What drives mesoscale atmospheric turbulence?

TL;DR

This paper investigates the nature of mesoscale atmospheric turbulence, proposing that large-scale coherent flows influence turbulence spectra and energy cascades, reconciling previous conflicting observations.

Contribution

It introduces a new explanation involving spectral condensates and large-scale shear flows to clarify mesoscale turbulence behavior.

Findings

Large-scale shear flows modify the third-order velocity moment.

Laboratory data supports the influence of spectral condensates.

Results suggest a unified view of atmospheric turbulence spectra.

Abstract

Measurements of atmospheric winds in the mesoscale range (10-500 km) reveal remarkably universal spectra with the $k^{-5/3}$ power law. Despite initial expectations of the inverse energy cascade, as in two-dimensional (2D) turbulence, measurements of the third velocity moment in atmosphere, suggested a direct energy cascade. Here we propose a possible solution to this controversy by accounting for the presence of a large-scale coherent flow, or a spectral condensate. We present new experimental laboratory data and show that the presence of a large-scale shear flow modifies the third-order velocity moment in spectrally condensed 2D turbulence, making it, in some conditions, similar to that observed in the atmosphere.