This year, field campaigns of special focus include recent projects that explore atmospheric transport, composition, and chemical processes in the spring Arctic UTLS, like ASCCI 2025 and COLD SABRE 2023.
The stratosphere is often considered to be dynamically stable with limited vertical exchange; however, episodic deep convection can even transport tropospheric air masses into the upper troposphere (UT) and even across the tropopause into lower stratosphere (LS). We deployed a newly developed airborne single particle mass spectrometer, Particle Analysis by Laser Mass Spectrometry – Next Generation (PALMS-NG), aboard a NASA ER-2 stratospheric aircraft to characterize aerosol particles in the UTLS during the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission. Here, we present observations revealing substantial perturbations of the stratospheric aerosol layer during an active convection and wildfire season in 2022.
We show that carbonaceous–sulfate particles of tropospheric origin account for up to 90% of stratospheric particles with physical diameters between 0.1 and 1.5 µm within an approximately 4 km layer above the tropopause. Approximately 43% of these stratospheric carbonaceous–sulfate particles are directly attributed to biomass burning. The injected particles are chemically complex and organic-rich, and some exhibit internally mixed signatures containing both tropospheric and stratospheric components.
Our observations further demonstrate that biomass-burning-related aerosols do not remain chemically unchanged following injections into the stratosphere. Instead, they undergo chemical mixing with stratospheric components, indicating a pronounced perturbation of the stratospheric aerosol layer driven by convective transport.
These results highlight the coupling between dynamics and chemistry in modulating UTLS aerosol populations. As wildfire frequency and intensity increase alongside enhanced deep convection in a warming climate, convective delivery of biomass-burning products to the stratosphere may become increasingly important, with implications for ozone chemistry and radiative forcing.
How to cite: Shen, X., Jacquot, J., Li, Y., Sharpe, S., Dykema, J., Schill, G., Bowman, K., Homeyer, C., Fraund, M., Moffet, R., Olayemi, T., Pittman, J., Rivera-Adorno, F., Murphy, D., Smith, J., Laskin, A., Keutsch, F., and Cziczo, D.: Stratospheric aerosol perturbation by tropospheric biomass burning and deep convection, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3004, https://doi.org/10.5194/egusphere-egu26-3004, 2026.
State-of-the-art Chemistry Climate Models (CCMs) exhibit a large model spread in their simulated chemical composition of the Upper Troposphere / Lower Stratosphere (UTLS). As the surface climate is highly sensitive to differences in greenhouse gas composition in the UTLS region, understanding and reducing this model spread is required for more confidence in climate projections. One large source of uncertainty in atmospheric simulations is the representation of convection. While heavily parameterised, convection is crucial for the water distribution in the air, the formation of clouds, and their radiative effect, as well as for the fast vertical transport in the troposphere. In addition to its direct effect on the UTLS composition, it may also have an indirect impact on transport into the stratosphere. By affecting the wind and temperature fields, convection influences the creation, propagation, and dissipation of Rossby waves that drive the Brewer-Dobson circulation in the stratosphere.
To investigate the effect of the convection parameterisation on the simulated UTLS composition, we performed sensitivity simulations with the CCM ECHAM/MESSy Atmospheric Chemistry (EMAC). Two simulations were performed under present climate conditions. The simulations are identical except for the applied convection parameterisation. The simulations were repeated, but with projected future climate boundary conditions, to investigate the effect of different convection parameterisations on the simulated UTLS composition under climate change.
Our results show that the simulated UTLS composition is highly sensitive to the applied convection parameterisation. The convective transport strength and outflow altitude vary strongly between different parameterisations, affecting the distribution of short-lived tracers in the upper troposphere as well as their transport into the tropical lower stratosphere. Significant differences in cloud and water distribution lead to changes in chemical reaction rates, particularly in the polar lower stratospheric ozone chemistry. Despite these differences, the effects of climate change on convective transport are in close agreement between the sensitivity simulations. Nevertheless, the strong coupling between temperature, water, and ozone creates large differences in the projected changes of the UTLS composition.
We found that the choice of the convection parameterisation influences the composition and the transport in the entire atmosphere, far beyond its direct effect in the troposphere.
How to cite: Menken, J. M., Jöckel, P., Tost, H., Garny, H., Jeske, A., and Schmidt, A.: The influence of the convection parameterisation on simulated present and future UTLS greenhouse gas distributions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6815, https://doi.org/10.5194/egusphere-egu26-6815, 2026.
The atmospheric distribution and variability of CO2 result from the interplay of different processes and mechanisms. Although these trace gas patterns contain valuable information on mixing and transport at different timescales, the information is difficult to extract from observed or simulated mole fractions, particularly in the upper troposphere and lower stratosphere (UTLS), due to the combination of long-term increase and the seasonal cycle of CO2.
Using a compilation of vertical trace gas profiles derived from measurements with the balloon-based AirCore technique together with ECHAM/MESSy Atmospheric Chemistry (EMAC) model data, we investigate how the seasonality of CO2 in the troposphere propagates into the lowermost stratosphere. Simulating an artificial, deseasonalised CO2 tracer enables us to separate and study the seasonal cycle in a unique way in remote areas and on a global scale. Our results show that the tropospheric CO2 seasonal cycle is strongly modulated in the extratropical UTLS region, characterised by a substantial change in amplitude, a phase shift of several months and a tilt in the shape of the seasonal cycle, which can be associated with the transport barrier related to the strength of the subtropical jet. In the stratosphere, we identified both a vertical and a horizontal “tape recorder” of the CO2 seasonal cycle. Originating in the tropical tropopause region this imprint is linked to the upwelling and the shallow branch of the Brewer-Dobson circulation.
To validate these model-based findings we developed a strategy to isolate the seasonal signal in observational data as well. This requires CO2-independent Age of Air (AoA) information to disentangle seasonality from the combined effect of transport and long-term trend. To achieve this, we choose an approach using a normalised methane vs. mean age correlation based on independent observational data. We present average vertical profiles of the isolated CO2 seasonal signal for latitude bands with sufficient AirCore measurement coverage. Statistical analyses are then used to assess the robustness and representativeness of these results and to determine whether AirCore observations can be used to constrain the CO2 seasonality in the UTLS.
How to cite: Degen, J., Baier, B. C., Jöckel, P., Lachnitt, H.-C., Menken, J. M., Schuck, T. J., Sweeney, C., and Engel, A.: The CO2 seasonal signal as a transport diagnostic in the UTLS , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11979, https://doi.org/10.5194/egusphere-egu26-11979, 2026.
Vertical transport processes, such as for example associated with Warm Conveyor Belt airstreams (WCBs) which is defined as a coherent strongly ascending airstream associated with extratropical cyclones, play a critical role in determining the distribution of greenhouse gases within the Upper Troposphere and Lower Stratosphere (UTLS). This study evaluates the performance of two global numerical weather prediction models, ICON-ART (ICOsahedral Nonhydrostatic model with Aerosol and Reactive Trace gases) and IFS (Integrated Forecasting System), in simulating CO₂ mixing ratios during the winter of 2022. Model outputs with different resolutions are compared against in situ measurements from the IAGOS (The In-service Aircraft for a Global Observing System, https://iagos.aeris-data.fr/) infrastructure during transatlantic flights during a period characterised by strong latitudinal CO₂ gradients and vigorous synoptic activity.
The analysis focuses on specific flight campaigns where measured CO₂ mixing ratios exhibited distinct enhancements of 4–6 ppm above background levels in the mid-Atlantic UTLS region. To attribute these anomalies to specific meteorological features, a multi-diagnostic approach is employed. A machine learning algorithm to detect footprints of WCB inflow, ascent and outflow regions (ELIAS 2.0; Quinting et al., 2022) is utilised alongside HYSPLIT Lagrangian backward trajectories initialised from flight coordinates to characterise air mass origin relative to cyclone evolution.
Results reveal persistent model–data discrepancies during January–February 2022, with both ICON-ART and IFS underestimating observed CO₂ spikes by 1–5 ppm. Our analyses show a spatial proximity between WCB activity and elevated CO2 anomalies suggesting vertical transport of air with distinct chemical signatures from the boundary layer into the upper troposphere through the WCB air stream. Specifically, we find co-located high WCB ascent probabilities (0.4 – 0.8). Moreover, trajectory origins over eastern North America confirm that surface-influenced air masses are lifted via the WCB airstream. We hypothesise that systematic biases in simulated CO₂ distributions stem from model misrepresentation of vertical transport processes and/or uncertainties in emission inventories and natural fluxes, as well as missing chemical production of CO2 in both modelling frameworks.
