Observations of Electromagnetic Electron Holes and Evidence of Cherenkov Whistler Emission

TL;DR

This paper reports multi-spacecraft observations of electromagnetic electron holes, highlighting the dominance of Cherenkov-emitted whistler waves in faster EHs and analyzing the magnetic field contributions of different mechanisms.

Contribution

It provides the first detailed analysis of the magnetic field contributions in electromagnetic electron holes, especially emphasizing Cherenkov whistler emission at higher EH speeds.

Findings

Cherenkov whistler waves dominate magnetic fields in fast EHs.

Magnetic field contributions vary with EH speed.

Whistler waves are kinetically damped and confined within EHs.

Abstract

We report observations of electromagnetic electron holes (EHs). We use multi-spacecraft analysis to quantify the magnetic field contributions of three mechanisms: the Lorentz transform, electron drift within the EH, and Cherenkov emission of whistler waves. The first two mechanisms account for the observed magnetic fields for slower EHs, while for EHs with speeds approaching half the electron Alfv\'en speed, whistler waves excited via the Cherenkov mechanism dominate the perpendicular magnetic field. The excited whistlers are kinetically damped and typically confined within the EHs.