A New Lidar‐Based Observational Estimate for a Short‐Term Longwave High‐Cloud Feedback

Abstract

High clouds play a substantial role in modulating the Earth's top‐of‐atmosphere radiative energy budget. Models project that changes in high‐cloud altitude and area in response to warming will have a net warming effect within the tropics. Yet, to our knowledge, a robust global observational constraint of a short‐term cloud feedback associated with high‐cloud interannual variability is lacking. Here, we employ a simple method to construct a short‐term longwave (LW) high‐cloud feedback that is based on the product of the interannual response of high‐cloud cover (HCC) to temperature and the sensitivity of LW cloud radiative effect to HCC changes. We compare the computed feedback between two sets of observations: cloud‐aerosol Lidar and infrared pathfinder satellite observation GCM‐oriented CALIPSO cloud product (CALIPSO‐GOCCP) that is particularly useful for detecting thin cirrus, and the clouds and the Earth's radiant energy system FluxByCldTyp (CERES‐FBCT) product that bins cloud cover and radiative fluxes in opacity‐altitude bins. Both data sets suggest a negative tropical LW high‐cloud feedback from both CALIPSO‐GOCCP and CERES‐FBCT, which is offset by a warming from thin high clouds outside of the tropics to produce a near‐zero LW high‐cloud feedback globally. However, CERES‐FBCT underestimates HCC compared to CALIPSO‐GOCCP. By decomposing the feedback contributions into vertical motion regimes, we find that the largest feedback magnitudes occur within the descent regime, which motivates using observations capable of detecting cirrus clouds. Our feedbacks are consistent with previously calculated LW high‐cloud feedbacks and our framework can be easily applied to model output for comparison and evaluation.