Principal investigators
Tina Jurkat-Witschas (DLR)
Christiane Voigt (JGU/DLR)

Brief Summary
Convective processes play a critical role in the Earth’s energy balance through the redistribution of heat, moisture and aerosols in the atmosphere. They are characterized by high updrafts with turbulent and diabatic processes where cloud formation and cloud properties differ from those formed in mid-latitude frontal systems. Particularly ice clouds evolving at the top of deep convective systems – so called anvil cirrus – exert a net heating at the top of the atmosphere. Locally, they can transport water vapor efficiently into the UTLS and the stratosphere e.g. in overshooting anvil tops. The representation of subgrid-scale convective cloud processes in models is yet a challenge and requires adequate parametrizations based on robust observations of cloud properties and water vapor transport pathways. The aerosol impact on cloud formation in convective systems has been the focus in many aerosol cloud interaction studies. However, disentangling the relative impact of the aerosol type and concentration and updraft velocities on the microphysical cloud properties over the lifetime of a convective cloud is one of the largest remaining questions in anthropogenic climate forcing and requires dedicated observations. Particularly the impact of aerosol concentration and updraft velocities as well as the impact of radiative and latent heating on ice particle number and ice mass concentrations in the anvil are important parameters to assess their climate impact.
Spaceborne observations of aerosol and cloud particle number that provide a large dataset on liquid and cirrus cloud properties have significantly advanced in the past. However observations of small scale processes that determine the life cycle of convective systems and anvil clouds need to be validated with high resolution measurements to improve retrieval methods for global observations. Here we attempt to partially fill this gap by proposing new in-situ measurements from a dedicated aircraft campaign with the DLR-Falcon 20 to detect water vapor, aerosol and cloud properties as well as updraft velocities in convective systems in the UTLS above continental Europe and the Mediterranean Sea. In-situ measurements of water vapor, the particle size distribution (PSD), as well as chemical and microphysical properties of aerosol and clouds will be performed in central and southern Europe in autumn 2021. The following research questions will be addressed: What is the aerosol concentration in the inflow region of convection above continental Europe and the Mediterranean Sea? Is there a measurable effect of pollutants on the PSD in convective systems? How do high-updraft regimes and diabatic processes change the water vapor distribution in the UT, the turbulent H 2 O flux into the LS and the radiation budget of the UTLS? Is the water vapor distribution near convection well represented in numerical weather prediction models? How do the cloud properties in convective cirrus differ from cirrus formed in other high updraft regimes such as WCBs? How do these processes affect the UTLS radiation budget and climate?

Principal investigators
Christiane Voigt (JGU/DLR)
Luca Bugliaro (DLR)

Brief Summary
Convection is an important atmospheric process since it controls the water and radiation budget in the UTLS in a decisive way through the transport of water and water vapor from the boundary layer. When the trapping of thermal radiation in ageing thinning anvil cirrus, the ice clouds originating from the convective outflow, outweighs the reflection of solar radiation, these UTLS clouds exert a warming effect at top of atmosphere. However, their net instantaneous radiative forcing strongly depends on cloud height, optical thickness and microphysical properties like ice crystal shape, size distribution and ice water content. Furthermore, ice cloud processes in the UTLS influence the water budget and the radiative properties of the UTLS. Finally, convection affects dynamics and thermodynamics and the transport of trace species from lower atmospheric levels to the upper troposphere. Despite their importance for weather and climate, convective cloud and anvil cirrus properties together with their temporal evolution from convective initiation to anvil dissipation still represent large uncertainties in climate and weather models. Especially in mid-latitudes only a few studies have tackled the temporal evolution of anvil clouds and their radiation effect. In this project we propose to use satellite observations to study the radiative effect of convective ice clouds in European mid-latitudes, in particular the interconnections between convective outflow macrophysical, microphysical and radiative properties. To this end, we plan to exploit geostationary Meteosat Second Generation (MSG) satellite observations of clouds with high temporal resolution since they allow to capture the life cycle of convection and to assess the envisaged ice cloud properties and their impact on radiation at top of atmosphere at different life stages. Airborne measurements of anvil clouds (project A01) will be used to investigate in situ anvil properties, cloud-radiation interactions and to validate MSG observations. Meteorological information will be gathered from numerical weather prediction models to interpret anvil observations. This exhaustive data set will be exploited to answer the following central research questions: How do the anvil cirrus properties – including microphysics – evolve with time throughout the life cycle? How does the radiative effect of convective clouds evolve with lifetime and what is the overall radiative effect of convective clouds over their life cycle?

Principal investigators
Joachim Curtius (GUF)
Holger Tost (JGU)

