BARREL observations of an ICME‐shock impact with the magnetosphere and the resultant radiation belt electron loss

Abstract The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) mission of opportunity working in tandem with the Van Allen Probes was designed to study the loss of radiation belt electrons to the ionosphere and upper atmosphere. BARREL is also sensitive to X‐rays from other sources. During the second BARREL campaign, the Sun produced an X‐class flare followed by a solar energetic particle event (SEP) associated with the same active region. Two days later on 9 January 2014, the shock generated by the coronal mass ejection (CME) originating from the active region hits the Earth while BARREL was in a close conjunction with the Van Allen Probes. Time History Events and Macroscale Interactions during Substorms (THEMIS) satellite observed the impact of the interplanetary CME (ICME) shock near the magnetopause, and the Geostationary Operational Environmental Satellites (GOES) were on either side of the BARREL/Van Allen Probe array. The solar interplanetary magnetic field was not ideally oriented to cause a significant geomagnetic storm, but compression from the shock impact led to the loss of radiation belt electrons. We propose that an azimuthal electric field impulse generated by magnetopause compression caused inward electron transport and minimal loss. This process also drove chorus waves, which were responsible for most of the precipitation observed outside the plasmapause. Observations of hiss inside the plasmapause explain the absence of loss at this location. ULF waves were found to be correlated with the structure of the precipitation. We demonstrate how BARREL can monitor precipitation following an ICME‐shock impact at Earth in a cradle‐to‐grave view; from flare, to SEP, to electron precipitation.