A modeling study of summer ocean circulation on the inner shelf south of Cape Cod, Massachusetts, has been conducted. The influences of winds, air-sea heat fluxes, tides, and shelfwide circulation are all incorporated. The model reproduces recognized features of the regional summer circulation: warm temperatures and weak eastward flow in Nantucket Sound, cool tidally mixed waters and an associated anticyclonic flow encircling the Nantucket Shoals, and strong stratification south of Martha's Vineyard. Comparisons with satellite and in situ observations show the model simulates the major features of the temperature patterns that develop during summer 2002. The evolution of the summer heat budget is characterized by three regimes: Nantucket Sound heats rapidly in June and then maintains warm temperatures with little net air-sea heat flux; tidal mixing on the Nantucket Shoals maintains perpetually cool ocean temperatures despite significant air-sea heating; and midshelf south of Martha's Vineyard the surface waters warm steadily through July and August because of sustained air-sea heating with only modest cooling resulting from the mean circulation. In the environs of the Martha's Vineyard Coastal Observatory tidal eddy heat flux emanating from Nantucket Sound produces a bowl of warm water trapped against the coast and significant local variability in the net role of advection in the heat budget. A suite of idealized simulations with forcing dynamics restricted, in turn, to only one of winds, tides, or shelfwide inflows shows that tidal dynamics dominate the regional circulation.
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