Speaker: Hyoji Kang (Imperial)
Title: A radiative effect of tropical upper-level clouds in climate feedback
Abstract: Tropical upper-level clouds, densely distributed over the tropics, exert a significant cloud radiative effect that spans a wide range. This effect is primarily influenced by cloud microphysical properties such as cloud fraction and optical thickness, as well as their interactions with lower-level clouds. However, due to observational uncertainties and the limitations of current climate model simulations, our understanding of the cloud radiative effect and its feedback of tropical upper- level clouds remains inadequate. To address these gaps, first, this study aims to simulate the cloud radiative effect of tropical upper-level clouds using a radiative transfer model, taking into account various cloud physical properties and their interactions with lower-level clouds. Second, this study analyzes the radiative impact of tropical upper-level clouds on global mean surface temperature. The analysis employs a radiative-convective equilibrium model to quantify tropical upper-level cloud radiative effect (the impact of tropical upper-level clouds on global mean surface temperature), in the unit of K/%, and identifies determining factors of tropical upper-level cloud radiative effect based on outputs from climate models and observation data. Lastly, this study proposes a new perspective on understanding tropical upper-level cloud feedback based on the concept of tropical upper-level cloud radiative effect investigated in the preceding analysis. By quantifying the radiative effect of tropical upper-level clouds and elucidating the factors that drive its variability under controlled framework, this study aims to advance a more integrated understanding of how tropical upper-level clouds regulate Earth’s radiative energy balance.