Bärbel Vogel

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 limiting in the UTLS as a highly variable transition region between the troposphere and stratosphere. We here present a new and unique dataset obtained from weather balloon-based sensors across the summer 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 flights, 37 focused on trace gases, with 18 near-simultaneous double launches quantifying the vertical distribution of water vapour and ozone as well as multiple halogenated species; thus, enabling access to the temporal evolution of many key UTLS components over a period of about five months. We here focus mainly on ozone-depleting chlorinated very short-lived substances (Cl-VSLSs) with model-based surface-origin tracers to investigate the source regions of the air masses. In particular, we investigate the influence of the Asian Summer Monsoon region – a source of Cl-VSLSs such as CH2Cl2 – as the upper-level anticyclone exports air masses into the global northern hemispheric UTLS during the monsoon season. We find that the “background” lower stratospheric composition in summer and autumn is clearly impacted by the Asian monsoon-related stratospheric entrance pathway, and for Cl-VSLSs much more so than estimated in previous studies.

Dichloromethane (CH₂Cl₂) is emitted mainly anthropogenically and suspected to delay stratospheric ozone recovery. We present in detail the first retrievals of mesoscale 2D distributions of CH₂Cl₂ from infrared limb observations. The airborne remote sensing instrument GLORIA-AB (Gimballed Limb Observer for Radiance Imaging of the Atmosphere, hereinafter “GLORIA”) was deployed aboard the German research aircraft HALO during the PHILEAS campaign in August and September 2023 to study the outflow of the Asian Summer Monsoon (ASM). During long-range flights from Alaska, GLORIA observed filaments with elevated CH₂Cl₂ above the North Pacific, Canada and Alaska. Filaments with horizontal extents along the flight track of up to ~1000 km and CH₂Cl₂ volume mixing ratios of locally up to ~400 pptv were observed in the free troposphere, corresponding to levels more than six times higher than the northern hemispheric background for that season. Moderate CH₂Cl₂ enhancements were detected locally also in air masses with characteristics of the extra-tropical lowermost stratosphere. We applied new high-resolution CH₂Cl₂ spectroscopic data, resulting in ~11 % lower volume mixing ratios than in previous analyses using commonly available absorption cross sections. The GLORIA measurements are consistent with in situ observations on HALO by HAGAR-V and GhOST. Using back-trajectory analysis and surface-origin tracers by the CLaMS model, observed filaments are traced back to the ASM region and potential source regions are identified. Mesoscale filaments are shown to rapidly transport substantial amounts of CH₂Cl₂ from the ASM across the North Pacific into the Northern Hemisphere Upper Troposphere and Lower Stratosphere (UTLS).

Locating the boundary of the Asian summer monsoon anticyclone (ASMA) in the upper troposphere-lower stratosphere (UTLS) (350 K–410 K potential temperature) is important for analyzing the transport of pollutants by the ASMA into the stratosphere. The definition of the ASMA boundary highly impacts the information about the anticyclone's behavior and affects the results when studying its spatio-temporal variability in particular regarding inferred trends over the last decades. In this work, we quantify the differences between methodologies based on potential vorticity (PV) and the Montgomery streamfunction (MSF) used to determine the location of the ASMA boundary. In addition, we apply the unsupervised machine learning spectral clustering method which combines both the PV and MSF fields to derive the location of the boundary. By analyzing the centroid position and boundary geometry for July and August 2023, we demonstrate that at 380 K, the PV-based, MSF-based, and spectral clustering methods exhibit good agreement during the Asian summer monsoon season. We find that the MSF-based method tends to incorporate the eastward-shed eddy over the Pacific around 140° E into the main anticyclone, whereas the PV-based method tends to separate it from the main body. Spectral clustering, however, can exhibit either behavior during the season. Finally, we compare the derived boundaries with satellite measurements of carbon monoxide, showing that the PV-based and MSF-based methodologies successfully enclose the core of elevated carbon monoxide levels as effectively as the spectral clustering method.

