Large solar energetic particle event that occurred on 2012 March 7 and its VDA analysis

摘要

On 2012 March 7, the STEREO Ahead and Behind spacecraft, along with near-Earth spacecraft(e.g. SOHO, Wind) situated between the two STEREO spacecraft, observed an extremely large global solar energetic particle(SEP) event in Solar Cycle 24. Two successive coronal mass ejections(CMEs) have been detected close in time. From the multi-point in-situ 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 and deviate remarkably from the nominal Parker spiral path length, which is likely due to the presence of interplanetary magnetic structures situated between the source and STB. Also, the VDA method seems to only obtain reasonable results at well-connected locations and the inferred release times of energetic particles in different energy channels are similar. We suggest that good-connection is crucial for obtaining both an accurate release time and path length simultaneously, agreeing with the modeling result of Wang &Qin(2015).