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 Effects of El Niņo around the world,
also known as Teleconnections.
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.