Solar UV index (UVI) long-term forecasting

The interactive tool gives to the user the opportunity to select from 23 points over Greece and a pop-up window appears with the long term forecast of UV index (UVI) up to 2 days ahead at 1 hour time intervals. The service is updated every day when the new operational forecast of cloudiness is available. System description:

• The clear-sky UVI is first calculated based on TEMIS forecast for ozone, Copernicus Atmospheric Monitoring Service (CAMS) forecasts (the 12:00UTC initialization) of aerosol optical depth for the aerosol information and climatological datasets for the other important parameters by interpolating in a pre-run Look-up Table (LUT) of UV.

• The current meteorological parameter of cloudiness (in %) is provided from BEYOND/NOA operational forecasting model, which uses the Advanced Research WRF (ARW) model that is a configuration of the Weather Research and Forecasting (WRF) model. WRF-ARW v.4 runs operationally on BEYOND/NOA servers daily and provides high-resolution forecasts over Europe (6-km) and Greece (2-km) for 60 forecasting hours. Initial and boundary data are provided by NCEP GFS 0.25-degree analyses and forecasts (12Z cycle).

• For the calculation of the forecasted all-skies UVI every 1 hour up to 2 days ahead, the UV cloud modification factor (CMF UV ) approach is used. The percentage of cloudiness (%) from the WRF model is transformed to CMF UV , which in turn are multiplied with the clear-sky values to finally derive the all-skies UVI.