Relativistic electron fluxes dropout in the outer radiation belt under different solar wind conditions

Abstract

In this study, we apply superposed epoch analysis to the 1.5–6.0 MeV electron flux dropout events observed on Solar, Anomalous, Magnetospheric Particle Explorer satellite for 110 magnetic storms related to coronal mass ejections (CMEs) associated with interplanetary shocks during 1998–2003, which can help to study one of the scientific objectives of the recently launched Van Allen Probe—to determine and quantify the mechanisms of the losses in the outer radiation belt. Results obtained in this paper show that the impact of high solar wind dynamic pressure (Pdy) on the magnetosphere would lead to much larger electron flux dropout than low dynamic pressure. Furthermore, it is shown that southward interplanetary magnetic field (IMF) condition can result in more significant dropout compared with northward IMF condition. In addition, the largest local dropout is caused by high Pdy with northward IMF at L∼5.1. Dropouts under high Pdy and southward IMF conditions are the largest, whereas dropouts under low Pdy and northward IMF conditions are the smallest. Our study tackles the problem of quantifying the dropouts of electrons by calculating the radiation belt content index and finding the spatial distribution of dropout and the location of maximum dropout. Another finding is that Pdy and IMF affect the dropouts in CME‐driven storms. These new findings provide insight into which mechanisms play a more important role in different dropout events.