Determination of Solar Wind Parameters in the Occurrence of Relativistic Electron Events at Geosynchronous Orbit

Abstract:

A strong connection between relativistic radiation belt electron fluxes enhancements and solar wind dynamics has been suggested. By identifying 47 different relativistic electron events during the years 1996 and 2006 using data from GOES 8 and 10 satellites and studying different solar wind parameters, we try to give a better understanding of under what conditions this events will trigger. In order to help distinguish necessary conditions, we also selected 12 dropout events during the same period that did not show flux recovery for a long period. It was found that large solar wind speeds (~450 km/s and up) and low solar wind proton densities (~6 cm-3 or less) are both necessary for relativistic electron events to occur. A drop in Dst index is not strictly necessary, but most events are associated with corotational interaction regions or with coronal mass ejections. However, at least a small amount of southward IMF B_z is necessary. Solar wind ULF power from Alfvenic oscillations seems to have an augmentative role, particularly when southward IMF B_z is low. This can be seen by comparing enhancements to dropout events that occur without enhanced southward B_z of enhanced ULF power, even when solar wind speed and proton density are appropriate for an enhancement to occur.