El Nino early warning sign

Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 22 February 2010

Weather experts say they have a tip that could give up to 14 months’ warning before the onset of an El Nino, the weather anomaly that whacks countries around the Pacific and affects southern Africa and even Europe.

El Niño is marked by warmer water in the central and eastern Pacific Ocean around the equator, shown in red and yellow on this false-color satellite image.

At present, scientists are unable to give little more than a few months’ notice that an El Nino is in the offing, which is often too late for farmers, fishermen and others to prepare for weather disruption.

El Nino occurs every two to seven years, when the trade winds that circulate surface water in the tropical Pacific start to weaken. A mass of warm water builds in the western Pacific and eventually rides over to the eastern side of the ocean.

The outcome is a major shift in rainfall, bringing floods and mudslides to usually arid countries in western south America and drought in the western Pacific, as well as a change in nutrient-rich ocean currents that lure fish. El Nino is ushered out by a cold phase, La Nina, which usually occurs the following year.

Meteorologists led by Takeshi Izumo of the Research Institute for Global Change in Yokohama, Japan, believe the world can gain a precious early warning from a similar event that occurs in the Indian Ocean. This oscillation, first identified in 1999, occurs roughly every two years.

Analysis of weather records from 1981 to 2009 found that when the so-called Indian Ocean Dipole was in a “negative” phase — with the waters warm in the west and cold in the east — an El Nino event in Pacific followed more than a year later. The driver for this pendulum appears to be a pattern in atmospheric circulation linking the two oceans, Izumo believes. The paper is published online on Sunday by the journal Nature Geoscience.

In a commentary, Peter Webster and Carlos Hoyos, earth scientists at the Georgia Institute of Technology, Atlanta, said that work was needed to delve into the past. The 1981-2009 period did indeed show a “strong two-year rhythm” in which the Dipole swung along with El Nino.

Other research, based on sea temperatures from 1890-2008, suggests the Indian Ocean pendulum may vary from decade to decade, the pair cautioned.

Source: The Citizen

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