Solar energetic particles (SEPs) are accelerated in corona at an early phase of solar energetic particle events (SEPE). The acceleration mechanism of SEPs in corona can only be inferred from an analysis of multi-band observational data, as the observation of SEPs is usually made around 1AU. In this context, people have investigated spectrums, charge state, solar release time (SRT), and multi-band data of SEPEs, in an attempt to judge the acceleration mechanism of SEPs. The SRT computation of SEPs is an important and commonly used approach to study the acceleration mechanism of SEPs in corona. This paper reviews some important findings concerning the SRT computation of SEPs, and analyzes different merits of each approach for such calculation, based on a range of SEPE case studies. This paper also analyzes and discusses both possible and actual acceleration mechanisms of a number of SEPEs, by calculating the SRT of the SEPEs. Finally, the paper summarizes the possible problems in studying an acceleration mechanism of SEPEs inferred from the SRT of SEP.
LE GuiMing1,2,3,4, TANG YuHua1 & HAN YanBen4 1 Department of Astronomy, Nanjing University, Nanjing 210093, China
Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motions,short life-time,and so on.These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity,ionization and radiation considered,we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere.The influence of different parameters,such as intensity of the magnetic field and anomalous resistivity,on the results are investigated.Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations.It is found that the typical features of the two phenomena can be qualitatively reproduced.
Xiao-Yan Xu 1,2,Cheng Fang 2,Ming-De Ding 2 and Dan-Hui Gao 2 1 Purple Mountain Observatory,Chinese Academy of Science,Nanjing 210008,China 2 Department of Astronomy,Nanjing University,Nanjing 210093,China
We study the properties of the He I 10830 A line in nine selected solar flares, using spectral data obtained with the Multi-channel Infrared Solar Spectrograph （MISS） at Purple Mountain Observatory （PMO） and photospheric images from the Michelson Doppler Imager （MDI） onboard the Solar and Heliospheric Observatory （SOHO）. Our results indicate that, over an area of 3″- 8″, the He I 10830 A line shows emission exceeding the continuum in nearby quiet region when the Geostationary Operations Environmental Satellite （GOES） X- ray class of the flare reaches a threshold value （C4.5）. The He I 10830 A line emission is detected only in the kernels of the Ha brightenings, but is not associated with the size of the flare. It is found that, whenever the He I 10830 Aline shows excess emission over the nearby continuum both the Ha and the Ca Ⅱ 8542 A lines display enhanced intensities exceeding their preflare intensities. The He I 10830A line emission can occasionally extend into the umbra of the involved sunspot, which is inconsistent with previous studies. The weak com- ponent of He I 10830A line changes from emission to absorption earlier than does the main component. Our results favor the photoionization-reconnection mechanism for the excitation of the He I 10830fi, line.
