Evaluation for the Seasonal Evolution of the Summer Monsoon over the Asian and Western North Pacific Sector in the WCRP CMIP3 Multi-model Experiments

Abstract

Based on the World Climate Research Programme's (WCRP's) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset, evaluation for the summer monsoon over the Asian and western North Pacific (WNP) sectors is made in terms of reproducibility of the seasonal mean structure. Also investigated is a stepwise eastward progress of convection center from the Indian Ocean toward the WNP in the course of the maturing process of the continental and oceanic monsoons.Most models roughly reproduce seasonal mean broad-scale features on the Asian summer monsoon (ASM), but lower-tropospheric circulation over East Asia (EA) through the WNP and the location and intensity of the North Pacific subtropical high exhibit large inter-model variability. Some of the models fail to reproduce a reversal of the upper-tropospheric meridional temperature gradient over the South Asia and the North Indian Ocean sector. Metrics on the reproducibility of lower-tropospheric circulation of the ASM are also presented, in order to evaluate the reproducibility of the ASM circulation quantitatively.The large inter-model variability over the EA-WNP domains could be attributed to insufficient reproducibility of the oceanic monsoon. In most of the models, the stepwise eastward progress of convection over the South China Sea and WNP commences in May almost concurrently with large-scale circulation, whereas the eastward progress of convection is faster in most of the models than in the observation over the WNP. It is suggested that a teleconnection pattern associated with an intensification of convective activity over the WNP in mid-July is one of the key phenomena in both the observation and the coupled models, given the withdrawal of the Baiu rainy season around Japan. The analysis based on metrics concerning the stepwise eastward progress of convection over the WNP and its vicinity suggests that these models still have some difficulties in reproducing the stepwise eastward progress of convection accurately.