WMOD00277

• Contract/Permit #: 14-06-D-6467
• Title: An Operational Adaptation Program for the Colorado River Basin
• Prepared By: Lewis O. Grant, Chappell, Crow, Mielke Jr., Rasmussen, Shobe, Stockwell, Wykstra
• Date: 10/1/1969
• State: CO
• Country: United States
• Weather Modification - Doc Type: Report

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MAXIMIZED CONDITIONS

UPWARD SPEED CRYSTAL RAOI.JS 500MB TEMPEfWURE

!'D CM/SEC 100,11 - 27'C
50CMlSEC 300,11 -25'C
5OCM/SEC ~p -23'C

ISCM/SEC 100,11 -2S"C
ISCMI SEe YJOp -23"C
ISCM/SEC 500,11 -21'C

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500MB TEMPERATURE ('C)

Figure 3. --The deficit (below) and excess (above) in
;effective ice nuclei concentration required to optimize
the precipitation efficiency for various crystal sizes
:and upward speeds as a function of the cloud top
temperature.

upward speed from 15 cps to 50 cps has the effect of
shifting the mode of maximized precipitation
efficiency 2C toward colder temperatures.

It is apparent from FIgure 3 that for all
crystal sizes and upward speeds depicted, the
naturally effective ice nuclei excess is one hundred
or more for 500 mb temperatures of -28C and
colder. Also, for the conditions displayed there is
a deficit of effective ice nuclei at all 500 mb tempera-
tures warmer than -21C, At -15C the effective ice
nuclei deficits range from 10 to 165 per liter.

The assumption of an ice crystal to
ice nuclei ratio of one is open to question. Results
of investigations by Mossop et al., (1967, 1968, 1969),
Hobbs (1969), Veal et al. (1969), and Grant (1968)
are shown in Figure 4. If the

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-- MOSSOP a ONO (1969)
- VEAL .1 01. (1969)
"' HOBBS (1969)

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TEMPERATURE (OC)

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Figure 4. --Relationship between the ratio of ice
crystal concentration to corresponding ice nuclei
concentration as a function of temperature. Crystal
habit s according to Magono and Lee (1966).

results of Grant and Hobbs are neglected for the
moment, the remainder of the observations indicate:
an average exponential increase of He ratio with
temperature (middle diagonal line in Figure 4).
This is a most interesting result. If this relation is
substituted into (12), the net ice crystals realized
in the cloud system as a function of temperature
completely erases all ice nuclei deficits for condi-
tions depicted in Figure 3. The incorporation of
this relation into the model therefore eliminates all
potential for modification in the range of conditions

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