Laboratory and In-flight Evaluation of a Cloud Droplet Probe (CDP)

Abstract. Laboratory and in-flight evaluations of measurements from a Cloud Droplet Probe (CDP) are presented. A description of a water droplet-generating device, similar to those used in previous studies, is provided along with validation of droplet sizing and positioning. Laboratory evaluations of a CDP using the droplet generating system indicate errors in sizing that depend on both droplet diameter and position within the sample area through which a droplet transited. For the smallest diameters tested, the CDP undersized droplets by 1–4 μm for the majority of those sampled. The remaining droplets were sized to within 1 μm of the actual diameter. Droplets with diameters of 17 and 24 μm were sized correctly, within 2 μm, which is the nominal CDP bin width for droplets of that size. For all larger diameters, the majority of droplets were oversized by 2–4 μm, while a small percentage were severely undersized, by as much as 30 μm. This combination leads to an artificial broadening of the spectra, although errors in higher order moments were generally less than 10 %. Comparisons of liquid water content (LWC) calculated from the CDP and that measured from a Nevzorov hotwire probe were conducted for 17,917 1 Hz in-cloud points. Although some differences were noted based on volume-weighted mean diameter and total droplet concentration, the CDP-estimated LWC exceeded that measured by the Nevzorov by approximately 20 %, more than twice the expected difference based on results of the laboratory tests and considerations of Nevzorov collection efficiency.