A Model of Drizzle Growth In Warm, Turbulent, Stratiform Clouds

Abstract

AbstractA model to describe the growth of precipitation sized drops in layers of warm, stratiform cloud is developed which combines the effects of stochastic turbulent diffusion with explicit microphysical calculations. the representation of diffusion is consistent with measured turbulence statistics, reproduces standard results and is used to define an ensemble of Lagrangian trajectories within which the effects of phase change, stochastic coalescence and vertical exchange due to gravitational settling can be calculated. Mean drop size distributions are predicted as functions of height within the cloud.The inclusion of realistic levels of turbulence is found to produce greatly increased numbers of larger (r >100 μm) drops throughout the depth of the cloud. the modelled steady‐state drop size distributions show good agreement with corresponding aircraft measurements in a case study. the effects of changing the turbulence intensity, cloud depth and liquid water content on the distribution of larger drops are investigated and implications for the cloud layer water balance and the cloud radiative properties are also considered.