Prediction of solar proton event occurrence probability and peak flux using its associated X-ray flux, impulsive time, and longitude

Solar proton events have been regarded to be very important in that they may cause the damage of spacecrafts and human activities. In this study, we examined the longitudinal dependence of solar proton events and their relationships with x-ray flares. For this we used NOAA proton events whose fluxes of > 10 MeV protons are greater than 10 particles cm-2 sec-1 ster-1 from 1976 to 2006, and their associated X- ray flare data. As a result, we found that 181 proton events, of which most of them (169/181) are associated with major flares (85 X-class and 84 M-class). Then we examined the fraction of proton events relative to total major X-ray flares and its longitudinal dependence. We found that about only 3.6%(2.0% for M-class and 20.7% for X-class) of the flares are associated with the proton events. This fraction strongly depends on helio-longitude; for example, the fraction for 30W