Abstract. Six collocated spectrophotometers based in Arosa/Davos, Switzerland, have been measuring ozone profiles continuously since 1956 for the oldest; Dobson instrument and since 2005 for the Brewer instruments. The datasets of these two ground-based triads (three Dobsons and three Brewers) allow for; continuous intercomparisons and derivation of long-term trend estimates. Mainly, two periods in the post-2000 Dobson D051 dataset show anomalies; when compared to the Brewer triad time series: in 2011–2013, an offset has been attributed to technical interventions during the renewal of the; spectrophotometer acquisition system, and in 2018, an offset with respect to the Brewer triad has been detected following an instrumental change on; the spectrophotometer wedge. In this study, the worldwide longest Umkehr dataset (1956–2020) is carefully homogenized using collocated and simultaneous Dobson and Brewer; measurements. A recently published report (Garane et al., 2022) described results of an independent homogenization of the same dataset performed by; comparison to the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) Global Modeling Initiative (M2GMI) model; simulations. In this paper, the two versions of homogenized Dobson D051 records are intercompared to analyze residual differences found during the; correction periods. The Aura Microwave Limb Sounder (MLS) station overpass record (2005–2020) is used as an independent reference for the; comparisons. The two homogenized data records show common correction periods, except for the 2017–2018 period, and the corrections are similar in; magnitude. In addition, the post-2000 ozone profile trends are estimated from the two homogenized Dobson D051 time series by dynamical linear modeling (DLM),; and results are compared with the DLM trends derived from the collocated Brewer Umkehr time series. By first investigating the long-term Dobson; ozone record for trends using the well-established multilinear regression (MLR) method, we find that the trends obtained by both MLR and DLM; techniques are similar within their uncertainty ranges in the upper and middle stratosphere but that the trend's significances differ in the lower; stratosphere. Post-2000 DLM trend estimates show a positive trend of 0.2 to 0.5 % yr−1 above 35 km, significant for Dobson D051 but lower and; therefore nonsignificantly different from zero at the 95 % level of confidence for Brewer B040. As shown for the Dobson D051 data record, the; trend only seems to become significantly positive in 2004. Moreover, a persistent negative trend is estimated in the middle stratosphere between 25; and 30 km. In the lower stratosphere, the trend is negative at 20 km, with different levels of significance depending on the period; and on the dataset.;
