growing flux region and to the general development
of the new flux. This study lead to our recognition of a spectrum of
possible relationships of growing flux regions to flares as follows:
(1) intimate interaction with adjacent old flux - flare sites centered
at new/old flux boundary, (2) forced or “intimidated” interaction
in which new flux pushes old field having lower flux density towards a
neighboring old polarity inversion line where a flare then takes place,
(3) “influential” interaction - magnetic lines of force over an old
polarity inversion line, typically containing a filament, reconnect to
the new emerging flux; a flare occurs with erupting filament when the
magnetic field overlying the filament becomes too weak to prevent its
eruption, (4) inconsequential interaction - new flux region is too small
or has wrong orientation for creating flare conditions, (5) incidental -
flare occurs without any significant relationship to new flux regions.
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Title: Consecutive homologous flares and their relation to sunspot
motions
Authors: Gesztelyi, L.
1984AdSpR...4g..19G Altcode: 1984AdSpR...4Q..19G
The large sunspot group in Hale region 17098 was in the decaying
phase of its development when a new flux emerged in its middle part
on 3 September 1980. This region displayed chromospheric activity
all that day. By the next day the spot of highest velocity (0.37 km
s<SUP>-1</SUP>) formed a delta-configuration with one of the spots of
following polarity of the old group. The centre of the observed flares
was not in the vicinity of this spot moving parallel to the magnetic
zero-line, it was in the western part of the group, where two spots
were moving nearly perpendicularly to the magnetic zero-line (v=0.09
km s<SUP>-1</SUP>), and deformed the border of a gulf of opposite
polarity. With the changing configuration the form of the observed
flares also changed.
---------------------------------------------------------
Title: The development of activity in Hale region 17098 (28 August -
8 September 1980).
Authors: Gesztelyi, L.; Kondás, L.
1983PDHO....5..133G Altcode: 1984PDHO....5..133G
Proper motions and some respects of chromospheric activities of a
relatively simple large sunspot group were studied on the basis of
full-disc white light photoheliograms and Hα filtergrams. The large
sunspot group consisted of two, subsequently developing groups. In
the course of their development, the umbrae of the two groups collided
with each other. The observed chromospheric activity was relatively low.
---------------------------------------------------------
Title: Motions in the solar atmosphere associated with the white
light flare of 11 July 1978
Authors: Dezso, L.; Gesztelyi, L.; Kondas, L.; Kovacs, A.; Rostas, S.
1980SoPh...67..317D Altcode:
Series of white light heliograms and oft- and on-band Hα filtergrams
have been obtained, with an average spatial resolution of 1″, to study
the flare active McMath region 15403 on 11 July, 1978. A great number
of accurate heliographic positions were determined for the umbrae, the
white light flare patches and several bright Hα flare knots, as well
as along the principal zero filament and an arch prominence. Using the
measured heliographic coordinates of these objects their motions could
be analyzed in some detail. The velocities of several different objects
could be deduced from the coordinates. Since the heliocentric angle
of the region was about 45°, the variation in apparent heliographic
coordinates also enabled some variations in heights to be determined.
---------------------------------------------------------
Title: Umbral proper motions in the large sunspot group of the great
flare activity of August 1972.
Authors: Gesztelyi, L.
1977PDHO....3...93G Altcode:
No abstract at ADS
