MHD-Test Particles Simulations of Moderate CME and CIR-Driven Geomagnetic Storms at Solar Minimum

Thursday, December 2, 2021

Outer zone radiation belt electron flux is highly variable and responds differently to different solar wind drivers. Coronal Mass Ejections (CMEs) which are common at Solar Maximum, when the sun is most active with sunspots every 11 years, create interplanetary shocks as they propagate towards Earth. These shocks compress the dayside magnetosphere and can cause rapid loss of outer zone electrons. Ensuing geomagnetic storms which accompany shocks can repopulate the magnetosphere on a rapid timescale. At solar minimum, the focus of this study, low latitude coronal holes, which are regions of open solar magnetic field lines attached and corotating with the sun (Corotating Interaction Regions, CIRs), allow high speed solar wind to reach the Earth and drive increases in outer zone electron flux over many days. Two geomagnetic storms during the 2019 Solar Minimum, one CME-driven and one CIR-driven, are investigated using a global model of the solar wind interaction with the magnetosphere and compared with measurements of electron flux from the twin Van Allen Probes spacecraft in the inner magnetosphere.

Two part colorful simulation
(a) CME-shock simulation shown at 2159 UT May 13, 2019, using GAMERA 3D MHD code coupled to the Rice Convection Model and TIEGCM ionospheric model (Pham et al., 2021). Meridional plot of MHD pressure is shown on the right, with northern and southern hemispheric field aligned currents in the polar regions shown as inserts. On the left, residual Bz (dipole subtracted) is plotted along with an insert showing RCM pressure in the inner magnetosphere. Upstream solar wind input is taken from OMNIWeb propagated to the 30 Re upstream boundary. (b) Initial test particle populations in the GSM equatorial plane, noon to the right. Injected (red) and trapped (black) are the same for both May and August–September 2019 event studies prior to weighting with Phase Space Density measured from Van Allen Probes.
Publication: Space Weather
First HAO Author: Mary K. Hudson
Authors as listed in article: Mary K. Hudson, Scot R. Elkington, Zhao Li, Maulik Patel, Kevin Pham, Kareem Sorathia, Alex Boyd, Allison Jaynes, Alexis Leali