Statistical study on the ascending time of solar energetic particle events

A total of 66 great gradual Solar Energetic Particle events (SEPs) from 1997 to 2006 were selected for analysis. The correlations were analyzed between the ascending time of the SEPs in time profile and the heliographic longitude of the source active region. The Coronal Mass Ejection (CME) and flares were also investigated in the ascending stage of the SEP flux profile. The results of statistical analysis indicate that the source regions of these great SEPs are mainly distributed in the western hemisphere, particularly within the area from 45° east longitude to 45° west longitude relative to the magnetic footpoint. In the presence of fast solar wind, the ascending time in low-energy channel has a good correlation with the relative longitude and the ascending time increases with the distance from magnetic footpoint. However, the correlation is unobvious in high-energy channel. Correlations have not been observed between the ascending time of the SEPs associated with full halo CMEs and the source region longitude. However, the relations between the ascending time of the SEPs and source longitude are well fitted with quadratic curves. The analytical results show that the flare acceleration process played an important role in the gradual phase of SEP time profile, especially for the SEPs associated with partial halo CMEs.