Energetic Electron Precipitation during Slot Region Filling Events

The region separating the inner and outer radiation belt, typically devoid of energetic electrons, is termed the slot region. The outer edge of the slot region marks the equatorward edge of the energetic electron precipitation (EEP) originating from the outer radiation belt. Its varying location is strongly linked to the plasmasphere and geomagnetic activity. As such, geomagnetic indices are used to estimate the equatorward extent of the EEP region. There are, however, numerous reports where the energetic electrons cross these boundaries and fill the slot region, during which energetic electrons that can precipitate into the atmosphere long after the geomagnetic activity subsides. This is a missing source of energy input in current EEP estimates based on geomagnetic indices.

This study explores the occurrence rate, reformation, local time dependence, and energy deposition of slot region filling events. Medium energy electron measurements from the NOAA/POES over a full solar cycle from 2004 to 2014 are applied. We combine observations from the MEPED 0° and 90° detectors together with theory of pitch angle diffusion by wave-particle interaction to estimate the precipitating fluxes. To explore the energy dependent characteristics, each of the MEPED energy channels, > 43, >114, and >292 keV are evaluated independently. Finally, we investigate the potential EEP impact on the NO density utilizing seven years of Envisat MIPAS NO observations from 2005 to 2011.