WMOD00400

• Contract/Permit #: 14-06-D-6801
• Title: Structure and Seedability of San Juan Storms
• Date: 11/1/1976
• Weather Modification - Doc Type: Report

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the mountain represents precipitation lost to the Colorado River Basin, and

indicates the seeding potential of these storms.

2. Ice crystal observations

a. Concentrations

. Ice crystal concentrations were surprisingly high. Concentrations above

SO/liter were observed on 29 December 1974 (flight 1), on 29 January 1975

(2), on 30 January 1975 (1 and 2), and on 22 March 1975 (1 and 2), and such

concentrations were found in regions that could have affected the precipita-

tion. Occasional regions of the clouds were found where the crystal concen-

trations were low; for example, a strong updraft region on 30 January 1975 (2)

was observed to have less than O.l/liter ice crystal concentration,

although its temperature was -14C. (See section V.D.3.e. for a description.)

Such regions were rare, and were generally associated with convection.

Fig. 3.4a shows the range of crystal concentrations observed, as a

function of temperature; little correlation between ice crystal concentra-

tion and temperature is evident. HC)1;vever, when only those regions of the

cloud are included for which an ice crystal origin can be determined, and

the plot is constructed as a function of the temperature where the ice

crystals originated, a very different picture emerges (Fig. 3.4b). There

is a high degree of correlation between temperature and crystal concentra-

tions. If N is the ice crystal concentration per liter and T is the tempera-

ture in degrees Celsius, the relation

-5 5
N = 2.5 x 10 (-T)
prov~des a reasonable representation of the observations in the range of

temperatures from -lOC to -20C. The ice crystal habits showed that high

ice crystal concentrations at warm temperatures were generally the result

of crystals falling from colder regions. Also, crystal concentrations

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