Statistics of Sudden Particle Enhancements at Low L-shells and Their Role as a Source of Earth's Inner Electron Radiation Belt

Abstract:

During some geomagnetically active periods, electrons ranging in energy from 10s of keV up to ~1 MeV can be quickly (in a few hours or less) injected into the slot and inner radiation belt (L < 3). Evidence has been shown that these injections may serve as the dominant source of of 10s to 100s of keV electrons in Earth’s inner radiation belt. Intriguingly, protons of the same energy are not injected in the same events, implying some species dependent process. Currently, the underlying physical mechanism responsible for these sudden particle enhancements at low L-shells (SPELLS) remains a mystery. Several example cases of SPELLS will be used to introduce their characteristics and what we currently know about them. Next, we will present new statistical results of SPELLS observed throughout the Van Allen Probes mission (>100 events). We focus on any preferential magnetospheric conditions for SPELLS event occurrence as well as any correlations between geomagnetic and solar wind activity and the energy limits and depth of penetration of SPELLS. We will also detail evidence that the injection mechanism responsible for SPELLS is localized in MLT. We conclude with a summary of what candidate mechanisms may be responsible for SPELLS based on the evidence collected so far.