A multi-model nesting approach for simulating deep ocean dynamics and topographic interactions

This paper describes a nesting approach for ocean models that is useful when the numerical model for the inner nest differs from the that used for the outer model. The typical use of nested grids in ocean modeling is to refine the horizontal resolution in a certain region, and often the same numerical model is employed for the outer and inner nests. In the application described here, a refinement of the vertical as well as the horizontal resolution is desired, and the structure of the vertical grid for the inner nest is necessarily different than that used in the outer model. In particular, this study is focused on simulation of bottom-intensified small-scale intense currents traveling along the Sigsbee Escarpment, a steep topographic feature found between roughly 1500-3000m depth in the northern Gulf of Mexico. The HYbrid Coordinate Ocean Model (HYCOM) is used to simulate large-scale upper ocean circulation features in the Gulf of Mexico, and a very-high resolution nest is applied using the Navy Coastal Ocean Model (NCOM) with a new quasi-vanishing sigma vertical coordinate over the Sigsbee Escarpment region.