A Quantitative Model of Energy Release and Heating by Time-dependent,Localized Reconnection in a Flare with Thermal Loop-top X-ray Source

We present a quantitative model of the magnetic energy stored and then released through magnetic reconnection for a flare on 26 February 2004. This flare, well observed by RHESSI and TRACE, shows evidence of non-thermal electrons for only a brief, early phase. Throughout the main period of energy release there is a super-hot (T?30 MK) plasma emitting thermal bremsstrahlung atop the flare loops. Our model describes the heating and compression of such a source by localized, transient magnetic reconnection. It is a three-dimensional generalization of the Petschek model, whereby Alfvén-speed retraction following reconnection drives supersonic inflows parallel to the field lines, which form shocks: heating, compressing, and confining a loop-top plasma plug. The confining inflows provide longer life than a freely expanding or conductively cooling plasma of similar size and temperature. Superposition of successive transient episodes of localized reconnection across a current sheet produces an apparently persistent, localized source of high-temperature emission. The temperature of the source decreases smoothly on a time scale consistent with observations, far longer than the cooling time of a single plug. Built from a disordered collection of small plugs, the source need not have the coherent jet-like structure predicted by steady-state reconnection models. This new model predicts temperatures and emission measure consistent with the observations of 26 February 2004. Furthermore, the total energy released by the flare is found to be roughly consistent with that predicted by the model. Only a small fraction of the energy released appears in the super-hot source at any one time, but roughly a quarter of the flare energy is thermalized by the reconnection shocks over the course of the flare. All energy is presumed to ultimately appear in the lower-temperature (T?20 MK) post-flare loops. The number, size, and early appearance of these loops in TRACE’s 171 Å band are consistent with the type of transient reconnection assumed in the model.     

Observational Study of a Peculiar Solar Limb Event Occurred on 11 January 2002

On 11 January 2002, using the Multi-channel Infrared Solar Spectrograph (MISS) at the Purple Mountain Observatory (PMO), we obtained Hα, Ca ii 8542 Å and He i 10?830 Å spectra and slit-jaw Hα images of a peculiar solar limb event. A close resemblance of its intensity to that of a small flare and the GOES X-ray flux indicates that it was an active prominence. However, its morphological evolution and velocity variation were different from general typical active prominences, such as limb flares, post-flare loops, surges and sprays. It started with the ejection of material from the flare site. In the early phase, the ejecta was as bright as a limb flare and kept rising until reaching the height of (8????10)×10⁴ km at an almost constant velocity of 91.7 km? s ^?1 with its lower part always connected to the solar surface. EUV images in 195 Å show similar structure as in the Hα line, indicating the coexistence of plasmas with temperatures differing by more than two orders of magnitude. Later some material started to fall back to another bright area on the solar surface. The falling material did not show the collimated structure of surges or the arc structure of flaring arches. A red-shift velocity of more than 200 km? s ^?1 was detected in a bright point close to the outer edge of the closed loop system formed later, which dispersed in a few minutes and became a part of the newly formed large loop. The ejected material did not leave the sun, indicating that the magnetic reconnection was not sufficient to remove the overlying field lines during the process. The spectral line profiles showed large widths and variable velocities, and therefore the line-pair method is not applicable to this event for the estimation of physical parameters.     

3D Evolution of a Filament Disappearance Event Observed by STEREO

A filament disappearance event was observed on 22 May 2008 during our recent campaign JOP 178. The filament, situated in the Southern Hemisphere, showed sinistral chirality consistent with the hemispheric rule. The event was well observed by several observatories, in particular by THEMIS. One day, before the disappearance, Hα observations showed up- and down-flows in adjacent locations along the filament, which suggest plasma motions along twisted flux rope. THEMIS and GONG observations show shearing photospheric motions leading to magnetic flux canceling around barbs. STEREO A, B spacecraft with separation angle 52.4°, showed quite different views of this untwisting flux rope in He ii 304 Å images. Here, we reconstruct the three-dimensional geometry of the filament during its eruption phase using STEREO EUV He ii 304 Å images and find that the filament was highly inclined to the solar normal. The He ii 304 Å movies show individual threads, which oscillate and rise to an altitude of about 120 Mm with apparent velocities of about 100 km?s^?1 during the rapid evolution phase. Finally, as the flux rope expands into the corona, the filament disappears by becoming optically thin to undetectable levels. No CME was detected by STEREO, only a faint CME was recorded by LASCO at the beginning of the disappearance phase at 02:00 UT, which could be due to partial filament eruption. Further, STEREO Fe xii 195 Å images showed bright loops beneath the filament prior to the disappearance phase, suggesting magnetic reconnection below the flux rope.     

