Zipser/Abstract ATM-9707301 In this project we will examine factores responsible for broadening the size distributions of cloud droplets in small cumulus clouds, with special attention to the roles of mixing and entrainment in that process. The main budget item is support for a graduate student, Richard Igau, who will work under the guidance of Drs. Ed Zipser of Texas A&M University and W. A. Cooper of the National Center or Atmospheric Research. The primary data source will be the Small Cumulus Microphysics Study (SCMS), a field program in Florida that used the NCAR CP2 dual-wavelength radar and three instrumented research aircraft. Many small cumulus clouds developed witin 10-20 km of this rdar during the project, and a good sample of these were studied by the three instrumented research aircraft. Conventional Forward Scattering Spectrometer Probes (FSSPs) and King liquid water probes were present on all aircraft, and in addition the Fast FSSP (FFSSP) of Brenguier et al. (1996), the Cloud Droplet Spectrometer (CDS) of Lawson and Cormack (1995), the Droplet Spaceing Monitor (DSM) of Baumgardner et al. (1993), and the PVM-100 liquid water content probe of Gerber et al. (1994) were all used in the SCMS. These new instruments provide much improved resolution in droplet size and in space, and so should help overcome the limitations of the standard FSSP which have compromised many past studies, and so should help overcome the limitatins of the standard FSSP which have compromised many past studies of droplet size distributions. In the course of this resesarch, we will assess ofthe characteristics and value of the new instruments for measuring droplet size distributions, will characterize typical droplet size distribuions in unmixed and mixed regions of cloud, and will compare the widths of these size distributions to theoretical predicitions. We will also study the entrainment and mixing process, as a topic in itself as well as for its influence on droplet size distributions. The new instruments should provide better characterization of droplet sizes than has been available to similiar studies in the past, and the goood simultaneous observations by a very sensitive radar should support better interpretation of the microphysical observations in terms of the life history and dynamics of the clouds. It should therefore be possible to test theoretical predictions critically, and so to develop an improveed understanding of how droplet size distributions develop in cumulus clouds.
