I had posted the other night about the first serious effort at weather modification, Project Cirrus. Despite the termination of Project Cirrus in 1952 due to a stalemate on the validity of the data between the project scientists and the US Weather Bureau, efforts at weather modification didn't quite end. The chief scientist of Project Cirrus, had many adherents in the aviation and meteorology disciplines willing to continue his work. During the mid-1950s, a series of destructive hurricanes hit the United States. During the 1954 Atlantic hurricane season, Hurricanes Carol and Edna both hit New England and Hurricane Hazel left a path of destruction from Haiti to as far north as Toronto, Canada. Several other storms followed in the few years following, but none were as destructive as the three storms of the 1954 season.
Irving Langmuir's work with Project Cirrus was resurrected in 1962 when leaders in Washington launched Project Stormfury with the cooperation of the US Navy and the US Department of Commerce (the cabinet department that the US Weather Bureau belonged to). This time, however, with memories fresh of the 1954 hurricane season, the mission would be to send aircraft deep into hurricanes to seed them with hopes of weakening their destructive forces. Project Stormfury missions were some of the most dangerous yet- aircraft like the hurricane hunting Douglas DC-6s of the US Weather Bureau and US Navy Lockheed WC-121 Warning Stars (later WP-3A Orions) were sent into the fiercest part of the hurricanes, the eyewall, in hopes that cloud seeding would weaken the hurricane. Various support aircraft flew on the periphery and even above the storms. Government scientists flew on the Stormfury missions as well to gather data on the internal dynamics of the hurricanes. At the peak of Project Stormfury in 1969, over $2 million was being spent a year on the missions, a hefty sum in those days for a project that still sat on dubious scientific ground.
Scientists had developed 130-pound bombs that contained silver iodide crystals to seed lower altitudes from safer altitudes higher up. Special silver iodide flares were developed that burned for over 30 seconds as they fell through the clouds. Many of Stormfury's scientists were convinced that concentrating the seeding on the eyewall would result in the energy being expended as rain. The tighter the eyewall, the stronger the winds. By flying around the eyewall at certain altitudes, the seeding methods would dissipate the eyewalls clouds as they released their moisture as rain. If they could "loosen" the eyewall as much as 10 miles outward, that corresponded with a significant decrease in the storm's destructive power.
Because of the size of hurricanes, the seeding missions often required approximately 10 aircraft flying laps around the eye within the turbulent eyewall. Radar was used not only to guide the aircraft day or night in the eyewall, but also to assist with coordination and station keeping as the seeding drops by all the aircraft had to be coordinated. It seemed the the seeding operations were working- the eyewalls of the storms "attacked" appeared to widen and the storms would drop in intensity. But keep in mind that these Stormfury flights were also gathering data on the internal dynamics of the hurricanes as well.
As the data was compiled, seeding came under closer scrutiny. Pilots before each mission were randomly given one of two envelopes- one that ordered them to seed the eyewall and one that had them fly the mission, but to not seed the storm. The blinded experiments set up by the US Weather Bureau showed that the Stormfury scientists weren't able to reliably determine if the storm had been seeded or not. In the early 1970s, the Atlantic hurricane season was unusually quiet and not enough storms developed within range of Florida for seeding experiments to be conducted. Once the hurricane seasons intensified again, political pressure prevented Stormfury missions from being flown again. Some of this was the post-Vietnam era environment of budget austerity; some of it was pressure from politicians from states like Florida that feared getting struck by a storm that had been modified and had inadvertantly gotten stronger. Stormfury's scientists then tried to get the missions flown in the Pacific, but the governments of China, Japan, and Australia were very explicit that they didn't want weather modification experiments in their part of the world.
The final nail in the coffin of Project Stormfury came in 1983 when several scientists, some of which were Stormfury participants, wrote a scientific analysis that showed that hurricane eyewalls cyclically weaken and intensify on their own, what we today call the "eyewall regeneration cycle" or ERC. In addition, their work also showed that the necessary ingredient for successful seeding, supercooled water, was several orders of magnitude less than what Project Stormfury's scientists had assumed. In their review of 21 years of seeding missions and the data collected, not a single storm had been conclusively disrupted and any decreases in strength were likely part of the observed eyewall regeneration cycle. That year, the Department of Commerce canceled Project Stormfury for good.
All wasn't lost, though. All those missions into hurricanes in the 21 years of Project Stormfury generated reams of data that gave meteorologists insights into the dynamics and mechanisms of hurricanes that improved weather forecasting. The data might otherwise not have been collected at the rate it was were it not for the intensity of the Stormfury missions that not only carried silver iodide, but also scientists and data-gathering equipment. Today, despite the fact that the US population on the Gulf and Atlantic Coasts has exploded exponentially, the risk of dying from a hurricane is less than 1% of what it was in 1900.
Source: Air & Space Smithsonian, July 2010, Vol. 25, No. 2. "Climate Control: Irving Langmuir tried to change the world one storm at a time" by Sam Kean, p55-57.