The influence of entrainment on the evolution of cloud droplet spectra: II. Field experiments at Great Dun Fell

Measurements have been made of the liquid water content and droplet‐size distributions within clouds enveloping the summit of Great Dun Fell, Cumbria. These covered extensive periods and a variety of meteorological situations. It was found that in highly stable atmospheric conditions cap clouds contain narrow drop‐size distributions and near adiabatic liquid water content. In less stable conditions mixing with the cloud environment was found to have a substantial effect on the microphysical properties of the cloud. In the cases studied the admixture of undersaturated air was found to produce a substantially subadiabatic liquid water content and the spectral shape experienced broadening in a way more consistent with the extreme inhomogeneous model of mixing described in Paper I* than with the classical treatment. In particular, it was found that a small number of large drops experience a greatly enhanced growth rate. In a particular study, it was observed that the interaction of the cap cloud with a pre‐existing strato‐cumulus deck produced a broad drop‐size distribution and an enhanced liquid water content.