Date:31/03/2006 URL: http://www.thehindubusinessline.com/2006/03/31/stories/2006033102041900.htm

Back `Australian cyclones augur well for Indian monsoon'

Vinson Kurian

The prevailing scenario jells well with the weak La Nina conditions observed over the past few months. Weathermen see signs of good tidings ahead

Thiruvananthapuram , March 30

A string of severe tropical cyclones roaring their way in from the Indian Ocean may have ravaged the coast Down Under, but weather forecasters here say the busy Australian season is a harbinger of good tidings for the impending Indian monsoon.

"The cyclones rising from the warm pool of ocean water to this (western) side of the Pacific can only signal good tidings for the Indian monsoon," said Dr K.J. Ramesh of the National Centre for Medium Range Weather Forecasting (NCMRWF).

The latest in the series of cyclones to hit the Australian coast was Glenda, a Category Four storm packing winds of up to 250 km per hour, that slammed into a major oil and mining region on the west coast.

The prevailing scenario jells well with the weak La Nina conditions observed in the Equatorial East Pacific over the past few months, Dr Ramesh told Business Line. La Nina has traditionally been identified with successful Indian monsoon.

Weak La Nina

But the Australian Bureau of Meteorology said in its latest update that, "when all things considered, the current conditions across the Pacific are looking less like a La Nina than they were two months ago."

Surface temperatures patterns across the Pacific resemble a weak La Nina, although negative anomalies along the equator have not been sustained at La Nina intensity. They have been weakening recently and are now confined to a narrow band.

This is particularly the case with sea-surface temperatures, which have been warming along the equator, and trade winds, which are not nearly as strong as those seen in December and January.

Factors that are found supporting the case for a La Nina event are the raised value of the Southern Oscillation Index (SOI, at +14) and the strongly suppressed cloudiness around the dateline. Both these observations are consistent with a La Nina.

The term `Southern Oscillation' refers to the variability of the strength of the Walker Circulation system and is quantified through the SOI.

The Walker circulation is an east-west atmospheric circulation pattern characterised by rising air and heavy rains over the western Pacific and the sinking air above the eastern Pacific. During a La Nina event, the Walker circulation becomes especially strong.