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Linking El Niņo with Other Places
Teleconnections means that weather changes at one location might be related to weather changes at other remote locations. People have been fascinated since at least the latter part of the nineteenth century by the prospect of identifying linkages among weather changes in various parts of the globe.
The relationship between El Niņo events and climatic variations in the Equatorial Pacific region is extremely strong and well-documented. The relationship outside this area is harder to prove. Weather anomalies occur all over the globe every year, but some do tend to recur with most or all El Nino events and are referred to as teleconnections. The Pacific weather system covers about 25% of the world's surface area, therefore it shouldn't be surprising that this system can affect weather in all parts of the world.
The first investigations of El Niņo teleconnections were carried out after the strong El Niņo of 1957. One result was the development of a model of the Equatorial atmosphere, comprising three major convective cells over the Pacific, Indian, and Atlantic Ocean. In each, warm moist air - characterized by clouds and rain - rises to a height of about 12 km, cools, and then lowers as cold, dry air. These "Walker Cells", named after the father of El Niņo - Sir Gilbert Walker, are the engines of atmoshperic circulation. Normally, the rising currents of warm air in the cells are situated over Indonesia, Africa, and the Amazon; the cold, dry air descends over the Pacific, Indian, and Atlantic Oceas, as shown in the figure on right.
During an El Niņo, as in 1982-83, the low-pressure zone over Indonesia and its associated warm, moist air move eastwards over the mid-Pacific. The patterns of Walker Cells are then greatly changed, as shown in this second figure. Becuase this warm air has moved to the east of its usual position, the cold, dry air that usually descends over the Pacific, Indian, and Atlantic Oceans is also moved further east than normal, and falls over Australia and Africa. This grealy alters global rainfall patterns because cold, dry air - associated with low rainfall - has replaced warm, moist air formerly centered over Australia/Indonesia and Africa. This would account for the droughts that occurred in Africa and Australia at the same time as the 1982-83 El Niņo. These movements in the location of the Walker cells can also be used to explain why other areas received exceptionally high rainfall during El Niņo events.
Recent studies have confirmed that ther are correlations in many othe areas of the world between changes in rainfall and El Niņo events. Correlations are strong in the following areas: the central Pacific and the south-east of South America have above-average rainfall during El Niņo months, as does Equatorial eastern Africa. Rainfall is well below average during El Niņo over Papua New Guinea, northern, eastern, and central Australia; north-eastern South America; and India and south-eastern Africa.
Clearly, the potential payoff to societies of research that identifies robust teleconnections far outweighs the costs associated with searching for them.