Rotating horizontal convection in a rectangular box

Abstract

We examine the effect of rotation on horizontal convection using laboratory experiments in a rectangular box domain. Horizontal convection is a basic model for the meridional overturning circulation (MOC) in the ocean; we also expect the MOC is influenced by the Earth's rotation. The Rayleigh number is two orders of magnitude larger than any previous study (Ra ~ 1012) to ensure the flow lies in a regime with a turbulent boundary layer and endwall plume (to better match realistic ocean conditions). Other governing parameters are the Prandtl number Pr ~ 5, aspect ratios AH = 0.16 and AW = 0.24, and Rossby number Ro ~ 0.001-0.1. Particle tracking velocimetry is used to measure horizontal velocity fields at three interior depths, away from the boundary layer that forms adjacent to the thermal forcing. With increasing rotation, the steady state time-averaged flow dynamics changes from a full length cyclonic gyre, to a series of five counter-rotating baroclinic eddies (at non-dimensional Rossby deformation scale of O(1)) and then to a large anticyclonic gyre. The large scale horizontal flow dynamics are largely independent of depth. The divergence and vorticity of the horizontal velocity fields are used to estimate the overturning, which consistently decreases with increases in rotation. Direct Numerical Simulations are ongoing, and will allow access to the energetics of this complicated system.