During an El Niño event, the surface waters in the central and eastern Pacific Ocean become significantly warmer than usual. That change is intimately tied to the atmosphere and to the winds blowing over the vast Pacific. Easterly trade winds (which blow from the Americas toward Asia) falter and can even turn around into westerlies. This allows great masses of warm water to slosh from the western Pacific toward the Americas. It also reduces the upwelling of cooler, nutrient-rich waters from the deep—shutting down or reversing ocean currents along the equator and along the west coast of South and Central America.

The circulation of the air above the tropical Pacific Ocean responds to this tremendous redistribution of ocean heat. The typically strong high-pressure systems of the eastern Pacific weaken, thus changing the balance of atmospheric pressure across the eastern, central, and western Pacific. While easterly winds tend to be dry and steady, Pacific westerlies tend to come in bursts of warmer, moister air.Because of the vastness of the Pacific basin—covering one-third of the planet—these wind and humidity changes get transmitted around the world, disrupting circulation patterns such as jet streams (strong upper-level winds). We know these large-scale shifts in Pacific winds and waters initiate El Niño. What we don’t know is what triggers the shift. This remains a scientific mystery.

What is not a mystery is that El Niño is one of the most important weather-producing phenomena on Earth, a “master weather-maker,” as author Madeleine Nash once called it. The changing ocean conditions disrupt weather patterns and marine fisheries along the west coasts of the Americas. Dry regions of Peru, Chile, Mexico, and the southwestern United States are often deluged with rain and snow, and barren deserts have been known to explode in flowers. Meanwhile, wetter regions of the Brazilian Amazon and the northeastern United States often plunge into months-long droughts.

El Niño events occur roughly every two to seven years, as the warm cycle alternates irregularly with its sibling La Niña—a cooling pattern in the eastern Pacific—and with neutral conditions. El Niño typically peaks between November and January, though the buildup can be spotted months in advance and its effects can take months to propagate around the world.

Though El Niño is not caused by climate change, it often produces some of the hottest years on record because of the vast amount of heat that rises from Pacific waters into the overlying atmosphere. Major El Niño events—such as 1972-73, 1982-83, 1997-98, and 2015-16—have provoked some of the great floods, droughts, forest fires, and coral bleaching events of the past half-century.

For Guidance of WBCS (Exe.) Etc. Preliminary , Main Exam and Interview, Study Mat, Mock Test, Guided by WBCS Gr A Officers , Online and Classroom, Call 9674493673, or mail us at – mailus@wbcsmadeeasy.in
Visit our you tube channel WBCSMadeEasy™ You tube Channel
Please subscribe here to get all future updates on this post/page/category/website