Quarterdeck 3.2
Recent Graduate
As a research assistant on Dr. Vastano's Texas Flow Experiment (TEXFLEX) project, the basic question I sought to answer was "What is the cause-and-effect relationship between wind forcing and surface-water motion on small time scales, from 10 days to less than 24 hours?" Detailed descriptions of surface circulation along the Texas coast over these temporal and associated spatial scales and in connection with the wind are of critical importance to realistic computer modeling. Such depictions were not evident in the literature, however, so I set out to fill the void with my dissertation.
[9K] Meandering drifter trajectories recorded in the Gulf of Mexico from October 10 to December 29, 1992. The large circles mark locations southeast of Galveston Bay where the drifters were launched.
I launched fifteen satellite-tracked, surface-current, drifting buoys (drifters) and used the resultant trajectories in my research to investigate the pragmatic relationship between the wind and the water. I analyzed successively smaller segments of the drifter paths, hoping to find wind-related order in regions of ostensibly chaotic flow, employing a new analysis tool, the Wind-Superimposed-on-Trajectory (WST) plot.
[9K] A Wind-Superimposed-on-Trajectory plot shows the effect of wind velocity recorded at six-hour intervals on a drifter trajectory in November 1992.
The WST plot showed that wind was clearly a driving mechanism on the Texas Shelf, albeit with a great deal of interference from background advection in some areas. The plot also evinced direct coupling of wind with water motion in as little as three hours or less, even in trajectory segments that appeared straight on the large scale. In fact, Texas Shelf surface waters respond directly to the anticyclonic (clockwise) rotation of wind velocity associated with the regular west to east propagation of synoptic weather systems. The common progression of such systems is characterized by an atmospheric high-pressure situation preceded and followed by the transit of a low-pressure system, or cold front (frontal passage), during the nine months between September and May. The resultant drift is often opposite to that expected from monthly mean flow patterns. Therefore, successful surface-flow prediction on the Texas Shelf is to a considerable extent a function of foreseeable wind changes between frontal passages.
Where will that water be tomorrow? It may be exactly where it is today, by following a circular path under the right wind conditions. Such knowledge would be of great value to those concerned with oil spill containment or search and rescue operations at sea.
Oceanography, Texas A&M
University
rshatto@ocean.tamu.edu
URL=http://oceanography.tamu.edu/Quarterdeck/QD3.2/Shaar/shaar.html
Updated September 15, 1995
