WMOD00405

• Title: Thermodynamic Features Affecting Convective Cloud Growth and Dynamic Seeding: A Comparitive Summary of HIPLEX Soundings 1975-1977
• Date: 7/1/1981
• Weather Modification - Doc Type: Report

These analyses determined the dominant type of convective cloud within

250 km of the site and the typical cloud within 75 km of the site if this

differed significantly from that within 250 km. Mesoscale cloud character-
istics within 250 km of the site were also described to distinguish

between organized or mesoscale-triggered convection and isolated "airmass"

1

1

convective cloud development. These satellite observations were used to
stratify cloud model thermodynamic analyses in 1976 and 1977.

3. Dynamic Seeding Hypothesis

The dynamic seeding hypothesis is one of the postulated methods for modifying
clouds containing supercooled water. When clouds having large quantities of
supercooled water are seeded with dry ice or silver iodide, it is hypothesized
(Simpson and Dennis, 1974) that the released latent heat of fusion and deposi-

tion stimulates the cloud buoyancy, which enhances cloud growth and may affect
the precipitation processes. The dynamic effects of increased buoyancy due to

seeding are postulated to cause the cloud to process more water through

increased low-level convergence which leads to a precipitation increase. The

dynamic seeding hypothesis requires a rapid release of latent heat of fusion

and deposition in supercooled regions of clouds. This is accomplished by

producing 10 to 100 ice crystals per liter by artificial seeding of super-
cooled volumes (Simpson and Dennis, 1974).

Simpson and Wiggert (1971) have related the dynamic seeding effect to Lagran-

gian parcel dynamics in a numerical model which diagnoses the expected growth
of convective cloud towers due to dynamic seeding (dynamic seedability). They
tested this hypothesis with observations from aircraft, radar, and rain gages.
The results of their model experiments showed a high correlation between

6