Nonlinear Landau resonant scattering of near equatorially mirroring radiation belt electrons by oblique EMIC waves

In response to solar wind disturbances, radiation belt (a few hundreds of keV to several MeV) electron fluxes can be depleted significantly over the entire equatorial pitch angle range. The frequently mentioned cyclotron resonant scattering is applicable only for electrons mirroring off the equator. Here we propose a new physical mechanism, nonlinear Landau resonance with oblique electromagnetic ion cyclotron (EMIC) waves, to effectively scatter the near equatorially mirroring electrons. Our test particle simulations show that the nonlinear Landau trapping can occur over a wide energy range and yield the net decrease in equatorial pitch angle Δαeq≈10° within several seconds. Our parametric studies further reveal that this nonlinear Landau‐trapping process is favored by a low plasma density, an intense wave field, a high wave frequency close to ion gyrofrequencies, and a large wave normal angle. Key Points Nonlinear Landau resonance between energetic electrons and oblique EMIC waves Pitch angle scattering of near equatorially mirroring radiation belt electrons Sensitivity to plasma density, electron energy, and wave characteristics