WMOD00306 ‎(2)‎

• Title: Discusison of "Weather Modification in Arizona in 1971" by Herbert A. Osborn
• Date: 6/1/1972
• State: AZ
• Weather Modification - Doc Type: Report

total circulation of the ring-vortex associated with the cloud.
Positively buoyant rising air and negatively buoyant descending air
do work that increases the circulation. and vice versa. The ARIDROP
treatment. leading to release of latent heat mainly in the central
updraft. and mainly during the phase of active cloud growth. increased
the total circulation at the critical time of active growth and rain
formation. It initiated the growth of frozen particles where they
enjoyed a competitive advantage with respect to unfrozen drops
(Douglas, 1959).

The dynamic effect of seeding that conforms to this model has been
well documented in fully randomized tests for clouds in Arizona
(Weinstein and Maceready, 1969) and elsewhere (e.g., Simpson, et aI,
1971) .

The Catalina treatment, on the other hand, placed the silver iodide
initially in a stratum of air through which the cloud (or cloud-
building updraft) rose, in air that was much drier and potentially
colder than the rising updraft. In the Murray model, entrainment
occurs mostly into the crown of the cloud, producing a cold cap
chilled by evaporation of moisture into the relatively dry environ-
mental air; this air descends along the outer part of the cloud and
eventually winds up either in the downdraft beneath the dying phase
of the cloud or as relatively impoverished cloud detritus outside
the main circulation region. Where the cloudy air was seeded it was
in like measure dried and chilled by the dilution and still further

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