In addition to X-rays, extreme ultraviolet (EUV) rays radiated from solar flares can cause serious problems, such as communication failures and satellite drag. Therefore, methods for forecasting EUV dynamic spectra during flares are urgently required. Recently, however, owing to the lack of instruments, EUV dynamic spectra have rarely been observed. Hence, we develop a new method that converts the soft X-ray light curve observed during large flare events into an EUV dynamic spectrum by using the Solar Dynamics Observatory / Atmospheric Imaging Assembly images, a numerical simulation, and atomic database. The simulation provides the solution for a coronal loop that is heated by a strong flare, and the atomic database calculates its dynamic spectrum, including X-ray and EUV irradiances. The coefficients needed for the conversion can be calculated by comparing the observed soft X-ray light curve with that of the simulation. We apply our new method to three flares that occurred in the active region 12673 on September 06, 2017. The results show similarities to those of the Flare Irradiance Spectral Model, and reconstruct some of the EUV peaks observed by the EUV Variability Experiment onboard the Solar Dynamics Observatory.
Toward Operational Solar Flare Peak Flux Nowcasting: A Strategy Combining Real-Time Data, Machine Learning, and NOAA Flare Detection Criteria
New Jersey Institute of Technology（新泽理工学院）；Sam Houston State University（山荷斯顿州立大学）；Big Bear Solar Observatory, New Jersey Institute of Technology（新泽理工学院大熊太阳观测站）
A universal scaling between damping time and period of quasi-periodic pulsations from solar EUV brightenings to X-ray stellar flares
Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium（太阳-星际卓越中心–SIDC，比利时皇家天文台）；Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven（KU鲁汶大学数学系数学等离子体天体物理学中心）；University of Exeter（埃克塞特大学）；Centre for Fusion, Space and Astrophysics, Physics Department, University of Warwick（华威大学物理部聚变、空间与天体物理学中心）；Engineering Research Institute “Ventspils International Radio Astronomy Centre (VIRAC)”, Ventspils University of Applied Sciences（文茨皮尔斯应用科学大学“文茨皮尔斯国际射电天文中心（VIRAC）”工程研究所）；Centro de Investigacion en Astronomía, Universidad Bernardo O’Higgins（贝尔纳多·奥希金斯大学天文学研究中心）；Aryabhatta Research Institute of Observational Sciences (ARIES)（阿亚玻塔观测科学研究所（ARIES））
The most energetic flares start with a filament rise followed by magnetic reconnection below this filament. The start of the reconnection corresponds to the beginning of the flare impulsive phase. In this paper we study processes before this phase. During the filament rise we recognize an unusual radio continuum with a starting boundary drifting toward lower frequencies. The estimated velocity of the agent generating this continuum boundary is about 400 km/s, similar to that of the rising filament. In association with this filament rise, transient X-ray sources and extreme ultaviolet (EUV) bri…
Recent observations in extreme-ultraviolet (EUV) wavelengths reveal an EUV late phase in some solar flares that is characterized by a second peak in warm coronal emissions ($\sim3$~MK) several tens of minutes to a few hours after the soft X-ray (SXR) peak. Using the model enthalpy-based thermal evolution of loops (EBTEL), in this paper we numerically probe the production of EUV late-phase solar flares. Starting from two main mechanisms of producing the EUV late phase, i.e., long-lasting cooling and secondary heating, we carry out two groups of numerical experiments to study the effects of thes…
极紫外光变率实验（EVE）在太阳耀斑期间观测到的Fe XVI 33.5 nm谱线辐照度的第二个峰值被称为极紫外光（EUV）晚期相。我们之前的论文（Liu et al. 2013）发现，晚期阶段的主要排放来自与后耀斑环（PFL）密切相关但不同的大规模环弧，我们还提出，没有额外加热的长期冷却过程可以解释晚期阶段。在本文中，我们定义了极大的后期阶段，因为它不仅在温暖的33.5辐照度轮廓中具有更大的峰值，而且比主阶段释放更多的EUV辐射能量。从三个角度对极紫外图像进行了详细的分析，发现除了后期的相位环弧外，后期的巨大相位弧的贡献主要来自于一个未喷发的热结构。这种热结构被认为是一个通量绳，它很快被耀斑重联所激励，然后在渐变阶段持续产生热能。未喷发的磁通绳与附加加热一起与后期环路拱廊一起产生了极大的EUV后期。
