1. Introduction
Solar radiation is an important
natural factor because it forms the Earths 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.