WMOD00540

• Project Name: Sierra Cooperative Pilot Project
• Title: A Review of the Sierra Cooperative Pilot Project
• Date: 5/5/1986
• Weather Modification - Doc Type: Report

Bulletin American Meteorological Society

Environmental Satellite) sateliite, animated GOES satellite
imagery, color radar imagery, and telemetered real-time ra-
diometer data. All of this information is used to "nowcast"
when seedable conditions will exist.
Following Hobbs (1975), a computer program is run in
real time to target the seeding effects to the desired location.
The program has two main parts. The first part is a quasi-
empirical airflow model that wnceptually incorporates the
basic features of more-theoretical simulations. The model
assumes the terrain to be a long two-dimensional ridge. At
each grid point, the flow component normal to the barrier is
computed on the basis of steady-state flow in constant-mass
flow channels, while an empirical location-dependent for-
mula is used to specify the component parallel to the ridge.
Model-input requirements consist of the latest rawinsonde
data and a wind profile obtained by the cloud-physics air-
craft duting its climb from McClellan. The second part of the
program is a trajectory-computation routine which uses the
model wind field, the sOl,!nding-temperature profile, and a
time-dependent crystal-growth and fall-speed subroutine.
Schematics illustrating both the flow model and trajectory
model are given as Figs. 6, 7,8, and 9.
By trial and error the seeding line is adjusted to make the
artificial snowflakes fall near the Kingvale site. The so-called
Q-point (seeding-line midpoint) and orientation of the 37-
km-long track are relayed back to the aircraft within five
minutes of receipt of the aircraft wind information. Treat-
ment involves a 1/3 CO2, 1/3 AgI, 1/3 placebo randomiza-
tion scheme if SLW is found above the -80C level, i.e., at

1984-85
SCPP Target Areas and
Instrumentation Locations

400
500
1> 600
.5-
f
~ 700
0.
600
900
1000

521

10
.. 15
'. ~ 30 4O~t
/~&

15

30

45 60 75. 90 105 120 135 150
Distance (km)

FIG. 8. X-Z plot of initially vertical seeding curtain showing po-
sition at five-minute intervals in a strongly sheared environment.
One time-dependent fall-speed function used for this depiction. En-
velope encloses crystals using method described in Fig. 7. st = slow-
est crystal from top, ft = fastest from top, sb = slowest from bot-
tom, Ib = fastest from bottom.

lower temperatures; and 1/2 CO2, 1/2 placebo if the SL W is
limited to regions below this level. The seeder aircraft dis-
penses the seeding material for two hours. The cloud-physics
aircraft flies perpendicular to the seeding track within the an-
ticipated seeding plumes to monitor the growth of the artifi-
cially produced ice and the depletion of the liquid water.
Data collected at Kingvale are averaged over the entire two
hours that treatment effects are calculated to be over the site.
The aircraft, the Skywater radar, and the Kingvale instru-
mentation constitute the primary seeding-response mea-

10 0
a..
· Belfort Weighing Gage 10 0
o Rawinsonde ................ . . . I
<&> Probe

1210
I

,
'1!.
,,' ~t.-
~,
,

10 20
.
10
.
12()0
I

30
.

49 . ~ kilometers
2? nautical miles

39030' -

FIG. 9. From seed line shown, fallout footprint from spectra of fall speeds as defined in Fig. 7.