Imaging Spectroscopy of a White-Light Solar Flare

We report observations of a white-light solar flare (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric Fe i line at 6173.34 Å and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning ±172 mÅ around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this was the first γ-ray flare of Cycle 24). The Fe i line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints.     

Simultaneous Observations of the Chromosphere with TRACE and SUMER

Using mainly the 1600 Å continuum channel and also the 1216 Å Lyman-α channel (which includes some UV continuum and C iv emission) aboard the TRACE satellite, we observed the complete lifetime of a transient, bright chromospheric loop. Simultaneous observations with the SUMER instrument aboard the SOHO spacecraft revealed interesting material velocities through the Doppler effect existing above the chromospheric loop imaged with TRACE, possibly corresponding to extended nonvisible loops, or the base of an X-ray jet.     

Extreme Ultraviolet Late-Phase Flares: Before and During the Solar Dynamics Observatory Mission

The solar extreme-ultraviolet (EUV) observations from the Solar Dynamics Observatory (SDO) have revealed interesting characteristics of warm coronal emissions, such as Fe xvi 335 Å emission, which peak soon after the hot coronal X-ray emissions peak during a flare and then sometimes peak for a second time hours after the X-ray flare peak. This flare type, with two warm coronal emission peaks but only one X-ray peak, has been named the EUV late phase (Woods et al., Astrophys. J. 739, 59, 2011). These flares have the distinct properties of i) having a complex magnetic-field structure with two initial sets of coronal loops, with one upper set overlaying a lower set, ii) having an eruptive flare initiated in the lower set and disturbing both loop sets, iii) having the hot coronal emissions emitted only from the lower set in conjunction with the X-ray peak, and iv) having the first peak of the warm coronal emissions associated with the lower set and its second peak emitted from the upper set many minutes to hours after the first peak and without a second X-ray enhancement. The disturbance of the coronal loops by the eruption is at about the same time, but the relaxation and cooling down of the heated coronal loops during the post-flare reconnections have different time scales with the longer, upper loops being significantly delayed from the lower loops. The difference in these cooling time scales is related to the difference between the two peak times of the warm coronal emission and is also apparent in the decay profile of the X-ray emissions having two distinct decays, with the first decay slope being steeper (faster) and the delayed decay slope being smaller (slower) during the time of the warm-coronal-emission second peak. The frequency and relationship of the EUV late-phase decay times between the Fe xvi 335 Å two flare peaks and X-ray decay slopes are examined using three years of SDO/EUV Variability Experiment (EVE) data, and the X-ray dual-decay character is then exploited to estimate the frequency of EUV late-phase flares during the past four solar cycles. This study indicates that the frequency of EUV late-phase flares peaks before and after each solar-cycle minimum.     

Multiwavelength Study of the M8.9/3B Solar Flare from AR NOAA 10960

We present a multiwavelength analysis of a long-duration, white-light solar flare (M8.9/3B) event that occurred on 04 June 2007 from AR NOAA 10960. The flare was observed by several spaceborne instruments, namely SOHO/MDI, Hinode/SOT, TRACE, and STEREO/SECCHI. The flare was initiated near a small, positive-polarity, satellite sunspot at the center of the active region, surrounded by opposite-polarity field regions. MDI images of the active region show a considerable amount of changes in the small positive-polarity sunspot of δ configuration during the flare event. SOT/G-band (4305 Å) images of the sunspot also suggest the rapid evolution of this positive-polarity sunspot with highly twisted penumbral filaments before the flare event, which were oriented in a counterclockwise direction. It shows the change in orientation, and also the remarkable disappearance of twisted penumbral filaments (≈35?–?40%) and enhancement in umbral area (≈45?–?50%) during the decay phase of the flare. TRACE and SECCHI observations reveal the successive activation of two helically-twisted structures associated with this sunspot, and the corresponding brightening in the chromosphere as observed by the time-sequence of SOT/Ca?ii H line (3968 Å) images. The secondary, helically-twisted structure is found to be associated with the M8.9 flare event. The brightening starts six?–?seven minutes prior to the flare maximum with the appearance of a secondary, helically-twisted structure. The flare intensity maximizes as the secondary, helically-twisted structure moves away from the active region. This twisted flux tube, associated with the flare triggering, did not launch a CME. The location of the flare activity is found to coincide with the activation site of the helically-twisted structures. We conclude that the activation of successive helical twists (especially the second one) in the magnetic-flux tubes/ropes plays a crucial role in the energy build-up process and the triggering of the M-class solar flare without a coronal mass ejection (CME).     

