Modeling the Response of an Idealized Coastal Ocean to a Traveling Storm and to Flow over Bottom Topography

Abstract

To validate a three-dimensional hydrodynamic model for use in coastal waters, two test cases with idealized geometry and forcing functions were performed. The tests involve the barotropic and baroclinic response of a coastal ocean with a uniform alongshore shelf to the passage of a storm and the circulation induced by flow over a topographic feature. The model used in this study is the estuarine, coastal, and ocean model developed by Blumberg and Mellor. The model is three dimensional and solves for three components of the current field, temperature, and salinity. The model has a terrain-following sigma (σ) coordinate system, a coastal-following curvilinear grid in the horizontal, and an embedded second-order turbulence closure submodel to provide vertical mixing coefficients and uses the free surface as a prognostic variable. At the open boundaries, a flow relaxation scheme (FRS) has been implemented to pass out internally generated disturbances with minimum reflection. The results from the first test case demonstrate that the model successfully reproduces the expected theoretical response to a traveling storm. Both standing and propagating shelf waves with the proper spatial structure are found. In the upper part of the ocean, wind-generated oscillations are the dominant response. In the second test case, a stationary anticyclone forms over the topographic feature and a cyclonic eddy is shed downstream in a time of the order of the advective timescale, in agreement with theory and previous studies. When investigating the long-term evolution, the model simulations reproduce the baroclinic instability mechanisms expected from analytical considerations.