Understanding cold electron impact on parallel-propagating whistler chorus waves via moment-based quasilinear theory

TL;DR

This paper develops a quasilinear theory to analyze how cold electrons in Earth's magnetosphere interact with parallel-propagating whistler chorus waves, revealing a secondary instability that can dampen primary wave amplitudes and influence wave observations.

Contribution

It introduces a moment-based quasilinear model for secondary instabilities, explaining energy transfer from whistler waves to cold electrons and their impact on wave amplitudes.

Findings

Secondary instabilities persist across various parameters.

They can cause near-complete damping of primary waves.

This mechanism explains the rarity of simultaneous high-amplitude oblique and field-aligned whistler waves.

Abstract

Earth's magnetosphere hosts a wide range of collisionless particle populations that interact through various wave-particle processes. Among these, cold electrons, with energies below 100eV, often dominate the plasma density but remain poorly characterized due to measurement challenges such as spacecraft charging and photoelectron contamination. Understanding the contribution of these cold populations to wave-particle interaction is of significant interest. Recent kinetic simulations identified a secondary drift-driven instability in which parallel-propagating whistler-mode chorus waves excite oblique electrostatic whistler waves near the resonance cone and Bernstein-mode turbulence. These secondary modes enable a new channel of energy transfer from the parallel-propagating whistler wave to the cold electrons. In this work, we develop a moment-based quasilinear theory of the secondary instabilities to quantify such energy exchange. Our results show that these secondary instabilities persist for a wide range of parameters and, in many cases, lead to nearly complete damping of the primary wave. Such secondary instability might limit the amplitude of parallel-propagating whistler waves in Earth's magnetosphere and might explain why high-amplitude oblique whistler or electron Bernstein waves are rarely observed simultaneously with high-amplitude field-aligned whistler waves in the inner magnetosphere.