Radial Response of Outer Radiation Belt Relativistic Electrons During Enhancement Events at Geostationary Orbit

Abstract

Forecasting relativistic electron fluxes at geostationary Earth orbit (GEO) has been a long term goal of the scientific community, and significant advances have been made in the past 30 years, but the relation to the interior region of the radiation belts, that is, to lower L−shells is still not clear. In this work we have identified 60 relativistic electron enhancement events observed at GEO to study the radial response of outer belt fluxes and the correlation between the fluxes at GEO and those at lower L−shells. The enhancement events occurred between 1 October 2012 and 31 December 2017 and were identified using GOES 15 >2 MeV fluxes at GEO, which we have used to characterize the radial response of the radiation belt, by comparing to fluxes measured by the Van Allen probes ECT-REPT between 2.5 < L < 6.0 at E = 2.1 MeV. We have found that in general the response of the radiation belts during enhancement events is cohesive for L > 5.0, and generally similar for L > 4.5. Post enhancement maximum fluxes show a remarkable correlation for all L > 4.0 although the magnitude of the pre-existing fluxes on the outer belt plays a significant role and makes the ratio of pre-to-post enhancement fluxes less predictable in the region 4.0 < L < 4.5. For L < 4 the fluxes are poorly correlated with geostationary orbit, but they also tend to be less variable. We have also examined the roles of the SYM-H, Kp and AE indices and found that depending on their magnitude, the response of different parts of the outer belt can be better quantified.

A Climatology of Long‐Duration High 2‐MeV Electron Flux Periods in the Outer Radiation Belt

“…The 10‐day time‐integrated fluxes obtained from GPS satellites at L ∼ 4.2–4.4 during these particular periods should also be weakly dependent on the exact magnetic field model used. The remarkable coherence of ∼1–2 MeV electron fluxes over the region 4.0 < L < 5.5 (with typical correlation lengths Δ L ∼ 0.5) after enhancement events (Pinto, Bortnik, et al., 2020; Walton et al., 2021) further confirms that the analyzed GPS fluxes obtained at L = 4.2–4.4 can be used as good proxies for fluxes at slightly higher L ‐shells.…”