MHD-test particles simulations of moderate CME and CIR-driven
geomagnetic storms at solar minimum
Abstract
As part of the Whole Heliosphere and Planetary Interactions (WHPI)
initiative, contrasting drivers of radiation belt electron response at
solar minimum have been investigated with MHD-test particle simulations
for the 13 – 14 May 2019 CME-shock event and the 30 August – 3
September 2019 high speed solar wind interval. Both solar wind drivers
produced moderate geomagnetic storms characterized by a minimum Dst = -
65 nT and - 52 nT, respectively, with the August - September event
accompanied by prolonged substorm activity. The latter, with
characteristic features of a CIR-driven storm, produced the hardest
relativistic electron spectrum observed by Van Allen Probes during the
last two years of the mission, ending in October 2019. MHD simulations
were performed using both the Lyon-Fedder-Mobarry global MHD code and
recently developed GAMERA model coupled to the Rice Convection Model,
run with measured L1 solar wind input for both events studied, and
coupled with test particle simulations, including an initial trapped and
injected population. Initial electron phase space density (PSD) profiles
used measurements from the Relativistic Electron Proton Telescope (REPT)
and MagEIS energetic particle instruments on Van Allen Probes for test
particle weighting and updating of the injected population at apogee.
Results were compared directly with measurements and found to reproduce
magnetopause loss for the CME-shock event and increased PSD for the CIR
event. The two classes of events are contrasted for their impact on
outer zone relativistic electrons near the end of Solar Cycle 24.