Improved measurements of the drop size distribution of a freezing drizzle event

Airborne measurements from a new digital holographic camera are compared with PMS 2D-C measurements during the Canadian Freezing Drizzle Experiment. The digital holographic camera is not affected by drop sizing errors associated with out of focus particles in the same way as the 2D-C probe. Recent theoretical simulations of 2D-C particle sizing errors and approaches for statistically correcting the measurements are discussed. The theoretical simulations predict that in freezing drizzle with drop diameters from about 50-200 mu m, uncorrected PMS 2D-C measurements can produce an artificial tail in the drop size distribution that extends out to about 325 mu m. The digital holographic camera does not see the artificial tail. 2D-C measurements of drop size distribution in freezing drizzle that have been statistically corrected show an improved agreement with the digital holographic measurements. Some digital images of drizzle drops and ice crystals from a recently improved version of the instrument, called a cloud particle imager (CPI), are also shown. (C) 1998 Elsevier Science B.V. All rights reserved.