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2011 February 15: Sunquakes Produced by Flux Rope Eruption

TL;DR: In this article, the authors 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.
Abstract: 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.

Summary (2 min read)

1. INTRODUCTION

  • Solar quakes, first observed by Kosovichev & Zharkova (1998), are seen as ripples in the photosphere which move radially outward from a source region.
  • The theoretical prediction that sunquakes should be produced by the energy released during major solar flares (Wolff 1972) was supported by their discovery on the Sun by Kosovichev & Zharkova (1998).
  • Not all flares show seismic activity as concluded by Besliu-Ionescu et al. (2005) and Donea et al. (2006b), who reported a catalog of only 17 flares of X and M class with measurable seismic activity detected by either holographic or time–distance approaches.
  • The energy released during an irreversible magnetic field change was found to be sufficient to account for the whole flare emission (Zharkova et al. 2005).

2. OBSERVATIONS AND DATA PROCESSING

  • The authors use full disk Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) observations, from which the helioseismic datacubes are extracted by remapping and derotating the region of interest using Postel projection and Snodgrass differential rotation rate.
  • From the velocity running difference datacubes the authors measure the acoustic egression following the processing as outlined in Donea et al. (1999), Lindsey & Braun (2000), and Donea et al. (2000).
  • The Green’s functions are obtained by solving the non- magnetic wave equation for monochromatic point source via geometric optics.
  • RHESSI observed the flare from the pre-cursor phase beginning at 01:27 UT until 02:30 UT, covering the entire impulsive phase.

3.1. Active Region Features

  • The sunquake occurred in NOAA active region 11158, which began emerging in the eastern hemisphere on the 2011 February 10.
  • The occurrence of a sigmoid in the active region gives strong support to the presence of a magnetic flux rope at this location (Green & Kliem 2009).
  • The halo CME was first seen in LASCO C2 above the occulting 3.
  • RHESSI images obtained with CLEAN procedure were used to provide spatially resolved light curves of the HXR sources in the vicinity of the egression sources and the main flare ribbons .

3.2. Two Seismic Sources

  • Computed egression power snapshots for 6, 7, and 10 mHz frequency bands taken around the times of the peak in the acoustic emission are shown in Figure 1.
  • The eastern source (Source 1), which corresponds to the acoustic source reported by Kosovichev (2011), is larger and stronger, clearly seen in all frequency bands of computed egression snapshots.
  • The strongest HXR emission is also situated primarily at the site of the flare loops , with the peaks apparently corresponding to the sites of maximum magnetic field changes, some distance away from the seismic sources.
  • In the velocity data the downward propagating shocks are seen around 01:49–01:50 UT at both sunquake locations.
  • The intensities of HXR emission in the locations of ribbons exceeds 100 times those in the locations of seismic sources .

4. DISCUSSION AND CONCLUSIONS

  • Unlike most previously detected sunquakes, the two seismic sources detected for this event are located away from the sources of very bright HXR emission.
  • Their J-shapes represent the location of the intersection of this QSL with the lower solar atmosphere (Démoulin et al. 1996).
  • This reconnection brings in surrounding arcade field and produces the flare loops seen in SXR and EUV emission , and also forms helical field lines that wrap around the flux rope body (Titov & Démoulin 1999) and further enhance the speed of the eruption .
  • The timing and the location of the egression emission sources indicate that not only are the seismic responses generated at the feet of the erupting flux rope, but that they are generated close in time to the flare/CME onset.
  • The authors thank Dr. B. Kliem for many useful discussions.

