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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />ABSTRACT OF DISSERTATION <br />PHYSICAL STRUCTURE OF NORTHERN COLORADO RIVER BASIN CLOUD SYSTEMS <br /> <br />This paper describes the physical structure and temporal evolution <br /> <br />of wintertime cloud systems over the Yampa River Basin, one of the eight <br />major subbasins supplying water to the Colorado River. The primary pur- <br />pose of this work was to provide a firm foundation for the evaluation of <br />precipitation augmentation potential of these cloud systems. The infor- <br />mation presented in this paper is based on data collected during two <br />wintertime field programs conducted near Colorado's Park Range. Data <br /> <br />from a wide variety of cloud systems were analyzed to determine the tem- <br /> <br />poral variation. physical distribution. and microphysical structure of <br /> <br />supercooled liquid water. Ice phase characteristics were studied in- <br /> <br />cluding crystal concentrations and habits. nucleation. secondary ice <br /> <br />particle production. and growth by deposition. accretion and aggrega- <br /> <br />tion. The following are the major conclusions of this analysis: <br /> <br />(1) The shallow orographic cloud system with cloud top temperature warm- <br /> <br />. <br /> <br />er than about -200C was identified as the system with the largest poten- <br />tial for precipitation augmentation. This type of cloud system was <br />found to have persistent and significant liquid water contents in three <br />regions: (1) near cloud top. (2) between cloud base and approximately <br /> <br /> <br />the -120C level. and (3) in regions of strong orographic forcing. Nu- <br /> <br /> <br />cleation observed near cloud top occurred by the condensation-freezing <br /> <br /> <br />mechanism upwind of the mountain crest. The primary habits of crystals <br /> <br />iii <br />