The Three?Dimensional Structure of Wind?Driven Gyres: Ventilation and Subduction
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Theories of the three-dimensional structure of wind-driven gyres have been developed during the past decade. Potential vorticity homogenization of the unventilated thermocline and potential vorticity conservation of the ventilated thermocline have been proposed and tested against observations and numerical experiments. Models with continuous stratification, including a mixed layer of horizontally varying density and depth, have also been formulated; they reproduce a three-dimensional structure of the wind-driven circulation in the upper ocean. These theories have been extended in different directions. First, buoyancy forcing is included in the models by parameterizing it in terms of interfacial mass flux. Second, the connection with the western boundary current, the recirculations, the equatorial undercurrents, and the cross-gyre communication have been further studied. Tracer studies have provided new information about ventilation processes in the oceans.