A dynamical analysis of currents near the New Jersey Coast

Abstract

A numerical model is used to analyze currents measured on the continental shelf near the shore of New Jersey. The model neglects longshore variations of current and all variations of density, but includes inertial accelerations and a nonlinear eddy viscosity. Local wind stress, sea level changes, and a constant longshore pressure gradient are the forcing terms. The model successfully reproduces most of the current variance; however, the predicted currents do not exhibit the dominant 4‐hour response time of the observed currents, and the model sometimes misses energetic current events. These differences are ascribed to three‐dimensional setup effects elsewhere in the New York Bight.

Circulation in the Coastal Ocean

“…One of the most revealing pieces of evidence on longshore pressure gradients is the asymmetric response of the Mid-Atlantic Bight to northeasterly versus southwesterly wind stress. This was documented clearly by Beardsley and Butman (1974) and was confirmed also by studies of Scott and Csanady (1976) and Bennett and Magnell (1979). Figure 8.2 above showed the isobars, i.e., approximately the wind stress field, of two storms producing respectively northeastward and southwestward longshore stress within the period of the coastal circulation study of Beardsley and Butman (1974).…”

“…Some evidence in support of this proposition comes from nearshore studies in different locations, arriving at different magnitudes of the longshore pressure gradient (e.g., Bennett and Magnell, 1979). The details of these trapped cells have not been elucidated so far, however, not at any rate in connection with a longterm mean circulation pattern.…”

“…This has been reported on a number of occasions, on the inner shelf for example by Scott and Csanady (1976) or Bennett and Magnell (1979), on the outer shelf by Beardsley and Butman (1974), , or Boicourt and Hacker (1976). Figure 8.15, from Pettigrew {1981), shows the association of longshore wind stress and depth-average velocity at 3, 6, and 12 km from shore off Long Island.…”

“…Such a linearized drag law appears to give good results in describing the mean circulation component in the Mid-Atlantic Bight, as well as frictional equilibrium storm currents in the same location, or hurricane driven currents in the Gulf of Mexico (Scott and Csanady, 1976;Bennett and Magnell, 1979;Forristal eta/., 1977). The appropriate value of r in all the quoted cases was empirically found to be of the order of 10-3 m s -1 • Such a value of r may be interpreted physically as an average bottom velocity magnitude of order 0.3 m s-1 , times a drag coefficient ca close to 3 X 10-3 •…”

Coastal Sedimentary Environments

“…Distinct features of currents have been identified over a wide range of spatial scales and frequencies. Papers reporting observations of coastal ocean currents and density fields have been published by Blanton and Murthy (1974), Scott and Csanady (1976), Bennett and Magnell (1979), Wiseman andRouse (1980), andSchwing et al (1983). The dynamics of the coastal boundary layer have been discussed by Csanady (1972Csanady ( , 1977Csanady ( a,b, 1978a, and Allen (1980).…”