It sounds like a great idea: Let's just blast hurricanes like Rita and Katrina out of the sky before they hurt more people. Or, at least weaken the storms and steer them away from cities.

Atmospheric scientists say it's wishful thinking that we could destroy or even 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 (see article at right).

Private companies have conducted tests on a much smaller scale, but have made little progress despite initially claiming to erase storm clouds from the atmosphere.

"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 (see article at right). 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 wasn't until 1961 that initial tests were conducted on Hurricane Esther with a Navy plane releasing silver iodide crystals. Some reports indicate winds were reduced by 10 percent to 30 percent.

Hurricane Esther 1961

During Stormfury, scientists also seeded hurricanes in 1963, 1969 and 1971 over the open Atlantic Ocean far from land. Researchers dropped silver iodide, a substance that serves as an effective ice nuclei, into clouds just outside of the hurricane's eyewall. The idea was that a new ring of clouds would form around the artificial ice nuclei. 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.

Sometimes, the experiments appeared to work. Hurricane Debbie in 1969 was seeded twice over four days by several aircraft. Researchers noted that its intensity waxed and waned by up to 30 percent.  For cloud seeding to be successful, clouds must contain sufficient supercooled water that is still liquid even though it is below 32 degrees Fahrenheit (0 Celsius). Raindrops form when the artificial nuclei and the supercooled water combine.

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."  This made it impossible to determine whether storm reductions were the result of human intervention.

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 say hurricanes would dwarf such measures. For example, Hurricane Rita measures about 400 miles across. According to the center for atmospheric research, the heat energy released by a hurricane equals 50 to 200 trillion watts or about the same amount of energy released by exploding a 10-megaton nuclear bomb every 20 minutes.

source: CBS NEWS ©MMV The Associated Press.

Since a hurricane's destructive potential increases rapidly as its strongest winds become stronger, a reduction as small as 10% would have been worthwhile. Modification was attempted in four hurricanes on eight different days. On four of these days, the winds decreased by between 10 and 30%, The lack of response on the other days was interpreted to be the result of faulty execution of the seeding or of poorly selected subjects.

These promising results came into question in the mid-1980s because observations in unmodified hurricanes indicated:

1. That cloud seeding had little prospect of success because hurricanes contained too much natural ice and too little supercooled water.
    
2. That the positive results inferred from the seeding experiments in the 1960s stemmed from inability to discriminate between the expected results of human intervention and the natural behavior of hurricanes.

Project STORMFURY came to a formal end in 1982, as no hurricane modification experiments had been flown in over a decade, and as serious doubts about the assumptions of STORMFURY came to be expressed. In part the new cloud physics data showed that the amount of supercooled liquid water available in a hurricane was far less than had been thought, and studies of the natural cycles of storm strength showed that the effect of seeding might have been nugatory. NOAA's Hurricane Research Division's scientists published a paper in 1985 demonstrating many of the flaws in the original STORMFURY premises.