  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).

Solar and Stellar Astrophysics