A New Design of the Wyoming Droplet Generator for Laboratory Testing and Evaluation of Airborne Cloud Probes

Measurements of cloud and precipitation hydrometeors provide investigators with information necessary to understand processes related to weather and climate. Such measurements can be obtained remotely via satellite or ground sensors, or they can be collected in situ using an instrumented aircraft. In situ observations can further be used for validating numerical simulations and remote sensing retrievals. Also, they allow scientists to better understand cloud-aerosol interactions and the effect of clouds on radiative balances in the atmosphere. Airborne in situ cloud and precipitation measurements are fundamental for understanding microphysical properties of clouds, cloud processes, and for validating local and global climate models. Quantifying limitations and uncertainties of measurements from cloud probes is essential. The University of Wyoming King Air (UWKA) research aircraft employs a variety of probes that operate under different physical principles, most commonly, optical array probes (OAPs) and scattering spectrometer probes. Several methods have been used to calibrate and evaluate the uncertainty associated with such probes, including the use of rotating discs, glass beads, a thin wire (Korolev et al. 1991, JAOTech), and laboratory-based droplet generators (Lance et al. 2010, AMT; Faber et al. 2018, AMT).

In 2016, the University of Wyoming (UW) developed a cloud droplet generator to test and calibrate operational probes from the UWKA and to evaluate proto-type instruments under development. These laboratory-based tests improved our understanding of instruments’ detection range, sizing, and counting capabilities. The design of the UW cloud droplet generator was successful in calibrating smaller probes such as the Cloud Droplet Probe (CDP). However, it did not allow testing and calibration of larger probes that comprise the majority of airborne cloud and precipitation instruments. Therefore, a new design was needed to provide the space required and the adjustability to handle a greater variety of probe types. Here we report on the redesigned UW droplet generator and provide some preliminary results from tests involving both the CDP and other (larger) OAPs. Ultimately, the new design will allow us to accommodate a wider variety of cloud probes and to quantify their uncertainties in a controlled, laboratory environment.