Brief Summary
We propose that aerosol nucleation involving Highly Oxidized Organic Molecules (HOMs) from monoterpenes and taking place in the outflow region of deep convective clouds above tropical forests is a major source of particles for the tropical troposphere. Identification of the nucleation mechanisms and the key nucleating species is the central goal of this project. Above rain forest regions we expect that monoterpenes as well as isoprene survive convective transport and are then oxidized to form extremely low-volatile organics that undergo strong nucleation in the UT. Over oceans, probably other substances dominate the nucleation process in the outflow of deep convection, especially sulfuric acid (SA) and methanesulfonic acid (MSA) from the oxidation of dimethyl sulfide (DMS). These particles, newly formed in the tropical UT, are likely the dominant source of CCN in the entire tropical troposphere
as well as the major source of the stratospheric background aerosol.
We plan to analyze the aircraft-based measurements of the low-volatility nucleating species measured by our CI-APi-TOF mass spectrometer during the missions CAFE-EU (2020), CAFE-BRAZIL (2021 or 2022, depending on Covid-19 situation) and CAFE-PACIFIC (2024) with the research aircraft HALO. The nucleation and early growth processes are studied at molecular level allowing the identification of the key nucleating species (role of HOMs, sulfuric acid, nitric acid, isoprene oxidation products, ammonia and their clusters for nucleation and early growth), assessment of the role of ions, low temperatures, low condensation sink, and high actinic flux as key elements for fostering the nucleation, as well as assessment of lightning-NOx for potentially reducing the formation of HOMs that are able to nucleate.
Besides the precursor concentrations, a second key variable for the UTLS nucleation measurements is the quantitative detection of nucleation mode particles at low ambient pressure. We plan to develop a dual-channel ultrafine condensation particle counter (uCPC) realizing two different cut-offs around 2.5 and 7 nm, to be operated onboard the Leajet for the planned UTLS experiment (see project B01). The instrument will be developed as a 19-inch rack component that will also be suitable for other research aircraft such as HALO.
The analysis will be complemented by model simulations for both the explanation of the observed mechanisms (via box modelling) using state-of-the-art aerosol nucleation and SOA schemes and the regional distributions of the aerosols (simulated with an identical aerosol scheme as in the box models) with the help of the regional chemistry climate modelling system MECO(n) and its nesting capabilities. This system is going to be applied in simulations for the CAFE campaigns. MECO(n) represents the convective uplifting either with the help of a convection parametrization and an associated tracer transport algorithm or by explicitly resolving the deep convection. For both variants an explicit scavenging / aqueous phase chemistry scheme is used, which is extended for the fate of dissolved species during freezing (i.e. retention). Hence, the complex chemical transformations in gas, aerosol and cloud phase are explicitly taken into account.

Principal investigators
Franziska Köllner (JGU)
Johannes Schneider (MPIC)
Stephan Borrmann (MPIC/JGU)

Brief Summary
The objective of this proposal is to study aerosol chemical composition and dynamics in the UTLS region from tropical monsoon to extratropical regions by using aircraft-based in-situ mass-spectrometric measurements. This includes conducting a detailed analysis of particle composition data from previous and upcoming tropical missions
with the research aircraft HALO, HIAPER, and Geophysica as well as studying small-scale aerosol dynamics in the extratropical UTLS. The main research topics are the role of vertical transport of both precursor gases and particles from the boundary layer into the UTLS, and the processes that lead to further transport into the stratosphere, either by large-scale upward motion in the tropics or by small-scale mixing processes at the extratropical tropopause.
The tropical datasets include data from the missions ACRIDICON-CHUVA (2014), EMeRGe (2018), CAFE-Africa (2018), StratoClim (2017), as well as from the upcoming missions ACCLIP and CAFE-Brazil, both currently scheduled for 2021. During these campaigns, we operated/will operate four different aerosol mass spectrometers, including the novel hybrid mass spectrometer ERICA, covering particles with diameters between 60 nm and roughly 3 μm. For studying extratropical small-scale aerosol gradients in the UTLS and aerosol cross-tropopause exchange,
a dedicated aircraft campaign is planned by this collaborative research center (CRC) using the German research aircraft Learjet that is equipped with a tow shuttle (AIRTOSS). We will operate two fast sizing instruments (UHSAS), one in the cabin and one in the AIRTOSS as well as the compact aerosol mass spectrometer CARIBIC-AMS in the cabin. The CARIBIC-AMS has been operated in the IAGOS-CARIBIC container between October 2018 and March 2020 and is currently scheduled to continue its regular UTLS measurements in late 2021. These data
are also available for studying the aerosol composition in the extratropical tropopause region. In the network of the CRC, the ambient chemical composition data will be complemented by laboratory studies on upper tropospheric secondary organic aerosol formation, including organic sulfates and -nitrates. Collaboration with the modelling groups of the CRC will enhance our understanding of the implications of particle transport into the UTLS, particle formation in the UTLS, the role of aged aerosol particles for cloud formation, and cross-tropopause exchange of particles for the radiative balance of the UTLS region.

Principal investigators
Alexander Vogel (GUF)
Thorsten Hoffmann (JGU)

Brief Summary
We propose a unique combination of laboratory and field experiments to identify the origin of secondary organic aerosol (SOA) in the UTLS. So far, it is unclear what are the sources and formation pathways of organic aerosols, and which volatile organic compounds (VOCs) are the precursor gases for the SOA observed in the UTLS. Since oxidation products of small VOCs, such as isoprene, have diverse functional groups including reactive carbonyl groups, these compounds may undergo condensed phase reactions in aqueous aerosol particles or liquid cloud droplets, which are likely to affect the formation of new particles in the outflow of convective systems.
A novel molecular fingerprinting approach will enable us to identify and attribute VOC-oxidation and condensed-phase-chemistry products to their parent VOC. In laboratory studies, we shall compile compound-resolved molecular fingerprints of the oxidation products of biogenic and anthropogenic VOCs. The molecular fingerprints are generated from measurements by high-performance liquid chromatography (HPLC) coupled to high-resolution mass spectrometry (HRMS), and subsequent nontarget analysis.
A novel cloud droplet unit shall be built, in which liquid droplets can be exposed to gas-phase VOC oxidation products that are formed in an oxidation flow reactor (OFR). This shall allow to simulate condensed phase reactions from the complex blend of oxidation products from VOC oxidation. Filter sampling of ambient UT organic aerosol shall be realized through the deployment of an airborne high-volume sampler. By comparing laboratory and ambient fingerprint patterns, we will be able to identify the origin and determine the contribution of individual VOCs to the total mass of SOA present in the UTLS. Comparison between aerosol particles sampled in the UT with samples from ground stations will reveal the importance of transport of boundary layer aerosol into the UT by warm conveyor belts (WCB) or convective cells.
Furthermore, we shall investigate the revolatilization of semi-volatile organic compounds (SVOCs) during atmospheric freezing processes in a set of laboratory experiments at the Mainz vertical wind tunnel laboratory. These experiments will test the hypothesis of the release of SVOCs from the condensed phase into the gas phase during freezing in the mixed phase zone of clouds. Another set of laboratory experiments intends to characterize the response of two aerosol mass spectrometers (ERICA and CARIBIC-AMS) toward organic nitrates (ON), aged organic SOA, organic sulfates (OS) and nitro-aromatic biomass burning markers. These experiments will combine a systematic evaluation of molecular-resolved fingerprint patterns with quantitative measurements by AMS.

