DENVER -- It sounds like a great idea: blast hurricanes like Rita and Katrina out of the sky before they cause damage, or at least weaken the storms and steer them away from cities.
Atmospheric scientists said it is wishful thinking that anyone could destroy or influence something as huge and powerful as a hurricane. They abandoned such a quest years ago after more than two decades of inconclusive government-sponsored research.
Private companies have conducted tests on a much smaller scale, but have made little progress despite initially claiming to erase storm clouds.
''It would be like trying to move a car with a pea shooter," said hydrometeorologist Matthew Kelsch of the National Center for Atmospheric Research in Boulder. ''The amount of energy involved in a hurricane is far greater that anything we're going to impart to it."
The federal government's hurricane-modification program was called Project Stormfury. The idea was raised during the Eisenhower administration after several major storms hit the East Coast in the mid-1950s, killing 749 people and causing billions in damages.
But it was not until 1961 that initial tests were conducted on Hurricane Esther; a Navy plane released silver iodide crystals. Some reports indicate winds were reduced by 10 percent to 30 percent.
During Stormfury, scientists also seeded hurricanes in 1963, 1969, and 1971 over the open Atlantic Ocean.
Researchers dropped silver iodide, a substance that serves as an effective ice nucleus, into clouds just outside the hurricane's eyewall. The theory was that a new ring of clouds would form around the artificial ice nucleus. The new clouds were supposed to change rain patterns and form a new eyewall that would collapse the old one. The reformed hurricane would spin more slowly and be less dangerous.
The experiments appeared to work sometimes. In 1969 several aircraft seeded Hurricane Debbie twice over four days. Researchers noted that its intensity changed by up to 30 percent.
For seeding to be successful, clouds must contain sufficient supercooled water that is still liquid even though it is below 32 degrees.
But scientists also learned that hurricanes contain less supercooled water than other storm clouds, so seeding was unreliable. And, hurricanes grow and dissipate all on their own, even forming new walls of clouds called ''concentric eyewall circles."
Project Stormfury was abandoned in the 1980s after hundreds of millions of dollars were spent.
Other storm-modification methods that have been suggested include cooling the tropical ocean with icebergs and spreading particles or films over the ocean surface to inhibit storms from evaporating heat from the sea.
Occasionally, somebody suggests detonating a nuclear weapon to shatter a storm. Researchers said hurricanes would dwarf such measures. According to the center for atmospheric research, the heat energy released by a hurricane equals 50 to 200 trillion watts, about the same energy released by exploding a 10-megaton nuclear bomb every 20 minutes.