Fig. 8: Bias of the annual mean potential temperature (°C) (a) at the surface, (b) at 1000 m depth averaged over 1985–2014 of the first ensemble member of historical simulations compared to the Polar Science Center Hydrographic Climatology (PHC, updated from Steele et al., 2001). (c) and (d) as (a) and (b) but for salinity (psu).
It turns out that below a depth of about 500 m in the ocean, the mean absolute error of the potential temperature is smaller in AWI-CM than in most of the CMIP5 models (Fig. 9a), while for salinity AWI-CM is comparable to CMIP5 models (Fig. 9c). Compared to the CMIP5 version of MPI-ESM, which shares a slightly older version (6.0 instead of 6.3) of the same atmosphere component and which is run at T63 corresponding to around 200 km horizontal resolution instead of T127 corresponding to around 100 km horizontal resolution, the potential temperature error is smaller in AWI-CM but the salinity error larger. When focusing on the North Atlantic Ocean, potential temperature (Fig. 9b) for which various models show a pronounced warm bias in 1000 to 2000 m (Rackow et al., 2019), AWI-CM performs well. However, for salinity, in the North Atlantic (Fig. 9d) and also in the Pacific (not shown) the mean absolute error is large compared to most of the CMIP5 models including MPI-ESM. Note that Fig. 9 shows results for DJF; for JJA results are very similar below around 300 m.
(a) (b)