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of any type, as snow does commonly occur in the higher terrain of the target area. The other differences in the Santa Barbara area is that the seeding is focused on convective bands which, by definition, should aid the vertical transport of seeding material into areas amenable to treatment by silver iodide and also the structure of the cloud mass is highly of the maritime composition. The convective bands have been shown to contain the raw material for the production of glaciogenic seeding effects; supercooled liquid water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . This proposal has several foci. The first of these is to trace the SF6 plumes (and by association the AgI plumes) from their sources to the target clouds. Another is to document the microphysical characteristics of the clouds comprising the convective bands of interest. A third is to verify (and if necessary modify) the predictive capabilities of the real-time numerical targeting model. Each of these and other ancillary tasks are described in greater detail in the following sections. 2.3 Tasks The research work plan comprises the following four tasks: Release of AgI and SF6 simutaneously Tracking of SF6 Measurement of cloud microphysics Modeling The rational and technical approach for the four tasks are discussed below: Airborne plume tracing involves the use of a specially equipped aircraft to track the motion and dispersion of AgI seeding plumes, An airborne gaseous tracer detector for sulfur hexafluoride (SF6), an inert tracer gas is proposed as the primary plume-sniffing sensor. Use of this technology is well documented (Benner and Lamb 1987), for it has been widely applied in air pollution studies for some years, and also for the tracking of cloud seeding agents (Stith and Benner 1987, Stith et al. 1990, Boe et at. 1992, Detwiler et al. 1996). Aircraft plume tracing can be done in VMC (visual meteorological conditions) or IMC (instrument meteorological conditions. However, in IMC, the aircraft must be flown no closer than 2,000 ft above the highest terrain found within a horizontal distance of 4 nautical miles from the course to be flown [FAA Rules, Part 91.177(a)(2)(i)]. The FAA will grant waivers for project-specific flights to within 1,000 ft above highest terrain if the need for specialized flight operations can be demonstrated. Such a waiver will be sought for this program. In convective bands, the transport will be vertical to large extent, and clearance of the mountains will be less a concern, even during IMC operations. In VMC operations, flight can be guided by vision, and safety is less an issue. Flights under VMC and modified visual flight rules (MVFR) would allow overflight closer to the ridge lines, and sampling of plumes closer to the mountains. However, microphysical sampling is not possible. Since the primary focus of this research is on convective bands, the desired mode of sampling will be within these bands operating under IMC conditions. Plume tracing will be undertaken during daylight, when the project forecaster believes a suitable convective band is approaching one of the three ground based flare sites. Weather Damage Modification Program 26