WMOD00394

• Contract/Permit #: 14-06-D-6467
• Project Name: Weather Modification Pilot Project
• Title: Weather Modification - A Pilot Project - San Juan Mountains, Colorado River Basin - Final Report
• Date: 2/1/1974
• Weather Modification - Doc Type: Report

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In other cases, ice growth by vapor deposition proceeds at a rate
sufficient to use cloud water as it condenses. In some weathe~
situations, the supply of ice crystals can be so great that particle
growth is restricted by water availability and fall trajectories
of the ice crystals relative to the ground may be adversely
affected.

These concepts have been specifically tested (Grant and Mielke,
1967;Grant et aI, 1968; Chappell, 1970; Jiusto and Holroyd, 1970
and 1971) and are demonstrated in Figure 1.

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Rate of Co"~cnsation ,
Difrusional Gro~th Rate of Ice

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---0-- Average Preclpitatio~ Observea (no: see';ed cnses)
---...--- A,erage Precipltatisn Ooserv",j (seeded c~.5es)

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Average Condensation Rate USln, 10.1 Prec.ipitation
Hours/Day "lith Upward Speed O' 11.8 cm./:.ec. at
-200 C Ad.lUsted at Other Ter'c,=ratures Ac:ordinQ
:-.; .Q(ldtl01l~ vi tnt: r:ori~:ontal __lnd SpF.ed

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For 460 HB Cloud Top
..)Iith r:atural lee Nuclei
Spectrum

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Number of Days
4 10 18
4 7 15 18

14 19 29 22 14
16 27 28 17
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-35 -30

-25 -20

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FiSure 1. Di~tribution of non-sE!cded precipitation at H....~O as ~
function of SO~ mb tcn;~~rature compared to a theor~tlcal distri-
bution cur;;putt:>d usinS" the mean diffu<.:;ional model. Precipitation
data are from Climax I sample (251) and values are a running mean
over a three-Jegree tetllperatllre interval.

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Curve A in Figure 1 shows the rate at which water can be consumed
by mountain clouds with various cloud top (500 mb) temperatures
assuming: (1) clouds with characteristics of those observed near
Climax, Colorado; (2) ice crystal concentrations comparable to
concentrations of natural ice nuclei activated at the respective
temperatures, and; (3) a growth rate of individual crystals
determined by Chappell (1970) based on the ice diffusional growth
equations. Curve B, for comparison, shows the mean rate at which
condensate becomes available for clouds with various 500 mb

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