A review of parameterizations of microphysical processes in clouds for application in models of regional atmospheric deposition

The literature on parameterizations of cloud microphysical processes was reviewed to examine the theoretical bases of those parameterizations and to evaluate their applicability to regional models. New parameterizations were produced by multiple regression upon the solution fields derived from simulations of a cloud model incorporating sophisticated microphysics. The currently available rates for cloud microphysical interactions were generally derived under the assumption that the size distribution functions for various hydrometeors are given. Such parameterizations must therefore be applied with caution because the spectral evolution of various types of hydrometeors in reality varies significantly during the stages of cloud development. Uncertainties exist in assigning values for aerodynamic properties such as the bulk collection efficiency, and the growth processes for various types of ice crystals are not well enough known for accurate multiphase cloud-microphysics parameterizations. The new parameterizations, in general, compare favorably with those currently available and are more efficient and applicable to regional models. The largest discrepancies occur in the autoconversion rates, whereas the accretion rates agree closely when the assumed collection efficiencies in other formulas are smaller than unity. 56 refs., 16 figs., 3 tabs.