These findings highlight the value of combining machine learning-based flow identification with in situ observations to diagnose transport errors in atmospheric models. As WCB activity is projected to intensify under climate change scenarios, improved representation of both synoptic-scale ascent and parametrised turbulent mixing is critical for reducing uncertainties in modelled CO₂ distributions and constraining the global carbon budget.
How to cite: Qor-el-aine, A., Versick, S., Oertel, A., and Agusti-Panareda, A.: Diagnosing CO2 Transport in the North Atlantic Upper Troposphere: Evaluation of ICON-ART and IFS using IAGOS Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2278, https://doi.org/10.5194/egusphere-egu26-2278, 2026.
Halogens deplete tropospheric and stratospheric ozone, but the role of iodine remains elusive. Nevertheless, recent research has demonstrated iodine’s wide-ranging impact on tropospheric photochemistry. We report airborne measurements of atmospheric iodine oxide (IO) concentrations up to 15 km altitude from two flights of the WISE (Wave-driven ISentropic Exchange) campaign over the mid-Atlantic in September and October 2017. IO was retrieved from limb-scattered skylight in the upper troposphere (UT) using the airborne mini-DOAS instrument onboard the German High Altitude and Long Range research aircraft (HALO). Up to sixfold elevated IO mixing ratios (up to 0.6 ± 0.1 ppt) above background levels were observed in the UT in air masses transported by the category 5 hurricanes Irma and Maria, as indicated by CLaMS back-trajectory analyses. Atmospheric iodine predominantly originates from marine inorganic (I₂, HOI) and organic (CH₃I, CH₂I₂, CH₂IBr, and CH₂ICl) emissions. Our findings suggest that enhanced IO mixing ratios are likely driven by enhanced marine iodine emissions associated with high surface wind speeds in the vicinity of hurricanes, photochemical conversion of source gases into reactive iodine and efficient vertical transport of these iodine-rich air masses by tropical cyclones. Furthermore, our observations imply a potentially significant role of iodine-driven chemistry in air masses affected by tropical storms.
How to cite: Voss, K., Vogel, B., Diederich, T., Engel, A., Grooß, J.-U., Keber, T., Kluge, F., Rotermund, M. K., Schuck, T., Weyland, B., Butz, A., and Pfeilsticker, K.: Tropical cyclones drive enhanced inorganic iodine in the mid-latitude upper troposphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7037, https://doi.org/10.5194/egusphere-egu26-7037, 2026.
The upper troposphere and lower stratosphere (UTLS) serves as the transition region between the two atmospheric layers. Chemical constituents, aerosols, and water are transported in coherent airstreams or mixed from their tropospheric source regions into the UTLS. Therefore, the vertical and geographical distribution of all these constituents in the UTLS strongly depends on the transport or mixing pathways and on their (tropospheric) sources. Furthermore, during the transport constituent concentrations can be modified due to many microphysical and chemical processes. A detailed understanding about the constituent concentrations in the UTLS is needed because of their dynamic-radiative-chemical coupling, which affects atmospheric tracer distributions, the radiative budget and the dynamics of the tropopause.
We present a 10-year climatology of selected aerosol (dust, sea salt, sulphate), tracer (CO) and greenhouse gas (CO2 and CH4) concentrations at the dynamical tropopause (2-pvu isosurface). We make use of the Copernicus Atmosphere Monitoring Service reanalysis datasets CAMSRA and CAMS GHG and combine these Eulerian climatologies with a Lagrangian troposphere-to-stratosphere transport (TST) climatology to determine and characterize the pathways from the constituent sources to the UTLS. This way, we analyse anomalies of aerosols and greenhouse gases at the tropopause that arise from the TST, and we compare them to seasonal atmospheric composition climatology.
We show that the TST trajectories that originated from the boundary layer (deep TST) lead to stronger anomalies at the dynamical tropopause. The concentration patterns at the dynamical tropopause for different species depend on the emissions at the surface, the exact dynamical pathway from the surface to the UTLS, and the sinks and sources along the way. For example, we demonstrate that dust concentrations at the dynamical tropopause over Asia are mostly from local dust source regions but they can be enhanced with dust advection from other regions.
How to cite: Müürsepp, T., Joos, H., Wernli, H., and Sprenger, M.: Aerosols and greenhouse gases at the dynamical tropopause: Lagrangian transport and climatology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8259, https://doi.org/10.5194/egusphere-egu26-8259, 2026.
Volcanic injections into the upper troposphere-lower stratosphere (UTLS) affect climate by altering Earth's radiation budget and atmospheric chemistry. However, the pathways by which mid-latitude eruptions spread globally remain poorly understood. We combine nighttime Compact Optical Backscatter Aerosol Detector (COBALD) profiles over Lhasa with ERA5-driven Chemical Lagrangian Model of the Stratosphere (CLaMS) backward trajectories and global three-dimensional sulfur dioxide (SO2)-based tracer simulations. With this integrated framework, we track the Raikoke plume (21-22 June 2019; VEI 4) as it evolved within the mature Asian Summer Monsoon Anticyclone (ASMA). Balloon-borne measurements capture the plume’s arrival, vertical spreading, and dilution by ASMA-interior air. Trajectories reveal two principal pathways from distinct Raikoke plumes: (i) an upper-level branch within the summertime stratospheric easterly flow (460-490 K) carrying the trailing filament of the vorticized volcanic plume (VVP), and (ii) a lower-level branch within the subtropical westerly jet (390-430 K) carrying the main plume. Although the ASMA can act as a transport barrier at certain potential-temperature levels, it admits in-mixing along jet-aligned filaments and redistributes aerosols internally. SO2-based tracer simulations are sensitive to how parameterized small-scale mixing is represented in CLaMS, underscoring the need to adjust subgrid-scale mixing parameterizations when model resolution changes (here, from ERA-Interim to ERA5 reanalyses). Portable Optical Particle Spectrometer (POPS) profiles over Boulder (USA) confirm the plume’s timing and altitude, providing an independent evaluation away from the ASMA region.
How to cite: Yang, Z.: Transport of volcanic aerosol from the Raikoke eruption in 2019 through the Northern Hemisphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11329, https://doi.org/10.5194/egusphere-egu26-11329, 2026.
For many important trace gases, precise observations in the upper troposphere and lower stratosphere (UTLS) are spatially and/or temporally sparse and/or inhomogeneous. This is particularly problematic since the UTLS features a highly variable transition region between the troposphere and stratosphere. We here present a new dataset obtained from weather balloon-based sensors from the Juelich Modular Balloon Observatory (JUMBO) across the summer and autumn of 2025. Between 27th May and 5th November, 46 balloons were launched on an almost weekly basis from near Jülich, Germany, typically reaching altitudes of around 30 km. Of those, 37 flights focused on trace gas composition, including 18 near-simultaneous double launches quantifying the vertical distribution of water vapour and ozone as well as multiple halogenated species. The JUMBO campaign was planned, among other objectives, to infer the impact of the Asian summer monsoon on the UTLS over Germany during the full monsoon period. The observations thus enabling access to the temporal evolution of many key UTLS components over a period of about 5 months. Focusing on chlorinated very short-lived substances (Cl-VSLSs) and water vapor in combination with a model-based regional tracer approach, we also investigate the influence of the Asian Summer Monsoon as the respective anticyclone increasingly exports air masses into the global northern hemispheric UTLS.
How to cite: Rolf, C., Laube, J., Geldenhuys, M., Mainika, A., Vogel, B., and Hegglin, M. I.: Balloon-based observations of trace gas composition over Europe/Germany in summer 2025, impacted by the Asian Summer Monsoon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10333, https://doi.org/10.5194/egusphere-egu26-10333, 2026.
The Asian Summer Monsoon (ASM) plays a major role in lifting surface pollutants into the upper troposphere, influencing air quality and climate at regional and global scales. We use 17 years (2007-2023) of carbon monoxide (CO) satellite observations from the Infrared Atmospheric Sounding Interferometer (IASI) to study variability in the ASM region. Seasonal cycles, long-term changes, and dynamical processes such as eddy shedding are analyzed to understand how pollution is transported within and beyond the ASM anticyclone.
