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Earth Sense: Himalayas impact weather across Asia
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No mountain system in the world has a greater influence on weather than the plateau of Tibet and its fringe, the Himalayas. Even the tallest chains in the U.S., the Rocky Mountains, Brooks Range, Cascades and Sierra Nevada, can’t rival the control that the Tibetan plateau exercises over climatic conditions in Pakistan, India, China and the many smaller countries of southeastern Asia.

Created 50 million years ago by the collision of the Indian and the Eurasian Plate, the Himalaya range is the highest, but also one of the youngest mountain chains. The plateau averages 15,000 to 17,000 feet in elevation. That’s more than twice the height of the tallest mountains in the Eastern U.S. Like a gigantic curbstone, it extends 1,500 miles west to east, and about 800 from north to south. Due to its size and height, it diverts the jet stream, which in turn controls the flow of rainstorms in much of Asia.

In winter, the jet stream is the “fast lane” of air traveling around the globe from west to east. It separates very cold air in Siberia from the warmer air south of the mountain ranges in India, Bangladesh, Myanmar and the rest of Southeast Asia.

The Tibetan Plateau is too high to be crossed by the jet stream. In the summer, it warms up considerably. So now the borderline between warm and cold moves to the north of the plateau. High-altitude air is streaming eastward across northern China, into the Koreas and Japan. This clears an avenue for warm, moist air farther south to push westward. It comes from the fringes of the Pacific Ocean, the Philippine Sea and the East China Sea, and moves onto Chinese mainland.

On a satellite image, the area around Shanghai on the coast, and all of Anhui Province farther west, show a persistent patch of cloudiness at this time of the year. At the moment, the university campus at my current location in Hefei, Anhui, is seeing a few grey days with light precipitation, alternating with patchy sunshine a few times a week. Currently, students have replaced their parasols and sun hats with rain ponchos, thanks to the moist air from the Pacific.

Later in the summer, the fact that the jet stream is far off to the north will create monsoon season. It makes enormous rain totals possible in the smaller countries of Southeast Asia, especially in India.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His email is rkiefer@brenau.edu.

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