Solar proton events during the solar cycle 23 and their association with CME parameters

We have studied the solar proton events associated with the coronal mass ejections (CMEs) and flares during the solar cycle 23 (1997-2006) in order to determine what physical parameters of the solar eruptions might control the SPE intensity and time profile. For total 63 SPEs, we found that (1) SPE rise time, duration time and decrease times depend on a CME speed (cc=0.34, 0.48 and 0.48) and (2) a SPE peak intensity depends on an earthward direction parameter of a CME as well as the CME speed and x-ray flare intensity (cc=0.40, 0.31 and 0.37). The SPEs were divided into two groups according to the correlation between the CME earthward direction parameter and the SPE intensity. First group consists of large six SPEs (>10,000 pfu at >10 MeV proton channel of GOES satellite) and shows a very good correlation (cc=0.65) between the SPE peak intensity and the CME earthward direction parameter. Second group has a relatively weak SPE peak intensity and shows no correlation (cc=0.01) between the SPE peak intensity and the CME earthward direction parameter we found that the first group SPEs are associated with a very fast halo CME (>1400 km/s) and most of those are located at disk except for only one case. Especially, large six SPEs have a good correlation with their associated CME earthward direction parameters, implying that these events are produced by ICME-driven shocks. We also found that those six SPEs are associated with the preceding CMEs originated from the same solar source region and a nearby pre-existing helmet streamer. Thus, we speculate that the preceding CME and helmet streamer might provide seed particles for CME-driven shocks and cause a clear separation between two groups.