The GAW-CH Atmospheric Radiation Monitoring Program

Radiation is the driving force in energy exchanges between the atmosphere, the oceans and the ground; furthermore, the most direct effect of global warming is expected to be an increase of the infrared radiation emitted from the atmosphere to the ground. Long-term observation of surface radiation fluxes is consequently a prominent component of climate change monitoring in which MeteoSwiss actively participate in the framework of the Global Atmosphere Watch (GAW).

The Swiss Alpine Climate Radiation Monitoring network (SACRaM) has been established for this purpose. One station of this network, the Payerne station, is also part of the international Baseline Surface Radiation Network (BSRN). Four main stations monitor radiation at the ground from the ultraviolet (UV) to the visible and infrared (IR) part of the spectrum. Two stations are located in the Swiss Alps - at Jungfraujoch and Davos

and the others in the plains

- at Payerne and Locarno-Monti.

These main stations are completed by two smaller stations monitoring the surface downward flux of solar and atmospheric radiation.

SACRaM follows the guideline of GAW and BSRN, and guarantees high accuracy operational measurement of radiation fluxes in the UV, short-wave (solar radiation) and long-wave (atmospheric infrared thermal radiation) part of the spectrum with state-of-the-art techniques. The measurements at the main stations include the following parameters:

Comparing monthly moving averages with mean annual cycles determined by averaging several years together allows the following observations for 2009: UV radiation was slightly higher than the norm during August and September at Davos, Locarno-Monti and Payerne, while at Jungfraujoch it was significantly higher than the norm. The same type of deviations also affects short-wave radiation (solar not restricted to the UV range). This suggests that cloud cover is responsible for these deviations.

Cloud coverage strongly affects both shortwave (SW, solar) and longwave (LW, infrared thermal) downward radiation, although the effect on these two wavelength range is opposite. While cloud most often reduces the amount of SW downward radiation, it usually increases LW downward radiation. However LW radiation is also influenced by the temperature of the atmosphere and its water vapor content. In 2009, during August and the beginning of September, SW radiation was higher than the norm, which resulted from a reduced cloud coverage.

This situation caused high atmospheric temperatures, which reduced the influence of the lower than usual cloud coverage on LW radiation. At Locarno Monti this situation persisted until October where the LW radiation was lower than usual during this month. At Jungfraujoch, SW radiation was slightly lower than usual during the first half-year, while LW radiation was higher than usual. At Davos finally, SW radiation was significantly lower than the norm in June and part of July without any deviation from the multi-year average being visible for LW radiation.