Simulation of ULF wave‐modulated radiation belt electron precipitation during the 17 March 2013 storm

Balloon-borne instruments detecting radiation belt precipitation frequently observe oscillations in the millihertz frequency range. Balloons measuring electron precipitation near the poles in the 100 keV to 2.5 MeV energy range, including the MAXIS, MINIS, and most recently the Balloon Array for Relativistic Radiation belt Electron Losses balloon experiments, have observed this modulation at ULF wave frequencies. Although ULF waves in the magnetosphere are seldom directly linked to increases in electron precipitation since their oscillation periods are much larger than the gyroperiod and the bounce period of radiation belt electrons, test particle simulations show that this interaction is possible. Three-dimensional simulations of radiation belt electrons were performed to investigate the effect of ULF waves on precipitation. The simulations track the behavior of energetic electrons near the loss cone, using guiding center techniques, coupled with an MHD simulation of the magnetosphere, using the Lyon-Fedder-Mobarry code, during a coronal mass ejection (CME)-shock event on 17 March 2013. Results indicate that ULF modulation of precipitation occurs even without the presence of electromagnetic ion cyclotron waves, which are not resolved in the MHD simulation. The arrival of a strong CME-shock, such as the one simulated, disrupts the electric and magnetic fields in the magnetosphere and causes significant changes in both components of momentum, pitch angle, and L shell of radiation belt electrons, which may cause them to precipitate into the loss cone.