ON THE SENSITIVITY OF CLOUD MICROPHYSICS UNDER INFLUENCE OF CLOUD DROP SIZE DISTRIBUTION

The unique Khrgian-Mazin size distribution is suggested as an alternat ive approximation of the entire drop spectra besides the conventional approximation in which the monodisperse and the Marshall-Palmer size d istributions for cloud droplets and raindrops are used, respectively. This approach is employed in bulk microphysics. It is shown that the e ffects of the changed drop size distribution are particularly pronounc ed in the case of the microphysical production terms with rain. This i s a consequence of the fact that the Khrgian-Mazin size distribution p roduces more small raindrops and less large ones compared to the Marsh all-Palmer one, where both have the same rain water mixing ratio. The new production terms with cloud water do not differ from those with th e monodisperse size distribution used. In order to show the sensitivit y of cloud microphysics with respect to the change of drop size distri bution function, the experiments are perform with the two versions of a forced 1-D time-dependent model. The first one involves the microphy sical production terms with the Khrgian-Mazin size distribution, while the other one uses the conventional approach. Experiments clearly sho w that cloud microphysics essentially depends on cloud drop size distr ibution. Some microphysical aspects of a model cloud with the new drop size distribution are in fair agreement with observations. (C) 1998 E lsevier Science B.V. All rights reserved.