Data Assimilation in a Simple Tropical Ocean Model with Wind Stress Errors

Abstract

A major error source in the numerical simulation of tropical oceans is the uncertainty in wind stress forcing. A reduced-gravity shallow-water model has been used to test how assimilated ocean data correct simulation errors caused by erroneous wind stress in the tropics. The geometry of the basin is rectangular and symmetric about the equator, and the long-wave approximation is applied. All experiments are of the identical-twin type: the ?observations? are generated by sampling the desired reference solution, and the data are assimilated by optimal interpolation into the same model, with wind stress forcing different from that in the reference case. In this paper, three types of wind stress errors are considered: errors of timing only, as well as persistent errors, systematic or stochastic. The relative usefulness of thermocline depth and current observations, and the effect of data distribution on state estimation are examined. The role of equatorial ocean waves in the process of data assimilation is also studied.