Cumulus Cloud Model - Rain Formation in Warm Clouds: General Systems Theory - page 47

Fig. 2.7 In-cloud rain rate (mm/h)

2.3 Warm Cloud Responses to Hygroscopic

Particle Seeding

In Sects. 1.3 and 1.4, it is shown that the production of buoyant energy released by
condensation in turbulent eddies is mainly responsible for the formation and growth
of the cloud. When warm clouds are seeded with hygroscopic particles, the turbulent
buoyant energy production increases due to condensation and results in enhance-
ment of vertical mass exchange. This would result in enhancement of convergence
in the sub-cloud layer and invigoration of the updraft in the cloud. If sufficient mois-
ture is available in the sub-cloud air layer, the enhanced convergence would lead to
increased condensation and cloud growth. According to the above physical concept
and theory of the cumulus cloud model presented in this chapter, it can be concluded
that hygroscopic particle seeding alters the dynamics of warm clouds.

2.3.1 Dynamic Effect of Salt Seeding

Woodcock and Spencer ( 1967 ) hypothesized that dispersion of NaCl particles in a
nearly water-saturated atmosphere would be sufficient to initiate a cumulus cloud.
Their experiments have produced visible clouds when dry NaCl particles in the
size range 0.5-20 μm diameter, were released from the aircraft in the warm moist
marine boundary layer near Hawaii. The temperatures in the salt-laden air were
about 0.4 °C higher than that of the environment on the average. Observations of