Principal investigators
Konrad Kandler (TUDa)
Martin Ebert (TUDa)
Joachim Curtius (GUF)

Brief Summary
Aerosol in the UTLS region may originate from extraterrestrial and terrestrial sources or may be secondarily formed in the atmosphere by gas phase or heterogeneous reactions. Refractory particles act as surface for heterogeneous reactions, but in most cases originate from space or the Earth’s surface. The main goal of this project is to realize an almost artefact free sampling of UTLS aerosol particles and to characterize the received particle samples by off-line electron microscopic individual particle analysis (EMIPA). By Transmission Electron Microscopy (TEM), conventional Scanning Electron Microscopy (SEM) and Environmental Scanning Electron Microscopy (ESEM) in Darmstadt three complementary methods will be applied. By use of all these electron microscopic methods data about the elemental composition, mineralogical phase composition, mixing state (internal/external mixtures, coatings, agglomerates, heterogeneous inclusions), volatility and aging of the refractory particles and low-volatility compounds in UTLS will be received. On base of this explicit and wide data set source apportionment will be performed, which will help to understand the main pathways of particulate components towards UTLS. It will contribute to the questions on how surface emissions influence the UTLS aerosol, how significant the contribution of meteoric smoke is, to what extent the particles are modified, and what would be implications of the composition, e.g., for optical properties and in this way for the radiation budget. Beyond that we will run a second airborne sampling system, which is optimized for the off-line physicochemical characterization of the ice nucleating properties of the UTLS aerosol particles. The physicochemical characteristics and the ice nucleating capabilities will be analyzed by the new established coupled analyzing method of the Frankfurt Ice Nucleation Experiment (FRIDGE) and Environmental Scanning Electron Microscopy (ESEM). In the first step of this analyzing procedure in FRIDGE information about the ice nucleating properties of the UTLS particle samples under different temperatures and humidities are determined and will enable the assessment of potential ice-nucleating particle (INP) concentration in the UTLS. In the second step each identified potential INP can directly be analyzed in the ESEM, revealing size, chemical composition and mixing state of the INPs. These investigations will contribute to the question which potential ice nucleating particles are present in the UTLS region and if these INPs play an important role for the occurrence of clouds (cirrus formation) in the UTLS.

Principal investigators
Miklos Szakáll (JGU)
Alexander Theis (MPIC)

Open positions
A07-PHD2-JGU

Brief Summary
One of the most important and yet unresolved issues in cloud chemistry and global models is how the ice phase in tropical deep convective clouds and in extratropical warm conveyor belts (WCB) contributes to the redistribution of atmospheric trace substances from the boundary layer to the UTLS. The understanding and proper representation of the underlying microphysical and transport processes are especially important in terms of the formation and
the atmospheric life cycle of secondary organic aerosol (SOA) particles. In this CRC subproject we will conduct laboratory measurements under simulated tropospheric conditions, i.e. at temperatures spanning a range from the melting level 0 °C up to those prevailing in the upper troposphere (−60 °C). These will help to understand the processing pathway of chemical compounds and focus on scavenging mechanisms relevant in the upper troposphere involving the ice phase. The main research question we address within this subproject is: How do the formation and growth processes of atmospheric ice particles in convective clouds and WCB influence the abundance of organic compounds in the UTLS region? We aim to tackle this issue by determining the partitioning of organic trace
substances such as SOA precursors during atmospheric freezing processes by the following set of investigations:
− Determination of the retention coefficients of SOA precursor gases and their mixtures during liquid-to-ice phase changes.
− Derivation of ice partitioning coefficients during the co-condensation of SOA precursor gases and water vapor.
− Implementation of new parameterizations based on experimental findings in a drop freezing model and investigation of the effect of liquid-ice boundary partitioning during freezing on the mass transfer of SOA precursors.
To reach the goals of this subproject we will design and conduct extensive laboratory studies utilizing the full capabilities of the Mainz vertical wind tunnel laboratory. The world-wide unique vertical wind tunnel facility of the Johannes Gutenberg University in Mainz allows the free suspension of single ice particles in a vertical airstream. In the walk-in cold room (WCR) of the Mainz wind tunnel laboratory, an acoustic levitator is installed. Based on an earlier setup developed in our laboratory, we will construct a new diffusion chamber to grow ice crystals by water vapor deposition. A one-dimensional model that simulates drop freezing and solute transport during liquid-to-ice phase changes will be further developed with new parameterizations derived from our experimental results. Collaborations within the CRC are planned with subprojects A03 and A05. Retention and partitioning coefficients of SOA precursor gases determined in our experiments will be implemented in the cloud resolving model employed in A03. Results from the aircraft campaign in A03 would help us to adapt our experimental proceedings. Together with A05 the synthesis and analysis of the complex chemical compounds used in our experiments will be performed.

