Numerical Simulation of Seeding Liquid Carbon Dioxide to Increase Precipitation

摘要

Using the improved three-dimensional cloud numerical seeding model, an experiment of aircraft seeding liquid carbon dioxide (LC) coolant to increase rain on September 13, 2002 in Yan’an region of Shaanxi Province was simulated and it was compared with seeding AgI ice nuclei. Results show that seeding cloud by LC and AgI in the appropriate part can induce notable change to cloud microphysical and dynamical parameters, accelerate updraft, produce earlier precipitation, change ground precipitation distribution and increase total precipitation on the ground. LC and AgI have different seeding effect though they are seeded according to the seeding rate that each usually use in the appropriate part in the cloud. On the basis of numerical simulation output data, the mechanism of seeding LC to increase rain was analyzed. Results show that after seeding LC in the cloud, rain water first grow through the process of mature ice particle (mainly graupel) thaw to rain (MLxr) when fall below 0°C level with the result of earlier appearance of precipitation particle, then further grow up by cloud-rain water collision and ground precipitation increased and precipitation period extent consequently.