A numerical study on convergence of alongshore flows over the Texas-Louisiana shelf

A hydrodynamic model is used to investigate convergent alongshore flows over the Texas-Louisiana shelf, characterized by down-coast flows over the northern shelf encountering up-coast flows over the southern shelf. The model's ability to reproduce realistic current, salinity, and surface elevation fields is demonstrated through positive model skill scores when comparing model simulations to observational data. The convergent flows are explored on both weather band and seasonal time scales. For weather band scales, this study focuses on wintertime convergent events. The model-predicted locations of convergent flows are supported by current measurements. We find that the formation of convergent flows is primarily caused by along-coast variation in the alongshore component of wind forcing, which in turn is due to the curvature of the Texas-Louisiana coastline. In general, the alongshore currents are well correlated with alongshore winds. However, the convergence points of currents and winds are not colocated, but rather, convergence points in ocean currents typically occur down coast of convergence points in the wind. This offset is demonstrated to be mainly caused by buoyancy forcing that can drive the convergence location in the currents farther down coast. No specific temporal pattern is found for the weather band convergence locations, whereas at seasonal time scales, the monthly mean convergence exhibits a prominent seasonal pattern, with up-coast migration of convergence locations in spring and summer and down-coast migration in fall and winter.