WMOD00412

• Title: Final Report on Utah Cloud Seeding Experimentation Using Propane During the 2003/04 Winter
• Date: 3/1/2005
• State: UT
• Weather Modification - Doc Type: Report

I

I

I

Twenty-two of the 35 plume edges (63%) were between 0.3 to 0.8 km south of the TAR. This tight
grouping was likely caused by a broad flat-topped hill, with highest terrain existing from about 0,6 to 0.9
Ian due south ofthe TAR. The hill is about 100 m above the TAR and appears to often block surface
plumes from being detected immediately east of it on the upwind highway. But plumes may have been
transported just above the hill in some cases. The local hill would not prevent any plume passing south of
it from being detected in the next minor canyon which heads at the upwind highway about 1.3 km south
of the TAR. That apparently happened in the remaining 13 cases (37%).

I

I

There is an apparent association in the plot for southern plume edges to be transported further south as
winds veered. This finding would be expected. While directions ranged between about 200 to 290 deg,
with a median of 232 deg, the large majority of HAS wind directions were between about 200 to 245 deg.
Those cases considered alone showed little association with the southern edge locations. The few cases
with winds north of about 260 deg carried plumes somewhat more south. It is encouraging that the
southern edge was south of the TAR in all cases, suggesting successful targeting was often achieved.
While these early 1994 van observations have not previously been analyzed in this detail, the van crew
developed the strong impression during sampling that HAS-released plumes usually crossed the upwind
highway in the vicinity of the TAR. That impression, shown here to be correct, led to the establishment
of the instrumented TAR for the 1994/95 and 1995/96 winter programs to be discussed, and for the
2003/04 randomized program.

I

I

I

I

A plot of the northern plume edges for the same 35 cases is presented in Fig. 5. All northern edges were
found along the highway, between 3.4 Ian north to 0.4 Ian south of the TAR. Unlike the previoUis figure
which shows that all southern edges were south of the TAR, not all northern edges were north of it. Four
northern edges were south of the TAR. That is, the entire plumes were too far south for successfiJl

I

3.5
3.0 .
2.5 .
.
~ .
'0 2.0
€ .
0
z
~ 1.5
, .
Q)
'"
'1:1 1.0
w .
Q) . .
E .
::J .
ii: . . .
€ 0,5 .
0 . .
z . .
0.0 TAR
.
.
-0,5
-1.0

I

N-S Positions of North
SF6 Plume Edges vs.
HAS Wind Directions.
Early 1994 Field Season

I

I

Y=8.202-O.030X
N=35, R-2=0.34

.

I

.

.

I

.

I

I
I

200 220 240 260 280 300
HAS Mean Wind Direction (deg true)
Fig. 5. Plot of northern SF6 plume edges north and south of the TAR versus HAS wind direction.

12

I