Principal investigators
Peter Hoor (JGU)
Holger Tost (JGU)

Brief Summary
In this project we will use a combination of in-situ measurements with modelling on different scales (employing several nested domains) to investigate the effect of small scale diabatic processes associated with cirrus occurrence and turbulence on the vertical gradients of humidity, trace gases and aerosols at the tropopause. We will combine a novel aircraft based approach using two measurement platforms with a state-of-the-art high resolution model system MECO(n), which allows convection permitting simulations from the sub-km-scale to the synoptic and global scale including comprehensive aerosol and chemical simulations.
The aircraft measurements will be partly performed with a dual platform system, measuring humidity, (potential) temperature, ozone, aerosol size distribution and backscatter simultaneously at two different altitudes separated typically less than 300 m. Therefore, we can deduce isentropic gradient changes of the UTLS composition particularly for highly transient small scale processes associated with cirrus clouds variability or turbulent mixing at the tropopause. With this setup we will identify cirrus internal convection and its potential effect on the chemical and thermodynamical structure of the tropopause region – specifically water and ozone, but also aerosols at the tropopause.
To put the local scale observations into a larger scale we will use simulations with the MECO(n) system, which includes the possibility to simulate processes utilizing nesting options with several nests for a dynamical downscaling with a grid size of a few 100 m and sample data along the flight track. Combined with its comprehensive chemistry and aerosol schemes this provides the unique possibility to study the processing of the chemical composition of air masses across scales and analyzing the impact of the composition on dynamics of the tropopause region.
This includes transport and processing of boundary layer aerosol and precursors to the extratropical tropopause by mid latitude convection and frontal uplift. We will focus on the evolution and representation of gradients of these species downwind these systems in different model resolutions. To infer information on mixing at the tropopause we will develop a novel representation of mixing particularly focusing on clear air turbulence (CAT) under different synoptic situations associated with mid-latitude cyclones especially in the ridges and above the jets of these systems. With the model the analysis will be put in a larger context, to estimate the importance of the underlying small scale processes on the regional and synoptic scale.

Principal investigators
Friederike Fachinger (MPIC)
Ralf Weigel (JGU)
Konrad Kandler (TUDa)

Brief Summary
By scattering and absorption of incoming solar and outgoing terrestrial radiation, aerosol in the Upper Troposphere/Lower Stratosphere (UTLS) has a direct effect on the Earth’s energy balance. In absence of any major explosive volcanic eruption since Pinatubo (1991), the UTLS aerosol number concentrations remained almost constant at least over the last 29 years. This suggests that UTLS aerosol, in particular the Junge layer, is maintained by mechanisms which balance an ambling but continuous sedimentation loss of particulate material, most likely due to entry of aerosol and precursors. However, the processing of aerosol and precursor material (formation, loss and cloud interaction) during transport, e.g. from the boundary layer into the UTLS, is not yet conclusively understood. It is also unknown whether and how the emission intensity and/or composition of different aerosol and precursor substances can affect this trace matter processing. The extent to which ground-level aerosol and precursor emissions at different emission strengths and compositions influence the properties of UTLS aerosols is also yet to be clarified.
The main goal of this project is to investigate the coupling between surface emissions of atmospheric trace matter (aerosols and aerosol precursors) and the trace matter in the UTLS. This implies that surface emissions reach UTLS altitudes, which requires an effective vertical transport mechanism. In order to investigate this, detailed ground-based trace matter measurements are combined with drone and balloon-borne measurements of aerosols in close proximity to locations where vertical uplift occurs. During field experiments, the coupling will be completed by detailed airborne measurements in the UTLS as well as modelling studies performed within other subprojects of this CRC. The following questions are in focus: Which processes dominate the coupling of surface emissions and UTLS trace matter composition? How effective are these processes and associated particle formation, transformation and loss mechanisms for different aerosol and precursor components? How do surface emissions influence the UTLS aerosol?

Principal investigators
Bodo Ahrens (GUF)
Juerg Schmidli (GUF)

Brief Summary
This project aims to improve the understanding of and quantify the role of the highest mountain ranges and plateaus in the transport of water vapor, other trace gases, and aerosols between the atmospheric boundary layer (ABL) and the UTLS. Reaching this goal will improve the understanding of the climate system and enhance the ICON-based climate modeling system that will be used and adapted in this project. Within the first phase of the CRC we will focus on ABL to UTLS exchange processes over the geographical area of the Tibetan plateau (TiP) and the Himalayas with its foothills. We plan to investigate two transport mechanisms: (a) dry deep mixing with tropopause folds and very deep ABLs (up to 5 km above the plateau level) in boreal winter and spring, and (b) deep convection over the TiP, the Himalayas, and Himalayan foothills in the monsoon season.
In winter and spring, deep convective ABLs (CBLs) frequently occur over the TiP. These deep CBLs lead to a strong coupling of near-surface air with the upper troposphere (UT) and enable the rapid transport of near-surface tracers into the UT (and vice versa). The UT is then coupled on longer time scales via quasi-horizontal transport with the lower stratosphere (LS), making the TiP, not only in the monsoon season, a global hotspot of troposphere-stratosphere exchange.
The Asian Mainland, including the TiP, is one of the primary source regions of deep convective transport into the UTLS, in particular in boreal summer. The project plans to investigate the unique deep convective and turbulent mixing processes over the TiP and beneath the Asian summer monsoon upper level anticyclone, which are not well represented in present day reanalyses and climate model simulations.
The project studies both transport mechanisms using a multi-scale modeling approach, including tracer and trajectory methods. Realistic and idealized modeling experiments using ICON in global parameterized convection (zoomed over the Asian monsoon region to D∼13 km), in limited-area convection-permitting (Dx∼3 km), and large-eddy simulation (Dx∼200 m) setups. This multi-scale approach will improve the understanding of the lifting processes in this active transport region and will deliver transport benchmarks for coarser-grid chemistry-transport and climate models.
The following CRC phases will extend the modeling-based process studies to other high mountain ranges and high plateau regions. These studies will test and extend the generated understanding and shall include explicit trace gases and aerosol in the transport modeling. Finally, we plan a climatic quantification of deep exchange in the different high and complex orography geographic regions compared to the deep exchange in other transport regions (like the storm track regions over the North Atlantic and North Pacific).

