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The WMO/UNEP Scientific Assessment of Ozone Depletion depend on a clear understanding of ozone trends and their significance as a function of altitude and latitude (WMO, 2014). A previous activity sponsored by SPARC, IO3C, IGACO-O3/UV and NDACC (SI2N) aimed at the evaluation of trends from long-term ground-based and satellite ozone profile records. While succesful at generating momentum for the creation of various merged data records, no coherent view on the significance of the trends emanated from SI2N (Harris et al., 2015). The consideration of errors linked to sampling and stability of the data sets proved especially challenging, and the impact of uncertainties from the regression analyses remained out of scope. The latter motivated the continuation of the initiative under the name of LOTUS, short for Long-term Ozone Trends and Uncertainties in the Stratosphere. LOTUS gathers about 30-40 experts to (a) update and extend stratospheric ozone observations to recent years, (b) to improve our understanding of crucial yet poorly known sources of uncertainties in trend studiesl, (c) to investigate how uncertainties interact and propagate through the different stages of the analysis chain, and (d) to re-evaluate current best practice(s) and possibly establish more suitable alternatives. Several members of ESA's Ozone_cci project coordinate and/or contribute to the LOTUS activities which will culminate in the publication of a SPARC Report in early 2018. More information can be found at


Preliminary results of a test of the regression model, the proxies and codes used by the participating groups (colours). Zonally averaged profile data (different panels) from the SBUV MOD v8.6 data record were regressed for long-term trends before (dashed) and after (solid lines) the turnaround in ozone depleting substances. Figure to appear in the LOTUS Report (2018).