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The Astrophysical Journal Letters, 741:L35 (6pp), 2011 November 10 doi:10.1088/2041-8205/741/2/L35
C
2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
2011 FEBRUARY 15: SUNQUAKES PRODUCED BY FLUX ROPE ERUPTION
S. Zharkov
1
, L. M. Green
1
, S. A. Matthews
1
, and V. V. Zharkova
2
1
UCL Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT, UK
2
Department of Mathematics, University of Bradford, Bradford BD7 1DP, UK
Received 2011 July 15; accepted 2011 October 4; published 2011 October 20
ABSTRACT
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.
Key words: Sun: coronal mass ejections (CMEs) Sun: helioseismology Sun: flares Sun: particle emission
sunspots Sun: X-rays, gamma rays
Online-only material: animation, color figures
1. INTRODUCTION
Solar quakes, first observed by Kosovichev & Zharkova
(1998), are seen as ripples in the photosphere which move
radially outward from a source region. They are produced as
acoustic waves travel into the Sun and refract back to the
photosphere. Sunquakes are normally detected via helioseismic
methods such as the construction of time–distance diagrams
(Kosovichev & Zharkova 1998; Kosovichev 2007; Zharkova
& Zharkov 2007) or acoustic holography’s egression analysis
(Donea et al. 1999; Donea & Lindsey 2005;Zharkovetal.2011).
Analysis of sunquakes offers us an opportunity to explore the
physical processes of energy transport in flaring atmospheres.
The theoretical prediction that sunquakes should be pro-
duced by the energy released during major solar flares (Wolff
1972) was supported by their discovery on the Sun by
Kosovichev & Zharkova (1998). Following the first quake obser-
vation, further events were detected with holography techniques
(Donea & Lindsey 2005; Donea et al. 2006a) and time–distance
(Kosovichev 2006, 2007). These events showed an associa-
tion either with X-class flares, such as those on 2003 Oc-
tober 28 and 29 (Donea & Lindsey 2005), or with M-class
flares such as that on 2001 September 9 (Donea et al. 2006a).
However, not all flares show seismic activity as concluded by
Besliu-Ionescu et al. (2005) and Donea et al. (2006b), who
reported a catalog of only 17 flares of X and M class with
measurable seismic activity detected by either holographic or
time–distance approaches. These observations posed the ques-
tion of how the energy and momentum are transported to the
solar surface and interior in order to produce sunquakes and why
some of the most powerful flares often do not deliver seismic
signatures.
Many of the previously detected seismic ripples and acoustic
sources associated with flares were found tobe cospatial with the
hard X-ray (HXR) source locations (the vast majority reported
in Besliu-Ionescu et al. 2005; Donea et al. 2006b), while in
some flares the seismic sources were cospatial with γ sources
(Zharkova & Zharkov 2007; Kosovichev 2007). These cases
support the idea of sunquakes being produced by hydrodynamic
shocks induced by the ambient plasma heating either by electron
(Kosovichev & Zharkova 1998; Kosovichev 2007)orproton
beams (Zharkova & Zharkov2007). Zharkova & Zharkov (
2007)
suggested that apart f rom high energy proton or electron beams,
jet protons with quasi-thermal energy distributions can also be
the source of acoustic emission and seismic ripples. Such jets,
with maxima shifted to several MeV, can be ejected from a
current sheet during the magnetic reconnection process (see, for
example, B
´
arta et al. 2011 and references therein).
Donea et al. (2006a) noted that in many cases considered
by Besliu-Ionescu et al. (2005) the location of acoustic sources
was cospatial with and had an energy range similar to the white
light emission from t hese flares. As a result, it was proposed
that back-warming heating of the photosphere by the overlying
radiation from the corona and chromosphere was the source of
acoustic emission (see, for example, Donea et al. 2006a; Donea
2011, and references therein).
On the other hand, Hudson et al. (2008) noted that the
energy associated with the reconfiguration of the magnetic
field during a flare, the so-called McClymont jerk, can eas-
ily account for the energy required for a sunquake. Ob-
servationally this reconfiguration is seen in the line-of-sight
magnetic field in the photospheric as an abrupt and perma-
nent magnetic field change (Kosovichev & Zharkova 2001;
Zharkova et al. 2005; Sudol & Harvey 2005). The energy
released during an irreversible magnetic field change was
found to be sufficient to account for the whole flare emis-
sion (Zharkova et al. 2005). Hudson et al. (2008) suggested
that the seismic emission is initiated directly by these mag-
netic pulses in the form of magnetoacoustic waves (Cally 2000;
Mart
´
ınez-Oliveros et al. 2008;Mart
´
ınez-Oliveros & Donea
2009). However, in a study of two flares with sunquakes
Mart
´
ınez-Oliveros & Donea (2009) found inconclusive results.
1

