我们利用数值模拟研究了太阳大气局部区域中耀斑后环的形成与动力学。MHD 方程主导了耀斑后结构的动力学演化，包括在 2.5D 切片上的空间相关磁电阻率和高度各向异性的热传导。我们使用由垂直电流片组成的初始磁场位形，这有助于触发磁重联过程。具体而言，我们研究了两种场景，一种仅有电阻率，第二种包含电阻率加热传导。数值模拟显示两种情况下耀斑后子结构的全局形态存在差异。具体而言，局部电阻率在与 Ritchmyer-Meshkov 不稳定性（RMI）相关的环上产生了更多子结构。另一方面，在电阻率加热传导的场景中，耀斑后环是平滑的，且没有发展出明显的子结构。此外，在 Res+TC 场景电流密度的 z 分量中，我们观察到沿电流片发展出了多个小磁岛。
英文摘要：
Using numerical simulations, we study the formation and dynamics of post-flare loops in a local region of the solar atmosphere. The MHD equations rule the post-flare structures' dynamic evolution, including space-dependent magnetic resistivity and highly anisotropic thermal conduction on a 2.5 D slice. We use an initial magnetic configuration consisting of a vertical current sheet, which helps trigger the magnetic reconnection process. Specifically, we study two scenarios, one with only resistivity and the second with resistivity plus thermal conduction. Numerical simulations show differences in the global morphology of the post-flare substructures in both cases. In particular, localized resistivity produces more substructure on the loops related to a Ritchmyer-Meshkov Instability (RMI). On the other hand, in the scenario with resistivity plus thermal conduction, the post-flare loops are smooth, and no apparent substructures develop. Besides, in the $z-$component of the current density for the Res+TC scenario, we observe the development of multiple small magnetic islands along the current sheet.
Solar flares are explosive events in the solar corona, representing fast conversion of magnetic energy into thermal and kinetic energy, and hence radiation, due to magnetic reconnection. Modelling is essential for understanding and predicting these events. However, self-consistent modelling is extremely difficult due to the vast spatial and temporal scale separation between processes involving thermal plasma (normally considered using magnetohydrodynamic (MHD) approach) and non-thermal plasma (requiring a kinetic approach). In this mini-review we consider different approaches aimed at bridging…
Solar flares are an explosive phenomenon, where super-sonic flows and shocks are expected in and above the post-flare loops. To understand the dynamics of post-flare loops, a two-dimensional magnetohydrodynamic (2D MHD) simulation of a solar flare has been carried out. We found new shock structures in and above the post-flare loops, which were not resolved in the previous work by Yokoyama and Shibata 2001. To study the dynamics of flows along the reconnected magnetic field, kinematics and energetics of the plasma are investigated along selected field lines. It is found that shocks are crucial …
Solar flares are energetic events taking place in the Sun's atmosphere, and their effects can greatly impact the environment of the surrounding planets. In particular, eruptive flares, as opposed to confined flares, launch coronal mass ejections into the interplanetary medium, and as such, are one of the main drivers of space weather. After briefly reviewing the main characteristics of solar flares, we summarize the processes that can account for the build up and release of energy during their evolution. In particular, we focus on the development of recent 3D numerical simulations that explain…
Solar active region 12673 produced two successive X-class flares (X2.2 and X9.3) approximately 3 hours apart in September 2017. The X9.3 was the recorded largest solar flare in Solar Cycle 24. In this study we perform a data-constrained magnetohydrodynamic simulation taking into account the observed photospheric magnetic field to reveal the initiation and dynamics of the X2.2 and X9.3 flares. According to our simulation, the X2.2 flare is first triggered by magnetic reconnection at a local site where at the photosphere the negative polarity intrudes into the opposite-polarity region. This magn…
Supra-arcade downflows (SADs) are sunward, generally dark, plasma density depletions originated above posteruption flare arcades. In this paper using 3D MHD simulations we investigate if the SAD cavities can be produced by a direct combination of the tearing mode and Kelvin-Helmholtz instabilities leading to a turbulent current sheet (CS) medium or if the current sheet is merely the background where SADs are produced triggered by an impulsive deposition of energy. We find that to give account of the observational dark lane structures an addition of local energy, provided by a reconnection even…
For decades it has been established that the amount of energy released by solar flares excites the acoustic oscillations propagating on the surface of the Sun (Wolff 1972). It is believed that these flares can excite velocity oscillations in active regions, especially those regions where a higher class solar flare has taken place (Kumar 2006). However, questions arise as to how the behaviors of acoustic oscillations within such a chaotic environment can birth other waves of the MHD type. Can we observe such events?
