|
<br />Stith, J. L., A. G. Detwiler, R. F. Reinking, and P. L. Smith, 1990: Investigating transport, mixing, and the
<br />formation of ice in cumuli with gaseous tracer techniques. Atmospheric Research, 25:195-216.
<br />
<br />Applications of tracer techniques using insoluble sulfur hexafluoride (SF6) to studies: of transport,
<br />mixing, and the activation of silver iodide (AgI) aerosols in cumuli are presented. One cumulus was
<br />treated with SF6 and aerosol near the cloud top (-13.50C), in a region of little vertical transport. Up to
<br />24% of the potential nuclei produced measurable ice particles 7 min after treatment, in accord with the
<br />results of recent laboratory measurements of activation of this aerosol by contact nucleation. A second
<br />cumulus was treated at the cloud base with SF6 and the aerosol. The materials were transported to and
<br />mixed through the upper regions of the cloud. Ice particles evidently formed near the cloud top
<br />(estimated cloud top temperature -13oC). Only low concentrations of natural ice were found in
<br />untreated regions of the cloud. In the treated regions, the ice particle concentrations in the cold, upper
<br />part of the cloud and in downdrafts at lower levels were consistent with the concentrations of AgI nuclei
<br />estimated from the tracer measurements. At lower levels of the cloud, the materials were not so well
<br />mixed, the most concentrated regions being found on the upshear side of the cloud and dilute regions
<br />downshear. Mid- and upper-level ice concentrations were greatest in downdrafts on the downshear side,
<br />suggesting that the downdraft was important in transporting the ice to lower levels of the cloud.
<br />
<br />Stith, J. L., and M. K. Politovich, 1989: Observations of the effects of entrainment and mixing on the droplet
<br />size spectra in a small,cumulus. Journal of the Atmospheric Sciences, 46:908-919.
<br />
<br />Sulfur hexafluoride was released at the base of a small, nonprecipitating, wann cumulus to study cloud
<br />mixing and entrainment processes. The tracer gas traveled to the top of the cloud where, during a
<br />2.5 min period, it had mixed to produce a dilute mixture containing 30%, 19%, and 51% of air from the
<br />original tracer region, an adjacent region of the same cloud, and the environment sUlTounwng the cloud,
<br />respectively. The droplet size distributions measured at the top of the cloud represented a mixture of
<br />larger droplets that had been growing from the base and smaller, recently activated droplets. The
<br />observations suggest that the source region for the small droplets was near cloud top. The large droplet
<br />concentration was conserved during the mixing process. These observations are compared with
<br />predictions from some recent models for cloud entrainment and droplet evolution.
<br />
<br />Stith, J. L., M. Politovich, R. Reinking, A. Detwiler, and P. Smith, 1988: Investigating mixing and the activation
<br />of ice with gaseous tracer aerosols. Preprints, 10th International Cloud Physics Conference,
<br />IAMAP/lUGG, Bad Homberg, F.R.G., August 15-20, 1988. Annalen der Meteorologie, No. 25,
<br />ISBN 3-88148-240-7, ll:588-590.
<br />
<br />No abstract.
<br />
<br />Stith, J. L., and R. L. Benner, 1987: Applications of fast response SF6 analyzers to in situ cloud studies.
<br />Journal of Atmospheric and Oceanic Technology, 4:599-612.
<br />
<br />The airborne applications of two recently developed analyzers for sulfur hexafluoride (SF6) to
<br />investigations of cloud top mixing and cloud seeding are described. The analyzers were developed
<br />by AeroVironment (A V) and by Washington State University (WSU). Both analyzers were capable
<br />of detecting cumulus-scale plume features. The more elaborate flow control mechanism in the
<br />A V analyzer was helpful in reducing the effects of altitude on the instrument response, while the faster
<br />response and lower baseline noise level of the WSU analyzer were necessary to detect many plume
<br />features.
<br />
<br />75
<br />
|