Differences in Ice Cloud Optical Depth from CALIPSO and Ground-Based Raman Lidar at the ARM SGP and TWP Sites

Abstract

Ice cloud column optical depths from the Cloud-Aerosol Lidar and Infrared Pathfinder Satel- lite Observations (CALIPSO) satellite and ground-based Raman lidars (RLs) at the Atmo- spheric Radiation Measurement (ARM) Southern Great Plains (SGP) and Tropical Western Pacific (TWP) sites are compared for 8 and 4 years, respectively. The cloudy mean ice cloud column optical depths from CALIPSO are 160% (88%) larger than those from RLs at SGP (TWP) for collocated transparent profiles. Of this total difference, 68% (20%) is attributed to differences in the lidar ratios at SGP (TWP) and 8% (46%) is attributed to differences in averaging resolution at SGP (TWP). Hence, differences in ice cloud column optical depth are more due to the lidar ratio than averaging resolution at SGP but vice versa at TWP. The remaining differences, especially at SGP, are due to very optically thin clouds only detectable by the higher-sensitivity RLs. This work also examines in detail the lidar ratios that are directly observed by RLs, which do not support the temperature-dependent parameterization of ice cloud lidar ratio used in CALIPSO’s Version 4 data product.