IASI measurements show good agreement with aircraft observations from the 2022 Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP) campaign, confirming the reliability of satellite data for assessing pollution in the upper troposphere. Climatological CO patterns reveal persistent enhancements associated with ASM circulation features, demonstrating IASI’s ability to capture monsoon dynamics over extended periods. Two case studies using IASI observations illustrate upper-tropospheric CO transport from the ASM: the first, supported by GEOS-FP (Goddard Earth Observing System – Forward Processing) simulations, shows consistent spatial structures over the Western Pacific during quiet and eddy shedding periods, while the second highlights how eddy shedding drives long-range transport of ASM-sourced CO across the Pacific towards North America.
These findings emphasize the value of long-term satellite observations for tracking upper-tropospheric pollution and understanding its regional and global impacts.
How to cite: Boynard, A., Viatte, C., Pan, L., Honomichl, S., Luque-Lazaro, A., Sinnathamby, S., Hadji-Lazaro, J., Smith, W., Liang, Q., D'Amato, F., Viciani, S., Campos, T., and Clerbaux, C.: Upper-Tropospheric pollution transport by the Asian Summer Monsoon from IASI observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12268, https://doi.org/10.5194/egusphere-egu26-12268, 2026.
Tropical cyclones (TCs) have received notable attention for their damaging hazards and impacts on the climate system. One under-investigated climate impact is stratosphere-troposphere exchange (STE) from TCs and accompanying upper troposphere and lower stratosphere (UTLS) composition change. STE irreversibly modifies the distribution and concentration of greenhouse gases such as water vapor and ozone in the UTLS, which is important for the radiation budget and climate. Prior case studies have individually identified multiple STE processes that can occur in TCs, however it remains unclear how these individual processes contribute to total STE in TCs, and how contributions vary by TC intensity and deep-layer shear. This study uses multiple idealized simulations conducted with Cloud Model 1 (CM1) to provide a more thorough understanding of STE in TCs, including the role of various STE process and how they vary based on TC intensity and deep-layer shear. UTLS composition change and STE is assessed using water vapor concentrations and a suite of custom passive tracers. Simulations suggest substantial hydration of the lower stratosphere occurs within the TC inner core, reaching up to 20 ppmv (4x stratospheric background) at 18.5 km (2 km above the tropopause). This hydration is spatially limited to the inner core of the TC due to surrounding cold temperatures near the tropopause. Overshooting tops within the TC and its inner core are shown to lead to substantial two-way transport. Downward transport of stratospheric air occurs (a) via subsidence within the eye and (b) in the upper portion of the near-tropopause outflow. Additional simulations reveal that TC intensity and deep-layer environmental wind shear are also important for TC STE.
How to cite: Gordon, A. and Homeyer, C.: Simulated Tropical Cyclone Impacts on Upper Troposphere Lower Stratosphere Composition , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14483, https://doi.org/10.5194/egusphere-egu26-14483, 2026.
The Arctic Springtime Chemistry Climate Investigations (ASCCI) aircraft campaign studied processes in the Arctic upper troposphere and lower stratosphere and their impact on midlatitudes in a changing climate. It was conducted between February and early April 2025 as a coordinated research effort by several German Universities and research institutes.
For the ASCCI mission, the German High Altitude and Long-Range Research Aircraft HALO was equipped with a payload consisting of a mixture of in-situ and remote sensing instruments, allowing for a detailed chemical and dynamical characterization of the lowermost polar stratosphere during late winter to early spring 2025. The campaign was especially designed to complement information from the POLSTRACC campaign carried out with HALO during the Arctic winter 2015 to 2016, and the SouthTRAC campaign in 2019 which was aimed at studying the Antarctic lower polar stratosphere during late winter and early spring. Our main aims were to study (i) the inter-annual variability of Arctic lower stratospheric ozone depletion in comparison to POLSTRACC, (ii) high latitude stratosphere-troposphere exchange and the structure of the high latitude tropopause and (iii) the impact of short-lived climate pollutants (ozone, aerosols) and their precursors on the Arctic upper troposphere.
The Arctic winter 2024/2025 was characterized by a record-cold mid-winter period, followed by an early stratospheric warming from which the polar vortex only partly recovered. Despite this warming, we were able to observe signs of heterogeneous redistribution of nitrogen species and of chemical ozone depletion. We will present an overview of the flights carried out during ASCCI and first results of the observations.
The ASCCI team
University of Mainz, Institute for Physics of the Atmosphere
Franziska Weyland, Peter Hoor, Vera Bense, Heiko Bozem, Jonas Blumenroth, Hans-Christoph Lachnitt,
Forschungszentrum Jülich (FZJ)
Jens-Uwe Grooß, Michaela Hegglin, Marc von Hobe, Tom Neubert, Felix Ploeger, Markus Retzlaff, Christian Rolf, Georg Schardt, Nicole Spelten, Martin Riese, Sebastian Rhode, Joern Ungermann.
University of Wuppertal
Michael Volk, Valentin Lauther, Johannes Strobel, Ronja von Luijt.
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Georgios Dekoutsidis, Andreas Fix, Silke Groß, Konstantin Krüger, Andreas Schäfler, Martin Wirth, Stefan Kaufmann, Mara Montag, Elisabeth Horst, Laura Tomsche, Christiane Voigt, Helmut Ziereis.
Karlsruhe Institute of Technology (KIT)
Bastian Kirsch, Simone Scheer, Florian Obersteiner, Andreas Zahn, Felix Friedl-Vallon, Michael Höpfner, Wolfgang Woiwode, Erik Kretschmer, Georg, Wetzel, Anne Kleinert, Guid Maucher, Hans Nordmeyer, Christog Piesch, Franziska Trinkl.
University of Heidelberg
Benjamin Weyland, Karolin Voss, Maximilain Albrecht, Andre Butz, Klaus Pfeilsticker
How to cite: Engel, A. and Sinnhuber, B.-M.: The Arctic Springtime Chemistry Climate Investigations – ASCCI aircraft campaign – an overview, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17846, https://doi.org/10.5194/egusphere-egu26-17846, 2026.
Transport and mixing strongly determine the trace gas composition of the Arctic upper troposphere / lower stratosphere (UTLS), but spatial and temporal variability of the relevant processes are still not well quantified. The Arctic lowermost stratosphere (LMS) is fed via, and thus controlled by, various transport paths from regions with very differing chemical composition - young tropospheric air from the subtropics or even directly from the boundary layer, to photochemically very old air descending slowly from the mid- and high-latitude stratosphere. The HALO aircraft mission ASCCI conducted from Kiruna, Sweden in late winter and early spring 2025 aimed at investigating transport and mixing processes and time scales in the Arctic UTLS region, especially stratosphere-troposphere exchange, and the role of chemistry and tropospheric pollution for ozone in the Arctic UTLS. For answering these questions, measuring a wide range of trace gases with different source regions and chemical lifetimes ranging from days to many years is crucial.
We present a survey of first results of in situ tracer measurements made with the High Altitude Gas AnalyseR - five channel version (HAGAR-V) instrument. HAGAR-V measured a suite of more than 30 trace gases including very short-lived NMHCs (e.g. Benzene, C2H2, C4H10), halogenated VOC (e.g. CH2Cl2, CHCl3, C2Cl4, CH2Br2), as well as longer-lived halocarbons (e.g. CH3Cl, CH3Br, CCl4, Halons, HCFCs, and HFCs) every 120 s using in-flight gas chromatography and mass spectrometry. Further very long-lived species, including the age-of-air tracer SF6, were measured every 40 s (CFC-12, SF6) and every 80 s (CFC-11, CFC-113, H1211) using electron capture detection. Additionally, very precise CO2 measurements by a NDIR analyser were conducted at high time resolution (5 s).
Using tracer-tracer relations of short-lived pollutants with long-lived tracers, we can distinguish between different transport and mixing processes in the Arctic UTLS. Besides observing mixing of fresh tropospheric air with older stratospheric air at the extratropical tropopause, we also identified rather young (several months) air transported from the tropical tropopause layer (TTL) to the high latitude stratosphere and mixing with old polar air at potential temperatures about 380 K. We also observed pollution by short-lived chlorinated substances such as CH2Cl2, CHCl3, C2Cl4 and 1,2-dichloroethanein the Arctic, likely from both regional and remote sources. Besides the analysis of transport processes, we also derived the mean age of air both from SF6 and CO2. Using both species independently increases the reliability of the calculated ages significantly.
