EDDY-FORCED AND WIND-FORCED SHELF CIRCULATION

Cochrane and Kelly (1986) proposed a cyclonic gyre as the large-scale mean circulation on the Louisiana-Texas (LATEX) shelf, produced by a c onvergence of coastal currents in the west and a divergence in the eas t. While currents near the coast are presumably wind and buoyancy driv en, 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 nearshore c onvergence and divergence, are not well understood. A numerical model is used to show that the western convergence and shelf break current a re driven by collision and stalling of westward propagating Loop Curre nt eddies in the northwest Gulf of Mexico and the divergence in the ea st is caused by shoreward intrusion in the Mississippi Canyon. The wes tern convergence and shelf break current are modulated by the wind cur l, strongest in summer and weakest in winter. On the shelf, westward t ransport is comparable to that observed (similar to 0.15 Sv, 1 Sv = 10 (6) m(3) s(-1)) only when the westward wind stress is significant (>0. 3 dyn cm(-2)). A peak transport of 0.21 to 0.25 Sv occurs in autumn, o f 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, buoya nt waters from the Mississippi do not spread onto the LATEX shelf.