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<br />An expression for the aggregation efficiency was fomlUlated. The primary factors governing <br />aggregation appear to be the aggregation efficiency. the ice particle number concentration, and the mean <br />diameter. The expression may be useful in larger numerical cloud models. Mean aggregation rate <br />constants were detennined for sub- and superexponential spectra. and for exponential Spl::ctra. The mean <br />aggregation rate constant for superexponential spectra was approximately 50% greater than for <br />subexponential spectra. <br /> <br />Finally. it was found that the degree of subexponential behavior predicted when v '" I was consistent <br />with that observed in various levels in stratifonn clouds. However, better measurements are needed to <br />substantiate this finding. <br /> <br />Mitchell, D. L.. and R. D. Borys, 1991: A field instrument for examining in-cloud scavenging mechanisms by <br />snow. Proceedings, 5th International Conference on Precipitation Scavenging and Atmosphere-Surface <br />Exchange Processes. [Award-Winning Poster], Richland, W A, July 15-19, 1991. Electric Power <br />Research Institute, U.S. Department of Energy, U.S. Environmental Protection Agency, NOAA, <br />Washington, DC. <br /> <br />No abstract. <br /> <br />Mitchell. D. L., 1990: Evolution of snow-size spectra predicted by the growth processes of diffusion, <br />aggregation and riming. Preprints, Conference on Cloud Physics, San Francisco, CA, Jully 23-27, 1990. <br />American Meteorological Society. Boston. MA. 270-277. <br /> <br />No abstract. <br /> <br />Mitchell, D. L., 1990: Modeling of microphysical and radiative properties of cirrus clouds. Preprints. <br />7th Conference on Atmospheric Radiation. San Francisco, CA, July 23-27, 1990. American <br />Meteorological Society. Boston. MA, J96-J101. <br /> <br />No abstract. <br /> <br />Mitchell, D. L., R. Zhang, and R. L. Piner. 1990: Mass-dimensional relationships for ice particles and the <br />influence of riming on snowfall rates. Journal of Applied Meteorology, 29:153-163. <br /> <br />The masses, dimensions. and habits of over 2800 natwral ice particles precipitating from orographic <br />winter stonns in the central Sierra Nevada were obtained using photomicrographs. Ice particles that <br />could be unambiguously classified were used to generate empirical expressions relating snow particle <br />masses and dimensions. Many of the ice particle types had not been investigated previously. The <br />influence of riming and aggregation on ice particle masses was examined. When possible, comparisons <br />are made between these results and those of other expl~rimental observations. By incorporating these <br />mass-dimensional relationships into an expression for the ice mass content in a snowstoIin, it was <br />possible to estimate the mass fraction of the fresh snowpack resulting from accreted supercooled cloud <br />water. The results from two stonns analyzed suggest that about 30% to 40% of the deposited snow is <br />composed of accreted cloud water during moderately riming snowfall. <br /> <br />Mitchell, D. L., and R. D. Borys, 1989: The effect of cloud and seeding on snow-size spectra and cloud <br />droplet removal. Proceedings. 5th WMO Scientific Conference on Weather Modification and Applied <br />Cloud Physics, Beijing, China, May 8-12, 1989. World Meteorological Organization, Geneva, <br />WMO/fD-No. 269, 1:217-220. ' <br /> <br />No abstract. <br /> <br />53 <br />