WMOD00425

• Title: Demonstration of Improved Operational Water Resources Management Through Use of Better Snow Water Equivalent Information
• Date: 9/1/2002
• Weather Modification - Doc Type: Report

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taken from increasing range with the first tilt (0.50), but also iftaken from the second (1.50) or
higher tilts. Either application will compensate for VPR sampling limitations, but FR doe$ not
account for the latter occurrence.

For our previously-used SAA parameters, Fe would become = (150/ac)**(1/2.0). Compare this
to equation (3), which is for FR. We can use these relationships to compare FR and Fe as a
function of range, as presented in table 1.

Table 1.-Range, FR' and clearance, Fe, correction factors as a function of range in km for the 0.50 tilt
(assuming flat terrain), a = 150, and 13 = 2.0
Range 0 10 20 30 40 50 60 70 80 90 100 110
FR 1.000 1.000 1.000 1.000 1.009 1.025 1.051 1.087 1.133 1.190 1.256 1.333
Fc 0.898 0.915 0.934 0.957 0.982 1.010 1.041 1.076 1.115 1.158 1.205 1.258
Range 120 130 140 150 160 170 180 190 200 210 220 230
FR 1.420 1.517 1.624 1.741 1.868 2.005 2.153 2.311 2.478 2.656 2.844 3.042
Fc 1.315 1.379 1.449 1.526 1.612 1.706 1.810 1.924 2.051 2.192 2.347 2.520

FR and Fe are graphed as a function of range in figure 5. For ranges up to 35 km, FR was fixed at
1.00 (no correction). It is evident that the VPR clearance correction factor results in less
calculated precipitation than does the earlier range
correction factor. Previously, at 230-km maximum
range, values were boosted by about a factor of three;
whereas with the clearance correction factor, they are
increased by a factor of about 2.5. The new factor is
based on more data from differing geographic regions
(as opposed to just Minnesota, and 21 versus 9 data
points), so it may have wider geographic applicability.
In practice, the difference between the two systems over
flat regions may not be noticed during real time:
operations. Again, however, the clearance correction
factor should reduce discontinuities associated with
changing tilts over complex terrain. Such a reduction
would be a major benefit.

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50

100 150
Range, km

200 230

Figure 5.-Range and clearance
correction factors as a function of range
for the 0.5-degree beam for old range
correction and new clearance correction
(both with a = 150 and 13 = 2.0).