Modeling the buoyancy-driven flow due to river discharge on the Texas-Louisiana continental shelf of the Gulf of Mexico

The buoyancy-driven flow due to river discharge from the Mississippi-Atchafalaya Rivers and the effect of wind forcing on the existing river plume over the Texas-Louisiana continental shelf are studied by using a three-dimensional, nonlinear primitive-equation ocean model. The model uses a horizontal curvilinear and a vertical terrain-following coordinate system to represent irregular coastal geometry and realistic bathymetry, respectively.; The first model experiment is forced by constant river fluxes from the Mississippi and Atchafalaya Rivers with homogeneous initial conditions. The model shows that freshened bulges are formed near the river mouths and a coastal current is developed along the coast toward the west. In the near field, the bottom current flows eastward, opposite to the surface current, indicating a first baroclinic mode structure. The model indicates that the bottom boundary layer is an important mechanism in adjusting the structure of the cross-shelf density front. The model also illustrates a significant interaction between the river plume and the Mississippi Canyon. An anticyclonic eddy associated with upwelling is found near the head of the canyon. The generation mechanism of this eddy is consistent with the theory of geostrophic adjustment.; In the second group of model experiments, four types of wind forcings are considered. The river plume is significantly altered by the surface wind stress, especially for the upcoast wind where a large amount of the plume water is moved across the shelf by the seaward surface Ekman transport and the coastal current also turns upcoast.; Finally, a short-term model prediction of the circulation on the Texas-Louisiana shelf during the summer of 1993 is made. The model is initialized by four hydrographic data sets and forced by hourly gridded winds and river fluxes during the summer of 1993. The model predicts that right-bounded coastal current completely vanishes during an upcoast wind period even though both rivers have extreme inflow such as the summer flood of 1993.