Short interval prediction of surface motion on the Texas continental shelf

A single layer, quasigeostrophic model is developed and applied to produce short interval predictions of surface motion on the Texas continental shelf. The simplicity of the model anticipates conditions under which its application would be appropriate: a rapid response to an oil spill with information on local conditions limited to remote sea-surface observations and available surface wind estimates and integrations needed for 4 days. A detailed development of the model is given from fundamental conservation equations through numerical implementation. The model is applied within a boundary-fitted orthogonal curvilinear coordinate system with realistic bottom topography. New numerical open boundary conditions are introduced and utilized. Several analytic tests verify the numerical implementation. Initial conditions are determined by fitting a velocity streamfunction to remote surface flow estimates subject to a constraint that the streamfunction remain zero on the landward boundary. Experiments from October 1992 and January 1993 provide data for model case studies, and several different simulations are examined for each case. Integrations of model parcel trajectories are compared against actual drifter observations. The model parcel trajectories closely resemble the observed trajectories over integrations of four days. Formulations are developed to account for time averaging in the initial conditions and for incorporating ageostrophic effects. The importance of realistic initialization data is examined. Model strengths and weaknesses are discussed, and important developments are identified.