Nonlinear sub-cyclotron resonance as a formation mechanism for gaps in banded chorus

TL;DR

This paper proposes a new nonlinear mechanism involving oblique whistler wave resonance to explain the formation of frequency gaps in magnetospheric chorus emissions, supported by Hamiltonian theory and test-particle simulations.

Contribution

It introduces a novel nonlinear resonance mechanism for chorus gaps, expanding understanding of wave-particle interactions in space plasmas.

Findings

Oblique whistler waves can resonate with electrons at fractional cyclotron frequencies.

Resonance leads to energy exchange, creating frequency gaps in chorus emissions.

The mechanism explains observed chorus gaps at 0.3, 0.5, and 0.6 times the electron cyclotron frequency.

Abstract

An interesting characteristic of magnetospheric chorus is the presence of a frequency gap at $\omega \simeq 0.5\Omega_e$, where $\Omega_e$ is the electron cyclotron angular frequency. Recent chorus observations sometimes show additional gaps near $0.3\Omega_e$ and $0.6\Omega_e$. 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.