WMOD00461

• Title: Weather Modification Assessment - Kingdom of Thailand
• Date: 9/1/1986
• Country: Thailand
• Weather Modification - Doc Type: Report

asked; therefore, a variety of models should be USE!d, with each having its
own strengths and weaknesses, to explore different aspects of cloud deve-
lopment and its susceptibility to intentional modi1:ication. Each model
would be used within its capabilities and would onl'y be as complex as the
problem being addressed demands. Five different classes of models are pro-
posed:

"Parcel II models. - In this class of model, a small portion of the
cloud is isolated from its surroundings and described in detail.
This sort of model i~ particularly good for looking at details of
cloud microstructure. Such models are usually father modest in their
computer requirements (many can be set to run on a modern personal
computer), but can be highly sophisticated in the physical processes
being described. Such models could be used to examine the initial
development of precipitation embryos following seeding with hygro-
scopic chemicals, quantifying the heat released from endothermic or
exothermic seeding chemicals, or the initiation and development of
ice in the upper reaches of the larger clouds.

o Trajectory models. - Like "parcel" models, trajectory models are good
for examining the initial development of prec:ipitation. In this
case, however, the growth and movement of individual precipitation
embryos are followed as they are carried aloft in an updraft. Like
IIparcel" models, trajectory models are rather modest in thetr com-
puter requirements. This sort of model should be used to quantify
the time necessary to develop precipitation-sized particles following
seeding, to identify the location in the cloud where the precipita-
tion would be expected to form and to determine the optimum size
seeding particle, that is one that is not so large that it falls out
of the cloud too soon nor so small that it does not fallout of the
cloud at all.

o

o One-dimensional steady-state cumulus dynamics, models. - Models of
this type can be used to examine the general dynamic structure of
convective clouds by examination of specific atmospheric soundings.
Thi s cl ass of model can be run successfully cln small personal com-
puters, but is usually run on larger "minP c:omputers to facilitate
upper air sounding data input. Such a model should be used with a
historical data base to obtain statistical sUlnrnaries of estimated
cloud depths, updraft velocities, and suscept.ibility to modification
by heat release - either by glaciation in the: supercooled portions of
the cloud.or by chemically induced heat releases in lower portions of
the cloud.

o Multilevel microphysical models. - This sort of model can duplicate
the detailed physics contained in parcel models, but within a more
complex multilevel framework to permit interactions between dynamics
and microphysics in a one- and a half dimensional cloud structure.
This produces a rather complex model which needs to be run on a
"minill or mainframe computer. Such a model should be used to unite
the results from the microphysical parcel or trajectory models with
the one-dimensional dynamics models previously discussed and provide

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