Laboratory experiments with a buoyancy forced circulation in a rotating basin

We consider the relative influence of buoyancy forcing and Coriolis effects on convection forced by a differential in heating at a horizontal surface in a rectangular basin. Laboratory experiments with water are reported for a rotating $f$-plane basin and a range of Ekman number $E=2\times10^{-7}-1\times10^{-5}$. Heating is applied over half of the base as a uniform flux and cooling applied over the other half as a uniform temperature, resulting in a flux Rayleigh number $Ra_F=O(10^{14})$ large enough to ensure turbulent convection, where $Ra_F$ defined in terms of domain length $L$. Compared to the non-rotating circulation where Nusselt number (a measure of the convective to conductive heat transfer) scales as $Nu\sim Ra_F^{1/6}$, the strongly rotating regime is determined by a geostrophic balance of the larger scales of horizontal flow in the inviscid thermal boundary with $Nu\sim Ro^{1/6}$, where $Ro=B^{1/2}/(f^{3/2}L)$ is the natural Rossby number ($B$ is buoyancy flux per unit area and $f$ is Coriolis parameter). We also find evidence for a further transition into a regime where the circulation is dominated by deep `chimney' convection in a field of small vortical plumes and $Nu$ is more weakly dependent on rotation.