On the use of quantitative diurnal cloud information for the calculation of daily UV dose maps over Europe

Abstract

The KNMI/ESA Tropospheric EMission Internet Service (TEMIS) publishes daily forecasts of the clear-sky UV index for today and 8-days ahead and analyses of the daily UV dose of yesterday and before. Near-real time ozone satellite observations are used to account for the variations in UV radiation as a function of the overhead ozone column. The daily UV dose depends critically on the assumptions that are made for the cloud correction factor. Cloud cover fraction is the most uncertain parameter for day-to-day variations in the daily UV dose under non-overcast cloud conditions. The cloud optical thickness is the most important parameter determining variations in daily UV dose for overcast situations. A good cloud mask is essential to identify cloud-free scenes. Still further improvements in the daily UV dose can be made, including the inclusion of the diurnal variation in cloud optical thickness as well as corrections for aerosols.