The World Health Organisation (WHO) and the World Meteorological Organisation (WMO) have
jointly recommended that the UV Index (UVI) should be used to inform the public about possible
health risks due to overexposure to solar radiation, especially skin damage. To test the current
operational status of measuring and modelling techniques used in providing the public with UVI
information, this article compares cloudless sky UVIs (measured using five instruments at four locations
with different latitudes and climate) with the results of 13 models used in UVI forecasting schemes. For
the models, only location, total ozone and solar zenith angle were provided as input parameters. In
many cases the agreement is acceptable, i.e. less than 0.5 UVI. Larger differences may originate from
instrumental errors and shortcomings in the models and their input parameters. A possible explanation
for the differences between models is the treatment of the unknown input parameters, especially
aerosols.