Assessing aerosol impacts on EarthCARE radiative closure using spectral radiation observations

Satellite-based radiation retrievals are essential for quantifying the Earth’s radiative energy budget and for climate-related studies. The EarthCARE (EC) mission aims to improve our understanding of how aerosols and clouds modify radiative fluxes by providing collocated radiation observations and products based on a three-dimensional representation of atmospheric constituents. The evaluation of these products is therefore crucial for accurately estimating aerosol and cloud radiative effects.

In this study, we assess EC radiation products and their associated aerosol and cloud inputs by conducting radiative closure experiments using ground-based spectral radiation and aerosol measurements acquired during the RACE-ECV (Radiation Closure Experiments for EarthCARE Validation) field campaign.

The RACE-ECV campaign was coordinated by PMOD/WRC — the world reference institute for solar measurements and aerosol optical depth as designated by the World Meteorological Organization (WMO) — with the participation of multiple institutions. Its primary objective was the validation of EarthCARE products through high-accuracy measurements of solar radiation and aerosols. The campaign was conducted in spring 2025 (April 22–May 22) at three coordinated sites in Thessaloniki area, aligned with EC satellite overpasses. High-accuracy sun photometers were deployed in synergy with other ground-based remote-sensing instruments, comprehensive observations of aerosols, clouds, and surface solar spectral radiation.

The radiative closure at the surface was assessed through an intercomparison between measured broadband and spectral solar fluxes and radiative transfer (RT) simulations driven by both ground-based and EC atmospheric inputs. In particular, EarthCARE reconstructed three-dimensional atmospheric fields were used as input to the 3D/1D MYSTIC code (Mayer, 2009) to assess the accuracy of surface radiation products, while simultaneously quantifying the contribution of individual input parameters (focusing on aerosols) to the observed discrepancies. In addition, simulated fluxes at the top of the atmosphere (TOA) were intercompared with EC Broadband Radiometer (BBR) observations.

This study provides insights into the use of EarthCARE observations for improving our understanding of the role of aerosols and clouds in modifying the Earth’s radiative energy fluxes. 

 References:

Emde, C., et al.: The libRadtran software package for radiative transfer calculations (version 2.0.1), Geosci. Model Dev., 9, 1647–1672, https://doi.org/10.5194/gmd-9-1647-2016, 2016

Mayer, B. (2009) Radiative transfer in the cloudy atmosphere, in: EPJ Web of Conferences, 75–99.

Mayer B. and Kylling A., Technical note: The libRadtran software package for radiative transfer calculations - description and examples of use. Atmos. Chem. Phys., 5: 1855-1877, 2005

Acknowledgements:

The authors acknowledge the project RACE-ECV, (SBFI-633.4-2021-2024/PMOD - EarthCARE 202/2) supported by SBFI, the the Horizon Europe European Research Council (grant no. 101137680, Cloud–aERosol inTeractions & their impActs IN The earth sYstem, CERTAINTY) and the Obs3RvE (Optimising 3D RT EarthCARE product using geostationary observations and AI) project, funded from the European Space Agency under Contract No. 4000147848/25/I/AG.