Modeling The Impact Of CCN Concentrations On AgI Seeding Of Mixed-phase Stratiform Clouds

Cloud condensation nuclei (CCN) concentrations directly affect the cloud droplet formation process, when cloud drop and ice crystal coexistence, water vapor move from cloud droplets to ice crystals, which may lead to precipitation, so the CCN concentration may indirectly affect the catalytic effect of ice-water mixed cloud. Using a1-D Category Cloud Model, a stratiform cloud precipitation process of Changchun on July12007in Jilin province was simulated, which can help us to understand the impact of initial CCN concentration on the catalytic process of Agl in the stratiform cloud.Studies show that: Firstly, the greater the initial CCN concentration was used, the less the precipitation enhancement effect of stratiform cloud was showed. Especially when it reached1500cm-3, the precipitation was inhibited by the catalyzation. The minimum of the increased precipitation was happened when AgI was at a amount of1.0×10-6g-kg-1. There was a negative correlation between the concentration of CCN and the amount of catalyzer, and the effect of rain enhancement was more obvious with the decreasing of initial CCN concentration. Thereinto,in the situation that CCN concentration is100cm-3and300cm-3, sow AgI in1.0×10-5g-kg-1; and CCN concentration is500cm-3, sow AgI in1.0×10-7g-kg-1; CCN concentration is1000cm"3, sow AgI in1.0×10-8g-kg-1, the increased precipitation gets larger. The radar echo intensity became greater with the increasing of initial CCN concentration. In the early stage of cloud precipitation, the catalyzer promoted the developing of the cloud, by contrast, the effect was opposite in the mature period. And with a lower concentration of CCN, the promoting effect was more obvious; however the inhibiting effect was greater with a high concentration of CCN. Secondly, moisture variables concentrated at0℃layer. Then with the using of AgI, the mass concentration of ice crystal and snow particles were increased while supercooled water droplet was decreased. Because of the large number of ice phase particles melted and transformed into water particles, a narrow and high mass concentration belt of droplets particles was formed at0℃level, its concentration reached0.7g-kg-1. Owing to consumption of A large number of supercooled water, the formation and growth of graupel particles were inhibited by catalysis. And the CCN concentration was greater, the inhibition of growth of graupel particles was more obvious. Below the0℃layer, the relationship between the mass concentration of water droplet and the concentration of CCN showed a positive correlation, and that between the mass concentration of water droplet and the dosage of catalyzer brought out a negative correlation.In addition, when the dosage of catalyzer was less than1.0×10-7g-kg-1, the mass concentration of ice crystal and snow particles was greater with the increasing of the concentration of CCN. In the cloud developing period, the production ratio of graupel particles increased with the increasing of initial CCN concentration. The sowing of catalyzer, Agl, promoted the occurring of some microphysical processes, the coalescences of snow particles, the deposition and riming of ice crystal particles and so on. In the mature period of cloud, the catalyzer promoted the deposition growing of ice crystal particles, consumed large amounts of supercooled water, and meanwhile, inhibited the condensation growing of supercooled water. In addition, the maximum of the production ratio of the graupel and snow particles was appeared near4000m.In the higher troposphere, the more AgI catalyst was sown, the higher the number concentration of ice crystals was shown, with lower supercooled cloud droplet number concentration and smaller the particle size. With the increasing of CCN concentration, number concentration of supercooled water droplets became more, its particle size became smaller, while particle size of ice crystals became greater. Catalysis broadened the ground water particle spectrum. CCN concentration increased, there were rightward shifts on particle spectrum. But in300minutes water droplet concentration was reduced as a result of catalytic. With CCN concentration increased, catalytic effects was more visible on the particle spectrum whose the ice crystals and droplets of5500m, and at ground and the height of4000m, its influence on water particle spectrum was diminished. With the representation that the spectrum of catalyzed water droplets particles is more close to which of case S0.