WMOD00532

• Title: The Rain Stimulation Campaign in Panama Summer 1983
• Date: 6/1/1984
• Weather Modification - Doc Type: Report

3. Operations for Rain ,Stimulation

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As soon as the decision had been reached to proceed
with a 90-day rain stimulation program and the neces-
sary agreements had been concluded, the Bureau of
Reclamation competitively sought to contract IA.>ith the
best qualified and lowest priced bidder to perform the
work. The contract, awarded on May 20, 1983 to the
CIC (Colorado International Corporation) of Boulder,
Colo., stated that operations were to begin as soon as
possible. CIC dispatched a meteorologist site director
and two specially equipped aircraft with pilots and
support personnel. Upon arriving on the site, they set
up headquarters at Paitilla Airport in Panama City and
brought in, or obtained locally, the necessary supplies.
On-site coordination was provided through the Meteor-
ology and Hydrology Branch of the Canal Commission's
Engineering Division. On May 31,1983, the first cloud-
seeding mission was flown.

During the 90-day operational period thus begun,
seeding missions were flown on 61 days. Ten days were
lost to mechanical failure. Twenty-one days were so dry
that no suitable clouds were found. On six days, clouds
formed and were seeded over the Bayano watl~rshed
but not over the canal watershed.

The clouds that formed in the Panama target areas
were recognized as being of the type that respond to
ice-phase seeding. Where they extended above the
freezing level (usually near 17,000 ft), their updrafts
contained large amounts of supercooled water droplets
which seeding would tend to change into precipitation
particles. Furthermore, the resulting additional release
of latent heat in the updrafts tended to affect the
dynamic structure of the clouds and cloud cluste:r. The
opportunity for response to hygroscopic seeding was
also recognized where this would lead to the earlier
formation of drizzle drops in the lower portion of the
cloud and thus speed up the release of precipitation.
However, primary emphasis was placed on ice..phase
seeding.

The airplane assigned to most of the seeding work was
a Piper Navajo equipped with four independent s.~eding
systems. The first used U.S. Navy Type TB-1 pyro-
technic flares, each charged with 20 grams of silver
iodide, that were discharged from a rack accom-

modating 60 flares. The second system was a smoke
generator burning a solution of silver and ammonium
iodide in acetone, capable of dispensing 4.5 grams per
minute of silver iodide. The third was a dispenser that
discharged dry ice (solid carbon dioxide) in pellets of
about 1 em diameter. The fourth system dispensed a
fine~ spray of hygroscopic solution from two wind-driven
rotary atomizer heads. The dispenser was calibrated to
disperse 6.3 liters per minute of a nearly saturated
ammonium nitrate-urea solution in droplets of about 50
micrometers mean diameter.

ThE! second airplane, a Beechcraft Baron, was equipped
for both cloud-seeding and cloud-physics observation
missions. Like the Navajo, it carried a 60-flare rack for
pyrotechnics and a dry ice dispenser. In addition, it
carried special cloud-physics instrumentation and an
onboard data recording and processing system. The
instrumentation included a PMS 2D-C probe capable of
imaging and classifying particles in the size range
between 30 and 200 micrometers (most important in
the early phases of precipitation particle formation); a
PMS forward-scattering probe for measuring cloud
droplets of smaller sizes; and a liquid-water-content
meter. After one month of duty in Panama, the Baron
had to return to the U.S. to fulfill previous obligations,
and it was replaced by a Piper Aztec similarly equipped
for pyrotechnic and dry ice seeding but without the
extEmsive cloud-physics instrumentation.

Figure 2 shows how the target was divided into four
operating areas for ease in exchanging information on
cloud developments and directing the operations of the
aircraft. The operational day began with study of the
analyzed Albrook rawinsonde (fig. 3) and facsimile
weather maps, permitting a review of all standard
meteorological data and analyses during the early
morning. Usually by mid-morning there was a briefing
and discussion with the flight crews that focused on the
previous day's outcomes and probable seeding missions
for the current day. A radar watch was kept on shower
dev,~lopment as the day progressed. Generally, midday
would find clouds in a developing stage. When seedable
clouds appeared imminent, one of the aircraft was
dispatched to make a visual assessment of cloud
devE~lopment and report to the field director.

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