Summit County Citizens Voice

Regional pressure fluctuations the key to unraveling monsoon mysteries

The first week of August 2010 brought extreme flooding and landslides to many parts of Asia. By August 11, floods in the Indus River basin had become Pakistan’s worst natural disaster to date, leaving more than 1,600 people dead and disrupting the lives of about 14 million people, reported Reuters. Across the border in northeast India, flash floods killed 185 with 400 still missing, reported BBC News. Floods in North Korea and northeast China buried farmland and destroyed homes, factories, railroads, and bridges. Photo courtesy NASA Earth Observatory.

By Summit Voice

FRISCO — Hawaii-based scientists say that tracking hemispheric climate patterns can help develop more accurate forecasts for the critical Asian monsoon season, which is critical to  the agriculture, economy, and people in the region.

Better monsoon forecasts have been a sort of Holy Grail for meteorologists, but season  seasonal predictions of these two types of weather phenomena are still poor. But the research done at the International Pacific Research Center, University of Hawaii at Manoa, shows the strength of the East Asian summer monsoon and  storm activity in the western North Pacific depend on fluctuations in the western Pacific Subtropical High, 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.

“Our findings create a promising way for predicting monsoon rainfall and tropical storm days during the East Asian summer,” said Bin Wang, meteorology professor at the University of Hawaii at Manoa 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,” Wang said.

With the help of computer modeling experiments, the scientists found that  fluctuations in the western Pacific Subtropical High are more than 65 percent 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.

The team traced the rainfall and storm variability in the Asian monsoon region to the feedback occurring between the WPSH and the underlying Indo-Pacific warm-pool ocean.

“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,” Wang said.

The study was published in the January 21 Proceedings of the National Academy of Sciences.

Filed under: climate and weather, Environment Tagged: | Asian monsoon, climate, Pacific Ocean, University of Hawaiʻi at Mānoa, weather, Weather forecasting