Variational Estimation of the Wind Stress Drag Coefficient and the Oceanic Eddy Viscosity Profile

Abstract

A variational optimal control technique is used to assimilate both meteorological and oceanographic observations into an oceanic Ekman layer model. An identical twin experiment is discussed first in which the ?observations? are created by the dynamic model. The field measurements from the LOTUS-3 (Long-Term Upper Ocean Study-3) buoy are then analysed. By fitting the model results to the data, the unknown boundary condition (the wind stress drag coefficient) and the unknown vertical eddy viscosity distribution are deduced simultaneously from the data, and an optimal estimate of the current field is obtained. Though the model is simple, the results show that the variational assimilation technique is capable of extracting from the available observations a reasonable wind stress drag coefficient and vertical eddy viscosity distribution.