David Marshall

Abstract:

For a parcel of fluid in the mixed layer to pass into the stratified thermocline - to subduct - it must be stratified by buoyancy input; this buoyancy can be supplied by local air-sea exchange and/or by lateral advective processes. A series of experiments is described in which a mixed layer, coupled to an ideal-fluid thermocline, undergoes differing seasonal cycles. The authors conclude that in ocean models that do not explicitly represent a seasonal cycle it is necessary to parameterize the process through a prescription of the winter mixed layer density and depth. The buoyancy forcing diagnosed from such models must be interpreted as the combined contribution of the annual air-sea exchange and lateral advective processes in the summer Ekman layer. -from Authors

Abstract:

The model developed by Pedlosky and Young is used to investigate the feedback of a Rhines-Young pool on a ventilated thermocline. It is found that the potential vorticity gradient in a ventilated layer is reduced due to the nonlinear coupling with a deep Rhines-Young pool. Physically, this occurs because part of the Sverdrup transport is carried by the deep pool. As a result, the subduction velocity, and in turn, the potential vorticity gradient of the subducted water, is decreased. -Authors