How to cite: Strobel, J., van Luijt, R., Lauther, V., Weyland, F., Bozem, H., Kessler, S., Hoor, P., and Volk, C. M.: Transport and mixing of pollutants into the Arctic LMS derived from HAGAR-V in situ observations of a wide range of trace gases during the HALO ASCCI mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20116, https://doi.org/10.5194/egusphere-egu26-20116, 2026.
The tropopause represents a central feature of the vertical structure of the atmosphere, marking the transition between the troposphere and stratosphere. While common definitions such as the thermal tropopause (TTP) defined by the WMO primarily rely on quantitates that are conserved under adiabatic processes, diabatic effects resulting from radiation, cloud processes, or turbulence are also decisive for the tropopause structure.
We propose a new definition of the tropopause based on the vertical gradient of the relative humidity with respect to ice (RHi), named the RHi Gradient Tropopause (RHi-GT). The RHi-GT is determined using a simple, robust gradient method. We demonstrate that the RHi-GT definition is generally consistent with the TTP but often provides a clearer characterization. In individual profiles, the RHi-GT coincides more closely with regions that mark a clear transition in atmospheric structure, such as sharp gradients in absolute humidity or increases in static stability. Furthermore, when examining mean profiles over the 10-year period relative to the RHi-GT, both RHi and static stability show a more coherent and distinct transition between the moist troposphere and the very dry stratosphere compared to when referenced to the TTP.
How to cite: Reutter, P. and Spichtinger, P.: The frosty frontier: redefining the mid-latitude tropopause using the relative humidity over ice, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1775, https://doi.org/10.5194/egusphere-egu26-1775, 2026.
Convection represents a major pathway of moisture and trace species into the upper troposphere. However, the role of convection for cross-tropopause transport is still under discussion, e.g., the processes of moisture entry into the lower stratosphere. Deep convection highly perturbs the local tropopause structure, which is partly reversible. It thus can either penetrate the tropopause, injecting trace species (including water) into the stratosphere, but it can also lead to a lifting of the tropopause as the thermals from below and their adiabatic cooling reach to higher altitude.
In this study, we analyse model results on the kilometer scale of idealised deep convective events and analyse the modifications of the tropopause above convection, using both thermal as well as dynamical tropopause definitions. Furthermore, we depict how the thermal structure of the atmosphere is modified after the convective event, effectively changing the tropopause altitude. Additionally, we determine the amount of water vapour transported to elevated altitudes above the original tropopause and how much water irreversibly enters the stratosphere. The exchange also encompasses downward transport of air masses with stratospheric characteristics into the troposphere. We analyse, which factors (e.g., vertical wind shear, CAPE and the strength of the initial disturbance) show the strongest influence on the tropopause modifications and, therefore, assess the effects of deep convection for the UTLS.
How to cite: Tost, H. and Hoor, P.: Convective local tropopause modifications and entrance into the stratosphere - a modelling perspective, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6812, https://doi.org/10.5194/egusphere-egu26-6812, 2026.
Long-term global trace gas observations can be used to define chemical tropopauses, which are not limited by the availability or resolution of vertical profiles or reanalysis data sets. Tracers that can be used for these definitions need to show clearly defined differences in stratospheric vs. tropospheric characteristics with notable examples being O3, N2O, CO or H2O.
We focus on two approaches: (1) the definition of an O3-based tropopause using a clearly defined climatology expressed as mixing ratios relative to the tropopause and (2) the filtering of stratospheric data by applying an iterative baseline filter on N2O measurements. Our objective is to provide clear, globally applicable definitions of these chemical tropopauses, that can be easily applied to new measurement data and provide a representative distance to the tropopause.
We analyse globally distributed ozone sonde measurements, as well as aircraft and balloon measurements of N2O, in combination with meteorological parameters from interpolated ERA5 reanalyses. By evaluating profiles for each month and geographical region, a representative distance to the tropopause can be assigned to any measurement of O3 or N2O. We further investigate the sensitivity of these assignments to spatial and temporal factors and apply these to separate measurement data sets.
Tropopause-relative coordinates are beneficial for trace gas analysis in regions close to the tropopause. However, this effect diminishes with greater distances. We examine for which lower and upper boundaries tropopause-relative coordinates remain beneficial.
How to cite: Bauchinger, S., Engel, A., Zahn, A., Bönisch, H., Lachnitt, H.-C., Krysztofiak, G., and Schuck, T.: Climatology-based chemical tropopauses from global O3 and N2O observations since 1980, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10707, https://doi.org/10.5194/egusphere-egu26-10707, 2026.
The tropopause is an important boundary (or transition layer) for many studies in the atmospheric sciences and is an indicator of global climate change. Numerous characteristics of the tropopause have been shown to exhibit significant long-term change over the most recent 40+ year period, including height, temperature, and the occurrence of multiple tropopauses. However, prior observational studies rely mostly upon suitable records of radiosondes, which are only available over land and vary in coverage globally. Observation-based model reanalyses have been used in many studies to provide global coverage but resulting assessments of tropopause characteristics are not always consistent with observational analyses. In recent decades, the emergence of global navigational satellite system (GNSS) radio occultation (RO) atmospheric profiles provides an observational record with global coverage and fine vertical resolution necessary for tropopause analysis. The GNSS-RO data record is now approaching the period length necessary for robust assessment of long-term changes (trends). In this study, we leverage a continuous record of nearly 25 years of GNSS-RO data and apply two universal tropopause definitions, the WMO temperature lapse-rate tropopause (LRT) and the potential temperature gradient tropopause (PTGT), to evaluate global tropopause characteristics and their long-term changes. We find widespread increases in multiple tropopause frequency in the midlatitudes, consistent with several recent radiosonde and reanalysis studies. We also find regionally varying changes in tropopause height and temperature, which in some cases imply changes in the width of the tropics. Results are generally insensitive to the choice of LRT or PTGT definition. Implications of the diagnosed changes and their relationships to drivers of climate variability will be discussed.
How to cite: Homeyer, C. and Tinney, E.: Long-term Changes in Global Tropopause Characteristics from GNSS-RO Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14224, https://doi.org/10.5194/egusphere-egu26-14224, 2026.
Methane is a potent greenhouse gas with an increasing trend in the atmosphere due to rising emissions. Aside from its climate impacts, it is important to monitor methane because its long lifetime of about ten years makes it a useful tracer of atmospheric transport. As a result, modelled methane fields can therefore be compared with observations to evaluate transport in atmospheric models. Several methods have been proposed for assessing the strength of the subtropical mixing barrier and the polar vortex edge using long-lived tracers, but most require high data density. In addition, it is difficult to separate the effects of mixing from those of chemical production and loss or from other aspects of atmospheric transport. In this study, we explore various methods of using methane probability density functions and time series to quantify the strength of the subtropical mixing barrier and the polar vortex edge, based on comparisons with relatively sparse satellite measurements from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). ACE-FTS is a solar occultation instrument with near-global coverage and 3–4 km vertical resolution, spanning the upper troposphere to the lower mesosphere. The focus of the comparisons is on a specified dynamics run of the Canadian Middle Atmosphere Model (CMAM39-SD) for the 2004-2018 period. In general, we find that the modelled subtropical mixing barrier is too weak in the lower stratosphere and too strong in the upper stratosphere. In contrast, CMAM39-SD reproduces methane variability near the polar vortex edge very well. To provide context, we also compare ACE-FTS with the air quality model GEM-MACH, the Earth system model MRI-ESM2, and the chemical transport model GEOS-Chem.
How to cite: Saunders, L., Walker, K., Plummer, D., Pendlebury, D., Whaley, C., Oshima, N., Sheese, P., Chien, R.-Y., Fu, J., Manney, G., and Millán, L.: Using ACE-FTS to assess mixing barrier strength in nudged chemistry-climate models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14363, https://doi.org/10.5194/egusphere-egu26-14363, 2026.
