Computations and observations of the slot formation during quiet storm recovery

Abstract:

In this presentation, we discuss how and how fast the slot region forms gradually during long and quiet storm recovery, contributing to depopulate the close-Earth magnetosphere of the large amount of electrons injected by the storm. The discussion is based on both dynamic Fokker-Planck simulations of the electron radiation belts and observations. Simulations are made for all energies and L-shells between 2 and 6 in the view of recovering the observations of the full radiation belts for a few events. We show pitch angle diffusion from wave-particle interactions is essential to the energy structure of the belts and slot region. Pitch angle diffusion is computed from data-driven spatially and temporally-resolved whistler mode hiss waves and ambient plasma observations from the Van Allen Probes satellites. Fokker-Planck simulations are performed either with a 3D formulation that uses our data-driven pitch angle diffusion coefficients or with a simpler reduced Fokker-Planck equation based on losses computed from data-driven electron lifetimes. Observations are also presented globally using the Magnetic Electron and Ion Spectrometer (MagEIS) flux measurements of the belts at all energy and L-shells. We discuss which models among the different choices of radial diffusion coefficients, electron lifetimes, and pitch angle diffusion coefficients, allow to recover the observed "S-shaped" energy-dependent inner boundary to the outer zone. We show how this full dynamic structure of the belts and the slot formation is due to wave-particle interactions caused by whistler hiss waves. Periods when the plasmasphere extends beyond L ~ 5 favor long-lasting losses of outer belt electrons from hiss waves.