ANALYSIS OF FLAGSTAFF DATA

The continuous particle collector proved capable of yielding quantitative droplet distribution data and qualitative information on larger hydrometeors. In the Flagstaff convective clouds the droplet concentrations were high, 600 to 2000 per cc near cloud base, and some correlation was noted versus upcurrent strength. Drizzle-size drops grew in the cloud cores by coalescence, starting from large droplets (substantially larger than the small-droplet population) which were present even at cloud base in concentrations of 20 per liter. A possible source of such large droplets is considered to be giant salt particles, perhaps augmented from a maritime condensation nuclei distribution by coalescence effects in previous clouds. The growth rate of droplets on such nuclei is calculated for several parcel ascent rates. Graupel was encountered regularly at -5 and -6C, mostly outside cell cores, suggesting the rapid freezing and rimming of the drizzle-size drops. The principles of cloud modification techniques are considered. They show that the transitory seeding methods used in 1962 and 1963 would not be expected to show large effects, and so techniques are suggested which consider diffusion effects and cloud seedability (especially buoyancy aspects). (Author) See also AD-627 147.