The flare of September 7, 1973: A typical example of a newly recognized class of solar transients

X-ray, extreme-ultraviolet and optical observations of a solar flare are discussed. It is shown that the flare exemplifies a class of transient events characterized by long duration and long decay time and by the development of high systems of loops, generally brighter at the top. In contrast with compact short lifetime events, the distinctive properties of this class of transients are:

1. The disruption of the magnetic configuration at the flare onset, as indicated by prominence eruption or activation and by associated white-light coronal transients;
2. a continuous energy deposition, presumably at the top of loops, during a large fraction of the flare development and well after the intensity peak;
3. a continuous supply of additional material to the top of loops, with subsequent downflows and out-of-hydrostatic equilibrium conditions.

     

Radio,Hard X-Ray,and Gamma-Ray Emissions Associated with a Far-Side Solar Event

The far-side solar eruptive event SOL2014-09-01 produced hard electromagnetic and radio emissions that were observed with detectors at near-Earth vantage points. Especially challenging was a long-duration >?100 MeV \(\gamma\)-ray burst that was probably produced by accelerated protons exceeding 300 MeV. This observation raised the question how high-energy protons could reach the Earth-facing solar surface. Some preceding studies discussed a scenario in which protons accelerated by a shock driven by a coronal mass ejection high in the corona return to the solar surface. We continue with the analysis of this challenging event, involving radio images from the Nançay Radioheliograph and hard X-ray data from the High Energy Neutron Detector (HEND) of the Gamma-Ray Spectrometer onboard the Mars Odyssey space observatory located near Mars. HEND recorded unocculted flare emission. The results indicate that the emissions observed from the Earth’s direction were generated by flare-accelerated electrons and protons trapped in static long coronal loops. They can be reaccelerated in these loops by a shock wave that was excited by the eruption, being initially not driven by a coronal mass ejection. The results highlight ways to address the remaining questions.     

Oscillations Accompanying a He <Emphasis Type="SmallCaps">i</Emphasis> 10830 Å Negative Flare in a Solar Facula

On 21 September 2012, we carried out spectral observations of a solar facula in the Si?i 10827 Å, He?i 10830 Å, and H\(\upalpha\) spectral lines. Later, in the process of analyzing the data, we found a small-scale flare in the middle of the time series. Based on the anomalous increase in the absorption of the He?i 10830 Å line, we identified this flare as a negative flare.The aim of this article is to study the influence of the negative flare on the oscillation characteristics in the facular photosphere and chromosphere.We measured the line-of-sight (LOS) velocity and intensity of all the three lines as well as the half-width of the chromospheric lines. We also used the Helioseismic and Magnetic Imager (HMI) magnetic field data. The flare caused a modulation of all these parameters. In the location of the negative flare, the amplitude of the oscillations increased four times on average. In the adjacent magnetic field local maxima, the chromospheric LOS velocity oscillations appreciably decreased during the flare. The facular region oscillated as a whole with a 5-minute period before the flare, and this synchronicity was disrupted after the flare. The flare changed the spectral composition of the LOS magnetic field oscillations, causing an increase in the low-frequency oscillation power.     

A Major Geoeffective CME from NOAA 12371: Initiation,CME–CME Interactions,and Interplanetary Consequences

In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum \(\mathrm{Dst} = -204\) nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 Å confirm the CME to be associated with a coronal sigmoid that displayed an intense emission (\(T \sim6\) MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km?s^?1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within \(\approx10\)?–?\(90~\mbox{R} _{\odot}\). The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19?–?21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015.     

