Timescales of Changes in Outer Radiation Belt Electrons During Sheath Regions of Coronal Mass Ejections Using the Global Positioning System Constellation

Turbulent and compressed sheath regions ahead of interplanetary coronal mass ejections couple strongly to the magnetosphere-ionosphere system. These large-scale solar wind structures are key drivers of dramatic changes in the electron fluxes in the Earths outer radiation belt. Our statistical study of sheath events using Van Allen Probes electron flux data shows how the outer belt response to sheaths is energy and L-shell dependent. Enhancement is common at 10s to 100s keV energies, while losses tend to occur at MeV energies. Both responses are more common at L > 4. We highlight that such significant changes are also caused by the non-geoeffective sheaths. Analysis of phase space density radial profiles aids in the identification of the physical processes leading to the enhancement and losses. The limited coverage of only the two Van Allen Probes, however, does not generally allow determining the timescale of these processes to better accuracy than a few hours. The Global Positioning System (GPS) constellation provides a superior temporal and spatial resolution in L-shell with its multiple satellites on various orbital planes, allowing determination of timescales of a few tens of minutes. Despite the less capable instrumentation on GPS satellites, the data compare reasonably well with Van Allen Probes fluxes and phase space densities. Using phase space densities calculated from the GPS dataset, we investigate the timescales of changes in outer belt electrons during sheaths.