Critical Issues in Weather Modification Research (2003) / Chapter Skim
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Appendix A: Glaciogenic and Hygroscopic Seeding: Previous Research and Current Status
Appendix A: Glaciogenic and Hygroscopic Seeding: Previous Research and Current Status
Pages 89-106
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From page 89... ...
PREVIOUS RESEARCH Glaciogenic Seeding Expel iments Stalic Seeding. Convective Clock Since convective storms produce a significant percentage of the rainfall occurring over many parts of the world, these cloud systems have been the subject of numerous seeding experiments to test the static seeding concepts.
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From page 90... ...
Results based on smaller clouds might not be transferable to more dynamically vigorous cloud complexes. Some of the initial steps in the chain of events of precipitation formation that have been demonstrated in field measurements arid laboratory and modeling studies include increased concentrations of ice crystals and the more rapid production of precipitation particles in cumulus clouds.
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From page 91... ...
This interaction explains the difficultly experienced in showing cause and effect through seeding experiments over flee Sierra Nevada (Desl~ler et al., 19903. Changes in the concentrations of precipitating ice crystals, ice nuclei, and precipitation rate have been observed after seeding in topographically forced regions (Figure A
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From page 92... ...
I.f ·.~.j FIGURE A 1 Observed concentrations of precipitating ice crystals, ice nuclei, and precipitation rate during one leer of Agl seeding between 0945 and 1045, December 15, 1994 in Utal~.
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From page 93... ...
. Since 1980 operational and research glaciogenic seeding experiments for rainfall enhancement based on the dynamic seeding concept have been conducted in Texas, Cuba, South Africa, and Thailand.
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From page 94... ...
This effect has been simulated with an explicit microphysics cloud model (Khain et al., 90011. In conclusion' glaciogenic seeding has produced clear proof of microphysical cleanses to simple cloud systems, Title indications based on statistical results that precipitation has been increased in some experiments.
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From page 95... ...
In both South Africa (Masher et al., 1997) and Mexico (WMO, 20003' hydroscopic flares were applied to mixed-phase convective cloud systems in physicalstatist~cal experiments (i.e., statistical randomized seeding experiments with concurrent physical measurements)
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From page 96... ...
The South African and Mexican results were analyzed for the first hour after seeding, and the seeding effect was evident 20~60 minutes after seeding based on the statistical results. In the Thai hydroscopic and glaciogenic seeding experiments the seeding effects were evident only after a few hours.
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From page 97... ...
This information together with the results from the hydroscopic seeding experiments, suggests an intriguing idea that hydroscopic seeding could be used to override damaging, inadvertent seeding effects that inhibit rainfall, xvith revote beneficial, deliberate seeding effects that enhance rainfall. This potential should be explored further.
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From page 98... ...
Over mountainous terrain the timely identification of regions of supercooled liquid water and else efficient targeting and dispersing of seeding material remain difficult problems. These clouds are part of major winter cyc]
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From page 99... ...
, seeding with hydroscopic material has usually appeared less attractive than seeding with ice nuclei due to the lack of physical understanding. Although promising statistical results have been obtained with hydroscopic seeding some fundamental questions regarding the physical processes need to be answered in order to provide a sound scientific basis for this technology.
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From page 100... ...
It is possible that some statistical results using radar-derived precipitation estimates might be due to seeding-induced drop size changes that affect the radar observations (Yin et al., 1998) Additional field measurements of r airdrop spectra are needed to address this issue Due to inherent assumptions of relating reflectivity from conventional weather radar to meteorological parameters there are limitations on discriminating between the liquid water arid ice phases arid changes in the concentrations and sizes of precipitation particles.
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From page 101... ...
1997. An independent evaluation of a South African hydroscopic cloud seeding experiment, 1 991 - I 995.
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1952. A new method of stimulating convective clouds to produce rain and hail.
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From page 103... ...
2001. Simulating convective clouds with sustained supercooled liquid water down to -37.5°C using a spectral microphysics model.
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1997. Results of flee South African cloud ~ seeding experiments using hydroscopic flares.
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1996. Seeding convective clouds with ice nuclei or hydroscopic particles: A numerical study using a mode} with detailed m icrophysics.
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From page 106... ...
2000a. Seeding convective clouds with hydroscopic flares: Numerical simulations using a cloud model with detailed microphysics.
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