Cloud structure and regime dependence of 3D radiative effects

• Applicants: Dr. Hartwig Deneke; Professor Dr. Bernhard Mayer
• Subject Area: Atmospheric Science
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513446258

The proposed research unit (RU) will establish a coordinated effort to better understand the impact of 3D radiative effects on climate, and to advance both atmospheric models and remote sensing techniques to better account for these effects. Project 2 (P2) is a key project since it provides the 3D radiative transfer modeling capabilities and expertise for the research unit. P2 targets an improved understanding of the magnitude and impact of cloud-related 3D radiative effects (compared to well-established one-dimensional approximations and 3D parameterizations) by means of forward radiative transfer modelling. While validated 3D radiative transfer models are available nowadays, our understanding of the magnitude of 3D radiative effects, their dependencies on cloud properties and structure, and their relevance for climate remains limited. While it is evident that current kilometer-resolution satellite imagers and atmospheric models cannot fully resolve cloud variability as needed to realistically represent 3D effects, it is not yet clear which spatial scales have to be considered to resolve biases and small-scale variability introduced by 3D radiative effects. Also, most studies investigating 3D effects have considered scenes with idealized cloud types, and the dependence of 3D effects on cloud type and/or regime remains elusive. These topics will be addressed by answering the following research questions: 1) How large are systematic biases and small-scale fluctuations in the radiation budget resulting from 3D effects? Can they be meaningfully partitioned by cloud regime? 2) What structural and physical cloud parameters determine 3D bias and variability? How do systematic and random 3D effects affect satellite cloud retrievals (jointly with P4)? 3) How well are the different instrumental perspectives able to resolve and constrain relevant structural parameters of clouds? 4) What model and observational resolution is required to quantify the complete 3D effect and how does that depend on cloud regime (jointly with P1)? Project P2 aims at resolving cloud-induced bias and small-scale variability in radiation, and to relate those to characteristic 3D cloud structural parameters obtained from realistic cloud reconstructions and cloud model simulations. Project P2 will refine existing 3D cloud reconstruction tools that combine active and passive ground-based and passive satellite-based remote sensing, and will apply those as input to a well established 3D radiative transfer model in order to arrive at an estimate of the regime-dependent cloud radiative effects. Together with the project partners, the overarching goal is to provide a combined model- and observation-based reconstruction of 3D cloud structure, using atmospheric models as prior information for unobserved aspects, that shall enable a global-scale consideration of 3D radiative transfer effects in climate modelling and remote sensing.

• DFG Programme: Research Units
• Subproject of: FOR 5626: Cloud Structure & Climate - Closing the 3D Gap