WMOD00311

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

700

600

~_.-------------
",,,~ -.~._._._._._._._.-
'''''....
,'/"
,y
l
J
,l

~ 500
1
..J 400
~
Z 300
~
~ 200
g

100

o
60

60

160

200

100

120 140
TIME (mi.)

160

40

35

..~--_.._------ _......_-_......
,l'"
,
./
:
,
,
.:
/'....,

,-30
J
126
~20
i 16
~.
lLo

o
60

160

160

200

80

100

120 140
TIME (mi.)

three-dimensional models. The initial response is

Fig. J 7. Total surface rain (top panel) and hail
(lower panel) versus time for the strong ND case.
The solid line is for the extreme maritime ron, the
dashed line for the extreme continental run, and the
dot-dash line for a saltflare seeding simulation.

increased precipitation for hygroscopic seeding and/or
maritime cases. The eventual results are mixed, due to
the complexity of interactions between the precipitation
downdraft and outflow with the environmental winds.
In general, weak to moderate clouds tend to respond
positively to hygroscopic seeding whereas the response
for strong clouds can go either direction.

V. FUTURE PROSPECTS

In the future, I expect to see increasingly more
complex models in terms of microphysical
sophistication and dimensionality applied to various
aspects of cloud seeding efforts. In particular, I
anticipate use of increasingly complex treatments in
operational decisions and evaluation efforts. There is
also likely to be increased research regarding large-
scale aspects of cloud seeding involving the interaction
of the seeded cloud and the mesoscale environment. Of
prime importance is research to identify and quantify
the forces and processes which determine the
interactions between a seeded cloud and neighboring
clouds. This needs to be done for both enhancing and
suppressing modes of influence.

I

I

Hygroscopic seeding will continue to receive a lot
of attention, especially efforts that seek to understand
the longer-term effects noted for recent field studies.
Toward that end, I am currently collaborating with
Roelof Bruintjes and others at NCAR in the
development of a new microphysical parameterization
scheme for the Clark model which is targeted
specifically for studies of hygroscopic seeding. The
basic requirement of this scheme is that it be of
sufficient detail and breadth to allow model simulations
which reproduce the basic character and evolution of
naturally-occurring clouds and cloud systems while
treating aerosols in enough detail that hygroscopic
seeding can be simulated in a realistic fashion.

I

I

I

I

The scheme includes the following features:
1.) Nucleation of both natural and artificial aerosols
treated directly, with explicit prediction of
supersaturation. 2.) Treatment of the warm rain process
with sufficient detail that development of drizzle and
rain is a function of the cloud droplet distributions
produced from the activated aerosols. 3.) Six
hydrometeor classes are used; cloud water and rain for
the liquid water spectra while the ice particle spectra is
divided into four classes - ice crystals, snow, graupel
and hail. 4.) Two moments of the size distribution,
number concentration and mixing ratio, are predicted
for each hydro meteor class, with the particle size
distributions given by gamma distributions.

I

I

I

I

Each hydro meteor class interacts with water vapor
and with the other hydrometeor classes through a series
of idealized representations or parameterizations of the
physical processes of the nucleation of cloud
condensation nuclei, condensation/evaporation,
collision/co-alescence including drop breakup, both
homogeneous and heterogeneous nucleation of ice
crystals, deposition/sublimation, collision/aggregation,
growth by accretion, freezing, melting and shedding,
and ice multiplication via the rime splintering
mechanism. The treatment of nucleation of CCN is
based on Cohard et al. (1998). Warm rain processes are
based on the treatment of Cohard and Pinty (2000) who
have extended the work of Ziegler (1985). The
treatment of ice is similar to the double-moment four-
class ice scheme developed by Ferrier (1994), although
the new formulation does not allow mixed-phase
particles.

The scheme just previewed is built on the
foundation laid by the pioneering work of Harry
Orville. It reflects many of principles he has
championed. It addresses many of the recognized
weaknesses of the current parameterization based on
Un et al. which Harry and I have discussed over the
years. Certain aspects of the current parameterization
are retained for the new scheme, particularly the

I

I

I

I

I

I

I

I

30

I