The Telegraph
Since 1st March, 1999
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Queen Jayalalithaa plays rain goddess in chopper chariots

Chennai, May 27: If the clouds are tight-fisted, trust Jayala-lithaa to try and squeeze the rain out of them.

Choppers are on standby in Chennai to take off at the sight of thick clouds, strafe them with silver iodide and see whether man can overtake the monsoon.

Cloud-seeding, a chemical-induced process that optimists believe can tease water out of rain-bearing clouds, has returned to the sweltering country after several years.

Unfazed by two unsuccessful trial runs last week, Tamil Nadu chief minister Jayalalithaa today said the state would press ahead with artificial rain-making in 15 sites in and around Chennai, which is going through an acute water shortage.

The gamble has been prompted by fears that the onset of the south-west monsoon could be delayed this year. The process is still considered a gamble as meteorologists in Pune had concluded after trials years ago that cloud-seeding was unviable.

Cloud-seeding is done in two phases. First, the atmospheric temperature is raised to the desired level using machines called ground generators. Then, silver iodide powder is fired into the clouds with blowers.

The rain falls when the silver iodide breaks down the moisture in the clouds into droplets of water. The chemical is preferred as it is not toxic.

In the Chennai trials, the blowers were placed on the top floor of a 10-storeyed building in the city centre. The government has now deployed a fleet of helicopters and a team for cloud-spotting. The experiment sites are spread over 60 km, covering the catchment areas of the three principal lakes that feed the Chennai reservoirs.

Science plays a central role in cloud-seeding, but so does nature. The experiment will work only in the right atmosphere: the clouds have to be thick, humidity has to be 70 per cent and the wind velocity less than 20 knots an hour. Scientists who took part in the two flop trials have blamed unsuitable atmospheric conditions.

Wind speed is crucial as it can blow the seeded clouds away, carrying the rain to an unintended target.

If the wind gathers speed in Tamil Naduís handpicked areas, Jayalalithaaís rain can fall in Chandrababu Naiduís Andhra Pradesh, where a killer drought is in full blast. The outer limit of the rain experimentís target area, Tiruttani, is 30 km from the Andhra temple town of Tirupati.

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