WMOD00311

• Title: Harold D. Orville Symposium - Forty Years of Modeling Clouds and Weather Modification
• Date: 4/26/2003
• Weather Modification - Doc Type: Report

introduction of third generation seeding techniques
along with improved microphysical representations
described in Lin et al. (1983). This development was
largely funded under NSF sponsorship, but came to full
fruition under Bureau of Reclamation funding for
HIPLEX.

Beginning with Hsie et al. (1980), cloud seeding
simulations began mimicking the conduct of real world
seeding experiments regarding such aspects as location,
amount and time of seeding. The results of the
simulations also began showing real world aspects such
as limited time and space windows for cloud seeding to
be

effective. Some aspects of the limited time window
seen in the simulations of Hsie et al. were exaggerated
due to improper assumptions in some of the
microphysical processes. This resulted in too rapid
icing of the simulated clouds, but the basic precept was
sound. The importance of indirect freezing effects also
became apparent around this time in the model results
of Orville and Chen (1982). They employed
differencing of model results with various physical
effects turned on and off to isolate the effects of latent
heating and precipitation loading associated with cloud
seeding. Figure 6 illustrates their technique.

Fig. 6. Comparison of second differences which indicate the effect due solely to cloud seeding caused
by precipitation loading (the left side of each frame) and by the latent heat of fusion (the right side of
eachframe) at 27 min of simulated time.

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