The large-scale zonal-mean transport of tracers, such as ozone and water vapor, is governed by global circulations. Because of the radiative effects of tracers, an accurate representation of their transport in climate models is essential for reliable climate simulations. Small-scale processes such as gravity waves and turbulence can significantly influence the transport and distribution of tracers. As these processes are unresolved in most weather and climate models, their effects must be parameterized. We present the novel parameterization for the direct impact of gravity waves on tracer transport (Knop et al., 2026). Using multiple-scale analysis of the governing atmospheric equations, we derive expressions for gravity wave–induced tracer fluxes, enabling a physically based parameterization. The parameterization is thoroughly validated by comparing idealized simulations with parameterized waves to wave-resolving reference simulations. Finally, we aim to extend the theory to include turbulent effects.
How to cite: Steiger, I., Suresh, D., Dolaptchiev, S., and Achatz, U.: Impact of Small-Scale Gravity Waves on Tracer Transport, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10858, https://doi.org/10.5194/egusphere-egu26-10858, 2026.
Winds in the tropical lower stratosphere raise difficulties for numerical weather prediction models: without geostrophy, winds decouple from temperature and direct observations are scarce. The Strateole 2 project explores the tropical lower stratosphere using superpressure balloons that drift for up to three months between 18 and 21 km altitude. Wind measurements from the technological campaign (2019–2020) and the first scientific campaign (2021–2022) are used to assess errors in the ERA5 reanalysis for latitudes between 18° S and 10° N. The comparison reveals significant errors, with standard deviations of 3.76 m s−1 for zonal and 3.24 m s−1 for meridional wind. Relative to a previous comparison in 2010, only a modest decrease of 20 % and 10 % is found, revealing the persistent difficulty of modeling winds in the tropical lower stratosphere.
Additionally, the errors in modelled balloon trajectories are also assessed, with a focus on the predictability of the trajectories. It is shown that the initial error in the wind gives a reliable indication on the skill of the subsequent forecast. Trajectory calculations have very variable skill, with median errors after 24 h of 260 km, but a tenth of the errors larger than 600 km. Factors leading to large errors, such as initial wind error and latitude are identified.
Certain instruments onboard Strateole 2 balloons measure features below the balloons (temperature, thin cirrus, water vapour..). While the sampling of air at balloon flight level is quasi-Lagrangian, observations of features below the balloon describe both spatial and temporal variations. In order to disentangle these and facilitate the interpretation of observations made below the balloons, we document the dispersion of air below the balloons (altitudes between about 15 and 21 km). Trajectory dispersion of air below the balloon is very variable, depending on the initial shear. The persistent errors highlight the need for regular obsevations of winds in the tropical lower stratosphere.
Overall, we emphasize the need for caution when using trajectory calculations for process studies.
How to cite: Plougonven, R., Cadiou, P., Podglajen, A., Hertzog, A., and Mac Farlane, A.: Strateole 2 superpressure balloons reveal persistent errors in reanalyzed winds in the tropical lower stratosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14427, https://doi.org/10.5194/egusphere-egu26-14427, 2026.
Tropical upwelling transports air masses across the tropical tropopause into the lower stratosphere and constitutes the ascending branch of the global mean stratospheric circulation. The strength of the tropical upwelling influences the thermal characteristics and chemical composition of the lower stratosphere and the transition region between troposphere and stratosphere, the tropical tropopause layer (TTL). Given the lack of direct measurements and the small magnitude of vertical velocities, the variability and long-term changes of tropical upwelling are difficult to determine and poorly constrained in meteorological analysis data.
Here we use water vapor measurements from the MLS (Microwave Limb Sounder) instrument to determine interannual variations and long-term changes in tropical upwelling in the lower stratosphere for 2005-2023. Our upwelling estimates represent an effective vertical transport velocity and provide an estimate of the speed of the vertical branch of the stratospheric circulation. We show that interannual variations of the tropical upwelling are anti-correlated with TTL temperatures derived from Global Navigation Satellite System – Radio Occultation (GNSS-RO) measurements with warmer (colder) temperatures coinciding with years of less (more) upwelling. A regression analysis results in a negative upwelling trend of consistent with positive temperature trends in the TTL. Upwelling is also found to be anti-correlated with independent time series of ozone and other gases in the lower stratosphere.
We compare the observational upwelling estimates to residual vertical velocity from four reanalysis and find very good agreement of the interannual variability between all data sets. The reanalysis eddy and momentum fluxes are used to investigate the impact of extratropical waves on tropical upwelling. Our analysis shows that a large fraction of the interannual variability in tropical upwelling is associated with waves propagating meridionally into the subtropical stratosphere.
How to cite: Tegtmeier, S., Abalos, M., and Randel, W.: Tropical upwelling in observations and reanalyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15393, https://doi.org/10.5194/egusphere-egu26-15393, 2026.
Posters on site: Thu, 7 May, 08:30–10:15 | Hall X5
With global warming, Canada is increasingly affected by extreme weather events, mainly wildfires. With more than 8.3 million hectares burned over the country, the 2025 Canadian fire season is the second-worst on record after 2023. The associated emissions injected an exceptional aerosol load in the Northern Hemisphere upper troposphere – lower stratosphere (UTLS). Part of the emitted aerosols reached the lower stratosphere and, over Europe, organized into a new “smoke-charged vortex” (SCV). SCVs – anticyclonic structures that confine polluted air into long-lived “smoke bubbles” – have already been documented and studied after the “Pacific Northwest Event” (PNE) in Canada in 2017 and the “Australian New Year” event (ANY) in Australia in 2019-2020, making the 2025 event the third such case identified to date. Once formed, their anticyclonic circulation tends to limit dilution and mixing with the ambient air, maintaining high black-carbon-rich aerosol concentrations and chemical species emitted from biomass burning – for weeks to months within these vortices. These include carbon monoxide (CO), water vapor (H2O), inorganic compounds such as nitrogen-(NOx) and chlorine-(ClOx) containing species, and a range of organic compounds such as non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs), all of which play key roles in atmospheric chemistry.
In this study, we track the SCV over Europe using vorticity anomaly, analyse its aerosol burden using balloon-borne and satellite observations and characterize its chemical composition. Together, these results provide a comprehensive overview on the SCV characteristics and place the 2025 event in context with the previously documented PNE and ANY cases.
How to cite: Vieille, L., Duchamp, C., Berthet, G., Jégou, F., Legras, B., and Podglajen, A.: The 2025 Canadian wildfires: a new formation of smoke charged vortex, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6721, https://doi.org/10.5194/egusphere-egu26-6721, 2026.
Water vapor in the lowermost stratosphere (LMS) plays a critical role in the climate system, as even small perturbations can significantly affect stratospheric temperatures and the position of the subtropical and eddy-driven jets. Climate models such as the ECHAM MESSy Atmospheric Chemistry (EMAC) model simulate strong wet biases in the LMS, reaching up to 400% compared with satellite observations. The strongest biases are found in the summer hemisphere. We find that 19% of air parcels in the LMS in the EMAC simulation exceed 30 ppmv in water vapor, a feature absent in both observations and independent Lagrangian model simulations. To diagnose the origin of this bias, we perform backward trajectory simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) to trace the pathways of LMS air parcels and sample their Lagrangian cold points (LCPs). EMAC-simulated large-scale dehydration near the tropical cold trap is consistent with the sampled LCPs and shows no indication of a moist bias. Hence, the excessive moistening must occur downstream during transport into the LMS rather than at entry into the stratosphere. We further analyze the processes contributing to the LMS model moist bias by interpolating the physical and chemical tendencies from the EMAC model along the trajectories, including convection, vertical diffusion, and methane oxidation, as well as ice water content. For the subset of anomalously moist air parcels (water vapor mixing ratios greater than 30 ppmv), these processes collectively explain at most 30% of the simulated water vapor mixing ratios. Among the model processes, ice sublimation provides the dominant contribution, followed by vertical diffusion and convection, while methane oxidation is negligible. The large unexplained residual strongly suggests that numerical diffusion during transport is the primary driver of the excessive climate model wet bias in the LMS.
How to cite: Wang, H., Konopka, P., Kerkweg, A., and Ploeger, F.: On the cause of climate model wet biases in the lowermost stratosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7539, https://doi.org/10.5194/egusphere-egu26-7539, 2026.
Chemically active chlorine species (ClOx) play a central role in the catalytic depletion of ozone in the polar winter and spring stratosphere. Together with the reservoir species HCl and ClONO2, they form inorganic chlorine (Cly). The amount and partitioning of Cly strongly influences the magnitude of polar ozone loss. Trends and variability in the upper troposphere lower stratosphere region (UTLS) are of particular importance, as this region is a large contributor to lower-stratospheric ozone change.
