Speaker
Description
During 10-19 May 2024, the largest storm in the past 20 years took place, characterized with minimum Dst index of -412 nT. In the storm main phase, dropouts of >700 keV relativistic electrons are observed by Arase and NOAA 18 satellites throughout the outer radiation belts. During the storm recovery phase, the fluxes of relativistic electrons locally increase by about more than two orders of magnitude at L > 2. To understand the mechanisms accounting for the relativistic electron dynamics during this storm, we perform simulations by using the Versatile Electron Radiation Belt (VERB) code. In these simulations, the measurements from Geostationary Operational Environmental Satellite (GOES) are used to set up the outer boundary. Magnetopause shadowing effect is included by using the location of magnetopause, which results in significant dropouts of relativistic electrons at L* > 4 during storm main phase. Due to the rapid erosion of the plasmapause (down to the inner belt), the local accelerations outside the plasmapause during the recovery phase are reproduced by including local diffusions driven by chorus waves, following by the appearance of slot region and remnant belt inside the plasmapause. We perform simulations using different radial diffusion coefficients and the density-dependent local diffusion coefficients. Our results show that only with realistic background plasma density, the simulations can reproduce the enhancement of multi-MeV electrons. We also investigate the decay of radiation belt electrons caused by hiss waves and dropout from the magnetopause shadowing effect.
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