分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Supra-arcade downflows (SADs) are dark structures descending towards post-reconnection flare loops observed in extreme ultraviolet or X-ray observations and are closely related to magnetic reconnection during solar flares. Due to the lack of statistical study on SADs in a single flare, evolutions of kinematic and thermal properties of SADs during the flare process still remain obscure. In this work, we identified 81 SADs in a flare that occurred on 2013 May 22 using observations of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). The kinematic properties of each SAD, including the appearance time, height, projective velocity, and acceleration were recorded. We found that the appearance heights of SADs become larger during the flare, which is likely due to the lift of the bottom of the plasma sheet. In the flare decay phase, the region where SADs mainly appear moves from the north part to the south side possibly related to a secondary eruption in the south side. The trajectories of most SADs can be fitted by one or two deceleration processes, while some special ones have positive accelerations during the descent. For the thermal properties, we selected 54 SADs, whose front and body could be clearly distinguished from the surrounding during the entire descent, to perform Differential Emission Measure analysis. It is revealed that the temperatures of the SAD front and body tend to increase during their downward courses, and the relationship between the density and temperature indicates that the heating is mainly caused by adiabatic compression.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zhenyong Hou
Hui Tian
Jing-Song Wang
Xiaoxin Zhang
Qiao Song
Ruisheng Zheng
Hechao Chen
Bo Chen
Xianyong Bai
Yajie Chen
Lingping He
Kefei Song
Peng Zhang
Xiuqing Hu
Jinping Dun
Weiguo Zong
Yongliang Song
Yu Xu
Guangyu Tan
摘要： We present a case study for the global extreme ultraviolet (EUV) wave and its chromospheric counterpart `Moreton-Ramsey wave' associated with the second X-class flare in Solar Cycle 25 and a halo coronal mass ejection (CME). The EUV wave was observed in the H$\alpha$ and EUV passbands with different characteristic temperatures. In the 171 {\AA} and 193/195 {\AA} images, the wave propagates circularly with an initial velocity of 600-720 km s$^{-1}$ and a deceleration of 110-320 m s$^{-2}$. The local coronal plasma is heated from log(T/K)=5.9 to log(T/K)=6.2 during the passage of the wavefront. The H$\alpha$ and 304 {\AA} images also reveal signatures of wave propagation with a velocity of 310-540 km s$^{-1}$. With multi-wavelength and dual-perspective observations, we found that the wavefront likely propagates forwardly inclined to the solar surface with a tilt angle of ~53.2$^{\circ}$. Our results suggest that this EUV wave is a fast-mode magnetohydrodynamic wave or shock driven by the expansion of the associated CME, whose wavefront is likely a dome-shaped structure that could impact the upper chromosphere, transition region and corona.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Extreme-ultraviolet late phase (ELP) refers to the second extreme-ultraviolet (EUV) radiation enhancement observed in certain solar flares, which usually occurs tens of minutes to several hours after the peak of soft X-ray emission. The coronal loop system that hosts the ELP emission is often different from the main flaring arcade, and the enhanced EUV emission therein may imply an additional heating process. However, the origin of the ELP remains rather unclear. Here we present the analysis of a C1.4 flare that features such an ELP, which is also observed in microwave wavelengths by the Expanded Owens Valley Solar Array (EOVSA). Similar to the case of the ELP, we find a gradual microwave enhancement that occurs about three minutes after the main impulsive phase microwave peaks. Radio sources coincide with both footpoints of the ELP loops and spectral fits on the time-varying microwave spectra demonstrate a clear deviation of the electron distribution from the Maxwellian case, which could result from injected nonthermal electrons or nonuniform heating to the footpoint plasma. We further point out that the delayed microwave enhancement suggests the presence of an additional heating process, which could be responsible for the evaporation of heated plasma that fills the ELP loops, producing the prolonged ELP emission.
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