WMOD00290

• Title: 1994 Field Operation Plan
• Date: 1/1/1994
• State: UT
• Weather Modification - Doc Type: Report

2. OVERVIEW OF THE EARLY 1994 FIELD PROGRAM

2.1 Introduction

The early 1994 field program will be conducted from January 16, 1994, through March 16, 1994, on the
Plateau east of Fairview, Utah. This is the same experimental area used for the early 1991 field campaign.
This region has proven to have considerable operational advantages while still being typical of many of the
mountain barriers seeded by the operational program. The all-weather road system over the Plateau, rare
for mountainous terrain, offers good access to a portion of the Plateau as shown on Fig. 1. Travel by
snowmobile is practical over much of the Plateau top.

The two primary aircraft sampling flight lines shown on Fig. 1 are the same as used in 1991. A secondary
line, not shown, will pass over the RRS and TAR sites. It will be used to sample the cross-barrier
distribution of SLW.

2.2 Objectives of the 1994 Field Program

The early 1994 field project will have four objectives:

1. One objective will be to expand upon the 1991 observations of the T&D of ground-released AgI
during winter storms, particularly in nonconvective cases which were uncommon during the 1991 field season.
Valley, canyon-mouth and high-altitude, windward slope seeding sites will all be tested, sometimes using AgI
and sometimes simulating AgI with sulfur hexafluoride (SF 6) tracer gas.

2. A second objective will be to document the ice crystal characteristics (concentrations, size spectra,
habits) produced by seeding, and the resulting snowfall at ground level. A series of direct detection
experiments will be conducted with seeding done at two high-altitude sites, using AgI generators for some
experiments and propane dispensers for others.

3. A third objective, closely related to the second and needed for the frrst, is to document the IPC
that results from seeding orographic clouds. The IPCs resulting from AgI seeding will be chiefly a function
of SL W temperature. Most past estimates of the IPCs expected to result from AgI seeding have been based
on other measurements (e.g., IN or SF 6). Such estimates have used AgI generator calibrations done in cloud
simulation laboratories. As previously noted, it is not known how closely such laboratory estimates
approximate orographic clouds.

The IPCs resulting from propane seeding are expected to show little temperature dependence, based on
previous studies. However, there is some question about the effectiveness of propane seeding (number of ice
particles created per mass of propane released). Documentation of propane seeding effectiveness has been
quite limited in winter orographic clouds. Consequently, further measurements would be useful in evaluating
propane seeding, especially at cloud temperatures between about 0 and -6 oC where AgI seeding is likely
ineffective.

4. The fourth objective will be to further examine temporal and spatial SLW distributions over the
Plateau using of one fixed and one mobile microwave radiometer, and aircraft measurements. The approach
of using a fixed and mobile radiometer, first attempted in 1991, provided a unique and interesting data set.
However, expansion of available observations is desirable, especially along-the-wind over the Plateau top.

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