Estimating the top altitude of optically thick ice clouds from thermal infrared satellite observations using CALIPSO data

Abstract

The difference between cloud-top altitude Z top and infrared effective radiating height Z eff for optically thick ice clouds is examined using April 2007 data taken by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and the Moderate-Resolution Imaging Spectroradiometer (MODIS). For even days, the difference ΔZ between CALIPSO Z top and MODIS Z eff is 1.58 ± 1.26 km. The linear fit between Z top and Z eff, applied to odd-day data, yields a difference of 0.03 ± 1.21 km and can be used to estimate Z top from any infrared-based Z eff for thick ice clouds. Random errors appear to be due primarily to variations in cloud ice-water content (IWC). Radiative transfer calculations show that ΔZ corresponds to an optical depth of ∼1, which based on observed ice-particle sizes yields an average cloud-top IWC of ∼0.015 gm -3, a value consistent with in situ measurements. The analysis indicates potential for deriving cloud-top IWC using dual-satellite data. Copyright 2008 by the American Geophysical Union.