The Astrophysical Journal Letters, 741:L35 (6pp), 2011 November 10 Zharkov et al.
Figure 1. First row: magnetogram, magnetogram difference, and intensity images. Second row: egression power snapshots at different frequencies taken on 2011
February 15. Third row (left to right): two AIA 1700 Å snapshots and an AIA 94 Å image showing flare ribbons. On all images, the blue contours are 2011 February
15 01:49:57 6 mHz egression power snapshots at 2.5 and 3 times quiet-Sun egression power. Red contours are the 10 mHz egression power (same time) at threeand
four times quiet-Sun egression power. The images are remapped onto heliographic grid; the distance is plotted in Megameters.
(A color version of this figure is available in the online journal.)
The 2011 February 15 X2.2-class flare was the first in the
much delayed rising activity phase of the new solar cycle
24. Kosovichev (2011) has reported that the flare produced a
sunquake clearly seen as propagating circular ripples in running
difference filtered velocity images of the surface. We present a
new study that detects more seismic sources in this flare using
holographic methods, and an investigation of their dynamics by
taking into account the morphology of the active region and
the occurrence of a coronal mass ejection (CME) in association
with the flare. We describe the data i n Section 2, report on
the photospheric and coronal observations in Section 3, and
discuss possible sunquake production in the context of a flux
rope eruption and two-ribbon flare model in Section 4.
2. OBSERVATIONS AND DATA PROCESSING
We use full disk Solar Dynamics Observatory (SDO) Helio-
seismic and Magnetic Imager (HMI) observations, from which
the helioseismic datacubes are extracted by remapping and de-
rotating the region of interest using Postel projection and Snod-
grass differential rotation rate. In this waywe obtain 45 s cadence
datacubes of HMI line-of-sight velocity, magnetogram, and in-
tensity images. The spatial resolution for the remapped data is
0.04 heliographic degrees per pixel. The center of the extracted
region is located at 20
latitude south and 11.
75 longitude to the
east. The series starts at 00:59 UT 2011 February 15 and runs
for 3 hr.
From the velocity running difference datacubes we measure
the acoustic egression following the processing as outlined in
Donea et al. (1999), Lindsey & Braun (2000), and Donea et al.
(2000). The Green’s functions are obtained by solving the non-
magnetic wave equation for monochromatic point source via
geometric optics. To study the flare onset we use the data
from SDOs Atmospheric Imaging Assembly (AIA) instrument
obtained for the same period at 1700 Å and 94 Å wavelengths.
The HXR data presented in this paper are derived from
RHESSI (Lin et al. 2002) with the Hinode X-Ray Telescope
(XRT; Golub et al. 2007) providing data for soft X-ray infor-
mation. RHESSI observed the flare from the pre-cursor phase
beginning at 01:27 UT until 02:30 UT, covering the entire impul-
sive phase. We used the CLEAN algorithm to produce images
at between 20 and 40 s cadences covering the duration of the
flare.
3. RESULTS
3.1. Active Region Features
The sunquake occurred in NOAA active region 11158, which
began emerging in the eastern hemisphere on the 2011 February
10. Two bipoles emerged side by side creating a complex
multipolar region. As the active region evolved through both
emergence and cancellation events the coronal loops became
increasingly sheared, and by late February 14 the loops in the
northern part of the active region showed a forward S-shaped
sigmoidal structure in soft X-rays and EUV emission (Figures 1
and 2). The occurrence of a sigmoid in the active region gives
strong support to the presence of a magnetic flux rope at this
location (Green & Kliem 2009). The sigmoid formed along a
polarity inversion line, where the flux cancellation provides the
mechanism by which the helical field lines of the flux rope can
be formed from a s heared arcade (van Ballegooijen & Martens
1989; Green et al. 2011).
2

