WMOD00303

• Title: Observational and Numerical Studies of Cloud and Precipitation Development with a View to Rainfall Enhancement
• Date: 4/1/1992
• Weather Modification - Doc Type: Report

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area of interest. In addition, due to the correlation between CLW and the low patterns,
CLW amounts could also change substantially in time and space mAlnJlg it even more
diflicult to predict seeding effects without proper knowledge of the low patterns. To
overcome this problem, some investigators proposed conducting continuous seeding during
the entire storm. duration in the hope that seeding would have positive effects when CLW
was present and no efFects when no CLW was present (Super and Holroyd, 1989; Super,
1990). However, this approach may further mask seeding efFects and can even have negative
effects in certain instances. Furthermore, indiscriminate seeding may explain why so
many seeding experiments in winter orographic regioD.8 have produced either inconclusive
or negative results, i.e. the initial Arizona seeding programs from 1957 to 1964 which
indicated decreases in rainfall due to cloud seeding (Battan and Kassander, 1967).

Developing an optimal delivery technique for effectively dispersing and transporting
seeding material to CLW regioD.8 is an urgent need (Rt'!inlnng and Meitin, 1989), and will
dift'er from one situation to the next. Warburton et al., (1986) provides an assessment
of experimental design consideratioD.8 for tranSport and dispersion of seeding material
and their work could serve as a guide for further developments. The low fields can clliFer
substantially from one storm. situation to the next and even during a single storm. event the
low fields can continually change in time. This will have to be cOD.8idered when developing
guidelines and strategies for dispersing seeding material. This also has in the past
severly limited the opportunities to document the chain of physical events when seeding
is dispensed from one location and most observational facilities are located in another
position. An important aspect that was emphasized in nearly all the past experiments, was
the need for more wind measurements in time and space between the seeding release site
and the target area. With the development of new remote sensing techniques (NefF, 1990;
Uttal et al., 1990), the technology now exists to obtain these much needed measurements.
However, especially in complex terrain, obtaining data at the resolution necessary to
document wind low patterns and CLW regions, requires a dense network of remote
sensors which will be an extremely costly venture. As a supplementary tool modelling
can be used to fill in the gaps of data in our measurement systems. The most prudent

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