With SDO observations and a data-constrained MHD model, we identify a confined multi-ribbon flare occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch (BP) flare with strong evidences. From the photospheric magnetic field observed by SDO/HMI, we find there is indeed magnetic BPs on the PILs which match parts of the flare ribbons. From the 3D coronal magnetic field derived from a MHD relaxation model constrained by the vector magnetograms, we find strikingly good agreement of the BP separatrix surface (BPSS) footpoints with the flare ribbons, and the BPSS itself wit…
Since their discovery by SDO/AIA in EUV, rapid (phase speeds of 1000 km/s), quasi-periodic, fast-mode propagating wave trains (QFPs) have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology. The reported waves usually originate from a single localized source associated with the flare. Here, we report the first detection of counter-propagating QFPs ass…
We present observations of a B7.9-class flare that occurred on the 24th January, 2015, using the Atmopsheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO), the EUV Imaging Spectrometer (EIS) and the X-Ray Telescope of Hinode. The flare triggers the eruption of a dense cool plasma blob as seen in AIA 171Å,\, which is unable to completely break out and remains confined within a local bundle of active region loops. During this process, transverse oscillations of the threads are observed. The cool plasma is then observed to descend back to the chromosphere along each loop strand. …
Context. On the sun, the magnetic field vector is measured routinely only in the photosphere. By using these photospheric measurements as boundary condition, we developed the magnetohydrostatic (MHS) extrapolation to model the solar atmosphere. The model makes assumption about the relative importance of magnetic and non-magnetic forces. While the solar corona is force-free, this is not the case in photosphere and chromosphere. Aim. The model has been tested with an exact equilibria in \cite{zw18}. Here we present a more challenging and realistic test of our model with radiative MHD simulation …
We performed two data-based magnetohydrodynamic (MHD) simulations for solar active region 12371 which produced an M6.5 flare. The first simulation is a full data-driven simulation where the initial condition is given by a nonlinear force-free field (NLFFF). This NLFFF was extrapolated from photospheric magnetograms approximately 1 hour prior to the flare, and then a time-varying photospheric magnetic field is imposed at the bottom surface. The second simulation is also a data-driven simulation, but it stops driving at the bottom before the time of flare onset and then switches to the data-cons…
The aim of this work is to investigate and characterise non-thermal particle behaviour in a three-dimensional (3D) magnetohydrodynamical (MHD) model of unstable multi-threaded flaring coronal loops. We have used a numerical scheme which solves the relativistic guiding centre approximation to study the motion of electrons and protons. The scheme uses snapshots from high resolution numerical MHD simulations of coronal loops containing two threads, where a single thread becomes unstable and (in one case) destabilises and merges with an additional thread. The particle responses to the reconnection…
We study the physical properties and behavior of the solar atmosphere during the GOES X1.6 solar flare on 2014 September 10. The steady plasma flows and the fast sausage MHD waves were analysed with the wavelet separation method. The magnetically coupled atmosphere and the forced magnetic field reconnection were studied with the help of the Vertical-Current Approximation Non-linear Force-Free Field code. We studied a mechanism of MHD wave transfer from the photosphere without dissipation or reflection before reaching the corona and a mechanism of the wave energy distribution over the solar cor…
We present results revealing microwave pulsations produced in a model of a flaring twisted solar coronal loop, without any external oscillatory driver. Two types of oscillations are identified: slowly-decaying oscillations with a period of about 70-75s and amplitude of about 5-10% seen in loops both with and without energetic electrons, and oscillations with period of about 40s and amplitude of a few tens of percent observed only in loops with energetic electrons for about 100s after onset of fast energy release. We interpret the longer-period oscillations as the result of a standing kink mode…
A New Framework for Modeling Solar Flares from MHD to Kinetic Processes
NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；SUPA School of Physics and Astronomy, University of Glasgow（苏格兰大学物理与天文学学院，格拉斯哥大学）；Department of Physics, Catholic University of America（天主教大学物理系）；Department of Physics, American University（美国大学物理系）；Astronomy Department, University of Maryland（马里兰大学天文系）；Institute for Research in Electronics and Applied Physics, University of Maryland（马里兰大学电子与应用物理研究所）；Heliophysics and Planetary Science Branch, NASA Marshall Space Flight Center（美国国家航空航天局马歇尔太空飞行中心日地物理学与行星科学处）
A Data-constrained Magnetohydrodynamic Simulation of Successive X-class Flares in Solar Active Region 13842 I. Dynamics of the Solar Eruption Associated with the X7.1 Solar Flare
