Evaluation of the Cyprus UV Index (UVI) Forecasting System Over One Year of Observations: Assessing the Impact of Ozone and Aerosols

Cyprus is characterized by some of the highest ultraviolet (UV) radiation levels in Europe, emphasizing the need for accurate UV Index (UVI) forecasting to support public awareness and health protection, atmospheric research. This study presents the evaluation of the Cyprus Erythemal Irradiance Forecasting System (CERYFOS), an operational system providing hourly UVI forecasts across Cyprus at a spatial resolution of 0.1° × 0.1°.

CERYFOS is based on radiative transfer simulations using libRadtran package, driven by aerosol optical properties from the Copernicus Atmosphere Monitoring Service (CAMS), satellite-based total ozone column forecasts from TEMIS, surface elevation information, and cloud related information derived from the Weather Research and Forecasting (WRF) model forecast for clear-sky and all-sky conditions.

The evaluation covers approximately one year of data (July 2024–September 2025) and is based on comparisons with high-quality ground-based measurements in Limassol, including a Kipp & Zonen SUV-E erythemal radiometer and a double monochromator Bentham DMc150 spectrophotometer, operated following established calibration and traceability protocols. Clear-sky conditions were identified using all-sky camera observations. In addition, CERYFOS forecasts are compared with CAMS UVI products, while satellite ozone data from the Ozone Monitoring Instrument (OMI) are used to assess the consistency and impact of forecasted ozone input on UVI forecast performance. The influence of aerosol input uncertainties is investigated through comparison of CAMS aerosol optical depth with co-located AERONET observations and their effect on UVI differences.

This work underscores the value of harmonized aerosol and ozone observations and traceable ground-based UV measurements for improving UVI forecasting systems and supports ongoing Harmonia efforts in aerosol–radiation interaction studies and UV exposure services.

 

Acknowledgments:

The authors acknowledge the ‘EXCELSIOR’: ERATOSTHENES: Excellence Research Centre for Earth Surveillance and Space-Based Monitoring of the Environment H2020 Widespread Teaming project (www.excelsior2020.eu). The ‘EXCELSIOR’ project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 857510, the Government of the Republic of Cyprus through the Directorate General for the European Programmes, Coordination and Development, and the Cyprus University of Technology. Authors would like to acknowledge the Action Harmonia CA21119 supported by COST (European Cooperation in Science and Technology). G.C., K.P., A.N., and S.K. acknowledge: “ATARRI: This project has received funding from the European Union’s Horizon Europe Twinning Call (HORIZON-WIDERA-2023-ACCESS-02) under grant agreement No. 101160258.