The T-S Gradient method, A new method of computing geostrophic currents over large ocean areas

Abstract

Requirements for indirect computation of geostrophic surface currents over large ocean areas are discussed. These requirements point to a need to simplify standard geostrophic computations, and to separate the first order thermal and haline contributions to geostrophic flow. The equations of motion for geostrophic flow are reviewed and the standard geostrophic computations discussed. Errors and limitations in the geostrophic method are reviewed. Previous attempts to simplify geostrophic computations are discussed and shown to be inadequate for synoptic computation over hemispheric ocean areas. It is shown that the Helland-Hansen equation can be rewritten such that the geostrophic velocity is composed of a temperature structure term and a salinity structure term. (Author)