Author name code: green
ADS astronomy entries on 2022-09-14
author:"Green, Lucie M."
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Title: The magnetic field environment of active region 12673 that
produced the energetic particle events of September 2017
Authors: Yardley, Stephanie L.; Green, Lucie M.; James, Alexander W.;
Stansby, David; Mihailescu, Teodora
Bibcode: 2022arXiv220812774Y
Altcode:
Forecasting solar energetic particles (SEPs), and identifying flare/CMEs
from active regions (ARs) that will produce SEP events in advance is
extremely challenging. We investigate the magnetic field environment
of AR 12673, including the AR's magnetic configuration, the surrounding
field configuration in the vicinity of the AR, the decay index profile,
and the footpoints of Earth-connected magnetic field, around the time
of four eruptive events. Two of the eruptive events are SEP-productive
(2017 September 4 at 20:00~UT and September 6 at 11:56~UT), while
two are not (September 4 at 18:05~UT and September 7 at 14:33~UT). We
analysed a range of EUV and white-light coronagraph observations along
with potential field extrapolations and find that the CMEs associated
with the SEP-productive events either trigger null point reconnection
that redirects flare-accelerated particles from the flare site to the
Earth-connected field and/or have a significant expansion (and shock
formation) into the open Earth-connected field. The rate of change of
the decay index with height indicates that the region could produce
a fast CME ($v >$ 1500~km~s$^{-1}$), which it did during events
two and three. The AR's magnetic field environment, including sites
of open magnetic field and null points along with the magnetic field
connectivity and propagation direction of the CMEs play an important
role in the escape and arrival of SEPs at Earth. Other SEP-productive
ARs should be investigated to determine whether their magnetic field
environment and CME propagation direction are significant in the escape
and arrival of SEPs at Earth.
Title: Disruption and eruption of magnetic flux ropes (observational
aspects)
Authors: Green, Lucie
Bibcode: 2022cosp...44.2409G
Altcode:
Observational studies of the source regions of coronal mass ejections
show increasing support for the progenitor of the eruption being a
twisted magnetic field configuration known as a flux rope, which exists
in the corona for some time before erupting through the interplay of
idea and non-ideal MHD processes. This talk will discuss the wide range
of observations that are used to infer the presence of a flux rope
before its eruption, and will emphasise the importance of monitoring
the evolution of the photospheric magnetic field and coronal plasma
emission structures over hours or days to support the conclusion of
flux rope presence. Furthermore, observations are able to supply
key information about the flux rope at the time of CME onset such
as estimated height and flux content, specific configuration of the
rope, plasma parameters. Once the eruption is underway observations
provide vital information about CME kinematics and the influence of
filament mass. These important observations are key to inform and
test CME models. A broad range of observational studies of flux rope
disruption and eruption will be reviewed, including those of soft
X-ray/EUV sigmoids, hot flux ropes, coronal cavities and stealth
CMEs. Illustrating a wide spectrum of events and helping understand
whether there are common aspects that may eventually build a canonical
description of CME processes.
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.
Bibcode: 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.
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
Bibcode: 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.
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.
Bibcode: 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.
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.
Bibcode: 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.
Title: Global Contributions of Active Regions to the Solar Wind
Authors: Stansby, David; Green, Lucie; van Driel-Gesztelyi, Lidia;
Horbury, Timothy
Bibcode: 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.
Title: Solar origins of a strong stealth CME detected by Solar Orbiter
Authors: O'Kane, Jennifer; Green, Lucie M.; Davies, Emma E.; Möstl,
Christian; Hinterreiter, Jürgen; Freiherr von Forstner, Johan L.;
Weiss, Andreas J.; Long, David M.; Amerstorfer, Tanja
Bibcode: 2021A&A...656L...6O
Altcode: 2021arXiv210317225O
Aims: We aim to locate the origin of a stealth coronal mass
ejection (CME) detected in situ by the MAG instrument on board Solar
Orbiter and make connections between the CME observed at the Sun and
the interplanetary CME (ICME) measured in situ.
Methods: Remote
sensing data were analysed using advanced image processing techniques to
identify the source region of the stealth CME, and the global magnetic
field at the time of the eruption was examined using potential field
source surface models. The observations of the stealth CME at the
Sun were compared with the magnetic field measured by the Solar
Orbiter spacecraft, and plasma properties were measured by the Wind
spacecraft.
Results: The source of the CME is found to be a quiet
Sun cavity in the northern hemisphere. We find that the stealth CME has
a strong magnetic field in situ, despite originating from a quiet Sun
region with an extremely weak magnetic field.
Conclusions: The
interaction of the ICME with its surrounding environment is the likely
cause of a higher magnetic field strength measured in situ. Stealth
CMEs require multi-wavelength and multi-viewpoint observations in
order to confidently locate the source region; however, their elusive
signatures still pose many problems for space weather forecasting. The
findings have implications for Solar Orbiter observing sequences with
instruments such as EUI that are designed to capture stealth CMEs.
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.
Bibcode: 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∘ in the corona, the solar wind they produce can reach
latitudes up to ±60∘. 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.
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
Bibcode: 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−1, 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−1 observed in
all active regions.
Title: The Magnetic Environment of a Stealth Coronal Mass Ejection
Authors: O'Kane, Jennifer; Mac Cormack, Cecilia; Mandrini, Cristina H.;
Démoulin, Pascal; Green, Lucie M.; Long, David M.; Valori, Gherardo
Bibcode: 2021ApJ...908...89O
Altcode: 2020arXiv201203757O
Interest in stealth coronal mass ejections (CMEs) is increasing due to
their relatively high occurrence rate and space weather impact. However,
typical CME signatures such as extreme-ultraviolet dimmings and
post-eruptive arcades are hard to identify and require extensive image
processing techniques. These weak observational signatures mean that
little is currently understood about the physics of these events. We
present an extensive study of the magnetic field configuration in which
the stealth CME of 2011 March 3 occurred. Three distinct episodes
of flare ribbon formation are observed in the stealth CME source
active region (AR). Two occurred prior to the eruption and suggest the
occurrence of magnetic reconnection that builds the structure that will
become eruptive. The third occurs in a time close to the eruption of
a cavity that is observed in STEREO-B 171 Å data; this subsequently
becomes part of the propagating CME observed in coronagraph data. We
use both local (Cartesian) and global (spherical) models of the coronal
magnetic field, which are complemented and verified by the observational
analysis. We find evidence of a coronal null point, with field lines
computed from its neighborhood connecting the stealth CME source region
to two ARs in the northern hemisphere. We conclude that reconnection
at the null point aids the eruption of the stealth CME by removing the
field that acted to stabilize the preeruptive structure. This stealth
CME, despite its weak signatures, has the main characteristics of
other CMEs, and its eruption is driven by similar mechanisms.
Title: Flaring activity and related eruptions from active regions
Authors: Green, Lucie; Long, David; Valori, Gherardo; O'Kane, Jennifer;
James, Alexander
Bibcode: 2021cosp...43E.992G
Altcode:
The Sun produces major eruptions, known as coronal mass ejections,
from a range of heights in its atmosphere and across a range of
kinematic and spatial scales. From compact, fast active region
eruptions to high-altitude, slow stealth CMEs. These eruptions are
the most energetic phenomena in the Solar System and CMEs that reach
the Earth can create severe space events. Many studies have now
shown that magnetic flux ropes are a fundamental component of the
pre-eruption corona in some cases. In addition, a key role appears
to be played by magnetic reconnection that evolves the pre-eruption
corona from a sheared arcade to a flux rope configuration, which can
then be destabilised by an ideal MHD process or by further magnetic
reconnection. This talk will look CMEs originating in active regions
covering the spectrum of events from energetic CMEs to low-energy
stealth CMEs, and will ask whether there are common processes taking
place across this wide range and whether flux ropes are involved in
all cases. A long-term perspective will be given using observational
and modelling results. The emergence of flux that forms the active
region will be discussed along with the evolution of this flux via
photospheric flows. Finally, thought will be given on the role of the
ambient coronal field on the destabilisation of the CME structure.
Title: Simulating the Coronal Evolution of Bipolar Active Regions
to Investigate the Formation of Flux Ropes
Authors: Yardley, S. L.; Mackay, D. H.; Green, L. M.
Bibcode: 2021SoPh..296...10Y
Altcode: 2020arXiv201207708Y
The coronal magnetic field evolution of 20 bipolar active regions (ARs)
is simulated from their emergence to decay using the time-dependent
nonlinear force-free field method of Mackay, Green, and van Ballegooijen
(Astrophys. J. 729, 97, 2011). A time sequence of cleaned photospheric
line-of-sight magnetograms, which covers the entire evolution of each
AR, is used to drive the simulation. A comparison of the simulated
coronal magnetic field with the 171 and 193 Å observations obtained
by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA), is made for each AR by manual inspection. The results show
that it is possible to reproduce the evolution of the main coronal
features such as small- and large-scale coronal loops, filaments and
sheared structures for 80% of the ARs. Varying the boundary and initial
conditions, along with the addition of physical effects such as Ohmic
diffusion, hyperdiffusion and a horizontal magnetic field injection
at the photosphere, improves the match between the observations and
simulated coronal evolution by 20%. The simulations were able to
reproduce the build-up to eruption for 50% of the observed eruptions
associated with the ARs. The mean unsigned time difference between the
eruptions occurring in the observations compared to the time of eruption
onset in the simulations was found to be ≈5 hrs. The simulations were
particularly successful in capturing the build-up to eruption for all
four eruptions that originated from the internal polarity inversion line
of the ARs. The technique was less successful in reproducing the onset
of eruptions that originated from the periphery of ARs and large-scale
coronal structures. For these cases global, rather than local, nonlinear
force-free field models must be used. While the technique has shown
some success, eruptions that occur in quick succession are difficult
to reproduce by this method and future iterations of the model need
to address this.
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.
Bibcode: 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.
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.
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.
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.
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. Movies associated to Figs. 4, 8, 12, and 14 are available at https://www.aanda.org
Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
Bibcode: 2020SSRv..216..131P
Altcode: 2020arXiv201010186P
A clear understanding of the nature of the pre-eruptive magnetic
field configurations of Coronal Mass Ejections (CMEs) is required
for understanding and eventually predicting solar eruptions. Only
two, but seemingly disparate, magnetic configurations are considered
viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
(MFR). They can form via three physical mechanisms (flux emergence,
flux cancellation, helicity condensation). Whether the CME culprit
is an SMA or an MFR, however, has been strongly debated for thirty
years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review
the status of the field across modeling and observations, identify
the open and closed issues, compile lists of SMA and MFR observables
to be tested against observations and outline research activities
to close the gaps in our current understanding. We propose that the
combination of multi-viewpoint multi-thermal coronal observations
and multi-height vector magnetic field measurements is the optimal
approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.
