An assessment of the Keily probe for the ground‐based measurement of drop size distributions in clouds

A series of experiments has been performed to calibrate and assess the reliability of the Keily probe for ground‐based measurements of droplet size distributions in cloud. Tests were conducted in natural and artificially produced water clouds at our field research station on Great Dun Fell, and in a specially constructed cloud tunnel. Comparisons were made with drop size distributions measured with a Knollenberg ASSP device and with MgO coated slides. Collection efficiencies were obtained for the Keily probe for various values of ventilation speed and orifice size. It was concluded that the instrument operated consistently and reliably within the range of conditions applicable to our ground‐based field research.