WMOD00310

• Title: Cloud Physics Investigations - University of Wyoming - 1977-1981
• Date: 11/1/1982
• State: WY
• Weather Modification - Doc Type: Report

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the total decay of the liquid water content (Lawson et al., 1980;

Lawson, 1981; Cooper et aI, 1982b,c), and the decay rates were similar

for seeded and un seeded clouds. These data lead to the conclusion that

the rapid decay of the liquid water content was mainly a result of

evaporation of the cloud droplets via entrainment of environmental air.

Basically, the entrainment of air can occur from three locations

outside the cloud. The cloud can dry from below in a manner described

by the bubble theory of convection (Scorer and Ludlam, 1953),

entrainment can occur laterally through the sides of the cloud as in

the classical plume model of convection (Squires and Turner, 1962), or

penetrative downdrafts can dry the cloud by entraining dry air through

the cloud top (Squires, 1958; Telford, 1975). It is also possible, of

course, that these mechanisms may operate in combination, and in

different regions of the same cloud.

Boatman (1981) found strong evidence that the cloudy air found in

HIPLEX clouds near the -80C level was predominantly a mixture of air

framcloud base and air from near cloud top (Fig. 2.14). His conclusions

for Montana were similar to those of Paluch (1979) for northeastern

Colorado. Other indications from NHRE (Fankhauser et al., 1982)

supporting lateral or sub-cloud entrainment are not necessarily in

conflict with the results of Boatman, since they are based on clouds

of different size and on observations at different typical levels in

the clouds.

The spatial structure of HIPLEX clouds reported by Rodi (1981)

suggests that organi~ed entrainment through the sides is improbable.

The spatial structure of the liquid water content measured on the

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