Circulation of the Pacific Ocean seen in a global ocean model: Ocean Circulation and Climate Advanced Modelling project (OCCAM)

This paper compares observations made in the Pacific Ocean and the 8-12 year climatology of a global numerical model. Meridional mass and heat transports and their divergences are calculated, and zonal averages compared with the air-sea exchange values of Doney et al. [1998] with mixed success. The large scale distribution of sea surface height and near-surface currents are shown to be well reproduced by the model, but their variance is underestimated, severely so in areas of weak variability. Synoptic wind forcing enhances the latter, though only slightly, while higher model resolution improves agreement in areas of strong variability. Model mean transports in the East Australian Current, in the Vitiaz Strait and in the Kuroshio exceed measurements by 10, 0, 18 Sv, respectively, and variability is underestimated by factors between 2 and 4. Near 1000 m and in strong currents the flow is overestimated, but over most of the ocean, model output does not match either the magnitude or the spatial variability of the observations. In contrast, the inflow of bottom water and its spreading path throughout both South and North Pacific is well described. Good agreement is found with measured transport through the Samoan Passage, but at 32 degrees S, east of the Ton,oa-Kermadec Ridge, the model yields only 60% of the observed value. The Sverdrup balance is shown to hold widely in the model interior. Utilizing the complete depth-integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents.