3-minute oscillations in the chromosphere are attributed to both slow magnetoacoustic waves propagating from the photosphere, and to oscillations generated within the chromosphere itself at its natural frequency as a response to a disturbance. Here we present an investigation of the spatial and temporal behavior of the chromospheric 3-minute oscillations before, during, and after the SOL2011-02-15T01:56 X2.2 flare. Observations in ultraviolet emission centered on 1600 and 1700 Angstroms obtained at 24- second cadence from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory are used to create power maps as functions of both space and time. We observe higher 3-minute power during the flare, spatially concentrated in small areas 10 pixels (4 arcseconds) across. This implies that the chromospheric plasma is not oscillating globally as a single body. The locations of increased 3-minute power are consistent with observations of HXR flare emission from previous studies, suggesting that these small areas are manifestations of the chromosphere responding to injection of energy by nonthermal particles. This supports the theory that the chromosphere oscillates at the acoustic cutoff frequency in response to a disturbance.
We investigate the Interface Region Imaging Spectrograph (IRIS) observations of the quiet-Sun (QS) to understand the propagation of acoustic waves in transition region (TR) from photosphere. We selected a few IRIS spectral lines, which include the photospheric (Mn~{\sc i} 2801.25~Å), chromospheric (Mg~{\sc ii} k 2796.35~Å) and TR (C~{\sc ii} 1334.53~Å), to investigate the acoustic wave propagation.The wavelet cross-spectrum reveals significant coherence (about 70\% locations) between photosphere and chromosphere. Few minutes oscillations (i.e., period range from 1.6 to 4.0 minutes) successfull…
We employ tomographic observations of a small region of plage to study the propagation of waves from the solar photosphere to the chromosphere using a Fourier phase-difference analysis. Our results show the expected vertical propagation for waves with periods of 3 minutes. Waves with 5-minute periods, i.e., above the acoustic cut-off period, are found to propagate only at the periphery of the plage, and only in the direction in which the field can be reasonably expected to expand. We conclude that field inclination is critically important in the leakage of p-mode oscillations from the photosph…
We report three-minute oscillations in the solar chromosphere driven by a strong downflow event in a sunspot. We used the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope and the Interface Region Imaging Spectrograph (IRIS). The strong downflow event is identified in the chromospheric and transition region lines above the sunspot umbra. After the event, oscillations occur at the same region. The amplitude of the Doppler velocity oscillations is 2 km/s, and gradually decreases with time. In addition, the period of the oscillations gradually increases from 2.7 minutes to 3.3 minu…
I review the literature on observational aspects of waves in the solar chromosphere in the first part of this contribution. High-frequency waves are invoked to build elaborate cool-star chromosphere heating theories but have not been detected decisively so far, neither as magnetic modes in network elements nor as acoustic modes in below-the-canopy internetwork regions. Three-minute upward-propagating acoustic shocks are thoroughly established through numerical simulation as the cause of intermittent bright internetwork grains, but their pistoning and their role in the low-chromosphere energy b…
Predicting the thermodynamics in the chromosphere from the translation of SDO data into the IRIS$^{2}$ inversion results using a visual transformer model
SETI Institute（SETI研究所）；Lockheed Martin Solar & Astrophysics Laboratory（洛克希德·马丁太阳与天体物理学实验室）；Henry M. Gunn Senior High School（亨利·M·冈恩高中）；Lockheed Martin Advanced Technology Center（洛克希德·马丁高级技术中心）
We study the properties of slow magneto-acoustic waves that are naturally excited due to turbulent convection and investigate their role in the energy balance of a plage region using three dimensional (3D) radiation-MHD simulations. We calculate the horizontally averaged (over the whole domain) frequency power spectra for both longitudinal and vertical (i.e. the component perpendicular to the surface) components of velocity. To compare our results with the observations we degrade the simulation data with Gaussian kernels having FWHM of 100 km and 200 km, and calculate horizontally averaged pow…
Waves and oscillations are important solar phenomena, not only because they can propagate and dissipate energy in the chromosphere, but also because they carry information about the structure of the atmosphere in which they propagate. The nature of the three-minute oscillations observed in the umbral region of sunspots is considered to be an effect of propagation of magnetohydrodynamic (MHD) waves upward from below the photosphere. We present a study of sunspot oscillations and wave propagation in NOAA AR 12470 using an approximately one-hour long data set acquired on 2015 December 17 by the A…
