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<br />002 5 7 2 <br /> <br />the Colorado River Basin, data collection has been limited, but is <br />expected to increase as the project progresses. <br /> <br />During 1978, climatological summaries of cloud population character- <br />istics for Montana and Kansas H1PLEX sites for the 1976 and 1977 <br />seasons were completed. These show the number of clouds, their <br />sizes, and location of development. Intensive case studies of <br />convective complexes illustrate the importance of mesoscale triggering <br />effects on cloud development at HIPLEX sites. <br /> <br />CONTRACTOR: National Center for Atmospheric Research/National <br />Science Foundation, Boulder, Colorado <br />CONTRACT NO. 6-07-DR-20040 <br />PRINCIPAL INVESTIGATOR: Gerhart Langer <br />PERIOD: October 30, 1975, to September 30, 197B <br />FUNDING: FY76 - $ B,OOO <br />T.Q. - $ <br />FY77 " $33,900 <br />FY78 - $37,500 <br /> <br />The primary emphasis of the NCAR (National Center for Atmospheric <br />Research) H1PLEX studies was. placed on development of membrane <br />filters to increase knowledge of ice-forming nucleus populations over <br />selected sites. A major problem was to determine whether the present <br />membane-developing system could be modified to enable detection of <br />ice-nucleatin9 particles. Efforts were made to improve the Allee-type <br />cloud condensation nuclei counter, especially at low saturations, to <br />obtain accurate data on droplet concentration. An electrostatic <br />separator was improved to extend its operation to particles up to <br />0.5 ~m and to make the device portable. <br /> <br />An aerosol particle classifier was used to extend previous work on <br />the ice nucleation characteristics of different chemical compounds <br />including those capable of suppressing ice nucleation. A study of <br />aerosols from silver iodide flares was done with a mobility anaylzer <br />complemented by laboratory investigations of monodisperse fractions <br />of aerosols from small flare samples. Findings indicate that parti- <br />cles below 0.1 ~m do not exhibit activity at temperatures above <br />-10 'c. <br /> <br />Studies were initiated on the effectiveness of dry ice as a seeding <br />agent and the NCAR ice nuclei counter was operated routinely at warm <br />temperatures, such as -6 'C. Dry ice pieces were dropped through a <br />special tube into the cloud chamber, exposing them to the supercooled <br />cloud for a short time. Preliminary results indicate that the <br />number of ice crystals formed may depend on the concentration of <br />drop 1 et s. <br /> <br />111-23 <br />