Sensitivity of a global ocean general circulation model to tracer advection schemes

Vertical diffusivity at the thermocline depths is now believed to be as sma ll as 1 x 10(-5) m(2) s(-1). In order to accomplish a reliable simulation o f the World Ocean for the Vertical diffusivity of 1 x 10(-5) m(2) s(-1), tw o advective tracer transport schemes, the Uniformly Third-Order Polynominal Interpolation Algorithm (UTOPIA) of Leonard et al, and the Multidimensiona l Positive Definite Advection Transport Algorithm (MPDATA) of Smolarkiewicz , are incorporated into an ocean general circulation model. Intercomparison is made among simulations using UTOPIA, MPDATA, and the centered differenc ing scheme. When UTOPIA or MPDATA is adopted, features at the thermocline d epths are realistically simulated. Increase in computational cost is modera te. Circulations associated with Antarctic Bottom Water (AABW) in the Atlan tic and Circumpolar Deep Water (CDW) in the Pacific are not reproduced at a ll for such small vertical diffusivity, although the circulation associated with North Atlantic Deep Water (NADW) has reasonable intensity. Another ex periment with UTOPIA for the vertical diffusivity of 5 x 10(-5) m(2) s(-1) shows that the circulation associated with NADW is relatively insensitive t o vertical diffusivity, compared with the circulation associated with AABW and CDW.