Examining dropouts of Earth's outer radiation belt electrons using multipoint observations of particles and waves

One of the most drastic events that occur in Earth's outer radiation belt is the sudden depletion of relativistic electron flux, known as a flux dropout. Dropouts are characterized by electron fluxes dropping by up to several orders of magnitude over a broad range of energies, L-shells, and equatorial pitch angles in only a few hours. Here, we provide preliminary results of an ongoing statistical study of outer belt dropout events using multipoint observations. For all of the events, we examine the MLT at which the dropout is first observed, the ranges of L-shells and equatorial pitch angles affected, and how long the loss persists for various electron energies (~30 keV to >1 MeV). To examine the role of magnetopause shadowing and subsequent outward radial transport, we compare the evolution of electron fluxes and phase space density in adiabatic coordinates measured near the magnetic equator by THEMIS to precipitating fluxes observed at low-Earth orbit by the NOAA-POES spacecraft. We show that most often, the flux of electrons precipitating into the atmosphere is insufficient to explain the observed non-adiabatic loss of electrons throughout the belt, particularly at L-shells greater than ~5. Furthermore, characteristics of the dropout as observed by THEMIS and GOES are examined, and they reveal that the dropouts often start at higher L-shells and propagate inward. The important role of ULF waves in breaking the third adiabatic invariant, allowing for radial transport across drift shells, is also presented using wave data from THEMIS and GOES. Finally, we also examine the role of electron precipitation by EMIC waves during dropout events by comparing observed EMIC wave activity and range with the evolution of electron radial and pitch-angle distributions from THEMIS and precipitating electrons from NOAA-POES.