Nonlinear Electron Interactions With Intense VLF Waves From Transmitters

Abstract The impact on electron lifetimes of nonlinear interactions with the most intense very low frequency (VLF) waves from transmitters has hitherto been neglected in radiation belt codes. Here, we show the presence of a small population of intense wave packets, originating from ground‐based VLF transmitters and reaching 10 mV/m around the magnetic equator at , in burst mode data from the Van Allen Probes. Despite their very small occurrence rate, such intense wave packets may carry of the order of 25% of the total electric field wave power of VLF waves from transmitters. Using test particle simulations, we demonstrate that the long‐term effects of electron nonlinear interactions with such intense wave packets through Landau and cyclotron resonances can be modeled by electron advection rates coupled with nonlinear diffusion rates, in both pitch‐angle and energy space. These numerically determined rates allow us to estimate the impact of these nonlinear interactions on electron loss timescales. We show that these rare nonlinear interactions could lead to a significantly faster decay of trapped 30–75 keV electron fluxes at than usual quasi‐linear interactions with moderate time‐averaged amplitude waves and Coulomb collisions. This may contribute to explain the short 30–75 keV electron lifetimes measured by the Van Allen Probes in this region, as well as observations of flattened electron flux energy spectra. Nonlinear interactions also increase the energy of precipitated electrons. This suggests a potential long‐term impact of nonlinear wave‐particle interactions on energetic electron fluxes in the inner radiation belt.