Spatial velocity, temperature, and backscatter time series from the southern flank of Georges Bank in 1999

K. Smith and R. Schlitz

Seven tripod mounted acoustic doppler current profiler (ADCP's) were deployed across the southern flank of Georges Bank during the spring and summer of 1999. The ADCP tripods were accompanied by three thermistor strings with 3 meter spacing near the surface and 5 meter spacing in mid and deep water. The ADCP's were deployed in a line from (41 deg 10.2 min N, 67 Deg 18.5 min W) to (41 deg 2.8 min N, 67 Deg 14.0 min W), a range of 14.4 km horizontally from 55 meters of water to 68 meters of water. The ADCP's collected velocity and backscatter in 1 meter bins every fifteen minutes. Movies of the vertical slice captured by the instruments between 3/20/1999 and 6/8/1999 have been made to show the temporal and spatial structure of the area.

The first movie depicts the low-pass filtered velocity data from the seven ADCP's. The vertical and horizontal structure of the field is presented by contouring the along bank component of the data. The crossbank and vertical velocities are interpolated onto a regular grid with approximately 3 meter vertical bins and 600 meter horizontal spacing using bilinear interpolation. The interpolated velocities are represented by a quiver plot. in the foreground. Along bank jests, upwelling, downwelling and other sub- tidal phenomenon form and dissipate as the season progresses.

The second movie supplements the along bank velocity field with a contoured 300 KHz backscatter field. The backscatter data have been normalized to accentuate the horizontal gradients. The effects of storms are evident in the early spring where the top 10 meters of backscatter show a strong response to wave height and wind speed. There is a weaker and delayed storm response in deeper water. Later in the season smaller horizontally structured patches of backscatter appear and evolve.

The third movie is shorter and depicts the temperature data during the onset of stratification. The low-passed temperature data from the seven ADCP's, three thermistor strings, and three thermistors on surface markers are contoured. The stratified water appears suddenly during a period of weak along bank flow.