We are usually concerned mostly with our local weather, unless a favorite sporting event, or a vacation to somewhere else is planned. Then we may care about somebody else's weather for a day or two. Recently though, a weather phenomenon has been making the headlines and getting nearly everyone's attention. El Nino: "the child" may sound innocent enough, but it is a phenomenon that affects people thousands of miles away, and for some, those effects are devastating.

     The appearance of El Nino affects weather around the globe. Usually it brings increased rainfall across the southern portions  of the US and in Peru. In turn, it has caused destructive flooding, and drought in the west Pacific. El Nino even reaches to Australia where it is  sometimes associated with devastating brush fires.

      But what exactly is El Nino? El Nino is a disruption of the ocean-atmosphere system in the tropical Pacific. Specifically, it is a warming of the ocean current that runs south along the coast of Ecuador. In exceptional years, concurrently with a southward shift in the tropical rain belt, the current may extend along the coast of Peru to 12° south. When this occurs, effects are even more severe: plankton and fish are killed in the coastal waters and a phenomenon somewhat like the red tide of Florida results.

     El Niño is one part of a cyclical process called called ENSO (El Niño Southern Oscillation). The Southern Oscillation is a biennial event whereby the stratospheric winds flip flop from west one year to east the next. The ENSO is a natural phenomenon and there is good evidence from cores of coral in the tropical Pacific and glacial ice in the Andes that it has been going on for millennia.

     The ocean and atmospheric conditions in the tropical Pacific are seldom "average", rather they fluctuate in an irregular cycle alternating between El Niño /the warm phase/ and La Nina /the cold phase consisting of a basin-wide cooling of the tropical Pacific. The average period of one full cycle is about 3 to 6 years. The most intense part of each phase
usually lasts about a year.

     A distinctive pattern of sea surface temperatures  in the Pacific Ocean sets the stage for an ENSO event. The main features are a "warm pool" in the tropical western Pacific with much cooler waters in the east Pacific, and a cold section along the equator that is most pronounced about October and  weakest in March. Distinctive patterns of sea surface temperatures are caused mainly by the winds.

     During El Niño, the warm waters from the western tropical Pacific migrate eastward as the trade winds weaken. This sets a chain of events in motion as this shifts the pattern of tropical rainstorms, further weakening the trade winds which further reinforces the changes in sea surface temperatures. A complex feedback is set up in the winds  circulation patterns and hence the jet stream. It should be noted that no two El Niño events are exactly alike. For typical El Niño events, higher than normal sea level pressure occurs over Australia, Indonesia, southeast Asia, and the Philippines, signaling drier than normal conditions or even droughts. Dry conditions also prevail in the Hawaiian Islands and extend west from Australia to parts of Africa and across the Atlantic to the northeast part of Brazil and Columbia. Excessive rains prevail over the central and eastern Pacific, along the west coast of South America near Uruguay, and southern parts of the United States in winter.

     Current data gathered over the past several months, shows a strong El Niño event is underway. It is expected to bring major weather events to a number of places in the world. See the map for areas expected to be affected the most. There are many questions unanswered about El Nino and each time it occurs scientists hope to learn more.