Electron Scattering Effect due to VLF transmitters in Near-Earth Space

Energetic electrons can exhibit flux decreases over a prolonged time period in the inner belt during quiet geomagnetic conditions, when wave-particle interactions can drive pitch angle scattering and affect distributions of energetic electrons in the inner belt. We quantify the energetic electron flux decay due to the interactions with ground-based very low frequency (VLF) transmitters observed by Van Allen Probes in the Earth's inner radiation belt and slot region. The gradual decay profiles of the energetic electrons at L shells < 3.0 have been observed by Van Allen Probes during a ~15-day quiet period. The energy of measured significant electron flux decay decreases with increasing L shells. By combining calculations of electron diffusion coefficients and two-dimensional Fokker-Planck simulations at L shells over 1.5 - 3.0 based on the observed VLF transmitter waves, and statistical wave models of lightning-generated whistlers, plasmaspheric hiss, and magnetosonic waves, we quantitatively analyze the roles of different wave modes in the electron flux decay process. Our results demonstrate that VLF transmitters can efficiently scatter electrons at L<~2.5 at energies of <~100 keV. VLF transmitters aided by lightning-generated whistlers and hiss, which can scatter electrons at higher L shells and higher energies, can provide a remarkable estimation of the electron flux decay in the inner belt. Our results provide direct evidence that VLF transmitters play a crucial role in the electron loss process in the near-Earth space.