Spectral Characteristics of Solar Flares in Different Chromospheric Lines and Their Implications

Using the spectral data of representative solar flares observed with the infrared detector system of the solar spectrograph at Purple Mountain Observatory, we study the spectroscopic characteristics of solar flares in the Hα, the Ca i i 8?542 Å, and the He i 10?830 Å lines in different phases and various locations of flares and discuss their possible implications coupled with space observations. Our results show that in the initial phase of a flare the Hα line displays a red shift only with no wide wing. Large broadenings of the Hα line are observed a few minutes after the flare onset within small regions of 3?–?5^′′ in both disk and limb flares with and without nonthermal processes. Far wings similar to those of damping broadening appear not only in the Hα line but in the He i 10?830 Å line as well in flares with nonthermal processes. Sometimes we even detect weak far-wing emission in the Ca i i 8?542 Å line in disk flares. Such large broadenings are observed in both the footpoints and the flare loop-top regions and possibly result from strong turbulence and/or macroscopic motions. Therefore, the so-called nonthermal wing of the Hα line profile is not a sufficient condition to distinguish whether nonthermal electrons are accelerated or not in a flare. The Ca i i 8?542 Å line shows lower intensity in the loop-top regions and higher intensity in the parts close to the solar surface. Emissions larger than nearby continuum in the He i 10?830 Å line are detected only in small regions with strong X-ray emissions and avoid sunspot umbrae.     

Trigger of Successive Filament Eruptions Observed by SDO and STEREO

Using multiwavelength observations from the Solar Dynamics Observatory (SDO) and the Solar Terrestrial Relations Observatory (STEREO), we investigate the mechanism of two successive eruptions (F1 and F2) of a filament in active region NOAA 11444 on 27 March 2012. The filament was inverse J-shaped and lay along a quasi-circular polarity inversion line (PIL). The first part of the filament erupted at \(\sim2{:}30\) UT on 27 March 2012 (F1), the second part at around 4:20 UT on the same day (F2). A precursor or preflare brightening was observed below the filament main axis about 30 min before F1. The brightening was followed by a jet-like ejection below the filament, which triggered its eruption. Before the eruption of F2, the filament seemed to be trapped within the overlying arcade loops for almost 1.5 h before it successfully erupted. Interestingly, we observe simultaneously contraction (\(\sim12~\mbox{km}\,\mbox{s}^{-1}\)) and expansion (\(\sim20~\mbox{km}\,\mbox{s}^{-1}\)) of arcade loops in the active region before F2. Magnetograms obtained with the Helioseismic and Magnetic Imager (HMI) show converging motion of the opposite polarities, which result in flux cancellation near the PIL. We suggest that flux cancellation at the PIL resulted in a jet-like ejection below the filament main axis, which triggered F1, similar to the tether-cutting process. F2 was triggered by removal of the overlying arcade loops via reconnection. Both filament eruptions produced high-speed (\(\sim1000~\mbox{km}\,\mbox{s}^{-1}\)) coronal mass ejections.     

Observations of a Propagating Disturbance in TRACE

TRACE observations from 13 June 1998 in 171 and 195 Å wavelengths show a propagating disturbance, initiated near the origin of a C-class flare. The wave moves through and disrupts diffuse, overarching coronal loops. Only these overlying structures are affected by the wave; lower-lying coronal structures are unperturbed. The front does not appear in contemporaneous Lyman-α observations. The disturbance creates two types of displacement: (1) that of the wave front itself, and (2) those of large anchored magnetic structures, which `bob' due to the wave and show transverse velocities an order of magnitude smaller than those of the front. Comparisons between the 171 and 195 Å data show that the front appears differently at different temperatures. Observations in 171 Å (approx. 0.95 MK) show strong displacement of individual magnetic structures, while 195 Å (approx. 1.4 MK) data reveals a strong wave front and associated dimming but resolve much less structural motion. There is also strong evidence of heating in the material engulfed by the wave front, and comparisons of the 171 and 195 Å data allow us to constrain the temperature of the plasma through which the wave is propagating to 1–1.4 MK. Examination of the trajectories and velocities of points along the front suggests that the disturbance is Alfvénic in nature but contains a compressive component. This is best explained by a fast-mode magnetoacoustic wave. A comparison of the motion of anchored structures to that of the wave front gives a constraint on pulse width. Comparisons with contemporaneous SOHO-EIT full-disk 195 Å data show evidence that the disturbance is contained within a set of transequatorial field lines, such that it propagates from a southern active region to a northern one with no extensive motion to the east or west. The associated transequatorial loops display residual motion for about a hour after they are initially disturbed. These results, coupled with the deflection of wave trajectories, lead us to speculate on field strength differences between the transequatorial loops and the region in the TRACE field of view.     

