Wind- and Eddy-Related Shelf/Slope Circulation Processes and Coastal Upwelling in the Northwestern Gulf of Mexico.
Walker, Nan. D.
Wind- and eddy-driven circulation on the Louisianan-Texas shelf and slope are investigated during 1993/94 by integrating measurements from satellite sensors (sea surface temperature, sea surface height) and in-situ measurements from satellite-tracked drifting buoys and mid-water current meters. Four distinct regimes were identified during autumn/winter including a down-coast jet on the Texas inner shelf, cross-shelf entrainment in the "Texas jet", seaward entrainment by slope eddies, and weak cyclonic circuation on the outer Louisiana shelf. The inner shelf coastal jet (20-98 cm s-1), driven by strong northeasterly winds, developed between the 10m and 30m isobaths along the main sea surface temperature front. Maximum current speeds were measured along the Texas coast between 29 degrees N and 26 degrees N. Although down-coast flow occured 80% of the time, current reverals of 1-3 days resulted from northwesterly winds during frontal passages. A high velocity cross-shelf jet (13-59 cm s-1) was identified at 28 degrees N, where anticyclone/cyclone eddy pairs entrained surface drifters onto the slope. During summer, up-coast currents resulted from the establishment of strong southerly wind stress over the south Texas shelf and southerly/southwesterly wind stress over the Louisiana shelf. A coastal upwelling region was identified from 23 degrees to 28 degrees N, characterized by cool waters (23-26 degrees C) within a 20 km wide coastal band. Although the 1994 summer upwelling season was abnormally intense and extended farther north than usual, measurements indicate that coastal upwelling and up-coast flow usually last four to six weeks in summer along the south Texas and north Mexican coast.