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)