Determination of Outer Radiation Belt MeV Electron Energization Rates and Delayed Response Times to Solar Wind Driving During Geomagnetic Storms

Abstract

Radiation Belt Storm Probes (RBSP) data show that seed electrons generated by sub-storm injections play a role in amplifying chorus waves in the magnetosphere. The wave-particle interaction leads to rapid heating and acceleration of electrons from 10's of keV to 10's of MeV energies. In this work, we examined the changes in the radiation belt during geomagnetic storm events by studying the RBSP REPT, solar wind, AL, SML, and Dst data in conjunction with the WINDMI model of the magnetosphere. The field-aligned current output from the model is integrated to generate a proxy E index for various energy bands. These E indices track electron energization from 40 KeV to 20 MeV in the radiation belts. The indices are compared to RBSP data and GOES data. Our proxy indices correspond well to the energization data for electron energy bands between 1.8 and 7.7 MeV. Each E index has a unique empirical loss rate term (τ_L), an empirical time delay term (τ_D), and a gain value, that are fit to the observations. These empirical parameters were adjusted to examine the delay and charging rates associated with different energy bands. We observed that the τ_L and τ_D values are clustered for each energy band. τ_L and τ_D consistently increase going from 1.8 to 7.7 MeV in electron energy flux E_e and the dropout interval increases with increasing energy level. The average trend of Δτ_D/ΔE_e was 4.1 hr/MeV and the average trend of Δτ_L/ΔE_e was 2.82 hr/MeV.