Modeling the Mechanisms for the Formation and Maintenance of the Weddell Polynya

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This proposed work concerns the development and application of a regional coupled general circulation model for the purpose of elucidating the mechanisms that initiate, maintain, and terminate the Weddell Polynya - a large area of open water within the winter sea ice cover of the Weddell Sea. This polynya was prominently seen in satellite-based passive microwave imagery, and at it height, from 1974 to 1976, exceeded 250,000 square kilometers in size.The fully linked model that will be used in this study is composed of an atmospheric planetary boundary layer model, a sea ice model that includes the effects of a snow cover, and a three dimensional ocean general circulation model. A flux coupler connects the three models by passing the relevant fluxes of energy, mass, and momentum among them. The fine-scale features of the polynya will be modeled on a high resolution version of the models that will be nested within the lower resolution grid of their large-scale domain versions.The basic initiating mechanism of the Weddell Polynya is thought to be the surfacing of Warm Deep Water (WDW) which is entrained into the Weddell Sea from its origins within the Antarctic Circumpolar Current. Normally this warm water (which is warm only by antarctic standards: its temperature is between 0 and +1 deg Centigrade) is kept below depth of about 300 meters by a colder but less saline (hence lighter) surface layer of Weddell Winter Water. Occasionally, it is speculated, this condition breaks down; the atmosphere/ocean dynamics remove the cold surface layer and allow the WDW not only to melt the existing ice, but keep new ice from forming. Eventually the WDW heat reservoir is exhausted and a cold surface layer is reestablished. The expected results of this study are a quantitative determination not only of the characteristic time evolution of the polynya, but also its characteristic recurrence interval, spatial scale, and its connection to the bottom topography of the Weddell Sea. It is a regional climatic event that has global consequences by affecting the formation and distribution rate of deep and bottom water thought the world ocean.