Published online by Cambridge University Press: 01 November 2006
Based on the neutron monitor counting rate profiles, soft X-ray emission from GOES, Yohkoh/HXT, RHESSI/HXT, ACE/SIS, and SOHO/LASCO CME catalog, the relationship between the onset time of solar cycle 23 Ground Level Enhancements(GLEs) and solar activity are analyzed. It was found that the correlation between the onset time of GLEs and flare maximum is better than that of the onset time of metric type II radio burst and CME. Average value of the ratio of Fe/O is about 2.65 times of coronal value in the range 30 – 40 MeV/n for all events. If considering the parent flare sites, the situation of proton acceleration in flares, and transport effect from flare sites (if it located in poorly-connected region) to well-connected region, several GLEs onset time are roughly at the peak time of the X-ray.