A numerical comparison study of cloud seeding by silver iodide and liquid carbon dioxide

摘要

A comparison study on dynamic and microphysical effects of cloud seeding by silver iodide (AgI) and liquid carbon dioxide (liquid CO_2) was made using a 3D cloud model with seeding processes. The model was initialized based on the rawinsonde sounding taken from Pinliang station located in the western China on 20 April 2001. The sounding air reflects moist and stable characteristics at middle and low layers. The model results show that the seeding by liquid CO_2 and AgI at - 15 to - 20 ℃ levels of cloud has almost the same dynamic effect on the simulated clouds. The seeding is able to induce the formation of weak convective cells in both seeded and unseeded regions due to latent heat released by the transformation from liquid saturation to ice saturation. However, the initial seeding conducted by liquid CO_2 in the region of maximum supercooled water with temperature of 0 to - 5 ℃ enable to produce much stronger dynamic effect and precipitation by forming many convective new cells at low levels in the later stage of seeded clouds. The accumulated precipitation at the surface can be increased and redistributed, and more concentrated in the downstream region of seeded clouds.