Changes in the distributions of trace gases, like water vapor and ozone, and thin cirrus clouds in the upper troposphere and lower stratosphere (UTLS) strongly impact radiative forcing of the Earth's climate and surface temperatures (e .g. Riese et al., 2012), and are of key importance for understanding climate change (e. g. Solomon et al., 2010). Mixing processes at the tropopause cover a scale range from the micro scale to planetary scales and have to be parameterized in global models. Uncertainties in the description of mixing, however, introduce large errors to the estimates of the radiative forcing and are thus of key importance for understanding climate change (Riese et al., 2012). It is therefore of great importance to quantify the physical and chemical processes (e.g. exchange of air masses, cirrus formation) that govern the composition of the UTLS. The so-called overworld above θ ≥ 380 K influences directly the composition of the extra-tropical stratosphere with significant contributions of air originating from the Asian monsoon circulation (Vogel et al., 2014; Ploeger et al., 2013). Below, the extra-tropical transition layer (ExTL) is strongly affected by bidirectional (quasi-isentropic) mixing across the tropopause (Hoor et al., 2010). The upper bound of the ExTL roughly coincides with the tropopause inversion layer (TIL), which constitutes a region of enhanced stability above the tropopause. The impact of radiatively active species like water vapour and ozone on the temperature structure makes the TIL a sensitive indicator for changes of ozone chemistry or changes of tropopause temperatures which directly affect water vapour which in turn feeds back into the static stability.
WISE will address the relation between composition and dynamical structure of the UTLS by focusing on the following three main research topics:
ST1) Interrelation of the tropopause inversion layer (TIL) and trace gas distribution
ST2) Role of Planetary wave breaking for water vapor transport into the extra-tropical lower stratosphere
ST3) Role of halogenated substances for ozone and radiative forcing in the UTLS region
ST4) Occurrence and effects of sub-visual cirrus (SVC) in the lowermost stratosphere
Figure 1: Schematic of the UTLS. Major UTLS features are the extra-tropical transition layer (ExTL) and the Tropopause Inversion Layer (TIL). The lowermost stratosphere (LMS) is the region in the extra-tropical stratosphere that is directly connected with the troposphere by isentropic surfaces. Wind contours (solid black lines 10ms−1 interval), potential temperature surfaces (dashed black lines), thermal tropopause (red dots) and potential vorticity surface (2PVU: light blue solid line) represent data from a cross section along 60◦ longitude on February 15, 2006 (adapted from Gettelman et al., 2011)
- What is the impact of wave-driven large scale eddy mixing on the composition of the mid- to high-latitude LMS?
- What is the role of the Asian Monsoon in moistening the extra-tropical UTLS in summer?
- What are typical time scales for mixing and how are these related to the underlying dynamical processes and source regions
- Does the TIL affect transport and mixing into the lower stratosphere and within the lower stratosphere?
- Which factors determine the formation of the TIL and how do these in turn affect transport?
- What is the link between Rossby wave breaking events and associated transport of water vapor and cirrus formation at mid latitudes?
HALO with its capabilities constitutes the ideal platform to address these questions. The aircraft is capable of carrying a payload up to altitudes of 15.5 km or θ = 420 K which is above the lowermost stratosphere (LMS) in mid latitudes (10 to 14 km). The region is particularly in the so-called overworld which is strongly affected by the Asian summer monsoon. The flight altitude is therefore ideal for profiling the LMS by infrared limb and lidar nadir observations in combination with drop sondes. The combination of in-situ and remote sensing instruments, which is currently only available for the HALO aircraft, will result in a consistent high resolution view of the LMS from the overworld to the tropopause with unprecedented detail and coverage. Currently, only HALO is capable of providing the long duration and the altitude coverage in combination with the unique payload. It allows to investigate the vertical temperature and trace gas structure in the extra-tropical UTLS and the interaction between thermodynamical and chemical processes, which are relevant for the global understanding of mixing processes in this region.