Title: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
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: The Magnetic Environment of a Stealth CME
Authors: O'Kane, J.; Mandrini, C.; Demoulin, P.; Green, L.; Valori,
G.; Long, D.
Bibcode: 2020SPD....5121005O
Altcode:
Interest in Stealth Coronal Mass Ejections (CMEs) is increasing due to
their relatively high occurrence rate and space weather impact. However,
typical CME signatures such as EUV dimmings and post-eruptive arcades
are hard to identify for stealth CMEs and require extensive image
processing techniques. These weak observational signatures mean little
is currently understood about the physics of these events. We present
an extensive study of the magnetic field configuration in which the
stealth CME of 3 March 2011 occurred. The magnetic field prior to the
eruption is evaluated using a Linear Force Free Field (LFFF) model
and a Potential Field Source Surface (PFSS) model, and complemented
by in-depth observational analysis. The models are verified using
observations of plasma emission structures in the stealth CME source
region and trans-equatorial loops. We find evidence of a high-altitude
null point in both the LFFF model and the PFSS model, with surrounding
field lines connecting two active regions on the solar disk. One of
these active regions in the Southern Hemisphere is shown to be the
source region of the stealth CME. Three distinct episodes of flare
ribbon formation are observed in AIA 304Å. Two occurred prior to
the eruption and suggest the occurrence of magnetic reconnection that
builds the eruptive structure. The third occurs at the same time as an
erupting cavity is observed in STEREO-B 171Å data; this subsequently
becomes part of the propagating CME observed in COR1. We conclude that
reconnection at the null point, driven by eruptive activity in the
complex northern active region, aids the eruption of the stealth CME
by removing field that acted to stabilise the pre-eruptive structure.
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.
Bibcode: 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 × 1020
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 × 1020 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 × 1031 ergs.
Title: Stealth Coronal Mass Ejections from Active Regions
Authors: O'Kane, Jennifer; Green, Lucie; Long, David M.; Reid, Hamish
Bibcode: 2019ApJ...882...85O
Altcode: 2019arXiv190712820O
Stealth coronal mass ejections (CMEs) are eruptions from the Sun that
have no obvious low coronal signature. These CMEs are characteristically
slower events but can still be geoeffective and affect space weather
at Earth. Therefore, understanding the science underpinning these
eruptions will greatly improve our ability to detect and, eventually,
forecast them. We present a study of two stealth CMEs analyzed using
advanced image processing techniques that reveal their faint signatures
in observations from the extreme-ultraviolet (EUV) imagers on board
the Solar and Heliospheric Observatory, Solar Dynamics Observatory,
and Solar Terrestrial Relations Observatory spacecraft. The different
viewpoints given by these spacecraft provide the opportunity to study
each eruption from above and the side contemporaneously. For each event,
EUV and magnetogram observations were combined to reveal the coronal
structure that erupted. For one event, the observations indicate the
presence of a magnetic flux rope before the CME’s fast-rise phase. We
found that both events originated in active regions and are likely
to be sympathetic CMEs triggered by a nearby eruption. We discuss the
physical processes that occurred in the time leading up to the onset
of each stealth CME and conclude that these eruptions are part of the
low-energy and velocity tail of a distribution of CME events and are
not a distinct phenomenon.
Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
Bibcode: 2019shin.confE.194P
Altcode:
Our thinking about the pre-eruptive magnetic configuration of Coronal
Mass Ejections has been effectively dichotomized into two opposing
and often fiercely contested views: namely, sheared magnetic arcades
and magnetic flux ropes. Finding a solution to this issue will have
important implications for our understanding of CME initiation. We
first discuss the very value of embarking into the arcade vs. flux rope
dilemma and illustrate the corresponding challenges and difficulties to
address it. Next, we are compiling several observational diagnostics of
pre-eruptive sheared magnetic arcades stemming from theory/modeling,
discuss their merits, and highlight potential ambiguities that could
arise in their interpretation. We finally conclude with a discussion
of possible new observables, in the frame of upcoming or proposed
instrumentation, that could help to circumvent the issues we are
currently facing.
Title: Coronal mass ejections: what can observations tell us about
the pre-eruptive magnetic field
Authors: Green, Lucie
Bibcode: 2019shin.confE.160G
Altcode:
Coronal mass ejections are the eruption of a vast volume of magnetised
plasma into the heliosphere and are the result of an energy storage and
release process. The energy to power these events is derived from free
energy in the coronal magnetic field. Understanding the processes that
lead to the accumulation of sufficient free energy, and the processes
by which the energy is released and used to drive the magnetised plasma
away from the Sun, are key questions in the study of CMEs. This talk
will give an overview of the current theories and show where we stand
in terms of our observations of CME source regions. In particular
the talk will discuss the origin and evolution of the pre-eruptive
magnetic field structure that goes on to form the core of the CME
as determined from EUV and soft X-ray emission structures that allow
us to probe the atmospheric magnetic field configuration and how it
evolves in the days before an eruption.
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
Bibcode: 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: The Origin, Early Evolution and Predictability of Solar
Eruptions
Authors: Green, Lucie M.; Török, Tibor; Vršnak, Bojan; Manchester,
Ward, IV; Veronig, Astrid
Bibcode: 2019sfsw.book..113G
Altcode:
No abstract at ADS
Title: Studying stealth CMEs using advanced imaging analysis
techniques
Authors: O'Kane, Jennifer; Green, Lucie; Long, David
Bibcode: 2018csc..confE..22O
Altcode:
Stealth coronal mass ejections (CMEs) are eruptions from the Sun that
have no obvious low coronal signature. These CMEs are characteristically
slower events, but can still be geoeffective and affect the space
weather at Earth. Therefore understanding the science underpinning
these eruptions will greatly improve our ability to detect and,
eventually, predict them. We present a study of two stealth CMEs
analysed using new advanced techniques that reveal their faint
signatures in observations from the EUV imagers onboard the SDO and
STEREO spacecraft. The different viewpoints of the events given by these
spacecraft provide the opportunity to study the eruption from above and
the side contemporaneously. For each event, we combined the AIA and HMI
observations to reveal the coronal structure that erupted and measured
the kinematics of the eruption. We discuss the physical processes that
occurred in the time leading up to the onset of each CME and comment
on whether these eruptions are the low-energy and velocity tail of the
distribution of CME events or whether they are a distinct phenomenon.
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
Bibcode: 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: 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.
Bibcode: 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: Coronal Magnetic Structure of Earthbound CMEs and In Situ
Comparison
Authors: Palmerio, E.; Kilpua, E. K. J.; Möstl, C.; Bothmer, V.;
James, A. W.; Green, L. M.; Isavnin, A.; Davies, J. A.; Harrison, R. A.
Bibcode: 2018SpWea..16..442P
Altcode: 2018arXiv180304769P
Predicting the magnetic field within an Earth-directed coronal
mass ejection (CME) well before its arrival at Earth is one of the
most important issues in space weather research. In this article,
we compare the intrinsic flux rope type, that is, the CME orientation
and handedness during eruption, with the in situ flux rope type for 20
CME events that have been uniquely linked from Sun to Earth through
heliospheric imaging. Our study shows that the intrinsic flux rope
type can be estimated for CMEs originating from different source
regions using a combination of indirect proxies. We find that only
20% of the events studied match strictly between the intrinsic and in
situ flux rope types. The percentage rises to 55% when intermediate
cases (where the orientation at the Sun and/or in situ is close to
45°) are considered as a match. We also determine the change in the
flux rope tilt angle between the Sun and Earth. For the majority of
the cases, the rotation is several tens of degrees, while 35% of the
events change by more than 90°. While occasionally the intrinsic flux
rope type is a good proxy for the magnetic structure impacting Earth,
our study highlights the importance of capturing the CME evolution
for space weather forecasting purposes. Moreover, we emphasize that
determination of the intrinsic flux rope type is a crucial input for
CME forecasting models.
Title: Key observations of Coronal Mass Ejections for improving
space weather Forecasting
Authors: Kilpua, Emilia; Palmerio, Erika; Pomoell, Jens; Lumme, Erkka;
Green, Lucie; James, Alexander; Asvestari, Eleanna
Bibcode: 2018EGUGA..20.8870K
Altcode:
Coronal mass ejections (CMEs) are key drivers of severe space weather
disturbances at Earth. The magnetic field is the most crucial parameter
in determining how geoeffective a particular CME will be. Unfortunately,
it is currently not possible to measure a CME's magnetic field remotely
in the corona or in the heliosphere and in-situ observations of Earth
impacting CMEs are only continuously available at the Lagrangian point
L1, from where it takes about 30 minutes for the solar wind to reach
Earth. This presents a huge limitation for accurate long-lead time
space weather forecasting. In this presentation, we discuss indirect
observational solar proxies that can be used to estimate a CME's
magnetic properties and the current status and challenges for using
photospheric magnetograms as the boundary conditions for data-driven
coronal or semi-empirical models
Title: Evaluating the forecasting skill of the near-Earth solar wind
using a space weather monitor at L5.
Authors: Thomas, Simon; Fazakerley, Andrew; Wicks, Rob; Green, Lucie
Bibcode: 2018EGUGA..20..273T
Altcode:
There is a considerable amount of interest from space agencies about
sending a space weather monitor to Lagrangian point 5 (L5). The
aim of such a mission would be to enable the forecasting of the
near-Earth solar wind and transient features embedded within in,
such as coronal mass ejections and corotating interaction regions,
from taking measurements at L5. Here, we use data from the STEREO and
ACE missions to find times when there are two spacecraft 60 degrees
apart to simulate this L5 to L1 scenario. When mapping the solar wind
data, we take into account the different orbits of the spacecraft and
the varying solar wind speed. We find that the predicted and observed
solar wind data are in generally very good agreement for each of the
periods. Using skill scores derived from meteorological forecasting, we
find that it is possible predict the solar wind much more effectively
from L5 than using a persistence forecast based on one solar rotation
before, with positive skill scores found for almost all events in a
number of important solar wind parameters. The skill improves further
for all time periods when removing coronal mass ejections which cannot
be predicted in this method. We also show that there is predictability
in the cross helicity, a parameter used to display the presence of
Alfvén waves in the solar wind.
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
Bibcode: 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: The Origin, Early Evolution and Predictability of Solar
Eruptions
Authors: Green, Lucie M.; Török, Tibor; Vršnak, Bojan; Manchester,
Ward; Veronig, Astrid
Bibcode: 2018SSRv..214...46G
Altcode: 2018arXiv180104608G
Coronal mass ejections (CMEs) were discovered in the early 1970s
when space-borne coronagraphs revealed that eruptions of plasma
are ejected from the Sun. Today, it is known that the Sun produces
eruptive flares, filament eruptions, coronal mass ejections and failed
eruptions; all thought to be due to a release of energy stored in
the coronal magnetic field during its drastic reconfiguration. This
review discusses the observations and physical mechanisms behind this
eruptive activity, with a view to making an assessment of the current
capability of forecasting these events for space weather risk and impact
mitigation. Whilst a wealth of observations exist, and detailed models
have been developed, there still exists a need to draw these approaches
together. In particular more realistic models are encouraged in order
to asses the full range of complexity of the solar atmosphere and the
criteria for which an eruption is formed. From the observational side,
a more detailed understanding of the role of photospheric flows and
reconnection is needed in order to identify the evolutionary path that
ultimately means a magnetic structure will erupt.
