The influence of subtropical forcing on the density structure of the tropical ocean

Three studies related to the flow of water within the ocean's ventilated thermocline have been carried out using a primitive equation general circulation model. In the first study, an ocean model of global domain was forced at the surface by climatological winds and temperatures. The flow within the ventilated thermocline of the model was investigated using a particle tracking method in which neutrally-buoyant Lagrangian particles were allowed to advect within the model velocity field. The trajectories of these particles show the pathways taken by water masses in the model after “subducting” from the mixed layer into the ventilated thermocline in the mid-latitudes. The results demonstrate that the varying background density structure and geometry of the different ocean basins alter these pathways and lead to distinct patterns of water mass exchange between the mid-latitudes and the equator in each basin.; In the second study, the surface forcing over the mid-latitude ocean was altered and the resulting changes in the thermocline ventilation and tropical/sub-tropical water mass exchange were investigated, with attention focused on how anomalies in extra-tropical forcing can alter the equatorial temperature structure. The experiments were performed over two model domains: (1) a global domain, in which a buoyancy anomaly was applied to the surface poleward of the 25° latitude circle to examine the sensitivity of the model's equatorial thermocline to mid-latitude surface temperatures; and (2) a Pacific basin domain, in which anomalies in both buoyancy and wind forcing were applied in separate experiments to investigate how the ensuing ocean anomalies propagate to the equator and their subsequent effect on the equatorial temperature structure.; In the third study, a numerical ocean simulation was performed in which the observed windstress and temperature fields at the ocean surface from the period between 1946 and 1998 were used to force an ocean model of the Pacific basin. The resulting data sets were analyzed to investigate changes in the equatorial density structure during the model run and the mechanisms through which extra-tropical thermocline anomalies generated by surface forcing reach the equatorial thermocline in the model.