The influence of CCN spectra and updraft velocities on the validity of the b2 parameterization of the condensation process

A detailed parcel model of condensational droplet growth, including surface tension and dissolved salts effects, is used for studying the validity of a parameterization based on the simplified droplet growth equation, the b2 scheme. In the b2 scheme, spectra are derived from the droplet distribution at the activation level, and the liquid water mixing ratio using a translation of the initial spectrum in the r2 scale. Spectra derived from the detailed model are thus compared to translated spectra. Four simplified CCN distributions are tested for updraft velocities in the range of 0.5 m/s to 5.0 m/s. It is shown that the b2 scheme is suitable for use in cloud models, except when the proportion of large nuclei in the CCN distribution is extremely high.