Immediate response of the outer radiation belt to sheath regions of coronal mass ejections

Milla Kalliokoski - University of Helsinki, Finland; Emilia Kilpua - University of Helsinki, Finland; Adnane Osmane - University of Helsinki, Finland; Drew Turner - The Johns Hopkins University Applied Physics Laboratory, United States; Allison Jaynes - University of Iowa, United States; Lucile Turc - University of Helsinki, Finland; Harriet George - University of Helsinki, Finland; Minna Palmroth - University of Helsinki, Finnish Meteorological Institute, Finland

Session: QV - Earth's Magnetosphere and Radiation Belts

Abstract

The energetic electron content in the Van Allen radiation belts surrounding the Earth can vary dramatically on timescales from minutes to days. These strong electron fluxes present a hazard for spacecraft traversing the belts. However, the response of the belts to solar wind driving is yet largely unpredictable – especially on short timescales. We investigate the immediate response of outer radiation belt electron fluxes to sheath regions preceding interplanetary coronal mass ejections. We also study the associated wave activity in the inner magnetosphere. We use measurements from the Van Allen Probes and GOES-15 (Geostationary Operational Environmental Satellite) during sheath events in 2012–2018. Our statistical analysis shows that wave activity in the inner magnetosphere is enhanced during sheath regions and that the response of outer belt electron fluxes depends on electron energy and radial distance from the Earth. Low-energy electron fluxes (tens to hundreds of keV) primarily increase, while high-energy electron fluxes (few MeV) mainly decrease. We also show that significant changes in the outer belt electron fluxes can be caused by events which do not cause prominent geomagnetic disturbances.