ELFIN Statistics of Electron Strong Diffusion in the Inner Magnetosphere

Abstract

Pitch‐angle diffusion of trapped electrons driven by whistler‐mode and EMIC waves and by field‐line curvature scattering (FLCS) plays an important role in energetic and relativistic electron loss from the inner magnetosphere. The strong diffusion regime, characterized by a nearly full loss cone, rarely occurs, but is expected to account for a significant part of electron precipitation, particularly during disturbed periods. Using the full set of ELFIN low‐altitude measurements of 60 keV to 1.1 MeV electron fluxes at adiabatic ‐shells , we estimate net precipitating‐to‐trapped flux ratios corrected for atmospheric backscatter and use them to identify strong diffusion events. We classify these events into three categories: FLCS‐driven, EMIC‐driven, and whistler‐mode‐driven. We provide comprehensive statistics of strong diffusion occurrence rates in the outer radiation belt, and determine the respective contributions of these drivers as a function of electron energy, , magnetic local time, auroral electrojet (AE) index, and solar‐wind dynamic pressure. Time‐averaged statistics and a superposed epoch analysis both show a clear link between elevated strong diffusion occurrence rates and high AE and solar‐wind dynamic pressure. After strong substorms, the total occurrence rate of strong diffusion at reaches 9.4 % at 300 keV and 5.8 % at 1.1 MeV. FLCS‐driven events occur closer to the last closed drift shell than EMIC‐driven events. Wave‐driven events prevail up to 300–1,100 keV, depending on AE and . Two drivers are often simultaneously important. Therefore, our statistics should be useful for evaluating electron loss in the outer radiation belt more accurately.