Experimental evidence and properties of EMIC wave driven electron precipitation

Abstract

One of the key drivers of electron losses from the radiation belts is the interaction between radiation belt electrons and the electromagnetic plasma waves that populate the magnetosphere. In particular, electromagnetic ion cyclotron (EMIC) waves have been touted as a potential sources of significant electron loss from the radiation belts. However, until recently there has been a lack of experimental evidence for this precipitation occurring. Because of this, there is little experimental evidence for the properties of the precipitation, in particular the lower energy limit of EMIC interactions with radiation belt electrons.

The main focus of this thesis is investigating a 17 year database of proton precipitation-associated relativistic electron precipitation events detected by the POES satellite constellation, believed to be driven by interactions with EMIC waves. This database represents an unheralded opportunity for in-depth study of EMIC waves and their interactions with energetic electrons. Unfortunately, the utility of this database has been limited due to the lack of accompanying wave observations; without direct evidence of EMIC wave activity, there remains significant doubt as to the true driver of the observed precipitation. In this thesis, we initially present two in-depth case studies of events from the precipitation database, showing clear evidence of concurrent EMIC wave activity and the observed precipitation. We follow up these studies with a broad statistical analysis of the precipitation database, comparing the event locations to ground-based magnetometers. We show a remarkable correlation between the precipitation events and EMIC waves observed on the ground, with as many as 90% of precipitation events occurring during periods of EMIC wave activity. We show that this correlation cannot be due to random chance, establishing a strong link between the precipitation events and EMIC wave activity. Finally, we also show that while our precipitation events imply wave activity, wave activity does not necessarily imply electron precipitation.

Given the results of these studies, we have significant confidence that our database represents EMIC-wave scattered electron precipitation. We present two further case studies, investigating in-depth the energy and intensity characteristics of two events from the precipitation database. Through comparison with the DEMETER satellite, we are able derive electron energy spectra for these events.