Mesoscale processes of cloud formation, cloud-radiation interaction, and their modelling with explicit cloud microphysics

Abstract

An analysis is made of a global distribution of clouds and the main processes of cloud formation in Earth climatic system. Mesostructure and microstructure of main cloud types are described. Methods for the calculation of the microphysical, optical and radiative properties of clouds in numerical models are discussed. Mesoscale cloud models with explicit microphysics and results of simulations for various cloud types are described with an example of a series of 2DT and 3DT models, developed at Central Aerological Observatory (CAO). The models are peculiar to the explicit description of the microphysical processes in clouds, based on the kinetic equations for droplet and crystal size distribution functions with division of droplet and crystal size spectra into 30 bins from 1 μm to 3.5 mm and with detailed account for CCN and ice nuclei activation, condensation/ deposition and coalescence/accretion growth. These equations are being solved along with supersaturation equation. This allows to make detailed calculations of the optical and radiative characteristics of clouds: scattering and absorption coefficients, single-scattering albedo, fluxes, albedo. Development of various cloud types (Sc in ABL, frontal stratiform, convective and Ci, orographic) and their interaction with longwave and solar radiation are reviewed on the basis of mesoscale modelling and some observational data. The results of such calculations can serve as a basis for a detailed parameterization of clouds and radiation in the GCM's. Recommendations for the GCM's and for the construction of a global semi-empirical cloud-radiation model are presented.