Reanalysis of total ozone measurements at Dombås and Oslo, Norway, from 1940 to 1949

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Abstract
Total ozone measurements from Dobson spectrometer number 8 at Dombås, Norway (62.1°N, 9.1°E), and Oslo, Norway (59.9°N, 10.7°E), from 1940 to 1949 have been examined and reanalyzed. New sets of Bass‐Paur absorption and Rayleigh scattering coefficients have been created, and total ozone values have been recalculated using the new coefficients. Approximately half of the ozone registrations at Dombås were based on direct Sun observations calculated from the CC′ wavelength pairs. The long C′ pair has provided valuable information about the effect of atmospheric aerosols on the ozone measurements. A method for determining aerosol corrections is presented which demonstrates that the monthly mean aerosol error can reach 4% total ozone, normally with a higher correction in the summer than in the winter. Also, the influence of SO2 on the Oslo ozone measurements is estimated. The D8 ozone series from 1940 to 1949 has been compared to ozone records from other European stations and to the D56 ozone series from Oslo 1978–1998. Studies of old and new Dobson data demonstrate that the annual variation in the ozone layer has changed during the last 50–60 years. The comparison indicates that the ozone decrease is relatively small for the summer months (2.9 ± 1.8%), whereas the average winter and spring values have deceased by 6.1 ± 3.9% from the 1940s to the 1990s. If the postwar increase in tropospheric ozone is taken into account, the depletion of the ozone layer is considerably higher, probably 8–9% for winter/spring. All the reanalyzed total ozone data from D8 for the period 1940 to 1949 are available at the World Ozone and Ultraviolet Radiation Data Center.

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