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 convective 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-conditioned by rotating a false bottom in the tank, thus generating a cyclonic or anticyclonic initial circulation in the tank as desired. Following the initiation of the buoyancy flux, a mixed layer forms above the buoyancy source and erodes the overlying thermal stratification. Initially confined by rotation, the growth of the mixed layer depth with time is described by a one-dimensional deepening law. The front separating the heated convecting fluid from the stratified, quiescent ambient fluid eventually becomes unstable, generating a field of baroclinic eddies. The rate of deepening of the mixed layer slows as the eddy field develops and transports both buoyant fluid from above the source region horizontally into the unheated sections of the tank and ambient fluid horizontally into the source region. Ventilation of the deep and relatively unstratified water beyond the thermocline is thus most likely to occur if the thermocline is penetrated before the eddy field becomes fully developed.