EFFECT OF WAVE-ENHANCED BOTTOM FRICTION ON STORM-DRIVEN CIRCULATION IN MASSACHUSETTS BAY

Massachusetts Bay is a shallow (35 m average depth) semienclosed embay ment, roughly 100 X 50 km, which opens into the Gulf of Maine at its e astern boundary. Surface waves associated with winter storm winds from the northeast cause large sediment resuspension events, and wave and circulation fields during these events have a quasi-steady response to the wind stress. Coupled wave, circulation, and boundary layer models indicate that wave-enhanced bottom friction has a significant damping effect on storm-driven circulation in Massachusetts Bay. The simulate d response exhibits significant three-dimensional structure, but still can be fundamentally understood using idealized models. The depth-int egrated momentum balance is dominated by along-bay stress, pressure gr adient, and bottom stress. The effective bottom drag coefficient durin g typical storm conditions is increased by a factor of 2-5 when wave e ffects are included, but the mean bottom stress is relatively unaffect ed by wave effects due to a reduction in bottom currents by 30-50%. Th e vertical mixing is also relatively unaffected by the waves, and the result is that the increased drag causes a nearly depth-independent of fset of the vertical current profiles. The alongshore transport in the bay is reduced 10-50%, depending on wind direction.