WMOD00288 ‎(3)‎

• Title: Atmospheric Tests of an Organic Nucleant in a Supercooled Fog
• Date: 12/2/1989
• State: CA
• Country: United States
• Weather Modification - Doc Type: Report

resort areas throughout the world. SnowmaxTh4 is a freeze-
dried preparation of the natural bacterium P. syringae
which is grown in large fermenters, frozen in a manner
similar to that used in freeze-dried food, and then sterilized
by electron beam radiation. SnowmaxTh4 is not a product
of engineering, it is a natural bacterium selected solely for
its ice nucleation ability.

In November 1987, representatives from Kodak
came to Fresno, California, where some preliminary tests
of SnowmaxTh4 material as a potential ice nucleus for
weather resources management programs were conducted
in the facility at Atmospherics Incorporated. Ice crystals
were artificially produced in a three-compartment freezer
chest, and these crystals were captured on Formvar coated
slides. The qualitative experiments were conducted in the
temperature range of -4OC to -20.C, with crystal habit and
temperature relationships noted (Henderson, 1987).

The results from these preliminary laboratory tests
were encouraging enough to warrant more sophisticated
characterization tests in the isothermal and dynamic cloud
chambers at Colorado State University. These more
quantitative tests were conducted in March 1988. The
results (Ward and DeMott, 1989) were so dramatic that
plans were organized for a field test of P. syringae. These
airborne tests were conducted by Atmospherics
Incorporated near Hawthorne, Nevada, During the two day
tests in September, 1988, it was demonstrated that
SnowmaxTh4 dry powder can be dispensed from aircraft and
significant visual glaciation effects can be produced at in-
cloud temperatures as warm as -soe. (Rogers, 1988),

Because of the constantly changing characteristics
of even small cumulus clouds, and the difficulty in dealing
with their dynamic properties, further tests were planned

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THE "MOLAS" PROGRAM
(MONO LAKE APIPS S.TUDY)
MONO LAKE, CALIFORNIA

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for areas where fog decks provided a more stable outdoor
laboratory.

2. DESIGN OF TIIE_ TESTS OF PSEUDOMONAS
SYRINGAE

The subsequent tests of the P. syringae organic
nucleant were made in ~uper-cooled fog over Mono Lake,
California (see Figure 1). These tests were make in the
context of a larger study of Aircraft-Produced Ice Particles
(APIPs), called MOLAS (Mono Lake APIPs Study).

Mono Lake is 1968 m MSL and has a surface area
of about 250 lan2. It has no outlet and is completely
surrounded by higher telTain rising to 3,500 m MSL nearby
to the west. During winter weather when a high pressure
system is well-established over California, the surface air
east of the Sierra range is cold and supercooled fog occurs
over Mono Lake and Mono Valley to the east. A
temperature inversion of a few degrees may persist for
periods of 3 to 5 days and the fog, which forms beneath the
inversion, is stabilized by condensation rates from the lake
surface being equal to the droplet evaporation/sublimation
at the top of the fog layer.

The flight tests were simple in design and execution.
A set amount of P. syringae was released as a fine powder
from a Cessna 421 test aircraft flying about 30 m below fog
top. The King Air 200T cloud physics aircraft of the
University of Wyoming followed closely behind the seeder
aircraft until it entered the fog and began its release of
nucleant. The scientist aboard the King Air set its pointer
to the position where the seeder aircraft initially entered
the fog and the pilot tht:n flew tracks that were orthogonal
to the track of the se(~der aircraft (see Figure 1). The

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Figure 1 Map showing the geographic context for the MOLAS (Mona Lake APIPs Study)
Program. The aircraft flight patterns have been superimposed,

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