Balloon Observations of Relativistic Electron Precipitation

Abstract:

Relativistic electron precipitation events lasting from minutes to hours have been observed by balloon-borne instrumentation since 1996. This collection of observations, including the recent BARREL observations, all occur in the noon to midnight sector. EMIC waves have been suggested as the precipitation mechanism for this type of event [Lorentzen et al., 2000 and Millan et al., 2002]. A recent study by Li et al., [2014] performed a case study which modeled the radiation belt relativistic electron pitch angle diffusion from EMIC waves which showed convincing agreement between the modeled results and the BARREL x-ray observations. A survey of the BARREL REP events suggests this type of precipitation is a very localized phenomena with most events only being observed by a single balloon at a time despite the extensive L-value and local time coverage of observations during the campaign. This result is consistent with the findings of Blum et al., [2013]. Furthermore, the balloon observations show local time energy dependence consistent with the SAMPEX observations reported by Comess et al, [2013]. In this work we address the following questions: based on the REP events observed by balloon-borne instrumentation, are these characteristics true for all identified REP events and does this support EMIC waves as the precipitation mechanism? Due to the localized region of precipitation, do these events represent a significant radiation belt loss process?