Asian Monsoon Predictions Take Great Leap Forward
There are few other weather phenomenon which effect a country's agriculture, economy, and people greater than the Monsoon. The monsoon is defined as a seasonal reversing of wind accompanied by a significant change in precipitation. For many parts of the world, and particularly south Asia, the monsoon provides much needed rainfall. However, the amount of rainfall and number of tropical storms brought about by each year's monsoon has been extremely difficult to predict. Scientists from the International Pacific Research Center at the University of Hawaii at Manoa have made a breakthrough for predicting the summer monsoon rainfall over East Asia as early as the spring of that year.
The East Asian monsoon affects parts of Indo-China, Philippines, China, Korea, and Japan. The researchers found that this monsoon and its related storm activity are controlled by fluctuations in the western Pacific Subtropical High (WPSH), a major circulation system centered over the Philippine Sea.
If the WPSH is strong during the summer, the rainfall tends to be above average in East Asia and there tend to be fewer tropical storms that make landfall.
Using computer modeling, they found out that summer fluctuations in the WPSH are over 65% predictable by the spring. Things that make the WPSH stronger than usual include dipolar sea surface temperature anomalies in the ocean. This happens when unusually warm Indian Ocean hits the unusually cool western North Pacific water. If this occurs, there will be greater summer monsoon rainfall over East Asia and the Ganges Valley in India.
"Our findings create a promising way for predicting monsoon rainfall and tropical storm days during the East Asian summer," concludes lead author Bin Wang, meteorology professor at the University of Hawaiʻi at Mānoa and faculty at the International Pacific Research Center. "As a first step, we use global general circulation models to predict the fluctuations in the WPSH, and then in a second step, we use this forecast to predict rainfall and storm days in regional analyses. We have done hindcasts from 1979 to 2009 using this approach and have found substantially improved skills over the use of dynamical climate models in predicting the East Asian Summer Monsoon rainfall and tropical storm activity."
This study has been published in the Proceedings of the National Academy of Sciences
Monsoon Clouds image via Shutterstock