WMOD00399

• Title: WMO Training Workshop on Weather Modification for Meteorologists - Lecture Notes
• Date: 12/1/1979
• Weather Modification - Doc Type: Report

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- 25 -

different parts of a cloud (Figure 11), both
according to Clark, 1973. 2-D models, how-
ever, have one defficiency, they represent
either clouds with slab or cylindrical
symmetry and leave no space for the complex-
ity in directions of air currents in clouds.
3-D models (Klemp and Wilhelmson, 1978;
Cotton and Tripoli, 1978) are much better in
that respect. The modeller realizes very
soon that the evolution of a cloud is con-
trolled by the boundary conditions and their
variation with time. Thus, for verification
purposes, extensive measurement programs in
nature are required to know how the boundary
conditions could be varied and what the end
product would be.

Further, it needs to be said that
the computational resources are enormous to
deal with the complexities of a single cloud.
An example: If one would start to worry in
one cloud about the growth of CCN to droplets
and the droplet collision problem then the
lower end of the space scale would be at lO-6
cm and that of the time scale at 10-7 seconds.

In all objectivity, however, it has
to be said that cloud dynamics and numerical
modelling has changed Cloud Physics drasti-
cally and has brought awareness of many
mechanisms and interactions which are so
important to the formation of precipitation.

7. Weather Modification Concepts

".

Historically weather modification
may have started by fighting the demons
behind the severe thunderstorms (the Hittite
in Asia Minor used bows and arrows about
1400 B.C. according to Pausanias). Later the
intent was to blow up or disperse hail clouds
by mortars (Leonardo da Vinci) or guns, a
method which was practiced up to 1930 in
regions near the alpes. In the mid thirties
the Swiss engineer named Zimmermann was using,
in the good tradition of William Tell, a
crossbow to shoot dynamite charges into
thunderstorms from an open cockpit aircraft.
With the development of war technology, the
shock delivery system shifted to rockets with
explosive charges. The results were never
such that any of those efforts were extended
over a sufficiently long period of time to
the satisfaction of the consumers.