CONVECTIVELY DRIVEN MIXED-LAYER GROWTH IN A ROTATING, STRATIFIED FLUID

A laboratory experiment has been conducted to examine deep convective processes in a stratified ocean. For convenience, cooling at the ocean surface is modelled in the laboratory by heating from below. A convec tive mixed layer was generated by heating over the central portion of the base of a rotating, thermally stratified fluid. In addition to the convective forcing, the initial stratification could also be pre-cond itioned by rotating a false bottom in the tank, thus generating a cycl onic or anticyclonic initial circulation in the tank as desired. Follo wing the initiation of the buoyancy flux, a mixed layer forms above th e buoyancy source and erodes the overlying thermal stratification. Ini tially confined by rotation, the growth of the mixed layer depth with time is described by a one-dimensional deepening law. The front separa ting the heated convecting fluid from the stratified, quiescent ambien t fluid eventually becomes unstable, generating a held of baroclinic e ddies. The rate of deepening of the mixed layer slows as the eddy fiel d develops and transports both buoyant fluid from above the source reg ion horizontally into the unheated sections of the tank and ambient fl uid horizontally into the source region. Ventilation of the deep and r elatively unstratified water beyond the thermocline is thus most likel y to occur if the thermocline is penetrated before the eddy field beco mes fully developed.