El Nino

El Nino

Typically, the level of ocean water around the world is higher in the western Pacific and lower in the eastern, near the Western coast of South and

North America. This is due primarily to the presence of easterly winds in the

Pacific, which drag the surface water westward and raise the thermocline relatively all the way up to the surface in the east and dampen it in the west.

During El Nino conditions, however, the easterlies move east, reducing the continuing interaction between wind and sea, allowing the thermocline to become nearly flat and to plunge several feet below the surface of the water, allowing the water to grow warm and expand. With the help of the National Oceanic and

Atmospheric Administration's weather satellites, tracking shifting patterns of sea-surface temperatures can be made easier. Normally, a "pool" of warm water in the western Pacific waters exists. Under El Nino conditions, this "pool" drifts southeast towards the coast of South America. This is because, in a normal year, there is upwelling on the western South American coastline, and cold waters of the Pacific rise and push westward. However, during an El Nino year, upwelling is suppressed and as a result, the thermocline is lower than normal. Finally, thermocline rises in the west, making upwelling easier and water colder. Air pressures at sea level in the South Pacific seesaw back and forth between two distinct patterns. In the high index phase, also called "Southern Oscillation", pressure is higher near and to the east of Tahiti than farther to the west near

Darwin. The east-west pressure difference along the equator causes the surface air to flow westward. When the atmosphere switches into the low index phase, barometers rise in the west and fall in the east, signaling a reduction, or even a reversal the pressure difference between Darwin and Tahiti. The flattening of the seesaw causes the easterly surface winds to weaken and retreat eastward.

The "low index" phase is usually accompanied by El Nino conditions.

The easterly winds along the equator and the southeasternly winds that blow along the Peru and Ecuador coasts both tend to drag the surface water along with them. The Earth's rotation then deflects the resulting surface currents toward the right (northward) in the...

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...rface water. In the presence of sunlight, phytoplankton can produce chlorophyll, a tiny green plant substance. In turn, this substance feeds zooplankton, which in turn feeds higher members of the food chain. During El Nino conditions, the water level rises in the east and lowers in the west, forcing many changes to happen among the plant and animal life. Sea birds in the east must leave their nests, abandoning their young and searching for food which is not there, because the critical upwelling which causes the plankton and other lower members of the food chain to be produced is not there. Water temperature is above normal, and tropical fish are displaced poleward or migrate, along with the anchovy and sardines. On land, the effects produced a great amount of rainfall, making the desert lands into a grassland with lush vegetation and abundant life. Grasshoppers come, fueling toad and bird populations, and the increase in rainfall produces lakes which fish come to inhabit, fish that had migrated upstream during floods produced by the rain and become somehow trapped. In some flooded coastal cities, shrimp production set records. So too did the number of mosquito-borne malaria cases.