On the theory of deep flow in the Hudson Shelf Valley

Abstract

The time averaged near‐bottom current in the New York Bight for a selected 3‐day period is idealized as a steady state response to the mean wind at the John F. Kennedy International Airport and the mean inflow condition across the Long Island shelf. The idealization invokes potential vorticity conservation in a homogeneous ocean subject to a linear bottom friction and results in shelf currents whose longshore components are in general agreement with the averages of the observed. In the Hudson Shelf Valley, qualitative agreement with the observation is achieved in the onshore component which is directed nearly along the valley axis. Nearshore, within 40 km or so of the coast, the response is, to a substantial degree, wind driven. Nearshore upvalley mean flow is due partly to shore‐parallel wind stresses that are directed away from the valley and is due partly to topographic deflection of an alongshore current that is driven in part by the inflow condition and in part by the alongshore component of the mean wind stress. Because of the important role of bottom friction, an alongshore current driven by longshore winds undergoes sharper (and more realistic) deflection across the valley than does an alongshore current driven by the inflow condition.