Inverse cascade in zonal flows

TL;DR

This study investigates whether inverse energy cascades, known in 2D systems, also occur in 3D deep convection systems relevant to Jovian planet atmospheres, using high-resolution simulations.

Contribution

It demonstrates the existence of inverse cascades in 3D rotating convection, driven by buoyancy, which was previously uncertain.

Findings

Inverse cascade observed in 3D convection simulations.

Strong mean flows emerge from turbulent chaos.

Buoyancy acts as a natural forcing mechanism.

Abstract

Zonal winds on Jovian planets play an important role in governing the cloud dynamics, transport of momentum, scalars, and weather patterns. Therefore, it is crucial to understand the evolution of the zonal flows and their sustainability. Based on studies in two-dimensional (2D) $\beta$ plane setups, zonal flow is believed to be forced at the intermediate scale via baroclinic instabilities, and the inverse cascade leads to the transfer of energy to large scales. However, whether such a process exists in three-dimensional (3D) deep convection systems remains an open and challenging question. To explore a possible answer, we perform Large Eddy Simulations at the geophysically interesting regime of $Ra=$$10^{12}$, $Ek=$$10^{-6}$,$10^{-7}$ and $10^{-8}$ in horizontally rotating Rayleigh-B\'enard convection setup and discover the existence of natural forcing through buoyancy and inverse cascade. The turbulent kinetic energy budget analysis and the spectral space assessment of the results corroborate the emanation of a strong mean flow from chaos.