Using high-resolution numerical simulations we investigate the plasma heating driven by periodic two-fluid acoustic waves that originate at the bottom of the photosphere and propagate into the gravitationally stratified and partially ionized solar atmosphere. We consider ions+electrons and neutrals as separate fluids that interact between themselves via collision forces. The latter play an important role in the chromosphere, leading to significant damping of short-period waves. Long-period waves do not essentially alter the photospheric temperatures, but they exhibit the capability of depositi…
We study the nature of quiet-Sun oscillations using multi-wavelength observations from TRACE, Hinode, and SOHO. The aim is to investigate the existence of propagating waves in the solar chromosphere and the transition region via analyzing the statistical distribution of power in different locations, e.g. in bright magnetic (network), bright non-magnetic and dark non-magnetic (inter-network) regions, separately. We use Fourier power and phase-difference techniques combined with a wavelet analysis. Two-dimensional Fourier power maps were constructed in the period bands 2-4 minutes, 4-6 minutes, …
We studied oscillations related to flare SOL2012-09-21T02:19 in the transition region and chromosphere based on Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Solar Dynamics Observatory (SDO) data, as well as data from a ground-based observatory. We found that 2-minute oscillations triggered by the flare first appeared in the RHESSI channels then subsequently showed up in the SDO 171 Å and 304 Å channels and after that in the chromospheric He I 10830 Å line. The delay of the chromospheric signal compared to the RHESSI signal is 7 minutes, which indicates that the wave pertur…
We developed a {\sl coronal non-linear force-free field (COR-NLFFF)} forward-fitting code that fits an approximate {\sl non-linear force-free field (NLFFF)} solution to the observed geometry of automatically traced coronal loops. In contrast to photospheric NLFFF codes, which calculate a magnetic field solution from the constraints of the transverse photospheric field, this new code uses coronal constraints instead, and this way provides important information on systematic errors of each magnetic field calculation method, as well as on the non-forcefreeness in the lower chromosphere. In this s…
We find that a sunspot with positive polarity had an obvious counter-clockwise rotation and resulted in the formation and eruption of an inverse S-shaped filament in NOAA active region (AR) 08858 from 2000 February 9 to 10. The sunspot had two umbrae which rotated around each other by 195 degrees within about twenty-four hours. The average rotation rate was nearly 8 degrees per hour. The fastest rotation in the photosphere took place during 14:00UT to 22:01UT on February 9, with the rotation rate of nearly 16 degrees per hour. The fastest rotation in the chromosphere and the corona took place …
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 17 February 2013. Observations of the corona, chromosphere and photosphere are brought together for the first time with a non-linear 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…
We have used Transition Region and Coronal Explorer (TRACE) 1600 Åimages and Global Oscillation Network Group (GONG) magnetograms to compare ultraviolet (UV) emissions from the chromosphere to longitudinal magnetic field changes in the photosphere during four X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred across more than ten pixels in the GONG magnetograms for each flare. These magnetic changes lagged the GOES flare start times in all cases, showing that they were consequences and not causes of the flares. Ultraviolet emissions were spatiall…
Oscillations in the solar atmosphere have long been observed in quiet conditions, and increasingly also in data taken during solar flares. The chromosphere is known for its 3-minute signals, which are particularly strong over sunspot umbrae. These signals are thought to be driven by photospheric disturbances and their periods determined by the chromosphere's acoustic cut-off frequency. A small number of observations have shown the chromospheric 3-minute signals to be affected by energetic events such as solar flares, however the link between flare activity and these oscillatory signals remains…
The first X-class flare of the current solar cycle 24 occurred in Active Region NOAA 11158 during its central meridian passage on 2011 February 15. This two ribbon white-light flare was well observed by the Helioseismic and Magnetic Imager (HMI) on board Solar Dynamics Observatory (SDO). During the peak phase of the flare, we detected magnetic and Doppler velocity transients appearing near the umbral boundary of the main sunspot. These transients persisted for a few minutes and showed spatial and temporal correspondence with the flare kernels. The observed magnetic polarity at the transients' …
