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≃0.5Ωe, where Ωe is the electron cyclotron angular frequency. Recent chorus observations sometimes show additional gaps near 0.3Ωe and 0.6Ωe. 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. Key Points Recent observations of chorus show multiple bands Nonlinear wave-particle resonances can occur at subcyclotron frequencies Subcyclotron resonance may lead to formation of gaps in banded chorus