Solar energetic particles inside magnetic clouds observed with the Wind spacecraft

Abstract

Solar energetic particles can be used to probe the structure of magnetic clouds. Since impulsive flare particles are accelerated within active regions, their presence inside a magnetic cloud implies that the cloud's magnetic field connects to an active region at the sun. We report on the fluxes and composition of low energy ions inside 13 magnetic clouds observed with instrumentation on the Wind spacecraft from November 1994 to February 1997. The STEP subsystem of the EPACT experiment on Wind resolves ³He and 4He and the most abundant heavy ion species from ∼20 keV/nucleon to ∼1 MeV/nucleon. Using STEP, we are able to measure the energetic particle composition in an energy range previously unexplored in the context of magnetic clouds. We find that when STEP measured significant ion fluxes inside a cloud, they were most likely from impulsive solar flares; this was the case in 4 events. We find that the 1/10/97 magnetic cloud decreased the interplanetary fluxes of ∼100 keV/nucleon ions by a factor of ∼10²; this was probably because the cloud disconnected Wind from the interplanetary particle source beyond 1 AU. In contrast, we observed particles from several impulsive solar flares inside the 10/18/95 event with fluxes ∼10³ higher than the fluxes measured inside the 1/10/97 cloud.