El Niño and La Niña Phenomena

El Niño and La Niña Phenomena

1) El Niño and La Niña are the names given to changes in the winds, atmospheric pressure, and seawater that occur in the Pacific Ocean near the equator. El Niño and La Niña are opposite phases of a back and forth cycle in the Pacific Ocean and the atmosphere above it. Unlike winter and summer, however, El Niño and La Niña do not change with the regularity of the seasons; instead, they repeat on average about every three or four years. They are the extremes in a vast repeating cycle, El Niño being the warm extreme and La Niña the cold extreme.

2) Although El Niño and La Niña take place in a small portion of the Pacific, the changes can affect the weather in large parts of Asia, Africa, Indonesia and North and South America. During 1982–83 El Niño was associated with record snowfall in parts of the Rocky Mountains, flooding in the southern United States, and heavy rain storms in southern California, which brought about floods and mud slides.

3) The name El Niño comes from Peruvian fishermen. They noticed that near the end of each year, the seawater off the South American coast became warmer, which made fishing much poorer. Because the change appeared each year close to Christmas, the fishermen called it El Niño, Spanish for "the boy child" referring to the Christ child. Every few years, the changes brought with El Niño were particularly strong or long lasting changes in weather. For example, normally dry areas on shore could receive abundant rain, turning deserts into fertile grasslands for as long as these strong El Niño lasted. In the 1950s and 60s it was found that strong El Niño were associated with increased sea surface temperatures throughout the eastern tropical Pacific. In recent years, these strong El Niños have been recognized as not just a local change in the sea, but as one half of a vast atmospheric-oceanic cycle.

4) The other half of the repeating cycle has been named La Niña, or the girl child. This phase is also sometimes called El Viejo, or the old man. La Niña was detected in the early 1920s by Sir Gilbert Walker. He was trying to understand the variations in the summer monsoons (rainy seasons) of India by studying the way atmospheric pressure changed over the Pacific Ocean. Based on meteorologists' previous pressure observations from many stations in the southern Pacific and Indian oceans, Walker established that over the years, atmospheric pressure went up and down back and forth across the ocean. In some years, pressure was highest over northern Australia and lowest over the southeastern Pacific, near the island of Tahiti. In other years, the pattern was reversed. The two pressure patterns had specific weather patterns associated with each, and the change from one phase to the other could mean the change from rainfall to drought, or from good harvests to famine.

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