Statistical Distributions of Bifurcation of Earth's Inner Radiation Belt due to VLF Transmitters

Abstract:

The Earth’s inner radiation belt typically exhibits one-peak radial structure peaking in the intensity at radial distances < ~2 Earth radii. Recent studies suggested that human-made very low frequency (VLF) transmitters leaked into the inner magnetosphere can efficiently scatter electrons, bifurcating the inner belt, which indicates practical human mitigation of natural particle radiation and better protection of near-Earth satellite. In this letter, we use 6 years of electron flux data from the Van Allen Probes to comprehensively analyze the statistical distributions of the bifurcated inner belts and their dependence on electron energy, season, and geomagnetic activity, which is crucial to understand when and where VLF transmitters can efficiently scatter electrons. We reveal that bifurcation of the inner belt can be frequently observed for tens of keV electrons under relatively quiet geomagnetic conditions after significant flux enhancements that elevate fluxes at L = 2.0 – ~2.5 providing the prerequisite for the formation of the bifurcation. The bifurcation typically lasts for a few days before interrupted by flux enhancement driven by injections or radial diffusion. The energy-dependent L shells of bifurcation dip and seasonal asymmetric occurrence of the bifurcation demonstrate that VLF transmitters play an important role in energetic electron loss in the near-Earth space.