Strong Relativistic Electron Flux Events in GPS orbit

Relativistic electrons cause internal charging on satellites and are a significant space weather hazard. In this study we analyze approximately 20 years of data from the US Global Positioning System (GPS) satellite NS41 to determine the conditions associated with the largest daily averaged fluxes of E = 2.0 MeV relativistic electrons. The largest flux events at L = 4.5 and L = 6.5 were associated with moderate to strong CME-driven geomagnetic storms. However, the majority of the 50 largest flux events at L = 4.5 (30 out of 50) and L = 6.5 (37 out of 50) were associated with high speed solar wind streams from coronal holes. Both solar drivers are thus very important for relativistic electron flux enhancements in GPS orbit. The 1 in 3 year flux level was not exceeded following any of the 15 largest geomagnetic storms as monitored by the Dst index, showing that the largest geomagnetic storms, most often associated with extreme space weather, do not result in significantly larger relativistic electron flux events in GPS orbit.