RHESSI Microflares: I. X-Ray Properties and Multiwavelength Characteristics

We study the general X-ray and multiwavelength characteristics of microflares of GOES class A0.7 to B7.4 (background subtracted) detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on 26 September 2003 comparing them with the properties of regular flares. All the events for which X-ray imaging was feasible originated in one active region and were accumulated in areas with intermixed magnetic polarities. During the events’ rise and peak phase, the RHESSI X-ray spectra show a steep nonthermal power-law component (4?γ?10) for energies ??10 keV. Further evidence for the presence of electron beams is provided by the association with radio type III bursts in 5 out of 11 events where AIP radio spectra were available. The strongest event in our sample shows radio signatures of a type II precursor. The thermally emitting flare plasma observed by RHESSI is found to be hot, 11?T?15 MK, with small emission measures, 10⁴⁶?EM?10⁴⁷ cm^?3, concentrated in the flare loop. In the EUV (TRACE 171 Å), the UV (TRACE 1600 Å) and Kanzelhöhe Solar Observatory Hα, impulsive brightenings at both ends of the RHESSI 3?–?6 keV X-ray loop source are observed, situated in opposite magnetic polarity fields. During the decay phase, a postflare loop at the location of the RHESSI loop source is observed in the TRACE 171 Å? channel showing plasma that is cooled from ??10 MK to ≈?1 MK. Correlations between various thermal and nonthermal parameters derived from the RHESSI microflare spectra compared to the same correlations obtained for a set of small and large flares by Battaglia et al. (Astron. Astrophys. 439, 737, 2005) indicate that the RHESSI instrument gives us a spectrally biased view since it detects only hot (T?10 MK) microflares, and thus the correlations between RHESSI microflare parameters have to be interpreted with caution. The thermal and nonthermal energies derived for the RHESSI microflares are \(\bar{E}_{\mathrm{th}}=7\times 10^{27}\) ergs and \(\bar{E}_{\mathrm{nth}}=2\times 10^{29}\) ergs, respectively. Possible reasons for the order-of-magnitude difference between the thermal and nonthermal microflare energies, which was also found in previous studies, are discussed. The determined event rate of 3.7 h^?1 together with the average microflare energies indicate that the total energy in the observed RHESSI microflares is far too small to account for the heating of the active region corona in which they occur.     

Evolution of a Coronal Loop System

The temporal variation of a loop system that appears to be changing rapidly is examined. The analyzed data were obtained on 15 May 1999, with the Transition Region and Coronal Explorer (TRACE) during an observing campaign and consist of observations in the Fe ix/Fe x 171?Å and Fe xii 195?Å passbands taken at a cadence of ～10 min. The special interest in this loop system is that it looks like one expanding loop; however, careful examination reveals that the loop consists of several strands and that new loop strands become visible successively at higher altitudes and lower loop strands fade out during the one hour of our observations. These strands have different widths, densities, and temperatures and are most probably consisting of, at least, a few unresolved thinner threads. Several geometric and physical parameters are derived for two of the strands and an effort is made to determine their 3D structure based on the extrapolation of the magnetic field lines. Electron density estimates allow us to derive radiative and conductive cooling times and to conclude that these loop strands are cooling by radiation.     

Pulsations of microwave emission and flare plasma diagnostics

We consider the modulation of nonthermal gyrosynchrotron emission from solar flares by the ballooning and radial oscillations of coronal loops. The damping mechanisms for fast magnetoacoustic modes are analyzed. We suggest a method for diagnosing the plasma of flare loops that allows their main parameters to be estimated from peculiarities of the microwave pulsations. Based on observational data obtained with the Nobeyama Radioheliograph (17 GHz) and using a technique developed for the event of May 8, 1998, we determined the particle density n≈3.7×10¹⁰ cm^?3, the temperature T≈4×10⁷ K, and the magnetic field strength B≈220 G in the region of flare energy release. A wavelet analysis for the solar flare of August 28, 1999, has revealed two main types of microwave oscillations with periods P₁≈7, 14 s and P₂≈2.4 s, which we attribute to the ballooning and radial oscillations of compact and extended flare loops, respectively. An analysis of the time profile for microwave emission shows evidence of coronal loop interaction. We determined flare plasma parameters for the compact (T≈5.3×10⁷ K, n≈4.8≈10¹⁰ cm^?3, B≈280 G) and extended (T≈2.1≈10⁷ K, n≈1.2≈10¹⁰ cm^?3, B≈160 G) loops. The results of the soft X-ray observations are consistent with the adopted model.     

