Solar wind turbulence from MHD to sub-ion scales: high-resolution hybrid simulations

TL;DR

This study uses high-resolution hybrid simulations to analyze solar wind turbulence across MHD and sub-ion scales, revealing spectral properties and cascade behaviors consistent with observations.

Contribution

It provides detailed simulation evidence of turbulence spectral evolution from MHD to sub-ion scales, supporting the generalized Ohm's law in solar wind turbulence.

Findings

Identification of two spectral regions with power-law scaling separated by proton scales

Spectral indices match observed solar wind fluctuations in the MHD inertial range

Enhanced magnetic compressibility and coupling at sub-proton scales

Abstract

We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wave numbers. The simulation results exhibit simultaneously several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magneto-hydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm's law.