Critical Balance and the Physics of MHD Turbulence

TL;DR

This paper critically examines the concept of critical balance in MHD turbulence, discussing its advantages, limitations, and related models, while presenting new insights into spectral features and timescales.

Contribution

It provides a comprehensive analysis of critical balance in MHD turbulence, highlighting its theoretical status, limitations, and connections to models like Reduced MHD, along with new spectral and timescale results.

Findings

Spectral anisotropy and timescale relationships clarified

Influence of mean magnetic field on turbulence discussed

New spectral features and timescales presented

Abstract

A discussion of the advantages and limitations of the concept of critical balance, as employed in turbulence phenomenologies, is presented. The incompressible magnetohydrodynamic (MHD) case is a particular focus. The discussion emphasizes the status of the original Goldreich & Sridhar (1995) critical balance conjecture relative to related theoretical issues and models in an MHD description of plasma turbulence. Issues examined include variance and spectral anisotropy, influence of a mean magnetic field, local and nonlocal effects, and the potential for effects of external driving. Related models such as Reduced MHD provide a valuable context in the considerations. Some new results concerning spectral features and timescales are presented in the course of the discussion. Also mentioned briefly are some adaptations and variations of critical balance.