WMOD00571

• Title: Static Mode Seeding of Convective Clouds - A Review
• Date: 5/23/1984
• Weather Modification - Doc Type: Report

The experimental units of HIPLEX-1 were semi-isolated cumulus congestus
clouds. Such clouds usually develop precipitation naturally through the
IRG mechanism (Cooper, 1978; Hobbs et al., 1980). Detailed criteria and
procedures for selecting and classifying test cases, for performing the
seeding and for the collection of observations to be used in calculating
response variables were prescribed. Based on preliminary exploratory stu-
dies, the cloud selection criteria (see Table 1) were expected to result in
a sample of clouds that would be amenable to seeding according to the sta-
tic hypothesis and last at least 30 min after treatment for the seeding to
be effective. It was expected that the seeding effects would be most
easily detected in clouds with tops in the -6 to -12 oC range (type A
clouds), but the experimental design permitted selection of rain clouds
with tops in the -12 to -20 oC range (type B clouds) as test cases when no
suitable type A clouds were pres1ent. Type A-2 clouds were included to
account for the occurrence of situations where SICP was found (Hobbs et
al., 1980; Hobbs and Cooper, 1981). The qualifying variables were measured
during a pretreatment pass by a cloud physics aircraft flying through a
visually promising cloud at the ..8 oC level and immediately evaluated by an
onboard computer to determine whl~ther or not the selection criteria for any
of the specified cloud types werl~ met. The seeding was conducted by
dropping a line of dry ice pellets from a jet aircraft at a rate of 0.1
kg/km near the -10 oC level within 2 min after a suitable cloud was
selected. Following the treatment, dry ice or placebo, both the seeding
and cloud physics aircraft made repeated passes at specified times and spe-
cified levels in and below the cloud to document the subsequent chain of
physical events as represented by the response variables (see Table 2).

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