A Data-Assimilative Numerical Model of the Northern Indian Ocean

Abstract

A primitive equation, three-dimensional, baroclinic circulation model has been configured for use in the North Indian Ocean. After having been spun up by climatological winds, the model was used to generate a hindcast for 1993?95 under synoptic forcing, both with and without assimilation of multichannel sea surface temperature (MCSST) and altimetric sea surface height (SSH) anomaly data. Without data constraints, the model captures many of the salient oceanographic features in this region including equatorial surface and subsurface currents, the Laccadive High Eddy, the Great Whirl, and the reversing Somali Current. However, assimilation of altimetric data enables it to depict these features more accurately. MCSST data enable the near-surface layers to be simulated more accurately. The National Aeronautics and Space Administration TOPEX precision altimeter has provided oceanographers with an important tool to study the variability in the circulation of the world?s oceans. The availability of SSH data from this altimeter provides a unique opportunity to assess the skill of a numerical model. More important, the assimilation of TOPEX altimetric observations, along with satellite-observed sea surface temperatures, greatly enhances the model?s ability to estimate the dynamical and thermodynamic state of the North Indian Ocean. The data-assimilative model provides therefore an additional tool for improving our understanding of the dynamical and thermodynamic processes in this region, through accurate hindcasts of the oceanic state. With the availability of real-time data streams, it also enables estimates of the oceanic state to be made in real-time nowcast/forecast mode.