Weak Turbulence in the Magnetosphere: Formation of Whistler Wave Cavity by Nonlinear Scattering

TL;DR

This paper investigates how weak turbulence and nonlinear scattering of whistler waves in Earth's magnetosphere can create a wave cavity that enhances electron scattering, potentially reducing radiation belt electron lifetimes.

Contribution

It introduces a new model of wave cavity formation through nonlinear scattering and reflections, explaining the dynamics of whistler waves in the magnetosphere.

Findings

Nonlinear scattering significantly alters wave propagation directions.

A wave cavity can form, trapping turbulent whistler waves.

Enhanced electron pitch-angle scattering reduces radiation belt electron lifetimes.

Abstract

We consider the weak turbulence of whistler waves in the in low-\beta\ inner magnetosphere of the Earth. Whistler waves with frequencies, originating in the ionosphere, propagate radially outward and can trigger nonlinear induced scattering by thermal electrons provided the wave energy density is large enough. Nonlinear scattering can substantially change the direction of the wave vector of whistler waves and hence the direction of energy flux with only a small change in the frequency. A portion of whistler waves return to the ionosphere with a smaller perpendicular wave vector resulting in diminished linear damping and enhanced ability to pitch-angle scatter trapped electrons. In addition, a portion of the scattered wave packets can be reflected near the ionosphere back into the magnetosphere. Through multiple nonlinear scatterings and ionospheric reflections a long-lived wave cavity containing turbulent whistler waves can be formed with the appropriate properties to efficiently pitch-angle scatter trapped electrons. The primary consequence on the Earth's radiation belts is to reduce the lifetime of the trapped electron population.