WMOD00497

• Title: The NOAA Federal/State Cooperative Program in Atmospheric Modification Research - Collected Publication Titles and Abstracts
• Date: 4/1/1993
• Weather Modification - Doc Type: Report

Czys, R. R., 1992: Temperature effect on the coalescence of precipitation-size drops in free fall. Proceedings,
11th International Conference on Clouds and Precipitation, Montreal, Canada, August 17-21, 1992.
International Commission on Clouds and Precipitation, International Association of Meteorology and
Atmospheric Physics, Innsbruck, Austria, 1-4.

No abstract.

Czys, R. R., S. A. Changnon, M. S. Petersen, R. W. Scott, and N. E. Westcott, 1992: Initial results from the
1989 cloud seeding experiment in Illinois. Journal of Weather Modification, 24:13-18.

Some early results from the 1989 cloud seeding experiment conducted in Illinois are reported in this
paper. This exploratory field project was designed to achieve four primary objectives: (1) to obtain
data on the largest possible sample of clouds (treated lUld natural); (2) to test some of the early physical
steps of the dynamic seeding hypothesis; (3) to provide data for the development of analytical tools for
discerning seeding effects; and (4) to improve basic knowledge about natural cloud and precipitation
processes in the Midwest. The treabnent randomization was based on "floating" experimental units,
initially defined by a single cumulus congestus: Analysis of predictor variables revealed significant
differences betw{:en the AgI and sand treated clouds all the time of treabnent in many aspects that might
govern future cloud growth. A Seedability Index composed of criteria physically consistent with the
dynamic seeding hypothesis is described which was de:veloped as an initial approach to addressing the
problem of the bad draw revealed by the predictor variable analysis. The temporal series of the
empirically-defined Seedability Index revealed that seedable conditions did not remain constant over the
course of the field experiment and that even the seedable conditions for pairs of experimental units
obtained on the same day were not always comparable. These findings illustrate the large inherent
natural variability which has come into play in other cloud seeding experiments, and has frustrated
efforts to randomly select two populations of clouds having sufficient similarity in individual
characteristics to allow valid comparisons.

Czys, R. R., and M. S. Petersen, 1992: A roughness-detection technique for objectively classifying drops and
graupel in 2-D image records. Journal of Atmospheric and Oceanic Technology, 9:242-257.

The development and evaluation of a new computerized technique for classifying drops and graupel in
two-dimensional (2D)-image records is described. The method is unique because images are classified
as drops or graupel on the basis of their exterior roughness rather than shape. The technique involves
using the method of least squares to fit a fourth-order polynomial to the outside curvature of each half
of large, symmetric, circular images. Fonnulations for detennining variance and polynomial coefficients
are reviewed. Roughness criteria detennined using 2D-C and 2D-P cloud data in a quadtree analysis of
maximum variance of the polynomial approximations and image diameters are illustrated. A method for
detennining the radius of "center-out" images is also reviewed. Size distributions fonned by combining
2D-C and 2D-P data for either drops or graupel are illustrated with error bars based on Poisson
statistics. Two different methods of calculating water GOntent based on size-distribution infonnation
for particles with diameters greater than 150 pm are demonstrated. An independent evaluation of the
objective classification technique using 2D-C and 2D-P' cloud data shows that the polynomial
classification of images as drops or graupel perfonned sufficiently well to give a population of
size-distribution parameters and water contents that welre generally not statistically different from those
obtained by human classification.

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