A Study in Cloud Phase Parameterization Using the Gamma Distribution

Abstract

A relatively sophisticated cloud phase parameterization scheme based on the gamma distribution is presented which, it is hoped, will eventually make it possible for cloud modellers to include the effects of microphysics more realistically than has been so far possible. Cloud phase calculations are presented using Lagrangian parcel theory, one-dimensional Eulerian formulation in the vertical, and two-dimensional Eulerian formulation in the horizontal and vertical directions. The solutions obtained using the parameterized scheme were compared with the more conventional finite-difference microphysical calculations of Clark and there was found to be very good agreement for all cases treated. The efficiency of the scheme allowed a one-dimensional study on the effect of vertical spatial resolution on the prediction of microphysical parameters such as droplet number concentration, mean droplet radius and supersaturation. It was found that poor spatial resolution results in a rather slight under-estimation of the droplet number concentration.