Analyzing Ice Cloud Lidar Ratio Derived from Ground-Based ARM Raman Lidars at SGP and TWP

 

Authors

Kelly Balmes — Cooperative Institute for Research in Environmental Sciences
Qiang Fu — University of Washington
Tyler Thorsen — NASA - Langley Research Center

Category

General topics – Clouds

Description

Measurements of ice cloud microphysical and optical properties from lidar systems are limited by the lidar ratio, the ratio of the particulate extinction to backscatter. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), a lidar system on board Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO), previously used an assumed single-value lidar ratio for ice cloud retrievals and now uses a temperature dependence of lidar ratio as derived from the transmission method. 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 (ARM) Climate Research Facility ground-based Raman lidar systems. Raman lidars contain multiple channels, allowing signal separation into particulate and molecular components to directly retrieve lidar ratios. The ARM sites included in this study are the Southern Great Plains (SGP) located near Lamont, 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 compare the directly measured lidar ratios from SGP and TWP by examining the dependences of ice-cloud lidar ratios on temperature, extinction, depolarization ratio, and latitude.