Objectives Phase 2 (Oct 2018 – Sep 2022)

The second phase of LOTUS activity will use updated ozone profile records, in particular new homogenized ozonesonde records that were not available for the first phase and thus were not included in the LOTUS Report. The focus will be on the unresolved issues after phase one, namely:

• Development of techniques to directly assess uncertainties in the merged records resulting from small relative drifts, from the conversion between geometric altitude and pressure-based vertical coordinates and from differences in sampling properties.
• Evaluation of long-term stability in satellite and ground-based data records.
• Optimization of the LOTUS trend model for analyses of the ground-based records in order to improve interpretation of dynamical processes that impact ozone changes over regions of limited spatial extent.
• Explore trends in polar regions and in the lower stratosphere. The latter will be done in conjunction with the OCTAV-UTLS SPARC activity dedicated to the assessment of atmospheric composition and its decadal changes in the UTLS region.
• Comprehensive evaluation of the coherence between stratospheric and total column ozone trends.

Results from the second phase of LOTUS were peer-reviewed and published as an ACP paper in September 2022.