Coronal flare emission is commonly observed to decay on timescales longer than those predicted by impulsively-driven, one-dimensional flare loop models. This discrepancy is most apparent during the gradual phase, where emission from these models decays over minutes, in contrast to the hour or more often observed. Magnetic reconnection is invoked as the energy source of a flare, but should deposit energy into a given loop within a matter of seconds. Models which supplement this impulsive energization with a long, persistent ad hoc heating have successfully reproduced long-duration emission, but…
Electric currents play a critical role in the triggering of solar flares and their evolution. The aim of the present paper is to test whether the surface electric current has a surface or subsurface fixed source as predicts the circuit approach of flare physics, or is the response of the surface magnetic field to the evolution of the coronal magnetic field as the MHD approach proposes. Out of all 19 X-class flares as observed by SDO from 2011 to 2016 near the disk center, we analyzed the only 9 eruptive flares for which clear ribbon-hooks were identifiable. Flare ribbons with hooks are conside…
Quasi-Periodic Fast-Mode Wave Trains Associated with the 2015-Jun-22 M6.5 Flare in AR~12371: Observations and 3D MHD Modeling
Catholic University of America（美国天主教大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；Bay Area Environmental Research Institute（湾区环境研究所）；Lockheed Martin Solar and Astrophysics Laboratory（洛克希德·马丁太阳与天体物理实验室）；Institute for Astronomy, University of Hawai‘i at Mānoa（夏威夷大学马诺阿分校天文学研究所）
Solar flare activity is characterised by different classification systems, both in optical and X-ray ranges. The most generally accepted classifications of solar flares describe important parameters of flares such as the maximum of brightness of the flare in the in optical range - $H_α$ flare class (change from F to B), area of the flare in $H_α$ (change from S for areas less than 2 square degrees to 4 for areas more than 24.7 square degrees) and the maximum amplitude of the soft X-ray (SXR-flux) in the band 0.1 -- 0.8 nm ($F_{0.1-0.8}^{max}$) -- X-ray flares of classes from C to X. A new clas…
Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6~m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing …
The review addresses the spatial frequency morphology of sources of sunspot oscillations and waves, including their localization, size, oscillation periods, height localization with the mechanism of cut-off frequency that forms the observed emission variability. Dynamic of sunspot wave processes, provides the information about the structure of wave fronts and their time variations, investigates the oscillation frequency transformation depending on the wave energy is shown. The initializing solar flares caused by trigger agents like magnetoacoustic waves, accelerated particle beams, and shocks …
Without any doubt solar flaring loops possess a multi-thread internal structure that is poorly resolved and there are no means to observe heating episodes and thermodynamic evolution of the individual threads. These limitations cause fundamental problems in numerical modelling of flaring loops, such as selection of a structure and a number of threads, and an implementation of a proper model of the energy deposition process. A set of 1D hydrodynamic and 2D magnetohydrodynamic models of a flaring loop are developed to compare energy redistribution and plasma dynamics in the course of a prototypi…
During the next solar maximum, two upcoming space-borne X-ray missions, STIX on board Solar Orbiter and MiSolFA, will perform stereoscopic X-ray observations of solar flares at two different locations: STIX at 0.28 AU (at perihelion) and up to inclinations of $\sim25^{\circ}$, and MiSolFA in a low-Earth orbit. The combined observations from these cross-calibrated detectors will allow us to infer the electron anisotropy of individual flares confidently for the first time. We simulated both instrumental and physical effects for STIX and MiSolFA including thermal shielding, background and X-ray C…
The chapter "Solar Active Region Electric Currents Before and During Eruptive Flares" is a discussion on electric currents in the pre-eruption state and in the course of eruptions of solar magnetic structures, using information from solar observations, nonlinear force-free field extrapolations relying on these observations, and three-dimensional magnetohydrodynamic (MHD) models. The discussion addresses the issue of neutralized vs. non-neutralized currents in active regions and concludes that MHD models are able to explain non-neutralized currents in active regions by the existence of strong m…
A Data-constrained Magnetohydrodynamic Simulation of Successive X-class Flares in Solar Active Region 13842. II. Dynamics of the Solar Eruption Associated with the X9.0 Solar Flare
Quasi-periodic pulsations (QPP) are common in solar flares and are now regularly observed in stellar flares. We present the detection of two different types of QPP signals in the thermal emission light curves of the X9.3 class solar flare SOL2017-09-06T12:02, which is the most powerful flare of Cycle 24. The period of the shorter-period QPP drifts from about 12 to 25 seconds during the flare. The observed properties of this QPP are consistent with a sausage oscillation of a plasma loop in the flaring active region. The period of the longer-period QPP is about 4 to 5 minutes. Its properties are…
