WMOD00506

• Title: The Persistence of Seeding Effects in a Winter Orographic Cloud Seeded with Silver Iodide Burned in Acetone
• Weather Modification - Doc Type: Report

seeding the seeder aircraft left the area, while the research airc~aft tracked

the seedline for 1.5 h.

c. Results of Seeding

Measurenents by the research aircraft at the seeding location 10 min

prior to seeding sho~ed 2D-C concentrations of 50 L-1

Images on the 2D-C

indicated that these particles were predominantly water drops. After seeding,

the research aircraft rr.ade 16 pene~rations of the seedline, the first one 5

min, and the last one 92 min, after seeding. The research aircraft used its

air parcel tracking capability for the first 11 penetrations of the seed1ine.

The average advection of an air parcel for these penetrations was 2420 at 17.7

m S-I. A strong signal on the ice nucleus counter confirmed seedline

interception for the first two penetrations at 5 and 12 min after seeding,

Fig. 2a. On the third and fourth penetrations, 19 and 24 min, however, only a

few ~ce nuclei were detected, Fig. 2b. No ice nuclei were measured on the
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next seven penetrations, 29-61 min after seeding. Natural particle

concentrations during these penetrations were high, and although changes in

particle concentration were observed at the seedline, they were not different

from changes observed away from the seedline. Examination of the 2D-C and

2D-P irr:ages indicated that the part~cles were a mixture of graupel, large

water drops, needles, and frozen crops with protruding needles or spikes, Fig.

3. It is interesting to note that changes in the FSSP droplet distribution at

the seedline indicated that evaporation was occurring there, sugges~ing a
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higher cOm.:c?u...r.a-eion of

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~e in the seedline compared to surrounding regionsu~

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