WMOD00402

• Project Name: Sierra Cooperative Pilot Project
• Title: Sierra Cooperative Pilot Project - Final Report for Period November 1984 - September 1986
• Date: 6/1/1987
• Weather Modification - Doc Type: Report

2.4

in the 1983-84 winter season. It was selected primarily to avoid contami-
nation of the snow samples with materials blown from HALO's maintenance
yard salt/sand piles. Tests were to be made to determine whether or not
there was a contamination problem. On one or two occasions during this
field season, two simultaneous sets of samples were collected. One set
was collected at HALO adjacent to the Ka-band radar while the other was
collected approximately 1 kIn to the east. Chemical comparisons of the
contents of the samples were then made to determine the magnitude if any
of contamination.

So that it was possible to track silver iodide from a particular
aerosol generator over the observing sites, two ground-based generators
were prepared for use at Cisco Butte directly upwind of the Kingva1e site.
In addition to the AgI unit already at Cisco, a mobile generator was also
taken to the site. This unit was to be used for releasing non-ice
nucleating indium sesquioxide aerosols simultaneously with or separately
from the AgIo

Between 1 January and 31 March 1985, all field activities related to
this task were completed for this 1984-85 winter season. The main effort
included the collection of one hundred ninety (190) freshly-fallen sequen-
tial snow samples at the Kingva1e site. See Table 2.1 for details of the
sampling. The samples were collected during the field season at intervals
of five to twenty minutes in duration depending on precipitation rate.,

All samples from HALO were to be analyzed for their 180 enrichment.
A preliminary group of fifteen (15) samples collected during the first
experimental unit conducted 7 February 1985 (2050h-2320h GMT) underwent
immediate processing into reaction tubes at the DRI laboratories. This
is the first step in converting oxygen in the snow samples into carbon
dioxide gas from which the 180/160 ratios are determined by mass spectro-
metry. The raw data from these initial samplings were discussed at the
May 1985 SCPP workshop in Auburn, California.

Selections were made of those samples to be analyzed for indications
of silver iodide seeding material and special tracer content. TWo special
tracers were used during the 1984-85 studies. The first, cesium (Cs), was
released from the seeder aircraft in flares containing CSI03 which produced
specially tagged ice nuclei (AgI'CsI). The second, indium (In), was released
from the ground-based generator located at Cisco Butte. The program in-
volves the analysis of two hundred (200) element-determinations. Therefore,
sixty-six (66) samples were to be analyzed each for silver (Ag), cesium (Cs)
and indium (In) contents.

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