Understanding satellite cirrus cloud climatologies with calibrated lidar optical depths

Abstract

Optical depth measurements of transmissive cirrus clouds were made using coincident lidar and satellite data to improve our interpretation of satellite cloud climatologies. The University of Wisconsin High Spectral Resolution Lidar was used to measure the optical depth of clouds at a wavelength of 532 nm, while the GOES and AVHRR window channel imagers provided measurements at a wavelength of 10.8 μm. In single-layer cirrus clouds with a visible optical depth greater than 0.3, the ratio of the visible to the IR optical depth was consistent with the approximate 2:1 ratio expected in clouds comprised of large ice crystals. For clouds with visible optical depths <0.3, the visible/IR ratios were nearly aways <2. It is likely that this reflects a measurement bias rather than a difference in cloud properties.