WMOD00416

• Title: Wintertime Cloud Systems Over the Rockies: Three Case Studies
• Date: 12/1/1980
• Weather Modification - Doc Type: Report

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collisions associated with turbulent air motions or ordered collisions

caused by a difference in terminal fall velocities between particles,

and 6) rimed ice evaporating in sub-saturated air, can occur when con-

vective elements are present (Hobbs, 1969; Vardiman and Grant, 1972;

Hallett and }mssop, 1974; Hess, 1974; Henmi and Grant, 1974; Aufender

and Larson, 1976; Mossop, 1976; 11ossop and Wishart, 1976; Vardiman,

1976). The updrafts of convective elements are a source of cloud water

and condensate that a stable orographic cloud would lack (Grant, et a1.,

1968; Elliott, 1969; Grant, et al., 1974; Marwitz, 1975; Cooper and

Saunders, 1976; Marwitz, et a!., 1976). As the above microphysical

mechanisms suggest, the presence of convective motions can significant-

ly alter the precipitation processes from those found in stable oro-

graphic clouds (Elliott and Schaffer, 1962; Elliott and Hovind, 1964;

Grant, et a1., 1965; Furman, 1967; Rhea, et a1., 1969; Orgill, 1971;

Grant, g a!., 1974; Marwitz, et al., 1976; Rhea, 1978; Reynolds and
Morris, 1978).

In addition to altering the microphysical processes of the oro-

graphic cloud system, the convective component may also function as a

transport mechanism for seeding material which is dispersed from ground-

based generators. This transport mechanism may be a help or a hindrance

to successful cloud modification (Rhea, et a!., 1969; Elliott, ~~.,

1971; Marwitz, 1974, 1975; Cooper and Saunders, 1976). As is suggested

above the presence or absence of the convective component strongly

affects the potential for static and dynamic modification. A static

modification potential may exist because of a difference between the

condensate supply rate, and the ice growth rate within a cloud system.

Evaporation also has an effect upon this modification potential. A

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