Radiation closure study under different cloudy conditions for a mid-latitude site

Clouds exert a dominant and highly variable influence on the Earth's surface radiation budget, yet their accurate representation remains one of the largest sources of uncertainty in climate models (IPCC, 2021). Radiation closure studies offer a valuable means for quantifying these uncertainties across a range of cloud conditions, for retrieving cloud properties and evaluating model performances. In this work, results for different cloudy conditions will be presented for the Meteorological Observatory Lindenberg (MOL), Germany (52.21°N, 14.12°E; 127 m a.s.l.).  MOL is a supersite, hosts the GRUAN lead centre and contributes to numerous international networks and facilities, such as Cloudnet, ACTRIS, GRUAN, BSRN, and AERONET. Thus, MOL provides high temporal and vertical resolution observations from both in-situ and ground-based remote sensing instrumentation. These synergetic data sets enable accurate characterisation of the atmospheric state — including thermodynamic profiles, aerosol and gas information — and are used as input for the radiative transfer calculations, conducted using libRadtran software package (Mayer and Kylling, 2005). The Cloudnet retrievals (Illingworth et al. 2007) provide the information on cloud macro- and microphysical properties for the simulations, and are also used to identify different cloud types based on the number of layers and their phase. The broadband shortwave and longwave fluxes collected within the BSRN framework (Driemel et al. 2018) provide the reference observations for the radiation closure evaluation. The present work focuses primarily on single-layer liquid water and ice cloud cases, selected from different years, and the sensitivity of calculated irradiances to cloud microphysical properties. Preliminary results show that good radiation closure can be achieved for liquid water clouds, especially for longwave irradiance, whereas larger discrepancies between simulated and observed fluxes occur for ice clouds, in particular for shortwave irradiance, highlighting the sensitivity of radiative transfer calculations to ice crystal habit and effective radius assumptions. Bibliography  Driemel et al. (2018): Baseline Surface Radiation Network (BSRN): structure and data description (1992–2017); doi: 10.5194/essd-10-1491-2018Illingworth et al. (2007): Cloudnet: Continuous evaluations of cloud profiles in seven operational models using ground-based observations; doi:10.1175/BAMS-88-6-883IPCC (2021): Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change; doi: 10.1017/9781009157896Mayer and Kylling (2005): Technical note: The libRadtran software package for radiative transfer calculations – description and examples of use; doi: 10.5194/acp-5-1855-2005