The Astrophysical Journal Letters, 741:L35 (6pp), 2011 November 10 Zharkov et al.
Figure 2. T op row shows RHESSI counts (over the whole region). The next row shows RHESSI data integrated over egression sources. The vertical lines correspond
to 01:50 UT and 01:56 UT. Bottom row (left to right): Hinode XRT image showing the sigmoid and RHESSI contours for the following energy ranges: 12–25 keV
(middle plot) and 6–12 keV (right). The arcsecond coordinates are plotted along the x-andy-axes. The red and blue contours are as in Figure 1.
(A color version of this figure is available in the online journal.)
Figure 3. AIA 94 Å data showing the evolution of the coronal structure at the onset of the flare, CME, and sunquake. A “loop-like” feature is seen to erupt away from
the body of the sigmoid (white arrow in left-hand panels). The stack plot shows a slice across the sigmoid in the direction of the motion of erupting structure. The
erupting structure is indicated by the black arrow in the stack plot (right) obtained along the line shown in the image at 01:48:26 UT. Distance along the line is plotted
along the y-axis in the stack plot, with values for 0 and 1 indicated in the snapshot.
(An animation and a color version of this figure are available in the online journal.)
On 2011 February 15, AR 11158 produced a CME with the
eruption being evidenced by the rise of a linear loop-like feature
in AIA 94 Å data (see Figure 3 and the online animation). The
CACTus CME catalog observed a halo CME in LASCO C2.
3
The halo CME was first seen in LASCO C2 above the occulting
3
The CME is actually listed as three separate CMEs: numbers 34, 35, and 36
at http://sidc.oma.be/cactus/catalog/LASCO/2_5_0/qkl/2011/02/.
3

The Astrophysical Journal Letters, 741:L35 (6pp), 2011 November 10 Zharkov et al.
Figure 4. Velocity, intensity, and magnetic field variations integrated over 6 mHz egression kernels (using a 2.5 factor of quiet-Sun egression value as a threshold).
The bottom plot is egression rms at 6 mHz. The vertical lines correspond to 01:50 UT and 01:56 UT.
disk to the southwest at 02:24 UT and had a plane-of-sky
velocity of between 274 and 469 km s
1
. The true CME velocity
may have been considerably higher as the CME originated near
Sun center.
The CME was accompanied by an X2.2-class two ribbon
flare and an EUV wave. The flare impulsive phase as seen
in the GOES 1.0 to 0.8 Å soft X-ray data occurs between
01:46 and 01:56 UT. Integrated HXR emission was observed
with RHESSI up to approximately 100 keV. γ -ray line emis-
sion was not observed by RHESSI during the flare. RHESSI
images obtained with CLEAN procedure were used to pro-
vide spatially resolved light curves of the HXR sources in the
vicinity of the egression sources and the main flare ribbons
(Figure 2).
3.2. Two Seismic Sources
Computed egression power snapshots for 6, 7, and 10 mHz
frequency bands taken around the times of the peak in the
acoustic emission are shown in Figure 1. The data are scaled
by the mean quiet-Sun egression power value at each frequency
and saturated at factor five for better contrast. At 6 mHz one can
clearly see the two strong acoustic sources located in the eastern
and western parts of the image. The locations of the sources
are plotted as contours over magnetogram and intensity images
in the top of Figure 1. The eastern source (Source 1), which
corresponds to the acoustic source reported by Kosovichev
(2011), is larger and stronger, clearly seen in all frequency bands
of computed egression snapshots. The western source (Source
2) is considerably smaller and best seen in the 6 mHz band,
becoming faint at 8 mHz.
In order to check the significance of acoustic sources, follow-
ing Donea et al. (1999), Donea et al. (2000), and Matthews et al.
(2011) we have performed rms analysis by spatially integrating
egression power over a 140 Mm
2
region obtained via morpho-
logical dilation of the egression kernels. The 6 mHz results are
shown in the bottom row of Figure 4. It is clear that the acoustic
signal at Source 1 is very strong, exceeding the mean value of the
series by a factor of up to 2.9. While Source 2 is clearly weaker,
the signal at 6 mHz band exceeds the mean by a factor of 2.4.
The largest magnetic, intensity, andvelocity variationsassoci-
ated with the CME/flare occurred along the flare-loop footpoints
away from the seismic sources. The strongest HXR emission is
also situated primarily at the site of the flare loops (Figure 2),
with the peaks apparently corresponding to the sites of max-
imum magnetic field changes, some distance away from the
4

