WMOD00299

• Title: Physical Structure of Northern Colorado River Basin Cloud Systems
• Date: 9/1/1985
• State: CO
• Weather Modification - Doc Type: Report

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of Fraser et"al. (1973), Hobbs et al. (1973), Young (1974b,c), and
Plooster and Fukuta (1975).
With any method, it is Daramount that the natural physical
structure and natural variability associated with the cloud system to be
modified is understood. Without such background, the tremendous
variability of the structure of the atmosphere, the complications of
scale interaction, and the certainty of the "bad draw" will ultimately
plunge the scientific results into controversy. This has been the fate
of many otherwise carefully planned and executed programs (e.g. Braham
et al., 1971, Hobbs and Rangno, 1979; Rangno and Hobbs, 1980; Smith and
Miller, 1984).
Weather modification research programs have been carried out in the
western United States for over 25 years. The immediate emphasis of the
majority of these programs has been to determine the effects of cloud
seeding on precipitation. Prior to 1977, little emphasis has been
placed on studying the natural physical structure of the cloud systems
to be modified. Two notable exceptions have been the Cascade Prpgram
(Hobbs, 1975a) and the Colorado River Basin Pilot Project (Cooper and
Marwitz, 1980). In the latter case, the majority of the measurements of
the natural physical structure of the clouds were made at the end of the
project. After 1977 ,_~he e]!1phaa;l..s ;in w!atherJ1pdificaUQ.nre~eftrch
.~.j~l'!l~~.J!.(LP.bys.~cal eVB;l~~ A muoh stronger emphasis was plaoed on
~tudy;ing natural cloud conditions. Two factors influenced this change.
lhe first was that physical results $uch as Hobbs (1975a) and Cooper and
Marwitz (1980) conflicted with the conceptual models of cloud system
structure that formed the basis of the hypothesis of the earlier
experiments. The second and major factor was that new instrumentation