Low-frequency circulation on the Texas-Louisiana continental shelf


  • J. D. Cochrane,

  • F. J. Kelly


For the Texas-Louisiana coast west of 92.5°W, long series of data from near Freeport, Texas, together with shorter series from other locations, show strong response of coastal current to wind stress in agreement with coastal jet concepts. We infer from coastal winds, scattered current measurements, and distributions of sea-surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation. The inshore limb of the gyre is the coastal jet driven by wind with a west or southward (downcoast) component which prevails along much of the coast except in July-August. Because the coast is concave, the shoreward prevailing wind results in a convergence of coastal currents, which marks the downcoast extent of the gyre. Corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre. A prevailing countercurrent (north or eastward flow) along the shelf break includes the outer limb of the gyre. The eastern, shoreward-flowing limb of the gyre corresponds to divergence along the coast centered near 92.5°W. The convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind, reaching south of the Rio Grande mouth in fall and the Cameron offing in July. The gyre is normally absent in July, but reappears in August-September when a downcoast wind component develops.