Kinetic features for the identification of Kelvin-Helmholtz vortices in \textit{in situ} observations

TL;DR

This paper identifies specific kinetic features in observational data that can reliably detect Kelvin-Helmholtz vortices, validated by simulation and spacecraft data, enhancing understanding of their structure and dynamics.

Contribution

It introduces a set of kinetic signatures for Kelvin-Helmholtz vortex identification, validated through comparison with hybrid Vlasov-Maxwell simulations and MMS satellite observations.

Findings

Edges associated with strong current sheets

Vortex center shows low total current density and non-Maxwellian ion distributions

Inside vortex, significant parallel temperature anisotropy and edge agyrotropies

Abstract

The boundaries identification of Kelvin-Helmholtz vortices in observational data has been addressed by searching for single-spacecraft small-scale signatures. A recent hybrid Vlasov-Maxwell simulation of Kelvin-Helmholtz instability has pointed out clear kinetic features which uniquely characterize the vortex during both the nonlinear and turbulent stage of the instability. We compare the simulation results with \textit{in situ} observations of Kelvin-Helmholtz vortices by the Magnetospheric MultiScale satellites. We find good agreement between simulation and observations. In particular, the edges of the vortex are associated with strong current sheets, while the center is characterized by a low value for the magnitude of the total current density and strong deviation of the ion distribution function from a Maxwellian distribution. We also find a significant temperature anisotropy parallel to the magnetic field inside the vortex region and strong agyrotropies near the edges. We suggest that these kinetic features can be useful for the identification of Kelvin-Helmholtz vortices in \textit{in situ} data.