Anisotropic magnetohydrodynamic turbulence driven by parametric decay instability: the onset of phase mixing and Alfv\'en wave turbulence

TL;DR

This study uses 3D MHD simulations to explore how parametric decay instability of Alfvén waves leads to anisotropic turbulence and phase mixing, contributing to solar wind heating.

Contribution

It demonstrates the transition from phase mixing to Alfvén wave turbulence in the nonlinear evolution of parametric decay instability in the solar wind.

Findings

Early nonlinear stage dominated by phase mixing.

Later stage characterized by imbalanced Alfvén wave turbulence.

Regions with large density fluctuations are heated by phase-mixed Alfvén waves.

Abstract

We conduct a three-dimensional magnetohydrodynamic (MHD) simulation of the parametric decay instability of Alfv\'en waves and resultant compressible MHD turbulence, which is likely to develop in the solar wind acceleration region. Because of the presence of the mean magnetic field, the nonlinear stage is characterized by filament-like structuring and anisotropic cascading. By calculating the timescales of phase mixing and the evolution of Alfv\'en wave turbulence, we have found that the early nonlinear stage is dominated by phase mixing, while the later phase is dominated by imbalanced Alfv\'en wave turbulence. Our results indicate that the regions in the solar atmosphere with large density fluctuation, such as the coronal bottom and wind acceleration region, are heated by phase-mixed Alfv\'en waves, while the other regions are heated by Alfv\'en wave turbulence.