The heating of the solar chromosphere remains one of the most important questions in solar physics. Our current understanding is that small-scale internetwork (IN) magnetic fields play an important role as a heating agent. Indeed, cancellations of IN magnetic elements in the photosphere can produce transient brightenings in the chromosphere and transition region. These bright structures might be the signature of energy release and plasma heating, probably driven by magnetic reconnection of IN field lines. Although single events are not expected to release large amounts of energy, their global …
Context. Penumbral microjets are elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes and are thought to originate from magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only. Aims. Here we i…
We present an analysis of the 15 February 2011 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24 (Kosovichev 2011). 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 hard X-ray footpoints derived f…
We present observations of persistent oscillations of some bright features in the upper-chromosphere/transition-region above sunspots taken by IRIS SJ 1400 Å and upward propagating quasi-periodic disturbances along coronal loops rooted in the same region taken by AIA 171 Å passband. The oscillations of the features are cyclic oscillatory motions without any obvious damping. The amplitudes of the spatial displacements of the oscillations are about 1 $^{"}$. The apparent velocities of the oscillations are comparable to the sound speed in the chromosphere, but the upward motions are slightly larg…
We found that oscillations of LOS velocity in H-alpha are different for various parts of faculae regions. Power spectra show that the contribution of low-frequency modes (1.2 - 2 mHz) increase at the network boundaries. Three and five- minute periods dominate inside cells. The spectra of photosphere and chromosphere LOS velocity oscillations differ for most faculae. On the other hand, we detected several cases where propagating oscillations in faculae were manifest with a five-minute period. Their initiation point on spatial-temporal diagrams coincided with the local maximum of the longitudina…
In this Letter we report the detection of chromospheric 3-minute oscillations in disk-integrated EUV irradiance observations during a solar flare. A wavelet analysis of detrended Lyman-alpha (from GOES/EUVS) and Lyman continuum (from SDO/EVE) emission from the 2011 February 15 X-class flare (SOL2011-02-15T01:56) revealed a $\sim$3-minute period present during the flare's main phase. The formation temperature of this emission locates this radiation to the flare's chromospheric footpoints, and similar behaviour is found in the SDO/AIA 1600Å and 1700Å channels, which are dominated by chromospheri…
Aims. Convective collapse, a theoretically predicted process that intensifies existing weak magnetic fields in the solar atmosphere, was first directly observed in a single event by Nagata et al. (2008) using the high resolution Solar Optical Telescope (SOT) of the Hinode satellite. Using the same space telescope, we performed a statistical analysis of convective collapse events. Methods. Our data sets consist of high resolution time series of polarimetric spectral scans of two iron lines formed in the lower photosphere and filter images in Mg I b2 and Ca II H, spectral lines that are formed i…
The magnetic network which consists of vertical flux tubes located in intergranular lanes is dominated by Hall drift in the photosphere-lower chromosphere region ($\lesssim 1 Mm$). In the internetwork regions, Hall drift dominates above $0.25 Mm$ in the photosphere and below $2.5 Mm$ in the chromosphere. Although Hall drift does not cause any dissipation in the ambient plasma, it can destabilise the flux tubes and magnetic elements in the presence of azimuthal shear flow. The physical mechanism of this instability is quite simple: the shear flow twists the radial magnetic field and generates a…
The first near-side X-class flare of the Solar Cycle 24 occurred in February 2011 and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (2011) followed by the discovery of a second sunquake by Zharkov et al (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 et al 2011) we prese…
Before the onset of a flare is observed in hard X-rays there is often a prolonged pre-flare or pre-heating phase with no detectable hard X-ray emission but pronounced soft X-ray emission suggesting that energy is being released and deposited into the corona and chromosphere already at this stage. This work analyses the temporal evolution of coronal source heating and the chromospheric response during this pre-heating phase to investigate the origin and nature of early energy release and transport during a solar flare. Simultaneous X-ray, EUV, and microwave observations of a well observed flare…
We recently reported extremely rapid changes in chromospheric fine structure observed using the IBIS instrument in the red wing of H alpha. Here, we examine data obtained during the same observing run (August 7 2010), of a mature active region NOAA 11094. We analyze more IBIS data including wavelength scans and data from the Solar Dynamics Observatory, all from within a 30 minute interval. Using a slab radiative transfer model, we investigate the physical nature of fibrils in terms of tube-like vs. sheet-like structures. Principal Component Analysis shows that the very rapid H alpha variations…