Principal investigators
Volkmar Wirth (JGU)
Daniel Kunkel (JGU)

Brief Summary
The occurrence of meso- and smaller-scale structures in the midlatitude tropopause region is likely to play an important role for mixing across the tropopause and, thus, for the composition of the lowermost stratosphere. Yet, these structures and processes are not well represented in current weather forecast and climate models. This project focuses on the advective formation of meso- and smaller-scale structures as well as on physical processes that operate on these scales. The key questions to be addressed are: (i) how do the structures form through conservative advection, in particular depending on the resolution of the underlying data as well as on the distance from the tropopause, (ii) how do the physical processes such as cloud physics, radiation, and turbulence affect the structure formation and stratosphere-troposphere exchange, and (iii) how well can coarse-gridded data reproduce tracer structures from high resolution measurements. The project focuses on quasi-horizontal dynamics in the framework of baroclinic life cycles both from idealized simulations with the ICON model and from ERA5 reanalysis data. Lagrangian methods will be applied to study the formation of structures in the advected tracers as well as in potential vorticity. The exchange of mass across the tropopause as well as the formation of the mixing layer in the lowermost stratosphere are investigated using trajectories in combination with a coarse-graining technique as well as with mixing diagnostics based on tracer-tracer correlations. The work will shed new light on the role of small-scale structures for stratosphere-troposphere exchange and for the composition of the lower stratosphere. It will bridge the gap between highly resolved airborne measurements and much coarser resolution numerical models. The results are also expected to provide guidance for future airborne measurements that focus on the extratropical tropopause region.

Principal investigators
Ulrich Achatz (GUF)
Juerg Schmidli (GUF)
Daniel Kunkel (JGU)

Open positions
B06-PHD1-GUF
B06-PHD2-GUF

Brief Summary
Zonal-mean tracer transport through the UTLS is characterized by the mean residual Brewer-Dobson circulation (BDC) and it is modified by mixing due to turbulence and partly gravity waves (GWs). Both GWs and turbulence occur on scales which require to be parameterized in weather and climate models. However, available parameterizations fail to reliably describe the effects on tracers. With the overall goal of mending this situation we want to pursue the following core objectives:
(1) We will further improve the newly developed GW model MS-GWaM in ICON to address the effects on tracers of the BDC, via corresponding diagnostics, and mixing, through passive-tracer simulations. In particular, we will focus on the description of the spontaneous-imbalance source, which is of major importance in the extratropical UTLS.
(2) The direct coupling of MS-GWaM to tracers will be addressed systematically through idealized investigations. This will allow us to further improve the description of this coupling in ICON/MS-GWaM and to study the consequences with regard to UTLS tracer transport.
(3) Current turbulence parameterizations do not take into account the complex nature of turbulence (non-homogeneous, anisotropic, non-Kolmogorov, patchy, and three-dimensional) in the strongly stratified UTLS. We therefore improve the corresponding approach in ICON using large-eddy simulations (LES) to quantify the transport and mixing in the UTLS and investigate the contribution of turbulent mixing in the UTLS.
(4) We will validate Objectives (1) – (3) by using suitable observations and wave-resolving simulations. For this purpose we will analyze high-resolution airborne measurements for GW properties and GW occurrence frequency. This will be supplemented by GW resolving ICON simulations of baroclinic life cycles, the ensuing spontaneous GW emission and related tracer effects.

Principal investigators
Peter Spichtinger (JGU)
Ulrich Achatz (GUF)

Brief Summary
Cirrus clouds, i.e. clouds containing exclusively of ice particles, occur quite frequently in the tropopause region. They have a crucial impact on the thermodynamic structure of the UTLS region by diabatic processes, i.e. latent heating due to phase transitions and radiative effects due to absorption and emission of radiation; actually, temperature gradients and water vapor distributions are actively changed by the formation and evolution of these
clouds. On the other hand, ice clouds in the cold temperature regime in the tropopause region are crucially affected by local dynamics. Gravity waves as well as dynamic and convective instabilities may have a strong impact on the life cycle of cirrus clouds, thus affecting also indirectly the tropopause region. The main goal of this project is the investigation of the interaction of dynamical processes and ice clouds in the tropopause region and their impact on the thermodynamic structure and composition of the tropopause region. Using theoretical investigations as well as numerical modeling, we will be able to develop a consistent parameterisation of these interactions and their impacts on the tropopause region for the use in coarse grid models.
The following central questions are addressed in this project:
− What are the dominant processes of interaction between cirrus clouds and dynamics for changing tropopause properties?
− How can theory and model approaches be used for developing state-of-the-art parameterisations of tropopause ice-cloud processes in coarse resolution models?
For addressing these questions we propose a two-fold approach combining theoretical investigations and numerical model simulations. We will use sophisticated mathematical methods in order to determine dominant processes and interactions between ice clouds and dynamical processes. These methods will also be used for deriving reduced order models. Complementary, we will use numerical simulations of relevant ice cloud scenarios in the tropopause region, using a hierarchy of models. Combining these two approaches we will develop prototype parameterisations, which will be implemented into the ICON model on the basis of an existing framework, developed for gravity wave parameterisations.

