WMOD00299 ‎(2)‎

• Title: Scientific Weather Modification Experimentation in the United States
• Date: 8/25/1984
• Weather Modification - Doc Type: Report

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Although equivalent intercomparisons between the aircraft and radiometer were
not possible due to the sampling differences (aircraft measured at one level),
it was found that if the radiometer detected liquid water, the aircraft did
also, and vice versa. If it was assumed that the amount of liquid detected at
one level by the aircraft was evenly distributed through the cloud depth, a very
close correspondence of vertically integrated liquid water values was found to
exist.

In comparisons between liquid water derived from the dual-wavelength and
satellite-receiver radiometers, the correlation coefficient between the two sets
of data points was 0.95 with the values from the dual wavelength system being
about 11 percent higher.

The Bureau of Reclamation is not the only group who is using the radiometer in
support of weather modification studies. Researchers at Utah State University
(Hill, 1984), the Desert Research Institute (Long and Walsh, 1984) and Colorado
State University (Rauber et a1., 1984) have all reported that radiometers are
very useful detectors of supercooled liquid water.

In the near future the Bureau of Reclamation plans to convene in a workshop with
others who operate radiometers in order to gain more knowledge regarding such
things as:

1. accuracy of vertically integrated liquid values
2. stability of measurements
3. intercomparabi1ity between radiometers
4. optimum calibration techniques
5. data gathering procedures (vertical pointing vs. scanning)
6. combining data from two or more radiometers to achieve reasonable esti-
mates of vertical profiles of liquid water

The workshop will consist of a field program using several radiometers supported
by a cloud physics aircraft followed by independent, but coordinated analyses to
assemble a comprehensive set of results and conclusions.

b. Ice nucleating characteristics of silver iodide

The real effectiveness of silver iodide as a seeding agent depends on the number
of ice crystals it produces at the cloud temperatures specified by the seeding
hypothesis. The ice crystal yield of the seeding material, as distinguished
from its cloud chamber calibration of effectivity (potential effectiveness), is
mainly determined by its nucleation rate and residence time in the portion of
the cloud of interest. The nucleation rate is, in turn, determined t~ the par-
ticular silver iodide agent's mode of nucleation and the cloud environment fac-
tors which affect it.

Using chemical kinetic theory and experimental methodology, scientists at the
Colorado State University Cloud Simulation and Aerosol Laboratory have investi-
gated the nucleation mode and nucleation time constants of a variety of silver
iodide seeding complexes. DeMott et a1., (1983) have shown that seeding agents
such as silver iodide-silver chloride and silver iodide-ammonium iodide appear
to act primarily by the contact-freezing nucleation mode and have long time

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