Dependence of solar proton events on their associated activities: Flare parameters

Abstract

In this study we have examined the occurrence probability of solar proton events and their peak fluxes depending on three flare parameters (X-ray peak flux, longitude, and impulsive time). For this we used NOAA solar energetic particle events from 1976 to 2006 and their associated X-ray flare data. As a result, we selected 166 proton events that were associated with major flares: 85 events associated with X-class flares and 81 events associated with M-class flares. The occurrence probability especially strongly depends on three parameters as follows. (1) We found that about only 3.5% (1.9% for M-class and 21.3% for X-class) of the flares are associated with the proton events. (2) It is also found that this fraction strongly depends on longitude; for example, the fraction for 30W < L 90W is about three times larger than that for 30E < L 90E. (3) We also note that the occurrence probability of solar proton events associated with long-duration (0.3 h) flares is about 2 (X-class flare) to 7 (M-class flare) times larger than that with short-duration (<0.3 h) flares. (4) The largest difference is found between the eastern short-duration M-class flare group (0.3%) and the western long-duration X-class flare group (46.5%). In addition, the relationship between X-ray flare peak flux and proton peak flux as well as its correlation coefficient are strongly dependent on longitude and impulsive time. Copyright 2010 by the American Geophysical Union.