Do Thin Cirrus Clouds Matter?

In this talk, we quantify the relative impact of thin cirrus clouds versus opaque cirrus in terms of total cloud occurrence and global and regional top-of-the-atmospheric cloud radiative forcing. We describe the relative influence of thin cirrus on TOA radiances measured by passive sensors and the resulting bias from unscreened cloudy pixels. We further distinguish differences in microphysical cloud properties in thin cirrus clouds versus opaque ones, including effective cloud particles sizes and ice crystal habits, which may ultimately influence attempts at static parameterizations of ice crystal properties for radiative transfer modeling. Our goal is to conceptualize the relative significance of thin cirrus clouds within the climate system versus more traditional thinking aligned with historical observations tuned toward opaque clouds. Lidar measurements are the basis for the recent recognition of thin cirrus cloud prominence overall in the atmosphere. Our community plausibly merits permanent standing in all future discussions of climate radiative monitoring from the unique sensitivity of lidar instruments to cirrus clouds as a whole. The relative influence of thin cirrus, however, has never been systematically explored, and thus our work here is designed to make a more focused argument as to the significance of lidar as a critical tool for resolving what proves to be the most common cloud genera in the atmosphere.