Resonant Scattering of Near‐Equatorially Mirroring Electrons by Landau Resonance With H+ Band EMIC Waves.

By investigating the resonant energy and latitudinal resonance region of Landau resonance between H+ band electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons and performing calculations of quasi‐linear diffusion coefficients, we find that Landau resonance with EMIC waves, characterized by a very broad range of resonant energies from below 1 eV to above 10 MeV and the strikingly small extent of the latitudinal resonance region well below 0.1°, can be a feasible candidate accounting for the pitch angle scattering of near‐equatorially mirroring electrons. Compared to the dominant pitch angle scattering caused by the cyclotron resonance for greater than ~2‐MeV electrons at equatorial pitch angles less than ~80° with the rates well above 10−4 s−1, Landau resonance with H+ band EMIC waves has the potential to drive more efficient pitch angle scattering of radiation belt electrons from ~10 MeV down to tens of kiloelectron volts at equatorial pitch angles greater than ~ 85°. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves are thought to be very important for pitch angle scattering of radiation belt electrons, which may play a crucial role for the rapid dropout of relativistic electrons fluxes in the outer radiation belt during a geomagnetic storm, or for the intense relativistic electron precipitation. Although cyclotron resonance with EMIC waves acts as an important loss process during geomagnetic storms, this mechanism is believed to solely affect trapped electrons with small pitch angles well away from 90°. In the present work, we introduce the Landau resonance between H+ band EMIC waves and radiation belt electrons. The crucial role for pitch angle scattering near‐equatorially mirroring electrons by Landau resonance is investigated by Quasilinear diffusion theory (QLT) calculations in our work. Key Points: H+ band EMIC waves drive the Landau resonance with radiation belt electrons over a very broad energy range from >10 MeV to tenths of an eVLandau resonance between H+ band EMIC waves and electrons at > ~60 degrees occurs in a very limited rangeEMIC scattering electrons due to the cyclotron resonance and Landau resonance occur at two distinct ranges of equatorial pitch angle [ABSTRACT FROM AUTHOR]