Weather Mod Critical Issues Report

• Project Type: General OWC
• Project Name: Weather Modification
• Title: Critical Issues in Weather Modification Research
• Date: 1/1/2004
• Water Conservation - Doc Type: Final Report

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i) Hailstorm cells with an active coalescence process react more positively to ice-
phase seeding than do more continental-type cloud cells, in some situations.

j) The location of favorable regions for hail embryos that produce the larger hail
can be identified.

k) The type of embryo, rather frozen rain or graupel, can be identified, and the
proportion of each that are used to produce hailstones,

I) The importance of shedding from graupel and hail to produce rain is
demonstrated.

General Results

m) Seeding agents (such as silver iodide and hygroscopic material) and dry ice
seeding have been simulated in cloud models. Conservation equations need to be used
for the seeding methods instead of making arbitrary decisions as to when and where to
change the ice crystal concentrations.

n) The seeding material generally affects only restricted portions of the clouds.

0) Hygroscopic seeding affects the coalescence process, and accelerates the
glaciation of the cloud. Consequently, hygroscopic seeding has the very real possibility
of providing both warm rain and cold rain modification effects.

p) Redistribution of the precipitation occurs in some of the seeding simulations.
Whether this occurs or persists over the duration of a field project needs to be determined
by observations and additional mesoscale simulations,

q) The amount of precipitation simulated or predicted by cloud models depends
sometimes on the proper amount of larger scale convergence and/or surface heating and
evaporation prescribed in the models, which can be obtained by observations.

r) Cloud particle initiation processes, although extremely small in magnitude,
need to be retained in the model microphysical equations. Otherwise, the critical paths to
precipitation (either liquid or ice) will not be captured correctly.

These results have come from cloud models of varying complexity. The grid
resolution is relatively fine, normally 100 to a few hundred meters. Bulk-water
microphysics is used to produce most of the results, although bin microphysics is being
used for the precipitating ice in the hail models (and is necessary for the prediction of
cloud seeding effects on hail spectra). Such models could be used to help in operational
cloud seeding projects, identifying those days that might be more susceptible to cloud
seeding attempts, Moderate computing power could provide near real-time results. The
NRC report is short on a discussion of possible modeling support for operational projects.

The NRC report emphasizes the use of bin microphysics in three-dimensional,

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