OCTAV-UTLS – Observed Composition Trends And Variability in the Upper Troposphere and Lower Stratosphere

Logo of the OCTAV-UTLS activity

Activity leaders

Peter Hoor
Johannes Gutenberg University, Mainz, Germany

Luis Millán
NASA Jet Propulsion Laboratory, Caltech, CA, USA

Irina Petropavlovskikh

Scientific Steering Committee:

Adam Bourassa (USASK, Canada), Geir Braathen (WMO, Switzerland), Harald Bönisch (KIT, German), Rob Damadeo (Nasa, LARC, USA), Michaela Hegglin (U. of Reading, UK), Thierry Leblanc (JPL, USA), Nathaniel Livesey (JPL, USA), Gloria Manney (NWRA, USA), Gabriele Stiller (JPL, USA), Susann Tegtmeier (GEOMAR, Germany), Valerie Thouret (LA/CNRS, France), Christiane Voigt (DLR, Germany), Kaley Walker (U. Toronto, Canada)

Activity description

The distribution of tracers in the Upper Troposphere and Lower Stratosphere (UTLS) shows a large spatial and temporal variability, caused by competing transport, chemical, and mixing processes near the tropopause, as well as variations in the tropopause itself. This strongly affects quantitative estimates of the impact of radiatively active substances, including ozone and water vapour, on surface temperatures, and complicates diagnosis of dynamical processes such as stratosphere troposphere exchange (STE). The incorrect description of dynamical processes at the tropopause and their effect on the UTLS composition contribute to uncertainties affecting near-time climate predictions (related to the WCRP Grand Challenge #7). The community thus faces challenge of optimally exploiting the existing portfolio of observations to better understand the physical composition of the UTLS. This approach will help with interpretation of the past long-term changes in trace gas distributions and the processes that control them.

This activity ultimately aims at improving the quantitative understanding of the UTLS’s role in climate and the impacts of stratosphere-troposphere exchange (STE) processes on air quality. Achieving this goal requires a detailed characterization of existing measurements (from aircraft, ground-based, balloon, and satellite platforms) in the UTLS, including understanding how their quality and sampling characteristics (spatial and temporal coverage, resolution) affect the representativeness of these observations.

One key aspect of this activity is to develop and apply common metrics to compare UTLS data using a variety of geophysically-based coordinate systems (e.g., tropopause, equivalent latitude, jet-focused) using meteorological information from reanalysis datasets. This approach provides a framework for comparing measurements with diverse sampling patterns and thus leverages the meteorological context to derive maximum information on UTLS composition and its relationships to dynamical variability.

The activity will produce recommendations for data comparisons in the UTLS region based on specific techniques/instruments. We will provide an assessment of gaps in current geographical/temporal sampling of the UTLS region that limit determining variability and trends, and suggest future measurement strategies that would help fill those gaps.

OCTAV-UTLS contributes to the research lead by a number of programmes (WCRP and GAW of WMO and IUGG), sponsored by the IO3C (International Ozone Commission) under the IAMAS (International Association of Meteorology and Atmospheric Sciences) and collaborates with other SPARC activities, such as LOTUS, SSRIC, S-RIP with links to FISAPS.

Partners for this activity are: SPARC, WMO and GAW.


Jeffery, P. S., Walker, K. A., Sioris, C. E., Boone, C. D., Degenstein, D., Manney, G. L., McElroy, C. T., Millán, L., Plummer, D. A., Ryan, N. J., Sheese, P. E., and Zou, J.: Water vapour and ozone in the upper troposphere – lower stratosphere: Global climatologies from three Canadian limb-viewing instruments. Atmos. Chem. Phys. Discuss. [preprint], doi: 10.5194/acp-2022-345, accepted for publication, 2022.

SPARC activity updates

SPARC Newsletter No. 55, 2020, p. 17: The third SPARC OCTAV-UTLS meeting, Thierry Leblanc, Luis Millán, Peter Hoor, and Irina Petropavlovskikh

SPARC Newsletter No. 53, 2019, p. 27: Report on the second SPARC OCTAV-UTLS meeting, Peter Hoor, Irina Petropavlovskikh, Luis Millán, Daniel Kunkel

SPARC Newsletter No. 50 , 2018, p. 10: Report on the first SPARC OCTAV-UTLS meeting, Boulder, CO, USA, 18-20 July 2017, D. Kunkel, P. Hoor, I. Petropavlovskikh, and G. L. Manney.


(see https://octav-utls.net/meetings)

  • Bern, Switzerland, ISSI meeting, February 2023
  • Table Mountain, CA, USA, March 2020
  • Mainz, Germany, November 2018
  • Boulder, USA, July 2017    

Website for further information