Bottom Topogrpaphy As A Control Parameter In An Ocean Circulation Model

Bottom topography is a major factor in determining the general circulation of the ocean. It is, however, inaccurately known in many regions, and even where accurately known, the best way to represent it in models is obscure. To begin to understand the influence of errors in bottom topography and of misrepresentations of both resolved and sub-grid scale structures, a linear barotropic shallow water model and its adjoint are developed in which depth is used as a control variable. Simple basin geometries are employed to explore the extent to which topographic structure determines the sea- surface elevation in a steady flow and, more directly, the information content about the bottom contained in elevation measurements. Experiments show that even perfect measurements of sea-surface elevation in a steady state cannot, by itself, uniquely determine the full structure of the bottom topography, but that as in most control prob- lems, a priori knowledge of its structure is necessary. The resolution of the bottom topography as a function of position is greatest where the flow velocities are greatest. The spatial correlation between the resolution of the bottom topography and the flow field is weaker when noise with realistically large variance is introduced into the data. Ultimately, bottom topography will likely be included generally as a control variable in GCMs of arbitrary complexity.