Title: Simulating the Coronal Evolution of AR 11437 Using SDO/HMI
Magnetograms
Authors: Yardley, Stephanie L.; Mackay, Duncan H.; Green, Lucie M.
Bibcode: 2018ApJ...852...82Y
Altcode: 2017arXiv171200396Y
The coronal magnetic field evolution of AR 11437 is simulated by
applying the magnetofrictional relaxation technique of Mackay et al. A
sequence of photospheric line-of-sight magnetograms produced by the
Solar Dynamics Observatory (SDO)/Helioseismic Magnetic Imager (HMI)
is used to drive the simulation and continuously evolve the coronal
magnetic field of the active region through a series of nonlinear
force-free equilibria. The simulation is started during the first
stages of the active region emergence so that its full evolution from
emergence to decay can be simulated. A comparison of the simulation
results with SDO/Atmospheric Imaging Assembly (AIA) observations
show that many aspects of the active region’s observed coronal
evolution are reproduced. In particular, it shows the presence of a
flux rope, which forms at the same location as sheared coronal loops
in the observations. The observations show that eruptions occurred
on 2012 March 17 at 05:09 UT and 10:45 UT and on 2012 March 20 at
14:31 UT. The simulation reproduces the first and third eruption,
with the simulated flux rope erupting roughly 1 and 10 hr before
the observed ejections, respectively. A parameter study is conducted
where the boundary and initial conditions are varied along with the
physical effects of Ohmic diffusion, hyperdiffusion, and an additional
injection of helicity. When comparing the simulations, the evolution
of the magnetic field, free magnetic energy, relative helicity and flux
rope eruption timings do not change significantly. This indicates that
the key element in reproducing the coronal evolution of AR 11437 is
the use of line-of-sight magnetograms to drive the evolution of the
coronal magnetic field.
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
Bibcode: 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: The 2013 February 17 Sunquake in the Context of the Active
Region's Magnetic Field Configuration
Authors: Green, L. M.; Valori, G.; Zuccarello, F. P.; Zharkov, S.;
Matthews, S. A.; Guglielmino, S. L.
Bibcode: 2017ApJ...849...40G
Altcode: 2017arXiv170904874G
Sunquakes are created by the hydrodynamic response of the lower
atmosphere to a sudden deposition of energy and momentum. In this study,
we investigate a sunquake that occurred in NOAA active region 11675
on 2013 February 17. Observations of the corona, chromosphere, and
photosphere are brought together for the first time with a nonlinear
force-free model of the active region’s magnetic field in order to
probe the magnetic environment in which the sunquake was initiated. We
find that the sunquake was associated with the destabilization of a
flux rope and an associated M-class GOES flare. Active region 11675
was in its emergence phase at the time of the sunquake and photospheric
motions caused by the emergence heavily modified the flux rope and its
associated quasi-separatrix layers, eventually triggering the flux
rope’s instability. The flux rope was surrounded by an extended
envelope of field lines rooted in a small area at the approximate
position of the sunquake. We argue that the configuration of the
envelope, by interacting with the expanding flux rope, created a
“magnetic lens” that may have focussed energy on one particular
location of the photosphere, creating the necessary conditions for
the initiation of the sunquake.
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.
Bibcode: 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: Evaluating the skill of forecasts of the near-Earth solar
wind using a space weather monitor at L5.
Authors: Thomas, Simon; Fazakerley, Andrew; Wicks, Rob; Green, Lucie
Bibcode: 2017EGUGA..19.3209T
Altcode:
There is a considerable amount of interest from space agencies about
sending a space weather monitor to Lagrangian point 5 (L5). The
aim of such a mission would be to enable the forecasting of the
near-Earth solar wind and transient features embedded within in,
such as coronal mass ejections and corotating interaction regions,
from taking measurements at L5. Here, we use data from the STEREO and
ACE missions to find times when there are two spacecraft 60 degrees
apart to simulate this L5 to L1 scenario. When mapping the solar wind
data, we take into account the different orbits of the spacecraft and
the varying solar wind speed. We find that the predicted and observed
solar wind data are in generally very good agreement for each of the
periods. Using skill scores derived from meteorological forecasting, we
find that it is possible predict the solar wind much more effectively
from L5 than using a persistence forecast based on one solar rotation
before, with positive skill scores found for almost all events in a
number of important solar wind parameters. The skill improves further
for all time periods when removing coronal mass ejections which cannot
be predicted in this method.
Title: Magnetic structure of Earth-directed events in the HELCATS
LINKCAT catalog during 2011-2013
Authors: Palmerio, Erika; Kilpua, Emilia; Bothmer, Volker; Isavnin,
Alexey; Möstl, Christian; Green, Lucie; James, Alexander; Davies,
Jackie; Harrison, Richard
Bibcode: 2017EGUGA..19.3874P
Altcode:
Coronal mass ejections (CMEs) are the main drivers of intense magnetic
storms and various subsequent space weather phenomena at Earth. The
parameter that defines the ability of a CME to drive geomagnetic
storms is the north-south magnetic field component. One of the most
significant problems in current long-term space weather forecasts is
that there is no practical method to measure the magnetic structure
of CMEs routinely in the outer corona. The magnetic structure of CME
flux ropes can however be inferred based on the properties of the
CME's source region characteristics, such as filament details, coronal
EUV arcades, X-ray sigmoids, taking into account nearby coronal and
photospheric features. The linked catalogue (LINKCAT) of solar CMEs
during the STEREO era is part of the HELCATS project. It aims at
connecting CME observations at the Sun and in interplanetary space,
using heliospheric imager observations from the HI1 cameras onboard the
two STEREO spacecraft to connect the different datasets. The HELCATS
LINKCAT catalogue contains 45 Earth-directed events in the period
2011-2013 (https://www.helcats-fp7.eu/catalogues/wp4_cat.html). Here we
present a statistical study based on the LINKCAT Earth-directed events
during 2011-2013 in which we determine the magnetic properties of
the erupting CMEs, i.e. their magnetic helicity sign, flux rope tilt,
and flux rope axial field direction, by using a synthesis of indirect
proxies based on multi-wavelength remote sensing observations from the
STEREO, SOHO, Hinode, and SDO satellites. These parameters define the
``intrinsic'' flux rope configuration at the time of the eruption which
is compared with the magnetic structures detected in situ near Earth.
Title: Determining the Intrinsic CME Flux Rope Type Using
Remote-sensing Solar Disk Observations
Authors: Palmerio, E.; Kilpua, E. K. J.; James, A. W.; Green, L. M.;
Pomoell, J.; Isavnin, A.; Valori, G.
Bibcode: 2017SoPh..292...39P
Altcode: 2017arXiv170108595P
A key aim in space weather research is to be able to use remote-sensing
observations of the solar atmosphere to extend the lead time of
predicting the geoeffectiveness of a coronal mass ejection (CME). In
order to achieve this, the magnetic structure of the CME as it
leaves the Sun must be known. In this article we address this issue
by developing a method to determine the intrinsic flux rope type of
a CME solely from solar disk observations. We use several well-known
proxies for the magnetic helicity sign, the axis orientation, and the
axial magnetic field direction to predict the magnetic structure of
the interplanetary flux rope. We present two case studies: the 2 June
2011 and the 14 June 2012 CMEs. Both of these events erupted from an
active region, and despite having clear in situ counterparts, their
eruption characteristics were relatively complex. The first event was
associated with an active region filament that erupted in two stages,
while for the other event the eruption originated from a relatively high
coronal altitude and the source region did not feature a filament. Our
magnetic helicity sign proxies include the analysis of magnetic
tongues, soft X-ray and/or extreme-ultraviolet sigmoids, coronal
arcade skew, filament emission and absorption threads, and filament
rotation. Since the inclination of the post-eruption arcades was not
clear, we use the tilt of the polarity inversion line to determine the
flux rope axis orientation and coronal dimmings to determine the flux
rope footpoints, and therefore, the direction of the axial magnetic
field. The comparison of the estimated intrinsic flux rope structure
to in situ observations at the Lagrangian point L1 indicated a good
agreement with the predictions. Our results highlight the flux rope
type determination techniques that are particularly useful for active
region eruptions, where most geoeffective CMEs originate.
Title: The Economic Impact of Space Weather: Where Do We Stand?
Authors: Eastwood, J. P.; Biffis, E.; Hapgood, M. A.; Green, L.;
Bisi, M. M.; Bentley, R. D.; Wicks, R.; McKinnell, L. A.; Gibbs, M.;
Burnett, C.
Bibcode: 2017RiskA..37..206E
Altcode:
Space weather describes the way in which the Sun, and conditions in
space more generally, impact human activity and technology both in
space and on the ground. It is now well understood that space weather
represents a significant threat to infrastructure resilience, and is
a source of risk that is wide-ranging in its impact and the pathways
by which this impact may occur. Although space weather is growing
rapidly as a field, work rigorously assessing the overall economic
cost of space weather appears to be in its infancy. Here, we provide
an initial literature review to gather and assess the quality of any
published assessments of space weather impacts and socioeconomic
studies. Generally speaking, there is a good volume of scientific
peer-reviewed literature detailing the likelihood and statistics
of different types of space weather phenomena. These phenomena all
typically exhibit "power-law" behavior in their severity. The literature
on documented impacts is not as extensive, with many case studies,
but few statistical studies. The literature on the economic impacts of
space weather is rather sparse and not as well developed when compared
to the other sections, most probably due to the somewhat limited data
that are available from end-users. The major risk is attached to power
distribution systems and there is disagreement as to the severity
of the technological footprint. This strongly controls the economic
impact. Consequently, urgent work is required to better quantify the
risk of future space weather events.
Title: <p>Prediction of In-Situ Magnetic Structure of Flux
Ropes from Coronal Observations.
Authors: Palmerio, E.; Kilpua, E.; James, A.; Green, L.; Pomoell,
J.; Isavnin, A.; Valori, G.; Lumme, E.
