On the Summer Circulation in New York Bight and Contiguous Estuarine Waters

The summer average circulation in the New York Bight, Long Island Sound and New York Harbor complex is investigated using a three-dimensional hydrodynamic circulation model. Unlike previous studies that have only concentrated on decoupled parts of the system, the present study emphasizes the importance of the coupling between them. Here the mean summer circulation is determined by mean temperature and salinity fields prescribed from climatological data. In addition, the model is forced by free surface elevation gradients along the northeastern and southwestern cross-shelf open boundaries; the elevation along the shelf-break is set to zero. The mean climatological summer wind stress is also imposed. A sensitivity study was conducted for the circulation and the hydrodynamic structure of the bight as functions of the mean wind and the cross-shelf elevation gradients. All the conclusions are based on simulations during which the whole system has spun up and reached a steady-state (after two days), wherein the total flows through the northeast and southwest cross-shelf open boundaries were approximately equal. Without winds and density structure, the circulation is a consequence of conservation of potential vorticity and follows f/H isopleths. When the density field is imposed, the circulation changes markedly. Clearly evident in the surface currents is the Hudson plume emanating out of New York Harbor. The plume makes an anticyclonic turn as it flows out of the harbor onto the continental shelf and forms a small eddy of size of the baroclinic Rossby radius of deformation. The near-bottom flow is onshore along the Hudson Canyon. This circulation is extremely sensitive to the wind. The southwesterly winds reverse the flow close to the New Jersey shore northeastward and lead to a significant intensification of the fresh water eddy structure. The water column in the Long Island Sound is strongly stratified and the classical, two-layer estuarine circulation pattern prevails. However, this pattern is also sensitive to the winds. Even moderate winds can change the magnitude and direction of the total transport through the East River. An analysis of the model results using mean summer forcing functions shows a total transport of approximately 160 m3/s from Long Island Sound to New York Harbor.