What is El Niño?

The phrase El Niño was rated as the one that appeared the most in print media a few years ago. Despite its appearance all over the world, not many people know the story behind El Niño. There are few that can tell you that El Niño refers to some climatic phenomena. The truth is that El Niño affects the way all of us live by dictating to us the foodstuff we can cultivate and cannot cultivate. El Niño has affected trade and commerce in manner and scale that cannot be quantified. El Niño was originally recognized by fishermen off the coast of South America as the appearance of unusually warm water in the Pacific ocean. El Niño is Spanish for "The Christ Child," because it comes about the time of the celebration of the birth of the Christ Child-Christmas.

El Niño is an abnormal warming of surface ocean waters in the eastern tropical Pacific, is one part of what's called the Southern Oscillation. Since the ocean warming and pressure reversals are, for the most part, simultaneous, scientists call this phenomenon the El Niño/Southern Oscillation or ENSO for short. The phenomenon known as El Niño has been observed as early as the 1600s off the coast of Peru. At varying intervals, anomalously warm waters off the Peruvian coast. During El Niño (bottom panel of the schematic diagram), the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. In normal, non-El Niño conditions (top panel of schematic diagram), the trade winds blow towards the west across the tropical Pacific.

Consequently the large area of warm water is not diminished by the continuous evaporation cycle, so instead widens, moving closer to the eastern tropics. No cold water rises from the depths so the waters continue to warm. This warming trend now begins to kill the important nutrients fish and other sea life needs to survive. Once the fish disappear other animals that rely on them for food suffer mass starvation. Under normal climatic conditions a huge area of warm water is situated along the equatorial Pacific. Heating and evaporation builds storm clouds, which are then carried west by the trade winds in a continuous cycle. Seawater lost to evaporation is replenished when cold water from the deep ocean rises, keeping temperatures closer to the surface at 60 - 70 degrees Fahrenheit.

El Niños seem to occur every 2 - 7 years. Once a cycle has run its course, atmospheric and oceanic conditions usually return to their normal patterns. In other less frequent cases another event called a "La Niña" follows close on the heels of her big brother. La Niña means, "The Little Girl" , but sometimes she is called "El Viejo", "anti-El Niño", or even just "a cold event". La Niñas occur when an excess of colder water rises in the tropical Pacific. This sudden surge causes the eastern trade winds to strengthen. The effect is completely opposite to that of El Niño. Cold water floods the upper ocean and temperature drop significantly. While an El Niño causes colder than normal winters in North America, a La Niña causes the opposite.

Scientists do not really understand how El Niño forms. The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific. This climatic shift may cause torrential rains in deserts and droughts in temperate regions like Asia and Australia. It is believed that El Niño may have contributed to the 1993 Mississippi and 1995 California floods. It is also believed that El Niño contributed to the lack of serious storms such as hurricanes in the North Atlantic which spared states like Florida from serious storm related damage.

Unfortunately not all El Niños are the same nor does the atmosphere always react in the same way from one El Niño to another. This is the main reason why scientists in the United States of America assiduously study El Niño.