Scalings of intermittent structures in magnetohydrodynamic turbulence

TL;DR

This paper investigates the statistical properties and scalings of intermittent dissipative structures in magnetohydrodynamic turbulence, revealing their role in energy dissipation and implications for astrophysical phenomena.

Contribution

It provides a detailed statistical analysis of intermittent structures in MHD turbulence and proposes phenomenological explanations for their scalings, advancing understanding of turbulence intermittency.

Findings

Intermittent structures in current density, vorticity, and Elsässer vorticities share similar statistical properties.

Intermittent structures occupy small volumes but dominate energy dissipation.

Proposed phenomenological models explain the observed scalings of these structures.

Abstract

Turbulence is ubiquitous in plasmas, leading to rich dynamics characterized by irregularity, irreversibility, energy fluctuations across many scales, and energy transfer across many scales. Another fundamental and generic feature of turbulence, although sometimes overlooked, is the inhomogeneous dissipation of energy in space and in time. This is a consequence of intermittency, the scale-dependent inhomogeneity of dynamics caused by fluctuations in the turbulent cascade. Intermittency causes turbulent plasmas to self-organize into coherent dissipative structures, which may govern heating, diffusion, particle acceleration, and radiation emissions. In this paper, we present recent progress on understanding intermittency in incompressible magnetohydrodynamic turbulence with a strong guide field. We focus on the statistical analysis of intermittent dissipative structures, which occupy a small fraction of the volume but arguably account for the majority of energy dissipation. We show that, in our numerical simulations, intermittent structures in the current density, vorticity, and Els\"{a}sser vorticities all have nearly identical statistical properties. We propose phenomenological explanations for the scalings based on general considerations of Els\"{a}sser vorticity structures. Finally, we examine the broader implications of intermittency for astrophysical systems.