Project C02:
Deriving transport timescales in the UTLS from age tracers and the propagation of the seasonal cycle of CO₂

Brief Summary

In this project we propose to perform regular observations of CO₂, CH₄ and CO using the AirCore technique which has been established in recent years at University Frankfurt and further developed especially with respect to the altitude attribution. The CO₂, CH₄ and CO profiles derived from the Air-Core observations will be used to investigate how the seasonality of CO₂ in the troposphere propagates into the lowermost stratosphere. For this we will combine these observations, which can reach altitudes up to about 27 km, with more extensive measurements available further down in the UTLS, e.g. from research aircraft andfrom regular airborne sampling programmes. It is expected that the propagation of this signal is largely modulated by the strength of the subtropical jet, which is weakest during summer, which should result in stronger exchange. While fluxes across the extratropical tropopause cannot be measured directly, the shift in the seasonal cycle is expected to be a good indicator of when the exchange is strong and also of how far into the lowermost stratosphere this occurs during which season.
The first central research question is how the strength of the coupling between the tropics and extratropics in the UTLS is modulated by the strength of the sub-tropical jet. This investigation is based on the propagation of the seasonal cycle of CO₂. Here we suggest to use our observations in combination with models to see how well this process is represented in models. This investigation will use special tracers in the model, in particular a CO₂-like tracer which has a similar seasonal cycle but no ling term trend. The second central research question is the strength of the overturning stratospheric circulation, the so-called Brewer-Dobson circulation, and its variation different geographical and temporal scales. For this analyses we will focus on the seasonality and latitudinal (using equivalent latitude) variability of mean age values in the lower and middle stratosphere. This informationcan be used to allow a better constraint on variabilities of mean age derived from the observations dating back to 1976.

Members

Publications

Schuck, T. J., J. Degen, E. Hintsa, P. Hoor, M. Jesswein, T. Keber, D. Kunkel, F. Moore, F. Obersteiner, M. Rigby, T. Wagenhäuser, L. M. Western, A. Zahn, and A. Engel (2024): The interhemispheric gradient of SF6 in the upper troposphere. Atmospheric Chemistry and Physics 24 (1), 689–705. doi: 10.5194/acp-24-689-2024.

Wagenhäuser, T., M. Jesswein, T. Keber, T. Schuck, and A. Engel (2023): Mean age from observations in the lowermost stratosphere: an improved method and interhemispheric differences. Atmospheric Chemistry and Physics 23 (7), 3887–3903. doi: https://doi.org/10.5194/acp-23-3887-2023.