WMOD00400

• Contract/Permit #: 14-06-D-6801
• Title: Structure and Seedability of San Juan Storms
• Date: 11/1/1976
• Weather Modification - Doc Type: Report

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52

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more definitive nucleus measurements of Hobbs et a1. (1975). In addition,

this result is consistent with the transport and diffusion calculations made

from the measurements of the inertial navigation system and air sensing probe

of the NCAR Q/A.
The stable stage of the San Juan storms is therefore unseedab1e, because

there is negligible liquid water present and because the seeding material

cannot reach cloud level from the ground-based generators.

b. The neutral stage

During the neutral stage, tl1ere is an extensive liquid water region well

ahead of the target area, as indicated in Fig. 3.3b. This region might be

seeded if the generators were further up'vind, because the neutral stratifi-

cation permits transport of the AgI to the cloud. However, most of this

upwind portion of the cloud is apparently glaciated naturally. A seeding

effect here would have to depend on glaciating the cloud earlier, so that

less of the ice would be carried over the mountain.

Because of the absence of convection, liquid water contents in the

region over the mountains are less in the neutral stage than in the unstable

stage. However, the lower updrafts make transport of the precipitation to

the target area somewhat easier. The absence of convection delays the entry

of the AgI into the cloud, so that AgI often first reaches cloud level near

the upwind edge of the target area, and only reaches a fraction of the

seedable liquid water. Seeding further up'vind might be more effective for

the neutral storm stage, because AgI could enter the liquid water region

over the mountains at greater heights and a greater fraction of the region

could be seeded.