Principal investigator
Annette Miltenberger (JGU)

Brief Summary
Extratropical cyclones are linked with organised, large-scale ascent that transport water vapour, trace gases, and aerosol particles to the UTLS. While the role of warm-conveyor belts (WCBs) is undebated, a quantification of their contribution to the extratropical UTLS composition is not available. Cloud and precipitation formation strongly modify transported water vapour and aerosol content during the ascent. The importance of different processes, the impact of the uncertainties associated with their representation in numerical models are not well understood, but are likely import for investigating the impact of WCBs on future UTLS composition.
The objective of this project is to develop a comprehensive understanding of the impact of WCBs on the composition of the extratropical UTLS. We will utilise high-resolution simulations and Lagrangian analysis methods to investigate the detailed moisture and aerosol budget along the ascent and to separate slantwise and embedded convective ascent. Perturbed parameter ensembles of two case studies are used to characterise the uncertainty of outflow moisture content and structure to parameter choices in the cloud microphysics. Combining these ensemble simulations with observational data from the DLR Falcon and enviscope Learjet campaigns conducted within this CRC will provide insight into the key processes controlling the transport and allow us to explore constraints on the model representations. The process-oriented, case-study based analysis will be complemented by novel high-resolution ensemble simulations, that explicitly link the individual ensemble members to their climatological significance. With this approach a climatology of WCB outflow properties and the role of convective and slantwise ascent is established from high-resolution simulations. The model climatology will be evaluated with long-term observational data from IAGOS and satellite observations. Finally, the impact of climate change on WCB moisture transport will be explored with the same approach and the results will be compared to global climate model simulations.

Principal investigators
Philipp Reutter (JGU)
Martina Krämer (FZJ)
Christian Rolf (FZJ)

Brief Summary
Water vapor (H₂O) in the upper troposphere and lower stratosphere (UTLS) is a key player for global radiation and surface climate (Riese et al., 2012). The processes which determine the H₂O concentration in the UTLS region are manifold and encompass large scale transport through the tropopause region as well as small scale processes like convection. Furthermore, its concentration is directly linked to the so-called ice-supersaturated regions (ISSRs, e.g. Gierens et al., 1999) that occur frequently in the mid-latitudes as well as the tropical tropopause regions (Krämer et al., 2020; Petzold et al., 2019). ISSRs are potential formation regions of cirrus clouds, which regulate the exchange of H₂O between the UT and the LS and, in addition, also have an impact on the Earth’s radiation balance (Boucher et al., 2013). Many measurements indicate that ISSRs with embedded cirrus clouds and the tropopause are closely related (Gettelman et al., 2011; Spichtinger et al., 2003). The main goal of this project is to investigate the large scale three-dimensional structure of ISSRs and cirrus clouds from the tropical to the boreal and austral mid and high latitude tropopause regions as well as the related transport pathways of water vapor.
The following central questions will be addressed in this project:
− What is the global temporal and spatial distribution of ISSRs?
− What is the common lifecycle of ISSRs and cirrus clouds, and how do they interact?
− What is the strength of the inter annual variability and the trend of the UTLS H 2 O distribution caused by ISSR properties ?
− What are the large scale transport pathways from the tropical (e.g. Asian monsoon) into the extratropical lower stratosphere (exLS)
− How is the amount of transported H₂O influenced by cirrus clouds and the ice saturation ratio?

Petzold, A., P. Neis, M. Rütimann, S. Rohs, F. Berkes, H. G. J. Smit, M. Krämer, N. Spelten, P. Spichtinger, P. Nedelec, and A. Wahner (2019): Ice-supersaturated air masses in the northern mid-latitudes from regular in-situ observations by passenger aircraft: vertical distribution, seasonality and tropospheric fingerprint. Atmos. Chem. Phys. Discuss. 2019, 1–29. doi: 10.5194/acp-2019-735.
Boucher, O., D. Randall, P. Artaxo, C. Bretherton, G. Feingold, P. Forster, V.-M.-. Kerminen, Y. Kondo, H. Liao, U. Lohmann, P. Rasch, S. Satheesh, et al. (2013): Clouds and aerosols. Climate Change 2013 the Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change 9781107057, 571–658. doi: 10.1017/CBO9781107415324.016.
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. Journal of Geophysical Research Atmospheres 117 (16), 1–10. doi: 10.1029/2012JD017751.
Gettelman, A., P. Hoor, L. L. Pan, W. J. Randel, M. I. Hegglin, and T. Birner (2011): The extratropical upper troposphere and lower stratosphere. Reviews of Geophysics 49 (3), RG3003. doi: 10.1029/2011RG000355.
Spichtinger, P., K. Gierens, and W. Read (2003): The global distribution of ice-supersaturated regions as seen by the Microwave Limb Sounder. Quarterly Journal of the Royal Meteorological Society 129 (595), 3391–3410. doi: 10.1256/qj.02.141.

Principal investigators
Andreas Engel (GUF)
Peter Hoor (JGU)

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.

Principal investigators
Felix Plöger (FZJ)
Peter Hoor (JGU)

