Wednesday, 11 July 2018: 2:30 PM
Regency D (Hyatt Regency Vancouver)
Cirrus clouds are frequently observed in the tropics and mid-latitudes, with fractions as high as 90%, and have implications for the Earth’s radiation budget. A top priority in current climate change research is to provide measurements of cirrus properties to test and improve cloud parameterizations in climate models. There are still lingering questions as to the relationship between cirrus properties and dynamic cloud generation mechanisms. In this study, we examine the relationship between thin cirrus cloud properties and dynamic formation mechanism through statistics of Cloud Physics Lidar (CPL) thin cirrus properties from more than 100 flights on NASA high-altitude aircraft. Many of these flights include coincident measurements of cirrus microphysical properties from polarimeters and in situ cloud probes. Cloud-Aerosol Transport System (CATS) lidar measurements from the Intentional Space Station (ISS) provide global perspective. 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 a consequence of colder cloud temperatures and the presence of more column-shaped ice particles compared to mid-latitude thin cirrus. Given that uncertainties in particle shape parameterizations can produce errors in the cirrus bidirectional reflectance and optical depth estimates greater than 30 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.
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