Dynamics and heat transfer in rotating horizontal convection at large Rayleigh number

We examine the circulation forced by a gradient in surface temperature, known as horizontal convection, in a rectangular basin under planetary rotation. Direct numerical simulations are carried out to examine the problem in a closed rectangular basin that is heated over half of the base and cooled over the other half. Three Rayleigh numbers are considered, Ra = 7.4 ×10⁸, 7.4 ×10¹¹ and 7.4 ×10¹², and Coriolis parameter is varied to give Ekman numbers in the range E = 6.4×10⁻⁸ −1.6×10⁻⁵. Other governing parameters are the Prandtl number Pr = 5 and vertical-to-length and horizontal-to-length aspect ratios, A = 0.16 and C = 0.24 respectively. The influence of rotation on flow dynamics and heat transfer depends on the natural Rossby number Ro = U/fL = (E/Pr)(RaE)^2/3 where U is the flow velocity in the thermal boundary layer that forms adjacent to the forced surface and f is the Coriolis parameter. When the system is in a rapidly rotation regime (Ro < 0.1) the flow is characterised by geostrophic balance in the thermal boundary layer. The heat transfer, expressed as a Nusselt number, decreases with rotation but increases with buoyancy forcing as Nu ~ (RaE)^1/3. A range of length scales are present in the rotating system that are associated with structures such as domain-scale gyres and full-depth convective vortices.