Minima in phase space density and how they relate to the multi-MeV electron radiation belt depletions

Abstract:

The analysis of electron radiation belt dynamics is complicated since some of the variations are reversible, or adiabatic, while others are irreversible. Separating adiabatic and nonadiabatic changes can be achieved by inferring phase space density (PSD) as a function of three adiabatic invariants. Our understanding of the acceleration and loss mechanics has been improved over the years; however, some questions still remain open. The loss of multi-MeV electrons can be a combination of various processes such as outward radial diffusion and/or electron scattering due to wave-particle interaction. The rapid loss of multi-MeV electrons is possible due to interaction with electromagnetic ion cyclotron (EMIC) waves, which may play a dominant role in the observed dropouts. The key signatures of such interactions can be found investigating the pitch-angle distribution (“bite-out”) and PSD profiles (local minima). In this study, we perform the analysis of Van Allen Probe measurements seeking the answer of when and under which conditions the observed dropouts are associated with local minima in PSD and what the role of EMIC waves and radial diffusion is in this process.