Most parameterizations of droplet concentration at cloud base in cloud models are derived under the assumption that all droplets at the cloud base form by nucleation of dry CCN crossing the lifting condensation level in updraft. In this study, a novel method of calculation of the supersaturation maximum and droplet concentration at cloud base is described that takes into account the existence of liquid at the level of droplet nucleation. Liquid exists in haze particles, as well as in the form of cloud droplets and raindrops. It is shown that the presence of liquid water inside non-activated CCN, as well as of cloud droplets and raindrops substantially decreases supersaturation maximum in case of high aerosol concentration. The possible effect of the supersaturation maximum decrease on formation of DSD in clouds is discussed. The method can be also applied to calculation of supersaturation and droplet nucleation at cloud edges.
Bibliographical noteFunding Information:
This research was supported by the Israel Science Foundation (grants 1393/14 ; 2027/17 ), the Office of Science (BER) ., Partial support for this work was provided from grants DE-SC008811 , DE-SC0014295 and ASR DE-FOA-1638 from the U.S. Department of Energy Atmospheric System Research program .
- Cloud base supersaturation maximum
- Droplet concentration