It is well known that the long-term evolution of the photospheric magnetic field plays an important role in building up free energy to power solar eruptions. Observations, despite being controversial, have also revealed a rapid and permanent variation of the photospheric magnetic field in response to the coronal magnetic field restructuring during the eruption. The Helioseismic and Magnetic Imager instrument (HMI) on board the newly launched Solar Dynamics Observatory (SDO) produces seeing-free full-disk vector magnetograms at consistently high resolution and high cadence, which finally makes …
Sunspot umbrae show a change in the dominant period of their oscillations from five minutes in the photosphere to three minutes in the chromosphere. In this paper, we explore the two most popular models proposed to explain the three-minute oscillations: the chromospheric acoustic resonator and the propagation of waves with frequency above the cutoff value directly from lower layers. We employ numerical simulations of wave propagation from the solar interior to the corona. Waves are driven by a piston at the bottom boundary. We have performed a parametric study of the measured chromospheric pow…
An analysis of line-of-sight velocity oscillation in nine solar faculae was undertaken with the aim of studying of phase relations between chromosphere (He i 10830 A line) and photosphere (Si i 10827 A line) five-minute oscillations. We found that time lag of the chromospheric signal relative to photospheric one varies from -12 to 100 seconds and is about 50 seconds on average.We assume that the small observed lag can have three possible explanations: i) convergence of formation levels of He i 10830 A and Si i 10827 A in faculae; ii) significant increase of five-minute oscillation propagation …
We investigate the emergence of magnetic flux in the quiet Sun at very small spatial scales, focusing on the magnetic connection between the photosphere and chromosphere. The observational data consist of spectropolarimetric measurements and filtergrams taken with the Hinode satellite and the Dutch Open Telescope. We find that a significant fraction of the magnetic flux present in internetwork regions appears in the form of Omega-shaped loops. The emergence rate is 0.02 loops per hour and arcsec^{-2}, which brings 1.1 x 10^12 Mx s^{-1} arcsec^{-2} of new flux to the solar surface. Initially, t…
Spicule oscillations involve high-frequency components with a typical period approximately corresponding to $40-50$ s. The typical time scale of the photospheric oscillation is a few minutes, and thus, the origin of this high-frequency component is not trivial. In this study, a one-dimensional numerical simulation is performed to demonstrate that the observed spicule oscillations originate from longitudinal-to-transverse mode conversion that occurs around the equipartition layer in the chromosphere. Calculations are conducted in a self-consistent manner with the exception of additional heating…
In this paper, we report the observed temporal correlation between extreme-violet (EUV) emission and magneto-acoustic oscillations in a EUV moss region, which is the footpoint region only connected by magnetic loops with million-degree plasma. The result is obtained from a detailed multi-wavelength data analysis to the region with the purpose of resolving fine-scale mass and energy flows that come from the photosphere, pass through the chromosphere and finally heat solar transition region or the corona. The data set covers three atmospheric levels on the Sun, consisting of high-resolution broa…
The solar chromosphere contains thin, highly dynamic strands of plasma known as spicules. Recently, it has been suggested that the smallest and fastest (Type II) spicules are identical to intermittent jets observed by the Interface Region Imaging Spectrograph. These jets appear to expand out along open magnetic field lines rooted in unipolar network regions of coronal holes. In this paper we revisit a thirty-year-old idea that spicules may be caused by upward forces associated with Alfven waves. These forces involve the conversion of transverse Alfven waves into compressive acoustic-like waves…
We study the C8.4 class solar flare SOL2016-05-14T11:34 UT using high-resolution spectral imaging in the Ca ii 8542 Å line obtained with the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope. Spectroscopic inversions of the Ca ii 8542 Å line using the non-LTE code NICOLE are used to investigate the evolution of the temperature and velocity structure in the flare chromosphere. A comparison of the temperature stratification in flaring and non-flaring areas reveals strong footpoint heating during the flare peak in the lower atmosphere. The temperature of the flaring footpoints b…
