Geostrophic and Wind-Driven Components of the Southern Ocean Water Dynamics

Abstract

The contributions of geostrophic and wind-driven factors to the formation of the mean Antarctic circumpolar current (ACC) climatic structure were studied using the general ocean circulation model INMOM (Institute of Numerical Mathematics Ocean Model). The aim of the study was to separate the geostrophic and wind-driven components of the ACC. The simulation was carried out for summer (February) and winter (August) conditions in the Southern Hemisphere during the climatic period from 1993 to 2012. It is shown that, despite strong winds over the Southern Ocean, the geostrophic circulation factor is usually much stronger than the wind-driven factor. Nevertheless, the contribution of the wind-driven component to the increase in the near-surface zonal velocity can reach 15–20\(\%\) of the geostrophic velocity. Winds contribute to a decrease in the mean dynamic topography (MDT) from the open ocean to the coast of Antarctica. The influence of wind on the formation of the barotropic stream function of the current is more pronounced than on the MDT. Geostrophic transport of the ACC remains nearly the same in winter and summer. Due to wind effects, the total transport of ACC around Antarctica increases on average by 10–15 Sv in summer and 15–20 Sv in winter. The three-jet structure of the ACC was confirmed using numerical modelling and the ‘‘diagnosis–adaptation’’ method according to EN4 data. It is demonstrated that the three-jet structure of the ACC has a geostrophic nature.