Dynamical linear modeling estimates of long-term ozone trends from homogenized Dobson Umkehr profiles at Arosa/Davos, Switzerland

Abstract

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.

Disentangling the Advective Brewer‐Dobson Circulation Change

“…This allows DLM to assess the non‐linear background trend which corresponds better with non‐stationary processes in the atmosphere (Laine et al., 2014). For these reasons, DLM has been recently used to estimate trends in ozone in model outputs (Ball et al., 2018; Karagodin‐Doyennel et al., 2022) and observational records (Bognar et al., 2022; Laine et al., 2014; Maillard Barras et al., 2022) quite extensively.…”

Comparison of the Climatic Characteristics of Ozone Valley Over the Tibetan Plateau and the Rocky Mountains

“…The low‐ozone air in the troposphere could be transported into the stratosphere by this updraft, thereby reducing the ozone concentration. In addition to ozone valleys that appear in summer, there are sporadical extremely low centers around the TP during winter, which are also caused by anomalously strong dynamical transport processes (Bian, 2009; Maillard Barras et al., 2022). The vertical profile of ozone in the UTLS over the other high terrains (e.g., Iranian Plateau) is very similar to that over TP (Borhani et al., 2023).…”

Microwave radiometer observations of the ozone diurnal cycle and its short-term variability over Switzerland

“…Following the success of the Montreal Protocol in 1987, full recovery of the ozone layer is expected for the 21st century with significant regional variability and uncertainties. In particular, there is a high degree of uncertainty about the lower stratospheric ozone recovery, and there is increasing observational evidence that ozone is still declining at some locations in the lower stratosphere (Ball et al, 2018;Maillard Barras et al, 2022a;Godin-Beekmann et al, 2022), without satisfactory explanation to date.…”