Three-dimensional simulations of the inhomogeneous Low Solar Wind

TL;DR

This study uses 3D MHD simulations to explore how perpendicular structuring in the solar corona influences turbulence and energy transfer in the solar wind, revealing faster dynamics and specific spectral characteristics.

Contribution

First 3D MHD simulations analyzing the impact of perpendicular structuring on solar wind turbulence, highlighting the role of phase mixing and self-cascade of kink waves.

Findings

Background structuring accelerates turbulence evolution.

Perpendicular energy spectrum follows a -3/2 or -5/3 power law.

Turbulence likely driven by self-cascade of transverse kink waves.

Abstract

In the near future, Parker Solar Probe will put theories about the dynamics and nature of the transition between the solar corona and the solar wind to stringent tests. The most popular mechanism aimed to explain the dynamics of the nascent solar wind, including its heating and acceleration is magnetohydrodynamic (MHD) turbulence. Most of the previous models focus on nonlinear cascade induced by interactions of outgoing Alfv\'en waves and their reflections, ignoring effects that might be related to perpendicular structuring of the solar coronal plasma, despite overwhelming evidence for it. In this paper, for the first time, we analyse through 3D MHD numerical simulations the dynamics of the perpendicularly structured solar corona and solar wind, from the low corona to 15 R_Sun. We find that background structuring has a strong effect on the evolution of MHD turbulence, on much faster time scales than in the perpendicularly homogeneous case. On time scales shorter than nonlinear times, linear effects related to phase mixing result in a 1/f perpendicular energy spectrum. As the turbulent cascade develops, we observe a perpendicular (parallel) energy spectrum with the power law index of -3/2 or -5/3 (-2), a steeper perpendicular magnetic field than velocity spectrum, and a strong build-up of negative residual energy. We conclude that the turbulence is most probably generated by the self-cascade of the driven transverse kink waves, referred to previously as `uniturbulence', which might represent the dominant nonlinear energy cascade channel in the pristine solar wind.