Sensitivities in Satellite Lidar-Derived Estimates of Daytime Top-of-the-Atmosphere Optically Thin Cirrus Cloud Radiative Forcing: A Case Study

An optically thin cirrus cloud was profiled concurrently with nadir-pointing 1,064 nm lidars on 11 August 2017 over eastern Texas, including NASA's airborne Cloud Physics Lidar (CPL) and space-borne Clouds and Aerosol Transport System (CATS) instruments. Despite resolving fewer (37% vs. 94%) and denser (i.e., more emissive) clouds (average cloud optical depth of 0.10 vs. 0.03, respectively), CATS data render a near-equal estimate of the top-of-atmosphere (TOA) net cloud radiative forcing (CRF) versus CPL. The sample-relative TOA net CRF solved from CPL is 1.39 W/m(2), which becomes 1.32 W/m(2)after normalizing by occurrence frequency. Since CATS overestimates extinction for this case, the sample-relative TOA net forcing is similar to 3.0 W/m(2)larger than CPL, with the absolute value reduced to within 0.3 W/m(2)of CPL due its underestimation of cloud occurrence. We discuss the ramifications of thin cirrus cloud detectability from satellite and its impact on attempts at TOA CRF closure.