Solar energetic particle events and Forbush decreases driven by the same solar sources

Nataly Shlyk, Anatoly Belov, Maria Abunina, Elena Belova, Artem Abunin, IZMIRAN, Russia

Athanasios Papaioannou, IAASARS, Greece

The characteristics of Forbush decreases (FDs) and solar energetic particle (SEP) events driven by the same solar source (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 MeV, E>100 MeV, and Ground Level Enhancements) and with different flux thresholds were considered independently. The obtained results were compared with the control group of FDs that had solar sources within the same longitudinal range but were not accompanied with 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 speeds of the corresponding CMEs.