Brief Summary
Long-term trends in the composition of the UTLS with radiatively active trace gas species like water vapour and ozone may cause substantial effects on the Earth’s radiation budget and on surface climate and need to be correctly represented in models for reliable predictions. A robust knowledge of the variability of UTLS transport on inter-annual to decadal time scales is a prerequisite for a reliable estimation and attribution of long-term anthropogenically forced trends. However, the representation of such variability, as related to the QBO, ENSO, volcanic aerosol, SSWs, solar cycle, and ODS is often incomplete in current climate model simulations, casting comparisons with measurements into doubt. The proposed project aims at investigating variability and long-term changes of transport pathways and time scales in the UTLS from a Lagrangian model perspective. The comprehensive research strategy combines reanalysis-driven simulations with the Lagrangian CLaMS model and free-running simulations with CLaMS coupled to the climate model EMAC, together with satellite and in-situ observations. Different powerful diagnostics will be used to evaluate transport pathways and time scales in the UTLS. In addition to simulating chemical species we will use a novel age spectrum analysis method, with the age of air spectrum being the distribution of transit times through the stratosphere. The model simulations will be compared to trace gas measurements from satellite instruments (e.g., MLS, ACE-FTS, MIPAS), and to airborne in-situ tracer measurements (e.g., from recent HALO- and G5-missions) provided by the other project partners. Combination of the tracer measurement data with the full model age spectrum, and related mass fractions of young and old air masses, will allow quantifying the effect of changing transport pathways and mixing time scales on the UTLS composition. Furthermore, analysis of the tracer and mean age budgets based on the tracer continuity equation will allow further insights into the roles of different processes (e.g., residual circulation and eddy mixing) in driving transport in the UTLS. Finally, consistent EMAC climate model simulations with both Eulerian and Lagrangian CLaMS tracer transport included will be investigated for effects of Lagrangian transport with reduced numerical diffusion on the model representation of the UTLS. The research questions focus on: (i) Variability and trends in UTLS transport time scales, (ii) the related impacts on trace gas composition, and (ii) the representation of UTLS pathways and time scales in different reanalysis and models.

Principal investigator
Andreas Engel (GUF)

Brief Summary
The project aims to investigate the seasonality of halogenated trace gases in the UTLS and to improve the understanding of the importance of different transport pathways. We suggest to use existing data from HALO missions and new observations from onboard the observation platform IAGOS-CARIBIC to investigate seasonality, variability, and long-term changes of halogenated gases with a focus on short-lived compounds (VSLS). These are expected to play a more important role in the halogen budget of the stratosphere as emissions of long-lived compounds decrease. Short-lived compounds impact mostly the lowermost stratosphere, depending on their local lifetime which varies with seasonal changes of temperature and solar radiation. IAGOS-CARIBIC is a scientific project for measurements of atmospheric composition in the UTLS from onboard a regular passenger aircraft, operated by the German airline Lufthansa. The project was paused in 2020 and will after a major refitting of the instrument package be resumed in 2022. We propose to perform regular collection of air samples followed by post-flight laboratory analysis for halogenated compounds. To do this, an existing air sampling unit needs to be modified during the first year of the CRC. Once the new CARIBIC instrumentation becomes operational, flights are expected to be performed regularly every 1–2 months. Laboratory analysis will be performed using an existing gas chromatograph/mass spectrometry set-up. As first observational data from CARIBIC flights become available, the project will focus on merging the new data-set with existing data from HALO missions. Past HALO projects from which halocarbon data are available had a strong focus on the Northern Atlantic, except for the SOUTHTRAC mission which was based in South America. CARIBIC data will add a wider longitudinal coverage with flights between Germany and the Americas or Asia and will extend seasonal coverage. To derive distributions of halogen VSLS and long-lived compounds, we propose to investigate different coordinate systems. All analyses will be performed using tropopause-centred vertical coordinates. One part of the project will investigate how the choice of the coordinates influences observed variabilities of trace gas mixing ratios. Based on the extended data base, we want to systematically compare the observed distributions with model fields and investigate the representation of the chemical and transport processes in the model.

Principal investigators
Thomas Birner (LMU)
Peter Hoor (JGU)

Brief Summary
The ozone reservoir in the lowermost stratosphere (LMS) greatly affects the potential for ozone to be transported downward into the troposphere and eventually to the surface where it has detrimental effects on human health. This project seeks to quantify transport of ozone into the LMS and thereby improve our understanding of the ozone budget of the LMS. Our central questions are: which transport processes regulate the ozone reservoir in the LMS, what is their relative strength, and how do they vary on seasonal and interannual time scales? For this purpose we will carry out a budget analysis of LMS ozone based on modern reanalyses, study the variability of individual budget terms and evaluate their contributions to events of reduced versus enhanced LMS ozone.
These budget analyses will be combined with observational analyses of ozone based on data sets from different observational platforms (particularly IAGOS-CARIBIC, HALO missions, satellites) as well as transport analyses and trajectories from the ClaMS model. The observational analyses will be carried out using a coordinate framework that takes into account major transport barriers (tropopause-relative, jet core-relative) to reduce the variability induced by quasi-reversible dynamical processes. Based on the observational tracer data and interpolated reanalysis data along the flighttrack an observational based air mass budget for the LMS will be determined and appllied to observed and reanalysis ozone data. Using the combined observational and renalysis data we will further address the question of reversible versus irreversible ozone transport by intrusions into the troposphere.

Principal investigators
Anna Possner (GUF)
Joachim Curtius (GUF)

Brief Summary
Several field campaigns within the tropics (Andreae et al., 2018 and references within Williamson et al., 2019) have demonstrated on a regional scale that UT NPF may contribute, or even dominate, LT CCN concentrations. Williamson et al. (2019) showed using staircase flight observations obtained during ATOM 1 and 2 that this could be the case generally throughout the tropics and sub-tropics. However a clear source-apportionment and in-depth analysis of the relevant transport time-scales and mechanisms could not be obtained in the observations or the associated numerical model experiments utilizing coupled aerosol-chemistry models of full complexity. Using the atmosphere-only version of ICON we will assess the horizontal and vertical transport of newly-formed UT particles using idealized tracer experiments. This will allow us to clearly identify regions of increased exposure to secondary UT particles.
Williamson, C. J., A. Kupc, D. Axisa, K. R. Bilsback, T. Bui, P. Campuzano-Jost, M. Dollner, K. D. Froyd, A. L. Hodshire, J. L. Jimenez, J. K. Kodros, G. Luo, et al. (2019): A large source of cloud condensation nuclei from new particle formation in the tropics. Nature 574 (7778), 399–403. doi: 10.1038/s41586-019-1638-9.
Andreae, M. O., A. Afchine, R. Albrecht, B. Amorim Holanda, P. Artaxo, H. M. J. Barbosa, S. Borrmann, M. A. Cecchini, A. Costa, M. Dollner, D. Fütterer, E. Järvinen, et al. (2018): Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin. Atmospheric Chemistry and Physics 18 (2), 921– doi: 10.5194/acp-18-921-2018.