Citations
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Journal ArticleDOI
TL;DR: In this article, the authors report the evolution of magnetic field and its energy in NOAA active region 11158 over 5 days based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO).
Abstract: We report the evolution of magnetic field and its energy in NOAA active region 11158 over 5 days based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). Fast flux emergence and strong shearing motion led to a quadrupolar sunspot complex that produced several major eruptions, including the first X-class flare of Solar Cycle 24. Extrapolated non-linear force-free coronal fields show substantial electric current and free energy increase during early flux emergence near a low-lying sigmoidal filament with sheared kilogauss field in the filament channel. The computed magnetic free energy reaches a maximum of ∼2.6 × 10 32 erg, about 50% of which is stored below 6 Mm. It decreases by ∼0.3 × 10 32 erg within 1 hour of the X-class flare, which is likely an underestimation of the actual energy loss. During the flare, the photospheric field changed rapidly: horizontal field was enhanced by 28% in the core region, becoming more inclined and more parallel to the polarity inversion line. Such change is consistent with the conjectured coronal field “implosion”, and is supported by the coronal loop retraction observed by the Atmospheric Imaging Assembly (AIA). The extrapolated field becomes more “compact” after the flare, with shorter loops in the core region, probably because of reconnection. The coronal field becomes slightly more sheared in the lowest layer, relaxes faster with height, and is overall less energetic.

422 citations

Journal ArticleDOI
TL;DR: The observations suggest that the instability of the magnetic flux rope triggers the eruption, thus making a major addition to the traditional magnetic-reconnection paradigm.
Abstract: Explosive energy releases in plasmas, such as in solar eruptions like flares and coronal mass ejections, are thought to be caused by magnetic reconnection in thin current sheets. Zhang et al. observed a magnetic flux rope during a solar eruption, highlighting its role in driving explosive energy releases.

349 citations

01 Oct 2011
TL;DR: In this paper, the authors report the evolution of magnetic field and its energy in NOAA active region 11158 over 5 days based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO).
Abstract: We report the evolution of magnetic field and its energy in NOAA active region 11158 over 5 days based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). Fast flux emergence and strong shearing motion led to a quadrupolar sunspot complex that produced several major eruptions, including the first X-class flare of Solar Cycle 24. Extrapolated non-linear force-free coronal fields show substantial electric current and free energy increase during early flux emergence near a low-lying sigmoidal filament with sheared kilogauss field in the filament channel. The computed magnetic free energy reaches a maximum of ∼2.6 × 10 32 erg, about 50% of which is stored below 6 Mm. It decreases by ∼0.3 × 10 32 erg within 1 hour of the X-class flare, which is likely an underestimation of the actual energy loss. During the flare, the photospheric field changed rapidly: horizontal field was enhanced by 28% in the core region, becoming more inclined and more parallel to the polarity inversion line. Such change is consistent with the conjectured coronal field “implosion”, and is supported by the coronal loop retraction observed by the Atmospheric Imaging Assembly (AIA). The extrapolated field becomes more “compact” after the flare, with shorter loops in the core region, probably because of reconnection. The coronal field becomes slightly more sheared in the lowest layer, relaxes faster with height, and is overall less energetic.

260 citations


Cites background from "2011 February 15: Sunquakes Produce..."

