Snuffing Out Nascent Hurricanes

Cloud physicists had continued to uncover the mechanisms for cloud development and precipitation during the 1950s. Some of those advancements had been crucial to the further understanding of hurricane development and behavior. Others had been critical to the development of more sophisticated weather modification techniques. Progress in all of these areas merged in a joint Department of Commerce, Environmental Science Services Administration, and U.S. Navy effort called Project STORMFURY. Its ultimate mission: to snuff out hurricanes.

The National Hurricane Research Laboratory had been studying hurricanes since 1956. Using aircraft, radar, and radiosondes to penetrate hurricane eyewalls, scientists had determined that these thick clouds contained a significant amount of supercooled water. Earlier cloud modification studies had shown that seeding such clouds could successfully produce rainfall. Scientists wanted to know whether seeding the supercooled eyewall clouds, the hurricane's primary energy cell, would modify the hurricane structure sufficiently to reduce its strength. In the meantime, cloud physicists at the Naval Ordnance Test Station in China Lake, California, had been experimenting with a new way to introduce silver iodide seeds into supercooled clouds. Their new technique introduced large quantities of subfreezing silver iodide nuclei into the tops of cumulus clouds extending thousands of feet into the atmosphere. This invention made hurricane modification experiments feasible.

Scientists intended to alter the balance of forces within a hurricane by seeding the eyewall clouds, precipitating the moisture, and causing the clouds to collapse. This would stop the "engine" and the storm would die. A preliminary test on Hurricane Esther (1961) caused part of the eyewall cloud to disappear. Although it re-formed within two hours, the test result was good enough to initiate STORMFURY, which, with National Science Foundation funding, was officially under way on July 30, 1962.

Led by the Weather Bureau's Dr. Robert H. Simpson (1912- ) and advised by a number of prominent meteorologists, STORMFURY participants conducted scientific experiments exploring the structure and dynamics of hurricanes. They wanted to understand better, predict, and possibly eliminate some of the destructive power of these storms. Using a new silver iodide generator, they fired small canisters packed with propellant from a navy aircraft. The canisters would fall 20,000 feet (6,100 m) through a cloud, producing a plume of silver iodide seeds for about 40 seconds. Additional navy planes took meteorological observations and photographs.

Without a good knowledge of hurricane behavior, scientists could not take a chance on seeding a hurricane that was close to populated areas. They outlined a target area in the Atlantic and waited for a hurricane to pass through so they could begin seeding. The first seedable hurricane was Hurricane Beulah in late August 1963. The silver iodide seeds missed the active eyewall on the first attempt, but the second created a pressure increase within the eye and the maximum wind zone moved away from the eyewall. (A hurricane's central pressure is always very low, so if it increases, the hurricane loses strength.) There was no proof that the seeding had caused either of these changes.

These results had raised researchers' hopes, but hurricanes failed to reach the target areas for the next four years. Turning their attention to improving seed delivery and developing numerical hurricane models, they discovered that seeding the first rainband outside the eyewall (as shown in the illustration on page 134) would be more effective than seeding the eyewall itself. The faster-moving air would be drawn away from the center, thus weakening the hurricane. The seeding teams finally had the opportunity to try this new technique in August 1969 on Hurricane Debbie. As expected, the winds died down—on one day by 31 percent and on another by 15 percent. One hurricane experiment does not provide proof. In subsequent years, researchers found themselves without appropriate hurricanes to seed.

There were other problems. Attempts to move STORMFURY to the Pacific Ocean, where there were more hurricanes, led to political disputes with surrounding countries, which declined to risk their populations to modified hurricanes. Aircraft were aging and the navy withdrew its support to fulfill higher-priority defense requirements. On the scientific side, the inability to replicate the experiments meant that researchers could not distinguish between the effects of seeding and naturally occurring hurricane behavior. Additional observations had exposed a fatal flaw in the project: The clouds contained far too many ice crystals and too few

By seeding the tropical cyclone before it grew to hurricane strength, STORMFURY meteorologists hoped to draw energy away from the circulating low-pressure center, causing it to dissipate.

DISSIPATING A HURRICANE

Seeding

Old eyewall weakens as new one grows

Old eyewall weakens as new one grows

New eyewall becomes dominant

© Infobase Publishing supercooled droplets. Once the underlying assumption for the experiments proved false, the rest of the project collapsed.

STORMFURY may not have been a success in hurricane modification, but it did lead to improved meteorological instrumentation and two decades of exciting and productive hurricane research that would improve hurricane forecasting. Considering the billions of dollars in damage that can be inflicted when a major hurricane strikes a heavily populated coast, the dream of snuffing out these dangerous systems will never really die. Scientists are now more realistic about their ability to influence the strength and path of Earth's largest storms.

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