On the sensitivity of cloud microphysics under influence of cloud drop size distribution

The unique Khrgian-Mazin size distribution is suggested as an alternative approximation of the entire drop spectra besides the conventional approximation in which the monodisperse and the Marshall-Palmer size distributions for cloud droplets and raindrops are used, respectively. This approach is employed in bulk microphysics. It is shown that the effects of the changed drop size distribution are particularly pronounced in the case of the microphysical production terms with rain. This is a consequence of the fact that the Khrgian-Mazin size distribution produces more small raindrops and less large ones compared to the Marshall-Palmer one, where both have the same rain water mixing ratio. The new production terms with cloud water do not differ from those with the monodisperse size distribution used. In order to show the sensitivity of cloud microphysics with respect to the change of drop size distribution function, the experiments are perform with the two versions of a forced 1-D time-dependent model. The first one involves the microphysical production terms with the Khrgian-Mazin size distribution, while the other one uses the conventional approach. Experiments clearly show that cloud microphysics essentially depends on cloud drop size distribution. Some microphysical aspects of a model cloud with the new drop size distribution are in fair agreement with observations. (C) 1998 Elsevier Science B.V. All rights reserved.