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CLOUD BASE HYGROSCOPIC SEEDING (estratto da Weather modification - Final Report) http://www.tanker-enemy.com/PDF/Weather-modification-Final-Report.pdf 14.4.2 Hygroscopic treatment While glaciogenic seeding is designed to accelerate the cold-cloud precipitation formation process by initiating ice development sooner than it would otherwise naturally occur, hygroscopic seeding has an entirely different objective. Maritime clouds contain relatively large cloud droplets, which with time grow to precipitation sizes through collision and coalescence. However, if the cloud is continental, there will be many, many, more droplets, but they will all be very small. Continental clouds that do not grow tall and cold enough to result in ice formation naturally are destined to collapse without producing any precipitation, for their very small droplets are not suitable for the development of precipitation through collision and coalescence. However, if the sizes of the cloud droplets in such clouds are increased, the cloud character is made more maritime, and the cloud as a whole thus becomes much more conducive to precipitation development by collision and coalescence (e.g. Mather et al., 1996). Cloud droplets first form as moist air rises and cools, eventually reaching an altitude where a brief supersaturation occurs. It is at this critical location and time that the cloud character (maritime or continental) is established, depending upon the available natural aerosols, specifically, the natural cloud condensation nuclei. If the cloud is to be modified by changing this initial character, treatment must occur at cloud base, with agents that will encourage the formation oflarge cloud droplets. Such agents, which attract water, are said to be hygroscopic. Hygroscopic treatment of continental clouds is best done through the use of special pyrotechnics comprised of simple salts (and oxidants, to produce a combustible mixture). Typically, such flares are about 1 kilogram mass, and comprised largely of calcium chloride (CaCl) or potassium chloride (KCl). Flares of these characteristics have been manufactured in France, and more recently in North Dakota. Typically, one flare is burned in updraft beneath each targeted turret. Because the flares are considerably more massive than other conventional bum-in-place flares, not all flare racks are suitable for their use. If full racks are to be carried, reinforcement and/or redesign may be necessary. While there is great potential for hygroscopic treatment of continental clouds, hygroscopic treatment is initially proposed only on an experimental basis, to determine when and where such treatment will prove most effective. 14.6 Hygroscopic Pyrotechnics and Sprays If hygroscopic seeding is to be conducted, pyrotechnics are by far the most cost-effective way to do it, although Rosenfeld and Woodley (personal communication, 2001) are now arguing that hygroscopic seeding with a brine spray may prove to be more effective. 14.7 Seeding Equipment Seeding equipment is available from several sources. Outwardly, the physical appearance varies little, and operating principles are the same, regardless of source. The primary concerns are of course functionality and reliability. Whether leasing or purchasing the equipment, the provider ought to be willing to provide assurances that, if properly maintained, it will perform dependably. Recently, some equipment manufacturers have redesigned some of the older "industry standard" equipment, so Figure 27. A wing rack of twelve 1 kg (1,000 g) yield hygroscopic cloud seeding flares. Each cloud turret is treated with a single flare, burned in updraft below cloud base. 14.7.1 Wing-tip generators Wing-tip ice nuclei generators are built in two forms. One, a design pioneered by Ora Lohse, uses ram air to pressurize the generator and force the seeding solution from the generator tank into the combustion chamber. Flow rates vary depending upon air speed. This generator, in a radically redesigned form, is presently only used in North Dakota. The second, more common design, uses a pressurized air tank to induce flow of the seeding agent. This design, credited to William Carley, is used widely for cloud base seeding operations. Though some care and preventive maintenance is required, the wing tip generator is a very costeffective means of treating convective cloud from below cloud base (Boe and DeMott 1999). Wing-tip generators are well suited to rainfall enhancement work, as they burn the seeding agent more slowly than pyrotechnics, typically releasing 2-3 grams per minute continuously over long periods, at relatively low cost. If well maintained, the wing-tip generators can be reliably turned on and off repeatedly during long missions. Help us caption & translate this video! https://amara.org/v/fIaW/ ... https://www.youtube.com/watch?v=6zKYZ2cnfJ0