WMOD00506

• Title: The Persistence of Seeding Effects in a Winter Orographic Cloud Seeded with Silver Iodide Burned in Acetone
• Weather Modification - Doc Type: Report

seedline penetrations are also show~. Note that the ascent of the seeding

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material between 61 and 92 min parallels the slope of the barrier.

The ascent

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rate of the seeding material was 0.2 m S-1 from the time of release out to 92

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min. Also show~ in Fig. 30 are predictions from a trajectory model used by ,-

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the SGPP (Rauber et al., 1988).

Predicted trajectories of ice crystals

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nucleated 5, 15, 30, and 45 min afLer release of seeding material are shown.

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These predictions of fallout gave an average advection of seeding material to

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the surface of 2330 at 12 m S-1 which is 6 m S-1 slower than the advection

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measured by the aircraft at 3.0 km. The trajectory calculation indicated that

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ice crystals would begin reaching the surface after 60 min. Yith this

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advection the southern end of the seedline crossed 3 precipitation gauges, but

passed to the north of KGV. For all three gauges intermittent precipitation

of 1 rr~ h-1, the minim~T. detectable signal, was obsePJed during the time of

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seedline passage. Thus there was no indication in the surface data of the

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effects of seeding.

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4. S~~ary and Conclusions

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One line of AgI NH~I NH4Cl04 was released at -60G in a stable post

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frontal stratiform cloud with naLural particle concentrations in excess of 50 .\~:~r>..:(J:-

L< on the 2D-C. The research ai:::-craft was able to track this seedline to the \~:,,:\.}-,
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dow~wind edge of cloud, some 100 km and 92 min after seeding. During irrtttal

penetrations of the seedline high cor.centrations of ice nuclei were measured,

but changes in particle concent:::-ation on the 2D-G or 2D-P were difficult to

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separate from the background. The seedline then apparently ascended above the

research aircraft. No ice nuclei were detected on penetrations between 19 and

61 min. Cpon clinbing the seeding material was again detected wi:h the ice

nacleus counter during penetrations between 64 and 92 min after seeding. The

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