The annual modes of tropical precipitation simulated by LASG/IAP ocean atmosphere coupled model Fgoals-s1.1.

This paper evaluates the performance of LASG/IAP ocean-atmosphere coupled model Fgoals -s1.1 on simulating the annual modes of tropical precipitation. To understand the impacts of air-sea coupling on the annual modes, the result of an off-line simulation of the atmospheric component of Fgoals-s1.1, e.g. LASG/IAP atmospheric general circulation model SAMIL, is also analyzed. It is shown that Fgoals-s1.1 can reasonably reproduce major characteristics of the annual modes of tropical precipitation. The simulated annul mean rainfall matches well with the observation in maximum centers. Nonetheless, the coupled model also shows clear biases, e.g. the overestimation of rainfall amount over the equatorial Pacif ic and tropical South Pacific, the underestimation of rainfall over the northern equatorial Pacific. The monsoon mode simulated by Fgoals-s1.1 shows an equatorial anti symmetric structure, which is close to the observation. The bias of the coupled model in simulating the global monsoon resembles that of SAMIL, especially over the subtropics. The main deficiency of Fgoals -s1.1 is its failure in simulating the springfall asymmetric mode. This is attributed to a false phase of the SST annual cycle over the equatorial central eastern Pacific and Indian Ocean, which has led to a serious bias of the Walker circulation over the equatorial Pacific and the anti-Walker circulation over the Indian Ocean in spring and autumn. In addition, the western North Pacific monsoon simulated by the coupled model occupies a smaller territory than reality, and this is also the case for the Indian monsoon. Our study suggests that the bias of a fully coupled ocean-atmosphere model can be partly attributed to the bias in its atmospheric component. The performance of Fgoals-s1.1 in simulating the annual cycle of equatorial SST needs to be further improved.