In this work we selected one particular fibril from a high resolution solar chromosphere observation from the Dutch Open Telescope, and tried to obtain a broad picture of the intricate mechanism that might be incorporated in the multiple layer of the Solar atmosphere in high cadence multi-wavelength observation. We analyzed the changingvfibril patter using multi-wavelength tomography, which consists of both H$α$ line center \& the blue wing, Doppler-signal, Ca II H, and the G-band. We have found that the intermittent ejected material through fibril from Doppler images has clearly shown oscilla…
The sunspot-associated sources at the frequency of 17 GHz give information on plasma parameters in the regions of magnetic field about B=2000 G at the level of the chromosphere-corona transition region. The observations of short period (from 1 to 10 minutes) oscillations in sunspots reflect propagation of magnetohydrodynamic (MHD) waves in the magnetic flux tubes of the sunspots. We investigate the oscillation parameters in active regions in connection with their flare activity. We confirm the existence of a link between the oscillation spectrum and flare activity. We find differences in the o…
It has long been known that magnetic plage and sunspots are regions in which the power of acoustic waves is reduced within the photospheric layers. Recent observations now suggest that this suppression of power extends into the low chromosphere and is also present in small magnetic elements far from active regions. In this paper we investigate the observed power supression in plage and magnetic elements, by modelling each as a collection of vertically aligned magnetic fibrils and presuming that the velocity within each fibril is the response to buffeting by incident $p$ modes in the surroundin…
We present a new method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots were analyzed to study the oscillation processes in the chromosphere-corona transition region in the layer with magnetic field B=2000 G. A high level of instability of the oscillations in the optical and …
Solar spicules are the fundamental magnetic structures in the chromosphere and considered to play a key role in channelling the chromosphere and corona. Recently, it was suggested by De Pontieu et al. that there were two types of spicules with very different dynamic properties, which were detected by space- time plot technique in the Ca ii H line (3968 A) wavelength from Hinode/SOT observations. 'Type I' spicule, with a 3-7 minute lifetime, undergoes a cycle of upward and downward motion; in contrast, 'Type II' spicule fades away within dozens of seconds, without descending phase. We are motiv…
Solar flares are currently understood as the explosive release of energy stored in the form of stressed magnetic fields. In many cases, the released energy seems to take the form of large numbers of electrons accelerated to high energies or alternatively plasma heated to very high temperatures. The transport of this energy into the remaining portion of the atmosphere results in violent mass motion and strong emission across the electromagnetic spectrum. One important phenomenon observed during flares is the appearance in coronal magnetic loops of large amounts of upflowing, soft X-ray emitting…
We obtained ultraviolet and optical spectra for 9 M~dwarfs across a range of rotation periods to determine whether they showed stochastic intrinsic variability distinguishable from flares. The ultraviolet spectra were observed during the Far Ultraviolet M~Dwarf Evolution Survey \emph{Hubble~Space~Telescope} program using the Space Telescope Imaging Spectrograph. The optical observations were taken from the Apache Point Observatory 3.5-meter telescope using the Dual Imaging Spectrograph and from the Gemini South Observatory using the Gemini Multi-Object Spectrograph. We used the optical spectra…
We investigated the quasi-periodic pulsation (QPP) in Lyman-alpha, X-ray and extreme-ultraviolet (EUV) emissions during two solar flares, i.e., an X-class (SOL2012-01-27T) and a C-class (SOL2016-02-08T). The full-disk Lyman-alpha and X-Ray flux during these solar flares were recorded by the EUV Sensor and X-Ray Sensor on board the Geostationary Operational Environmental Satellite. The °are regions were located from the EUV images measured by the Atmospheric Imaging Assembly. The QPP could be identified as a series of regular and periodic peaks in the light curves, and its quasi-periodicity was…
Sunspots host a large variety of oscillatory phenomena, whose properties depend on the nature of the wave modes and the magnetic and thermodynamic structure of the spot. Umbral chromospheric oscillations exhibit significant differences compared to their photospheric counterparts. They show an enhanced power and a shorter dominant period, from waves with an amplitude of a few hundred meters per second in the five-minute band at the photosphere, to amplitudes of several kilometers per second in the three-minute band at the chromosphere. Various models have been proposed to explain this behaviour…
The umbral oscillations of velocity are commonly observed in the chromosphere of a sunspot. Their sources are considered to be either the external p-mode driving or the internal excitation by magnetoconvection. Even though the possibility of the p-mode driving has been often considered, the internal excitation has been rarely investigated. We report the identification of the oscillation patterns that may be closely related to the events of internal excitation from the observations of velocity oscillations in the temperature minimum region of two sunspots. The velocities were determined from th…
