Critical balance in magnetohydrodynamic, rotating and stratified turbulence: towards a universal scaling conjecture

TL;DR

This paper proposes that the concept of critical balance can serve as a universal framework for understanding the energy spectra in various anisotropic turbulent systems like MHD, rotating, and stratified turbulence, unifying their scaling behaviors.

Contribution

It introduces a novel, testable energy cascade scenario based on critical balance for anisotropic turbulence, applicable across different physical systems.

Findings

Proposes a universal critical balance-based scaling conjecture for anisotropic turbulence.

Suggests a natural transition from anisotropic to isotropic turbulence at small scales.

Links observed spectral scalings to wave polarization and alignment phenomena.

Abstract

It is proposed that critical balance - a scale-by-scale balance between the linear propagation and nonlinear interaction time scales - can be used as a universal scaling conjecture for determining the spectra of strong turbulence in anisotropic wave systems. Magnetohydrodynamic (MHD), rotating and stratified turbulence are considered under this assumption and, in particular, a novel and experimentally testable energy cascade scenario and a set of scalings of the spectra are proposed for low-Rossby-number rotating turbulence. It is argued that in neutral fluids, the critically balanced anisotropic cascade provides a natural path from strong anisotropy at large scales to isotropic Kolmogorov turbulence at very small scales. It is also argued that the kperp^{-2} spectra seen in recent numerical simulations of low-Rossby-number rotating turbulence may be analogous to the kperp^{-3/2} spectra of the numerical MHD turbulence in the sense that they could be explained by assuming that fluctuations are polarised (aligned) approximately as inertial waves (Alfven waves for MHD).