WMOD00311

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

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For Case 1, a positive effect is obtained. Seeding
results in enhanced concentrations of graupel sized
particles earlier in the life of Cell 3 which then
compete for the available supercooled cloud water,
resulting in the formation of numerous small
hailstones. Many of these then melt before reaching
the ground. Seeding in this case results in substantial
decreases in hail fallout (44%) and in hail impact
energy (58%) for Cell 3 with a slight increase (3%) in
surface accumulations of rain. Figure 14 compares
the surface

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'ACCtlU.ATED RAI" AT T- 84.00 ItIN

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precipitation for the unseeded and seeded runs of
Case I. Seeding of Cell 3 leads to very different
.results for Case II, with the warm rain process turned
off. The earlier formation and increased
concentrations of graupel sized particles in the seeded
run of Case n increases the precipitation efficiency of
Cell 3. The results displayed in Fig. 15 translate into
a 340% increase in rain and a 280% increase in hail
for the seeded Cell 3, although the precipitation
amounts are fairly small.

ACC':"U1EO RAIN A1 1-102.00 HIN

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Fig. 14. Horizontal distribution of surface rainfall, hai/jall and hail impact energy
for unseeded (solid) and seeded (dashed) runs of Case I. Results shown at 84
(dominated by Cell 3) and 102 min (storm complex).

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