Study On The Initial Release Process Of Solar Energetic Particles Based On Multi-spacecraft Observations

The study on the acceleration and release process of energetic particles near the sun in gradual solar energetic particle (SEP) events is one of the key issues in understanding the relationship between SEP events and the coronal mass ejections(CMEs). In this paper, we investigated the characteristic times (onset time tob, and solar particle release time tsr) and their longitudinal distribution of 30 gradual SEP events with distinct enhancement of the particle flux from 2011 to 2014. Also, we analyzed the large SEP event that occurred on 20.12 March 7 separately. The main conclusions are as follows:Firstly, on 2012 March 7, the STEREO Ahead and Behind spacecraft, along with near-Earth spacecraft observed an extremely large global SEP event. Two successive CMEs have been detected close in time. From the multi-point in-suit observations,it can be found that this SEP event was caused by the first CME,but the second one was not involved. Using velocity dispersion analysis (VDA),we find that for a well magnetically connected point, the energetic protons and electrons are released nearly at the same time. The path lengths to STEREO-B(STB) for protons and electrons have a distinct difference. The results show that the VDA method seems to only obtain reasonable results at well-connected locations and the interplanetary structures may affect the propagation path differences of energetic protons and electrons.Secondly, by analyzing the characteristic time of SEP events, it's found that the SEP events observed by multi-spacecraft are associated with the wider CME, which are always almost Halo CME, than the general SEP events. The onset time difference of energetic particles observed by two spacecraft presents a good linear correlation with the longitude difference of two spacecraft, and east-west hemispheric asymmetry. The time intervals between onset time and release time and the flare onset are positively correlated with the relative longitude of the detector to active region. For two characteristic times in different energy channels in the same SEP event,the range of onset time or release time (tslow-tfast) shows a good positive correlation with the relative longitude of spacecraft, and the release time range in different energy channels shows a distinct longitudinal distribution. Also, the release time interval between high and low energy channel is also correlated with CME speed. All of these results imply that the two characteristic times,in-situ onset time and solar particle release time near the sun,reveal obvious longitudinal distribution,and they have a strong correlation with the associated CME.