Thin Cirrus Properties and Statistics from Airborne, Ground-Based, and Space-Based Lidars

Cirrus clouds have a significant effect on the earth’s radiation budget and climate due to their prevalence in the tropics and mid-latitudes. Quantifying these effects remains a challenge due to a lack of studies across the wide spectrum of cirrus properties and dynamic formation mechanisms, uncertainties in cirrus model parameterizations, and the difficulties of measuring cirrus in situ. In this study, we will compile statistics of thin cirrus properties from the Cloud Physics Lidar (CPL), which has flown more than 100 flights on NASA high-altitude aircraft. Cloud-Aerosol Transport System (CATS) lidar measurements from the Intentional Space Station (ISS) provide global perspective of cirrus properties that complement the CPL dataset. Ground-based data from multiple MPLNET sites are also presented.

The lidar ratios and depolarization ratios retrieved from CPL and CATS for thin cirrus clouds formed by synoptic-scale uplift over land are lower than convectively-generated thin cirrus over tropical oceans. These higher depolarization ratios for tropical thin cirrus are likely a consequence of colder cloud temperatures and the presence of more column-shaped ice particles compared to mid-latitude thin cirrus. CPL thin cirrus backscatter color ratios are directly proportional to depolarization ratio for synoptically-generated cirrus, suggesting particle shape is a function of particle size. Given that uncertainties in particle shape parameterizations can produce errors in the cirrus radiative forcing estimates greater than 60 percent, the relationship between cirrus properties and dynamic formation mechanism needs to be considered when studying the impact of cirrus on the Earth’s climate system.