Validating Mixed-Phase Cloud Optical Depth Retrieved From Infrared Observations With High Spectral Resolution Lidar

Single-layer mixed-phase clouds are prevalent in the Arctic atmosphere. The properties of mixed-phase clouds, including the optical depth of both the liquid and ice components, can be retrieved from spectrally resolved infrared radiance observations that are made in both the 8-13-mum and 17-24-mum windows. The accuracy of the retrieved properties from this algorithm has been established in single-phase clouds (i.e., clouds that contain only liquid or only ice) but not in mixed-phase clouds. A polarization-sensitive high spectral resolution lidar (HSRL) was deployed to the Atmospheric Radiation Measurement Program´s Barrow, Alaska site during the fall of 2004. The HSRL measures optical depth directly, and the phase can be discriminated using the depolarization ratio measured by the lidar. Comparisons of the infrared retrieved optical depths with the optical depths directly observed by the lidar in clouds that consist of supercooled liquid layers precipitating ice are in good agreement, with the slope and correlation being 1.055 and 0.65 for the ice portion of the mixed-phase cloud and 0.954 and 0.82 for the liquid portion.