Controlling supergranule aggregation in convection by weak rotation

Thermal convection in a periodic, horizontally extended layer of aspect ratio $\Gamma = 60$ that is driven by a constant heat flux is analysed by means of high-resolution spectral element simulations of three-dimensional turbulent Rayleigh-B\'enard convection. In this case, a process of gradual aggregation results -- independently of the varying Rayleigh number in a range from Ra $\sim 10^{4}$ to Ra $\sim 10^{7}$ at fixed Prandtl number Pr $= 1$ -- in a domain-filling convection cell.

Here we report the extension of this previous study by the inclusion of (weak) rotation around the vertical axis, limiting the gradual process effectively. Although global statistical measures are mostly unaffected, the final pattern size is governed by the strength of rotation which is characterized by Rossby numbers in the range $\infty \geq$ Ro $\geq 1$. Several series of simulations at different Ra indicate a linear scaling law of the final pattern size with Ro. This implies that pattern formation can be influenced already by weak rotation, similar to the behaviour at the onset of rotating, flux-driven convection.

Our studies might have interesting implications for atmospheric and stellar convection processes where heat fluxes are typically prescribed at the boundaries of the convection zone.