TILL recently, weather watchers knew ofonly I weather-monster - the El Nino.The Child Christ is a demon that disrupts the Pacific ocean, triggeringdroughts and floods over large and farflung areas of the planet. But new cluesreveal that El Nino is not alone. Thereare similar but lesser fiends that rule theIndian and Atlantic Oceans (NewScientist, Vol 146, No 1977).
Like El Nino, the new phenomenahave also been linked to the pattern ofrainfall over parts of the surroundingcontinents. Meteorologists in Britainand Australia are already using temperature variations - which trigger thesedemons - to predict rainfall inAustralia and Brazil.
El Nino's lesser known cousins werediscovered thanks to the WorldMeteorological Organization's recentlyconcluded marathon 10-year TropicalOcean Global Atmosphere (TOGA)exper 'iment to monitor sea-surface temperatures. This study was supported byanother international effort, called theWorld Ocean Circulation Experiment.
The new phenomena operate in themanner of El Nino, but their impact isless. When the El Nino whirls intoaction, a warm pool surrounding eastern Indonesia undergoes a winteryphase, reducing the difference in temperature between the pool and centralPacific towards South America. Thisweakens the trade winds, unleashing aflood of warmer water eastwards acrossthe Pacific, bringing in its wake tropicalstorms. These changes cause widespreadnuisance including drought in easternAustralia and floods in Peru.
One of the newcomers, called theIndian Ocean dipole, was first noticed inthe early '80s by meteorologists investigating the connection between surfacetemperatures in the Indian Ocean andrainfall across Australia's deserts.Scientists took a decade to decipher itsnature.
The dipole is a twin system of awarmer than average band of waterbetween northern Australia and Javaand an unusually cold band of waterrunning northwest into the IndianOcean from Australia's west coast.
The other newcomer operates fromthe tropical Atlantic. Chris Folland andcolleagues at the British MeteorologicalOffice's Hadley Centre for ClimatePrediction and Research in Berkshirehave been monitoring changes in sea-surface temperatures in this region.
They can now use these data to predictthe amount of rainfall in northeastBrazil during the rainy season. But hereEl Nino's influence must be reckonedbefore venturing any predictions.Folland says that tropical Atlanticblows hot and cold betweenJanuary and May. When thesea in the Southern tropicsbecomes warmer than usualand water to the north of theequator cools, it rains cats anddogs in northeast Brazil.When the pattern is reversed,the season is drier.The links between thesetemperature vicissitudes andrainfall are still tenuous. Toget better handle on El Nino'scousins, scientists will becurrent looking at them more closelyunder a 15-year study of climate's capricious nature.Unlike the TOGA experiment, which wasset up chiefly to tease out the connections between the atmosphere and thePacific current, the new experiment willtrain its guns on the 2 new members ofthe climate underworld.