Understanding the tropical high-cloud feedback through the ice-water-path lens

Abstract

The response of tropical high clouds to global warming has the potential to produce an important climate feedback but remains poorly constrained. To improve our understanding of the tropical high-cloud feedback, we develop a conceptual model of the high-cloud radiative effect as a function of the ice water path (IWP) and surface temperature. This model provides a framework for analysing how changes in IWP distribution and cloud top height with surface warming can generate a tropical high-cloud feedback. By including the entire IWP range, it improves on previous conceptual models that rely on cloud fractions. To parameterize our conceptual model, we use atmospheric profiles from global simulations with the ICOsahedral Nonhydrostatic weather and climate model (ICON) with 5 km horizontal resolution, which are used to calculate the radiative fluxes offline with the line-by-line Atmospheric Radiative Transfer Simulator (ARTS). This setup allows us to “switch off” the high clouds in the radiative transfer calculations to better study the radiative effect of high clouds over low clouds. Our conceptual model represents the main physical processes underlying the high-cloud radiative effect and is able to reproduce the results from the ARTS simulations. It therefore provides a valuable framework for analysing the tropical high-cloud feedback produced by climate models and helps to understand the origin of the associated uncertainties.