Bibcode: 2016AGUFMSH14A..03P
Altcode:
Coronal mass ejections (CMEs) are believed to be the main drivers
of intense magnetic storms and various space weather phenomena at
Earth. The most important parameter that defines the ability of a
CME to drive geomagnetic storms is the north-south magnetic field
component. One of the most significant problems in current long-term
space weather forecasts is that there is no method to directly
measure the magnetic structure of CMEs before they are observed in
situ. In recent years, CMEs have been successfully modeled as unstable
expanding flux ropes originating from low-corona, force-free flux
equilibria (either containing or forming a flux rope in the wake of the
instability). Due to their influence on the coronal plasma environment,
the magnetic structure of CME flux ropes can be indirectly estimated
based on the properties of the source active region and characteristics
of the nearby structures, such as filament details, coronal EUV arcades
and X-ray sigmoids. We present here a study of two CME flux ropes,
aiming at determining their magnetic properties (magnetic helicity
sign, flux rope tilt, and direction of the flux rope axial field)
when launched from the Sun by using a synthesis of indirect proxies
based on multi-wavelength remote sensing observations. In addition,
we employ a data-driven magnetofrictional method that models the CME
initiation in the corona to determine the magnetic structure in the
two case studies. Finally, the predictions given by the observational
synthesis and coronal modeling are compared with the structure detected
in situ at Earth.
Title: Prediction of in-situ magnetic structure of flux ropes from
coronal observations
Authors: Palmerio, Erika; Kilpua, Emilia K. J.; Pomoell, Jens;
James, Alexander; Green, Lucie M.; Isavnin, Alexey; Valori, Gherardo;
Lumme, Erkka
Bibcode: 2016usc..confE..33P
Altcode:
Coronal Mass Ejections (CMEs) are built at the Sun as nearly force-free
(J x B = 0) magnetic flux ropes. It is well-established that CMEs
are the main drivers of intense magnetic storms and various space
weather phenomena at Earth. The most important parameter that defines
the ability of a CME to drive geomagnetic storms is the north-south
magnetic field component. One of the most significant problems in
current long-term space weather forecasts is that there is no method
to directly measure the magnetic structure of CMEs before they are
observed in situ. However, due to their influence on the coronal
plasma environment, the magnetic structure of CME flux ropes can be
indirectly estimated based on the properties of the source active
region and characteristics of the nearby structures, such as filament
details, coronal EUV arcades and X-ray sigmoids. We present here a
study of two CME flux ropes, aiming at determining their magnetic
properties (magnetic helicity sign, flux rope tilt, and direction
of the flux rope axial field) when launched from the Sun by using a
synthesis of indirect proxies based on multi-wavelength remote sensing
observations. In addition, we employ a data-driven magnetofrictional
method that models the CME initiation in the corona to determine the
magnetic structure in the two case studies. Finally, the predictions
given by the observational synthesis and coronal modeling are compared
with the structure detected in situ at Earth.
Title: The Evolution of Active Regions
Authors: Green, Lucie
Bibcode: 2016usc..confE.109G
Altcode:
The solar corona is a highly dynamic environment which exhibits
the largest releases of energy in the Solar System in the form of
solar flares and coronal mass ejections. This activity predominantly
originates from active regions, which store and release free magnetic
energy and dominate the magnetic face of the Sun. Active regions can
be long-lived features, being affected by the Sun's convective flows,
differential rotation and meridional flows. The Sun's global coronal
field can be seen as the superposed growth and subsequent diffusion
of all previously formed active regions. This talk will look at active
regions as an observable product of the solar dynamo and will discuss
the physical processes that are at play which lead to the storage and
release of free magnetic energy. What happens to flux that emerges
into the corona so that it goes down an evolutionary path that leads
to dynamic activity? And how does this activity vary with active
region age? When an active region reaches the end of its lifetime,
his much of the magnetic flux is recycled back into subsequent solar
cycles? The current status of observations and modelling will be
reviewed with a look to the future and fundamental questions that are
still be be answered.
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.
Bibcode: 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 × 1021 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 ×
1021 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: 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
Bibcode: 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: Tracking the magnetic structure of flux ropes from eruption
to in-situ detection
Authors: Palmerio, Erika; Kilpua, Emilia; Green, Lucie; James,
Alexander; Pomoell, Jens; Valori, Gherardo
Bibcode: 2016EGUGA..18.1641P
Altcode:
Coronal Mass Ejections (CMEs) are spectacular explosions from the
Sun where huge amounts of plasma and magnetic flux are ejected into
the heliosphere. CMEs are built at the Sun as a force-free (J ×B =
0) magnetic flux rope. It is well-established that CMEs are the main
drivers of intense magnetic storms and various space weather effects
at the Earth. One of the most significant problems for improving the
long lead-time space weather predictions is that there is no method to
directly measure the structure of CME magnetic fields, neither in the
onset process nor during the subsequent propagation from the solar
surface to the Earth. The magnetic properties of the CME flux rope
(magnetic helicity sign, the flux rope tilt and the direction of the
flux rope axial field) can be estimated based on the properties of the
source active region and characteristics of the related structures, such
as filament details, coronal EUV arcades and X-ray sigmoids. We present
here a study of two CME flux ropes. We compare their magnetic structure
using the synthesis of these indirect proxies based on multi-wavelength
remote sensing observations with the structure detected in-situ near
the orbit of the Earth.
Title: Meeting contribution: At the edge: how leaving the solar
system can tell us more about the Sun
Authors: Green, L.
Bibcode: 2016JBAA..126R.114G
Altcode:
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.
Bibcode: 2016SoPh..291..335G
Altcode: 2015SoPh..tmp..179G
No abstract at ADS
Title: Mass ejections from the Sun
Authors: Green, Lucie M.
Bibcode: 2016IAUS..320..211G
Altcode:
Coronal mass ejections are the most spectacular form of solar activity
and they play a key role in driving space weather at the Earth. These
eruptions are associated with active regions and occur throughout
an active region's entire lifetime. All coronal mass ejection models
invoke the presence of a twisted magnetic field configuration known
as a magnetic flux rope either before or after eruption onset. The
observational identification of magnetic flux ropes in the solar
atmosphere using remote sensing data represents a challenging task,
but theoretical models have led to the understanding that there are
signatures that reveal their presence. The range of coronal mass
ejection models are helping build a more complete picture of both the
trigger and drivers of these eruptions.
Title: Spectroscopic Signatures Related to a Sunquake
Authors: Matthews, S. A.; Harra, L. K.; Zharkov, S.; Green, L. M.
Bibcode: 2015ApJ...812...35M
Altcode: 2015arXiv150807216M
The presence of flare-related acoustic emission (sunquakes (SQs))
in some flares, and only in specific locations within the flaring
environment, represents a severe challenge to our current understanding
of flare energy transport processes. In an attempt to contribute
to understanding the origins of SQs we present a comparison of
new spectral observations from Hinode’s EUV imaging Spectrometer
(EIS) and the Interface Region Imaging Spectrograph (IRIS) of the
chromosphere, transition region, and corona above an SQ, and compare
them to the spectra observed in a part of the flaring region with
no acoustic signature. Evidence for the SQ is determined using both
time-distance and acoustic holography methods, and we find that unlike
many previous SQ detections, the signal is rather dispersed, but that
the time-distance and 6 and 7 mHz sources converge at the same spatial
location. We also see some evidence for different evolution at different
frequencies, with an earlier peak at 7 mHz than at 6 mHz. Using EIS
and IRIS spectroscopic measurements we find that in this location, at
the time of the 7 mHz peak the spectral emission is significantly more
intense, shows larger velocity shifts and substantially broader profiles
than in the location with no SQ, and there is a good correlation between
blueshifted, hot coronal, hard X-ray (HXR), and redshifted chromospheric
emission, consistent with the idea of a strong downward motion driven by
rapid heating by nonthermal electrons and the formation of chromospheric
shocks. Exploiting the diagnostic potential of the Mg ii triplet lines,
we also find evidence for a single large temperature increase deep in
the atmosphere, which is consistent with this scenario. The time of the
6 mHz and time-distance peak signal coincides with a secondary peak
in the energy release process, but in this case we find no evidence
of HXR emission in the quake location, instead finding very broad
spectral lines, strongly shifted to the red, indicating the possible
presence of a significant flux of downward propagating Alfvén waves.
Title: Evolution of Active Regions
Authors: van Driel-Gesztelyi, Lidia; Green, Lucie May
Bibcode: 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: Sunquakes and their relationship with coronal magnetic topology
Authors: Green, Lucie; Zharkov, Sergei; Matthews, Sarah; Zharkova,
Valentina
Bibcode: 2015IAUGA..2253942G
Altcode:
Sunquakes were first predicted in 1972 by Wolff and are seen in
the Sun’s photosphere as a burst of outwardly emanating ripples,
caused by sudden a release of energy below the surface that produces
sound waves. Typically the formation of a sunquake is discussed in the
context of a solar flare in which a propagation of energy and momentum
downward from the corona occurs via accelerated particles, Lorentz
force transients, MHD wave conversion or so-called back-warming from
coronal and chromospheric radiation at the footpoints of the flare
loops. But many sunquakes also occur in concert with a coronal mass
ejection and therefore within a magnetic field that is evolving on an
active region-wide scale. More specifically, the locations of some of
these sunquakes have a magnetic connection to the erupting magnetic
field rather than the flare loops themselves.So, how can the sunquake
generation scenarios be informed/constrained by considering the overall
magnetic field configuration in which they are formed? This talk will
use data spanning the photosphere to corona to reveal the magnetic field
configuration and its evolution, so that sunquake generation scenarios
can be placed in the context of an erupting magnetic configuration
with associated energy and momentum transport.
Title: Mass eruptions from the Sun
Authors: Green, Lucie
Bibcode: 2015IAUGA..2253985G
Altcode:
This review talk will address the recent developments and current
understanding of the physical mechanisms that underlie the ejection
of matter and magnetic field from the atmosphere of the Sun, known
as coronal mass ejections. These eruptions are intitiated within and
between active regions throughout an active region's entire lifetime;
from the emergence phase, when strong and concentrated magnetic
fields are present, through the long decay phase during which time the
active region magnetic field fragments and disperses over a larger and
larger area, eventually fading into the background quiet sun magnetic
field. All coronal mass ejection models invoke the presence of a
twisted magnetic field configuration known as a magnetic flux rope
either before or after eruption. The observational identification of
these structures using remote sensing data of the lower solar atmosphere
will be discussed. Do such magnetic field configurations exist in the
solar atmosphere prior to the eruption? And if so what can they tell
us about the physical mechanisms that trigger and drive coronal mass
ejections and the timescales over which an eruptive magnetic field
configuration forms? However, not all coronal mass ejections are easily
identifiable at the Sun. For example, in situ observations of coronal
mass ejections in interplanetary space reveal small magnetic flux rope
coronal mass ejections which are not detected leaving the Sun using
the remote sensing data. And so-called stealth coronal mass ejections
which also have no lower atmosphere signatures. Are there different
populations of flux ropes that have different origins? And what might
this say about the physical mechanisms behind coronal mass ejections
and the consequences for the Sun's evolving global magnetic field?
