Observations of rapidly growing whistler waves in front of space plasma shock

TL;DR

This study uses high-resolution spacecraft data and a new analysis method to observe and understand the growth and evolution of whistler waves in space plasma, revealing electron and ion contributions to wave instability.

Contribution

The paper introduces a novel approach to separate electron velocity fluctuations and captures the resonance with electromagnetic fields, advancing understanding of wave growth mechanisms.

Findings

Successful separation of electron velocity fluctuations from background.

Identification of electron resonance with high-frequency electromagnetic fields.

Quantification of wave growth rate and ion influence on wave evolution.

Abstract

Whistler mode wave is a fundamental perturbation of electromagnetic fields and plasmas in various environments including planetary space, laboratory and astrophysics. The origin and evolution of the waves are a long-standing question due to the limited instrumental capability in resolving highly variable plasma and electromagnetic fields. Here, we analyse data with the high time resolution from the multi-scale magnetospheric spacecraft in the weak magnetic environment (i.e., foreshock) enabling a relatively long gyro-period of whistler mode wave. Moreover, we develop a novel approach to separate the three-dimensional fluctuating electron velocity distributions from their background, and have successfully captured the coherent resonance between electrons and electromagnetic fields at high frequency, providing the resultant growth rate of unstable whistler waves. Regarding the energy origin for the waves, the ion distributions are found to also play crucial roles in determining the eigenmode disturbances of fields and electrons. The quantification of wave growth rate can significantly advance the understandings of the wave evolution and the energy conversion with particles.