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<br />2. Hygroscopic particle seeding leads to increased precipitation by producing <br />microphysical effects that improve the precipitation efficiency of warm and cold <br />convective clouds. No dynamic effects occur as a result of the exothermic or <br />endothermic nature of the hygroscopic chemicals. <br /> <br />3. Of the four hygroscopic chemicals investigated, seeding with dry CaCl2 (calcium <br />chloride) particles produces the largest seed/no-seed ratios. <br /> <br />4. For clouds with limited lifetime, the largest seedlno-seed ratios are achieved with 50- <br />micrometer-radius CaCl2 partides for both cloud base and near cloud top seeding. For <br />clouds of longer duration, the best results are achieved with smaller radius CaCl2 <br />particles: 30-micrometer-radius particles for cloud base seeding and 10-micrometer- <br />radius particles or less for cloud top seeding. Seeding with readily purchased size <br />distributions of CaCl2 results in smaller seed/no-seed ratios than seeding with <br />mono disperse particles; nevertheless, observable seedlno-seed ratios are achieved. <br /> <br />5. The seedlno-seed ratios for CaCl2 seeding increase with increasing seeding <br />concentration or dosage; however, logistical considerations will place an upper limit <br />on what is possible. <br /> <br />6. Cloud base seeding with CaCl2 produees larger seedlno-seed ratios than near cloud top <br />seeding. <br /> <br />7. Seeding with CaCl2 particles :is most effective when conducted early in the life of a <br />growing cloud (about 5 minutes after cloud formation), when the precipitation <br />initiation process can still be influenced. <br /> <br />8. Hygroscopic particle seeding can increase precipitation from both warm and cold <br />clouds. <br /> <br />9. Hygroscopic flares can increase precipitation from both warm and cold clouds, but <br />their effectiveness is highly dependent on the existing natural nuclei spectrum. <br /> <br />10. Warm cloud seeding with hygroscopie particles can produce seeding effects that result <br />in measurable increases in precipitation. <br /> <br />3.5 Implications of Model Seedling Results on the Design of the Warm Cloud <br />Seeding Demonstration Project <br /> <br />Combining the analyses of scientific feasibility (see appendix D) with considerations of <br />economic and logistical practicability leads to the following recommendations for the warm <br />cloud seeding demonstration project: <br /> <br />3.5.1 Seeding agent <br /> <br />Polydisperse CaCl2 particles as purchased if! recommended as the seeding agent. Storage and <br />handling procedures that prevent the degradation of the spectra should be instituted. <br />Monodisperse distributions are not recommended because the cost of acquiring and <br />maintaining such distributions is prohibitive. <br /> <br />25 <br />