El nino, or the warm phase of the El nino southern oscillation (ENSO), is a recurring natural phenomenon and is defined as a prolonged warming of the Pacific Ocean sea surface temperatures (SST) when compared to average values. This sounds simple enough, but there is a lot more involved than just SSTs.
So far this year, we have seen rain in drought-plagued California, fires in the tropics, floods in the southern U.S. and above normal temperatures on the Eastern Seaboard. But from December to February, El Nino will be associated with warmer than normal conditions across southeastern Asia, southeastern Africa, Japan, southern Alaska and western/central Canada, southeastern Brazil and southeastern Australia, while there should be cooler than normal conditions during December through February along the Gulf coast of the United States.
What has caused 2015’s El nino?
Here is a quick geography lesson. If you look at a map of the world, you will see the Pacific Ocean. Find the Equator. Southern Asia and Australia are to the West, and South America is to the East. Normally, Pacific trade winds move from east to west, toward Australia and south Asia, pushing the ocean’s surface water along on the journey. As the warmer water evaporates, the air fills with moisture, and this brings the monsoon seasons to Australia and southern Asia.
But while scientists have not been able to define exactly what happens, when an El nino begins, for some reason, the trade winds are reduced or stop moving from east to west across the Pacific in the lower atmosphere, while the west-to-east winds over the eastern tropical Pacific in the upper atmosphere near the tropopause also are reduced.
Martin Hoerling, a research meteorologist at the National Oceanic and Atmospheric Administration (NOAA) talked with the New York Times. He said, “A variety of factors can start the cycle in motion at any given time. In any given El Niño, sometimes after the fact, it becomes evident which precursor seemed to tip the balance.”
Climate scientists now have enough evidence to know that once the El nino event begins to unfold, it will go through a predictable cycle that lasts 12 months or more. El nino events occur every two to seven years, with the current one being identified about six months ago, although scientists don’t as yet know what set it off.
Will El nino bring rain to California this winter?
In a study presented at the American Geophysical Union meeting in San Francisco on Tuesday, NASA scientists explained how 15 years of observation by NASA’s fleet of Earth-observing satellites have shown how El Ninos impact on multiple Earth systems. One of the big questions answered was whether this year’s El nino will bring any relief to drought-stricken California, and NASA climate scientists say they believe it will.
NOAA’s Martin Hoerling was also at the meeting and said his agency ran a statistical analysis of the relationship between past El Niño strength and precipitation. “It’s the strength of the El Niño that determines its impact on total rainfall in California, he said.
“What we learned is weak El Niños don’t necessarily change the odds of precipitation being much different from normal,” said Hoerling. “The rare occurrence of a strong El Niño, like what we’re currently experiencing, however, greatly increases the odds of a wet California winter.”
Changes in atmospheric dynamics shifts the rainfall
Part of the presentation was a study on how El Nino effects change the distribution and severity of wildfires around the globe. As we have seen, during an El nino event, the number and size of wildfires are increased in tropical forests in Australia, Asia and South America.
“The change in atmospheric dynamics (the trade winds) shifts the rainfall,” Jim Randerson, an Earth system scientist at the University of California, Irvine said. “So El Niño causes less rain to fall in many areas of the tropics, making forests more vulnerable to human-ignited fires.”
The latest word from NOAA is that El Niño is expected to remain strong through the Northern Hemisphere winter of 2015-16, finally coming to an end during the late spring or early summer 2016.
NASA, NOAA and the National Weather Service are all working in concert with local, national and international climate organizations in using space to increase our knowledge and understanding of our planet, and at the same time, protect our future.
