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<br />A midcloud injection of SF6 was followed as it mixed through the tops of a small cumulus cloud. The <br />tracer plume was fIrst detected upshear, then mixed through the cloud top region as the cloud top began <br />to collapse. <br /> <br />A plume of AgI cloud seeding agent mixed with SF6 was used to investigate the activation and growth <br />of ice particles in a stratocumulus cloud which was overseeded. The SF6 tracer and ice particle plumes <br />remained collocated during the 45-min sampling period, except for one region of ice particles which had <br />begun to separate from the SF6 26 min after the cloud was treated. The growth of ice was limited by <br />water vapor diffusion into the seeding plume. The measured tracer concentrations were used to estimate <br />the fraction of the seeding nuclei which had activated and grown to detectable sizes. A maximum <br />fraction of 54% was observed 17.5 min after seeding. <br /> <br />Several other applications for SF 6 tracer applications are recommended. <br /> <br />Stith, J. L., D. A. GriffIth, R. L. Rose, J. A. Flueck, J. R. Miller, Jr., and P. L. Smith, 1986: Aircraft <br />observations of transport and diffusion in cumulus clouds. Journal of Climate and Applied Meteorology, <br />25:1959-1970. <br /> <br />A gaseous tracer, sulfur hexafluoride, was used to follow the path of two different AgI cloud seeding <br />aerosols in cumulus clouds. The materials were released at cloud base or midlevels. Plumes sampled at <br />midlevels were found to be relatively narrow and embedded within updrafts or downdrafts; relatively <br />high concentrations of the tracer were observed in some downdrafts. Plumes with diameters comparable <br />to tte cloud diameters were found in the upper 20% of the clouds. These observations suggest only <br />limited dispersion of the plumes in the clouds, with greater mixing occurring at cloud top. Similar <br />behavior of the in-cloud plume is observed in results from a two-dimensional, numerical cloud model <br />used to simulate the introduction of seeding materials into convective clpuds. Observations of the <br />ice crystal production rates are consistent with the results of recent laboratory fIndings concerning the <br />properties of the seeding agents. The usefulness of this tracer technique in studying transport, diffusion, <br />and ice activation in cumulus clouds is discussed. <br /> <br />Stith, J. L., 1985: Following the path of cloud seeding agents in cumulus clouds'with a gaseous tracer. <br />Proceedings, 4th WMO ScientifIc Conference on Weather ModifIcation, A Joint WMO/lAMA? <br />Symposium, Honolulu, HI, August 12-14, 1985. World Meteorological Organization, Geneva, <br />WMOrrD-No. 53, 247-250. <br /> <br />No abstract. <br /> <br />Stith, J. L., 1983: Limitations to dynamic seeding of North Dakota summer clouds. Journal of Weather <br />Modification, 15(1):28-33. <br /> <br />During the summer of 1981, cumulus clouds in North Dakota were unlikely candidates for dynamic <br />seeding. Ice particle concentrations were well below l00/liter in feeder-type clouds associated <br />with seeded convective storms. Comparisons of aircraft measurements and the output from a one- <br />dimensional steady-state cloud model were also made. <br /> <br />Stone, R. H., and J. A. Warburton, 1989: The dispersion of silver iodide in mountainous target areas of the <br />western United States. Proceedings, 5th WMO ScientifIc Conference on Weather ModifIcation and <br />Applied Cloud Physics, Beijing, China, May 8-12, 1989. World Meteorological Organization, Geneva, <br />WMOrrD-No. 269, 1:167-169. <br /> <br />No abstract. <br /> <br />76 <br />