  • ...Interesting evidence also arises from the “sunquake” observation reported by Zharkov et al. (2011) following the initial report by Kosovichev (2011)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, a 3D MHD simulation for eruptive solar flares is presented, where the magnetic fluxes and flare energies in the model are calculated in a wide paramater space.
Abstract: Context. Solar flares strongly affect the Sun’s atmosphere as well as the Earth’s environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics. Aims. The largest solar flares observed over the past few decades have reached energies of a few times 10 32 ergs, possibly up to 10 33 ergs. Flares in active Sun-like stars reach up to about 10 36 ergs. In the absence of direct observations of solar flares within this range, complementary methods of investigation are needed to assess the probability of solar flares beyond those in the observational record. Methods. Using historical reports for sunspot and solar active region properties in the photosphere, we scaled to observed solar values a realistic dimensionless 3D MHD simulation for eruptive flares, which originate from a highly sheared bipole. This enabled us to calculate the magnetic fluxes and flare energies in the model in a wide paramater space. Results. Firstly, commonly observed solar conditions lead to modeled magnetic fluxes and flare energies that are comparable to those estimated from observations. Secondly, we evaluate from observations that 30% of the area of sunspot groups are typically involved in flares. This is related to the strong fragmentation of these groups, which naturally results from sub-photospheric convection. When the model is scaled to 30% of the area of the largest sunspot group ever reported, with its peak magnetic field being set to the strongest value ever measured in a sunspot, it produces a flare with a maximum energy of � 6 × 10 33 ergs. Conclusions. The results of the model suggest that the Sun is able to produce flares up to about six times as energetic in total solar irradiance (TSI) fluence as the strongest directly-observed flare from Nov 4, 2003. Sunspot groups larger than historically reported would yield superflares for spot pairs that would exceed tens of degrees in extent. We thus conjecture that superflare-productive Sun-like stars should have a much stronger dynamo than in the Sun.

207 citations


Cites background from "2011 February 15: Sunquakes Produce..."

  • ...To be specific, there are photospheric sunquakes (Zharkov et al. 2011), chromospheric ribbons (Schmieder et al. 1987), coronal loop restructuration (Warren et al. 2011) and oscillation (Nakariakov et al. 1999), large-scale coronal propagation fronts (Delannée et al. 2008), and driving of…...

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors discuss 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.
Abstract: 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.

198 citations

References
More filters
Journal ArticleDOI
TL;DR: RHESSI as discussed by the authors is a Principal Investigator (PI) mission, where the PI is responsible for all aspects of the mission except the launch vehicle, and is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/gamma-ray continua emitted by energetic electrons, and of gamma-ray lines produced by energetic ions.
Abstract: RHESSI is the sixth in the NASA line of Small Explorer (SMEX) missions and the first managed in the Principal Investigator mode, where the PI is responsible for all aspects of the mission except the launch vehicle. RHESSI is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/gamma-ray continua emitted by energetic electrons, and of gamma-ray lines produced by energetic ions. The single instrument consists of an imager, made up of nine bi-grid rotating modulation collimators (RMCs), in front of a spectrometer with nine cryogenically-cooled germanium detectors (GeDs), one behind each RMC. It provides the first high-resolution hard X-ray imaging spectroscopy, the first high-resolution gamma-ray line spectroscopy, and the first imaging above 100 keV including the first imaging of gamma-ray lines. The spatial resolution is as fine as ~ 2.3 arc sec with a full-Sun (≳ 1°) field of view, and the spectral resolution is ~ 1–10 keV FWHM over the energy range from soft X-rays (3 keV) to gamma-rays (17 MeV). An automated shutter system allows a wide dynamic range (> 107) of flare intensities to be handled without instrument saturation. Data for every photon is stored in a solid-state memory and telemetered to the ground, thus allowing for versatile data analysis keyed to specific science objectives. The spin-stabilized (~ 15 rpm) spacecraft is Sun-pointing to within ~ 0.2° and operates autonomously. RHESSI was launched on 5 February 2002, into a nearly circular, 38° inclination, 600-km altitude orbit and began observations a week later. The mission is operated from Berkeley using a dedicated 11-m antenna for telemetry reception and command uplinks. All data and analysis software are made freely and immediately available to the scientific community.