Title: Carrington-L5: The UK/US Operational Space Weather Monitoring
Mission
Authors: Trichas, Markos; Gibbs, Mark; Harrison, Richard; Green,
Lucie; Eastwood, Jonathan; Bentley, Bob; Bisi, Mario; Bogdanova,
Yulia; Davies, Jackie; D'Arrigo, Paolo; Eyles, Chris; Fazakerley,
Andrew; Hapgood, Mike; Jackson, David; Kataria, Dhiren; Monchieri,
Emanuele; Windred, Phil
Bibcode: 2015Hipp....2l..25T
Altcode: 2015Hipp....2...25T
Airbus Defence and Space (UK) has carried out a study to investigate
the possibilities for an operational space weather mission, in
collaboration with the Met Office, RAL, MSSL and Imperial College
London. The study looked at the user requirements for an operational
mission, a model instrument payload, and a mission/spacecraft concept. A
particular focus is cost effectiveness and timelineness of the data,
suitable for 24/7 operational forecasting needs. We have focussed
on a mission at L5 assuming that a mission to L1 will already occur,
on the basis that L5 (Earth trailing) offers the greatest benefit for
the earliest possible warning on hazardous SWE events and the most
accurate SWE predictions. The baseline payload has been selected to
cover all UK Met Office/NOAA's users priorities for L5 using instruments
with extensive UK/US heritage, consisting of: heliospheric imager,
coronograph, magnetograph, magnetometer, solar wind analyser and
radiation monitor. The platform and subsystems are based on extensive
re-use from past Airbus Defence and Space spacecraft to minimize the
development cost and a Falcon-9 launcher has been selected on the same
basis. A schedule analysis shows that the earliest launch could be
achieved by 2020, assuming Phase A kick-off in 2015-2016. The study
team have selected the name "Carrington" for the mission, reflecting
the UK's proud history in this domain.
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.
Bibcode: 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: Atmospheric Response of an Active Region to New Small Flux
Emergence
Authors: Shelton, D.; Harra, L.; Green, L.
Bibcode: 2015SoPh..290..753S
Altcode: 2014arXiv1412.5623S; 2015SoPh..tmp....5S
We investigate the atmospheric response to a small emerging flux region
(EFR) that occurred in the positive polarity of Active Region 11236
on 23 - 24 June 2011. Data from the Solar Dynamics Observatory's
Atmospheric Imaging Assembly (AIA), the Helioseismic and Magnetic
Imager (HMI), and Hinode's EUV imaging spectrometer (EIS) are used
to determine the atmospheric response to new flux emerging into a
pre-existing active region. Brightenings are seen forming in the upper
photosphere, chromosphere, and corona over the EFR location whilst
flux cancellation is observed in the photosphere. The impact of the
flux emergence is far reaching, with new large-scale coronal loops
forming up to 43 Mm from the EFR and coronal upflow enhancements of
approximately 10 km s−1 on the north side of the EFR. Jets
are seen forming in the chromosphere and the corona over the emerging
serpentine field. This is the first time that coronal jets have been
seen over the serpentine field.
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.
Bibcode: 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: 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.
Bibcode: 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 (1010 cm-3) 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: Simulating the Formation of a Sigmoidal Flux Rope in AR10977
from SOHO/MDI Magnetograms
Authors: Gibb, G. P. S.; Mackay, D. H.; Green, L. M.; Meyer, K. A.
Bibcode: 2014ApJ...782...71G
Altcode:
The modeling technique of Mackay et al. is applied to simulate the
coronal magnetic field of NOAA active region AR10977 over a seven day
period (2007 December 2-10). The simulation is driven with a sequence
of line-of-sight component magnetograms from SOHO/MDI and evolves
the coronal magnetic field though a continuous series of non-linear
force-free states. Upon comparison with Hinode/XRT observations, results
show that the simulation reproduces many features of the active region's
evolution. In particular, it describes the formation of a flux rope
across the polarity inversion line during flux cancellation. The flux
rope forms at the same location as an observed X-ray sigmoid. After five
days of evolution, the free magnetic energy contained within the flux
rope was found to be 3.9 × 1030 erg. This value is more
than sufficient to account for the B1.4 GOES flare observed from the
active region on 2007 December 7. At the time of the observed eruption,
the flux rope was found to contain 20% of the active region flux. We
conclude that the modeling technique proposed in Mackay et al.—which
directly uses observed magnetograms to energize the coronal field—is
a viable method to simulate the evolution of the coronal magnetic field.
Title: Constraining magnetic flux emergence from a timeseries of
helicitigrams
Authors: Dalmasse, Kévin; Pariat, Etienne; Green, Lucie M.; Aulanier,
Guillaume; Demoulin, Pascal; Valori, Gherardo
Bibcode: 2014cosp...40E.612D
Altcode:
Magnetic helicity quantifies how globally twisted and/or sheared is
the magnetic field in a volume. Observational studies have reported
the injection of large amounts of magnetic helicity associated with
the emergence of magnetic flux into the solar atmosphere. Because
magnetic helicity is conserved in the convection zone, the injection of
magnetic helicity into the solar corona reflects the helicity content
of emerging magnetic flux tubes. Mapping the photospheric injection
of magnetic helicity thus seems to be a key tool for constraining the
parameters of the emerging flux tubes in numerical case-studies of
observed active regions. We recently developed a method to compute the
distribution of magnetic helicity flux. Contrary to previous proxies,
this method takes into account the 3D nature of magnetic helicity, and
is thus, better-suited to study the distribution of helicity flux. After
introducing this method, we will present the results of its application
to the NOAA AR 11158. We will show that, the distribution of helicity
flux is complex, with patterns of real mixed signals of helicity flux
related to the specific topology of the active region's magnetic
field. Finally, we will discuss the implications of our results on
the evolution and dynamics of this active region.
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
Bibcode: 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-1 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.
Bibcode: 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: Flares, CMEs and sunquakes
Authors: Zharkov, Sergei; Matthews, Sarah A.; Green, Lucie M.;
Zharkova, Valentina
Bibcode: 2014cosp...40E3823Z
Altcode:
Solar flares and coronal mass ejections (CMEs) are believed to be
manifestations of a sudden and rapid release of the accumulated magnetic
energy in the corona. Only recently, the photospheric changes due to
the reconnection and coronal magnetic field reconfiguration have been
seriously considered from the theoretical point of view. Analysis of
seismic emission (sun-quakes) induced in the solar interior in the
vicinity of flares offers us an opportunity to explore the physical
processes of energy transport in flaring atmospheres. Only a limited
number of M and X-class flares have been reported to show seismic
signatures in the form or ripples or egression sources, revealing
that some of the most powerful flares often do not produce any seismic
signatures. In fact, the most powerful signatures were recorded from
an M-class flare. This raises important questions about how the flare
energy and momentum are transported to the solar surface and interior
in order to produce sun-quakes. Using observations by Hinode, RHESSI
and SDO we analyse and test the new theories, gaining insight into
the flare physics using flare seismology.
Title: Observations of flux rope formation prior to coronal mass
ejections
Authors: Green, Lucie M.; Kliem, Bernhard
Bibcode: 2014IAUS..300..209G
Altcode: 2013arXiv1312.4388G
Understanding the magnetic configuration of the source regions
of coronal mass ejections (CMEs) is vital in order to determine
the trigger and driver of these events. Observations of four CME
productive active regions are presented here, which indicate that
the pre-eruption magnetic configuration is that of a magnetic flux
rope. The flux ropes are formed in the solar atmosphere by the process
known as flux cancellation and are stable for several hours before the
eruption. The observations also indicate that the magnetic structure
that erupts is not the entire flux rope as initially formed, raising
the question of whether the flux rope is able to undergo a partial
eruption or whether it undergoes a transition in specific flux rope
configuration shortly before the CME.
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.
Bibcode: 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: 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.
Bibcode: 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: First observational application of a connectivity-based
helicity flux density
Authors: Dalmasse, K.; Pariat, E.; Valori, G.; Démoulin, P.; Green,
L. M.
Bibcode: 2013A&A...555L...6D
Altcode: 2013arXiv1307.2838D
Context. Measuring the magnetic helicity distribution in the solar
corona can help in understanding the trigger of solar eruptive
events because magnetic helicity is believed to play a key role in
solar activity due to its conservation property.
Aims: A new
method for computing the photospheric distribution of the helicity
flux was recently developed. This method takes into account the
magnetic field connectivity whereas previous methods were based
on photospheric signatures only. This novel method maps the true
injection of magnetic helicity in active regions. We applied this
method for the first time to an observed active region, NOAA 11158,
which was the source of intense flaring activity.
Methods: We
used high-resolution vector magnetograms from the SDO/HMI instrument
to compute the photospheric flux transport velocities and to perform
a nonlinear force-free magnetic field extrapolation. We determined
and compared the magnetic helicity flux distribution using a purely
photospheric as well as a connectivity-based method.
Results:
While the new connectivity-based method confirms the mixed pattern
of the helicity flux in NOAA 11158, it also reveals a different, and
more correct, distribution of the helicity injection. This distribution
can be important for explaining the likelihood of an eruption from the
active region.
Conclusions: The connectivity-based approach is
a robust method for computing the magnetic helicity flux, which can
be used to study the link between magnetic helicity and eruptivity of
observed active regions.
Title: Properties of the 15 February 2011 Flare Seismic Sources
Authors: Zharkov, S.; Green, L. M.; Matthews, S. A.; Zharkova, V. V.
Bibcode: 2013SoPh..284..315Z
Altcode: 2012SoPh..tmp..292Z; 2012arXiv1208.4284Z
The first near-side X-class flare of Solar Cycle 24 occurred in
February 2011 (SOL2011-02-05T01:55) and produced a very strong
seismic response in the photosphere. One sunquake was reported
by Kosovichev (Astrophys. J. Lett.734, L15, 2011), followed by
the discovery of a second sunquake by Zharkov, Green, Matthews
et al. (Astrophys. J. Lett.741, L35, 2011). The flare had a
two-ribbon structure and was associated with a flux-rope eruption
and a halo coronal mass ejection (CME) as reported in the CACTus
catalogue. Following the discovery of the second sunquake and
the spatial association of both sources with the locations of the
feet of the erupting flux rope (Zharkov, Green, Matthews et al.,
Astrophys. J. Lett.741, L35, 2011), we present here a more detailed
analysis of the observed photospheric changes in and around the seismic
sources. These sunquakes are quite unusual, taking place early in
the impulsive stage of the flare, with the seismic sources showing
little hard X-ray (HXR) emission, and strongest X-ray emission sources
located in the flare ribbons. We present a directional time-distance
diagram computed for the second source, which clearly shows a ridge
corresponding to the travelling acoustic-wave packet and find that
the sunquake at the second source happened about 45 seconds to one
minute earlier than the first source. Using acoustic holography we
report different frequency responses of the two sources. We find strong
downflows at both seismic locations and a supersonic horizontal motion
at the second site of acoustic-wave excitation.
Title: On the Seismicity of September 7, 2011 X1.8-class Flare
Authors: Zharkov, S.; Green, L. M.; Matthews, S. A.; Zharkova, V. V.
