Abstract
Extending across seven countries, the Alps represent an important
element for climate and atmospheric circulation in Central Europe. Its
complex topography affects processes on different scales within the
atmospheric system. This is of major relevance for the decadal trends in
Surface Solar Radiation (SSR), also known as Global Dimming and
Brightening (GDB). In this study we analysed data from 14 stations in
and around the Swiss and Austrian Alps, over a period ranging from the
1960s up to the 2010s, with the aim of characterizing the
spatio-temporal variations of the GDB and understanding the causes for
such trends in this region. Our results showed a different behavior in
the SSR decadal trends in the western part of the Alps in comparison to
the eastern part. We also identified a remarkable difference between the
causes of such trends in the stations at low altitudes in comparison to
the station at higher altitudes. The SSR trends under cloudy conditions
revealed strong evidence for a control of the decadal trends by cloud
optical depth at high elevation sites, in contrast with a strong
clear-sky forcing at low elevations. Results from previous literature
and available data suggest that such phenomena could be associated with
the indirect and direct aerosol effect, respectively, due to differing
pollution levels.