WMOD00571

• Title: Static Mode Seeding of Convective Clouds - A Review
• Date: 5/23/1984
• Weather Modification - Doc Type: Report

ice crystals in dry ice seeded clouds and concluded that an effectiveness
of 108 to 109 crystals per gram was consistent with their observational
data. Other investigators have reported values, based on laboratory stu-
dies, in the range of 1010 to 1011 crystals per gram (Weickmann, 1957;
Eadie and Mee, 1963; Fukuta et al., 1971). Hol royd et al. (1978) con-
ducted dry ice seeding experiments in supercooled convective clouds and
obtained empirical nucleation effectiveness values of 2 to 5 x 1011
crystals per gram. Hobbs et al. (1978) deduced values of 2 x 1010 to 1011
crystals per gram from field measurements. Horn et al. (1982) determined
from theoretical and laboratory research that the effectiveness of dry ice
is at least 1013 crystals per gram and could approach values in excess of
1014 crystals per gram. Most recently, Morrison et ale (1984) reported
that laboratory and model studies indicated that dry ice effectiveness was
moderately temperature dependent, ranging from about 1011 crystals per
gram at -2 oC to almost 1013 crystals per gram at -20 oC. Thus estimates
of dry ice effectiveness have almost come full circle since its inception
as a seeding agent, spanning a range from 108 to 1016 crystals per gram in
the process.

The third question, related to the first two, concerns the appropriate
seeding rate or dosage. A wide range of seeding rates have been used with
no indication that a specific seeding rate is most effective in initiating
precipitation. Squires and Smith (1949) and Bowen (1952), among others,
claimed successful precipitation inducement using about one hundred
kilograms of dry ice in a single turret. However, claims of success were
also reported for experiments using a seeding rate of about one kilogram

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