WMOD00555

• Project Name: Sierra Cooperative Pilot Project
• Title: Results of the Shakedown Season for the First Precipitation Augmentation Experiment of the Sierra Cooperative Pilot Project
• Date: 6/1/1982
• Weather Modification - Doc Type: Report

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JUNE

INTERNATIONAL SYMPOSIUM ON HYDROMETEOROLOGY
AMERICAN WATER RESOURCES ASSOCIA nON

1982

RESULTS OF THE SHAKEDOWN SEASON FOR THE
FIRST PRECIPITATION AUGMENTATION EXPERIMENT OF THE
SIERRA COOPERATIVE PILOT PROJECT

Larry Vardiman:l

ABSTRACT: The Sierra Cooperative Pilot Project (SC~P) conducted
a shakedown of an exploratory precipitation augmentation experi-
ment in the winter of 1981-82. Equipment and procedures were
tested for suitability in the experiment. Dry ice was released from
an aircraft in post-frontal convection over the central Sierra Nevada.
Seeding was conducted over three-hour time blocks along 20-mile
legs parallel to the mountain. Seeding effects were observed byair-
craft, radar, and precipitation gages.
Results of the shakedown season are described in terms of the
seeding responses observed, the procedures developed, and the
equipment utilized in the experiment. The modified experimental
design, to be implemented in the winter of 1982-83, is described
with estimates of the expected seeding effects.
(KEY TERMS: weather modification; precipitation enhancement;
snowpack augmentation; cloud seeding.)

INTRODUCTION

The SCPP (Sierra Cooperative Pilot Project) conducted
the shakedown of an exploratory precipitation augmenta-
tion experiment in the winter of 1981-82 based on a design
developed over four previous years of experimentation,
L. Vardiman and J. D. Marwitz (1981) and Vardiman
(1982). Equipment and procedures were tested for suit-
ability in such an experiment over the central Sierra
Nevada. Dry ice seeding was conducted by aircraft in post-
frontal convection over three-hour time blocks along 20-
mile legs parallel to the mountain barrier. Seeding effects
were observed by aircraft, radar, and precipitation gages.
Based upon the results of this shakedown season the
experimental design will be modified and hopefully a multi-
year experiment will be initiated in the winter of 1982-83.

OPERATIONS

Ten experimental units were obtained during the shake-
down season. Table 1 shows the dates and times of the
experimental units. The experimental units were classified
into three categories of seeding potential - A, B, and C.
The greater the amount of supercooled liquid water in a

cloud and the fewer the ice crystals, the greater the
seeding potential. The ratio of liquid water content (LWC)
to ice crystal concentration (ICC) in units of micrograms/
crystal was used to classify the clouds. Category A had the
highest seeding potential, exceeding 100 micrograms of
LWC per crystal over 10 percent or more of a measured
portion of an experimental region. Category B had the
next highest, exceeding 10 micrograms per crystal and
cat,egory C was the lowest, exceeding 1 microgram per
crystal.
Unfortunately, the three most seedable OCCUrrences of
experimental conditions were not seeded because of sus-
pensions due to flood threat or severe weather. Seeding
was conducted in both Band C conditions and yielded
detectable seeding signatures, at least in aircraft measure-
ments.

TABLE I, 1982 SCPP-l Experimental Units

Seedability* Seed/
D~lte Time (Z) Category No Seed"
Jan 18 2006-2306 C S
Jan 19 2058-2358 C S
Jan 21 1858-2158 A NS
Jan 28 2014-2314 B R(NS)
Mar 02 2228-0128 C R(S)
Mar 03 2001-2301 B R(S)
Mar 15 2007-2307 B R(S)
Mar 16 2201-0101 C R(NS)
Mar 18 1945-2245 A NS
Mar 19 2020-2320 A NS

*General Cloud Seedability (LWC/ICC is the ratio of liquid water
content to the ice crystal concentration in the experimental
region).
A: LWC/ICC;;. 100 j.lgm/crystal
B: LWC/ICC;;. 10 j.lgm/crystal
C: LWC/ICC ;;. Ij.lgm/crystal
**Seeding Mode
S: Seeded
NS: Not Seeded
R: Seeding Decision Randomized

1 Christian Heritage College, 2100 Greenfield Drive, El Cajon, California 92021.

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