The importance of storm time steady magnetospheric convection in determining the final relativistic electron flux level

Abstract

AbstractRelativistic electrons pose a space weather hazard to satellites in the radiation belts. Although about half of all geomagnetic storms result in relativistic electron flux enhancements, other storms decrease relativistic electron flux, even under similar solar wind drivers. Radiation belt fluxes depend on a complex balance between transport, loss, and acceleration. A critically important aspect of radiation belt enhancements is the role of the “seed” population—plasma sheet particles heated and transported earthward by magnetotail processes—which can become accelerated by wave‐particle interactions with chorus waves. While the effect of substorms on seed electron injections has received considerable focus, in this study we present a previously unexplored connection between quasi‐steady convection during steady magnetospheric convection (SMC) events and the transport and energization of electrons. SMC events are long‐duration intervals of enhanced convection without any substorm expansions and are an important mechanism in coupling magnetotail plasma populations to the inner magnetosphere. We find that storms with SMCs in the recovery phase are more likely to increase relativistic electron flux levels, while storms without SMCs are more likely to result in a decrease. Using particle measurements from the Time History of Events and Macroscale Interactions During Substorms mission, we show that phase space density of seed electron populations increases 1 h before SMC start and stays elevated through the duration of SMCs. Chorus activity is also elevated during SMC events. These results suggest that rather than hindering electron acceleration by diverting plasma away from the inner magnetosphere, SMC events appear to act to enhance and maintain seed electron populations.