Outer Radiation Belt Flux and Phase Space Density Response to Sheath Regions: Van Allen Probes and GPS Observations. Issue 2 (15th February 2023) - Kalliokoski, Milla M. H.
Abstract: Turbulent and compressed sheath regions preceding interplanetary coronal mass ejections strongly impact electron dynamics in the outer radiation belt. Changes in electron flux can occur on timescales of tens of minutes, which are unlikely to be captured by a two‐satellite mission. The recently released Global Positioning System (GPS) data set generally has shorter revisit times (at L ∼ 4–8) owing to the large number of satellites in the constellation equipped with energetic particle detectors. Investigating electron fluxes at energies from 140 keV to 4 MeV and sheaths observed in 2012–2018, we show that the flux response to sheaths on a timescale of 6 hr, previously reported from Van Allen Probes (RBSP) data, is reproduced by GPS measurements. Furthermore, GPS data enables derivation of the response on a timescale of 30 min, which further confirms that the energy and L ‐shell dependent changes in electron flux are associated with the impact of the sheath. Sheath‐driven loss is underestimated over longer timescales as the electrons recover during the ejecta. We additionally show the response of electron phase space density (PSD), which is a key quantity in identifying non‐adiabatic loss from the system and electron energization through wave‐particle interactions. The PSD response is calculated from both RBSP and GPS data for the 6 hr timescale, as well as from GPS data for the 30 min timescale. The response is divided based on the geoeffectiveness of the sheaths revealing that electrons are effectively accelerated only during geoeffective sheaths, while loss commonly occurs during all sheaths. Key Points: Global Positioning System measurements confirm 6 hr RBSP outer belt electron flux response to interplanetary coronal mass ejection‐driven sheaths at 6 hr and 30 min timescales Phase space density (PSD) response shows that electron energization is associated only with geoeffective sheaths but loss occurs in response to all sheaths Impacts in electron flux and PSD presented here are related to sheaths, and the lost electrons are replenished during the early ejecta