The Dew Point as Nucleation Limit in a Cloud

Abstract

Consider a rain cloud near the dew point, where droplets appear from the water vapor. Then, the nucleation equation previously derived for polymer solutions could be thought of as applying in reverse, water vapor--->water droplets in a cloud. The “solution” would then be the air phase with water vapor mixed with the constituents of the atmosphere and the new phase is the pure water droplet. This paper explains how the author’s nucleation equation pertains to the rain-producing cloud in reverse in equation (5), where T is the temperature of the cloud, To, the temperature it needs to cool to for water droplets to form and n2/n, the vapor pressure of water/air pressure. In this paper, n2/n is eliminated to give measurable quantities. Presumably, atmospheric chemists have access to proper data from altostratus and nimbostratus clouds and could better predict when clouds will nucleate with this very simple formula.