LASP Magnetosphere Seminars

Abstract

Enhancement of relativistic electron flux at L = 3 and protons at L =2 has been reported from the CEASE-3 instrument on the USSF Weather System Follow-on Microwave satellite, the European PROBA-V satellite and the University of Colorado CIRBE cubesat, all in LEO orbits, associated with the May 2024 superstorm. This storm was initiated by a complex interplanetary shock compression of the dayside magnetosphere which produced a Storm Sudden Commencement (SSC) of +62 nT, almost identical to the 24 March 1991 prompt electron and proton injection with an SSC of +63 nT, which produced a new electron belt at L = 2.5 with a peaked energy spectrum and a new proton belt due to SEP trapping. It was shown for the March 1991 event using a simple analytic model1 and MHD-test particle simulations2 that the inward radial transport of trapped outer zone electrons on a drift timescale was responsible for the new electron belt which persisted into the era of SAMPEX observations. Shock compression of the dayside magnetosphere launches a magnetosonic azimuthal electric field impulse propagating tailward inside the dawn and dusk flanks of the magnetopause which was observed in detail for similar weaker events by the Van Allen Probes spacecraft, and for the March 1991 event by the CRRES satellite on the nightside1. This impulse propagates from the dayside around dawn and dusk tailward, accelerating electrons and protons in drift resonance across the dayside and along the flanks. Inward radial transport follows from conservation of the first adiabatic invariant. It will be shown that the same mechanism can operate both for initially trapped protons and a SEP source, producing SEP trapping3. MHD test particle simulations for the May 2024 superstorm will be presented which reproduce the long-lived new proton belt at L = 2, while the transient outer zone electron enhancement at higher L requires local heating, as well as tail injection of plasmasheet electrons resolved by the MHD test particle simulations.

1Li et al., GRL, 1993

2Elkington et al., JASTP, 2004

3Hudson et al., JGR, 1997; 2023