We present new in-situ measurements from the HALO campaign ASCCI (Arctic Springtime Chemistry and Climate Investigations), obtained in spring 2025. The total organic chlorine (CCly) is directly derived from the major chlorine species measured by the Gas Chromatograph for Observational Studies using Tracers (GhOST). From these measurements, inorganic chlorine is derived, allowing an observational assessment of the chlorine budget in the Arctic UTLS. Additional in situ observations of the reservoir species HCl and ClONO2 from the Airborne Chemical Ionisation Mass Spectrometer (AIMS) are used to constrain the abundance of chemically active chlorine (ClOx) and to investigate chlorine activation and deactivation processes during spring 2025.
The new ASCCI data are compared with observations from previous aircraft campaigns, including PGS (Arctic measurements in 2015) and SOUTHTRAC (Antarctic measurements from 2019) both performed during hemispheric springtime, allowing for an assessment of hemispheric differences between Arctic and Antarctic conditions as well as temporal changes in chlorine loading and partitioning. These comparisons place the new measurements in the context of declining stratospheric chlorine and ozone recovery.
How to cite: Diederich, T., Bozem, H., Horst, E., Hoor, P., Kaufmann, S., Keber, T., Kessler, S., Lachnitt, H.-C., Montag, M., Schuck, T., Tomsche, L., Voigt, C., Weyland, F., and Engel, A.: Chlorine Chemistry and Partitioning in the arctic UT/LS during Spring 2025 from in-situ measurements during ASCCI , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12720, https://doi.org/10.5194/egusphere-egu26-12720, 2026.
The persistence of aircraft contrails and their climate impact are strongly controlled by the extent, lifetime, and properties of ice-supersaturated regions (ISSRs). Reliable prediction of such conditions remains challenging due to uncertainties in the representation of water vapor in numerical weather prediction models at typical cruising altitudes in the upper troposphere. In-situ airborne observations are therefore essential for evaluating model performance and assessing the potential benefit of additional humidity data sources.
This study employs three complementary data sources: (1) high-resolution in-situ water vapor measurements obtained with the Sophisticated Hygrometer for Atmospheric Research (SHARC) and a modified Water Vapor Sensing System II (WVSS-II) aboard the High Altitude and Long-Range Research Aircraft (HALO); (2) routine aircraft observations from the Aircraft Meteorological Data Relay (AMDAR) program using WVSS-II sensors; and (3) numerical weather model output from the ICON-DREAM reanalysis of the German Weather Service (DWD).
To evaluate the data quality of WVSS-II sensors on commercial aircraft, comparisons between HALO reference measurements and AMDAR observations with spatial overlap during the Arctic Springtime Chemistry Climate Investigations (ASCCI) field campaign are conducted. An indirect comparison uses the entire dataset to analyze water vapor concentration (H₂O) and relative humidity with respect to ice (RHi) as a function of potential temperature. In addition, a short parallel flight segment of HALO and a commercial flight at the same altitude was performed which allows for a direct comparison of both sensors. For both comparison approaches, agreement and variability between the datasets are assessed using statistical metrics. Furthermore, the HALO dataset is used to evaluate and quantify the representation of RHi in ICON first-guess fields, covering multiple campaign periods between 2012 and 2025 with a total of 878 flight hours.
Building on the previous steps, ongoing work investigates the use of AMDAR humidity observations in dedicated ICON data assimilation experiments to evaluate their impact on humidity prediction. Differences between routine model simulations and assimilation runs are analyzed to assess potential improvements in upper-tropospheric humidity forecasts relevant for ISSR prediction.
How to cite: Montag, M., Kaufmann, S., Tomsche, L., Neumann, M., Emmel, C., and Schraff, C.: Airborne Water Vapor Observations for ISSR Analysis and improved Humidity Prediction in the Upper Troposphere using the ICON Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11858, https://doi.org/10.5194/egusphere-egu26-11858, 2026.
Troposphere-to-Stratosphere Transport (TST) can inject anthropogenic pollutants from the Earth’s surface into the Upper Troposphere – Lower Stratosphere (UTLS), changing its chemical composition and influencing the radiative processes. Furthermore, TST may play a key role in sustaining the long-range transport of pollutants across the globe, particularly during extreme weather events. Indeed, during such events, a large quantity of pollutants can be transported from the Boundary Layer (BL) to the free atmosphere, enhancing the probability of long-range transport as the contaminants reach higher altitudes. The various mechanisms that contribute to TST have not yet been fully resolved due to the multi-scale nature of this transport process. In our study, we investigated the TST processes triggered by the transition of the typhoon Molave over the Philippines in the autumn 2020, combining a Lagrangian modeling tool with the Weather Research and Forecasting model. Our findings supported the proposal of a novel TST mechanism based on the interaction between typhoon updrafts, convection, orographic lifting, and gravity waves. Firstly, our results demonstrate that this interaction can rapidly transport air from the BL to the UTLS region, carrying a significant amount of pollutants despite deposition processes. Secondly, our work highlights the importance of gravity waves in the mixing processes close to the tropopause region. Overall, our study suggests that the interplay between typhoon episodes and mountainous regions can play an important, yet previously insufficiently considered, role in TST. This interaction influences key topics that are relevant to our society, such as the long-range dispersion of pollutants.
How to cite: Martina, M., Villalba Pradas, A., Bartoň, Š., and Šácha, P.: Novel mechanism for troposphere-to-stratosphere transport due to the interaction between typhoons and orography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9641, https://doi.org/10.5194/egusphere-egu26-9641, 2026.
Chlorine dioxide (OClO) is a by-product of the ozone depleting halogen chemistry in the stratosphere and serves as an indicator of the chlorine activation in polar regions during polar winter and spring at twilight conditions because of the nearly linear dependence of its formation on chlorine oxide (ClO) and its detectability by UV-VIS spectral instruments.
The TROPOspheric Monitoring Instrument (TROPOMI) is an UV-VIS-NIR-SWIR instrument on board the Sentinel-5P satellite developed for monitoring the composition of the Earth’s atmosphere. Launched on 13 October 2017 in a near polar orbit, it provides continuous monitoring of many constituents including the observation of OClO at an unprecedented spatial resolution.
The EMAC (ECHAM5-MESSy Atmospheric Chemistry) model is a chemistry climate model based on a general circulation model including interactive gasphase and aerosol atmospheric chemistry simulation and is nudged to the meteorology (in particular ERA5).
In this study we analyse the time series of slant column densities (SCDs) of chlorine dioxide (OClO) at polar regions and compare them with EMAC simulations in particular for the periods of the 2019/2020 Australian megafires and the Hunga volcanic eruption (January 2022).
While in the aftermath of the Australian megafires an increased, anomalous pattern of OClO is found for a period of two years no such an anomaly can be seen with respect to the Hunga eruption, both being well in agreement between the model and the measurements.
How to cite: Pukite, J., Ziegler, S., Brühl, C., Pozzer, A., and Wagner, T.: Additional OClO formation due to major forest fires and volcanic eruptions: comparison between TROPOMI measurements and EMAC model simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13578, https://doi.org/10.5194/egusphere-egu26-13578, 2026.
Ozone and water vapor in the lowermost stratosphere (LMS) modify the Earth’s radiative budget, influence large-scale dynamics, and affect tropospheric air quality through exchange processes at the tropopause. Despite this importance, the variability and long-term trends of LMS ozone and, in particular, water vapor (WV) remain highly uncertain. This uncertainty is compounded by variability in the thermodynamic structure of the LMS itself: extratropical tropopause height, tropical tropopause temperatures, and the latitudinal width of the tropical tropopause have all shown systematic changes in recent decades.
In this study we present an LMS partial column framework that explicitly accounts for the variable LMS boundaries and explore the partial column as an UTLS diagnostics for global observations and models.
The LMS limits are defined from ERA5 reanalysis and partial columns of ozone and WV are obtained by integrating satellite measurements from the Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) within these limits. Unlike conventional mixing-ratio analyses, the partial column approach also incorporates the density and area effects of the spherical atmosphere.
Our analysis shows that the extratropical LMS comprises a considerable amount of the total stratospheric mass, stratospheric WV mass, and stratospheric ozone mass. The spatial and seasonal variability of LMS partial column ozone and WV is largely influenced by variations in total LMS mass. LMS partial column ozone shows very good agreement across the data sets whereas LMS partial column WV exhibits a larger spread. Calculated long-term trends result from a complex interplay of LMS mass and mixing-ratio changes.
