Objectives Phase 3 (Oct 2022 – Sep 2026)

The 2022 WMO Scientific Assessment on Ozone Depletion is being finalized. While the Assessment does not make recommendations, it does outline several questions and knowledge gaps. LOTUS will respond to these needs and has outlined six topics to be explored over the next few years in support of the next Ozone Assessment.

1. Analysis Techniques

 Goal   Improve existing and/or investigate / develop new analysis techniques to better quantify trends and improve confidence of trend results.

 Motivation   There are always challenges and caveats in applying different analysis techniques to the data that must be considered when trying to ascertain trends. As such, it is important to always reconsider what the best practices may be and/or what new tools are available to use for trend studies. For proper attribution of trends, the analysis shall be applied to state-of-the -art chemistry-climate-models (CCMs) and Chemistry-Transport models (CTMs) as well (e.g., from CCMI-2022).

2. Partial Column Trends

 Goal   Derive ozone trends from observations in partial columns, in collaboration with both TOAR-II and OCTAV-UTLS, to explore, at a minimum, the separate contributions of the stratospheric and tropospheric columns to the total column.

 Motivation   The 2022 WMO Ozone Assessment specifically calls out how trends in total column ozone may not be the best metric to assess ozone recovery. This is because, in some areas, increasing tropospheric ozone may be masking a potential continued decline of the stratospheric column. So far, this separate attribution has been shown by models and ground-based tropospheric data shows a positive trend in the tropospheric column. However, a comprehensive analysis of stratospheric column trends from satellite or ground-based observations has not been done yet. Trend analysis will be done in close collaboration with TOAR-II, the latter focusing on tropospheric ozone trends.

3. Trends in the UTLS with OCTAV-UTLS

 Goal   Focus on trends in the UTLS region, specifically by supporting OCTAV-UTLS, which is investigating dynamical coordinate systems, in an effort to improve both trend uncertainties and our understanding of physical causes of long-term changes.

 Motivation   The past Ozone Assessments have shown that ozone trends derived in the UTLS are never statistically significant, yet this region is critically important for assessing the climate impact on the recovery of the ozone layer and the impact of ozone trends on the climate itself. These larger uncertainties are a combination of reduced data quality (primarily from satellite-based observations) and enhanced variability in ozone itself (primarily from dynamical influences). Any analyses that can be performed that may improve our understanding of how ozone is changing in the UTLS and why should be explored.

4. Data Consistency between Satellite- and Ground-based Observations

 Goal   Assess the consistency between satellite and ground-based records.

 Motivation   Intercomparisons between satellite- and ground-based records as well as ground-based records at the same location continue to show discrepancies that sometimes even exceed the limits of their uncertainties. However, it is critical that we understand the cause of these discrepancies in order to facilitate their correction, particularly in light of a possible near-term future with limited satellite observational coverage to continue the data record.

5. Trends in the Polar Regions

 Goal   Apply newer analysis techniques and our improved understanding thereof to derive trends in the polar regions.

 Motivation   Thus far, efforts within LOTUS have almost entirely focused on ozone trends outside of the polar regions, but the evolution of ozone (and the ozone hole) at the poles is just as important.

6. Interconnections with Temperature and GHGs

 Goal   Investigate the connections between ozone and temperature trends in close collaboration with ATC as well as potentially other connections such as water vapor trends.

 Motivation   Trends in stratospheric/tropospheric temperature are just as much a part of SPARC as trends in ozone. Temperature trends are primarily investigated as part of the Atmospheric Temperature Changes and their Drivers (ATC) activity. Since ozone is also a greenhouse gas, it can be difficult to decouple how long-term changes in temperature (and temperatureinduced changes in chemistry and dynamics) affect ozone when ozone itself affects these processes. There are, of course, interconnections between ozone and other greenhouse gases such as water vapor that can potentially be explored in more detail. The quality of water vapor observations has been assessed multiple times by SPARC (i.e., WAVAS, WAVAS-II), but extensive trend analyses or the use of regression analyses to further assess agreement between datasets have not been explored.