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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size rain shower in the CCOPE field study. Several characteristics of the actual storm
were captured in the simulation,

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A three-dimensional framework is preferable, but sometimes not practical. The
two-dimensional cloud models have been tested in several WMO workshops (WMO,
1985, 1988, 1994) and reported in the literature (Tuttle et aI., 1989; Helsdon and Farley,
1987a; Hjelmfelt et aI., 1989). The models simulated satisfactorily many of the
characteristics of cloud and storm systems, including the development of realistic radar
signatures and the production of microbursts. Their greatest disadvantage is the too rapid
development of rain from coalescence of the cloud water in the bulk-water models. (This
is more of a concern in weaker cloud situations than in strong, convective continental
type clouds where the ice processes dominate and rain forms predominantly from the
melting of graupel or hail.) Their advantage over one-dimensional models is that they
simulate realistic airflows and water contents to produce reasonable simulations of rain or
hail in the cloud and fallout at the ground. They can and have been used in real-time
forecasting to analyze the potential of an atmospheric sounding to support the production
of precipitation (Tuttle et aI., 1989; Kopp and Orville, 1994), This was done during the
NOTP in 1989, and to a lesser extent in the NOTE in 1993.

Separate from these microphysical discussions is the fact that the cloud modeling
of the past two to three decades has indicated the importance of including the effects of
larger scale convergence and the heating and evaporation at the earth's surface in the
simulations (Chen and Orville, 1980). Observations and modeling results indicate that
convergence or divergence values of order] 0-5 s-I may affect significantly the degree of
cloud development and should be included in models trying to predict or simulate real
clouds. The convergence has an effect on the frequency of cloud merger. Similarly, the
inclusion of reasonable heating and evaporation rates at the ground can be very important
to the amount of rainfall predicted. Thus there are many things in addition to the
microphysics that should be considered to produce realistic predictions and simulations
of clouds and storm systems.

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Atmospheric electricity modeling, The NRC report speculated about the possible
influence of atmospheric electricity in natural precipitation and in cloud seeding results.
Helsdon and Farley (1987b) published the first simulation, including atmospheric
electricity effects, of a cloud that produced lightning, Further work has advanced to
simulations in the 3D Clark/Farley model that include the actual simulation of the
lightning flashes in the storms and more refined atmospheric electricity modeling
(Helsdon et aI., 1992, 200 I, 2002; Zhang, et aI., 2003), The models are too complicated
for real-time application in cloud seeding operations at this time. Bulk-water
microphysics has been used to develop the theory.

Following are some of the findings and predictions from cloud models employing
realistic cloud seeding and storm simulations, Background material for most of the
statements can be found in Orville (1996) and in the references listed therein,

Convective-type Clouds (cumulus congestus to cumulonimbus)

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