Large scale circulation in the Bellingshausen and Amundsen seas as a variational inverse of climatological Data

Abstract

Atmospheric and oceanic climatological data are combined with the World Ocean Circulation Experiment S4 section hydrology in the framework of a variational data assimilation scheme into a steady state nonlinear model of the large-scale circulation. The reconstructed fields of density and three-dimensional velocity are dynamically balanced and provide qualitative and quantitative estimates of the circulation features of the Amundsen and Bellingshausen seas. Natural assumptions on the spatial structure of the density covariance matrices enable us to obtain realistic coastal currents near the continental slopes of Antarctica within the framework of model equations. The horizontal circulation pattern reveals along shore westward current with typical velocities of 1 cm s-1 and cyclonic gyres in the Amundsen and Bellingshausen seas transporting 2 and 0.5 Sv, respectively. Three eastward branches of the Antarctic Circumpolar Current are observed in offshore regions. Their transports are diagnosed as 19, 12, and 6 Sv. The lower layer is characterized by westward countercurrent in the northwestern part of the basin with the transport of 8 Sv. Average Ekman upwelling rate in the major part of the basin amounts to 20-25 m yr-1. Downwelling in the shelf regions of the Bellingshausen and Amundsen seas is estimated as 250-350 m yr-1. Copyright 1998 by the American Geophysical Union.