A Numerical Study of the Warm Rain Process in Orographic Clouds

Abstract

A technique for numerical simulation of a stationary, two-dimensional laminar flow process is described. Based on this technique, a model for warm rain microphysics in an orographic cloud was developed. The model includes condensation, coalescence and sedimentation. The coalescence process depletes the cloud droplets, causing the supersaturation ratio to rise and may cause additional cloud condensation nuclei to activate. The model predicts the initial shape of droplet spectra fairly well for large drops compared with the field observations. There was a discrepancy, however, between the predicted and observed droplet spectra. It was found that the observed coalescence rate was much faster than the calculated rate. The implications are discussed.