Bounce resonance scattering of ring current electrons by H+ band EMIC waves

Abstract

We present a detailed investigation of bounce-resonant pitch angle scattering of ring current electrons caused by electromagnetic ion cyclotron (EMIC) waves. It is found that H+ band EMIC waves can resonate with near-equatorially mirroring electrons over a wide range of L shells (i.e., 3≤L≤6) and energies and lead to the efficient transport of ring current electrons (i.e., ∼10 keV to 100 keV) from near 90° pitch angles to lower pitch angles. Computations of the bounce-resonant pitch angle scattering rates show a strong dependence on the L shell, electron energy, and resonance harmonics. When the L-shell increases, the orders of bounce resonance contributing to the whole scattering coefficient decrease, and meanwhile, it becomes difficult for the bounce resonance of higher orders to occur. Furthermore, when the electron energy increases, the bounce resonance orders decrease. Our results demonstrate that bounce-resonant scattering by H+ band EMIC waves can be an important loss mechanism for ∼10–100 keV electrons because of the absence of cyclotron resonance for ring current electrons interacting with EMIC waves. We conclude that bounce resonant scattering by H+ band EMIC waves should be incorporated into future modeling efforts of the ring current electron dynamics.