Addressing the WISE objectives requires a unique set of 3D measurements of temperature and static stability (N2), various trace gases (e. g. water vapor, ozone, tracers), and cirrus clouds obtained from remote sensing instruments of unprecedented resolution and data coverage, in combination with high precision in-situ observations. The 3D measurement capabilities of the new GLORIA infrared limb imager play an important role for the quantification of dynamical structures (e.g. N2) and trace gas structures associated with cross-tropopause exchange. A unique combination of limb and nadir remote sensing instruments (IR limb imaging/ lidar / uv-vis) will be used for innovative studies of optically and vertically thin cirrus clouds in the UTLS region. High-precision in-situ observations provide detailed information on mixing processes and tracer structure with high spatial resolution, which is essential to perform tracer-tracer analyses (e.g. CO-O3 correlations).
The evolution of baroclinic life cycles and Rossby wave breaking events and their role for cross tropopause exchange can be best observed over the Atlantic and North Sea. This includes the interaction of water vapor transport with the TIL and with the formation of SVC. An optimal campaign base would be Ireland with the opportunity of a stop on the Azores or Canary Islands. This would allow studying the temporal evolution of tracer structure and TIL on subsequent days during wave breaking events. The largest water vapor values in the UTLS occur during September/October. This is a result of wave-driven transport of water vapour, which is large from July until October in this altitude region. September/October is therefore the best period to investigate the impact of the Asian monsoon summer outflow on the composition of the LMS along with the effect of water vapor on the upper tropopause occurrence of cirrus and the feedback of the TIL and vice versa.
- Universities of Mainz, Frankfurt/Main, Heidelberg, Wuppertal
- Forschungszentrum Jülich, Karlsruhe Institute for Technology, IPA-DLR, PTB Braunschweig
- Hoor, P., Wernli, H., Hegglin, M. I., and Bönisch, H.: Transport timescales and tracer properties in the extratropical UTLS, Atmos. Chem. Phys., 10, 7929-7944, doi:10.5194/acp-10-7929-2010, 2010.
- Jurkat, T., et al. (2014), A quantitative analysis of stratospheric HCl, HNO3, and O3 in the tropopause region near the subtropical jet, Geophys. Res. Lett., 41, 3315–3321, doi:10.1002/2013GL059159.
- Kunkel, D., Hoor, P., and Wirth, V.: The tropopause inversion layer in baroclinic life-cycle experiments: the role of diabatic processes, Atmos. Chem. Phys., 16, 541-560, doi:10.5194/acp-16-541-2016, 2016
- Müller, S., Hoor, P., Berkes, F., Bozem, H., Klingebiel, M., Reutter, P., Smit, H. G. J., Wendisch, M., Spichtinger, P. and Borrmann, S. (2015), In situ detection of stratosphere-troposphere exchange of cirrus particles in the midlatitudes. Geophys. Res. Lett., 42: 949–955. doi: 10.1002/2014GL062556.
- Müller, S., Hoor, P., Bozem, H., Gute, E., Vogel, B., Zahn, A., Bönisch, H., Keber, T., Krämer, M., Rolf, C., Riese, M., Schlager, H., and Engel, A.: Impact of the Asian monsoon on the extratropical lower stratosphere: trace gas observations during TACTS over Europe 2012, Atmos. Chem. Phys., 16, 10573-10589, doi:10.5194/acp-16-10573-2016, 2016.
- Ploeger, F., P. Konopka, R. Müller, S. Fueglistaler, T. Schmidt, J. C. Manners, J.-U. Grooß, G. Günther, P. M. Forster, and M. Riese (2012), Horizontal transport affecting trace gas seasonality in the Tropical Tropopause Layer (TTL), J. Geophys. Res., 117, D09303, doi:10.1029/2011JD017267.
- Riese, M., F. Ploeger, A. Rap, B. Vogel, P. Konopka, M. Dameris, and P. Forster (2012), Impact of uncertainties in atmospheric mixing on simulated UTLS composition and related radiative effects, J. Geophys. Res., 117, D16305, doi:10.1029/2012JD017751
- Riese, M., et al. (2014), Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) scientific objectives, Atmos. Meas. Tech., 7, 1915-1928.
- Vogel, G. Günther, R. Müller, J.-U. Grooß, P. Hoor, M. Krämer, S. Müller, A. Zahn, and M. Riese (2014), Fast transport from Southeast Asia boundary layer sources to northern Europe: rapid uplift in typhoons and eastward eddy shedding of the Asian monsoon anticyclone, Atmos. Chem. Phys., 14, 12745-12762, doi:10.5194/acp-14-12745-2014, 2014.