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

Changnon, S. A., 1991: Cloud and precipitation development re:lated to the St. Louis precipitation anomaly.
SWS Contract Report 532, NOAA Cooperative Agreements NA90AAHOA175 and NA27RA017301.
Illinois State Water Survey, Champaign, IL, 28 pp.

No abstract.

Changnon, S. A., 1991: The dilemma of climatic and hydrologic forecasting for the Great Lakes. Proceedings,
Symposium of the Great Lakes Water Level Forecasting and Statistics, Windsor, Ontario, May 16-17,
1991. Great Lakes Commission and NOAA Great Lakl~S Environmental Research Laboratory,
Ann Arbor, MI, 13-25.

No abstract.

Changnon, S. A., R. R. Czys, S. E. Hollinger, F. A. Huff, K. E. Kunkel, M. S. Petersen, R. W. Scott,
D. W. Staggs, and N. E. Westcott, 1991: Analysis and planning for Precipitation Augmentation for
Crops Experiment. Annual Report, NOAA Cooperative Agreement NA90AAHOAI75. Illinois State
Water Survey, Champaign, IL, 122 pp. (available from National Technical Infonnation Service,
5285 Port Royal Rd., Springfield, V A 22161).

No abstract.

Changnon, S. A., R. R. Czys, R. W. Scott, and N. E. Westcott, 1991: Illinois precipitation research: A focus on
cloud and precipitation modification. Bulletin of the American Meteorological Society, 72:587-604.

At the heart of the 40-year atmospheric research endeavors of the Illinois State Water Survey have been
studies to understand precipitation processes in order to learn how precipitation is modified purposefully
and accidentally, and to measure the physical and socioeconomic consequences of cloud and
precipitation moditication. Major field and laboratory activities of past years are briefly treated as a
basis for describing the key fmdings of the past ten years. Recent studies of inadvertent and purposeful
cloud and rain modification and their effects are emphasized, including a 1989 field project conducted
in Illinois and key findings fro~ an ongoing exploratory experiment addressing cloud and rain
modification. Results are encouraging for the use of dynamic seeding on summer cumulifonn clouds of
the Midwest.

Typical in-cloud results at -lOoC reveal multiple updrafts that tend to be filled with large amounts of
supercooled drizzle and raindrops. Natural ice production is vigorous, and initial concentrations are
larger than expected from ice nuclei. However, natural ice production is not so vigorous as to preclude
opportunities for seeding. Radar-based studies of such c:1ouds reveal that their echo cores usually can be
identified prior to desired seeding times, which is significant for the evaluation of their behavior. Cell
characteristics show considerable variance under different types of meteorological conditions. Analysis
of cell mergers reveals that under conditions of weak vertical shear, mid-level intercell flow at 4 Ian
occurs as the reflectivity bridge between cells rapidly intensifies. The degree of intensitication of
single-echo cores after they merge is strongly related to the age and vigor of the cores before they join.
Hence, cloud growth may be enhanced if seeding can encourage echo cores to merge at critical times.
Forecasting research has developed a technique for objectively distinguishing between operational
seeding and non operational days and for objectively predicting maximum cloud-top height and seeding
suitability. An accuracy rate of up to 60% in predicting maximum echo-top height using four categories
has been achieved and suggests its use as a covariate in future experimentation. Impact studies illustrate
that sizable summer rain increases would be necessary to produce economically beneficial outcomes for
Corn Belt agriculture. Increases of ~25% in July rainfall across certain high-production crop districts of
the Corn Belt would produce economic effects realized nationally.

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