Identification of coupled Landau and anomalous resonances in space plasmas

TL;DR

This paper reports spacecraft observations of coupled Landau and anomalous resonances in space plasmas, revealing how these resonances interact through overlapping resonance islands, advancing understanding of wave-particle interactions.

Contribution

It provides the first direct evidence of simultaneous Landau and anomalous resonances coupling via overlapping resonance islands in space plasmas.

Findings

Observation of phase-space rings indicating Landau resonance

Detection of phase-bunched distributions showing anomalous resonance

Evidence of resonance coupling through overlapping resonance islands

Abstract

Wave-particle resonance, a ubiquitous process in the plasma universe, occurs when resonant particles observe a constant wave phase to enable sustained energy transfer. Here, we present spacecraft observations of simultaneous Landau and anomalous resonances between oblique whistler waves and the same group of protons, which are evidenced, respectively, by phase-space rings in parallel-velocity spectra and phase-bunched distributions in gyro-phase spectra. Our results indicate the coupling between Landau and anomalous resonances via the overlapping of the resonance islands.