Finite dissipation and intermittency in magnetohydrodynamics

TL;DR

This paper analyzes high-resolution numerical simulations of decaying magnetohydrodynamic turbulence, revealing that dissipation tends to a constant at high Reynolds numbers, indicating potential for fast magnetic reconnection, and confirms stronger intermittency compared to fluids with differences between velocity and magnetic field exponents.

Contribution

It provides the first detailed analysis of dissipation and intermittency in high-Reynolds-number MHD turbulence using large-scale simulations, highlighting differences between velocity and magnetic field statistics.

Findings

Dissipation asymptotes to a constant at high Reynolds numbers.

Intermittency in MHD turbulence is stronger than in fluids.

Measurable differences exist between velocity and magnetic field exponents.

Abstract

We present an analysis of data stemming from numerical simulations of decaying magnetohydrodynamic (MHD) turbulence up to grid resolution of 1536^3 points and up to Taylor Reynolds number of 1200. The initial conditions are such that the initial velocity and magnetic fields are helical and in equipartition, while their correlation is negligible. Analyzing the data at the peak of dissipation, we show that the dissipation in MHD seems to asymptote to a constant as the Reynolds number increases, thereby strengthening the possibility of fast reconnection events in the solar environment for very large Reynolds numbers. Furthermore, intermittency of MHD flows, as determined by the spectrum of anomalous exponents of structure functions of the velocity and the magnetic field, is stronger than for fluids, confirming earlier results; however, we also find that there is a measurable difference between the exponents of the velocity and those of the magnetic field, as observed recently in the solar wind. Finally, we discuss the spectral scaling laws that arise in this flow.