UV Index estimation from global radiation and total ozone observations in Azores.

MCM9 UV Conference. Davos, Switzerland, 17-20 September 2007.The UV Index (UVI) is a public-oriented meteorological kind of information about the damaging ultraviolet radiation at the ground (Vaniceck et al., 1999). Its use begins to be so popular as temperatures highs, wind chill, fire risk index, air quality index and other meteorological indexes and parameters. A UVI scale was already defined by WHO (WHO, 2002) in order to provide a correspondence between UVI levels and protective measures to avoid damaging effects on humans. However, UVI is usually given in integer units, so the required precision for the public must be less or equal than 0.5 UVI units. While UV dependence on ozone is well understood and easily to model, clouds dependence is more difficult do model and its effect on daily variability is also important. In addition, atmospheric UV measurements are more expensive than global radiation measurements and therefore fewer. However, global radiation is much less dependent on ozone and its variability depends basically on clouds. Therefore, global radiation measurements can be used to correct a simple radioactive transfer model for clear sky conditions with respect to the actual cloudiness. The scope of this work is to find an approach to derive UVI from actual global radiation and ozone measurements with acceptable error for public awareness