Effects similar to those of El Nino have been observed in the Indian and Atlantic Oceans
TILL recently, weather watchers knew of
only I weather-monster - the El Nino.
The Child Christ is a demon that disrupts the Pacific ocean, triggering
droughts and floods over large and farflung areas of the planet. But new clues
reveal that El Nino is not alone. There
are similar but lesser fiends that rule the
Indian and Atlantic Oceans (New
Scientist, Vol 146, No 1977).
Like El Nino, the new phenomena
have also been linked to the pattern of
rainfall over parts of the surrounding
continents. Meteorologists in Britain
and Australia are already using temperature variations - which trigger these
demons - to predict rainfall in
Australia and Brazil.
El Nino's lesser known cousins were
discovered thanks to the World
Meteorological Organization's recently
concluded marathon 10-year Tropical
Ocean Global Atmosphere (TOGA)
exper 'iment to monitor sea-surface temperatures. This study was supported by
another international effort, called the
World Ocean Circulation Experiment.
The new phenomena operate in the
manner of El Nino, but their impact is
less. When the El Nino whirls into
action, a warm pool surrounding eastern Indonesia undergoes a wintery
phase, reducing the difference in temperature between the pool and central
Pacific towards South America. This
weakens the trade winds, unleashing a
flood of warmer water eastwards across
the Pacific, bringing in its wake tropical
storms. These changes cause widespread
nuisance including drought in eastern
Australia and floods in Peru.
One of the newcomers, called the
Indian Ocean dipole, was first noticed in
the early '80s by meteorologists investigating the connection between surface
temperatures in the Indian Ocean and
rainfall across Australia's deserts.
Scientists took a decade to decipher its
nature.
The dipole is a twin system of a
warmer than average band of water
between northern Australia and Java
and an unusually cold band of water
running northwest into the Indian
Ocean from Australia's west coast.
The other newcomer operates from
the tropical Atlantic. Chris Folland and
colleagues at the British Meteorological
Office's Hadley Centre for Climate
Prediction and Research in Berkshire
have been monitoring changes in sea-
surface temperatures in this region.
They can now use these data to predict
the amount of rainfall in northeast
Brazil during the rainy season. But here
El Nino's influence must be reckoned
before venturing any predictions.
Folland says that tropical Atlantic
blows hot and cold between
January and May. When the
sea in the Southern tropics
becomes warmer than usual
and water to the north of the
equator cools, it rains cats and
dogs in northeast Brazil.
When the pattern is reversed,
the season is drier.
The links between these
temperature vicissitudes and
rainfall are still tenuous. To
get better handle on El Nino's
cousins, scientists will be
current looking at them more closely
under a 15-year study of climate's capricious nature.
Unlike the TOGA experiment, which was
set up chiefly to tease out the connections between the atmosphere and the
Pacific current, the new experiment will
train its guns on the 2 new members of
the climate underworld.
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