WMOD00591

• Title: Investigations of Winter Storms over the Wasatch Plateau during the 1994 NOAA-Utah Field Research Program - Final Report
• Date: 7/1/1996
• State: UT
• Weather Modification - Doc Type: Report

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natural precipitation.

2. Seeding Plumes Documented by the Instrumented Van and Aircraft
The 5tarship and research aircraft were very successful in detecting the AgI and SF 6 plumes
during the seeding experiment. The Starship detected the plume persistently on Highway 31 between
RRS and the 264.31 Junction, as well as over the middle of the plateau between RRS and TAR. The
aircraft detected the plume on both of the standard east and west flight tracks, as well as at a
location about 9 kIn dO\m\\ind of TAR. The aircraft plume was detected between 3150 m and 3600
m t - 15~ to -18(\ An example of a Starship SF 6 plume interception is shovm in Fig. 56 and a
summary of all aircraft SF" plume interceptions is shown in Fig. 57. Finally a plan view of both
Starship and aircraft SF c plume interceptions is given in Fig. 58. The envelope connecting the plume
end points in Fig. 58 gives an integrated picture of the spatial coverage of the plume over a period
slightly greater than two hours. The envelope encompassed four precipitation gage locations and the
target site, but the plume stayed slightly north of RRS. Ice nuclei counts in Fig. 23 verify that the
seeding plume did not affect RRS, and data from the TAR site in Fig. 59 show that ice nuclei were
detected over that site from about 0945 through 1100.
Four individual aircraft passes through the seeding plume are shown in Figs. 60-63. The first
plot documents a plume interception about 22 min after the start of seeding, at an altitude of 3400
m ( - 180) and at a location about 6 kIn downwind of the seeding generator. The third panel on the
right of Fig. 60 shows the 2D-C ice concentration (I-see data) for particles> 100 11m diameter, and
the bottom panel shows the SF6 and IN concentrations. There was an apparent ice crystal plume
coincident \\ ith the SF" plume, but closely adjacent to the north there was a natural ice plume which
had concentrations of similar magnitude. The liquid water content in the ice region was minimal.
A later penetration on the west track at 0831 (not sho\\n) revealed an isolated ice crystal plume in
coincidence with both an SF!> and Di plume. The ice concentration peaked at about 28 r' dt this
altitude of about 3250 m ( -18"). Ice concentrations on either side of the plume on this later pass
were generally less than.2 ri.
A second set of aircraft passes took place on the east track. Figure 61 shows one of these
centered at about 0909:30, at an altitude of 3300-3400 m (-160to -17), and a distance of 14.5 Ian

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