4.1 Surface air temperature and precipitation
The ensemble mean climatological annual cycle of the surface air temperature (Tair) and precipitation (P) for nine representative high-latitude, midlatitude, and tropical regions for CAS-FGOALS-g3, and the observational estimates for both variables, are shown in Fig. 2 and Fig. 3, respectively. For the G3 simulations of the temperature, the overall results showed that the annual cycle of the G3 simulations in the nine regions mimicked the observations. Among the comparisons, the simulated temperature seasonal cycle data were at high-latitude and mid-latitude regions were closer to the observations than those of the tropical regions, where the Amazon region depicted a high temperature bias in JFM (January to March) and SON (September to November), the Sahel region depicted a lower temperature bias in MAM (March to May) and SON, and the Indian region depicted a systematically higher seasonal cycle (Fig. 2).
Inspection of the regionally averaged seasonal cycles of precipitation are shown in Fig. 3. Unlike that of the temperature, comparison of the regionally averaged seasonal cycles of precipitation with the observations do not show obvious trends at specific latitudes. Systematic overestimations of precipitation appeared in Alaska and the Amazon, and the seasonal cycle was too low and did not follow the phase of the observations in central Canada. For places like the eastern USA and Europe, the seasonal cycle was out of phase with the observations. For Sahel, on the other hand, an earlier peak of the cycle appeared in May, rather than in August in the observations. Overall, the seasonal cycle of precipitation depicted poorer results than that of the temperature seasonal cycle, and this bias of the seasonal cycle did not show obvious features in terms of latitude.