In the 1950's, when rocket methods of studying the upper atmosphere were just beginning to be developed, Soviet scientist I. S. Shklovskiy and English scientist D. R. Bates suggested the idea of creating an artificial luminous cloud.
They proposed discharging a small quantity of sodium vapor into the atmosphere by rockets, thinking that because of resonant emission, the sodium atoms illuminated by the sun should form a luminous cloud in the atmosphere which would be clearly visible from the Earth.
The idea of creating luminous clouds to study the physicochemical and dynamic processes in the upper atmosphere proved to be so intriguing that it was rapidly developed in many ro~ket experiments.
Project Foggy Cloud
Foggy Cloud I was a series of experiments in observation, modification, and treatment of fog and stratus clouds conducted at or near the Arcata-Eureka airport, Humboldt County, Calif., from late March through mid- November 1968. A wide range of propsective seeding agents, including smokes, liquids, and powders, that were thought to offer promise for stabilization or clearance of fog were systematically screened by ground-based and airborne dissemination. The major emphasis was placed upon the elimination of fog rather than upon simply improving visibility. Those agents showing enough identifiable effects to indicate promise were investigated in detail and improved upon. Observations were made of fog characteristics, visual effects, changes in cloud physics parameters, and of the fallout from the fog. Hygroscopic smokes were found useful for intensifying, stabilizing, and forming fog and stratus. Hygroscopic powders, including sodium chloride, urea, and calcium chloride, were tried. Of these, calcium chloride showed the most promise, but testing was not completed. Hygroscopic liquids showed the most immediate results, and successful tests were made with ammonium nitrate in solution. In October, a solution consisting of ammonium nitrate, urea, and water was developed that was used in several very successful field trials.
Project Gulf Q
Project Gulf Q was conducted 11 through 28 May 1969 at Brownsville, Tex. The objective was to study the modification of warm tropical cumulus clouds by seeding them with hygroscopic solutions that had exhibited considerable warm cloud modification potential. These solutions were sprayed from aircraft on all of the 16 tests completed during the project period. Effects attributable to this treatment were observed in all tests. When cloud growth occurred afterseeding, there were frequently marked increases in liquid water content and turbulence, especially in the upper half of the target cloud. On five tests the seeded clouds completely dissipated within 5 to10 minutes after treatment.