Wednesday, 12 July 2006
Grand Terrace (Monona Terrace Community and Convention Center)
Recent in-situ observations on the vertical profile of microphysical properties of mixed-phase boundary layer Arctic stratus were obtained during MPACE by the University of North Dakota Citation. An algorithm applied to each 30 second sample of in-situ data identifies the phase as either ice, mixed, or liquid by assessing whether cloud particle images from the Cloud Particle Imager (CPI), the two-dimensional cloud probe (2DC) and high volume precipitation sampler (HVPS) are spherical, by determining if the voltage change of the Rosemount icing detector exceeds a given threshold, by examining the spectral shape of the small particle size distribution measured by the forward scattering spectrometer probe (FSSP) and by determining if the total water content measured by the Counterflow Virtual Impactor (CVI) probes exceeds the liquid water content measured by the King probe. Size distributions are computed for the liquid, mixed and ice phases separately using data from the FSSP, the one-dimensional cloud probe (1DC), 2DC and HVPS. The in-situ data are then used to construct vertical profiles of how number concentration of ice crystals and water droplets, ice mass content, liquid water fraction, and effective radius of liquid and ice vary as a function of normalized cloud altitude for single-layer and multiple layer Arctic boundary layer clouds. The observed microphysical profiles are compared against profiles computed from parameterization schemes used in current large-scale models that depend on temperature and total water content, with the impact of differences assessed in terms of radiative forcing. The contributions of water and ice to bulk microphysical and scattering properties are also assessed and compared against results from previous field campaigns.
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