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TL;DR: In this paper, a model for the magnetic field associated with solar prominences is considered, and it is shown that flux cancellation at the neutral line of a sheared magnetic arcade leads to the formation of helical field lines which are capable, in principle, of supporting prominence plasma.
Abstract: A model for the magnetic field associated with solar prominences is considered. It is shown that flux cancellation at the neutral line of a sheared magnetic arcade leads to the formation of helical field lines which are capable, in principle, of supporting prominence plasma. A numerical method for the computation of force-free, canceling magnetic structures is presented. Starting from an initial potential field we prescribe the motions of magnetic footpoints at the photosphere, with reconnection occurring only at the neutral line. As more and more flux cancels, magnetic flux is transferred from the arcade field to the helical field. Results for a particular model of the photospheric motions are presented. The magnetic structure is found to be stable: the arcade field keeps the helical field tied down at the photosphere. The axis of the helical field moves to larger and larger height, suggestive of prominence eruption. These results suggest that prominence eruptions may be trigered by flux cancellation.

941 citations


"2011 February 15: Sunquakes Produce..." refers background in this paper

  • ...The sigmoid formed along a polarity inversion line, where the flux cancellation, provides the mechanism by which the helical field lines of the flux rope can be formed from a sheared arcade (van Ballegooijen & Martens 1989; Green et al. 2011)....

    [...]

Journal ArticleDOI
TL;DR: The X-ray Telescope (XRT) of the Hinode mission as mentioned in this paper provides an unprecedented combination of spatial and temporal resolution in solar coronal studies, and the high sensitivity and broad dynamic range of XRT, coupled with the spacecraft's onboard memory capacity and the planned downlink capability, will permit a broad range of solar studies over an extended period of time for targets ranging from quiet Sun to X-flares.
Abstract: The X-ray Telescope (XRT) of the Hinode mission provides an unprecedented combination of spatial and temporal resolution in solar coronal studies. The high sensitivity and broad dynamic range of XRT, coupled with the spacecraft’s onboard memory capacity and the planned downlink capability will permit a broad range of coronal studies over an extended period of time, for targets ranging from quiet Sun to X-flares. This paper discusses in detail the design, calibration, and measured performance of the XRT instrument up to the focal plane. The CCD camera and data handling are discussed separately in a companion paper.

763 citations


"2011 February 15: Sunquakes Produce..." refers methods in this paper

  • ...The hard X-ray data presented in this paper are derived from RHESSI (Lin et al. 2002), with Hinode XRT (Golub et al. 2007) providing data for soft X-ray information....

    [...]