Extreme ultraviolet (EUV) solar flare emissions evolve in time as the emitting plasma heats and then cools. Although accurately modeling this evolution has been historically difficult, especially for empirical relationships, it is important for understanding processes at the Sun, as well as for their influence on planetary atmospheres. With a goal to improve empirical flare models, a new simple empirical expression is derived to predict how cool emissions will evolve based on the evolution of a hotter emission. This technique is initially developed by studying 12 flares in detail observed by t…
Revealing Flare Energetics and Dynamics with SDO EVE Solar Extreme Ultraviolet Spectral Irradiance Observations
Laboratory for Atmospheric and Space Physics, University of Colorado（科罗拉多大学大气与空间物理实验室）；Johns Hopkins University, Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；High Altitude Observatory, National Center for Atmospheric Research（美国国家大气研究中心高空观测站）；Naval Research Laboratory（海军研究实验室）
{We报告我们在2011年10月15日观测到的与耀斑相关的极紫外线漩涡喷流。{We利用SDO/AIA的EUV观测。我们沿喷流轴提取了一条宽缝，沿喷流轴提取了12条细缝，以研究喷流的纵向运动和横向旋转。我们还使用STEREO/EUVI的数据来研究射流的3D结构。基于地面的H $α$图像提供了一个很好的机会，探讨冷涌和热射流之间的关系。SDO/HMI的LOS磁图使我们能够研究耀斑/喷流事件的磁演化。{The喷流爆发的开始时间与C1.6耀斑脉冲相的开始时间相吻合。纵向运动的初速度和加速度分别为254 $\pm10$ km s $^{-1}$和$-97\pm5$ m s $^{-2}$。喷流在喷发初期呈现螺旋状结构和横向旋转运动。逆时针旋转从平均速度PDMATHAMR 122 km s $^{-1}$减慢到PDMATHAMR 80 km s $^{-1}$。在持续1个周期的旋转过程中，射流的相互缠绕的粗丝解捻成多个细丝，周期为$\sim$ 7 min，振幅从底部的$\sim$ 3.2 μ m增加到上部的$\sim$ 11 μ m。之后，喷流的幕状前缘继续上升，没有旋转，留下一个昏暗的区域，然后回落到太阳表面。变暗的出现/消失与急流的纵向上升/下降运动相对应。同空间H $α$浪涌和EUV调光表明，调光是由冷浪涌吸收热EUV辐射造成的。耀斑/喷流事件是由耀斑开始前持续的磁抵消引起的。喷流与AR…
We present SDO/AIA observation of three types of fast-mode propagating magnetosonic waves in a GOES C3.0 flare on 2013 April 23, which was accompanied by a prominence eruption and a broad coronal mass ejection (CME). During the fast rising phase of the prominence, a large-scale dome-shaped extreme ultraviolet (EUV) wave firstly formed ahead of the CME bubble and propagated at a speed of about 430 km/s in the CME's lateral direction. One can identify the separation process of the EUV wave from the CME bubble. The reflection effect of the on-disk counterpart of this EUV wave was also observed wh…
The Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory obtains extreme-ultraviolet (EUV) spectra of the full-disk Sun at a spectral resolution of ~1 A and cadence of 10 s. Such a spectral resolution would normally be considered to be too low for the reliable determination of electron density (N_e) sensitive emission line intensity ratios, due to blending. However, previous work has shown that a limited number of Fe XXI features in the 90-60 A wavelength region of EVE do provide useful N_e-diagnostics at relatively low flare densities (N_e ~ 10^11-10^12 cm^-3). H…
The reflection, refraction, and transmission of large-scale extreme ultraviolet (EUV) waves (collectively, secondary waves) have been observed during their interactions with coronal structures such as active regions (ARs) and coronal holes (CHs). However, the effect of the total reflection of EUV waves has not been reported in the literature. Here, we present the first unambiguous observational evidence of the total reflection of a quasi-periodic EUV wave train during its interaction with a polar CH. The event occurred in NOAA AR 12473, located close to the southeast limb of the solar disk, an…
It is generally accepted that densities of quiet sun and active region plasma are sufficiently low to justify the optically thin approximation, and it is commonly used in the analysis of line emissions from plasma in the solar corona. However, densities of solar flare loops are substantially higher, compromising the optically thin approximation. This study begins with a radiative transfer model that uses typical solar flare densities and geometries to show that hot coronal emission lines are not generally optically thin. Further, the model demonstrates that the observed line intensity should e…
