Connecting wall modes and boundary zonal flows in rotating Rayleigh--B\'enard convection

TL;DR

This study uses direct numerical simulations to connect wall modes and boundary zonal flows in rotating Rayleigh-Bénard convection, revealing their roles in heat transport across different regimes relevant to geophysical and astrophysical systems.

Contribution

It establishes a quantitative link between linear wall modes and boundary zonal flows, enhancing understanding of heat transport in the geostrophic regime of rotating convection.

Findings

Wall modes precede bulk convection onset.

Boundary zonal flows coexist with turbulence.

Heat transport contributions are characterized across regimes.

Abstract

Using direct numerical simulations, we study rotating Rayleigh-B\'enard convection in a cylindrical cell for a broad range of Rayleigh, Ekman, and Prandtl numbers from the onset of wall modes to the geostrophic regime, an extremely important one in geophysical and astrophysical contexts. We connect linear wall-mode states that occur prior to the onset of bulk convection with the boundary zonal flow that coexists with turbulent bulk convection in the geostrophic regime through the continuity of length and time scales and of convective heat transport. We quantitatively collapse drift frequency, boundary length, and heat transport data from numerous sources over many orders of magnitude in Rayleigh and Ekman numbers. Elucidating the heat transport contributions of wall modes and of the boundary zonal flow are critical for characterizing the properties of the geostrophic regime of rotating convection in finite, physical containers and is crucial for connecting the geostrophic regime of laboratory convection with geophysical and astrophysical systems.