Project C03:
Variability in UTLS transport from model age of air and impacts on composition

Brief Summary

Long-term trends in the composition of the UTLS with radiatively active trace gas species like water vapour and ozone may cause substantial effects on the Earth’s radiation budget and on surface climate and need to be correctly represented in models for reliable predictions. A robust knowledge of the variability of UTLS transport on inter-annual to decadal time scales is a prerequisite for a reliable estimation and attribution of long-term anthropogenically forced trends. However, the representation of such variability, as related to the QBO, ENSO, volcanic aerosol, SSWs, solar cycle, and ODS is often incomplete in current climate model simulations, casting comparisons with measurements into doubt. The proposed project aims at investigating variability and long-term changes of transport pathways and time scales in the UTLS from a Lagrangian model perspective. The comprehensive research strategy combines reanalysis-driven simulations with the Lagrangian CLaMS model and free-running simulations with CLaMS coupled to the climate model EMAC, together with satellite and in-situ observations. Different powerful diagnostics will be used to evaluate transport pathways and time scales in the UTLS. In addition to simulating chemical species we will use a novel age spectrum analysis method, with the age of air spectrum being the distribution of transit times through the stratosphere. The model simulations will be compared to trace gas measurements from satellite instruments (e.g., MLS, ACE-FTS, MIPAS), and to airborne in-situ tracer measurements (e.g., from recent HALO- and G5-missions) provided by the other project partners. Combination of the tracer measurement data with the full model age spectrum, and related mass fractions of young and old air masses, will allow quantifying the effect of changing transport pathways and mixing time scales on the UTLS composition. Furthermore, analysis of the tracer and mean age budgets based on the tracer continuity equation will allow further insights into the roles of different processes (e.g., residual circulation and eddy mixing) in driving transport in the UTLS. Finally, consistent EMAC climate model simulations with both Eulerian and Lagrangian CLaMS tracer transport included will be investigated for effects of Lagrangian transport with reduced numerical diffusion on the model representation of the UTLS. The research questions focus on: (i) Variability and trends in UTLS transport time scales, (ii) the related impacts on trace gas composition, and (ii) the representation of UTLS pathways and time scales in different reanalysis and models.

Members

Publications

Ploeger, F., T. Birner, E. Charlesworth, P. Konopka, and R. Müller (2024): Moist bias in the Pacific upper troposphere and lower stratosphere (UTLS) in climate models affects regional circulation patterns. Atmospheric Chemistry and Physics 24 (3), 2033–2043. doi: https://doi.org/10.5194/acp-24-2033-2024.

Charlesworth, E., F. Ploeger, T. Birner, R. Baikhadzhaev, M. Abalos, L. Abraham, H. Akiyoshi, S. Bekki, F. Dennison, P. Jöckel, J. Keeble, D. Kinnison, O. Morgenstern, D. Plummer, E. Rozanov, S. Strode, G. Zeng, and M. Riese (2023): Stratospheric water vapor affecting atmospheric circulation. 14, doi: https://doi.org/10.1038/s41467-023-39559-2. 

Ebert, M., R. Weigel, S. Weinbruch, L. Schneider, K. Kandler, S. Lauterbach, F. Köllner, F. Plöger, G. Günther, B. Vogel, and S. Borrmann (2023): Characterization of refractory aerosol particles collected in the tropical UTLS within the Asian Tropopause Aerosol Layer (ATAL). EGUsphere 2023, Preprint, 1–45. doi: 10.5194/egusphere-2023-2245.

Harzer, F., H. Garny, F. Ploeger, H. Bönisch, P. Hoor, and T. Birner (2023): On the pattern of interannual polar vortex–ozone co-variability during northern hemispheric winter. Atmospheric Chemistry and Physics 23 (18), 10661–10675. doi: 10.5194/acp-23-10661-2023.

Ploeger, F. and H. Garny (2022): Hemispheric asymmetries in recent changes in the stratospheric circulation. Atmospheric Chemistry and Physics 22 (8), 5559–5576. doi: https://doi.org/10.5194/acp-22-5559-2022.