Proton Events and X-ray Flares in the Last Three Solar Cycles

A database joining the available information about proton enhancements near the Earth and their possible solar sources is organized on the basis of proton measurements of the GOES and IMP-8 satellites, the data of neutron monitors, and GOES X-ray measurements. One thousand one hundred and forty-four proton events with energy > 10 MeV have been selected in the period from 1975 to 2003. More than a half of these events can be reliably related to X-ray solar flares. A statistical analysis shows the probability of observing solar protons near the Earth and their maximum flux value to be strongly dependent on the importance of a flare and its heliolongitude. Proton events are recorded after all suitably located (western) flares with X-ray importance > X5. The heliolongitude of a flare predetermines the character of the time profile of proton events in many respects. The relationship of proton events with the other characteristics of flares is established. The flares associated with proton enhancements are characterized by longer duration, slower rise to the X-ray maximum, smaller temperature, and larger length of the X-ray loops.