A La Nina event recurs every three to five years; the last one occurred in 2000-2001 and was a weak episode.

Our Bureau

Thiruvananthapuram, Feb. 10

THE latest update from the Australian Bureau of Meteorology (BoM) indicates that climate patterns in the Pacific evolving during January and February have continued to support a likely La Nina event in early 2006.

The Climate Prediction Centre of the National Oceanographic and Atmospheric Administration (NOAA) of the US had earlier last week announced the "official return" of La Nina.

A condition characterised by cooler than normal sea surface temperatures (SSTs) across much of the equatorial and central Pacific, La Nina is the reverse of El Nino. It has been known to generate higher than average precipitation in Australia, India and Indonesia.

Sea surface temperatures have continued to cool during January, with cooler than average conditions extending further west to cover much of the equatorial Pacific.

Recent weeks have seen a slight intensification of these cool temperatures. A La Nina event recurs about every three to five years. The last one occurred in 2000-2001 and was a weak episode.

According to the BoM, should the current conditions over the eastern and central equatorial Pacific persist for another three months, it will be an official La Nina event. Subsurface waters in the eastern equatorial Pacific are particularly cool, but surface temperatures are only bordering on La Nina thresholds.

The prolonged period of decreased cloudiness is in keeping with the cooling trend observed in ocean temperatures, and is similar to that expected in a weak to moderate La Nina.

Another strong indicator was the value of the Southern Oscillation Index (SIO), which was above +10.

The SOI is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

Sustained negative values of the SOI often indicate El Nino episodes.

But positive values are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia signifying a typical La Nina event.

All computer models predict neutral eastern Pacific conditions in June 2006, though five predict weak La Nina conditions over the next few months.

(This article was published in the Business Line print edition dated February 11, 2006)
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