Content - Ozone Trends

LOTUS – Long-term Ozone Trends and Uncertainties in the Stratosphere

Activity leaders

Irina Petropavlovskikh

Daan Hubert
BIRA-IASB, Belgium

Sophie Godin-Beekmann
LATMOS, France

Activity description

For the WMO/UNEP 2018 Ozone Assessment, a clear understanding of ozone trends and their significance as a function of altitude and latitude is still needed, nearly 20 years after the peak of ozone depleting substances in the stratosphere. A previous activity sponsored by SPARC, IO3C, IGACO-O3/UV and NDACC (SI2N) aimed at the evaluation of trends from long-term ozone profile records (ground-based and satellites, including merged satellite data records). However, a clear evaluation of uncertainties in trend studies and in particular the consideration of errors linked to the sampling and stability of (merged) data sets could not be achieved by the end of SI2N. Since then, new merged satellite data sets and long awaited homogenized ozonesonde data series are being produced. There is thus a strong interest in the scientific community to use these newer observations to evaluate ozone recovery and to understand the limitations in determining the significance of long-term trends. In order to address the issues left pending after the end of SI2N, a comprehensive evaluation of all long-term data sets available together with their relative drifts is needed. Evaluation of error propagation in ozone trend calculation is also required.

 The LOTUS project aims (a) to update and extend stratospheric ozone observations to recent years, (b) to improve our understanding of crucial yet poorly known sources of uncertainties in trend retrieval, (c) to investigate how uncertainties interact and propagate through the different stages of analysis chain, and (d) to re-evaluate current best practice(s) and possibly establish more suitable alternatives.

During the LOTUS activity, several new satellite and ground-based ozone profile data sets will be updated and made available to the community. A SPARC Report will accompany this data release and discuss the progress made on several key open issues identified by previous assessments, most notably on the understanding of uncertainties in the trend analysis chain. An important part of the report will be devoted to an update of the assessment of long-term trends and their significance, in different regions of the stratosphere. A section will list further requirements on data sets and analysis methods that have been identified during the project. In addition, a SPARC Newsletter will be written after project kick-off, after the workshop and after the project closure.

The timing of LOTUS is driven by the objective to provide timely input to the 2018 WMO/UNEP Ozone Assessment. This means that all data sets, regression analyses and the SPARC Report will be finalized and published by March-April 2018.

Website for further information

Find a dedicated website on the LOTUS activity at