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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the physical structure of clouds and precipitation including crystal

concentrations, habits, sizes, fallspeeds, and characteristics of rime

and aggregation. Information relative to this study will be discussed in

more detail in Chapter 4.

(3) SCpp

The SCPP is an ongoing weather modification research program

conducted by the Bureau of Reclamation since 1976 in the central Sierra.

A large number of reports and publications have been generated by the

program concerning natural cloud conditions. These include aircraft

observations (Marwitz et al., 1978, 1979; Stewart, 1979; Stewart and

Marwitz, 1980; Marwitz and Stewart, 1979; Gordon and Marwitz, 1981;

Bradford et a1., 1981; Heggli et a1., 1983), ground observations

(Vardiman and Humphries, 1979; Humphries and Moore, 1981) and radar

observations (Johnston, 1981.; Huggins, 1981). Studies of the

microphysical effects of seeding and dispersion of seeding material have

also been reported (Marwitz and Stewart, 1981; Stewart and Marwitz,

1982a,b; Rodi, 1984; Huggins, 1984, Hartner, 1984; Humphries, 1984).

Cloud systems affecting the central Sierra in winter are extremely

complex at all scales. Marwitz and Stewart (1979) classified the cloud

~ystems into three distinct groups which included stable orographic,

bands and unstable orographic. Huggins (1981) expanded this description

to seven groups based on precipitation echo types. Aircraft

observations in most cases indicated that ice crystal concentrations.

were one to several orders of magnit~de higher than expected, based on

,tandard ice nuclei spectra. Studies such as Stewart (1979), and

Vardiman and Humphries (1979) have indicated that the ice multiplication

process described by Hallett and Mossop> (1974) is frequently active in