Study on the formation process of warm rain using quasi-real scale artificial cloud experimental system

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The initiation of warm rain is critically dependent on the presence of cloud droplets larger than 50mum in diameter. The conditions that determine the size distribution of cloud droplets was studied using a quasi-real scale artificial cloud experimental system. Many parameters affect the size distribution of cloud droplets. From observations of the size distribution of cloud droplets that were formed on various aerosol concentrations introduced into a vertical shaft, it was proved in practice that a large number of small-sized cloud droplets are formed in the case of a high CCN concentration and a small number of large-size cloud droplets are formed in the case of a low CCN concentration.Next, numerical simulations were carried out under the conditions that air parcels move upward in the shaft and grow into cloud droplets by condensation. The effects of only the relative humidity at the bottom of the shaft and only differences in CCN spectra on the cloud droplet spectra were quantitatively estimated.The artificial cloud experimental system was later transferred from Kamisunagawa to Kamaishi, but experimental studies were continued. Using the previous numerical model of cloud droplets formed by condensation, the effects of only the elemental components of aerosol and only the vertical velocity on the cloud droplet spectra were quantitatively estimated. The results elucidated the formation mechanism of warm rain.