Eddy‐ and wind‐forced shelf circulation

Abstract

Cochrane and Kelly (1986) proposed a cyclonic gyre as the large‐scale mean circulation on the Louisiana‐Texas (LATEX) shelf, produced by a convergence of coastal currents in the west and a divergence in the east. While currents near the coast are presumably wind and buoyancy driven, the origin of the eastward flow on the outer shelf and shelf break, which forms the seaward limb of the gyre, as well as the near shore convergence and divergence, are not well understood. A numerical model is used to show that the western convergence and shelf break current are driven by collision and stalling of westward propagating Loop Current eddies in the northwest Gulf of Mexico and the divergence in the east is caused by shoreward intrusion in the Mississippi Canyon. The western convergence and shelf break current are modulated by the wind curl, strongest in summer and weakest in winter. On the shelf, westward transport is comparable to that observed (∼0.15 Sv, 1 Sv = 106 m3 s−1) only when the westward wind stress is significant (>0.3 dyn cm−1). A peak transport of 0.21 to 0.25 Sv occurs in autumn, of which 0.1 Sv is due to wind, 0.07 Sv is due to river buoyancy, and 0.04 to 0.08 Sv is due to eddies. Without the mean westward wind, buoyant waters from the Mississippi do not spread onto the LATEX shelf.