TOTAL OZONE SERIES AT AROSA (SWITZERLAND) - HOMOGENIZATION AND DATA COMPARISON

Five Dobson and two Brewer spectrophotometers were used for total ozon e observations at Arosa, beginning in 1926 and providing the world's l ongest Series. In this paper we present the results of our attempts to provide a homogeneous series and discuss the data quality problems of the record. From the mid-1950s to 1992, Dobson instrument D15 was cal ibrated by the statistical Langley plot method. In 1986 the calibratio n of another Dobson spectrometer at Arosa (D101) was changed by the in tercomparison with the primary world Dobson instrument (D83). A statis tical model based on simultaneous measurements of D101 and D15 of the period from 1987 to 1990 was used to obtain a total ozone series in Li ne with the primary Dobson spectrophotometer, including a correction f or an optical disalignment problem of D15. The series of D101 from 199 0 to 1995 was corrected on the basis of data from the Dobson intercomp arisons of 1990 and 1995 and comparisons with other total ozone measur ements of Brewer and Dobson spectrophotometers at Arosa. A transfer fu nction between Dobson and Brewer spectrophotometric measurements of Ar osa is presented, and total ozone measurements of Arosa are compared w ith version 7 daily overpass data of the satellite instrument the tota l ozone mapping spectrometer (TOMS) which operated on board Nimbus 7 f rom autumn 1978 to spring 1993. Available information allowing us to t rack back the total ozone measurements of Arosa to the measurements of the primary Dobson spectrometer reveal that the total ozone series of Arosa fluctuated no more than approximately 1% against D83 in the per iod from 1978 to 1995. Average shift of Arosa total ozone data against the TOMS instrument was -1.12 (+/-0.1)% over the lifetime of the TOMS instrument.