Energetic Electron Precipitation During Slot Region Filling Events

Abstract

The slot region marks the equatorward boundary of the energetic electron precipitation (EEP). There are, however, numerous reports where energetic electrons cross these boundaries and fill the slot region. The ensuing EEP will occur long after the geomagnetic activity subsides. This is a missing energy input in current EEP estimates scaled by geomagnetic indices. This study explores the occurrence rate, duration, and local time dependence of slot region filling events using observations from the National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites over a full solar cycle from 2004 to 2014. The EEP flux estimates are based on the Medium Energy Proton Electron Detector 0° and 90° detectors and the theory of pitch angle diffusion by wave-particle interaction. The occurrence rates of >43, >114, and >292 keV events are found to be strongly energy and solar cycle dependent. Higher energy events are more likely to be associated with Coronal Mass Ejections and stronger geomagnetic deflections compared to lower energy events. Solar wind speed, Bz, and Ey reveal a calm period before the events, potentially important for preconditioning the ensuing magnetospheric mass convection. The slot region reforms more efficiently closer to the plasmapause, which creates a double EEP band throughout the recovery period. The slot region EEP maximizes around noon throughout the afternoon/evening sector, consistent with pitch angle scattering from plasmaspheric hiss and lightning induced whistler mode waves. Concurrent with slot region filling events, the Michelson Interferometer for Passive Atmospheric Sounding/Envisat nitric oxide density show an increase at <55° corrected geomagnetic latitudes. This demonstrates the importance of including slot region EEP when assessing the EEP impact on the atmosphere.