An investigation of wintertime midlevel mixed-phase clouds with supercooled water droplets using in-situ measurements

In general, the number of aircraft accidents due to weather hazards has been declining with the technology advancement over the past decades. However, In-flight icing is still very challenging and remains a serious aviation hazard. Aircraft flying through mixed-phase clouds in which supercooled water droplets often coexist with ice particles can result in rapid ice accretion on the wings and frames, which can directly cause aircraft crashes. Many efforts have been made to develop reliable techniques for identifying and forecasting icing conditions using various data sources, but our limited knowledge of these mixed-phase clouds has been responsible for the uncertainties in satellite retrievals, surface radar observations, and numerical weather prediction models that these techniques rely on. Although detailed understanding of the characteristics and microphysical properties of the mixed-phase clouds is essential in aviation safety, studies of these clouds have been significantly limited particularly due to lack of extensive in-situ measurements.

In this study, spaceborne radar/lidar data and aircraft in-situ measurements are analyzed in order to better understand the structures and microphysical characteristics of non-precipitating midlevel mixed-phase clouds such as altostratus and altocumulus. Satellite data from CloudSat, CALIPSO, and MODIS of the Aqua satellite are used. We also take advantage of rich data sources from in-situ aircraft measurements during C3VP/CLEX-10 field experiment. The tenth Cloud Layer Experiment (CLEX-10) is part of an ongoing research project for a study of non-precipitating midlevel mixed-phase clouds at CIRA/Colorado State University funded by the Department of Defense's Center for Geosciences/Atmospheric Research. It collaborated with the Canadian CloudSat/CALIPSO Validation Project (C3VP) that took place from 31 October 2006 to 1 March 2007 over Southern Ontario and Southwestern Quebec. The cloud features detected by various sensors are represented for the cases showing mixed phase signatures. The spatial distributions of liquid/ice phase hydrometeors and corresponding atmospheric sounding data are also investigated. This study will provide an observational basis for the improvement of numerical model schemes and satellite retrieval algorithms of midlevel mixed-phase clouds and thus have significant benefits to the aviation community.