We propose a magnetic confinement nuclear fusion mechanism for the evolution of a solar flare in solar atmosphere. The mechanism agree with two observed characteristics of explosive flares and coronal mass ejections (CMEs) that have proved to be very difficult to explain with previous mechanisms: the huge enrichments of $^{3}He$ and the high energy gamma ray radiation. The twisted magnetic flux rope is a typical structure during the solar flares, which is closely related to the solar active region that magnetic fields have almost complete control over the plasma. Consequently, the plasma insid…
The prediction of the evolution of individual solar cycles is a developing field, faced with divergence of forecasts even for a few years in the future. Specifically for solar flares, long-term modeling is practically absent even in rough terms. In this article a forecast for the evolution of solar cycle 25 in terms of solar flares activity is presented. It is derived from an existing phenomenological model based on the coupling of an internal solar component and a planetary component. In addition to competent temporal resolution, the predictions are characterized by features which both differ…
The Geostationary Orbital Environmental Satellites (GOES) Soft X-ray (SXR) sensors have provided data relating to, inter alia, the time, intensity and duration of solar flares since the 1970s. The GOES SXR Flare List has become the standard reference catalogue for solar flares and is widely used in solar physics research and space weather. We report here that in the current version of the list there are significant differences between the mean duration of flares which occurred before May 1997 and the mean duration of flares thereafter. Our analysis shows that the reported flare timings for the…
The Influence of Solar Flares on the Lower Solar Atmosphere: Evidence from the Na D Absorption Line Measured by GOLF/SOHO
据推测，太阳耀斑对太阳大气层的最深层有影响，但这种影响的观测证据很少。使用十年的测量Na D $_{1}$和Na D $_2$夫琅和费线，测量的GOLF船上SOHO，我们表明，这光球线确实是受耀斑。个别耀斑的影响被太阳振荡所掩盖，但基于条件平均的统计分析揭示了一个清晰的信号。虽然GOLF只能探测一个单一的波长在同一时间，我们表明，两翼的钠线仍然可以比较。变化的线不对称性可以被解释为在耀斑的峰值期间来自低层太阳大气的向上的等离子体运动，随后是向下的运动。
Red-shifted components of chromospheric emission lines in the hard X-ray impulsive phase of solar flares have recently been studied through their 30 s evolution with the high resolution of IRIS. Radiative-hydrodynamic flare models show that these redshifts are generally reproduced by electron-beam generated chromospheric condensations. The models produce large ambient electron densities, and the pressure broadening of hydrogen Balmer series should be readily detected in observations. To accurately interpret upcoming spectral data of flares with the DKIST, we incorporate non-ideal, non-adiabati…
The boundary conditions for the ideal MHD equations on a plane dis- continuity surface are investigated. It is shown that, for a given mass flux through a discontinuity, its type depends only on the relation between inclina- tion angles of a magnetic field. Moreover, the conservation laws on a surface of discontinuity allow changing a discontinuity type with gradual (continu- ous) changes in the conditions of plasma flow. Then there are the so-called transition solutions that satisfy simultaneously two types of discontinuities. We obtain all transition solutions on the basis of the complete sy…
With the aim of understanding the physical mechanisms of confined flares, we selected 18 confined flares during 2011-2017, and classified the confined flares into two types based on their different dynamic properties and magnetic configurations. "Type I" of confined flares are characterized by slipping reconnection, strong shear, and stable filament. "Type II" flares have nearly no slipping reconnection, and have a configuration in potential state after the flare. Filament erupts but is confined by strong strapping field. "Type II" flares could be explained by 2D MHD models while "type I" flar…
We often find spectral signatures of chromospheric cold plasma ejections accompanied by flares in a wide range of spatial scales in the solar and stellar atmospheres. However, the relationship between physical quantities (such as mass, kinetic energy, and velocity) of cold ejecta and flare energy has not been investigated in a unified manner for the entire range of flare energies to date. This study analyzed the spectra of cold plasma ejections associated with small-scale flares and solar flares (energy $10^{25}-10^{29}\,\mathrm{erg}$) to supply smaller energy samples. We performed H$α$ imagin…
On the basis of the 30-year ago ground-based photometry and the recent Kepler space experiment there have been considered frequencies of occurrence and energetics of the solar-type stellar flares. It was concluded that frequencies of occurrence of such flares are proportional to sizes of stellar surfaces, and estimates of maximum flare radiation from the results of the ground-based photometry and space observations practically coincide.
As the Lyman-alpha (Lya) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Lya of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ~8500 flares greater than B1 class to determine the contribution that flares make to changes in the solar EUV irradiance. Using the peak of …
