Validation of sub‐grid‐scale mixing schemes using CFCs in a global ocean model

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Abstract
Three sub‐grid‐scale mixing parameterizations (lateral/vertical; isopycnal; Gent and McWilliams, 1990) are used in a global ocean model in an attempt to determine which yields the best ocean climate. Observed CFC‐11 distributions, in both the North and South Atlantic, are used in evaluating the model results. While the isopycnal mixing scheme does improve the deep ocean potential temperature and salinity distributions, when compared to results from the traditional lateral/vertical mixing scheme, the CFC‐11 distribution is worse in the upper ocean due to too much mixing. The Gent and McWilliams (1990) parameterization significantly improves the CFC‐11 distributions when compared to both of the other schemes. The main improvement comes from a reduction of CFC uptake in the southern ocean where the ‘bolus’ transport cancels the mean advection of tracers and hence causes the Deacon Cell to disappear. These results suggest that the asymmetric response found in CO2‐increase experiments, whereby the climate over the southern ocean does not warm as much as in the northern hemisphere, may be due to the particular mixing schemes used.