Small Ice Particle Observations in Tropospheric Clouds: Fact or Artifact? Airborne Icing Instrumentation Evaluation Experiment

Alexei Korolev Environment Canada
Edward Emery NASA - Glenn Research Center
J. Walter Strapp Environment Canada
Stewart Cober Environment Canada
George Isaac Meteorological Service of Canada
Mohammed Wasey Environment Canada
Brad Baker SPEC, Inc.
Paul Lawson SPEC, Inc.

Category: Cloud Properties

Working Group: Cloud Life Cycle

Understanding the formation and evolution of small ice particles in clouds has been a long-standing problem in cloud physics. Debates around this problem extend well over three decades and began when optical particle size spectrometers became accepted instruments for airborne cloud-particle sampling. Early airborne measurements suggested that in glaciated clouds, the number concentration of ice particles is dominated by small particles with sizes less than 100 µm. Recently, increasing evidence has suggested that in many cases, concentrations of small ice particles may be the consequence of larger particle impacts on probe tips and inlets followed by shattering into small fragments. Environment Canada has recently undertaken efforts to modify cloud particle probes’ inlets to deflect bouncing particles and shedding water away from the sample volume and optical field apertures, thereby mitigating the effect of shattering on measurements. The performance of the modified and standard probe tips was then studied in the Cox wind tunnel using high-speed video recording. In the spring of 2009, Environment Canada conducted the Airborne Icing Instrumentation Evaluation (AIIE) flight campaign, which attempted to quantify the effect of shattering on ice measurements and improve our understanding of the problem of small ice particles in clouds. The evaluation of this shattering effect was focused on the CIP, FSSP, and OAP-2DC probes installed on the National Research Council of Canada Convair-580. The results of the AIIE project demonstrate that the contamination of particle size distributions by shattering is a significant problem for the airborne microphysical characterization of ice clouds. Shattering may contaminate the ice crystal spectrum up to sizes of ~500 µm, particularly when large ice particles are present, resulting in overestimation of the total number concentration of particles of up to 100 times or more. Existing data processing algorithms cannot effectively filter out all shattering events on all probes.

This poster will be displayed at ASR Science Team Meeting.