. Why are we sufferingsuch severe weather this summer? In case you have not heard, we areexperiencing a weather phenomenon called El Nino. What is El Nino, and How Long Will This Last? According to MichaelMcPhaden, director of the Tropical Atmosphere Ocean Array, an El Ninois born when west-blowing Pacific trade winds relax or reverse. Withoutthe wind at its back, seawater that typically piles up on the jaggedwestern edge of the Pacific — around Indonesia, the Philippines andAustralia — slides back toward the Americas.
The sliding water movesin what scientists call Kelvin waves. “It pushes the cold water down. That causes the initial warming,” said McPhaden. At the same time, thePacific reacts to the lost wind by building another series of wavesunder water. Called , they roll west toward Indonesia, the Philippinesand Australia. Eventually, the series of waves strikes the coasts ofthose countries.
Then, it reverses and heads back toward South America,traveling along the equator. “As it passes,” McPhaden said, “it leavescold water closer to the surface. “El Nino normally occurs around Christmas and usually last for a fewweeks to a few months. Sometimes an extremely warm event can developthat last for much longer time periods. A strong El Nino developed in1991 and lasted until 1995. We are apparently experiencing one of thesestronger El Ninos, as this one has lasted for nearly six months .
Buthow long will this last? And then what?The Onset of La Nina After an El Nino event, weather conditions usuallyreturn to normal. However, in some years the trade winds can becomeextremely strong and an abnormal accumulation of cold water can occurin the central and eastern Pacific. This event is called La Nina. WhereEl Nino refers to a body of unusually warm water astride the equator bySouth America, La Nina describes a sea that’s abnormally cool. Twoindependent computer models that forecast El Nino see on the horizon apronounced cooling of the same area of the Pacific.
Sometimes, the coldwater is just enough to return ocean temperatures to normal. Notalways. “Sometimes, it overshoots,” McPhaden said. “That would bring aLa Nina after El Nino. “”The models say .
. . there will be a cold effect sometime next year –magnitude and timing to be determined,” said Tim Barnett, one of themodel makers at Scripps Institution of Oceanography in La Jolla. Theother model with the La Nina forecast comes from the Center forOcean-Land-Atmosphere Studies, a research institute in Calverton, Md.
Climate experts agree that the forecasts should be viewed withconsiderable caution. Even without consulting computers, it’s a reasonably safe assumptionthat the present warm spell will be followed, eventually, by a coldone. That’s because the makings of a La Nina are built in to an ElNino. As McPhaden puts it, “The seeds for the demise of El Nino aresown even at its onset. ” So maybe it’s time we stopped blaming El Ninofor all of our maladies.
From now on, we can start blaming the onset ofLa Nina. Most people will not notice the transition from El Nino to LaNina, as the weather will still be hot and there will initially beincreased rainfall, particularly in California, which we may from thispoint forward refer to as CaliforNina.