Formation of Rotational Discontinuities in Compressive three-dimensional MHD Turbulence

TL;DR

This study investigates the formation of rotational discontinuities in 3D compressive MHD turbulence, revealing they originate from Alfvén wave steepening caused by nonuniform Alfvén speeds, with implications for solar wind turbulence.

Contribution

It demonstrates how rotational discontinuities form from Alfvén wave steepening in 3D MHD turbulence, providing detailed analysis of their structure and evolution.

Findings

Rotational discontinuities are formed from Alfvén wave steepening.

Discontinuities exhibit sharp magnetic field rotations with little intensity variation.

The nonuniformity of Alfvén speed causes wave steepening leading to RDs.

Abstract

Measurements of solar wind turbulence reveal the ubiquity of discontinuities. In this study, we investigate how the discontinuities, especially rotational discontinuities (RDs), are formed in magnetohydrodynamic (MHD) turbulence. In a simulation of the decaying compressive three-dimensional (3-D) MHD turbulence with an imposed uniform background magnetic field, we detect RDs with sharp field rotations and little variations of magnetic field intensity as well as mass density. At the same time, in the de Hoffman-Teller (HT) frame, the plasma velocity is nearly in agreement with the Alfv\'{e}n speed, and is field-aligned on both sides of the discontinuity. We take one of the identified RDs to analyze in details its 3-D structure and temporal evolution. By checking the magnetic field and plasma parameters, we find that the identified RD evolves from the steepening of the Alfv\'{e}n wave with moderate amplitude, and that steepening is caused by the nonuniformity of the Alfv\'{e}n speed in the ambient turbulence.