Field studies of the optical and microphysical characteristics of clouds enveloping Great Dun Fell

In an effort to study aspects of their evolution, simultaneous measurements have been made, in two separate studies, of the microphysical properties of cap clouds over Great Dun Fell, in Cumbria, at two vertically displaced sites along the line of the wind. Dynamical, optical (10.6 γm) and acoustic sounder measurements were also made. Influences upon the cloud properties of humidity fluctuations near to cloud base, turbulent deposition of droplets to ground, additional activation caused by orographically induced accelerations within the clouds, entrainment of environmental air and long‐wave radiation to space were identified and examined. The clouds studied exhibited structure in their microphysical and optical properties on all scales from a few metres to several hundred metres. The cloud model of Carruthers and Choularton was found to predict the optical and microphysical characteristics of clouds not significantly influenced by entrainment, to a reasonable degree of accuracy.