WMOD00299 ‎(2)‎

• Title: Scientific Weather Modification Experimentation in the United States
• Date: 8/25/1984
• Weather Modification - Doc Type: Report

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firmatory experiment (FACE-2) were conducted to test whether seeding in this
manner increased rai nfall on the ground. Although a conceptual modE~l and chai n
of physical events following seeding were specified (Woodley et al., 1982b), no
attempt was made to verify it through di rect observation and measurl~ment of the
i ntermedi ate processes. Both F ACE-1 and F ACE-2 were prima rily lib 1 ack-box"
experiments, with the evaluation of the results based on the statistical dif-
ferences in rainfall characteristics of the seed and non-seed populations.

Candidate experimental days were selected by evaluating a daily suitability
index that was based on maximum model-predicted seedability and morning shower
activity as observed by radar. Individual cloud suitability was based on visual
appearance and aircraft observations of cloud top height, updraft velocity and
liquid water. When the suitability criteria were met, pyrotechnic flares that
produced either 70 g of AgI or sand were ejected from an aircraft in the top of
the clouds on randomly selected seed and non-seed days, respectively. Typically
5 to 10 flares per seeding pass were released in the actively growing portion of
the treated clouds. Ground-level rainfall was estimated using S-band radar
observations after adjustment by rain gages.

The results of FACE-1 (Woodley et al., 1982b) provided evidence of precipitation
increases due to seeding. Analyses without predictors suggested apparent
increases in both location (mean and median) and the dispersion (standard
deviation and interquartile range) characteristics of rainfall due to seeding in
the total target (TT) and floating target (FT), the most intensely treated por-
tion of the target. Approximately 50% and 25% increases in the means for the FT
and TT variables, respectively, were found, with substantial statistical support
for the FT results and lesser statistical support for the TT results (i.e., P
values of 0.01 to 0.09, respectively). Time profiles of FT and TT rainfall com-
posited with respect to the time of the initial treatment pass also provided
substantial evidence for a treatment effect in FACE-I, with rainfall peaking
higher and later in the seeded cases. Analyses of covariance using meteorologi-
cally based covariates suggested an even larger effect of seeding than the
overall results with stronger statistical support. The FACE-2 experiment was
conducted in an effort to confirm the indications of positive seeding effects on
rainfall from FACE-I.

FACE-2 was conducted during the summers of 1978, 1979, and 1980. There were 61
days of experimentation of which 10 were A days (days on which less than 60 AgI
flares were used) and 51 were B days (days on which 60 or more AgI flares were
used). Of the 10 A days, 3 were seed days and 7 were non-seed days. Of the 51
B days, 25 were seed days and 26 were non-seed days.

The confirmatory specifications (Woodley et al., 1982a) and final data sets
(Barnston et al., 1982) for FACE-2 were identified prior to any disclosure of
the treatment decisions. The confirmatory specifications were:

1. The first and weakest level of confirmation will have been attained
if the seed FT and TT rainfall time profiles are greater in magnitude
and peak later than the corresponding control rainfall profiles with
substantial probability support in the adjusted (for mUltiplicity) P
values. Failure to achieve this first level of confirmation preclu-
des moving to the second level.

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