MeteoSwiss maintains two operational sites for ozone measurements: the Arosa Licht Klimatische Observatorium (LKO) and the Payerne Ozone Sounding Station.
At Arosa, the atmospheric transparency to UV sun radiation is recorded using Dobson and Brewer sun spectrophotometers. The two systems are based on the measurement of the intensity of solar radiation lines at the edge of the ozone absorption spectrum between 305 - 335 nm. Pairs of wavelenghts are selected so that one is strongly absorbed by atmospheric ozone while the other is only weakly absorbed. The Dobson instrument relies on a calibrated attenuator for balancing the intensities of these two lines. In the Brewer instrument, the intensity of both lines is measured and the calibration of the apparatus is maintained with standard lamps tests. The Dobson, developed in the years 1920 to 1940, is a manual instrument requiring the presence of a trained operator. The Brewer, developed in the years 1970 - 1980, is a fully automatic instruments. Nevertheless, both types of instruments require careful maintenance and calibration programs with daily control and cleaning of the optical components in contact with the outside environment.
At Arosa, the atmospheric transparency to UV sun radiation is recorded using Dobson and Brewer sun spectrophotometers. The two systems are based on the measurement of the intensity of solar radiation lines at the edge of the ozone absorption spectrum between 305 - 335 nm. Pairs of wavelenghts are selected so that one is strongly absorbed by atmospheric ozone while the other is only weakly absorbed. The Dobson instrument relies on a calibrated attenuator for balancing the intensities of these two lines. In the Brewer instrument, the intensity of both lines is measured and the calibration of the apparatus is maintained with standard lamps tests. The Dobson, developed in the years 1920 to 1940, is a manual instrument requiring the presence of a trained operator. The Brewer, developed in the years 1970 - 1980, is a fully automatic instruments. Nevertheless, both types of instruments require careful maintenance and calibration programs with daily control and cleaning of the optical components in contact with the outside environment.
Inside the Dobson shelter, the two Dobson instruments are mounted on a rotating table for easy operation across the same roof opening.
Brewer instrument on the terrasse of the Arosa site.
The long record of the Arosa series (which started in 1926) shows the onset of the thinning of the ozone layer above Switzerland in the early eighties. A pronounced change occurs over the Winter and Spring season while minor changes occur in Summer and Fall as seen below: the monthly averaged data for the period 1926 to 1969 are systematically higher than the corresponding values for the year 2004. The analysis of the vertical profiles from the Payerne soundings reveals that the ozone has decreased in the stratosphere (above ~10km) while it has increased in the troposphere (below ~10km).
The figure below also shows the large day to day variation of the ozone amount, especially in the Winter period due to the alternance of "low ozone" tropical airmass, respectively of "rich ozone" polar airmass transport over mid-latitudes.
The figure below also shows the large day to day variation of the ozone amount, especially in the Winter period due to the alternance of "low ozone" tropical airmass, respectively of "rich ozone" polar airmass transport over mid-latitudes.
Annual cycle of the total ozone amount above Arosa. The blue line is the monthly mean data for the period 1926-1969 which represents the state of the atmosphere before the ozone layer thinning. The red line is the corresponding data for the year 2004 while the black line visualize the daily average measurements.
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