Generation of zonal flows in convective systems by travelling thermal waves

TL;DR

This study investigates how travelling thermal waves induce zonal flows in convective systems across different regimes, revealing the underlying mechanisms and validating results through numerical simulations relevant to geophysical and astrophysical contexts.

Contribution

It demonstrates the generation of zonal flows by travelling thermal waves in convective systems and clarifies the driving mechanisms in different regimes, supported by numerical and theoretical analysis.

Findings

Travelling thermal waves induce strong zonal flows.

Reynolds stresses drive retrograde flows in diffusion regimes.

Mean flow advection dominates in convection regimes, leading to prograde flows.

Abstract

This work addresses the effect of travelling thermal waves applied at the fluid layer surface, on the formation of global flow structures in 2D and 3D convective systems. For a broad range of Rayleigh numbers ($10^3\leq Ra \leq 10^7$) and thermal wave frequencies ($10^{-4}\leq \Omega \leq 10^{0}$), we investigate flows with and without imposed mean temperature gradients. Our results confirm that the travelling thermal waves can cause zonal flows, i.e. strong mean horizontal flows. We show that the zonal flows in diffusion dominated regimes are driven purely by the Reynolds stresses, always travelling retrograde, while in convection dominated regimes, mean flow advection, caused by tilted convection cells, becomes dominant, which generally leads to prograde mean zonal flows. By means of direct numerical simulations we validate theoretical predictions made for the diffusion dominated regime. Furthermore, we make use of the linear stability analysis and explain the existence of the tilted convection cell mode. Our extensive 3D simulations support the results for 2D flows and thus confirm the relevance of the findings for geopyhsical and astrophysical systems.