| 其他摘要 | Magnetic reconnection is closely related to many solar eruptive activities (e.g., coronal mass ejection (CME), flare, eruption filament, jet, the transition region ex- plosive event, etc.). In these phenomena, the magnetic reconnection process converts magnetic energy into kinetic and thermal energy of the plasma and produces energetic particle beams. Magnetic field and plasma properties (such as, temperature, density, and flow speed) vary from case to case in the solar atmosphere, which may result in different performance and consequences of the eruptive activities governed by mag- netic reconnection. In our works, we concluded observational research on two selected activities, and utilized the results of magnetohydrodynamics (MHD) numerical exper- iments to explain and discuss the observed phenomena and features. The first event is a bi-directional jet that occurred in the upper chromosphere, the second one is a high-temperature fan-shaped structure above the top of the flare loop system in a major eruptive process. On 2014 August 12, a transient brightening bi-directional jet occurred in the active region NOAA 12135 was observed by SDO and IRIS, which provide high spatial- temporal resolution observational data of (extreme) ultraviolet images, spectrum, and magnetogram. The jet was observed in multiple bands of SDO/AIA and manifested clear bi-directional flows in IRIS observations. The emission profiles of the Si IV 1402 Å line of the jet exhibited non-Gaussian feature and double-peak curve, with the Doppler velocity and the non-thermal broadening up to 100 km s-1 and 160 km s-1, respectively. The average flow speeds of the jet on the sky plane were about 26.8 km/s and 33.5 km/s, respectively. The plasma flows of the jet projected on the sky plane and in the line- of-sight (LOS) are the typical observational evidence of magnetic reconnection. The asymmetric feature of spectral line profile, the Doppler velocity, and the non-thermal broadening show clear oscillating feature. The EM loci curves indicated that the plasma contains multi-temperature components. The result deduced from the DEM method and changes in intensity of several spectral lines imply that the temperature of the plasma in the jet could be heated to at least 105.6 K. The electron density was about 1011cm-3 according to the intensity ratios of the O IV 1399.77/1401.16 ÅÅ doublet and Si IV1402.77/O IV 1401.16 ÅÅ lines. We reached the conclusion that the jet occurred in the upper chromosphere, and resulted from the magnetic reconnection between the moving magnetic structure and the magnetic field nearby. On 2017 September 10, a major eruption on the west solar limb produced a class X-8.2 flare and a super fast coronal mass ejection (CME). During the eruptive process, the geometric topology of the erupting magnetic configuration presented a clear CME-current sheet (CS)-flare structure. Analysing the images and spectral data from SDO/AIA, IRIS, and Hinode/EIS, we studied the supra-arcade fan (SAF) region between the bottom of CS and the top of flare loops in the south part of the erupting configuration. Our results indicated that the SAF contained hot plasma of temperature up to 107 K and mean electron density of 3.5×109 cm-3, and the fast variation component (FVC) of the SAF lightcurve shown by the IRIS slit-jaw images (SJI) displayed a quasi- periodic oscillating feature with the period of 76.8 s. We utilized the Athena code to simulate detailed evolutionary features of the magnetic structure of a typical two-ribbon flare. The numerical experiments duplicate observational features in many respects, including the spatial distribution and evolution in structures of the plasma and magnetic field, the turbulence and the termination shock (TS) in the SAF. Our results suggest that the SAF is a high temperature structure that possibly contains the TS. The quasi-periodic oscillating characteristics of the lightcurve indicates that the magnetic reconnection that drives the eruption process is in the impulsive bursty fashion. In this work, we analyzed two explosive events. Although they occurred in different locations and with different spatial scales, the results indicate that they both originated from the magnetic reconnection process that causes the release of the magnetic energy. Oscillations series of the lightcurve, Doppler shift and non-thermal broadening of the spectral lines in two events indicate the turbulent characteristics and nature of the magnetic reconnection process. To some extent, these oscillating features also indicate that the magnetic reconnection process that drives solar eruptions generally takes place in the form of turbulence. |
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