The ISUV[1]​ (acronym for Intensidad de Radiación Solar Ultravioleta), according to the National Meteorological Service "Servicio Meteorológico Nacional (Argentina)"),[2]​ of Argentina, corresponds to the maximum expected value of the intensity of ultraviolet solar radiation (around solar noon) under clear sky conditions. This varies day by day very slowly since it depends on the solar radiation (UV-A and UV-B radiation) that reaches the earth's surface daily and the evolution of the ozone layer. While ISUVn corresponds to the minimum value expected for this radiation, under the shadow of the forecast clouds, this is why it can vary abruptly from one day to the next since it depends on the ISUV and the cloudiness that is expected to be recorded during solar noon that day. In mountain areas and with snow, the index must be increased by one rating (except for the extreme). This index gives an indication of the risk of overexposure to the Sun with values ​​and ratings related to the minimum time for redness and eventual burning of the skin.