Comment on Perez et al [PRX 2, 041005 (2012), arXiv:1209.2011]

TL;DR

This paper critically examines Perez et al's claims about the spectral slope of MHD turbulence, identifying errors and arguing that their numerical evidence actually contradicts their original conclusion.

Contribution

It provides a detailed critique of Perez et al's interpretation of MHD turbulence data, correcting misconceptions and highlighting methodological issues.

Findings

Perez et al's data do not support a -3/2 spectral slope.

The supposed measurement of inertial range scaling is actually a calculation.

The original claims about universal alignment are challenged.

Abstract

Recently Perez et al [arXiv:1209.2011] wrote on the spectral slope of MHD turbulence claiming that it is consistent with -3/2. This work contains a number of errors, factual inaccuracies and puzzling methods in the interpretation of numerics. We argue that the numerical evidence that the authors presented is actually against -3/2 slope and the assumption of universal alignment, opposite to what they claim. Perhaps the most puzzling is the Fig.8 that claims that the authors measured the inertial range length and that it is consistent with Re^2/3 scaling. At a close inspection it appears that the datapoints are not the result of a measurement, but rather were calculated by a formula.