分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We investigate various dynamic processes including magnetic reconnection, chromospheric evaporation, and coronal rain draining in two limb solar flares through imaging and spectroscopic observations from the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. In the early phase of the flares, a bright and dense loop-top structure with a cusp-like shape can be seen in multi-wavelength images, which is co-spatial with the hard X-ray 25--50 keV emission. In particular, intermittent magnetic reconnection downflows are detected in the time-space maps of AIA 304 {\AA}. The reconnection downflows are manifested as redshifts on one half of the loops and blueshifts on the other half in the IRIS Si {\sc iv} 1393.76 {\AA} line due to a projection effect. The Si {\sc iv} profiles exhibit complex features (say, multi-peak) with a relatively larger width at the loop-top region. During the impulsive phase, chromospheric evaporation is observed in both AIA images and the IRIS Fe {\sc xxi} 1354.08 {\AA} line. Upward motions can be seen from AIA 131 {\AA} images. The Fe {\sc xxi} line is significantly enhanced and shows a good Gaussian shape. In the gradual phase, warm rains are observed as downward moving plasmas in AIA 304 {\AA} images. Both the Si {\sc iv} and Fe {\sc xxi} lines show a relatively symmetric shape with a larger width around the loop top. These results provide observational evidence for various dynamic processes involved in and are crucial to understand the energy release process of solar flares.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we present a detailed morphological, kinematic, and thermal analysis of two homologous magnetic flux ropes (MFRs) from NOAA 11515 on 2012 July 8--9. The study is based on multi-wavelength and dual-perspective imaging observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory Ahead spacecraft, which can well reveal the structure and evolution of the two MFRs. We find that both of the MFRs show up in multiple passbands and their emissions mainly consist of a cold component peaking at a temperature of $\sim$0.4--0.6 MK and a hot component peaking at $\sim$7--8 MK. The two MFRs exhibit erupting, expanding, and untwisting motions that manifest distinctive features from two different viewpoints. Their evolution can be divided into two stages, a fast-eruption stage with speeds of about 105--125 km s$^{-1}$ for MFR-1 and 50--65 km s$^{-1}$ for MFR-2 and a slow-expansion (or untwisting) stage with speeds of about 10--35 km s$^{-1}$ for MFR-1 and 10--30 km s$^{-1}$ for MFR-2 in the plane of sky. We also find that during the two-stage evolution, the high temperature features mainly appear in the interface region between MFRs and ambient magnetic structures and also in the center of MFRs, which suggests that some heating processes take place in such places like magnetic reconnection and plasma compression. These observational results indicate that the eruption and untwisting processes of MFRs are coupled with the heating process, among which an energy conversion exists.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ying Li
Qiao Li
De-Chao Song
Andrea Francesco Battaglia
Hualin Xiao
Säm Krucker
Udo Schühle
Hui Li
Weiqun Gan
M. D. Ding
摘要： The hydrogen Lyman-$\alpha$ (H {\sc i} Ly$\alpha$) emission during solar flares has rarely been studied in spatially resolved images and its physical origin has not been fully understood. In this paper, we present novel Ly$\alpha$ images for a C1.4 solar flare (SOL2021-08-20T22:00) from the Extreme Ultraviolet Imager aboard Solar Orbiter, together with multi-waveband and multi-perspective observations from the Solar Terrestrial Relations Observatory Ahead and the Solar Dynamics Observatory spacecraft. It is found that the Ly$\alpha$ emission has a good temporal correlation with the thermal emissions at 1--8 \AA\ and 5--7 keV, indicating that the flaring Ly$\alpha$ is mainly produced by a thermal process in this small event. However, nonthermal electrons play a minor role in generating Ly$\alpha$ at flare ribbons during the rise phase of the flare, as revealed by the hard X-ray imaging and spectral fitting. Besides originating from flare ribbons, the Ly$\alpha$ emission can come from flare loops, likely caused by plasma heating and also cooling that happen in different flare phases. It is also found that the Ly$\alpha$ emission shows fairly similar features with the He {\sc ii} 304 \AA\ emission in light curve and spatio-temporal variation along with small differences. These observational results improve our understanding of the Ly$\alpha$ emission in solar flares and also provide some insights for investigating the Ly$\alpha$ emission in stellar flares.
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