Numerical study of the AgI seeding principle for decreasing the convective cloud rainfall

After two prognostic variables are added, an AgI seeding scheme is coupled with the three-dimensional cloud model, considering four nucleation modes. A case of convective cloud rainfall is simulated using this model. Numerical seeding experiments of releasing AgI in cloud are simulated to study the possibility to decrease the convective rainfall intensity. Several tests in the different locations and different concentrations of seeding particles are designed. The results show that overseeding in updraft area with supercooled water can not only reduce the amount of rainfall, but also reduce the maximum rainfall strength. With 2×108 kg-1 seeding concentration, rainfall amount can be decreased up to 32%, which greatly lowers the possibility of causing flood. After seeding with large amounts of AgI, numerous AgI particles are nucleated, and these ice particles consume most supercooled water. The falling speeds of graupel and raindrops become weaker after seeding. The decrease of melting amount of graupel to rain in seeding cloud causes the decrease of rain amount, but later the much more evaporation of rain causes less rainfall amount. The results show that the condensation freezing and immersion freezing are the dominant nucleation modes in this convective cloud. The over-seeding methods in this research are able to be used in field operation.