WMOD00473

• Title: Evaluation of Bridger Range Winter Cloud Seeding Experiment Using Control Gages
• Date: 12/12/1983
• Weather Modification - Doc Type: Report

DECEMBER 1983

ARLIN B. SUPER AND JAMES A. HEIMBACH, JR.

2005

TABLE 10. Summary of statistics for two Ridge temperature partitions using the single Gallatin Range gage for control.
44 s* Control Zone I Zone 2 Zone 3
Temperature ~ -9OC 56 ns** (I gage) (12 gages) (9 gages) (7 gages)
Target-control correlation All 0.67 0.67 0,71
coefficients s 0.65 0.60 0.63
ns 0.74 0.74 0.80
Mean precipitation (mm) s 2.30 3.21 1.51 1.31
ns 3.13 2.90 1.54 1.28
Median precipitation (mm) s 1.02 1.98 0.65 0.49
ns 1.78 2.10 0.61 0.20
Days with zero precipitation s 16 2 9 7
at all gages ns 10 3 II 10
One-tailed probabilities Wilcoxon 0.06 0.11 0.11
MRPP 0.09 0.10 O.ll
Double ratio Mean 1.51 1.33 1.39
Median 1.65 1.87 4,30
22 s* Control Zone I Zone 2 Zone 3
Temperature ~ -13 oC 27 ns** (I gage) (12 gages) (9 gages) (7 gages)
Target-control correlation All 0.67 0.46 0.40
coefficients s 0.66 0.40 0.42
ns 0.68 0.61 0.50
Mean precipitation (mm) s 1.58 2.29 1.35 1.21
ns 2.55 2.46 0.94 0,76
Median precipitation (mm) s 0.38 1.86 0.62 0.40
ns 1.27 1.71 0.40 0.15
Days with zero precipitation s 8 0 4 2
at all gages ns 7 0 5 4
One-tailed probabilities Wilcoxon 0;05 0.02 0.04
MRPP 0.03 0.02 0.05
Double ratio Mean 1.50 2.31 2.55
Median 3.62 5.24 9.17
* seeded.
** nonseeded.

residt in view of the marked temperature dependence
of suggested seeding effects previously shown.

f Further consideration of the Main Ridge temperature
partitions

As noted in Section 3a, one of the three precipitation
gages used as a control was located 28 km south of
the southern seeding site in the Gallatin Mountain
Range as shown in Fig. 1. This gage was always in-
tended to serve as a control as stated in reports to the
sponsoring agency at the beginning of the BRE. The
type of analysis envisioned was the target-control using
a gamma distribution and a parametric statistical test.
As briefly described in Part II, such an analysis was
attempted but yielded no apparent eff~cts of seeding,
possibly due to the relatively low variance in target
area precipitation explained by the single control gage.
Some might object to use of the other two control

l

gages located at the seeding sites because they were
not specified as controls prior to the BRE and/or be-
cause of danger of contamination by seeding. The latter
is believed improbable in view of the results presented
in Section 4. At any rate, it was decided to repeat the
analysis of the lower Ridge temperature partitions using
only the Gallatin Range gage as control. Results are
shown in Tables 9 and 10 which have the same formats
as Tables 3 and 5 respectively.
Comparison of Tables 5 and 10 shows that the single
Gallatin Range gage is less highly correlated with Zone
1 gages than is the mean of all 3 control gages. However,
the difference is not great. For the downwind zones,
the single control gage has practically the same cor-
relation coefficients as the mean of three gages. While
the probability values in Table 9 are not as low as
those of Table 3, they still suggest a seeding effect for
the colder cases in all 3 zones.
It will be recalled from the discussion in Section 5