Bibcode: 2013JPhCS.440a2046Z
Altcode: 2013arXiv1304.5805Z
We present results of our preliminary analysis of acoustically active
X-class flare of September 7, 2011. We report two acoustic sources
detected via acoustic holography and verified by finding a ridge
in time-distance diagrams. We compare the directional information
extracted from time-distance and acoustic holography, showing a good
agreement in this case. We report that the direction where amplitude of
the wave-front is the largest lies through the strong magnetic field
and sunspot, suggesting that absorption of the acoustic wave power
by magnetic field can be ruled out as a wave anisotropy mechanism in
this case.
Title: Photospheric Flux Cancellation and the Build-up of Sigmoidal
Flux Ropes on the Sun
Authors: Savcheva, A. S.; Green, L. M.; van Ballegooijen, A. A.;
DeLuca, E. E.
Bibcode: 2012ApJ...759..105S
Altcode:
In this study we explore the scenario of photospheric flux cancellation
being the primary formation mechanism of sigmoidal flux ropes in
decaying active regions. We analyze magnetogram and X-ray observations
together with data-driven non-linear force-free field (NLFFF) models of
observed sigmoidal regions to test this idea. We measure the total and
canceled fluxes in the regions from MDI magnetograms, as well as the
axial and poloidal flux content of the modeled NLFFF flux ropes for
three sigmoids—2007 February, 2007 December, and 2010 February. We
infer that the sum of the poloidal and axial flux in the flux ropes for
most models amounts to about 60%-70% of the canceled flux and 30%-50%
of the total flux in the regions. The flux measurements and the analysis
of the magnetic field structure show that the sigmoids first develop
a strong axial field manifested as a sheared arcade and then, as flux
cancellation proceeds, form long S-shaped field lines that contribute to
the poloidal flux. In addition, the dips in the S-shaped field lines are
located at the sites of flux cancellation that have been identified from
the MDI magnetograms. We find that the line-of-sight-integrated free
energy is also concentrated at these locations for all three regions,
which can be liberated in the process of eruption. Flare-associated
brightenings and flare loops coincide with the location of the X-line
topology that develops at the site of most vigorous flux cancellation.
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
Bibcode: 2012ExA....34..273T
Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1'' and 0.3''), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with
0.14'' per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
Title: Hinode Observations of an Eruption from a Sigmoidal Active
Region
Authors: Green, L. M.; Wallace, A. J.; Kliem, B.
Bibcode: 2012ASPC..454..391G
Altcode:
We analyse the evolution of a bipolar active region which produces an
eruption during its decay phase. The soft X-ray arcade develops high
shear over a time span of two days and transitions to sigmoidal shortly
before the eruption. We propose that the continuous sigmoidal soft X-ray
threads indicate that a flux rope has formed which is lying low in the
solar atmosphere with a bald patch separatrix surface topology. The
formation of the flux rope is driven by the photospheric evolution
which is dominated by fragmentation of the main polarities, motion due
to supergranular flows and cancellation at the polarity inversion line.
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.
Bibcode: 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: Photospheric flux cancellation and the build-up of sigmoidal
flux ropes
Authors: Savcheva, Antonia Stefanova; Green, L.; van Ballegooijen,
A.; DeLuca, E.
Bibcode: 2012shin.confE.122S
Altcode:
The magnetic structure of sigmoidal active regions is generally
associated with the presence of a twisted flux rope held down by a
potential arcade. There are competing theories of how the flux rope
develops - by flux emergence, cancellation, or footpoint motions. We
look at how flux cancellation in several sigmoidal regions, observed
with XRT, affects the buildup of the underlying flux ropes. We use
MDI magnetograms to quantify the flux cancellation, and the flux rope
insertion method to construct non-linear force free field models of the
regions. These models allow us to produce 3-D magnetic field models
and see how the fields evolve in time. The models show how the flux
ropes energy and magnetic flux changes during the different stages in
the flux cancellation. Flux cancellation events are associated with
build up of twist in the region in accordance with the accepted flux
cancellation picture. The location of flares and build-up of free
energy is well correlated with flux cancellation events.
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.
Bibcode: 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.
Bibcode: 2012SoPh..278....1G
Altcode:
No abstract at ADS
Title: On Signatures of Twisted Magnetic Flux Tube Emergence
Authors: Vargas Domínguez, S.; MacTaggart, D.; Green, L.; van
Driel-Gesztelyi, L.; Hood, A. W.
Bibcode: 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: The Effect of Flux Cancellation on Building Sigmoidal Flux
Ropes
Authors: Savcheva, Antonia; Green, L.; van Ballegooijen, A.; DeLuca, E.
Bibcode: 2012AAS...22041105S
Altcode:
The magnetic structure of sigmoidal active regions is generally
associated with the presence of a twisted flux rope held down by a
potential arcade. There are competing theories of how the flux rope
develops - by flux emergence, cancellation, or footpoint motions. We
look at how flux cancellation in several sigmoidal regions, observed
with XRT, affects the buildup of the underlying flux ropes. We use
MDI magnetograms to quantify the flux cancellation, and the flux rope
insertion method to construct non-linear force free field models of the
regions. These models allow us to produce 3-D magnetic field models
and see how the fields evolve in time. The models show how the flux
ropes energy and magnetic flux changes during the different stages in
the flux cancellation. Flux cancellation events are associated with
build up of twist in the region in accordance with the accepted flux
cancelation picture. The location of flares and build-up of free energy
is well correlated with flux cancellation events.
Title: Solar Particle Acceleration Radiation and Kinetics (SPARK). A
mission to understand the nature of particle acceleration
Authors: Matthews, Sarah A.; Williams, David R.; Klein, Karl-Ludwig;
Kontar, Eduard P.; Smith, David M.; Lagg, Andreas; Krucker, Sam;
Hurford, Gordon J.; Vilmer, Nicole; MacKinnon, Alexander L.; Zharkova,
Valentina V.; Fletcher, Lyndsay; Hannah, Iain G.; Browning, Philippa
K.; Innes, Davina E.; Trottet, Gerard; Foullon, Clare; Nakariakov,
Valery M.; Green, Lucie M.; Lamoureux, Herve; Forsyth, Colin; Walton,
David M.; Mathioudakis, Mihalis; Gandorfer, Achim; Martinez-Pillet,
Valentin; Limousin, Olivier; Verwichte, Erwin; Dalla, Silvia; Mann,
Gottfried; Aurass, Henri; Neukirch, Thomas
Bibcode: 2012ExA....33..237M
Altcode: 2011ExA...tmp..124M
Energetic particles are critical components of plasma populations
found throughout the universe. In many cases particles are accelerated
to relativistic energies and represent a substantial fraction of
the total energy of the system, thus requiring extremely efficient
acceleration processes. The production of accelerated particles
also appears coupled to magnetic field evolution in astrophysical
plasmas through the turbulent magnetic fields produced by diffusive
shock acceleration. Particle acceleration is thus a key component
in helping to understand the origin and evolution of magnetic
structures in, e.g. galaxies. The proximity of the Sun and the range
of high-resolution diagnostics available within the solar atmosphere
offers unique opportunities to study the processes involved in particle
acceleration through the use of a combination of remote sensing
observations of the radiative signatures of accelerated particles, and
of their plasma and magnetic environment. The SPARK concept targets the
broad range of energy, spatial and temporal scales over which particle
acceleration occurs in the solar atmosphere, in order to determine how
and where energetic particles are accelerated. SPARK combines highly
complementary imaging and spectroscopic observations of radiation from
energetic electrons, protons and ions set in their plasma and magnetic
context. The payload comprises focusing-optics X-ray imaging covering
the range from 1 to 60 keV; indirect HXR imaging and spectroscopy
from 5 to 200 keV, γ-ray spectroscopic imaging with high-resolution
LaBr3 scintillators, and photometry and source localisation
at far-infrared wavelengths. The plasma environment of the regions
of acceleration and interaction will be probed using soft X-ray
imaging of the corona and vector magnetography of the photosphere
and chromosphere. SPARK is designed for solar research. However,
in addition it will be able to provide exciting new insights into the
origin of particle acceleration in other regimes, including terrestrial
gamma-ray flashes (TGF), the origin of γ-ray bursts, and the possible
existence of axions.
Title: Forecasting a CME by Spectroscopic Precursor?
Authors: Baker, D.; van Driel-Gesztelyi, L.; Green, L. M.
Bibcode: 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−1 for three days at the AR's eastern and
western edges. However, on the fourth day, velocities intensified up to
20 km s−1 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: Implications for energy transport in solar flares from the
recent observations of sun-quakes
Authors: Matthews, S. A.; Zharkov, S.; Zharkova, V. V.; Green, L.;
Pedram, E.
Bibcode: 2011AGUFMSH51E..02M
Altcode:
Analysis of seismic emission (sun-quakes) induced in the solar
interior in the vicinity of flares offers us an opportunity to
explore the physical processes of energy transport in flaring
atmospheres. Only about 17 M and X-class flares have been reported to
show seismic signatures in the form or ripples or egression sources,
revealing that some of the most powerful flares often do not produce
any seismic signatures. In addition, the most powerful signatures
were recorded from an M-class flare. This raises important questions
about how the flare energy and momentum are transported to the solar
surface and interior in order to produce sun-quakes. Observations
of ripples associated with the first few sun-quakes suggested that
hydrodynamic shocks arising from a hydrodynamic response of the
ambient plasma to precipitation of energetic particles (electrons or
protons) are plausible sources of the seismic emission. Later, noting
that sun-quakes are often co-spatial with hard X-ray and white light,
another source of seismic emission was proposed related to back-warming
of the photosphere by the enhanced chromospheric and coronal radiation
caused by physical processes in flares. A third mechanism proposed to
account for sun-quakes is related to possible Lorentz force transients
that occur as a result of the coronal restructuring of the magnetic
field in flares. Recent work comparing samples of white-light flares
with and without sun-quakes, and new observations with GONG, Hinode
and SDO of seismic emission associated with the X-class flares of 14
December 2006 and 15 February 2011 demonstrate inconsistencies with
some existing models. In this paper these inconsistencies are explored
and possible alternative scenarios are discussed.
Title: 2011 February 15: Sunquakes Produced by Flux Rope Eruption
Authors: Zharkov, S.; Green, L. M.; Matthews, S. A.; Zharkova, V. V.
Bibcode: 2011ApJ...741L..35Z
Altcode: 2011arXiv1110.2005Z
We present an analysis of the 2011 February 15 X-class solar flare,
previously reported to produce the first sunquake in solar cycle
24. Using acoustic holography, we confirm the first, and report a
second, weaker, seismic source associated with this flare. We find
that the two sources are located at either end of a sigmoid, which
indicates the presence of a flux rope. Contrary to the majority of
previously reported sunquakes, the acoustic emission precedes the peak
of major hard X-ray (HXR) sources by several minutes. Furthermore,
the strongest HXR footpoints derived from RHESSI data are found to be
located away from the seismic sources in the flare ribbons. We account
for these discrepancies within the context of a phenomenological model
of a flux rope eruption and accompanying two-ribbon flare. We propose
that the sunquakes are triggered at the footpoints of the erupting flux
rope at the start of the flare impulsive phase and eruption onset,
while the main HXR sources appear later at the footpoints of the
flare loops formed under the rising flux rope. Possible implications
of this scenario for the theoretical interpretation of the forces
driving sunquakes are discussed.
