To assess the reduction of the solar flux by anthropogenic
aerosol in Europe.
Aerosol particles in the atmosphere reflect solar radiation and thus form a cooling factor. The cooling induced by anthropogenic aerosol counterbalances the warming by the man made greenhouse gases. However, the magnitude of the compensation factor is very uncertain. The dominant problem in quantifying the 'aerosol' effect on radiation is the localized character of the aerosol.
The effect of anthropogenic aerosol on local radiation/climate in Europe is being assessed. This is realized along 3 interconnected approaches. In recent estimates of the reduction in radiation in Europe the value for light scattering by aerosol was taken from United States measurements. This value is compared with the actual value in Europe. Furthermore, the historical trend in solar flux is related to the historic trend in aerosol loadings. Finally, the full effect of aerosol on radiation/climate is modelled. The radiation module being developed is validated with special field campaigns. In these experiments the relevant aerosol characteristics are determined and from these the reduction in solar radiation is calculated and compared with the measured reduction.
Aerosol particles reflect solar radiation back into space and thus less
heat reaches the earth surface. Aerosol does not intercept the outgoing
terrestrial radiation and thus the net result is a cooling, which is
estimated to compensate the warming by the greenhouse gases
Because of the very localized character of aerosol, a localized
assessment of the aerosol-forcing is required. This is realized along
three interconnected approaches.
The recent estimates of the reduction in radiation by aerosol in Europe
are extrapolations of ground-level light-scattering measurements in the
US. It is checked here which data are available in Europe and what the
actual scattering by European aerosol is. The European aerosol has a
large nitrate-content and the light-scattering of this compound will be
studied in detail. These results will be used in support of the next two
A decrease in solar flux over the last decades has been observed in three
countries in Europe. Here, the trend on the cloudless days is analyzed.
A search is made for available data on aerosol loadings in the same
period to be compared with the trend in the solar flux. The relation will
give an empirical factor for the aerosol forcing.
A simple 1-D version of the climate model ECHAM is made and aerosol is
parametrized in this model, for a calculation of the local cooling effect
of aerosol. First, the radiative forcing is calculated with a module
which uses the averaged parameters of the standardized "Climatology"
aerosol. This aerosol seems outdated and new detailed measurements are
made to check its validity. Simultaneously, solar radiation and relevant
meteorological parameters are measured.
The reduction in solar flux is calculated from the measured aerosol
parameters and this is compared to the measured reduction in solar flux.
The reduction will also be compared to the reduction calculated with the
"Climatology" aerosol and so the best up-to-date aerosol parameters are
A last validation of the aerosol/radiation model comes from a comparison
of modeled and measured trends in radiation.
A start is made of assessing which type of (anthropogenic) aerosol
particles serve as cloud nuclei for the climate-relevant clouds in
Funding SchemeCSC - Cost-sharing contracts