Study of two-stage coronal jet associated with a C1.4 class solar flare

We study an active region coronal jet that evolved from southward of a major sunspot of NOAA AR12178 on 04 October 2014. This jet is associated with an onset of the GOES C1.4 flare. We use SDO/AIA, SDO/HMI, GONG \(H\upalpha\) and GOES data for analysing the observed event. We term this jet as a two-stage confined eruption of the plasma. In the first stage, some plasma erupts above the compact flaring region. In the second stage, this eruptive jet plasma and associated magnetic field lines interact with another set of distinct magnetic field lines present in its south-east direction. This creates an X-point region, where the second stage of the jet eruption is deflected above it on a curvilinear path into overlying corona. The lower part of the jet is followed by a cool surge eruption, which is visible only in \(H{\upalpha}\) emissions. The magnetic flux cancellation at the footpoint causes the triggering of C-class flare eruption. This flare energy release further triggers first stage of the coronal jet eruption. The second stage of the jet eruption is a consequence of an interaction of two distinct sets of magnetic field lines in the overlying corona. The first stage of the coronal jet and co-spatial but lagging cool surge may have common origin due to the reconnection generated heating pulses. This complex evolution of the coronal jet involves flare heating induced first stage plasma eruption, guiding of jet’s material above a junction of two distinct sets of field lines in the corona, and intra-relationship with cool surge. In effect, it imposes rigid constraints on the existing jet models.     

The interaction and eruption of two adjacent filaments

We present a case study of two successive filament eruptions at the southeast limb of the Sun observed by Solar Dynamics Observatory (SDO) on 2012 April 19. At the initial stage of the first filament (F1) eruption, one leg of the F1 moved toward the second filament (F2) and swept the F2. The interaction between two filaments occurred. After the leg of the F1 swept the F2, it returned from northeast to southwest following the F1 expansion. During the F1 eruption, the middle of the F1 exhibited an obvious twisted structure. The rising speed of the F1 was 85.6 km/s. The partial material of the F1 fell back to the surface along the other leg of the F1 after the F1 eruption and the falling speed was 311.6 km/s. A CME was observed by SOHO/LASCO after the F1 eruption. One of the bright flare ribbons and the dimming regions formed after the F1 eruption were found to move toward the F2. The propagation speeds of the flare ribbons were 4.7 km/s and 4.1 km/s and the propagation speeds of the dimmings were 3 km/s and 6.3 km/s. The small active region was emerging in the northern flank of the F2. The ejection and the falling plasma in the small active region produced the disturbance to the right part of the F2. When the F1 erupted, the large-scale overlying coronal loops of the F1 were pushed out toward the southeast of the Sun by its expanding. During the F1 eruption, the large-scale overlying coronal loops of the F2 began to open toward the southeast. Following the opening of the large-scale overlying coronal loops, the F2 became instable and began to erupt. The rising speed of the F2 was 300.1 km/s. A two-ribbon flare and a weak CME were formed after the F2 eruption. These observations evidenced that the interaction of two filaments and the opening of the large-scale overlying coronal loops caused by the F1 eruption are the most important reason that led to the F2 eruption. Our observations also support the standard solar flare model.     

Transient Magnetic and Doppler Features Related to the White-Light Flares in NOAA 10486

Rapidly moving transient features have been detected in magnetic and Doppler images of super-active region NOAA 10486 during the X17/4B flare of 28 October 2003 and the X10/2B flare of 29 October 2003. Both these flares were extremely energetic white-light events. The transient features appeared during impulsive phases of the flares and moved with speeds ranging from 30 to 50 km?s^?1. These features were located near the previously reported compact acoustic (Donea and Lindsey, Astrophys. J. 630, 1168, 2005) and seismic sources (Zharkova and Zharkov, Astrophys. J. 664, 573, 2007). We examine the origin of these features and their relationship with various aspects of the flares, viz., hard X-ray emission sources and flare kernels observed at different layers: i) photosphere (white-light continuum), ii) chromosphere (Hα 6563 Å), iii) temperature minimum region (UV 1600 Å), and iv) transition region (UV 284 Å).