Tropical Biases

Abstract

This chapter evaluates the double ITCZ bias in the south-central equatorial Pacific for the latest versions of two coupled models (FGOALS-g2 and FGOALS-s2) that participated in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The results demonstrate that the double ITCZ bias still exists in the two coupled models, both of which simulate a spurious rain belt in the south of the equator. The Sea Surface Temperature (SST) and surface wind also appear distinctly different to the observations, particularly in FGOALS-g2, corresponding to the anomalous distribution of precipitation. Feedback analysis in the south-central equatorial Pacific shows that the shortwave radiation and SST feedbacks are significantly weaker on both models than in the observations. This is one of the factors contributing to the double ITCZ bias. The two models share the same oceanic component, while their simulated general atmospheric and oceanic circulation patterns are considerably different. Comparison with the results of the AMIP run demonstrates that the bias in coupled models results primarily from the atmospheric component.