UV Index from ERA5 reanalysis

Area of Science:

• Atmospheric Science
• Environmental Health
• Climate Data Analysis

Background:

• Ultraviolet (UV) radiation exposure significantly impacts human health, necessitating accurate UV climatological data.
• The UV Index (UVI) is crucial for assessing UV overexposure risks, calculated using spectral weighting functions.
• Existing ERA5 datasets lack direct UVI, hindering comprehensive UV risk analysis.

Purpose of the Study:

• To develop and validate a model for computing hourly UVI exclusively from ERA5 data.
• To enable direct access to UVI statistics via the Copernicus Climate Change Service (CDS).
• To potentially support the integration of a dedicated UVI product into ERA5.

Main Methods:

• Developed a model using simulated UV spectra under clear-sky conditions with the uvspec radiative transfer model.
• Incorporated parameters such as atmosphere type, solar zenith angle, visibility, altitude, albedo, total ozone, and aerosol type.
• Validated the model against ground-based UVI measurements and Copernicus Atmospheric Monitoring Service (CAMS) UVI data.

Main Results:

• The model accurately computes hourly UVI from ERA5 data, showing small biases and differences compared to ground measurements and CAMS.
• Performance slightly degrades under cloudy conditions (cloud cover > 0.4), but relative uncertainties remain acceptable for health risk categories.
• The model demonstrates good performance across various atmospheric conditions and geographical regions (tropical, mid-latitude, subarctic).

Conclusions:

• The proposed model successfully computes hourly UVI using solely ERA5 data, offering a valuable tool for UV health risk assessment.
• This methodology enhances accessibility to UVI statistics, facilitating large-scale analysis and potential integration into climate services.
• The findings support the use of ERA5 data for deriving crucial UV climatological information.