1.6 Mass closure studies using size distributions and bulk water contents measured in arctic cirrus during the Indirect and Semi-Direct Aerosol Campaign (ISDAC)

Monday, 28 June 2010: 10:00 AM
Cascade Ballroom (DoubleTree by Hilton Portland)
Robert Jackson, University of Illinois, Urbana, IL; and G. M. McFarquhar, A. V. Korolev, J. W. Strapp, and P. Lawson

Data collected by the National Research Council (NRC) of Canada Convair-580 in arctic cirrus during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) are used to conduct mass closure tests whereby ice water contents (IWCs) derived from measured size distributions are compared against those measured by bulk probes. An unprecedented 19 cloud probes, including those with and without shrouds and inlets, were installed on the NRC Convair-580 during ISDAC, offering a unique opportunity to evaluate probe consistency and quantify potential effects of particle shattering. Size distributions covering the complete range of particle sizes were determined from various combinations of the Cloud Droplet Probe (CDP), Forward Scattering Spectrometer Probe, Two-Dimensional Cloud Probe, Two-Dimensional Precipitation Probe (2DP), Cloud Imaging Probe, and the Two-Dimensional Stereo Probe (2DS). Bulk IWCs were measured by the Cloud Spectrometer and Impactor (CSI) and Nevzorov shallow- and deep-cone probes. Significant differences between IWCs from the CSI and shallow cone probes compared to IWCs from the deep cone Nevzorov probe are discussed. IWCs estimated from the CDP, 2DS and 2DP size distributions and mass-dimension relations derived from habit mixtures derived from an automated shape recognition scheme applied to data collected by a Cloud Particle Imager are most consistent with those from the deep-cone Nevzorov probe. The dependence of these comparisons on the use of different combinations of probes for determining size distributions, on different techniques for computing particle mass and determining particle habits, and on median mass dimension, particle maximum dimension , true air speed, dominant habit, and aircraft pitch/roll angle are determined. Implications for determining a climatology of arctic cirrus microphysical properties are discussed.
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