An Investigation of Ice Cloud Lidar Ratio Derived from Ground-Based ARM Raman Lidars

Ice cloud optical properties measured via lidar systems are limited by the lidar ratio, which is the ratio of the backscatter coefficient to the extinction coefficient. In particular, Cloud- Aerosol Lidar with Orthogonal Polarization (CALIOP), a lidar system on board Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO), uses an assumed single value lidar ratio for ice cloud retrievals. To better understand the distribution and functional controls for ice cloud lidar ratios, the updated Feature Detection and Extinction (FEX) retrieval algorithm, which was developed by Thorsen et al. (2015) and Thorsen and Fu (2015), was applied to the measurements of the Department of Energy (DOE) Atmospheric Radiation Measurement Program (ARM) ground-based Raman lidar systems. The ARM sites included in this study are Southern Great Plains (SGP) located near Lahmont, Oklahoma (36.61°N, 97.49°W) and Tropical Western Pacific (TWP) located near Darwin, Australia (12.43°S, 130.89°E).  The time periods of the measurements considered are from August 2008 to present at SGP and from December 2010 to January 2015 at TWP.  We will analyze the ice cloud lidar ratio in terms of its probability density frequencies and explore ice cloud lidar ratios functional controls for temperature, extinction and depolarization ratio. We will compare the lidar ratios derived from the Raman method with those from the transmission-loss method.  We will systematically examine ice cloud radiative effects using the ice cloud extinction derived with a single lidar ratio and those with consideration of lidar ratio PDFs and parameterizations, as compared with the reference ice cloud radiative effects where the directly measured lidar ratio will be used.