Hans C. Graber, Lynn "Nick" K. Shay, Brian K. Haus
Office of Naval Research, Coastal Dynamics and Remote Sensing Programs
The overall scientific goal of this study is to understand the dynamics and temporal and spatial variability of the circulation over the inner to mid-shelf region and to examine which mechanisms and interactions are responsible for observed surface flow features. A better understanding of the shelf circulation and its scales of variability is critical to improve the fundamental understanding of larval dispersal (and settlement) rates and the ocean and sediment dynamics.
(2) To determine the plausible mechanisms and interactions which drive the circulation over the inner and mid shelf.
(3) To evaluate the alongshore variability of the cross-shelf transport.
(4) To investigate the ocean current response of the inner-shelf waters to wind and wave effects, including the transfer of wave momentum to the mean flow.
(5) To resolve the surface and subsurface internal wave response (from f to the Nyquist frequency of 1.5 cph) over the shelf region including barotropic and baroclinic tidal effects.
During DUCK94, a dual frequency HF (25.4 MHz) Doppler radar was deployed to map the surface current vectors in "near real" time and at high spatial and temporal resolution over a wide region in shallow coastal waters from two shore-based sites. To map the surface vector currents over a 700 km2 area the RSMAS Ocean Surface Current Radar (OSCR) system was deployed along the shoreline near the U.S. Army Corps of Engineers Field Research Facility (FRF) during the month of October 1994. The OSCR system consists of two stations that transmit and receive radar signals. The two stations were separated by a distance of about 27 km with a range of about 45 km with a spatial resolution of 1 km. Maps of surface vector currents were collected every 20 minutes.
Our goal is to use these high resolution and accurate surface current vectors to perform a combined analyses of this data set with subsurface point measurements to determine more precisely which mechanisms drive the ocean circulation over the continental shelf. Our analyses will determine estimates of the contributions to the observed shelf flow due to internal wave dynamics, wind-driven currents, tidally forced motions and the effect of the surface gravity wave field. Specifically, we will proceed as follows:
(2) characterize the time-space scales of the surface features between the inner and mid shelf and Gulf Stream by decomposing the observed currents into a mean, tidal, and internal wave flow structures;
(3) estimate cross-shelf transport of heat and momemtum associated with the surface and subsurface currents by estimating the divergence of the Reynolds stress as well as the cross-shelf advection of heat and salt from the mooring data;
(4) resolve the surface and subsurface internal wave signatures (from f to the Nyquist frequency of 1.5 cph) by combining surface current observations from the OSCR with CoOP and directional discus subsurface current meter mooring data; and
(5) quantify the influence of surface waves on momentum transfer from the winds to mean flows.
(2) Post-processing, quality control and internal consistency checks completed for entire data set.
(3) Full tidal analysis for each grid cell completed.
(4) Identified and classified numerous interesting flow patterns such as coastal intensifications (buoyant coastal jets), storm-induced and tidally-forced currents. Figure 1 shows an example of the surface current field observed by OSCR on 12 October 1994, 08:00 UTC with the presence of a coastal jet.
For a list of addresses of the investigators involved in Duck 94 click here.