Jonah Bromwichdec :
Rain in California. Fires in the tropics. Floods in the southern United States. Unseasonably warm weather on the Eastern Seaboard. All have followed El Niño events in past years.
The recurring meteorological phenomenon formed again in 2015, and, according to Martin Hoerling, a research meteorologist at the National Oceanic and Atmospheric Administration, it is “ranking up with the biggest in the historical record that we have.”
To understand El Niño, it’s useful to remember some basic geography. Picture the equatorial Pacific, the large stretch of ocean with South Asia and Australia to the west, and South America to the east.
The Pacific trade winds that blow over the region usually move from east to west, pushing the water at the ocean’s surface toward South Asia and Australia. As the warmest water evaporates, the air fills with moisture and contributes to the monsoon seasons in Asia and Australia.
El Niño occurs when the trade winds stop moving. Scientists have been unable to immediately pinpoint the cause of this shift. “A variety of factors can start the cycle in motion at any given time,” Mr. Hoerling said. “In any given El Niño, sometimes after the fact it becomes evident which precursor seemed to tip the balance.”
The weather phenomenon known as El Niño can cause dramatic effects around the world. Henry Fountain explains where it comes from. By Henry Fountain, Aaron Byrd and Ben Laffin on Publish Date September 9, 2014.
He added: “But once these conditions begin to unfold, they go through a life cycle that lasts on the order of 12 months or so, and there’s a lot of predictability in that.”
El Niño events typically occur every two to seven years. The current event was identified about six months ago, though scientists are not yet sure what caused it.
Scientists do know what happens after the winds stop blowing. The weather reverses: Australia and South Asia experience drought instead of rain, and the Pacific Coast of South America is drenched by a rainy season. The paths of other winds, known as jet streams, are altered. One of them drives Pacific storms to California.
Strong El Niño events deliver heavy rain to California (Mr. Hoerling predicted that those could arrive this month), and push warm air across the northern United States and Canada, which helps to explain the current unseasonable warmth on the East Coast.
Outside the United States, rains increase along the equatorial Pacific, which means that normally arid regions such as the Galápagos get quite wet. A weak Atlantic hurricane season, like the one this summer, also tends to follow El Niño. And the typhoon season in the tropical west Pacific tends to become very active because the warm ocean spawns more atmospheric disturbances that can develop into storms.
Notable effects linked to the 2015 event include drought in Indonesia, which contributed to extensive wildfires in the country. (A similar effect was caused by the last strong El Niño.) Typhoon Melor, which prompted the evacuation of thousands in the Philippines, is also consistent with the effects seen during past El Niños.
According to NASA, fishermen in Latin America recognized that they usually saw the effects of the phenomenon close to Christmas. El Niño, which means the boy in Spanish, refers to the birth of Christ. (Though for some, it will always be associated with Chris Farley).
Evidence suggests that El Niño has been happening for thousands of years. That said, three of the strongest events in the historical record, which goes back about 120 years, have taken place in the last 30 years. Mr. Hoerling said that the question of climate change causing stronger events is being researched.
Because the phenomenon has been recurring for so long, it is built into ecosystems around the world. Mr. Hoerling pointed out that “some areas that never get rain, only get rain in this phenomenon. It’s a very important climate feature of those regions.” He pointed to parts of California and the Southwestern United States, where the rain delivered by El Niño is essential to the ecology.
At the same time, El Niño can cause typhoons, rainstorms and droughts. So while the phenomenon cannot necessarily be categorized as positive or negative, it can have adverse effects on human populations that are best combated by understanding El Niño as well as we can. Hopefully, we’ve helped you to do that.
From New York Times
