Measurements of historical total ozone from the Chalonge-Divan stellar spectrum program: A reanalysis of the 1953–1972 data and a comparison with simultaneous Dobson Arosa measurements



[1] We report new determinations of total ozone obtained by reanalyzing a unique set of astronomical observations that were made in the mid-20th century at observatories in France (Haute-Provence) and Switzerland (Jungfraujoch) for the purpose of calculating nightly atmospheric extinction coefficients in the UV (Rayleigh scattering and total ozone) as part of a program to measure absolute stellar fluxes. Only a small fraction of the original ozone results, corresponding to data obtained during 1958–1959, are in the public domain at the World Ozone and Ultraviolet Data Centre; the rest were on handwritten sheets and were stored at Haute-Provence. Both astronomical sites are close enough geographically to Arosa (Switzerland) that the respective ozone values can be compared directly. The comparison reveals a generally very close resemblance, even down to the pattern of daily variations, with a correlation coefficient of 0.78, but an overall negative bias of 6–7% in the stellar results. The bias appears to be slightly larger prior to 1958.