Simulations of the interdecadal variations of summer rainfall over China are assessed from 5 coupled AOGCMs from the Data Distribution Center (DDC) of the Intergovernmental Panel in Climate Change (IPCC) under the IPCC-Special Report in Emission Scenarios (SRES) A2 and B2 scenario. We examined their ability in simulating the interdecadal variations of summer precipitation over China from 1951 to 1990. The difference before and after the mid-1960’s and the late 1970’s is given respectively to check the capability of the models, especially in reproducing the rainfall jump in North China. We also investigated the interdecadal variations simulated by the models in the 1990’s and the average of 2001-2020 in the future under the scenario A2 and B2. The analysis shows that the current AOGCMs is not good enough in simulating the interdecadal variations of summer precipitation in China. The interdecadal variations of summer rainfall simulated by most of the models cannot reproduce the observation in North China. Higher resolution models are suggested to well simulate the interdecadal variability in regional scale.
The mechanism of the locking of the El Nino event onset phase to boreal spring (from April to June) in an intermediate coupled ocean-atmosphere model is investigated. The results show that the seasonal variation of the zonal wind anomaly over the equatorial Pacific associated with the seasonal variation of the ITCZ is the mechanism of the locking in the model. From January to March of the El Nino year, the western wind anomaly over the western equatorial Pacific can excite the downwelling Kelvin wave that propagates eastward to the eastern and middle Pacific by April to June. From April to December of the year before the El Nino year, the eastern wind anomaly over the equatorial Pacific forces the downwelling Rossby waves that modulate the ENSO cycle. The modulation and the reflection at the western boundary modulate the time of the transition from the cool to the warm phase to September of the year before the El Nino year and cause the strongest downwelling Kelvin wave from the reflected Rossby waves at the western boundary to arrive in the middle and eastern equatorial Pacific by April to June of the El Nino year. The superposition of these two kinds of downwelling Kelvin waves causes the El Nino event to tend to occur from April to June.