Title: Recent sunquakes: new implications for energy transport in
solar flares
Authors: Zharkov, S.; Green, L. M.; Matthews, S. A.; Zharkova, V. V.
Bibcode: 2011sdmi.confE..89Z
Altcode:
It is well established that solar flares are initiated by magnetic
reconnection in the solar atmosphere/chromoshpere and extend to solar
corona with unconnected magnetic helical field and the material that
it contains sometimes violently expanding outwards forming a coronal
mass ejection. However, the flare energy transport to the underlying
photosphere is less understood. Sunquakes are tsunami-like acoustic
waves induced in the solar interior by solar flares. The theoretical
prediction that flares can excite acoustic waves in the underlying
photosphere was made in Wolff 1972, with first observations of the
phenomena reported in Kosovichev & Zharkova, 1998. Yet only a
limited number of M and X-class flares are known to have produced
seismic signatures in the form of ripples or egression sources, with
many of the most powerful flares being acoustically quiet. Furthermore,
some of the most powerful signatures were recorded from an M-class
flares. This raises important questions about how the flare energy
and momentum are transported to the solar surface and interior in
order to produce sun-quakes. Observations of ripples associated with
the first few sun-quakes suggested that hydrodynamic shocks arising
from a hydrodynamic response of the ambient plasma to precipitation of
energetic particles (electrons or protons) are plausible sources of the
seismic emission. Later, noting that sun-quakes are often co-spatial
with hard X-ray and white light, another source of seismic emission was
proposed related to back-warming of the photosphere by the enhanced
chromospheric and coronal radiation caused by physical processes
in flares. A third mechanism proposed to account for sun-quakes is
related to possible Lorentz force transients that occur as a result of
the coronal restructuring of the magnetic field in flares. Recent work
comparing samples of white-light flares with and without sun-quakes,
and new observations with GONG, Hinode and SDO of seismic emission
associated with the X-class flares of 14 December 2006 and 15 February
2011 demonstrate inconsistencies with some existing models. In this
work these inconsistencies are explored and possible alternative
scenarios are discussed.
Title: Photospheric Flux Cancellation and the Build-up of Sigmoidal
Flux Ropes
Authors: Savcheva, Antonia; Green, L.; DeLuca, E.; van Ballegooijen, A.
Bibcode: 2011SPD....42.1806S
Altcode: 2011BAAS..43S.1806S
The magnetic structure of sigmoidal active regions is generally
associated with the presence of a twisted flux rope held down by a
potential arcade. There are competing theories of how the flux rope
develops - by flux emergence, cancellation, or footpoint motions. We
look at how flux cancellation in several sigmoidal regions, observed
with XRT and AIA, affects the buildup of the underlying flux ropes. We
use MDI and HMI magnetograms to quantify the flux cancellation, and the
flux rope insertion method to construct non-linear force free field
models of the regions. We present magnetic maps and the 3D flux rope
structure. We correlate the locations of flares and build-up of free
energy and helicity with flux cancellation events. We show how the
flux ropes energy and flux budget changes with the different stages
in the flux cancellation.
Title: Modeling the Dispersal of an Active Region: Quantifying Energy
Input into the Corona
Authors: Mackay, Duncan H.; Green, L. M.; van Ballegooijen, Aad
Bibcode: 2011ApJ...729...97M
Altcode: 2011arXiv1102.5296M
In this paper, a new technique for modeling nonlinear force-free fields
directly from line-of-sight magnetogram observations is presented. The
technique uses sequences of magnetograms directly as lower boundary
conditions to drive the evolution of coronal magnetic fields between
successive force-free equilibria over long periods of time. It is
illustrated by applying it to SOHO: MDI observations of a decaying
active region, NOAA AR 8005. The active region is modeled during a
four-day period around its central meridian passage. Over this time,
the dispersal of the active region is dominated by random motions
due to small-scale convective cells. Through studying the buildup of
magnetic energy in the model, it is found that such small-scale motions
may inject anywhere from (2.5-3) × 1025 erg s-1
of free magnetic energy into the coronal field. Most of this energy
is stored within the center of the active region in the low corona,
below 30 Mm. After four days, the buildup of free energy is 10%
that of the corresponding potential field. This energy buildup is
sufficient to explain the radiative losses at coronal temperatures
within the active region. Small-scale convective motions therefore
play an integral part in the energy balance of the corona. This new
technique has wide ranging applications with the new high-resolution,
high-cadence observations from the SDO:HMI and SDO:AIA instruments.
Title: Photospheric flux cancellation and associated flux rope
formation and eruption
Authors: Green, L. M.; Kliem, B.; Wallace, A. J.
Bibcode: 2011A&A...526A...2G
Altcode: 2010arXiv1011.1227G
Aims: We study an evolving bipolar active region that exhibits
flux cancellation at the internal polarity inversion line, the formation
of a soft X-ray sigmoid along the inversion line and a coronal mass
ejection. The aim is to investigate the quantity of flux cancellation
that is involved in flux rope formation in the time period leading up
to the eruption.
Methods: The active region is studied using
its extreme ultraviolet and soft X-ray emissions as it evolves from
a sheared arcade to flux rope configuration. The evolution of the
photospheric magnetic field is described and used to estimate how much
flux is reconnected into the flux rope.
Results: About one third
of the active region flux cancels at the internal polarity inversion
line in the 2.5 days leading up to the eruption. In this period, the
coronal structure evolves from a weakly to a highly sheared arcade
and then to a sigmoid that crosses the inversion line in the inverse
direction. These properties suggest that a flux rope has formed prior
to the eruption. The amount of cancellation implies that up to 60% of
the active region flux could be in the body of the flux rope. We point
out that only part of the cancellation contributes to the flux in the
rope if the arcade is only weakly sheared, as in the first part of the
evolution. This reduces the estimated flux in the rope to ~30% or less
of the active region flux. We suggest that the remaining discrepancy
between our estimate and the limiting value of ~10% of the active region
flux, obtained previously by the flux rope insertion method, results
from the incomplete coherence of the flux rope, due to nonuniform
cancellation along the polarity inversion line. A hot linear feature
is observed in the active region which rises as part of the eruption
and then likely traces out the field lines close to the axis of the
flux rope. The flux cancellation and changing magnetic connections at
one end of this feature suggest that the flux rope reaches coherence
by reconnection immediately before and early in the impulsive phase
of the associated flare. The sigmoid is destroyed in the eruption but
reforms quickly, with the amount of cancellation involved being much
smaller than in the course of its original formation.
Title: Pre-Flare Flows in the Corona
Authors: Wallace, A. J.; Harra, L. K.; van Driel-Gesztelyi, L.; Green,
L. M.; Matthews, S. A.
Bibcode: 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 1.38×1020 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: Meeting Report: Looking ahead for space science
Authors: Green, Lucie; Forsyth, Colin; Wild, Jim
Bibcode: 2010A&G....51c..23G
Altcode:
MEETING REPORT A joint UKSP/MIST missions forum was held as part
of this year's National Astronomy Meeting. It was a lively session
with discussion focused on current and future mission plans in the
area of heliospheric physics, and on how young researchers can be
involved. Lucie Green, Colin Forsyth and Jim Wild report.
Title: Discussion of a high-energy mission for solar eruptions in
ESA's Cosmic Vision Programme
Authors: Kontar, Eduard; MacKinnon, Alexander; Klein, Karl-Ludwig;
Vilmer, Nicole; Green, Lucie M.; Matthews, Sarah A.
Bibcode: 2010cosp...38.2983K
Altcode: 2010cosp.meet.2983K
In this paper we emphasize the effect of a self-induced electric field
on the distributions of electron beams during their precipitation
into flaring atmospheres and their hard X-ray (HXR) and microwave (MW)
emission. For the beam precipitation the time-dependent Fokker-Planck
approach is applied by taking into account collisional and Ohmic
losses in a converging magnetic field with different level of
convergence. The energy range of beam electrons covers from 12 keV to
1.2 MeV, for HXR emission angle-dependent relativistic cross-sections
are considered, for MW the effects of radiative transfer of ordinary
and extra-ordinary waves are also taken into account. We compare the
effects of self-induced electric field on the HXR and MW emission and
polarization in flares. We also produce some recommendation for future
interpretation of the simultaneous HXR and MW 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.
Bibcode: 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-1, whereas
downflows of up to 30 km s-1 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-1
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: Flux Rope Formation Preceding Coronal Mass Ejection Onset
Authors: Kliem, Bernhard; Green, L. M.
Bibcode: 2009SPD....41.2120K
Altcode:
We analyse the evolution of a sigmoidal (S shaped) active region toward
eruption, which includes a coronal mass ejection (CME) but leaves part
of the filament in place. The X-ray sigmoid is found to trace out three
different magnetic topologies in succession: a highly sheared arcade
of coronal loops in its long-lived phase, a bald-patch separatrix
surface (BPSS) in the hours before the CME, and the first flare loops
in its major transient intensity enhancement. The coronal evolution
is driven by photospheric changes which involve the convergence and
cancellation of flux elements under the sigmoid and filament. The data
yield unambiguous evidence for the existence of a BPSS, and hence a
flux rope, in the corona prior to the onset of the CME.
Title: Flux Rope Formation Preceding Coronal Mass Ejection Onset
Authors: Green, L. M.; Kliem, B.
Bibcode: 2009ApJ...700L..83G
Altcode: 2009arXiv0906.4794G
We analyze the evolution of a sigmoidal (S-shaped) active region toward
eruption, which includes a coronal mass ejection (CME) but leaves part
of the filament in place. The X-ray sigmoid is found to trace out three
different magnetic topologies in succession: a highly sheared arcade
of coronal loops in its long-lived phase, a bald-patch separatrix
surface (BPSS) in the hours before the CME, and the first flare loops
in its major transient intensity enhancement. The coronal evolution
is driven by photospheric changes which involve the convergence and
cancellation of flux elements under the sigmoid and filament. The data
yield unambiguous evidence for the existence of a BPSS, and hence a
flux rope, in the corona prior to the onset of the CME.
Title: Temperature Tomography of a Coronal Sigmoid Supporting the
Gradual Formation of a Flux Rope
Authors: Tripathi, Durgesh; Kliem, Bernhard; Mason, Helen E.; Young,
Peter R.; Green, Lucie M.
