Projections of climate change rely on an adequate representation of UTLS processes and their feedbacks in climate models. In the Collaborative Research Centre TPChange this will be addressed by a combination of field measurements, laboratory studies, theoretical approaches, and multiscale numerical modelling. Based on an improved understanding of relevant processes at different scales, we will develop parameterisations to improve state-of-the-art climate models. Our goal is to specify the impact of UTLS processes on composition, dynamics and ultimately on future climate and climate variability..

OCTAV-UTLS is a SPARC activity, which analyses trends of ozone and water vapour specifically in the UTLS region. The activity is lead by Irina Petropavlovkhikh (NOAA), Peter Hoor (JGU) and Luis Millan (JPL) who replaces Gloria Manney (NWRA)

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.

Water vapor variations in the extratropical upper troposphere and lower stratosphere (UTLS) have been shown to crucially affect atmospheric circulation and climate. For example, climate feedbacks due to stratospheric water vapor are dominated by trends in this region. Although UTLS water vapor has been the subject of considerable research due to its importance for climate, progress in understanding its impacts has been limited. This is largely because satellite and in-situ observations carry large uncertainties, and atmospheric models exhibit some of their largest biases in this region. The proposed ISSI team will bring together experts from the different fields of satellite and in-situ observations, process and climate modelling, dynamics and process understanding to make significant progress in understanding, observing and simulating water vapor in the UTLS.

The Priority Program (Schwerpunktprogramm) SPP 1294 “Atmospheric and Earth System Research with HALO” – “High Altitude and Long Range Research Aircraft” – is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). It supports research for the investigation of atmospheric and Earth system related processes.

Our group led several campaigns with HALO in the past focusing on topics in the upper troposphere and lower stratosphere (WISE, SouthTRAC, PHILEAS).
Additionally, our group participated in several campaigns (TACTS/ESMVal, ASCCI, NAWDIC).