Editing IPCC:AR6/WGI/Chapter-3 (section)

===== 3.5.1.2.2 Tropical Atlantic Ocean =====

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Fundamental features such as the mean zonal SST gradient in the tropical Atlantic were not reproduced in CMIP5 models. Studies have proposed that weaker than observed alongshore winds, underestimation of stratocumulus clouds, coarse model resolution, and insufficient oceanic cooling due to a deeper thermocline depth and weak vertical velocities at the base of the mixed layer in the eastern basin, underpinned these tropical Atlantic SST gradient biases ( [[#Hourdin--2015|Hourdin et al., 2015]] ; [[#Richter--2015|Richter, 2015]] ). The SST gradient biases still remain in CMIP6. On average the cold bias in the western part of the basin is reduced while the warm bias in the eastern part has slightly increased (Figure 3.24b,c; [[#Richter--2020|Richter and Tokinaga, 2020]] ). Several CMIP6 models, however, display large reductions in biases of the zonal SST gradient, such that the eastern equatorial Atlantic warm SST bias and associated westerly wind biases are mostly eliminated in these models ( [[#Richter--2020|Richter and Tokinaga, 2020]] ). The high resolution (HighResMIP) CMIP6 models show a better representation of the zonal SST gradient (Figure 3.24b,c), but some lower resolution models also perform well, suggesting that resolution is not the only factor responsible for biases in Tropical Atlantic SST ( [[#Richter--2020|Richter and Tokinaga, 2020]] ).

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