TRR 301:  The tropopause region in a changing atmosphere

• Subject Area: Geosciences
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428312742

Climate change is without doubt the most urging global problem of the near future and climate projections are of enor-mous political and socioeconomic relevance. Such estimates are highly dependent on the accurate representation of the atmospheric dynamics, chemical composition, aerosol loading, cirrus clouds and circulation feedbacks in the altitude region of 10 km to 20 km, the upper-troposphere/lower stratosphere (UTLS) region. However, knowledge about even the present day global distribution of key constituents that are of relevance for climate in this region, such as water vapour, ozone, ice particles, and aerosols is surprisingly incomplete leading to, e.g. UTLS ozone trend estimates with partly opposite signs in observations and climate models. Gaps in the understanding of microphysical, chemical and dynamical processes and their feedbacks in the UTLS together with their insufficient implementation in climate models introduce uncertainties in radiative forcing estimates in the 0.5 W m−2 range. The complexity of this region is a result of the coupling of processes from the nano- or micrometer scale, e.g. atmospheric aerosol formation, turbulence and mixing to the regional and planetary scale. This complexity challenges the capabilities of climate models to correctly capture the impact of UTLS processes on current surface temperatures and circulation as well as for future projections. Therefore, a synergistic approach is required, which combines the expertise from different research areas to improve our understanding of this highly important region.In this CRC we will identify, disentangle, and quantify dynamical, microphysical, and aerosol-chemical 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. Based on an improved process understanding, we will develop parametrisations of relevant small-scale processes to improve state of the art climate models and to better quantify the impact of UTLS processes on composition and dynamics and on Earth‘s future climate.The scientific projects in this CRC are organised in three main Research Areas:Research Area A will focus on the role of aerosol and ice particles in the UTLS, their formation, evolution and ef-fect on the atmospheric radiation budget.Research Area B will investigate the interaction of dynamical, chemical and microphysical processes in the UTLS.Research Area C will focus on large scale processes and the impact of processes of all scales on UTLS composition and variability, their future changes and their impact on present and future climate.

• DFG Programme: CRC/Transregios

Current projects

• A01 - Aerosol-Cloud inTeractIon and water Vapour transport in high UPdraft regimes (ACTIV-UP) (Project Heads Jurkat-Witschas, Tina ;  Voigt, Christiane )
• A02 - Radiative effects of convective ice clouds in the UTLS from satellite observations (SAT-ICE) (Project Heads Bugliaro, Luca ;  Voigt, Christiane )
• A03 - Aerosol nucleation in the upper troposphere (Project Heads Curtius, Joachim ;  Tost, Holger )
• A04 - Sources and processes controlling aerosol composition in the UTLS- From tropical monsoon to extratropical regions (Project Heads Borrmann, Stephan ;  Köllner, Franziska ;  Schneider, Johannes )
• A05 - Molecular fingerprints of organic aerosol in the UTLS region (Project Heads Hoffmann, Thorsten ;  Vogel, Alexander Lucas )
• A06 - Source apportionment of UTLS refractory aerosol and ice-nucleating particles (Project Heads Curtius, Joachim ;  Ebert, Martin ;  Kandler, Konrad )
• A07 - Processing of organic compounds in ice particles during deep convective transport into the UTLS (Project Heads Szakáll, Miklós ;  Theis, Alexander )
• B01 - Fine scale composition gradients and mixing at the tropopause region (Project Heads Hoor, Peter ;  Tost, Holger )
• B02 - Transport of aerosols and precursors from the planetary boundary layer into the UTLS- BrIdging Surface emissions, Transport and UTLS Matter (BISTUM) (Project Heads Fachinger, Friederike ;  Kandler, Konrad ;  Weigel, Ralf )
• B03 - Deep exchange with the UTLS: the Tibetan pipe (Project Heads Ahrens, Bodo ;  Schmidli, Ph.D., Juerg )
• B04 - Structure formation and mixing in the extratropical tropopause region (Project Heads Kunkel, Daniel ;  Wirth, Volkmar )
• B06 - Impact of small-scale dynamics on UTLS transport and mixing (Project Heads Achatz, Ulrich ;  Kunkel, Daniel ;  Schmidli, Ph.D., Juerg )
• B07 - Impact of cirrus clouds on tropopause structure (Project Heads Achatz, Ulrich ;  Spichtinger, Peter )
• B08 - Lagrangian analysis of the role of extratropical cyclones for UTLS aerosol and humidity (Project Head Miltenberger, Annette )
• C01 - Large scale variations of water vapour and ice supersaturated regions (Project Heads Krämer, Martina ;  Reutter, Philipp ;  Rolf, Christian )
• C02 - Deriving transport timescales in the UTLS from age tracers and the propagation of the sea-sonal cycle of CO2 (Project Heads Engel, Andreas ;  Hoor, Peter )
• C03 - Variability in UTLS transport from model age of air and impacts on composition (Project Heads Hoor, Peter ;  Plöger, Felix )
• C04 - Seasonality, variability and trends of halogenated trace gases in the UTLS (Project Head Engel, Andreas )
• C05 - Transport processes regulating the lowermost stratospheric ozone reservoir (Project Heads Birner, Thomas ;  Hoor, Peter )
• C06 - The importance of upper troposphere aerosol transport and processing for low and mid troposphere aerosol concentrations (Project Heads Curtius, Joachim ;  Possner, Anna )
• C07 - The composition of the global UTLS nowadays and at the end of the 21st century (Project Heads Jöckel, Patrick ;  Tost, Holger )
• Z01 - Central coordination and observational data synthesis (Project Head Hoor, Peter )
• Z02 - Data management and computing (Project Head Kunkel, Daniel )
• Z03 - Joint model development and modelling synthesis (Project Heads Achatz, Ulrich ;  Tost, Holger )

• Applicant Institution: Johannes Gutenberg-Universität Mainz
• Co-Applicant Institution: Goethe-Universität Frankfurt am Main
• Participating University: Ludwig-Maximilians-Universität München; Technische Universität Darmstadt
• Participating Institution: Forschungszentrum Jülich; Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) ; Standort Oberpfaffenhofen ; Institut für Physik der Atmosphäre; Max-Planck-Institut für Chemie (Otto-Hahn-Institut)
• Spokesperson: Professor Dr. Peter Hoor