A new method for estimating UV fluxes at ground level in cloud-free conditions

Abstract : A new method has been developed to estimate the global and direct solar irradiance in the UV-A and UV-B at ground level in cloud-free conditions. It is based on a resampling technique applied to the results of the k-distribution method and the correlated-k approximation of Kato et al. (1999) over the UV band. Its inputs are the aerosol properties and total column ozone that are produced by the Copernicus Atmosphere Monitoring Service (CAMS). The estimates from this new method have been compared to instantaneous measurements of global UV irradiances made in cloud-free conditions at five stations at high latitudes in various climates. For the UV-A irradiance, the bias ranges between −0.8 W m −2 (−3 % of the mean of all data) and −0.2 W m −2 (−1 %). The root mean square error (RMSE) ranges from 1.1 W m −2 (6 %) to 1.9 W m −2 (9 %). The coefficient of determination R 2 is greater than 0.98. The bias for UV-B is between −0.04 W m −2 (−4 %) and 0.08 W m −2 (+13 %) and the RMSE is 0.1 W m −2 (between 12 and 18 %). R 2 ranges between 0.97 and 0.99. This work demonstrates the quality of the proposed method combined with the CAMS products. Improvements, especially in the modeling of the reflectivity of the Earth's surface in the UV region, are necessary prior to its inclusion into an operational tool.