Investigation of Optimal Design for Supercooled Cloud Dispersal Equipment and Techniques

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  • a Technical Operations Research Inc., Burlington, Mass.
  • | b Air Force Cambridge Research work Laboratories, Bedford, Mass.
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Abstract

To determine optimal cloud-seeding techniques and optimal design specifications for a dry-ice seeding machine (the Cloudbuster), multiple strip seeding of stratiform decks was performed during which seeding rate, pellet size, and strip orientation with respect to wind were systematically changed from strip to strip. Concurrently, the physical properties of the cloud decks were measured and cloud response (i.e., hole size, growth rate, etc.) to the varying treatments was measured photogrammetrically. Results showed that both the dry-ice seeding rate and pellet size, as well as the cloud temperature, exerted a strong influence on cloud response. Seeding rate had an optimum of 8 to 9 lb per nautical mile of CO2 pellets whereafter additional quantities failed to produce consistently any increase in response. Generally, clouds failed to respond to treatment at 1.9 lb per n mi. A minimum recommended quantity of CO2 pellets is 4 lb per n mi using a 1 × 1 × 1-cm pellet of 0.6 gm cm−3 density. This CO2 pellet has a fall distance of 1200 ft. When combined with other machine functions, this seeding rate and pellet size allow an output of 10,500 pellets per n mi. Cloud response approximately doubles between −5 and −11C. A response failure point exists between −3 and −4C. Strips should be seeded across the wind. Seeding altitude for the aircraft should be coincident with the top of the deck for all but thickest decks (>1200 ft). For thick decks, penetration into the top one-half to one-third of the cloud decks is recommended as well as enlargement of the seeded zone by a second seeding along the perimeter of the expanding ice crystal zone.

Abstract

To determine optimal cloud-seeding techniques and optimal design specifications for a dry-ice seeding machine (the Cloudbuster), multiple strip seeding of stratiform decks was performed during which seeding rate, pellet size, and strip orientation with respect to wind were systematically changed from strip to strip. Concurrently, the physical properties of the cloud decks were measured and cloud response (i.e., hole size, growth rate, etc.) to the varying treatments was measured photogrammetrically. Results showed that both the dry-ice seeding rate and pellet size, as well as the cloud temperature, exerted a strong influence on cloud response. Seeding rate had an optimum of 8 to 9 lb per nautical mile of CO2 pellets whereafter additional quantities failed to produce consistently any increase in response. Generally, clouds failed to respond to treatment at 1.9 lb per n mi. A minimum recommended quantity of CO2 pellets is 4 lb per n mi using a 1 × 1 × 1-cm pellet of 0.6 gm cm−3 density. This CO2 pellet has a fall distance of 1200 ft. When combined with other machine functions, this seeding rate and pellet size allow an output of 10,500 pellets per n mi. Cloud response approximately doubles between −5 and −11C. A response failure point exists between −3 and −4C. Strips should be seeded across the wind. Seeding altitude for the aircraft should be coincident with the top of the deck for all but thickest decks (>1200 ft). For thick decks, penetration into the top one-half to one-third of the cloud decks is recommended as well as enlargement of the seeded zone by a second seeding along the perimeter of the expanding ice crystal zone.

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