Bibcode: 2009ApJ...698L..27T
Altcode: 2009arXiv0904.4782T
Multiwavelength observations of a sigmoidal (S-shaped) solar coronal
source by the EUV Imaging Spectrometer and the X-Ray Telescope
aboard the Hinode spacecraft and by the EUV Imager aboard STEREO are
reported. The data reveal the coexistence of a pair of J-shaped hot
arcs at temperatures T>2 MK with an S-shaped structure at somewhat
lower temperatures (T ≈ 1-1.3 MK). The middle section of the S-shaped
structure runs along the polarity inversion line of the photospheric
field, bridging the gap between the arcs. Flux cancellation occurs
at the same location in the photosphere. The sigmoid forms in the
gradual decay phase of the active region, which does not experience
an eruption. These findings correspond to the expected signatures
of a flux rope forming, or being augmented, gradually by a topology
transformation inside a magnetic arcade. In such a transformation, the
plasma on newly formed helical field lines in the outer flux shell of
the rope (S-shaped in projection) is expected to enter a cooling phase
once the reconnection of their parent field line pairs (double-J shaped
in projection) is complete. Thus, the data support the conjecture that
flux ropes can exist in the corona prior to eruptive activity.
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.
Bibcode: 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: 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.
Bibcode: 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: 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
Bibcode: 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.
Bibcode: 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: Multi-Spacecraft Study of the 21 January 2005 ICME. Evidence of
Current Sheet Substructure Near the Periphery of a Strongly Expanding,
Fast Magnetic Cloud
Authors: Foullon, C.; Owen, C. J.; Dasso, S.; Green, L. M.; Dandouras,
I.; Elliott, H. A.; Fazakerley, A. N.; Bogdanova, Y. V.; Crooker, N. U.
Bibcode: 2007SoPh..244..139F
Altcode:
We examine the near-Earth Interplanetary Coronal Mass Ejection (ICME)
apparently related to the intense Solar Energetic Particle (SEP) event
of 20 January 2005. Our purpose is to contribute to the understanding of
the macroscopic structure, evolution and dynamics of the solar corona
and heliosphere. Using Cluster, ACE and Wind data in the solar wind,
and Geotail data in the magnetosheath, we perform a multi-spacecraft
analysis of the ICME-driven shock, post-shock magnetic discontinuities
and ejecta. Traversals by the well-separated near-Earth spacecraft
provide a coherent picture of the ICME geometry. Following the shock,
the ICME sequence starts with a hot pileup, i.e., a sheath, followed by
a fast ejecta characterised by a non-compressive density enhancement
(NCDE), which is caused essentially by an enrichment in helium. The
plasma and magnetic observations of the ejecta are consistent with the
outskirts of a structure in strong expansion, consisting of nested
magnetic loops still connected to the Sun. Within the leading edge
of the ejecta, we establish the presence of a tilted current sheet
substructure. An analysis of the observations suggests that the tilted
current sheet is draped within the overlying cloud canopy, ahead of a
magnetic cloud-like structure. The flux rope interpretation of this
structure near L1, confirmed by observations of the corresponding
magnetic cloud, provided by Ulysses at 5.3 AU and away from the Sun -
Earth line, indicates that the bulk of the cloud is in the northwest
sector as seen from the Earth, with its axis nearly perpendicular to
the ecliptic. This is consistent with the primary direction of travel
of the fast halo CME observed at the Sun. Moreover, the NCDE and helium
enrichment are consistent with the position near the streamer belt of
the flaring active region NOAA 10720 associated with the CME. However,
differences between interplanetary and solar observations indicate a
large rotation of the erupting filament and overlying arcade, which
can be attributed to the flux rope being subject to the helical kink
instability.
Title: Reaching out through the heliosphere
Authors: Green, Lucie
Bibcode: 2007A&G....48d..24G
Altcode:
No abstract at ADS
Title: Green: International Heliophysical Year: International
Heliophysical Year is here
Authors: Green, Lucie
Bibcode: 2007A&G....48b..21G
Altcode:
Understanding the fundamental processes that take place throughout
the solar system requires a research programme on an international
scale. International Heliophysical Year, launched on 19 February this
year, aims to bring this research area to centre-stage and provide
a focus and a co-ordinated approach. Here I describe the aims and
approaches of UK scientists in this international arena.
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.
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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: Cellular and molecular effects of high-LET radiation on human
neural stem cells and neurons
Authors: Vazquez, M.; Guida, P.; Green, L.; Chang, P.; Otto, S.
Bibcode: 2004cosp...35.3061V
Altcode: 2004cosp.meet.3061V
Because successful operations in space depend in part on the performance
capabilities of astronauts, radiation-induced neurological damage could
jeopardize the successful completion of mission requirements, as well
as have long-term consequences on the health of astronauts. As such,
understanding the nature of this risk may be vital to the effective
performance of astronauts during future missions in space. This paper
describes the neural cell responses to conventional and charged
particles radiation in cell culture systems. One of the goals
is to characterize radiation-induced neural cell damage pathways;
especially those related to apoptosis induction and its modification
by pharmacological manipulation. Our laboratory utilizes the method
of flow cytometry to measure the induction of apoptosis and necrosis
in cells. Neural stem cells (NT2) were exposed to the different ions;
we measured a dose-dependent induction of apoptosis. NT2 cells were
exposed to graded doses of 1 and 5 GeV/n Fe, 0.29 GeV/n C, 1 GeV/n
Ti, and 0.6 GeV/n Si ions and samples were taken at 48 hours after
exposure. The percentage of apoptotic cells in culture was measured
by FITC-Annexin V by flow cytometry. Similar data obtained from
NT2 cells exposed to 255 MeV/n protons and 137Cs are included for
comparison. Preliminary RBE calculations demonstrated that iron
ions are more effective in inducing apoptosis. Exposure of cells
to ionizing radiation produces changes in the expression of many
genes as cells react to this insult. At present, the identities
of the molecular changes that occur in response to HZE radiation
remain largely unknown. In an effort to reveal this information, we
screened an array (Superarray) of p53-related genes with RNA purified
from NT2 cells mock irradiated or exposed to 50 cGy of 1 GeV/n iron
ions. Preliminary results indicated that the expression of numerous
critical genes was altered 3 hours after HZE radiation exposure. By
performing Western blot analysis on NT2 cells exposed to 5 GeV/n iron
ions, we demonstrated a time and dose dependent increase in p53 protein
levels. This induction occurred as early as 6 hours post-irradiation,
and was detectable with a dose as low as 10 cGy. Meanwhile, the levels
of the structural protein actin did not change in these cell samples,
assuring accurate protein quantization and equal loading from sample
to sample. We have also shown a time and dose dependent increase in p53
protein levels in terminally differentiated human neuronal (hNT) cells
exposed to 1 GeV/n iron ions. Using a more detailed protocol of early
harvesting times, we determined that p53 accumulated in these neuronal
cells within 8 hours after irradiation. Our laboratory's demonstration
that HZE radiation exposure results in a dose dependent induction of
p53 protein, concomitant with our finding of a dose dependent induction
of apoptosis in the neural stem (NT2) cells, strongly implies that
p53 plays a major role in this HZE radiation-induced apoptosis response.
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.
Bibcode: 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 soft X-ray characteristics of solar flares, both with
and without associated CMEs
Authors: Kay, H. R. M.; Harra, L. K.; Matthews, S. A.; Culhane, J. L.;
Green, L. M.
Bibcode: 2003A&A...400..779K
Altcode:
The complex relationship between solar flares and coronal mass ejections
is investigated using a comparison of flare parameters for a total
of 69 ejective and non-ejective flares. In the case of solar flares
which do not show mass ejection there seems to be a clear relationship
between the peak intensity and duration, with higher intensity events
being of longer duration. Systematic differences in the relationship
between peak temperature and intensity for the two types of event are
also evident, with flares associated with CMEs tending to have lower
peak temperatures than non-ejective events of the same intensity. Whilst
there appears to be a clear relationship between the length of rise and
decay phase in a flare, there are no systematic differences in these
parameters for ejective and non-ejective flares. A total of eleven
``EIT waves'' were found, all of which were associated with CMEs. There
is no apparent correlation between the occurrence of an EIT wave and
the peak temperature, intensity or rise time of the associated flare.
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.
Bibcode: 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: 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.
Bibcode: 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
(≈−7×1042 Mx2) 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: 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.
Bibcode: 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: 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.
Bibcode: 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: Active region helicity evolution and related coronal mass
ejection activity.
Authors: Green, L.; Mandrini, C.; van Driel-Gesztelyi, L.; Demoulin, P.
Bibcode: 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: Magnetic field configurations and the likelihood of coronal
mass ejections
Authors: Culhane, J. L.; Glover, A.; Green, L. M.; Harra, L. K.;
Matthews, S. A.; Hori, K.
Bibcode: 2001ESASP.493..193C
Altcode: 2001sefs.work..193C
No abstract at ADS
Title: Coronal mass ejections and their association to active
region flaring.
Authors: Green, L. M.; Harra, L. K.; Matthews, S. A.; Culhane, J. L.
Bibcode: 2001SoPh..200..189G
Altcode:
Since the discovery of coronal mass ejections (CMEs), flaring has been
thought to be associated in some way with the ejection in either cause
or effect. When CMEs were first discovered in the 1970s it was suggested
that they were powered by solar flares (e.g., Dryer, 1982). Research
since then (Harrison, 1986) has indicated that there is an associated
flare that occurs shortly after the CME. To investigate this further,
and making no assumption that a particular flare is causally connected
to the CME, flaring activity in nine active regions that show one or
more CME signatures has been studied for several hours before and after
CME launch. Although the initiation of the CME may occur on size scales
larger than the active region itself, definite changes are seen in
the flaring activity which may be related to the ejection. This work
indicates that the energy released from the active region magnetic
field via flaring is greater prior to the CME launch than after.
Title: Cepheus X-4
Authors: Roche, P.; Green, L.; Hoenig, M.
Bibcode: 1997IAUC.6698....2R
Altcode: 1997IAUC.6698R...1R
P. Roche and L. Green, University of Sussex; and M. Hoenig, Institute
of Astronomy, Cambridge, report: "We propose the identification of the
transient 66-s x-ray pulsar Cepheus X-4 = GS 2138+56 (IAUC 2493, 2512,
4575, 4577), with a V = 14.2 Be star, located at R.A. = 21h39m30s.6,
Decl. = +56d59'12".9 (equinox 2000.0), based on positional coincidence
with the ROSAT error circle of Schulz, Kahabka and Zinnecker (1995,
A.Ap. 295, 413). The object displays Balmer (H-alpha equivalent width
= 5.3 nm) and Fe II emission on a B0 or earlier spectrum, indicating
a strong Be phase. Given current indications of x-ray activity from
RXTE ASM, optical and infrared monitoring are encouraged."
Title: God and the Big-Bang
Authors: Green, L.
Bibcode: 1985JRASC..79..160G
Altcode:
Modern ideas of the origin of the Universe in a unique event, the "Big
Bang", are discussed in the light of some traditional philosophies
and of Christian theology.