Radiation Belt Slot Region Filling Events: Sustained Energetic Precipitation Into the Mesosphere

Precipitation of energetic electrons to the atmosphere is both a loss mechanism for radiation belt particles and a means by which the geospace environment influences the Earth's atmosphere; thus, it is important to fully understand the extent of this precipitation. A set of polar orbiting satellites have been used to identify periods when energetic charged particles fill the slot region between the inner and outer radiation belts. These suggest that electrons with energies >30 keV penetrate this region, even under levels of modest geomagnetic activity. Those events with sufficient fluxes of particles produce enough ionization to be detected by a ground-based radar in Antarctica; this precipitation lasts for similar to 10 days on average. Analysis of these data reveals that the average precipitation penetrates to the stratopause (similar to 55-km altitude). For some (if not all) of these events, the likely cause of the most energetic precipitation is an interaction between (relativistic) electrons and plasmaspheric hiss leading to little, if no, local time variation in precipitation. This does not preclude a longitudinal effect given that all radar measurements are fixed in longitude. During winter months the radar is under the stable southern polar atmospheric vortex. This transports atmospheric species to lower altitudes including the ozone destroying chemicals that are produced by energetic precipitation. Thus, the precipitation from the slot region in the Southern Hemisphere will likely contribute to the destruction of ozone and changes to atmospheric heat balance and chemistry; more work is required to determine the true impact of these events. Plain Language Summary Precipitation of energetic electrons to the atmosphere is both a loss mechanism for radiation belt particles and a means by which the geospace environment influences the Earth's atmosphere; thus, it is important to fully understand the extent of this precipitation. A set of polar orbiting satellites have been used to identify periods when energetic charged particles fill the slot region between the inner and outer radiation belts. These suggest that electrons with energies >30 keV penetrate this region, even under levels of modest geomagnetic activity. Those events with sufficient fluxes of particles produce enough ionization to be detected by a ground-based radar in Antarctica; this precipitation lasts for similar to 10 days on average. Analysis of these data reveals that the average precipitation penetrates to the stratopause (similar to 55-km altitude). For some (if not all) of these events, the likely cause of the most energetic precipitation is an interaction between (relativistic) electrons and plasmaspheric hiss leading to little, if no, local time variation in precipitation. This does not preclude a longitudinal effect given that all radar measurements are fixed in longitude. During winter months the radar is under the stable southern polar atmospheric vortex. This transports atmospheric species to lower altitudes including the ozone destroying chemicals that are produced by energetic precipitation. Thus, the precipitation from the slot region in the Southern Hemisphere will likely contribute to the destruction of ozone and changes to atmospheric heat balance and chemistry; more work is required to determine the true impact of these events.