Robert Simpson

Stormfury Cumulus Seeding Experiment 1965: Statistical Analysis and Main Results

Abstract A randomized seeding experiment was carried out on 23 tropical oceanic cumulus clouds on 9 days in the summer of 1965 as part of the joint Navy-ESSA Project Stormfury. Following instructions in sealed envelopes, an aircraft seeded 14 of the clouds with 8-16 pyrotechnic silver iodide generators called Alecto units. Each unit releases about 1.2 kg of silver-iodide smoke. The nine remaining clouds were studied in an identical manner as controls, using the same stack of four instrumented aircraft to penetrate the cloud before and after the seeding run. Cloud growth was documented by aircraft, radar and photogrammetry. The seeded clouds grew vertically an average of 1.6 km more following the seeding run than did the control clouds; the difference is significant at the 0.01 level. A numerical model of cumulus dynamics was specified in advance of the field program. This model integrates the equation for the vertical acceleration of an entraining cumulus tower, predicting top heights of unseeded and seed...

Stormfury Cumulus Experiments: Preliminary Results 1965

Abstract This paper is a preliminary summary of results of a tropical cumulus seeding experiment. Individual supercooled cumuli were seeded by silver iodide pyrotechnics and studied before and after by radar, photography and multi-aircraft penetrations. The choice of “seeded” versus “control” cloud was made from sealed instructions opened on the seeding aircraft. Twenty-two cases were studied on nine days, with fifteen seeded and seven controls, largely in matched pairs. Two-thirds of the properly seeded clouds underwent marked vertical growth while six-sevenths of the controls did not. It is suggested that this and sequel experiments can delineate conditions under which seeding may have different effects upon clouds.