Simulation of the leading mode o f AsianAustralian monsoon interannual cariability with the Beijing Climate Cen ter atmospheric general circulation model

The performance of Beijing Climate Center (BCC) atmospheric general circulation model version 2.0.1 (BCC-AGCM) was evaluated in reproducing the leading mode of AsianAustralian monsoon (A-AM) rainfall interannual variability forced by historical sea surface temperature covering the period of 1979-2000. The observed first mode revealed by the seasonalreliant EOF analysis is associated with the turn about of warming to cooling in the (ENSO) and is featured by the seasonal evolution of the precipitation anomalies over the southeastern Indian Ocean and the western North Pacific Ocean. This mode has a quasi biennial oscillation and a low frequency component (4-6 year). The corresponding model r esults indicate that the model can reasonably reproduce the year toyear tempo ral variations of the first leading mode, as well as its relationship with ENSO evolution. The deficiency of BCCAGCM lies in reproducing the spatial pattern o f the first mode, which is possibly related to the model biases in simulating ge neral circulation. The observed western North Pacific (WNP) anticyclone is onset in D (0) JF (1), while the simulated one is onset in SON(0). This deficiency ma y be due to the systematic eastward shift of simulated circulation over this reg ion. In addition, the phase locking of the South Indian Ocean (SIO) anticyclone reproduced by BCC is boreal winter, one season later than its counterpart in obs ervation. It may be related to the strategies of the standalone AGCM simulatio n in which the local air-sea coupling process that is important for the evoluti on of the SIO anticyclone is neglected. Furthermore, the model has the lowest sk ill in reproducing rainfall distribution in boreal summer. Further discussion su ggests that this lowest skill may be related to simulated bias in mean state of summer rainfall, especially the lack of precipitation over the southeastern Indi an Ocean, which is possibly resulted from the convection scheme.