A second emission enhancement in warm coronal extreme-ultraviolet (EUV) lines (about 2-7 MK) during some solar flares is known as the EUV late phase. Imaging observations confirm that the late phase emission originates from a set of longer or higher loops than the main flare loops. Nevertheless, some questions remain controversial: What is the relationship between these two loop systems? What is the heating source of late phase emission, a heating accompany the main phase heating or occuring quite later? In this paper, we present clear evidence for heating source in a late-phase solar flare: m…
The chromospheric Lyman-alpha line of neutral hydrogen (\lya; 1216Å) is the strongest emission line in the solar spectrum. Fluctuations in \lya\ are known to drive changes in planetary atmospheres, although few instruments have had the ability to capture rapid \lya\ enhancements during solar flares. In this paper we describe flare-associated emissions via a statistical study of 477 M- and X-class flares as observed by the EUV Sensor on board the 15th Geostationary Operational Environmental Satellite, which has been monitoring the full-disk solar \lya\ irradiance on 10~s timescales over the cou…
One of the objectives of the NASA LWS Institute on Nowcasting of Atmospheric Drag for LEO Spacecraft was to investigate whether and how to increase the accuracy of atmospheric drag models by improving the quality of the solar forcing inputs, namely Extreme Ultraviolet (EUV) irradiance information. In this focused review, we examine the status of and issues with EUV measurements and proxies, discuss recent promising developments, and suggest a number of ways to improve the reliability, availability, and forecast accuracy of EUV measurements in the next solar cycle.
In this study, we present the observations of extreme-ultraviolet (EUV) waves associated with an M6.5 flare on 2013 April 11. The event was observed by Solar Dynamics Observatory (SDO) in different EUV channels. The flare was also associated with a halo CME and type II radio bursts. We observed both fast and slow components of the EUV wave. The speed of the fast component, which is identified as a fast-mode MHD wave, varies in the range from 600 to 640 km s^-1 , whereas the speed of the slow-component is ~140 km s^-1 . We observed an unusual phenomenon that, as the fast-component EUV wave pass…
We report multi-wavelength observations of four solar flares on 2014 July 07. We firstly select these flares according to the soft X-ray (SXR) and extreme ultraviolet (EUV) emissions recorded by the Extreme Ultraviolet Variability Experiment and Geostationary Orbiting Environmental Satellites. Then their locations and geometries are identified from the full-disk images measured by the Atmospheric Imaging Assembly (AIA), and the time delays among the light curves in different channels are identified. The electron number densities are estimated using the Differential Emission Measure method. We …
Secondary Waves, and/or the "Reflection" From and "Transmission" Through a Coronal Hole of an EUV Wave Associated With the 2011 February 15 X2.2 Flare Observed With SDO/AIA and STEREO/EUVI
We present observations of a powerful solar eruption, accompanied by an X8.2 solar flare, from NOAA Active Region 12673 on 2017 September 10 by the Solar Ultraviolet Imager (SUVI) on the GOES-16 spacecraft. SUVI is noteworthy for its relatively large field of view, which allows it to image solar phenomena to heights approaching 2 solar radii. These observations include the detection of an apparent current sheet associated with magnetic reconnection in the wake of the eruption and evidence of an extreme-ultraviolet wave at some of the largest heights ever reported. We discuss the acceleration o…
