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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 6 | Copyright
Atmos. Meas. Tech., 11, 3645-3659, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jun 2018

Research article | 25 Jun 2018

Laboratory and in-flight evaluation of measurement uncertainties from a commercial Cloud Droplet Probe (CDP)

Spencer Faber1, Jeffrey R. French1, and Robert Jackson1,a Spencer Faber et al.
  • 1Department of Atmospheric Science, University of Wyoming, Laramie, WY 82071, USA
  • apresent address: Argonne National Laboratory, Environmental Science Division, Argonne, IL 60439, USA

Abstract. Laboratory and in-flight evaluations of uncertainties 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. Seven experiments with droplet diameters of 9, 17, 24, 29, 34, 38, and 46µm tested sizing and counting performance across a 10µm resolution grid throughout the sample area of a CDP. Results indicate errors in sizing that depend on both droplet diameter and position within the sample area through which a droplet transited. The CDP undersized 9µm droplets by 1–4µm. Droplets with diameters of 17 and 24µm were sized to within 2µm, which is the nominal CDP bin width for droplets of that size. The majority of droplets larger than 17µm were oversized by 2–4µm, while a small percentage were severely undersized, by as much as 30µm. This combination led to an artificial broadening and skewing of the spectra such that mean diameters from a near-monodisperse distribution compared well (within a few percent), while the median diameters were oversized by 5–15%. This has implications on how users should calibrate their probes. 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 hot-wire probe were conducted for 17917 1Hz 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.

Publications Copernicus
Short summary
Laboratory and in-flight evaluations of uncertainties of measurements from a cloud droplet probe are presented. This study extends results of earlier studies by examining instrument response over a greater range of droplet sizes throughout the entire sample volume. Errors in droplet sizing based on the laboratory measurements tend to be less than 10 %, significantly less than typically quoted sizing accuracy for this class of instrument.
Laboratory and in-flight evaluations of uncertainties of measurements from a cloud droplet probe...