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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a) Dynamic seeding effects have been simulated, primarily the increased updrafts
associated with the freezing of supercooled liquid water. Of particular importance here
was the demonstration that near instantaneous freezing of the supercooled water was not
possible (but had been used in the one-dimensional, steady-state cloud models), Much of
the latent heat of freezing is released over the period of a few minutes by the accretion of
the supercooled water by larger ice particles,

b) Microphysical or "static" seeding effects have also been simulated; they show
an effect on the cloud and environmental airflow and emphasize that static seeding has
dynamic effects. The primary effect here is the early fallout of the seeded precipitation
and the generation of new cloud cells, Downdrafts in the cloud and in the subcloud layer
are affected.

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c) The interactions of the precipitation with the internal circulations ofthe seeded
cloud and the environmental airflow are often crucial to the total precipitation from a
cloud and cloud system.

d) Greater seeding effects occur in moderate size convective clouds (cloud depths
in the 3 to 7 km range, tops _100 C to -250C). The one-dimensional cloud models have
been key in demonstrating this feature. Field studies in Cuba and in Texas have also
shown such effects (Koloskov et aI., 1996; Rosenfeld and Woodley, 1993).

Stratiform-type Clouds (often orographic clouds)

e) "Dry" as well as "wet" clouds may respond to dynamic seeding, yielding more
vigorous circulations in the cloud and greater precipitation on the ground. This is caused
by the transformation of the heavily seeded cloud region to saturation with respect to ice
instead of saturation with respect to liquid water (Orville et aI., 1984, 1987). The
production of embedded cells in orographic upslope airflow may be caused in some
instances by these effects.

f) The "Goldie-locks" effect is evident, i.e., some conditions are too warm, some
too cold, and some just right for ice-phase seeding to be effective.

g) Transport of the seeding material 10 proper parts of the clouds may not be
possible in some situations, but may be predictable by cloud-resolving mesoscale models
that include conservation equations for the seeding agent.

Hailstorms

h) Hailstone spectra within the storm are being simulated and the effects of
seeding modeled. Observations of hail fall at the ground appear reasonably similar to that
predicted in an unseeded case.

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