Vortex core radius in baroclinic turbulence: Implications for scaling predictions

TL;DR

This paper revisits vortex-gas scaling theory in baroclinic turbulence, deriving new scaling laws for vortex core radius at low drag and validating these predictions through numerical simulations.

Contribution

It introduces a modified scaling prediction for vortex core radius in baroclinic turbulence, especially under quadratic drag, extending previous vortex-gas models.

Findings

Vortex core radius departs from Rossby deformation radius at low bottom drag.

Scaling laws for eddy diffusivity change under quadratic drag at low coefficients.

Numerical simulations confirm the new scaling predictions.

Abstract

We revisit the vortex-gas scaling theory for heat transport by baroclinic turbulence based on the empirical observation that the vortex core radius departs from the Rossby deformation radius for very low bottom drag coefficient. We derive a scaling prediction for the vortex-core radius. For linear bottom drag this scaling dependence for the vortex-core radius does not affect the vortex-gas predictions for the eddy diffusivity and mixing-length, which remain identical to those in Gallet and Ferrari (Proc. Nat. Acad. Sci. USA, 117, 2020). By contrast, for quadratic drag the scaling dependence of the core radius induces new scaling-laws for the eddy diffusivity and mixing length when the quadratic-drag coefficient becomes asymptotically low. We validate the modified scaling predictions through numerical simulations of the two-layer model with very low quadratic-drag coefficient.