Effects of equatorial chorus wave normal azimuthal distribution on wave propagation

TL;DR

This study develops a ray tracing model to analyze non-ducted VLF wave propagation in the inner magnetosphere, revealing wave-normal dynamics, reflection conditions, and chorus emission distributions aligned with measurements, aiding radiation belt research.

Contribution

The paper introduces a new ray tracing software incorporating realistic wave-normal distributions and magnetic field models to study chorus wave propagation.

Findings

Whistler waves reflect when lower hybrid resonance exceeds wave frequency.

Quasi-longitudinal approximation is invalid for magnetospheric whistler propagation.

Simulated chorus wave-normal distributions agree with CLUSTER measurements.

Abstract

The non-ducted propagation characteristics of the VLF waves in the inner magnetosphere were studied with respect to their frequency, source localization, and initial wave normal angle, between the wave-normal and the background magnetic field. The ray tracing software based on multi-components cold plasma approach was developed by use of the IGRF magnetic field model and the GCPM model of plasma density. We described dynamics of the wave-normals direction during its propagation and magnetospheric reflection. We showed that whistler waves can be reflected when lower hybrid resonance frequency becomes greater than the wave frequency: w_LH>w. It corresponds to the magnetic latitude of ~50 degrees. The simulation results confirmed the inapplicability of the quasi-longitudinal approximation to describe the propagation of magnetospheric whistlers. The simulation results of chorus emissions propagation, which used realistic distributions of waves on the initial parameters were presented. Particularly, we obtained distributions of chorus emission waves in dependence on the wave-normal directions for different magnetic latitudes. It is required for studying diffusive processes in the radiation belts. The results were found to be in a good agreement with the CLUSTER STAFF-SA measurements.