Alexei Korolev, Research Scientist
Meteorological Service of Canada, Toronto
Date: Wednesday, September 9, 2009
3:00 pm: Conversation and Cookies in Room 108 Atmospheric Sciences Building
3:30 pm: Seminar in Room 114 Transportation Bldg.
Understanding the existence of small ice particles in tropospheric clouds has been a long-standing problem in cloud physics. Debates about this issue began over three decades ago when optical particle spectrometers were first used for sampling airborne cloud particle spectra, and ice particle concentrations measurements in glaciated could were found to be dominated by small particles with sizes less than 50-80um. Small ice particles may play a significant role in the radiation transfer and precipitation formation. Parameterizations of ice crystal spectra based on in-situ observations have been included in many numerical climate and weather prediction models. Over the last few years, an increasing body of evidence has suggested that small ice particle measurements may result from, or be enhanced by artifacts created by bouncing and/or shattering of real ice particles on probe surfaces ahead of the sample volume. To date, efforts to eliminate these artifacts from data sets have included using particle interarrival time, artifact image detection algorithms, and particle minimum-acceptable size thresholds, but in some cases these techniques are not sufficient. Environment Canada, in collaboration with NASA Glenn, has undertaken a series of efforts to better understand and quantify the effect. New probe arms and tips, specifically designed to deflect shattered particles away from the measuring beam, were built and implemented.. Shattering and bouncing of ice particles from probe inlets was documented using high-speed video during dedicated wind tunnel tests. From March to April 2009, Environment Canada conducted the Airborne Icing Instrumentation Evaluation (AIIE) flight campaign dedicated to studying the effects of shattering on cloud microphysical measurements. The results convincingly demonstrate that in specific situations the inlets of conventional probes may increase the raw measured ice particle number concentration by a factor of ten or more. The paper summarizes our knowledge about shattering and its effect on the airborne cloud particle measurements, and provides some examples of the magnitude of its impact.
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