Andreas Münchow, IMCS, Rutgers University, New Brunswick, NJ 08901

Alexander E. Yankovsky, GCMS, University of Delaware, Newark, DE 19716

Using a new three-dimension ADCP detiding algorithm, we present quasi-synoptic velocity and density fields during the onset of an episodic upwelling event in June/July of 1996. The data were collected during a 6-day 2-ship survey of the inner shelf north of Atlantic City, NJ. Both ships contained continuously profiling 1228 kHz ADCPs. The study area extends to the 35-m isobath in the across-shore and about 50-km in the along-shore directions. Semi-diurnal and diurnal tidal currents vary from less than 2 cm/s to more than 12 cm/s both in the vertical and horizontal directions. The detiding scheme extends two dimensional biharmonic spline interpolation techniques (Candela et al., 1992) to 3 spatial dimensions. Test and sensitivity studies using synthetic and historical data indicate that the method reduces tidal currents with an rms error of less than 4 cm/s anywhere within our study area (Münchow, 1998).

In the absence of winds the pycnocline intersects the bottom near the 15-m isobath as the buoyancy driven Hudson Coastal Currents passes through our study area. Within less than 3 days of strong upwelling favorable winds, the bottom density front develops into a surface density front that over time moves offshore. Inshore of this front thermal stratification is maintained by the offshore heat flux associated with the near bottom onshore advection of cold waters and a vertical heat flux into the surface by solar radiation. Intense fog formation takes place at the air-sea interface inshore of the front for the first 3-5 days of intense upwelling events. Offshore of the surface front we observe the development of an upwelling jet with vertical and lateral current shears that exceed 20 cm/s in 5-m and 5-km, respectively. It appears that the buoyancy of the Hudson Coastal Current adds to the intensity of the upwelling jet through enhanced lateral density gradients. The temporal amplitudes of a complex empirical orthogonal function (CEOF) analysis of mooring data suggest that this upwelling event is the most energetic during the summer of 1996 (Münchow and Chant, 1998).

Candela,J., R.C. Beardsley, and R. Limeburner, 1992: Separation of tidal and subtidal currents in ship-mounted acoustic Doppler current profilers. J. Phys. Res., 97, 769-788.

Münchow, A., 1998: Detiding three-dimensional velocity survey data in coastal waters. J. Atmos. Ocean. Tech., submitted.

Münchow, A. and R.J. Chant, 1998: Kinematics of inner shelf motions during the summer stratified season off New Jersey. J. Phys. Oceanogr., submitted.