A MODEL OF THE THERMAL BAR CIRCULATION IN A LONE BASIN

A thermal bar is defined here as a zone of descending water at or near the fresh water temperature of maximum density. In the present study, we model physical properties such as velocity, temperature, turbulent fluxes, time of onset, and migration speed of the thermal bar in an i dealized basin. Unlike models using prescribed eddy viscosity and diff usivity coefficients: our model uses a second-order turbulence closure scheme to model mixing due to turbulence. The only inputs in the calc ulation are the surface wind, the surface heat flux, and the initial s tate of the fluid. Numerical simulations of the resulting circulation are presented for flow in a long rotating basin under prescribed surfa ce heat and wind conditions. The results show the influence of the rel ative magnitudes of mechanical and thermal forcing on the circulation. A comparison with field observations shows reasonable agreement betwe en computed and measured bar migration speeds. The time necessary for the formation of the bar is computed, and is found to depend on the su rface forcing.