How 3D cloud radiative effects are influenced by microphysics of low-level clouds

Key words: Cloud Radiative Effects (CRE), Three-Dimensional Radiative Transfer, ICON, MYSTIC, Low-Level Clouds, Cloud Microphysics

Abstract: The microphysical properties of low-level clouds play a critical role in influencing threedimensional (3D) cloud radiative effects (CRE), yet significant uncertainties and approximations persist in their parametrizations. Our research investigates how detailed microphysical parameterizations and high-resolution simulations can advance the representation of 3D CREs. We intend to establish a thorough framework for examining cloud-radiation interactions by integrating regional and local simulations with data from extensive observational campaigns. As a first step towards this objective, we present preliminary results from nested simulations of the ICON model at hectometer resolution, targeting specific low-level cloud regimes over the Lindenberg Observatory in Germany. Cloud microphysics is simulated with a two-moment microphysical scheme. The 3D cloud radiative effects are estimated from the application of the 3D radiative transfer model MYSTIC in offline mode. The resulting model data are extensively evaluated against observed ground-based radiation fluxes and cloud radar data. We discuss how spatial cloud heterogeneity and microphysical complexity significantly modulate the deviations between 1D and 3D CRE estimates. By integrating high-resolution simulations with advanced observational datasets, this work provides critical insights into the mechanisms driving cloud radiative effects and their representation in climate models. Ultimately, this project will lay the foundations for refining parameterizations of cloud feedbacks and enhancing the realism of atmospheric radiation schemes.