Journal ArticleDOI
TL;DR: In this article, a zero-β magnetohydrodynamic (MHD) simulation of an initially potential, asymmetric bipolar field, which evolves by means of simultaneous slow magnetic field diffusion and sub-Alfvenic, line-tied shearing motions in the photosphere, is used to analyze the physical mechanisms that form a three-dimensional coronal flux rope and later cause its eruption.
Abstract: We analyze the physical mechanisms that form a three-dimensional coronal flux rope and later cause its eruption. This is achieved by a zero-β magnetohydrodynamic (MHD) simulation of an initially potential, asymmetric bipolar field, which evolves by means of simultaneous slow magnetic field diffusion and sub-Alfvenic, line-tied shearing motions in the photosphere. As in similar models, flux-cancellation-driven photospheric reconnection in a bald-patch (BP) separatrix transforms the sheared arcades into a slowly rising and stable flux rope. A bifurcation from a BP to a quasi-separatrix layer (QSL) topology occurs later on in the evolution, while the flux rope keeps growing and slowly rising, now due to shear-driven coronal slip-running reconnection, which is of tether-cutting type and takes place in the QSL. As the flux rope reaches the altitude at which the decay index –∂ln B/∂ln z of the potential field exceeds ~3/2, it rapidly accelerates upward, while the overlying arcade eventually develops an inverse tear-drop shape, as observed in coronal mass ejections (CMEs). This transition to eruption is in accordance with the onset criterion of the torus instability. Thus, we find that photospheric flux-cancellation and tether-cutting coronal reconnection do not trigger CMEs in bipolar magnetic fields, but are key pre-eruptive mechanisms for flux ropes to build up and to rise to the critical height above the photosphere at which the torus instability causes the eruption. In order to interpret recent Hinode X-Ray Telescope observations of an erupting sigmoid, we produce simplified synthetic soft X-ray images from the distribution of the electric currents in the simulation. We find that a bright sigmoidal envelope is formed by pairs of -shaped field lines in the pre-eruptive stage. These field lines form through the BP reconnection and merge later on into -shaped loops through the tether-cutting reconnection. During the eruption, the central part of the sigmoid brightens due to the formation of a vertical current layer in the wake of the erupting flux rope. Slip-running reconnection in this layer yields the formation of flare loops. A rapid decrease of currents due to field line expansion, together with the increase of narrow currents in the reconnecting QSL, yields the sigmoid hooks to thin in the early stages of the eruption. Finally, a slightly rotating erupting loop-like feature (ELLF) detaches from the center of the sigmoid. Most of this ELLF is not associated with the erupting flux rope, but with a current shell that develops within expanding field lines above the rope. Only the short, curved end of the ELLF corresponds to a part of the flux rope. We argue that the features found in the simulation are generic for the formation and eruption of soft X-ray sigmoids.

618 citations


"2011 February 15: Sunquakes Produce..." refers background in this paper

  • ...The observation of the sigmoid and the erupting loop-like feature gives strong support for the presence of a flux rope before and during the eruption (McKenzie & Canfield 2008; Aulanier et al. 2010; Green et al. 2011)....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors search for plasma ejections in eight impulsive compact-loop flares near the limb, which are selected in an unbiased manner and include also the Masuda flare, 1992 January 13 flare.
Abstract: Masuda et al. found a hard X-ray source well above a soft X-ray loop in impulsive compact-loop flares near the limb. This indicates that main energy release is going on above the soft X-ray loop, and suggests magnetic reconnection occurring above the loop, similar to the classical model for two ribbon flares. If the reconnection hypothesis is correct, a hot plasma (or plasmoid) ejection is expected to be associated with these flares. Using the images taken by the soft X-ray telescope aboard Yohkoh, we searched for such plasma ejections in eight impulsive compact-loop flares near the limb, which are selected in an unbiased manner and include also the Masuda flare, 1992 January 13 flare. We found that all these flares were associated with X-ray plasma ejections high above the soft X-ray loop and the velocity of ejections is within the range of 50-400 km s-1. This result gives further support for magnetic reconnection hypothesis of these impulsive compact-loop flares.

542 citations


"2011 February 15: Sunquakes Produce..." refers background or result in this paper

  • ...…loops seen in SXR and EUV emission (shown in blue in Figure 5), and also forms helical field lines that wrap around the flux rope body (Titov & Démoulin 1999) and further enhance the speed of the eruption (Zhang et al. 2004) (shown in green in Figure 5, see also Figure 1 in (Shibata et al. 1995))....

    [...]

  • ...Absence of strong HXR is in line with Shibata et al. (1995) model for two ribbon flare....

    [...]

Related Papers (5)
Frequently Asked Questions (2)
Q1. What contributions have the authors mentioned in the paper "2011 february 15: sunquakes produced by flux rope eruption" ?

The authors 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, the authors confirm the first, and report a second, weaker, seismic source associated with this flare. Contrary to the majority of previously reported sunquakes, the acoustic emission precedes the peak of major hard X-ray ( HXR ) sources by several minutes. The authors 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. Furthermore, the strongest HXR footpoints derived from RHESSI data are found to be located away from the seismic sources in the flare ribbons. 

Further studies with high resolution and high cadence data are now needed to determine the mechanisms behind sunquake production in the context of an erupting magnetic configuration and associated particle transport, rather than only focusing on flare-related mechanisms.