Parameterization of the droplet effective radius of warm layer clouds

Two pertinent parameterizations representing respectively the cloud droplet effective radius of maritime and continental warm layer clouds are presented. They are obtained by assuming that warm layer clouds are adiabatic. In order to derive these parameterizations, a theoretical expression of the mean adiabatic cloud droplet effective radius is first developed. This expression depends upon the cloud droplet concentration, the liquid water path and a parameter A that relates linearly the liquid water content to the distance above cloud base. Secondly, an analytic expression of the adiabatic liquid water content is derived and reveals that A depends exclusively upon the cloud base characteristics. By using climatological cloud base values to determine the A value as well as two “standard” droplet concentrations representing respectively droplet concentrations in maritime and continental clouds, one obtains parameterized expressions of the droplet effective radius that depend exclusively upon the liquid water path. The maritime parameterization is validated by using observational data.