Cloud Microphysical Observations of Relevance to the Texas Cold-Cloud Conceptual Seeding Model

Daniel Rosenfeld, William L Woodley

Abstract


Three pairs of seeded and non-seeded supercoled convective clouds, obtained in west Texas during August 1995, are studied because of their relevance to the cold-cloud conceptual seeding model that is guiding randomized seeding experimentation in this region. In comparing seeded and non-seeded clouds without supercooled rain drops on the initial pass, seeding appeared to result in: 1) graupel growth that was too slow to convert cloud water into precipitable size particles during the lifetime of the updraft, except for the most vigorous and vertically developed clouds, 2) a glaciation rate that was too slow for enhancement of the updraft and 3) glaciation during the collapse of the cloud which accelerated its dissipation, leaving holes in the cloud field.  In contrast, in clouds with supecooled rain drops on the initial pass, seeding appeared to result in: 1) fast freezing of the supercooled rain drops and their continued growth as graupel, 2) enhanced growth of the grapuel as comared to supercooled rain drops in accordance with theoretical considerations and 3) rapid glaciation within the updraft, which increased cloud buoyancy and invigorated the updraft, providing a mechanism for the support of the growing graupel particles.  Considering the small sample, these results are tentative.  This research effort is continuing.

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