Nonlinear subcyclotron resonance as a formationmechanism for gaps in banded chorus

Abstract

An interesting characteristic of magnetospheric chorus is the presence of a frequency gap at ω≃0.5Ω_e, where Ω_e is the electron cyclotron angular frequency. Recent chorus observations sometimes show additional gaps near 0.3Ω_e and 0.6Ω_e. Here we present a novel nonlinear mechanism for the formation of these gaps using Hamiltonian theory and test particle simulations in a homogeneous, magnetized, collisionless plasma. We find that an oblique whistler wave with frequency at a fraction of the electron cyclotron frequency can resonate with electrons, leading to effective energy exchange between the wave and particles.