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

• Published in: Journal of geophysical research. Space physics 2024-07, Vol.129 (7), p.n/a
• Main Authors: Srinivas, P., Spencer, E.
• Format: Article
• Language: English
• Subjects: Chorus waves; Electron energy; Electrons; Energy; Energy bands; Energy flux; Energy levels; Geomagnetic storms; Geomagnetism; Jupiter; Magnetic storms; magnetosphere; Magnetospheres; Outer radiation belt; Particle interactions; Radiation; Radiation belts; RBSP; Solar wind; Storms; Time lag; WINDMI
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2023JA032115

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 (τL), an empirical time delay term (τD), 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 τL and τD values are clustered for each energy band. τL and τD consistently increase going from 1.8 to 7.7 MeV in electron energy flux Ee and the dropout interval increases with increasing energy level. The average trend of ΔτD/ΔEe was 4.1 hr/MeV and the average trend of ΔτL/ΔEe was 2.82 hr/MeV. Key Points The energization rate τL and the time delay τD between initial dropout and subsequent energization of the electrons consistently increase going from the 1.8–7.7 MeV electron energy bands The τL and τD values are clustered together for each energy level despite the different storm intervals and intensities The dropout interval increases with an increase in energy level which was obtained based on sub‐storm onsets predicted within the dropout range