Solar proton enhancements and Forbush decreases with the same sources

Abstract

The characteristics of Forbush decreases (FDs) and solar energetic particle (SEP) events driven by the same solar sources (i.e. coronal mass ejection and associated solar flare) are investigated. The part of the solar disk (E04–W35) was chosen in which most of the solar events lead both to an FD and SEP event at Earth. SEPs for different energies (E 10, 100 MeV, and ground level enhancements) and with different flux thresholds were considered independently. The obtained results were compared with the control group of solar events that had solar sources within the same longitudinal zone but did not lead to any SEPs. It is shown that coronal mass ejections (CMEs) followed by SEPs have a very high probability to create a large FD in the Earth’s orbit and further to cause a geomagnetic storm. It is also obtained that the accelerative and modulating efficiencies of such driving solar events are well correlated; this can be explained mostly by high solar wind speeds of the corresponding CMEs.