Pulse of WNP Subtropical High Shaping Monsoon and Tropical Cyclone

The interannual variation of the western North Pacific (WNP) subtropical high (WNPSH) during summer of 1979-2009 represents the strength of East Asian summer monsoon (r=–0.92), the total tropical storm days over the subtropical WNP (r=–0.73), the total number of tropical storms landing on Japan, Korea, East China and Taiwan (r=–0.66), and the first two leading modes of rainfall variability of the entire Asian summer monsoon (r=0.58 and 0.56, respectively). Skillful prediction of the WNPSH is of utmost importance to seasonal forecast and future projection of Asian-Pacific climate. Here we demonstrate that WNPSH fluctuation is primarily caused by a remote cooling/warming in the equatorial central Pacific and a local positive thermodynamic feedback between the WNPSH and a dipolar sea surface temperature anomaly in the Indo-Pacific warm pool. A conceptual model based on the characteristics of these two physical processes can surprisingly capture about 88% of the WNPSH intensity change. A physically-based empirical prediction model built on these physical understandings has comparable performance with those of state-of-the-art coupled global climate models in re-forecasting the strength of the WNPSH. These results have profound ramification for understanding the predictability and direct application to prediction of Asian summer monsoon rainfall and landing tropical storm activity.