The Southern Ocean Thermohaline Circulation: A Numerical Model Sensitivity Study

Abstract

A two-dimensional primitive equation model is developed to study the thermohaline circulation of the Southern Ocean. The primary objectives are to identify those elements of the ocean climate model important for the thermohaline balance, and to assess the capability of the numerical formulations. The simplified configuration adopted here permits extended runs from rest to equilibrium for a variety of configurations and parametric conditions. The model is driven by surface flux of momentum, heat and salt, and is implemented with and without the dynamic component in order to delineate important thermodynamic interactions. Additional experiments analyze the effects of seasonal forcing versus annual mean conditions, the eddy coefficient parameterizations, resolution, and convective adjustment schemes. Reasonable qualitative agreement is found between the model and observations. The fundamental climatic balance is characterized by downward and poleward diffusion of heat, predominantly by diffusive processes, and subsequent convection at high latitudes. The balance is sensitive to seasonal effects, particularly salt-forced convection in winter, and the details of the parameterizations. The convection and diffusion representations are critical for Antarctic water mass formation and frontogenesis as they not only determine the large-scale climatic environment, but also the seasonal production rates of various water masses.