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

of ice was other than an incidental characteristic due to the lower

temperature or that it substantially altered the course of the coales-

cence produced shower.

In seeded clouds, ice was encountered first in the central updraft
regions, where ice particles were observed to grow to precipitation size
as they reached the upper part of the cloud during its actively growing
phase. The initial growth phase was followed not by immediate decay as
was the case with unseeded clouds, but by a dynamic rejuvenation that
was accompanied by the reappearance of supercooled liquid water and con-
tinued hydrometeor growth. In 7 out of IS cases the cloud rejuvenation
was accompanied by such severe icing conditions in the cloud that air-
plane penetrations had to be broken off. This reinforcement of cloud
growth by the dynamic effect and rejuvenation of active condensation
(processing of additional water vapor) and precipitation led to pro-
longation of the precipitating phase and to augmentation of the precip-
itation amount.

In short, though there does exist a rational basis for comparing the

effectiveness of radar and dense rain gage networks as estimators of

total rainfall at the ground, Osborn fails to give evidence for the

superiority of the latter, especially in the rugged terrain of Arizona

and especially where the microphysics, dynamics, and rainfall of indi-

vidual clouds are concerned.

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