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

TL;DR

This study analyzes a large solar energetic particle event in 2012 using multi-point observations and velocity dispersion analysis, revealing insights into particle release times, path lengths, and the importance of magnetic connectivity.

Contribution

It demonstrates the effectiveness and limitations of VDA in determining particle release times and path lengths, emphasizing the role of magnetic connectivity in SEP analysis.

Findings

Well-connected points show near-simultaneous proton and electron release.

Path lengths deviate from the nominal Parker spiral, indicating magnetic structures.

VDA yields reasonable results mainly at well-connected locations.

Abstract

On 2012 March 7, the STEREO Ahead and Behind spacecraft, along with the 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, and the second one was not involved. Using the velocity dispersion analysis (VDA), we find that for well magnetically connected point, the energetic protons and electrons are released nearly at the same time. The path lengths to STEREO-B(STB) of protons and electrons have 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 the STB. Also the VDA method seems only to obtain reasonable results at well-connected locations and the inferred energetic particles release times in different energy channels are similar. We suggest that good-connection is crucial for obtaining both accurate release time and path length simultaneously, agreeing with the modeling result of Wang & Qin (2015).