09 Jul 2021

09 Jul 2021

Review status: this preprint is currently under review for the journal ACP.

Aerosol properties and aerosol–radiation interactions in clear sky conditions over Germany

Jonas Witthuhn1, Anja Hünerbein1, Florian Filipitsch2, Stefan Wacker2, Stefanie Meilinger3, and Hartwig Deneke1 Jonas Witthuhn et al.
  • 1Leibniz Institute of Tropospheric Research (TROPOS), Leipzig, Germany
  • 2German Weather Service (DWD), Meteorological Observatory Lindenberg, Tauche, Germany
  • 3University of Applied Sciences Bonn-Rhein-Sieg, Sankt Augustin, Germany

Abstract. The clear-sky radiative effect of aerosol-radiation interactions is of relevance for our understanding of the climate system. The influence of aerosol on the surface energy budget is of high interest for the renewable energy sector. In this study, the radiative effect is investigated in particular with respect to seasonal and regional variations for the region of Germany and the year 2015 at the surface and top of atmosphere using two complementary approaches.

First, an ensemble of clear-sky models which explicitly consider aerosols is utilized to retrieve the aerosol optical depth and the surface direct radiative effect of aerosols by means of a clear sky fitting technique. For this, short-wave broadband irradiance measurements in the absence of clouds are used as a basis. A clear sky detection algorithm is used to identify cloud free observations. Considered are measurements of the shortwave broadband global and diffuse horizontal irradiance with shaded and unshaded pyranometers at 25 stations across Germany within the observational network of the German Weather Service (DWD). Clear sky models used are MMAC, MRMv6.1, METSTAT, ESRA, Heliosat-1, CEM and the simplified Solis model. The definition of aerosol and atmospheric characteristics of the models are examined in detail for their suitability for this approach.

Second, the radiative effect is estimated using explicit radiative transfer simulations with inputs on the meteorological state of the atmosphere, trace-gases and aerosol from CAMS reanalysis. The aerosol optical properties (aerosol optical depth, Ångström exponent, single scattering albedo and assymetrie parameter) are first evaluated with AERONET direct sun and inversion products. The largest inconsistency is found for the aerosol absorption, which is overestimated by about 0.03 or about 30 % by the CAMS reanalysis. Compared to the DWD observational network, the simulated global, direct and diffuse irradiances show reasonable agreement within the measurement uncertainty. The radiative kernel method is used to estimate the resulting uncertainty and bias of the simulated direct radiative effect. The uncertainty is estimated to −1.5 ± 7.7 and 0.6 ± 3.5 W m−2 at the surface and top of atmosphere, respectively, while the annual-mean biases at the surface, top of atmosphere and total atmosphere are −10.6, −6.5 and 4.1 W m−2, respectively.

The retrieval of the aerosol radiative effect with the clear sky models shows a high level of agreement with the radiative transfer simulations, with an RMSE of 5.8 W m−2 and a correlation of 0.75. The annual mean of the REari at the surface for the 25 DWD stations shows a value of −12.8 ± 5 W m−2 as average over the clear sky models, compared to −11 W m−2 from the radiative transfer simulations. Since all models assume a fixed aerosol characterisation, the annual cycle of the aerosol radiation effect cannot be reproduced. Out of this set of clear sky models, the largest level of agreement is shown by the ESRA and MRMv6.1 models.

Jonas Witthuhn et al.

Status: open (until 20 Aug 2021)

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Jonas Witthuhn et al.

Data sets

Dataset for the publication: "Aerosol properties and aerosol-radiation interactions in clear sky conditions over Germany" Witthuhn, Jonas; Hünerbein, Anja; Filipitsch, Florian; Wacker, Stefan; Meilinger, Stefanie; Deneke, Hartwig

Model code and software

Source code for the publication: "Aerosol properties and aerosol-radiation interactions in clear sky conditions over Germany" Witthuhn, Jonas

Jonas Witthuhn et al.


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Short summary
Knowledge on aerosol-radiation interactions is important for understanding the climate system and for the renewable energy sector. Here, two complementary approaches are used to assess the consistency of the underlying aerosol properties and the resulting radiative effect in clear-sky conditions over Germany in 2015. An approach based on clear-sky models and broadband irradiance observations is contrasted to the use of explicit radiative transfer simulations using CAMS reanalysis data.