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

During a research flight conducted on 11 August 2017, a thin cirrus cloud was coincidently measured by the aircraft (WB-57)-mounted NASA Cloud Physics Lidar (CPL) and the NASA Cloud Aerosol Transport System (CATS) lidar flying aboard the International Space Station (ISS), as part of the Navel Research Lab (NRL) Radiative Effects of Thin cirrus (REThinC) field campaign. The purpose of this flight was to understand the sensitivities in resolving cirrus cloud microphysical and radiative properties from the satellite versus the higher-resolution depiction available with the aircraft. Therefore, we compare estimates of top-of-the-atmosphere (TOA) cloud forcing solved using the Fu-Liou-Gu radiative transfer model based on the satellite-derived CATS extinction coefficient profile versus that of CPL.

CPL cloud detection was 94%, while CATS was 37% with prevalence toward denser clouds. Estimates of the TOA net cloud radiative forcing (CRF) using CPL and CATS extinction coefficient and meteorological profiles at their native vertical resolutions (30 m and 60 m from 0-20 km, respectively) prove inconsistent. Upon re-resolving CPL at the 60 m CATS resolution, the anomaly is suppressed, resulting in a TOA net CRF of 0.27 and 0.35 W/m², respectively. Despite observing fewer and denser clouds, CATS data render a near equal result to that of CPL, while non-linearities in ice physical parameterizations driving 1-dimensional radiative transfer simulations induce inconsistencies in flux estimates at varying resolutions.