Cirrus cloud ice water content in the uppermost troposphere: Six years of observations from the Cloud and Aerosol Lidar with Orthogonal Polarization

The Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) has been continuously measuring cirrus cloud particle backscatter and transmittance for more than six years from low Earth orbit. Cloud particle extinction and ice water content is retrieved from these measurements, based on detailed information about cirrus cloud microphysics from numerous aircraft field campaigns. This provides an unprecedented global vertically-resolved data set for the study of high altitude clouds. The lidar has a vertical resolution of 60 m, and sensitivity to cloud ice of 0.1 mg/m3. Assessment of the quantity and distribution of the ice content of high-altitude cirrus is critical for accurate modeling of the atmospheric radiative balance, because cirrus can have a net warming effect at high altitude. An overview of the six-year CALIOP ice water content data set is presented here. We describe the parameterization of cirrus cloud ice water content, and show how CALIOP ice water content data compares with other satellite sensors and in situ measurements. We provide an assessment of seasonal and inter-annual variability of cloud ice in the Tropical tropopause transition layer, with associated uncertainty. Finally, we map estimates of the radiative impact of upper tropospheric cloud ice based on CALIOP observations to the nighttime 532 nm signal-to-noise ratio, and to uncertainty in the ice water content retrieval process.