Refined critical balance in strong Alfvenic turbulence

TL;DR

This paper provides numerical evidence that in strong Alfvenic turbulence, the critical balance principle remains scale-invariant when local field alignment is considered, highlighting its robustness amidst intermittent turbulence.

Contribution

It demonstrates that the critical balance principle is scale-invariant in strong Alfvenic turbulence when local alignment is included, supported by numerical and solar wind data.

Findings

Critical balance is scale-invariant when local Elsasser field alignment is accounted for.

Alignment increases with fluctuation amplitude, driven by mutual shearing.

Critical balance remains robust despite intermittent scale-dependent quantities.

Abstract

We present numerical evidence that in strong Alfvenic turbulence, the critical balance principle---equality of the nonlinear decorrelation and linear propagation times---is scale invariant, in the sense that the probability distribution of the ratio of these times is independent of scale. This result only holds if the local alignment of the Elsasser fields is taken into account in calculating the nonlinear time. At any given scale, the degree of alignment is found to increase with fluctuation amplitude, supporting the idea that the cause of alignment is mutual dynamical shearing of Elsasser fields. The scale-invariance of critical balance (while all other quantities of interest are strongly intermittent, i.e., have scale-dependent distributions) suggests that it is the most robust of the scaling principles used to describe Alfvenic turbulence. The quality afforded by situ fluctuation measurements in the solar wind allows for direct verification of this fundamental principle.