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Master's Defense

Department of Atmospheric Science

Wed., Apr. 25, 2:10 pm, EN6085

Cloud particle shape discrimination and improving hydrometeor characterization with in-situ optical array probe measurements

Darcy Jacobson

University of Wyoming

Abstract

Measurements of individual particles within clouds are essential for studies of cloud microphysical processes and developing parametrizations for numerical models. Optical array probes provide two-dimensional images of cloud liquid drops, ice crystals, and precipitation when flown on board research aircraft. From these measurements, cloud particle concentrations, size distributions, and types are derived and used to describe the microphysical properties of clouds. Certain physical limitations exist when imaging cloud particles and are considered when attempting to characterize hydrometeors. Particle images collected by optical array probes can appear hollow due to the diffraction of light around them impacting our ability to accurately quantify particle dimensions and shape. A method to correct holes within particle images is explored and the resulting estimations of diameter, area, and perimeter are used to quantify particle circularity. Cloud imaging probe (CIP) and two-dimensional stereo (2DS) probe measurements collected primarily during the Precipitation and Cloud Measurements for Instrument Characterization and Evaluation (PACMICE) field campaign are analyzed. Particle shape characterization is evaluated for periods of only liquid and only ice to develop a method of distinguishing particles as circular or non-circular and applied to a mixed phase period. It is shown that correcting for image holes yields better characterized particle shape parameters and therefore an improved discrimination of particle type.


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