ИСТИНА

The UV-index (UVI) is a measure of the erythemally effective solar radiation reaching the Earth surface. It was introduced to alert people about the need of sun protection and to help for elaborating recommendations about safety exposure to solar UV radiation. Therefore, the UVI has to be determined with adequate accuracy and its forecast appears to be an essential task. To minimize the risk of too high sunburn levels, the UVI previsions are usually made for clear sky conditions (cloud and aerosol free atmosphere). For the UVI forecast for the Bulgarian region are used GOME-2 satellite forecast data with a resolution of 0.25 by 0.25 degrees. Higher resolution maps to about 1/200 degree (corresponding to about 1km) are produced by downscaling taking into account the topography, based on satellite data of the Shuttle Radar Topography Mission. More over the UVI index was corrected for the underlying surface albedo: First a correction was performed the albedo of snow, which the most important correction in the UV spectral region, and second for the beach sand albedo. Snow maps for Bulgaria were constructed by help of daily Northern Hemisphere Snow and Ice data of the Snow and Ice Mapping System (IMS) with a resolution of 1 km. This type of maps allow the determination of the coastline. A sequence of UVI maps, for sea level, for the mean elevation of 1 by 1 km area, and of snow and coast-line corrected maps are presented for winter 2020.