Relativistic Electron Precipitation: Satellite Observations of EMIC Wave Driven REP

Abstract

Many recent studies have identified relativistic electrons interacting with electro- magnetic ion cyclotron (EMIC) waves and being precipitated out of the radiation belts into the Earth’s atmosphere. These studies have generally only investigated a few specific geomagnetic storm events, and therefore it is impossible to deter- mine any overall characteristics or trends to do with these events. Therefore, we have undertaken a similar examination of this phenomena, but using a vastly larger dataset; our research utilises all available data from the SEM-2 instrument onboard the NOAA spacecraft collected between 1998 and 2010.

A total of 436,422 half orbits from six satellites are inspected by an automatic- detection algorithm, looking for specific characteristics determined to be signatures of EMIC-driven relativistic electron precipitation. 2,331 precipitation events are identified and logged into a database, where other corresponding geomagnetic indices are also included. Statistical analysis of this database identified trends in the data, including in- creased likelihood of event occurrence during geomagnetic disturbances, preference for dusk and night sectors as determined by MLT and the occurrence of the majority of the events outside of the plasmasphere, as determined through use of statistical plasmapause models. Comparison of this database with other studies in the literature provided strong evidence linking our precipitation events with simultaneous observations of EMIC waves. The electron precipitation events are seen to show different characteristics than the proton precipitation events which while occurring simultaneously with our events, more commonly occur without electron precipitation. Our database provides an unique opportunity for comparison with any other study of EMIC waves during the 1998-2010 period. It also provides insights into the relationship of EMIC-driven relativistic electron precipitation with geomagnetic indices, allowing for additional input into any future modeling of electron dynamics in the radiation belts.