WMOD00296 ‎(2)‎

• Contract/Permit #: 14-06-D-5640
• Title: Park Range Atmospheric Water Resources Program Final Report
• Date: 9/30/1969
• Weather Modification - Doc Type: Report

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rate set irito the range. As the range gate servoed out, a recording was
made of the AGC voltage and slant range.

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(3) When the range had reached a pre-determined value, the range
was slewed to zero, the antenna elevation angle decreased and a new scan
started. This procedure was repeated until the antenna elevation angle was
just large enough to miss ground targets.

The values for range, elevation angle and AGC voltage were then coded on
punch cards for computer analysis. The computer prepa:red a graph of the
resultant data in which the abscissa is height and the ordinate horizontal
range. At various points within this graph were plotted values of Z or I ob-
tained from the AGC scans. An isopleth sketch was then made encircling
points of high intensity. Using this method it is possible to readily look for
an increase or decrease in signal intensity which might be related to seed-

ing.

2.6

Snow Crystal Replica Collection and Analysis

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Many hundreds of plastic-coated glass slides were posed for the collection
of- snow crystaTreplicas during operational perio s in the Park Range. Most
of the slides were exposed at Rabbit ~Ea!U~ ' although special series were
occasionally taken at other locations in the experiment area, notably at
Buffalo Pass in the 1966-67 season and at Valley View, Steamboat Springs,
Emerald Mountain, and occasionally at Mt. Harris during 1965-66.

The snow crystal replicas were collected by exposing 3t x 4 inch glass
slides coated with 10/0 formvar in ethylene dichloride solution. Exposure
time varied from about 30 seconds t9 three minl!t~e depending on snowfall
rate. The water content of the crystals was then allowed to sublimate away
while the slide dried at subfreezing temperatures for 12 hours. Sampling
frequency ranged from 5 minutes to 30 minutes with most series collected
at 5, 10, or 15 minute intervals.

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2. 7 Identification of Silver Iodide Particles as Ice Nuclei

Knowledge of the geographical distribution of silver-in-precipitation concen-
tration is helpful in studying the effects of cloud seeding using silver iodide.
However, silver iodide can occur in precipitation samples due to (1) AgI
particles acting as ice nuclei. (2) scavenging of AgI particles by precipitation,
and (3) sedimentation of AgI particles. Therefore, in order to determine
whether or not (and to what degree) AgI particles participate as ice nuclei
in the precipitation process, it is necessary to identify individual AgI part-
icles in relation to individual ice crystals.

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In the 1967 -68 operational season, an electron microscope technique origi-

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