WMOD00299

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

Robert M. Rauber
Atmospheric Science Department
Colorado State University
Fort Collins. Colorado 80523
Fall. 1985

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produced by these cloud systems were dendritic. Aggregation. fragmenta-

tion and accretion were all active processes in these cloud systems.

(2) Deep cloud systems with tops colder than -200C generally were found

to have less potential for precipitation augmentation based on their re-

duced liquid water contents and frequent larger precipitation rates.

Liquid water contents in deep stratiform cloud systems were generally

limited to the region near the mountain crest. Exceptions were cloud

systems where considerable decoupling between the upper and lower cloud

layers occurred. The data suggested that deposition or sorption nuclea-

tion may predominate at cold temperatures in deep clouds. In general.

most particles arriving at the surface had irregular habits. Accretion

was negligible, except in cases where decoupling occurred. Aggregation

was generally limited to small combinations of cold temperature parti-

cles.

(3) Radiometric data suggested that organized convective regions ini-

tially contained significant superCOOled water. but in a short time.

convert to the ice phase. Particles falling from such clouds were fre-

quently rimed and aggregated. Many crystal habits were observed. sug-

gesting complex growth processes.

Three hypotheses for precipitation augmentation are formulated

based on the physical distribution of liquid water and evolution of pre-

cipitation processes observed in Park Range clouds. Field experiments

to test each of the individual hypotheses are described.

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