Radial gradients of phase space density of the outer radiation belt electrons prior to sudden solar wind pressure enhancements

Abstract

When Earth's magnetosphere is impacted by a sudden solar wind pressure enhancement, dayside trapped electrons are transported radially inwards, conserving their first and second adiabatic invariants (μ and K). Thus, with magnetic field and particle flux measurements at geosynchronous orbit (GEO) before and after the impact, the phase space density (PSD) radial gradients of the particles prior to the impact can be reconstructed. We show two examples, in which the PSD of low‐μ electrons, which correspond to energies less than ∼100 keV, increases slightly with increasing radial distance for one event and remains unchanged for the other, while that of high‐μ electrons decreases significantly with increasing radial distance from GEO for both events. These results suggest that the PSD radial gradients are μ dependent, and a significant heating, which violates μ and K, occurs inside GEO for the high energy electrons for the two cases examined.