OPEN-OCEAN BOUNDARY-CONDITIONS FROM INTERIOR DATA - LOCAL AND REMOTE FORCING OF MASSACHUSETTS-BAY

Massachusetts and Cape Cod Bays form a semienclosed coastal basin that opens onto the much larger Gulf of Maine, Subtidal circulation in the bay is driven by local winds and remotely driven flows from the gulf. The local-wind forced flow is estimated with a regional shallow water model driven by wind measurements, The model uses a gravity wave radi ation condition along the open-ocean boundary. Results compare reasona bly well with observed currents near the coast. In some offshore regio ns however, modeled flows are an order of magnitude less energetic tha n the data. Strong flows are observed even during periods of weak loca l wind forcing. Poor model-data comparisons are attributable, at least in part, to open-ocean boundary conditions that neglect the effects o f remote forcing. Velocity measurements from within Massachusetts Bay are used to estimate the remotely forced component of the flow, The da ta are combined with shallow water dynamics in an inverse-model formul ation that follows the theory of Bennett and McIntosh [1982], who cons idered tides. We extend their analysis to consider the subtidal respon se to transient forcing. The inverse model adjusts the a priori open-o cean boundary condition, thereby minimizing a combined measure of mode l-data misfit and boundary condition adjustment. A ''consistency crite rion'' determines the optimal trade-off between the two. The criterion is based on a measure of plausibility for the inverse solution. The ' 'consistent'' inverse solution reproduces 56% of the average squared v ariation in the data, The local-wind-driven flow alone accounts for ha lf of the model skill. The other half is attributable to remotely forc ed flows from the Gulf of Maine. The unexplained 44% comes from measur ement errors and model errors that are not accounted for in the analys is.