Modeling Kelvin-Helmholtz instability-driven turbulence with hybrid simulations of Alfv\'enic turbulence

TL;DR

This study compares MMS observations of KH-driven plasma turbulence at Earth's magnetopause with high-resolution hybrid simulations, revealing universal cascade properties and a quasi-2D nature of turbulence across scales.

Contribution

It demonstrates the quantitative agreement between observations and simulations, highlighting the universality of turbulence properties from MHD to sub-ion scales driven by KH instability.

Findings

Simulation matches in situ spectral and cascade properties.

Turbulence exhibits a quasi-2D nature.

Cascade rate is significantly higher during KH events.

Abstract

Magnetospheric Multiscale (MMS) observations of plasma turbulence generated by a Kelvin-Helmholtz (KH) event at the Earth's magnetopause are compared with a high-resolution two-dimensional (2D) hybrid direct numerical simulation (DNS) of decaying plasma turbulence driven by large-scale balanced Alfv\'enic fluctuations. The simulation, set up with four observation-driven physical parameters (ion and electron betas, turbulence strength, and injection scale) exhibits a quantitative agreement on the spectral, intermittency, and cascade-rate properties with in situ observations, despite the different driving mechanisms. Such agreement demonstrates a certain universality of the turbulent cascade from magnetohydrodynamic (MHD) to sub-ion scales, whose properties are mainly determined by the selected parameters, also indicating that the KH instability-driven turbulence has a quasi-2D nature. The validity of the Taylor hypothesis in the sub-ion spatial range suggests that the fluctuations at sub-ion scales have predominantly low frequencies, consistent with a kinetic Alfv\'en wave-like nature or with quasi-static structures. Finally, the third-order structure function analysis indicates that the cascade rate of the turbulence generated by a KH event in the magnetopause is an order of magnitude larger than in the ambient magnetosheath.