Studying an effect of salt powder seeding used for precipitation enhancement from convective clouds

Abstract

Abstract. The experimental and theoretical studies of cloud microstructure modification with the "optimal" salt powder for obtaining additional precipitation amounts from convective clouds are performed. The results of experiments carried out in the cloud chamber at the conditions corresponding to the formation of convective clouds have shown that the introduction of the salt powder before a cloud medium is formed in the chamber results in the formation on the large-drop "tail" of additional large drops. In this case seeding with the salt powder leads to enlargement of the whole population of cloud drops and to a decrease of their total concentration as compared to the background cloud medium. These results are the positive factors for stimulating coagulation processes in clouds and for subsequent formation of precipitation in them. An overseeding effect, which is characterized by increased droplet concentration and decreased droplet size, was not observed even at high salt powder concentrations. The results of numerical simulations have shown that the transformation of cloud drop spectra induced by the introduction of the salt powder results in more intense coagulation processes in clouds as compared to the case of cloud modification with hygroscopic particles with relatively narrow particle size distributions, the South African hygroscopic particles from flares being an example of such distributions. The calculation results obtained with a one-dimensional model of a warm convective cloud demonstrated that the effect of salt powder on clouds (total amounts of additional precipitation) is significantly higher than the effect caused by the use of hygroscopic particles with narrow particle size distributions at comparable consumptions of seeding agents. Here we show that seeding at rather low consumption rate of the salt powder precipitation can be obtained from otherwise non precipitating warm convective clouds.