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

has been chosen for the most advanced weather modification experiments.
indicating its widespread acceptance.

An additional important advantage of radar measurements over a dense
rain gage is the yield of information about precipitation parameters
such as height of echo top that cannot be obtained from rain gages. and
the chance to incorporate these data into experimental designs and
evaluations directly related to the cloud microphysics and dynamics.
The contributions of insights gained in this way to the development of
the Flagstaff treatment technology (Smith and Weinstein. 1971) should
not be overlooked. Among the findings that are pertinent to the ques-
tions raised by Osborn concerning precipitation decrease are the
following:

In unseeded clouds, ice was in all cases first encountered in decaying,
downdraft, or well-dissipated regions of the cloud. spreading into the
rest of the cloud as this also began to decay. This glaciation phase
tended to follow closely upon the phase in which the cloud. if it pro-
duced precipitation at all, had converted most of the available condensed
liquid to precipitation through a coalescence process. In the decaying
phase, a change from relatively few rapidly growing ice particles to a
large number of small crystals was taken to indicate the operation of
some crystal-multiplication mechanism. Since the showers themselves
went through the same phases of growth and decay already well documented
for all-water shower clouds, no indication was found that the appearance

10