Aerosols in forecasts of the UV index: A comparison of different approaches

The DWD provides forecasts of the UV Index as a public service to raise awareness for the negative influence of UV radiation on human health. Revising the current forecast algorithm, alternative descriptions for the aerosol effect are evaluated in order to improve the accuracy of the forecasts and the reliability of UV warnings. Numerical experiments are carried out making use of two alternative formulations for the aerosol load: a monthly climatology based on the combination of model data sets with ground-based measurements, and 3-hourly forecasts based on the combination of formal descriptions of aerosol sinks and sources with the ECMWF Integrated Forecasting System. With respect to the observation based climatology currently in use, the aerosol optical depth of the alternative approaches shows small differences in Middle Europe but differs in some regions out of Europe by more than a factor of 10. The alternative approaches are evaluated by comparison with ground-based observations and an updated proce...