Cross-helicity and transition from magnetohydrodynamics to kinetics in space plasmas

TL;DR

This paper investigates the transition from magnetohydrodynamic to kinetic regimes in space plasmas, highlighting two types of transitions using simulations and spacecraft data, and discusses implications for planetary magnetosheaths.

Contribution

It identifies and characterizes two generic transition types from MHD to kinetic regimes in space plasmas, supported by simulations and spacecraft measurements.

Findings

Two types of MHD to kinetic transition identified

Existence of cross-helicity dominated chaos in space plasmas

Observations from multiple planetary magnetosheaths discussed

Abstract

Cross-helicity dominated distributed chaos (CHDC) for magnetohydrodynamic (large-scale) and kinetic (small-scale) ranges of space plasmas has been studied using results of direct numerical simulations and of measurements made in the Earth's magnetosheath and in free solar wind by the instruments onboard of the Magnetospheric Multiscale Mission and CLUSTER spacecrafts. Existence of two generic types of transition from the magnetohydrodynamic (MHD) to kinetic range has been shown: 1) from the Kolmogorov-like (scaling) MHD turbulence to the kinetic CHDC and 2) from the magnetohydrodynamic CHDC to the kinetic CHDC. Results of measurements in the magnetosheath of some other planets: Saturn (Cassini observations), Jupiter (Galileo observations), and Mercury (Messenger observations), have been briefly discussed in this contest.