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P. Kornfeld

Abstract

The growth of cloud droplets by condensation of vapor upon soluble and insoluble nuclei was computed for different nuclei distributions. The set of equations used takes into account the interdependence of vapor condensation and changes of temperature and pressure in the vertically moving air. The results show that the spectrum of cloud droplets is broader if the nuclei distribution includes hygroscopic and insoluble nuclei together, rather than different sizes of salt nuclei only. If different numbers of nuclei are assumed in neighboring air parcels, then the size spectrum in the cloud is even broader. The width of the spectrum obtained in this study seems to be broad enough to initiate the process of raindrop growth by coalescence. Results for different updraft velocities and a non-constant vertical velocity of the air parcel show that the final sizes of the drops are almost the same when measured at a certain altitude z, no matter what the vertical velocity was.

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P. Kornfeld

Abstract

The effectiveness of warm fog clearing by seeding with hygroscopic nuclei was studied numerically. A parcel of air with a known distribution of fog droplets was assumed to be seeded with hygroscopic nuclei. While new drops were formed upon the seeding nuclei due to condensation, the fog droplets became smaller due to evaporation. The new distribution of drops and the corresponding visibility are given for 60 and 100 sec after seeding. The results indicate that seeding may be effective if the type of fog to be cleared is known as to droplet distribution and the seeding nuclei are chosen accordingly.

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