Monitoring Ultra Violet Irradiance at the Surface of the Earth: The Belgian Network

Abstract:

The observation and monitoring of solar irradiance, in general, and UV (Ultra Violet) irradiance, in particular, is important due to its impact on human health and environment on regional and global scale. The UV irradiance, hence, the UV index (UVI), is affected by various atmospheric parameters, e.g., the solar zenith angle, the ozone overhead column and other atmospheric absorbers and scatters such as clouds and aerosols.

In order to investigate the modifications induced on human environment due to the UV irradiance, it is important to quantify the various factors affecting the UV irradiance, both UV-A and UV-B. Particularly, clouds are responsible for a great deal of the observed irradiance variability that in turn requires the examination of extensive observation data sets by detailed radiative transfer models using co-located meteorological and ozone measurements together with satellite based estimations.

These factors are continuously monitored over Uccle, Belgium, since 1993 by means of station based observations producing spectral measurements of UV irradiance together with UVI computation that constitutes the European UV network. Today there are six stations representing Belgium in this European network. These measurements give a good insight into the trend of UV irradiance and associated atmospheric parameters over Belgium. Here we present some of the recent results from these measurements and radiative transfer modelling, e.g., the relation between the cloudiness, uncertainty in the cloudiness due to measurements, and UVI, ozone trend and UVI, among others. It is seen that since 2000 despite of a stable ozone concentration UV irradiance continues to increase. Modelling studies show that 1% of ozone reduction implies 2% of UVB increase.

These station based measurement data will be used to study solar irradiance – cloud - aerosol interactions by merging them with satellite based measurements.