Mobile anti-aircraft guns will be deployed to control hailstorms.

"Our experiments and research have shown that we can only artificially reduce the level of rainfall on a comparatively small scale," said Wang Yubin, deputy chief engineer of the Beijing Meteorological Bureau (BMB).

Planes and rockets will spread silver iodine and dry ice high into the air. These agents will act like catalysts, targeting rain-heavy cumulonimbus clouds and inducing rainfall before the clouds reach the Olympic venues.

Beijing plans to ramp up its climate control efforts this year, with officials hoping to control an area with a radius of 120 km of the National Stadium.

Analysis of weather records from 1971 to 2003 shows there is a 50 percent chance of rain souring the Games' opening ceremony next year in Beijing's Chaoyang District, where the 'Bird's Nest' is located.

But the weather rockets have a good chance of clearing the sky, according to BOCOG Executive Vice-President Jiang Xiaoyu. Half of the rainfall in the area over the last 30 years was light, and no heavy downpours have occurred there in the last decade, he said.

Standing at the forefront of scientific advances in artificial rain reduction, Beijing will deploy planes, rockets and other modern artillery to combat both rain and hail, said Wang, adding that the city conducted six experiments in this area last year. Three planes are already available and two more will arrive by July to join the exercises.

These are aimed at establishing three lines of defense around the Bird's Nest, with respective radiuses of 15-20 km, 45-60 km and 90-120 km, said Zhang Qiang, an official from the same bureau.

Beijing began working to improve the accuracy of its weather reports in 2002 and has been carrying out experiments since 2005 that have already met with a measure of success, said BMB Director Xie Pu.

However, a recent slip forced the bureau to issue a public apology on March 22 after three days of incorrect forecasts of up to 6.2 degrees Celsius that undermined confidence in its ability to provide accurate 'weather maps' for the 2008 Olympics.

In a bid to tighten its operations, the bureau has sent unmanned vehicles into the clouds over the last three summers to probe and collect first-hand data on what causes hailstorms and how to combat them. From mid-2005 to 2006 it successfully reduced rainfall three times using silver iodine, Xie added.

Meanwhile, meteorological departments will step up their monitoring and forecasting work so that people will be able to set their watch by the weather during the Games, Xie said. Warnings of high temperatures and storms will also be issued to local residents, visitors and athletes.

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