WMOD00376

• Contract/Permit #: 14-06-D-5640
• Project Name: Park Range Atmospheric Water Resources Program
• Title: Park Range Atmospheric Water Resources Program - Phase II - Parts A and B
• Date: 10/6/1967
• Weather Modification - Doc Type: Report

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concentration of ice nuclei, The zmc sulfide unit threshold is realistically

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of. the order of. 1000 particles per m , Coupled with the lower particle per

second output of the trace l' dispenser, the zinc sulfide system is Ie s s sen-

sitive than the AgI system. This explains several cases when a nucleus

count signal was found and no corresponding zinc sulfide signal was obser-

ved during case s of dual tracer release,

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GROUND-BASED DIFFUSION TESTS DURING PRECIPITATION PERIODS -
C, E, Robertson

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This section describes measurements of free-air ice nuclei con-

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centrations made at ground level at Rabbit Ears Pass, Buffalo Pass and

Thunderhead Mountain during precipitation periods in FY67,

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An examination of. the data from the FY67 winter season shows

that a simple relationship often (39% of observation times) exists between

the ice nucleus concentration measured at Rabbit Ears Pass and the wind

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velocity measured atop the 100 ft. tower at Emerald Mountain, An example
is found in the data of 7 December 1966, Figure l3. The one cycle per hour
pulses of AgI seeding can be recognized in the nuclei data, and in the fore-
cast pulse arrival as determined by the Emerald wind speed. The Emerald
wind (plotted as hourly means) is in the direction of Rabbit Ears Pass from
Emerald Mountain (294 degree heading) and is aligned with the upper air
wind, Seeding was started on the half hour and terminated on the hour,
as indicated by the solid, straight lines, The path of the nuclei is thought
to be up Walton Creek Canyon, which is aligned with Rabbit Ears and
Emerald,

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Table IIIlists the transport times for each of the seven pulses,

both calculated from the wind speed and measured from the plot of nuclei

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concentration versus time, Relatively large differences are seen between

transport times of individual pulses; however, the average time of travel

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f.or the seven pulses is essentially the same.

- 30 ~.

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