How to cite: Weyland, F., Hoor, P., Kunkel, D., Plöger, F., Birner, T., and Millán, L.: A partial column perspective on ozone and water vapor in the lowermost stratosphere from satellite observations, reanalysis, and model data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13154, https://doi.org/10.5194/egusphere-egu26-13154, 2026.
Stratospheric aerosols play a crucial role in atmospheric chemistry and climate through heterogeneous chemical reactions and radiative forcing. Although sulfate aerosols in the stratosphere have been extensively studied, the organic fraction remains poorly characterized, despite its potential importance for both climate and chemical processes.
The Stratospheric Aerosol Processes, Budget, and Radiative Effects (SABRE) 2023 campaign deployed the WB-57 high-altitude aircraft with a payload designed to improve characterization of stratospheric aerosols. Aerosol particles with aerodynamic diameters between 0.18 and 3.2 μm were collected using a cascade impactor (Mini-MOUDI 135, MSP) for offline analysis. We apply Scanning Transmission X-ray Microscopy coupled with near-edge X-ray absorption fine structure (STXM-NEXAFS) to characterize the composition and morphology of individual stratospheric aerosol particles. Carbon K-edge spectra are used to classify particles by organic carbon, elemental carbon, and inorganic content, enabling investigation of aerosol mixing state, morphology, and carbon functional group distributions. NEXAFS analysis also measures potential tracers, such as potassium associated with biomass burning, and other anthropogenic organic species. Using a radial distance shell-based classification scheme, we present preliminary results highlighting the complexity and diversity of particle morphologies. These microphysical properties help constrain the impacts of stratospheric aerosols on radiative forcing and ozone chemistry. We compare results across multiple flights, distinguishing aerosols sampled within and outside the polar vortex. Together, these observations advance our understanding of the chemical and radiative roles of stratospheric aerosols in Earth’s atmosphere.
How to cite: Abou-Rizk, S., Li, Y., Cooper, T., Gee, M., Cheng, Z., China, S., Lai, Z., O'Callahan, B., Vandergrift, G., and Keutsch, F.: Characterizing Organic Stratospheric Aerosols by Functional Group Analysis from the SABRE 2023 Campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15566, https://doi.org/10.5194/egusphere-egu26-15566, 2026.
Determining the atmospheric abundance and the emission sources of carbonyl sulfide (OCS) plays a crucial role for the sulfur budget in the atmosphere.
In addition to its main anthropogenic and biogenic sources, biomass burning is assumed to be an essential, but not well constrained source of OCS.
From November 2019 onward extensive bushfires along the eastern coast of Australia released huge amounts of trace species into the atmosphere; during one flight of the SouthTRAC campaign air masses were observed carrying signatures of these fires along the southern coast of South America.
We present an analysis of the composition of air masses inside and outside the plume, revealing distinct differences in the trace species abundances. Specifically, our results indicate that OCS shows no enhancement in its atmospheric mixing ratio due to the Australian fires and thus highlights the varying emission strength of OCS for different types of biomass burning.
How to cite: Kessler, S., Emig, N., Lachnitt, H.-C., Kunkel, D., Bozem, H., Bense, V., Joppe, P., Kaluza, T., Grooß, J.-U., Zahn, A., Ziereis, H., Riese, M., and Hoor, P.: Biomass burning in Australia: No evidence for carbonyl sulfide (OCS) enhancement in fire plumes from in-situ measurements during SouthTRAC, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13914, https://doi.org/10.5194/egusphere-egu26-13914, 2026.
The chemical composition throughout the atmosphere changes as a consequence of urbanization, developing industry and anthropogenic activities. Especially the upper troposphere and lower stratosphere (UTLS) is highly sensitive to these changes in chemical composition. With increasing anthropogenic emissions, the urgency to understand the changing chemical composition and its impact on the UTLS grows.
Organophosphates are one of the most prominent anthropogenic tracers, as they are solely man-made and found ubiquitously in the environment. They are widely used as flame retardants and plasticizers and have already been found in pristine environments such as the Arctic and are considered as chemicals of emerging concern. So far, they have been studied in air, water, sediment, and sludge and their human exposure and human and ecological risk has been assessed (Wang et al. 2020). Research on outdoor air and particle-bound organophosphates has been steadily growing over the years, however, the UTLS remains a poorly studied region.
In this study, we target the question of how meteorological conditions influence the chemical composition and thereby use organophosphates as anthropogenic tracers throughout the UTLS. Here, we present results from the TPEx campaign, conducted during June 2024 over Germany. Results from eight scientific flights, probing different regions of the UTLS during different meteorological conditions, were analyzed. With our in-house developed and manufactured Sampler for Organic Aerosol Particles (SOAP), we were able to collect a total of 27 filters throughout the whole campaign. Subsequently using ultra-high performance liquid chromatography, coupled with high-resolution Orbitrap mass spectrometry, we analyzed the organic fraction of aerosols. With this setup a non-target analysis allowed for the identification of unknown compounds and especially yet understudied organophosphates in the UTLS.
We identified five distinct meteorological conditions by using tracer-tracer correlations, cloud water content as well as water vapor content and categorized each filter respectively. For each meteorological condition, a distinct chemical composition was identified using molecular fingerprinting. As a first result, compounds like C8H19O4P and C8H19O3PS, which are found in the troposphere as well as the stratosphere, seem to disappear during cloudy conditions and are less abundant in combination with high water vapor mixing ratios. Simultaneously, a mix of thiophosphates, which are possible transformation products of organophosphates, becomes more abundant during high water vapor mixing ratios. We further aim to quantify various organophosphates and transformation products to understand occurrence, transportation and potential global distribution, as they are unambiguous tracers for the anthropogenic impact.
Wang, X., Zhu, Q., Yan, X., Wang, Y., Liao, C., Jiang, G. (2020c). A review of organophosphate flame retardants and plasticizers in the environment: Analysis, occurrence and risk assessment. Sci. Total Environ. 731, 139071. https://doi.org/10.1016/j.scitotenv.2020.139071
How to cite: Breuninger, A., Rolf, C., Konjari, P., Bozem, H., Emig, N., Hoor, P., Miltenberger, A., Merkel, L., Kutschka, A., Waleska, P., Hofmann, S., Hoffmann, T., and Vogel, A. L.: Organophosphates in the UTLS - Understanding the link between meteorology and occurrence of anthropogenic aerosol tracers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16920, https://doi.org/10.5194/egusphere-egu26-16920, 2026.
Mixing between the upper troposphere (UT) and the lower stratosphere (LS) occurs on short timescales compared to dynamic processes within the stratosphere. These mixing processes form the Extratropical Transition Layer (ExTL). Due to the nature of the tropopause as transport barrier, tracers exhibit strong vertical gradients within the ExTL. The ExTL is often identified based on the correlations of airborne trace gas measurements. However, inner-stratospheric variability on longer time scales can also lead to enhanced variability and thus might cause false identification of the ExTL.
Our goal is to distinguish the ExTL from stratospheric variability on longer timescales. Therefore, the choice of tracers is crucial, particularly for species with stratospheric sources like CO or H2O. To circumvent this problem, comparisons with tracers that have only tropospheric sources such as C2H6 are necessary. For this purpose, simultaneous measurements of C2H6 and CO have been conducted during the PHILEAS (Probing High Latitude Export of air from the Asian Summer Monsoon) campaign and the ASCCI (Arctic Springtime Chemistry Climate Investigations) campaign using the University of Mainz QCL-based Spectrometer (UMAQS).
Our results show that similarly to CO, stratospheric variability of C2H6 is also non-zero up to potential temperatures of 400 K. Therefore, dynamic processes rather than chemical sources most likely are the origin of this variability. By using tracer-tracer correlations, we are able to account for the longer-term variability and to separate cross-tropopause mixing from transport and mixing on longer timescales.
When applying this method to PHILEAS data (autumn of 2023) and ASCCI data (spring of 2025) from the northern lowermost stratosphere (LMS), the ExTL can be isolated in vertical tracer profiles, showing a similar extent in autumn and spring. Further, the LMS structure in winter shows a surprisingly well separation from the overworld, indicating two different transport timescales in the background lower stratosphere.
