WMOD00311

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

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Figure 2 - a) cloud water, b) rainwater, c) rain
charge density, and d) vertical electric field.

Takahashi (1979) conducted simulations with a
model similar to Chiu's, except that the
microphysics were described by multiple
categories rather than as bulk quantities.
Takahashi's results indicated that inductive
charging in warm clouds would not lead to strong
electrification. Apparently neither Chiu nor
Takahashi were aware of studies by Jennings
(1975) that showed inductive charging between
rain and cloud droplets to be self extinguishing
(the separation probability goes to zero) when the
electric field exceeds 30 kV/m, indicating that
strong electrification by inductive charging of warm
clouds could not occur. Despite this, the
adaptation of the processes mentioned above to
the multidimensional, coupled model environment
achieved by Dr. Chiu was a significant step
forward for electrical modeling and came about as
a result of Dr. Orville's men~orship.
During this period, I was working on my PhD
at the State Univ. of NY at Albany under Dr.
Richard Orville. I was developing my own 20,
slab-symmetric model of warm-rain electrification
and was having trouble deciding on a final focus
for my dissertation research, in addition to some
problems with. numerics. I was familiar with the
work going on at South Dakota Tech and when Dr.
Orville came to Albany to visit his brother, I was
eager to meet with him. We met on a Saturday
morning and discussed my modeling work for 4
hours. During that time Dr. Orville gave me
suggestions for clearing up the problems I was
having with numerical methods as well as
suggesting an avenue of investigation, the effect
of chaff-produced ions on the electrical state of a
storm, that became the subject of my dissertation
(Helsdon, 1979).
Because of his interest in weather

modification, Dr. Orville was aware of recent work
done by Holitza and Kasemir (1974) and Kasemir
et al. (1976) to test the feasibility of suppressing
lightning by dispensing conducting chaff fibers in a
thunderstorm and suggested that I focus my
dissertation research on modeling the effects of
chaff dispensed into the model storm. While I was
aware that the water/water inductive process was
unlikely to be a primary mechanism responsible
for thunderstorm electrification, the mechanism
could be used to create fields large enough to
simulate ion production by chaff fibers distributed
within the cloud and their effect on the strength of
the electrification. In the last year of my research,
the accident leading to the death of Dr. Chiu
occurred and an advertisement to fill the vacant
position was published. Dr. Richard Orville
brought this ad to my attention and encouraged
me to apply for the position, which I did. I was
fortunate to be accepted and upon completion of
my dissertation, I began working at the lAS in
February of 1979 in close collaboration with Dr.
Orville and Richard Farley, a collaboration that
continues to this day.
Within the first year, we converted the model
to run on NCAR computers and I submitted a
manuscript based on my dissertation to the
Journal of Applied Meteorology (Helsdon, 1980).
The results showed that chaff seeding reduced the
electric field in two ways: 1) directly by producing
ions that neutralize charge on hydrometeors by
conduction and convection, and 2) indirectly by
reducing the electric field globally in such a
manner to reduce the charge separation by
induction throughout the cloud. Results also
showed that early or late seeding achieved nearly
identical overall results, although there were
differences in the initial field variation. Figure 3
shows results from (A) early and (B) late seeding
cases compared with a non-seeded case.
After the chaff seeding work was completed,
rather than continue with the model that had been.
developed at Albany, we began adding the various
charging mechanisms to the most recent version
of the IAS cloud model (Orville and Kopp, 1977).
In 1981 the Cooperative Convective Precipitation
Experiment (CCOPE) was carried out near Miles
City, MT. On 19 July a small, marginal (one
recorded lightning flash) thunderstorm was well
observed by aircraft and radar. Among the
observations was a rather comprehensive set of
electrical data obtained by the Desert Research
Institute Aerocommander and the NCAR sailplane
(Gardiner et al., 1985; Dye et al., 1986). The
development of the Storm Electrification Model
(SEM) reached the testing phase after the

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