A PARAMETERIZATION OF THE WEGENER-BERGERON-FINDEISEN EFFECT

The Wegener-Bergeron-Findeisen (WBF) process is a mechanism by which i ce crystals grow from the vapour supplied by cloud droplets thus gener ating large cloud particles at the expense of smaller particles withou t draining vapour from the interstitial cloud air. Therefore the net r esult in a cloud is similar to that of coalescence and riming. Treatin g the WBF process like coalescence is an artificial but convenient way of introducing ice physics in cloud models. This trick may be too cru de for sophisticated cloud models but it is shown to work in a simple cloud model where it economizes on computer time.