Principal investigators
Patrick Jöckel (DLR)
Holger Tost (JGU)

Brief Summary
In this project we will conduct and analyze computer simulations with the chemistry climate model EMAC, which participates in the AerChemMIP multi-model intercomparison project (as part of CMIP6) to investigate the evolution of the chemical composition of the UTLS on the global scale. The analysis will focus on the one hand side on the inter-hemispheric differences of the chemical composition of the UTLS and the temporal behaviour of both trace gas and aerosol concentrations as deduced from hindcast experiments in comparison with observations, and also an analysis for up to future chemistry-climate projections (following scenarios developed within the framework of CMIP6). The radiatively active compounds also play a substantial role for the climate sensitivity of chemistry climate models, which is mainly driven by the radiative forcing of the individual radiative active compounds, but also the inherent feedback processes.
In this project phase we will focus on the sensitivity of the radiative forcing by process parameterizations, from which in a later stage a climate sensitivity of the model can be deduced. The current project plan will also focus on a quantification of the chemistry-climate interactions of ozone, water vapour and aerosol particles (both direct aerosol-radiation interactions and aerosol-cloud-radiation interactions) and associated feedback processes in the UTLS with implications for the whole atmosphere from the surface to the stratopause. In addition to the analysis of existing model simulations, we will conduct specific sensitivity simulations to estimate the effect of parameterized processes (in this project convection) on the UTLS chemical composition with the help of sensitivity simulations to quantify 1) the impact of the respective processes on the composition and 2) a sensitivity of the climate response via its associated radiative forcings to the representation of these processes.
Therefore, it is the goal of the project to also analyse the impact of chemistry-aerosol-radiation interactions on the circulation patterns within the UTLS and resulting exchange fluxes between the troposphere and the stratosphere. A detailed analysis of the chemical composition of the UTLS, especially including aerosol particles and their chemical composition in the UTLS has hardly been undertaken so far; we also plan to include tagging to determine the origin of aerosol particles or the location of new particle formation events to estimate the role of transported versus in-situ formed aerosol particles for the aerosol budget of the UTLS and the role of chemistry-climate interactions. To evaluate the model simulations and the respective process representations we will make use of comprehensive observation data sets, e.g. from the HALO database from recent campaigns, in which substantial data in the UTLS haves been acquired, and also the (e.g. the HALO database, IAGOS/CARIBIC/ and MOZAIC and additional campaign data. This will be conducted for both, the “specified dynamics” simulation, for which a point-to-point comparison can be made, as well as repeated for the other anticipated simulations in this project, for which a more statistically based analysis will be performed. Furthermore, this project provides opportunities for several other projects within the CRC to put individual and local results into the context of global chemistry-climate simulation data.

Principal investigator
Peter Hoor (JGU)

Brief Summary
In this proposal we request the funds for the central coordination of CCR 301. The project serves most of all the promotion of cooperation and communication among the individual scientific projects and clusters of the CRC 301. The funds for measures to promote gender equality are managed and the training of young researchers is coordinated, in collaboration with the local graduate schools. The international visibility of CCR 301 will be fostered, e.g., via special sessions at international conferences or publication of special issues. A web page will be set up and maintained.
The logistic organization and scientific planning of the extensive observational campaigns within CRC 301 will be supported by project Z01. Public outreach activities will be organized and coordinated between the different partners. To support the speaker and the deputy speaker of CRC 301 in conducting these tasks, staff for one and a half position of a scientific administrator and a secretary in Mainz and Frankfurt are applied for.

Principal investigator
Daniel Kunkel (JGU)

Brief Summary
This project will be responsible for implementing the data management plan for TPChange. In this context data management includes three essential parts. First, a software code repository will allow for managing code by project members and exchanging code between projects as well as publishing code. For this a git-based application hosted at the JGU will be used. Second, a data exchange server will allow for fast exchange of various data types. For this the high performance computing facility MOGONII will provide access to server capabilities which will host model and experimental data as well as data jointly used and analyzed by several sub-projects. Third, a data archive using iRODS allows for long term storage of data. In particular, this is essential for data which is used in publications and for data which is necessary to repeat experiments and data analyses. Along with technical support of the outlined infrastructure, this project will also provide continuous user support including user training throughout the first phase of the CRC.

Principal investigators
Holger Tost (JGU)
Ulrich Achatz (GUF)

Brief Summary
In this project we aim at joining and synthesizing the modelling efforts within the CRC to develop a consistent modelling system for the UTLS region based on the ICON model with the prognostic gravity-wave module MS-GWaM, utilising the MESSy interface structure. The project will involve the collaboration from all modelling projects within the CRC and is coordinated with the core development team of the MESSy system (which consists partly of PIs of the CRC). At the end of the current phase of the CRC, we will provide a chemistry-climate modelling system including aerosols with ICON as the dynamical core and with the novel parameterisations developed in the CRC, e.g. expansions of MS-GWaM to include subgrid-scale effects on tracer transport and mixing and also a flow-dependent gravity-wave source due to jets and fronts. All code will be implemented in ONE combined, comprehensive model distribution, such that for the upcoming phases of the CRC a unified modelling system can be utilised (with the option of a choice of relevant processes for the respective studies).