Scientific Themes

Transport and Dynamics in the SH UTLS: SOUTHTRAC-DYN

The dynamical processes which determine the composition of the southern hemispheric UTLS differ from its northern hemispheric counterpart in strengths and seasonality. Similar to the NH the SH UTLS will be influenced by a combination of global scale transport by the BrewerDobson circulation (BDC) and of transport across the extratropical tropopause. However, the relative importance of these processes differs from the Northern hemisphere as well as the composition and dynamical structure.

In SOUTHTRAC DYN-1 we will disentangle these differences by combining measurements of long-lived tracers of different lifetime and CLaMS age spectral information to gain insight in the relevant time scales. Shorter-lived tracers as well as remote sensing observation of the thermal and chemical structure will reveal the role of tropopause based processes in forming the TIL and ExTL, which both show different structure and properties in the southern hemisphere UTLS (Hegglin et al., 2009). The tropopause related processes, which affect the TIL and ExTL structure also control the abundance of particular water vapor in the SH UTLS. Transport and abundance of H2O into the SH UTLS significantly differ from the northern hemisphere, which is strongly affected by water vapour transport from the Asian summer monsoon (Vogel et al., 2016; Rolf et al., 2018).

SOUTHTRAC DYN-2 will focus on the generation, propagation and dissipation of GWs being strongest at the Andes in SH winter.

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Chemical composition aspects: SOUTHTRAC-CHEM

The main aim of SOUTHTRAC-CHEM is to determine the chemical composition of the SH-UTLS and the processes affecting the composition with a special emphasis on differences to the much better studied NH-UTLS. The chemical composition will be characterized by both insitu and remote sensing observations (survey flights) providing information on a wide range of chemically and radiatively important species (see payload). We will characterize the chemical composition of the SH-UTLS in an unprecedented way, allowing also to investigate the processes controlling this composition. Next to this overall goal of composition characterization, we will address two specific topics, where the SH-UTLS differs significantly from the northern hemisphere.

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Hegglin, Michaela I. and Theodore G. Shepherd (2009). “Large climate-induced changes in ultraviolet index and stratosphere-to-troposphere ozone flux”. In: Nat. Geosci. 2.10, pp. 687–691. DOI: 10.1038/ngeo604.

Rolf, Christian, Bärbel Vogel, Peter Hoor, Armin Afchine, Gebhard Günther, Martina Krämer, Rolf Müller, Stefan Müller, Nicole Spelten, and Martin Riese (2018). “Water vapor increase in the lower stratosphere of the Northern Hemisphere due to the Asian monsoon anticyclone observed during the TACTS/ESMVal campaigns”. In: Atmos. Chem. Phys. 18.4, pp. 2973–2983. DOI: 10.5194/acp-18-2973-2018.

Vogel, Bärbel, Gebhard Günther, Rolf Müller, Jens-Uwe Grooß, Armin Afchine, Heiko Bozem, Peter Hoor, Martina Krämer, Stefan Müller, Martin Riese, Christian Rolf, Nicole Spelten, Gabriele P. Stiller, Jörn Ungermann, and Andreas Zahn (2016). “Long-range transport pathways of tropospheric source gases originating in Asia into the northern lower stratosphere during the Asian monsoon season 2012”. In: Atmos. Chem. Phys. 16.23, pp. 15301–15325. DOI: 10.5194/acp-16-15301-2016.

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