1.  Introduction

Solar radiation is an important natural factor because it forms the Earth’s climate and has a significant influence on the environment. The ultraviolet part of the solar spectrum (UV) plays an important role in many processes in the biosphere. It has several beneficial effects but it may also be very harmful if UV exceeds ”safe” limits. If the amount of UV radiation is sufficiently high the self-protection ability of some biological species is exhausted and the subject may be severely damaged. This also concerns the human organism, in particular the skin and the eyes. To avoid damage from high UV exposures, both acute and chronic, people should limit their exposure to solar radiation by using protective measures.

The diurnal and annual variability of solar UV radiation reaching the ground is governed by astronomical and geographical parameters as well as by the atmospheric conditions. Since human activities affect the atmosphere, such as polluting the air and influencing the ozone layer, they also affect the UV radiation reaching the ground. As a consequence, solar UV radiation is a highly variable environmental parameter that differs widely in time and space. The need to reach the public with simple-to-understand information about UV and its possible detrimental effects led scientists to define a parameter that can be used as an indicator of the UV exposures. This parameter is called the UV Index. It is related to the well known erythemal effects of solar UV radiation on human skin and it has been defined and standardised under the umbrella of several international institutions such as WMO, WHO, UNEP and ICNIRP (see Appendix E).

The UV Index (UVI) is now widely used in many operational weather reports and forecasts. In Europe, for example, there are more than a dozen forecasting centres that release estimated UVI values for countries or regional areas. Different methods are used to predict the UVI and all kinds of information systems and presentations are seen. To co-ordinate these activities and to improve their scientific background an international research project was established under the program ”Cooperation in Science and Technology” (COST) of the European Commission. The project titled COST-713 action (UV-B Forecasting) was initiated in 1996. The following European countries participated: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Italy, Poland, Portugal, Spain and Switzerland. A list of the participating institutions is given in Appendix A.

The development of efficient methods for dissemination of the UVI forecasts and the improvement of how they are interpreted by the public were key tasks for COST-713. This booklet is one product of the action and is mostly intended for users coming from different professional communities who can assist in a wider use of the UVI. It may also be useful to users who want to know about the details of the physical and biological background.

It is expected that the readers will use this information not only in their professional activities but also for communication to the public. The international and local institutions listed in the booklet (Appendix B) may serve as reference centres for further information and assistance.



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