Understanding of the mixed-phase clouds with both liquid and ice phase hydrometeors is important for radar, lidar, satellite retrievals, and climate/weather numerical modeling. However, detection of mixed-phase clouds in which supercooled liquid water coexists with ice is still very challenging work and their microphysics are not well understood. Our limited knowledge of mixed-phase cloud structure and characteristics is responsible for the uncertainties in radiative transfer modeling and satellite measurements because these clouds have not been accurately represented in weather/climate models and satellite retrievals. Although they are more common than single-phase clouds in the real atmosphere, remote sensing studies on their physical properties have been restricted. In general, studies of cloud phase-composition for mixed-phase clouds have been significantly limited by a lack of intensive in situ measurements that can discriminate between the ice and liquid phases.

This work presents a study of the mixed-phase clouds using satellite passive/active microwave observations and aircraft in situ measurements. In this study, we attempt to interpret and characterize the wintertime mixed-phase clouds by analyzing satellite data, especially from spaceborne radar and high microwave channels that are sensitive to both liquid and ice particles. The features of mixed-phase clouds detected by various satellite sensors and the vertical distributions of liquid/ice hydrometeors in the clouds are represented. For studying the vertical structure of clouds, data from the recently launched CloudSat are used. CloudSat is designed to measure the vertical structure of clouds and precipitation from space with a 94-GHz cloud profiling radar, which observes the cloud condensate and precipitation within its nadir field of view and provides profiles of these properties with a vertical resolution of 500m. The AMSU-B (Advanced Microwave Sounding Unit – B) data onboard NOAA satellite series are used to explore the response to mixed-phase clouds at higher frequencies, 89, 150 GHz, and three water vapor channels at 183.3±1, 183.3±3, and 183.3±7 GHz. MODIS (Moderate-Resolution Imaging Spectroradiometer) images of the Aqua satellite are used to examine cloudy areas. Aircraft observations during C3VP/CLEX10 (the Canadian CloudSat/CALIPSO Validation Project / the tenth Cloud Layer Experiments) are also shown. The CLEX is part of an ongoing effort funded by the Department of Defense's Center for Geosciences/Atmospheric Research to observe and characterize the microphysical properties, dynamics and morphology of non-precipitating, mid-level, mixed-phase clouds. The C3VP is the extensive validation of the satellite products performed by the Meteorological Service of Canada as part of the international CloudSat program, which is mainly to validate measurements and retrieved products from the CloudSat and CALIPSO satellites. These field experiments were jointly conducted during 2006-2007 winter seasons focused on the Great Lakes and surrounding areas.

We try to answer the following questions here: What are the important features of mixed-phase clouds detected by various satellite sensors? How do the mixed-phase clouds respond at microwave frequencies? How are the vertical distributions of liquid/ice phase hydrometeors in the clouds in different regions? Preliminary results from in situ aircraft measurements are also discussed as well as satellite observations.

Three cases on 2 December 2006, 5 December 2006, and 26 January 2007 showing mixed phase signatures during C3VP/CLEX10 are analyzed. To understand how liquid and ice hydrometeors respond at microwave frequencies, brightness temperatures in various channels and their combinations are shown. For each case, we examine how different patterns appear at each microwave frequency and how the signatures from the mixed-phase clouds can be interpreted even when having complex surface features. From CloudSat products and the aircraft observations, LWC and IWC distributions in the vertical through the multilayered systems are analyzed and evaluated. It is also discussed that intensive in situ observations are necessary to improve our understanding of mixed-phase clouds and the radiative properties from these results.