Scientists working at the International Pacific Research Center, University of Hawaii at Manoa, have now made a promising breakthrough for predicting in spring both the summer monsoon rainfall over East Asia and the number of tropical storms affecting East Asian coastal areas. The study is published in the January 21, 2013, Proceedings of the National Academy of Sciences.
The scientists have shown that both the East Asian summer monsoon and the storm activity in the western North Pacific are controlled by fluctuations in the western Pacific Subtropical High (WPSH), a major atmospheric circulation system in the global subtropics centered over the Philippine Sea.
When this system is strong in summer, then monsoon rainfall tends to be greater than normal over East Asia, and in the western North Pacific there tend to be fewer tropical storms that make landfall.
With the help of computer modeling experiments, the scientists found that these summer fluctuations in the WPSH are more than 65% predictable in spring. When the Indo-Pacific warm pool shows a dipolar sea surface temperature anomaly (that is, an unusually warm Indian Ocean together with an unusually cool western North Pacific) or the central Pacific tends to cool in spring, then the WPSH will be strong and stable with ensuing greater summer monsoon rainfall over the East Asian monsoon front and the Ganges River Valley in India, but fewer tropical storms will affect East Asian coastal areas and the western subtropical Pacific....
Monsoon rains in Punjab, shot by Sanyambahga, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license
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