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

===== 3.5.1.2.1 Tropical Pacific Ocean =====

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In CMIP5, mean state biases in the tropical Pacific Ocean including the excessive equatorial cold tongue, erroneous mean thermocline depth and slope along the equator remained but were improved relative to CMIP3 ( [[#Flato--2013|Flato et al., 2013]] ). Misrepresentation of the interaction between the atmosphere and ocean via the Bjerknes feedback and vertical mixing parameterizations, and a bias in winds were among the suggested reasons for the persistent biases ( [[#Li--2014|Li et al., 2014]] ; [[#Zhu--2018|Zhu and Zhang, 2018]] ). Moving to CMIP6, a reduction of the cold bias in the equatorial cold tongue in the central Pacific is found on average in the CMIP6 models (Figure 3.24b; [[#Grose--2020|Grose et al., 2020]] ; [[#Planton--2021|Planton et al., 2021]] ), however, this reduced bias is not statistically significant when considered across the multi-model ensemble ( [[#Planton--2021|Planton et al., 2021]] ). It is also noteworthy that the longitude of the 28°C isotherm is closer to observed in CMIP6 than in CMIP5, with a coincident reduction in the CMIP6 inter-model standard deviation ( [[#Grose--2020|Grose et al., 2020]] ). The latter result implies that there is an improvement in the representation of the tropical Pacific mean state in CMIP6 models. Comparison of biases in individual HighResMIP models with biases in lower resolution versions of the same models indicates that there is no consistent improvement in SST biases in most of the equatorial Pacific with resolution (Figure 3.3e; [[#Bock--2020|Bock et al., 2020]] ).

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