A model of the circulation on the outer Scotian Shelf with open boundary conditions inferred by data assimilation

The circulation on Western Bank. is described using data collected in sprin g 1991 and 1992 as part of an interdisciplinary study of the early life his tory of Atlantic cod (Gadus morhua). The mean circulation over the crest of the bank is weak, of the order of a few centimeters per second, and is fla nked to the south and west by an anticyclonic flow with a speed of about 10 cm s(-1). A thermal wind calculation shows the mean circulation is due pri marily to horizontal variations in the density field. The Mt tidal constitu ent is dominant and reaches speeds of about 20 cm s(-1). The tidal residual s have a standard deviation of about 10 cm s(-1) and characteristic time an d length scales of several days and tens of kilometers, respectively. In or der to help collect and interpret biological data from Western Bank, we dev eloped a hydrodynamic model of the near-surface flow that could be used ope rationally. The model is based on a decomposition of the flow into componen ts driven by (1) local wind stress, (2) horizontal density gradients, and ( 3) flows through the open boundaries of the model. The wind-driven componen t is calculated using a simple slab model driven by the observed wind. The other two components are estimated through the assimilation of observed bot tom pressures, dynamic heights, and currents into the hydrodynamic model. T he hindcast skill of the model is quantified by cross validation and shown to be higher than that of four simple, statistically based schemes.