The linkage between intraseasonal oscillation and heavy precipitation in Asian Monsoon region

Formation and development of heavy precipitations in East Asia are strongly influenced by their large-scale environments. Intraseasonal oscillation (ISO) has been suggested to be an important climate factor to the formation and development of heavy precipitations in East Asia. In the early summer, the heavy precipitation events in Taiwan dramatically increase, after the 30-60 day convection over the South China Sea reach their maximum intensity and start to propagate northward. In the boreal and late summer, the mean location of tropical storm (TS) and the number of TS formation in the western North Pacific are highly correlated with the 30-60 day oscillation. To improve the medium and long-range forecast of heavy precipitation in East Asia, one may need to understand the mechanisms responsible for the eastward and northward propagation of 30-60 day convective oscillation in GCM simulation. Several IPCC AR4 air-sea coupled model simulations and their corresponding AGCM AMIP simulations are investigated in this study. In general, the multi-model ensemble forecasts greatly improved the performance of the individual models in Asian monsoon region. However, the pattern correlation of CGCM and AGCM declined from April and reached minimum value in May. The occurrence of this poor performance of model simulation of ISO in May is coincided with the sudden northward movement of 30-60 day OLR in May. The 30-60 day convections in AGCM simulation propagate much faster than the observation and their period are shorter than the observation. Inclusion of the air-sea interaction in CGCM reduces the development and northward propagation speed of 30-60 day circulation and convection in Bay of Bengal. While CGCM simulation is better then the AGCM simulation in Bay of Bengal, the initiation and development of ISO over the South China Sea are complicated and are less predictable in AGCM and CGCM.