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

What is OCTAV?

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 of dynamical processes such as stratosphere troposphere exchange (STE). The community thus faces challenge of optimally exploiting the existing portfolio of observations to better understand the physical composition of the UTLS, including past long-term changes in trace gas distributions and the processes that control them. 

This activity will focus on 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 will be 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 will provide a framework for comparing measurements with diverse sampling patterns and thus will leverage 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.