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Colloquium

Department of Atmospheric Science

Tues., Sept. 6, 3:10 pm, EN6085

Microphysical properties of convective clouds sampled during the Convective Precipitation Experiment (COPE) experiment

Robert Jackson

University of Wyoming

Abstract

The Convective Precipitation Experiment (COPE), occurring in the southwest UK during Summer 2013, was motivated to improve quantitative precipitation forecasting, in part, with the aim to increase understanding of both warm and cold precipitation processes that can lead to heavy convective rainfall. In particular, we analyze observations from aircraft in situ microphysical probes and airborne and ground-based radar to examine the relative importance of various microphysical processes and ultimately improve the representation of these processes in numerical models. To characterize the evolution of maturing thunderstorms, the University of Wyoming King Air sampled the tops of fresh turrets between -15℃ and 0℃ on four days in July and August. The microphysical properties of updraft cores from in situ airborne particle measurement probes are investigated. Information about the overall cloud structure that provides context for the interpretation of the detailed cloud microphysical measurements is provided by the Wyoming Cloud Radar (WCR), an airborne W-band radar, and a ground based X-band radar operated by the National Centre for Atmospheric Science.  A novel algorithm for identifying the probability that a particle image from an optical array probe is spherical or ice using a Bayesian classification algorithm is also presented using the COPE data.

                 For a given temperature level, there was a wide variability in the observed liquid and ice crystal concentrations. Significant ice was observed on days where the warm rain process was active, consistent with studies suggesting that raindrops freezing into graupel embroyos as they ascend are critical to ice production in these clouds. In the clouds with graupel and raindrops greater than 1 mm in size present, the WCR reflectivity shows multiple turrets in the sampled clouds, suggesting an environment favorable for precipitation recycling into the updraft. The in situ observations and WCR radar reflectivity also suggest that differences in the amount of liquid water present compared to ice in the updraft core can also be influenced by the depth of the previously formed cloud layer encountered by the turret. The rapid increase in ice concentrations at temperatures from -5 to -8℃ suggests that secondary ice production processes are responsible for the ice concentrations observed. It is shown that greyscale capability for identifying out of focus particles as well as a 10 µm resolution is recommended for distinguishing between spherical and ice particles at sizes useful for identifying first ice initiation in convection.

 


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