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 9 - Energy dissipation (1010 J) vs. time (top left), energy dissipation vs. charge transfer (top right),
total cloud ~ 0.1 g/kg (bottom left), NO mixing ratio ~ 1 ppbv (middle), N02 mixing ratio ~ 0.5 ppbv (bottom
right) at 90 min for 10 July 1996 STERAO simulation.

SE cloud in significant concentrations. In contrast
the NO mixing ratio is decaying following the
cessation of lightning activity in the other two cells.
This is even more evident in the N02 plot.
Interestingly, there is a plume of N02 to the
surface similar to that seen in the simpler 3D run
shown in Fig. 8.
In general the model did a reasonable job of
predicting the NOx mixing ratios in a qualitative
sense, but over-predicted the absolute values by
about an order of magnitude. Zhang (2002)
determined that there are several modifications
that can be made to the model to bring the results'
in harmony with the observations without
compromising the physics. Some of the more
important modifications include addition of
radiative transfer effects within the model cloud,
using the breakeven field for lightning initiation
rather than the breakdown field (Marshall et al.,
1995; MacGorman et al., 2001), and adding a
pressure (altitude) dependence to the NO
production rate for lightning (Wang et al., 1998).
These modifications are currently pending.
As can be seen, much progress has been
made in the 30+ years since Dr. Orville and his
students and colleagues pioneered the inclusion of
electrical effects in multidimensional, coupled

cloud models. Interestingly, since the initial work
on the influence of electric forces on cloud
dynamics and microphysics, little has been done
in this area using more recent and more
sophisticated models. The primary reasons for
this are that early studies indicated potential
effects to be small, there is lack of detailed
information on how charges and fields might
influence interaction coefficients (collision
efficiencies, etc.), and the prevalent thinking (right
or wrong) is that other areas related to cloud
electrification are more worthy of study.

4. WHERE ARE WE NOW?

Currently there are two high resolution,
coupled, 3D models - the SO Tech SEM and the
Univ. of Oklahoma/NSSL model (as used by
MacGorman et al., 2001 and Mansell et al., 2002),
being used to simulate the electrification of storms.
Both models have small ions, inductive and
noninductive processes, and a lightning scheme.
There are some differences between the models
with respect to microphysics and lightning
schemes, but for the most part they have similar
capabilities. These models are state-of-the-art
and are being used to address the critical issues

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