Understanding the Driver of Energetic Electron Precipitation Using Coordinated Multisatellite Measurements

Magnetospheric plasma waves play a significant role in ring current and radiation belt dynamics, leading to pitch angle scattering loss and/or stochastic acceleration of the particles. During a non-storm time dropout event on 24 September 2013, intense electromagnetic ion cyclotron (EMIC) waves were detected by Van Allen Probe A (Radiation Belt Storm Probes-A). We quantitatively analyze a conjunction event when Van Allen Probe A was located approximately along the same magnetic field line as MetOp-01, which detected simultaneous precipitation of >30 keV protons and energetic electrons over an unexpectedly broad energy range (>similar to 30keV). Multipoint observations together with quasi-linear theory provide direct evidence that the observed electron precipitation at higher energy (>similar to 700keV) is primarily driven by EMIC waves. However, the newly observed feature of the simultaneous electron precipitation extending down to similar to 30keV is not supported by existing theories and raises an interesting question on whether EMIC waves can scatter such low-energy electrons.