Cloud radiative effects from ground-based vertically resolved cloud & radiation observations and radiation closure

• Applicants: Dr. Christine Knist; Professor Dr. Gunther Seckmeyer
• Subject Area: Atmospheric Science
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513446258

This project is part of the research unit programme “Cloud Structure & Climate - Closing the 3D Gap” and addresses the 3-dimensinal (3d) nature of cloud structure and the corresponding 3d cloud-radiative effect using ground-based long-term and novel remote sensing observations of clouds and their radiative properties. The surface remote sensing cloud observations including cloud macrophysical and microphysical properties are vertically resolved and provide along with the high-resolution radiation observations a valuable dataset for improved characterization of the 3d radiative effects of clouds. Therefore, we calculate empirical-derived and statically-robust cloud-radiation correlations from long-term surface observations covering common cloud-types and cloud regimes as well as their natural variability. Furthermore, we determine the cloud-radiative effect, which is defined as the difference between the measured all-sky and the respective calculated cloudless sky radiation quantities, and analyse the cloud-radiative effect sensitivity to main atmospheric parameters. We extend this analysis with a long-term radiation closure experiment by comparing the radiation observations at the surface and top of the atmosphere to those calculated from radiative transfer models using as input the atmospheric state and the cloud properties measured or retrieved from the surface remote sensing observations. In this way, the measured and derived cloud properties can be evaluated with regard to their accuracy. In addition, the effects of a simplified 1d cloud structure in the radiative transfer model can be characterised by comparing radiative observations with radiative transfer model results from 1d vertically-resolved and 3d reconstructed clouds. The observation of the individual components of the 3d cloud effect such as for instance shortwave side and downward escape are important for the validation of model calculations and require measurements of the spectral sky radiance. The latest development of the advanced multidirectional spectroradiometer (AMUDIS) provides spectral radiance measurements from the upper hemisphere in more than 140 directions in the wavelength range from 280 – 1700 nm within 1 second and is presently unique worldwide. These novel observations serve as independent quantities for the calculation of correlations between the spectral radiance and different cloud types (e.g., homogeneous cloud cover vs. broken cloud layers) and for a complementary radiation closure.The analysis of the ground-based cloud and radiation remote sensing observations is an important complement to the satellite measurements and model perspective of the research unit programme to improve our ability to observe, understand and model the cloud radiative effects.

• DFG Programme: Research Units
• Subproject of: FOR 5626: Cloud Structure & Climate - Closing the 3D Gap
• Co-Investigator: Dr. Stefan Wacker