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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nated by Koenig (1959) and modified in the EG&G laboratory was used to
identify AgI particles which had behaved as ice nuclei in collected snow
samples. However, this technique required skillful, tedious, and expen-
sive operations, which were not practical for large scale field experiments.

Consequently, a more simple, inexpensive method was developed in the
EG&G laboratory. and at about the same time by Knight (1969), and used
during the 1968-69 season with good results. This new technique was based
on the simple principle that any submicron size particle can act as a seed
in its own supersaturated solution and can thus grow to any desired size.

Using this principle, snow crystal replica slides collected in the Park Range
Project Area were partially immersed in a supersaturated AgI-KI aqueous
solution for 2 to 3 hours, and then allowed to dry. Crystal photographs
taken prior to immersion and drying were compared to photographs taken
after treatment, and the percentage of individual crystal replicas which grew
microscopically visible AgI crystals at the replica centers was computed.
Examples of the visual appearance of crystal replicas with AgI centers are
shown in Figures 9 and 10. Evidence of AgI scavenged on dendrite arms is
visible in Figure 11.

2. 8 Silver Content of Snow Water

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An atomic absorption spectrophotometer has been used to analyze collected
snow samples for the past two seasons. The methodology is described in
detail by Parungo and Robertson (1969). Analysis for silver concentration
in precipitation was performed by this technique using ~ 1000 snow samples
from the 1967-68 operational season and 321 samples from the 1968-69
season.

Initially, snow samples were taken from snow boards and through the snow-
pack after periods on the order of a week. Though some success was
achieved, the primary fact learned was that it was rr.ore fruitful to add time
resolution by taking individual shorter time period samples through a pre-
cipitation period, rather than taking one sample at the end of a long precipi-
tation period. This proved more fruitful for two reasons:

(1) If the release time is short compared to the total precipitation
duration, the sample is likely to be diluted below the practical threshold of
analysis.

(2) Transport and dispersion characteristics change over a short
time period so that the desired, or significant, results during a short time
period may be diluted or masked by negative or indeterminate results during
some other time period.

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