The Tropopause Region in a Changing Atmosphere

Kelvin-Helmholtz instabilities rendered visible by clouds during a flight above a warm conveyor belt during the WISE (Wave-driven ISentropic Exchange) campaign. The wave structure indicates mixing processes at the tropopause that redistribute water vapour and ice particles. (Photo: Peter Hoor)

Climate change is without doubt one of the largest and most pressing global problems and reliable climate projections are therefore of enormous political and socioeconomic relevance. Such estimates are highly dependent on the accurate representation of the altitude region between 10 km and 20 km, the tropopause region.

Surface temperatures are highly sensitive to perturbations of the atmospheric composition in the tropopause region. However, knowledge about even the present day global distribution of key constituents of climate relevance, e.g. water vapour, ozone, ice particles and aerosols, is surprisingly incomplete. Likewise, the microphysical, chemical and dynamical processes controlling the abundance of these constituents are partly unknown or misrepresented in current climate models. This leads to large uncertainties in the calculation of radiative forcing.

The complexity of this region is, on the one hand, a result of the coupling of processes over many spatial scales, ranging from the nanometer scale to the planetary scale. On the other hand, relevant processes from different components of the climate system interact in the tropopause region and contribute to these uncertainties by complex feedback mechanisms involving dynamics, chemistry, microphysics and radiation. Therefore, a synergistic approach is required, which combines the expertise from different research areas to improve our understanding of this highly important region.

In the new Collaborative Research Centre TPChange we will identify, analyse, and quantify the processes that are relevant for the UTLS composition and its role in climate. This will be achieved by field measurements, laboratory studies, theoretical approaches, and multiscale numerical modelling. Researchers at seven locations (JGU, GU Frankfurt, TU Darmstadt, LMU München, MPI für Chemie Mainz, FZ Jülich, DLR Oberpfaffenhofen) collaborate in order to make fundamental progress in process understanding of the tropopause region, its role for atmospheric composition, circulation, and climate variability. In this way, TPChange will contribute to expand the understanding of the present and future climate and to minimise uncertainties.