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Last modified
7/28/2009 2:33:38 PM
Creation date
3/20/2008 1:00:24 PM
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Weather Modification
Title
Twelve Basin Investigation - Volume I
Prepared For
Bureau of Reclaimation
Prepared By
Robert D. Elliot, Jack F. Hannaford, Russell W. Chaffer
Date
5/15/1973
Weather Modification - Doc Type
Report
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<br />i <br />\ <br /> <br /> <br />, <br /> <br />and observed precipitation. The area. of effect model requires detailed up-wind <br />sounding data, terrain features, see:ding source data (natural or artificial), <br />and cloud top data or estimates. The latter is also a requirement of the CSU model. <br />The area of effect model discriminate~s the potential for seeding increases in the <br />differences between calculated seeded and not seeded precipitation rates, based on <br />the detailed sounding data and observed hourly precipitation data. The finer pre- <br />cipitation-aerological parameter (cloud tops, bases, etc.) relationships possible <br />using hourly precipitation data led to the selection of the area of effect model _.// <br />(with modifications) for the analysis in the Twelve Basin Investigation. <br />1. 2 .1.1 Modification of model in the evaluation of the Upper Colorado <br />River Basin Pilot Project. In the evaluation of the Colorado River Basin Pilot Pro- <br />ject (Elliott and Court, 1973), the basic area of effect model (Elliott, 1969) was <br />modified to yield quantitative predictions of precipitation rates along a profile <br />across the San Juan Mountains using upwind rawinsonde data and assuming either arti- <br />ficial or natural nucleation. The basic features of the model are shown in Figure <br />1. 2-1. A well mixed nucleant plume expands initially at the rapid rate known <br />(Orgill et aI., 1971) to exist in rough terrain; above a level corresponding to <br />cloud top the plume remains level. Lateral expansion is also large up to the same <br />point, slow beyond. The cloud physics of the area of effect model is employed for <br />stepwise nucleation, diffusional and accretional growth, and fallout of ice parti- <br />cles. Ice crystals evaporate in the lee-side descending flow. <br />An additional modification of the area of effect model was the development of <br />a different model for determining thE! height at the top of a lifted cloud, given <br />the height at the top of a cloud in the valley and other information from a sound- <br />ing as shown in Figure 1. 2-2. The streamlines are assumed to be equally spaced <br />straight lines compressed beneath a nodal surface in passing from valley edge to <br />mountain crest. The formula is: <br /> <br />-, <br />\ <br />\ <br />\ <br />\ <br /> <br />LCT = PRC - (PVF - OCT) (PRC - PNS) / (PVF - PNS). <br />All quantities are pressures (mb): <br /> <br />PNS at nodal surf<1ce <br />LCT at top of lifted cloud <br />PRC at ridge crest <br />OCT at top of observed cloud OVE!r Durango <br />PVF at valley floor or top of dead layer at Durango <br />crT at top of positive area on adiabatic chart <br /> <br />1-4 <br /> <br />'.'~" <br />
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