We study a granular-sized magnetic flux emergence event that occurred in NOAA 11024 in July 2009. The observations were made with the CRISP spectropolarimeter at the Swedish 1 m Solar Telescope achieving a spatial resolution of 0.14". Simultaneous full Stokes observations of the two photospheric Fe I lines at 630.2 nm and the chromospheric Ca II 854.2 nm line allow us to describe in detail the emergence process across the solar atmosphere. We report here on 3D semi-spherical bubble events, where instead of simple magnetic footpoints, we observe complex semi-circular feet straddling a few granu…
The umbrella effect: Magnetic canopy topology modulates spatially averaged chromospheric three-minute power
Queen’s University Belfast（贝尔法斯特女王大学）；University of Oslo（奥斯陆大学）；California State University Northridge（北岭加州州立大学）；ASI Italian Space Agency（意大利航天局）；ESA Science and Operations Department（欧洲空间局科学与运营部）；Northumbria University（诺森比亚大学）；Institute of Theoretical Astrophysics（理论天体物理研究所）
Origin of small-scale evaporation flows deep in the chromosphere during a solar flare
Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系统研究所）；Grupo de Estudios en Heliofísica de Mendoza, CONICET, Universidad de Mendoza（门多萨日物理研究组，阿根廷国家科学研究委员会，门多萨大学）；Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（暗物质和空间天文重点实验室，中国科学院紫金山天文台）
On the Relationship between Solar Spicules and Propagating Coronal Disturbances: The Role of Shocks
Udaipur Solar Observatory, Physical Research Laboratory（乌代浦尔太阳观测台，物理研究实验室）；Indian Institute of Technology, Gandhinagar（印度理工学院，甘地纳加尔）；Indian Institute of Astrophysics（印度天体物理研究所）；Pondicherry University（本地治里大学）；School of Science, University of Newcastle（纽卡斯尔大学理学院）；Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematical and Physical Sciences, University of Sheffield（谢菲尔德大学数学与物理科学学院太阳物理与空间等离子体研究中心）；Department of Astronomy, Eötvös Loránd University（罗兰大学天文系）；Gyula Bay Zoltán Solar Observatory (GSO), Hungarian Solar Physics Foundation (HSPF)（久洛·拜·佐尔坦太阳观测台，匈牙利太阳物理基金会）
In the classical flare picture, hard X-ray emission from the chromosphere is succeeded by soft-X-ray emission from hot plasma in the flare loop, the soft X-ray emission being a direct consequence of the impact of the non-thermal particle beam. However, observations of events exist in which a pronounced increase in soft X-ray emission is observed minutes before the onset of the hard X-ray emission. Such pre-flare emission clearly contradicts the classical flare picture. For the first time, the pre-flare phase of such solar flares is studied in detail. We want to explain the time evolution of th…
Solar flares observed in the 200-400 GHz radio domain may exhibit a slowly varying and time-extended component which follows a short (few minutes) impulsive phase and which lasts for a few tens of minutes to more than one hour. The few examples discussed in the literature indicate that such long-lasting submillimeter emission is most likely thermal bremsstrahlung. We present a detailed analysis of the time-extended phase of the 2003 October 27 (M6.7) flare, combining 1-345 GHz total-flux radio measurements with X-ray, EUV, and Hα observations. We find that the time-extended radio emission is, …
Inversion codes allow reconstructing a model atmosphere from observations. With the inclusion of optically thick lines that form in the solar chromosphere, such modelling is computationally very expensive because a non-LTE evaluation of the radiation field is required. In this study, we combine the results provided by these traditional methods with machine and deep learning techniques to obtain similar-quality results in an easy-touse, much faster way. We have applied these new methods to Mg II h&k lines observed by IRIS. As a result, we are able to reconstruct the thermodynamic state (tempera…
Flare kernels are compact features located in the solar chromosphere that are the sites of rapid heating and plasma upflow during the rise phase of flares. An example is presented from a M1.1 class flare observed on 2011 February 16 07:44 UT for which the location of the upflow region seen by EIS can be precisely aligned to high spatial resolution images obtained by the Atmospheric Imaging Assembly (AIA) and Heliospheric Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). A string of bright flare kernels is found to be aligned with a ridge of strong magnetic field, and one ker…
Solar flares typically have an impulsive phase that followed by a gradual phase as best seen in soft X-ray emissions. A recent discovery based on the EUV Variability Experiment (EVE) observations onboard the Solar Dynamics Observatory (SDO) reveals that some flares exhibit a second large peak separated from the first main phase peak by tens of minutes to hours, which is coined as the flare's EUV late phase. In this paper, we address the origin of the EUV late phase by analyzing in detail two late phase flares, an M2.9 flare on 2010 October 16 and an M1.4 flare on 2011 February 18, using multi-…
