Fig. 9: Profiles of mean absolute error calculated from each grid point for the (a) globe and (b) North Atlantic ocean of potential temperature (°C) for DJF 1985–2014 of the five ensemble members of the historical AWI-CM simulation (in colors) and for DJF 1976–2005 of CMIP5 simulations (in black, each line representing one CMIP5 model, green representing the MPI-ESM CMIP5 model). (c) and (d) as (a) and (b) but for salinity (psu). The reference climatology is the Polar Science Center Hydrographic Climatology (PHC, updated from Steele et al., 2001).

4.5 Sea ice

The general patterns of observed Arctic and Antarctic sea ice concentration are well represented in AWI-CM over the last 30 years of historical simulations (Figs. 10 and 11). Both Arctic and Antarctic sea ice concentration are overestimated in late winter in the marginal ice zones and underestimated in late summer in most areas. This hints to a too pronounced annual cycle of sea ice cover which can also be seen in the sea ice extent as shown in Fig. 15. Nevertheless, Arctic sea ice extent and thickness are remarkably well represented especially over the last few years (Figs. 15 and 16). While late winter Arctic sea ice concentration biases are very similar to MPI-ESM, late winter Antarctic sea ice concentration in MPI-ESM has a substantial negative bias especially northeast of the Weddell Sea and a slight negative bias in East Antarctic marginal seas (Müller et al., 2018, their Fig. 4) rather than a slight positive bias. This difference is consistent with the reduced Southern Ocean warm bias in AWI-CM compared to MPI-ESM.
(a) (b) (c)