How It Happens – El Niño

The phenomenon called El Niño can disrupt weather patterns around the world. In 1988 it caused devastating floods and mudslides in California. Around the same time, it also caused these floods across the south. But it all started thousands of miles from each location.
Picture the Equatorial Pacific. That’s South Asia and Australia on the left and South America on the right. Pacific trade winds normally blow from east to west, pushing warm surface water with them. The warm water evaporates, adding moisture to the air and bringing on the annual monsoons to the region. In the Eastern Pacific, as the surface water is pushed westward, cold water wells up from the deep to replace it. The cold water helps keep the air and the South American coast dry.
But sometimes the trade winds stop. Scientists don’t know precisely why but when they do, the warm water moves back east. That’s when El Niño takes hold. The pattern of rainfall is reversed. Australia and South Asia suffer drought and coastal South America is hit by storms but warm water in the Eastern Pacific causes other changes as well.
High atmosphere winds, called jet streams, circle the planet. El Niño can alter the path of those winds, driving pacific storms to California. As the jet stream winds continue across the continent, they can keep the colder Arctic temperatures at bay. That can make for a warmer winter in the Northeast and Northwest. That’s why in 2010, when El Niño once again brought flooding to California, farther up the west coast in Vancouver, the Winter Olympics were hampered by unusually warm weather. It was all thanks to El Niño.

Source: nytimes

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