Direct numerical simulation of deep-ocean convection in a rotating stratified fluid.

Deep-ocean convection is observed at high latitudes and occurs under the influence of intense surface cooling. DNS are performed to understand the small-scale turbulent processes in a scaled-down configuration while keeping the Rossby number relevant to the realistic ocean convection. The effect of the Earth's rotation on the convection process is studied by varying the Rossby number Ro=B₀^1/2/(Hf)^3/2, where H is the depth, f is the Coriolis parameter, and B₀ is the magnitude of surface buoyancy flux. The initial evolution of the flow is governed solely by the B₀ and thermal diffusivity κ_t. At a later time t>100(κ_t/B₀)^1/2, the flow becomes turbulent and the plumes lose their coherence. When time t>2π/f, rotational effects become prominent thereby stabilizing the flow due to the diminished conversion of potential to kinetic energy. At moderate to low rotation rates(Ro>0.1), the turbulent fluid spreads as gravity current along the bottom surface. However, at high rotation rates(Ro<0.1), the flow reaches a quasi-steady state. Due to the complex nature of the flow physics and multiple controlling parameters, it has been found that a simple parametric scaling for length and velocity scales cannot be proposed, in contrast to the findings from some of the previous studies.