NUMERICAL-SIMULATION OF HYGROSCOPIC SEEDING IN A CONVECTIVE CLOUD

An axisymmetrical nonhydrostatic convective cloud model with detailed treatment of warm cloud microphysics is presented. The microphysical p rocesses considered are nucleation on cloud condensation nuclei, conde nsation/evaporation, collisional coalescence/breakup (Low and List ker nel), and sedimentation. An accurate multimoment treatment is implemen ted in the calculations of the microphysical processes. The results in dicate that the collisional breakup process is very important in warm clouds and inhibits the growth of drops to large sizes where spontaneo us breakup is significant. This diminishes the importance of the Langm uir chain-reaction mechanism for rain formation. The effects of salt s eeding are examined for three different cases: one maritime case and t wo continental cloud cases. No significant effect followed the injecti on of up to half a ton of salt particles for the maritime case, while the effect was very significant for the continental clouds. The sensit ivity to various seeding parameters was also investigated, including s ize of seeding particles, quantity of seeding material, timing and dur ation of seeding, and location of seeding. The size of the seeded part icles and the timing of seeding were found to be crucial parameters. P remature seeding could have a negative effect. Up to 71% increase in t otal rainfall was obtained under optimal seeding conditions.