Project STORMFURY: A Scientific Chronicle 1962–1983

Abstract

Between 1962 and 1983, research in hurricane modification centered on an ambitious experimental program, Project STORMFURY. The proposed modification technique involved artificial stimulation of convection outside the eye wall through seeding with silver iodide. The artificially invigorated convection, it was argued, would compete with the convection in the original eye wall, lead to reformation of the eye wall at larger radius, and thus produce a decrease in the maximum wind. Since a hurricane's destructive potential increases rapidly as its maximum wind becomes 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 experiment or poorly selected subjects. These promising results have, however, come into question because recent observations of unmodified hurricanes indicate: 1) that cloud seeding has little prospect of success because hurricanes contain too much natural ice and too little supercooled water, and 2) that the positive results inferred from the seeding experiments in the 1960s probably stemmed from inability to discriminate between the expected effect of human intervention and the natural behavior of hurricanes.

The Zurich Ice Nucleation Chamber (ZINC)-A New Instrument to Investigate Atmospheric Ice Formation

“…While there is now a good understanding of particle properties that affect CCN activation, there is still a lack of understanding as to which intrinsic properties of aerosol particles determine their ice nucleation capabilities (Szyrmer and Zawadzki 1997;Cantrell and Heymsfield 2005). While ice nucleation was studied intensely in the 1970s in the scope of weather modification programs (Bruintjes 1999;Federer et al 1986;Willoughby et al 1985), contem-porary interest focuses more on the climate impact of natural and anthropogenic ice nuclei through the so-called aerosol indirect effect. The indirect effect traditionally refers to an increase in cloud droplets due to anthropogenic aerosols (Baker 1997).…”

Simulation of hurricane response to suppression of warm rain by sub-micron aerosols

“…1E) was addressed by glaciogenic cloud seeding. Hurricane mitigation was first attempted between 1962 and 1983 in the framework of project STORMFURY by the US government (Willoughby et al, 1985). The envisioned modification technique involved artificial stimulation of convection at the outer periphery of the eyewall through seeding of strong convective cloud towers with silver iodide for the purpose of freezing super-cooled water (water in liquid state but colder than 0 • C).…”

“…Although the maximum winds of some of the seeded TCs decreased, the change in hurricane intensity was attributed to natural intensity fluctuations rather than to seeding. The analysis of the microphysical structure of tropical convective (TC) clouds (Willoughby et al, 1985) showed that at the levels where seeding was applied there was too little supercooled water and a significant amount of cloud ice. Consequently, the glaciogenic seeding was not likely to affect cloud dynamics, at least in the way assumed in the STORMFURY conceptual model.…”

Hurricane Intensity and Eyewall Replacement

“…The cloud-seeding approach ultimately proved ineffective (3,4). Many strong, mature tropical cyclones exhibit a natural "eyewall replacement" process (5) in which a new (outer) eyewall takes over from the original (inner) eyewall, just as had been hypothesized-but with no cloud seeding taking place.…”