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

===== 3.5.1.2.3 Tropical Indian Ocean =====

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The tropical Indian Ocean mean state is reasonably well simulated both in CMIP5 and CMIP6 (Figure 3.24b,c). However, CMIP5 models show a large spread in the thermocline depth, particularly in the equatorial part of the basin ( [[#Saji--2006|Saji et al., 2006]] ; [[#Fathrio--2017b|Fathrio et al., 2017b]] ), which has been linked to the parameterization of the vertical mixing and the wind structure, leading to a misrepresentation of the ventilation process in some models ( [[#Schott--2009|Schott et al., 2009]] ; [[#Richter--2015|Richter, 2015]] ; [[#Shikha--2018|Shikha and Valsala, 2018]] ). A common problem with the CMIP5 models is therefore a warm bias in the subsurface, mainly at depths around the thermocline, which is also apparent in the CMIP6 models (Figure 3.25g).

In the CMIP6 multi-model mean, the western tropical Indian Ocean shows a slightly larger warm bias compared to CMIP5 (Figure 3.24 b,c), which in part could be related to excessive supply of warm water from the Red Sea ( [[#Grose--2020|Grose et al., 2020]] ; [[#Semmler--2020|Semmler et al., 2020]] ). The HighResMIP models show decreases in SST bias across the Indian Ocean with increasing resolution (Figure 3.3e; [[#Bock--2020|Bock et al., 2020]] ), though as a group the SST biases in the HighResMIP models are no smaller than those of the full CMIP6 ensemble.

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