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Last modified
7/28/2009 2:27:39 PM
Creation date
10/1/2006 2:12:02 PM
Metadata
Fields
Template:
Weather Modification
Applicant
Steven M. Hunter
Sponsor Name
California Energy Commission
Project Name
Optimizing Cloud Seeding for Water and Energy in California
Title
Optimizing Cloud Seeding for Water and Energy in California
Prepared For
California Energy Commission
Prepared By
Steven M. Hunter
Date
3/31/2006
State
CA
Country
United States
Weather Modification - Doc Type
Report
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<br />seeding materials, to produce desired precipitation augmentation. Assessment of the ability of <br />seeding to meet these critcria can be done through direct observations or possibly through <br />modcling. <br /> <br />As related in the NRC rcport12, computer modeling has secn great advances in the last two to <br />three decadcs, and weather modification should capitalize on its use. Three-dimensional cloud <br />models capable of simulating T&D and cloud microphysics related to seeding effects have <br />already been used in research, Examples include experiments in Utah5.\ the Nevada WDMp51, <br />Colorado WDMp54, and a fcasibility study for a new Wyoming cloud sceding pilot project55. <br />Such modeling can bc used to prcdict seeded plume T &0 for optimum placement of secding <br />generators, as well as verilication of secding cffect (precipitation enhancement). While thcre <br />have becn signiticant advances in modeling, most investigators agree that models are not <br />currently sophisticated cnough to accurately simulate all relevant cloud processes, and thereforc <br />they should not bc the only tools used in prcdiction and veritication. This is where dircct <br />observations can hclp, <br /> <br />Direct physical measurements have been madc in weather modification for many ycars. An <br />important type of such mcasuremcnts has been tr..lcers, Examplcs of tracers are gases such as <br />sulfur hexalluoride (SF6) or chemicals like silver, indium, cesium or rubidium. The chcmicals <br />arc otten released simultaneously with aircraft or ground relcased seeding materials, and can be <br />detected downwind of thosc sources. The silver content from the seeding material itself (Agl) <br />has frequently bccn used as a tracer. This silvcr can cither be scavenged from clouds by natural <br />(not secded) prccipitation, or it can be deposited in thc snowpack as a rcsult of ice nucleation, <br />growth and fallout. Therefore. comparativc use of the other chemicals that can be scavenged, but <br />do not havc ice-nuclcating properties, can provide strong evidence that the sceding plume <br />produced additional precipitation over the target area56. Failure to measure silver in snow at <br />grcater than natural background levels, however. indicates that a silver iodide seeding plume did <br />not interact \...,ith clouds and precipitation in the target arca in such a way to make sceding efTcctive. <br />Othcr physical measuremcnts may bc llsed to distinguish seedcd !ium natural ice particles, For <br />example, thc sizes and habits of those particlcs can be measurcd by clcctronic probes or dift.'Ct <br />capture. Also. the density of various laycrs in the snowpack corresponding to sceded or unseeded <br />periods can be compared for any diOcrences. ^ 1994 SCE research project52 mcasured density <br />incrcases in secded snow layers to estimate a minimum 8% increase in snow water from seeding. <br />Morc such rescarch could cnhance the physical basis of projcct evaluation. <br /> <br />Onc of thc greatest uncertainties in both modcling and physical measuremcnt of seeded plumes is <br />the concentration of icc crystals produced by seeding, It is believed that concentrations <br />exceeding 20 pcr liter of air arc rcquircd to produce significant precipitation rates57;47. <br />Asscssmcnt of crystal concentrations (1/ (I gi\'en location in the targct area depends on a) the <br />plume concentrations at a singlc time and b) the spatial meander of the plume with time. As seen <br />from Figure 5, both a) and b) can be highly variable, ~tore research into ice nuc1eants. both <br />natural and sceded. is needed to address these uncertainties, <br /> <br />20 <br />
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