How to cite: Blumenroth, J., Lachnitt, H.-C., Bozem, H., Weyland, F., Emig, N., Kessler, S., Kunkel, D., Ort, L., Joppe, P., Zahn, A., Engel, A., Riese, M., Plöger, F., and Hoor, P.: Separation of tropopause mixing from long-term stratospheric variability using in-situ measurements during PHILEAS and ASCCI, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20189, https://doi.org/10.5194/egusphere-egu26-20189, 2026.
The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is a cooled limb-imaging Fourier-Transform spectrometer (iFTS) providing mid-infrared spectra with high spectral resolution. A newly developed, compact and uncooled version of GLORIA (called GLORIA-Lite) is significantly smaller and lighter thanks to state-of-the-art infrared sensors, tailored electronics and innovative manufacturing technology. The development of this instrument enabled the first transcontinental stratospheric balloon flight from northern Sweden via Greenland to Canada, which took place in June 2024. The objectives of observation have been primarily its technical qualification and the provision of a first imaging hyperspectral limb-emission dataset (spectral sampling 0.2 cm-1 in the wavelength range 750-1450 cm-1) from 5 to 40 km altitude as well as the retrieval of key stratospheric and tropospheric species (level-2 data).
In this contribution we will demonstrate the performance of GLORIA-Lite with regard to level-2 data, consisting of retrieved altitude profiles of a variety of trace gases. We will show examples of selected results together with uncertainty estimations, altitude resolution as well as comparisons to atmospheric model simulations.
How to cite: Wetzel, G. and the GLORIA-Lite Team: Transcontinental stratospheric and upper tropospheric measurements with the new GLORIA-Lite instrument, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6306, https://doi.org/10.5194/egusphere-egu26-6306, 2026.
Total reactive nitrogen and its distribution between the gas and particle phases are key parameters for understanding the processes controlling the ozone budget in the polar winter stratosphere. Observations in the lowermost stratosphere reflect heterogeneous processes in the stratosphere above, leading to denitrification and later to nitrification below the vortex.
In the late winter of 2025, aircraft measurements were carried out as part of the ASCCI mission (Arctic Springtime Chemistry Climate Investigations) using the HALO (High Altitude and Long-Range Research Aircraft) research aircraft from Kiruna/Sweden and Oberpfaffenhofen/Germany. Tracer-tracer correlations were used to investigate the vertical redistribution of gas-phase total reactive nitrogen.
The winter of 2024/2025 was characterized by low temperatures in the polar vortex at the beginning of the winter, which enabled the formation of polar stratospheric cloud (PSC) particles. In March, the polar vortex collapsed. The observations of total reactive nitrogen in the lowermost stratosphere showed a mixture of different fingerprints of Arctic nitrogen chemistry. Elevated levels of reactive nitrogen are indicative of the evaporation of sinking PSC particles from the middle stratosphere. On the other hand, the sinking air from the polar vortex in late winter can show considerable denitrification.
During the ASCCI field measurement campaign in March, periods of elevated reactive nitrogen concentrations alternated with periods when concentrations were lower than would be expected for undisturbed chemistry. In some cases, more than 40 % of the observed total reactive nitrogen could be attributed to evaporating PSC particles, while in other flights air masses with a deficit of about 30 % of total reactive nitrogen were measured. At the end of the observation period, air masses with undisturbed background concentrations were probed.
These results from 2025 are compared with those obtained during the POLSTRACC aircraft mission in winter 2025/2016. Both missions show similar behavior regarding the redistribution of total reactive nitrogen in the lowermost stratosphere. However, lower values were observed during the most recent mission. The present observations are also compared with CLaMS model simulations.
How to cite: Ziereis, H., Hoor, P., Grooß, J.-U., Zahn, A., Stock, P., Lichtenstern, M., Engel, A., and Sinnhuber, B.-M.: Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere in late winter 2024/2025: Comparison with the findings during the cold winter 2015/2016, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10542, https://doi.org/10.5194/egusphere-egu26-10542, 2026.
The composition of the extratropical transition layer (ExTL), in particular the mixing ratios of ozone and water vapor, has a high impact on the radiative budget of the atmosphere. It is characterized by states originating from merging and mixing of tropospheric and stratospheric characteristics. The transport pathways into the ExTL governing this composition are (1) quasi-isentropic mixing at the subtropical jet with sources in the higher tropical troposphere, (2) diabatic downwelling as part of the overturning circulation with sources in the stratosphere and (3) diabatic transport and mixing across the extratropical tropopause with sources in the extratropical troposphere. The pathway (3) is partially suppressed by the high static stability above the tropopause, such that only strong diabatic processes are able to facilitate mixing between the troposphere and the ExTL.
Here we present in situ measurements taken during the TPEx campaign in summer 2024 over the North Sea, that provide evidence for turbulent mixing across the tropopause caused by strong wind shears above the jet stream. The measurements are complemented by Lagrangian analyses of ICON (icosahedral non‐hydrostatic) model simulations which yield atmospheric context and history of the probed airmasses. We use measurements of N2O, CO, O3 and H2O as well as ice particles to confirm cross-tropopause mixing with special emphasis on the simultaneous occurrence of ice particles in subsaturation and stratospheric chemical signature of the probed air mass. For the identification of turbulence as the responsible process we use high resolution acceleration measurements that are in good agreement with the occurrence and strength of simulated turbulence from ICON. The Lagrangian analysis shows suitable conditions for the turbulent mixing of cirrus particles an hour before the measurements.
This analysis confirms the occurrence of cross-tropopause mixing caused by shear induced turbulence at the jet stream. This process is sufficiently fast to transport ice particles into the strongly subsaturated lower stratosphere where they are sampled before complete evaporation. Thus this turbulent mixing represents a possible transport pathway of tropospheric air, and therefore a source of water, into the ExTL.
How to cite: Emig, N., Afchine, A., Bozem, H., Hoor, P., Krämer, M., Lachnitt, H.-C., Miltenberger, A., Tost, H., and Li, Y.: In situ observations of turbulent cross-tropopause mixing of cirrus particles at the jet stream over the North Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17925, https://doi.org/10.5194/egusphere-egu26-17925, 2026.
The composition of the UTLS plays a critical role in shaping Earth’s radiation budget, large-scale dynamics, and not least surface weather and air quality. Yet, its high spatiotemporal variability - driven by diverse transport and mixing pathways on different time scales - remains poorly quantified, limiting predictive capabilities.
In this study, we use a trace gas budget approach to quantify contributions of different transport and mixing pathways into the lowermost stratosphere (LMS). Especially the contribution of aged and partially chemically processed polar vortex air masses is difficult to determine due to isentropic transport and mixing with air masses originating in the extratropical troposphere.
We present an empirical approach using in-situ N2O, NOy, SF6 and CO measurements from three winter-to-spring aircraft campaigns using the HALO aircraft (ASCCI 2025, SouthTRAC 2019 and POLSTRACC 2016). We apply the contrasting trace gas lifetimes (N₂O: ~100 years; CO: ~months) to partition LMS air masses into three dynamically distinct fractions constituting of 1) a tropospheric fraction of air transported and mixed across the extratropical tropopause, 2) a stratospheric fraction, originating from diabatic downwelling and 3) a further separation of the stratospheric contribution accounting for vortex and extra-vortex air.
We present climatologies of the individual contributions, comparing the three campaigns. A focus is set on the evolution of the vortex fraction from winter to spring. Furthermore, robust validation against independent CH₄, SF6 and NOy measurements builds confidence in the framework’s ability to reconstruct distributions of other long-lived species from the three resolved fractions. We furthermore argue that the N2O-CO budget approach provides a quantitative, observation-based separation of LMS transport pathways, enabling improved evaluation of climate models and process studies.
How to cite: Hoor, P., Weyland, F., Bense, V., Bozem, H., Blumenroth, J., Emig, N., Kunkel, D., Lachnitt, H.-C., Engel, A., Joppe, P., Ort, L., Lauther, V., Ploeger, F., Sinnhuber, B.-M., Strobel, J., Volk, M., Ziereis, H., Zahn, A., and Riese, M.: Empirical air mass budgets in the winter-spring lower stratosphere from in-situ measurements during ASCCI, SouthTRAC and POLSTRACC missions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16654, https://doi.org/10.5194/egusphere-egu26-16654, 2026.
