Downdrafts as Linkages in Dynamic Cumulus Seeding Effects

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  • 1 Laboratory for Atmospheric Sciences (GLAS), Goddard Space Flight Center, NASA, Greenbelt, MD 20771
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Abstract

Downdrafts are postulated as a primary linkage dynamically seeded invigorated cloud towers and those events near and below cloud bases which cause enhanced inflow, new tower growth leading to cloud expansion, and frequent merger with neighboring clouds. Evidence is taken from two series of seeding experiments on relatively isolated cumuli in the tropics and subtropics, and combined with evidence derived from observational material on downdrafts collected since the late 1960's. Because all the events discussed can occur naturally, postulates concerning the effects of the seeding and their detection are proposed. It is suggested how acceleration of the cloud tops invigorated by seeding can lead to enhanced dynamic entrainment, increased evaporation, and hence to more rapidly formed and stronger downdrafts than would be the case without seeding. Supporting model results on natural clouds are cited.

Abstract

Downdrafts are postulated as a primary linkage dynamically seeded invigorated cloud towers and those events near and below cloud bases which cause enhanced inflow, new tower growth leading to cloud expansion, and frequent merger with neighboring clouds. Evidence is taken from two series of seeding experiments on relatively isolated cumuli in the tropics and subtropics, and combined with evidence derived from observational material on downdrafts collected since the late 1960's. Because all the events discussed can occur naturally, postulates concerning the effects of the seeding and their detection are proposed. It is suggested how acceleration of the cloud tops invigorated by seeding can lead to enhanced dynamic entrainment, increased evaporation, and hence to more rapidly formed and stronger downdrafts than would be the case without seeding. Supporting model results on natural clouds are cited.

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