Comparison of Two Acoustic Ice Nucleus Counters
AbstractTwo acoustical ice nucleus counters (a.k.a. “NCAR counters”) were compared at the Weather Modification, Inc. facilities in Fargo, ND, 17 – 19 September 2007. One counter was one of three built by NCAR in 1976 based on the design of the inventor (andone of the authors, Langer), and is traceable to the Colorado State University Cloud Simulation and Aerosol Laboratory. The other counter was built for WMI in 2006 by the first author. The purpose of the comparison was to document the reliability and reproducibility of the devices undercontrolled conditions. Both counters were brought to operating specifications, then comparisons were run using two types of AgI aerosols sampled through a common source: AgI-NH4I-acetone and AgI-NH4I-C6H4Cl2-NaClO4-acetone. The former was assumed to produce contact nuclei and the latter fast-acting condensation-freezing nuclei. The counters showed close agreement to within a factor of 1.04 to 1.66, depending on the type of AgI aerosol. Times to first indication of plume encounters were on the order of 20 to 30 s depending on the concentration of nuclei, and the instrument-induced smoothing of plume encounters were similar. The results indicate that these devices can provide similar quantitative measurements of different AgI ice nuclei, not merely yes/no indications of AgI presence.
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