Enhanced azimuthal rotation of the large-scale flow through stochastic cessations in turbulent rotating convection with large Rossby numbers

TL;DR

This study investigates how stochastic cessations influence the azimuthal rotation of large-scale flow in turbulent rotating convection at high Rossby numbers, revealing a constant rotation speed ratio and the mechanism behind enhanced retrograde flow.

Contribution

It introduces a low-dimensional stochastic model explaining the retrograde rotation of large-scale circulation influenced by cessations at large Rossby numbers.

Findings

Persistent retrograde rotation across all Rossby numbers studied

Constant rotation speed ratio of approximately 0.13 for 10<Ro<70

Enhanced rotation speed at Ro>70 due to stochastic cessations

Abstract

We present measurements of the azimuthal orientation {\theta}(t) and thermal amplitude {\delta}(t) of the large-scale circulation (LSC) of turbulent rotating convection within an unprecedented large Rossby number range 1<Ro<314. Results of {\theta}(t) reveal persistent rotation of the LSC flow in the retrograde direction over the entire Ro range. The rotation speed ratio remains a constant of 0.13(${\pm}$0.01) for 10<Ro<70, but starts to increase with increasing Ro when Ro>70. We identify the mechanism through which the mean retrograde rotation speed can be enhanced by stochastic cessations in the presence of weak Coriolis force, and show that a low-dimensional, stochastic model provides predictions of the observed large-scale flow dynamics and interprets its retrograde rotation.