Dichloromethane (CH₂Cl₂) is emitted mainly anthropogenically and suspected to delay stratospheric ozone recovery. We present in detail the first retrievals of mesoscale 2D distributions of CH₂Cl₂ from infrared limb observations. The airborne remote sensing instrument GLORIA-AB (Gimballed Limb Observer for Radiance Imaging of the Atmosphere, hereinafter “GLORIA”) was deployed aboard the German research aircraft HALO during the PHILEAS campaign in August and September 2023 to study the outflow of the Asian Summer Monsoon (ASM). During long-range flights from Alaska, GLORIA observed filaments with elevated CH₂Cl₂ above the North Pacific, Canada and Alaska. Filaments with horizontal extents along the flight track of up to ~1000 km and CH₂Cl₂ volume mixing ratios of locally up to ~400 pptv were observed in the free troposphere, corresponding to levels more than six times higher than the northern hemispheric background for that season. Moderate CH₂Cl₂ enhancements were detected locally also in air masses with characteristics of the extra-tropical lowermost stratosphere. We applied new high-resolution CH₂Cl₂ spectroscopic data, resulting in ~11 % lower volume mixing ratios than in previous analyses using commonly available absorption cross sections. The GLORIA measurements are consistent with in situ observations on HALO by HAGAR-V and GhOST. Using back-trajectory analysis and surface-origin tracers by the CLaMS model, observed filaments are traced back to the ASM region and potential source regions are identified. Mesoscale filaments are shown to rapidly transport substantial amounts of CH₂Cl₂ from the ASM across the North Pacific into the Northern Hemisphere Upper Troposphere and Lower Stratosphere (UTLS).

Dichloromethane (CH2Cl2) is emitted mainly anthropogenically and suspected to delay stratospheric ozone recovery. We present in detail the first retrievals of mesoscale 2D distributions of CH2Cl2 from infrared limb observations. The airborne remote sensing instrument GLORIA-AB (Gimballed Limb Observer for Radiance Imaging of the Atmosphere, hereinafter “GLORIA”) was deployed aboard the German research aircraft HALO during the PHILEAS campaign in August and September 2023 to study the outflow of the Asian Summer Monsoon (ASM). During long-range flights from Alaska, GLORIA observed filaments with elevated CH2Cl2 above the North Pacific, Canada and Alaska. Filaments with horizontal extents along the flight track of up to ~1000 km and CH2Cl2 volume mixing ratios of locally up to ~400 pptv were observed in the free troposphere, corresponding to levels more than six times higher than the northern hemispheric background for that season. Moderate CH2Cl2 enhancements were detected locally also in air masses with characteristics of the extra-tropical lowermost stratosphere. We applied new high-resolution CH2Cl2 spectroscopic data, resulting in ~11 % lower volume mixing ratios than in previous analyses using commonly available absorption cross sections. The GLORIA measurements are consistent with in situ observations on HALO by HAGAR-V and GhOST. Using back-trajectory analysis and surface-origin tracers by the CLaMS model, observed filaments are traced back to the ASM region and potential source regions are identified. Mesoscale filaments are shown to rapidly transport substantial amounts of CH2Cl2 from the ASM across the North Pacific into the Northern Hemisphere Upper Troposphere and Lower Stratosphere (UTLS).

Locating the boundary of the Asian summer monsoon anticyclone (ASMA) in the upper troposphere-lower stratosphere (UTLS) (350 K–410 K potential temperature) is important for analyzing the transport of pollutants by the ASMA into the stratosphere. The definition of the ASMA boundary highly impacts the information about the anticyclone's behavior and affects the results when studying its spatio-temporal variability in particular regarding inferred trends over the last decades. In this work, we quantify the differences between methodologies based on potential vorticity (PV) and the Montgomery streamfunction (MSF) used to determine the location of the ASMA boundary. In addition, we apply the unsupervised machine learning spectral clustering method which combines both the PV and MSF fields to derive the location of the boundary. By analyzing the centroid position and boundary geometry for July and August 2023, we demonstrate that at 380 K, the PV-based, MSF-based, and spectral clustering methods exhibit good agreement during the Asian summer monsoon season. We find that the MSF-based method tends to incorporate the eastward-shed eddy over the Pacific around 140° E into the main anticyclone, whereas the PV-based method tends to separate it from the main body. Spectral clustering, however, can exhibit either behavior during the season. Finally, we compare the derived boundaries with satellite measurements of carbon monoxide, showing that the PV-based and MSF-based methodologies successfully enclose the core of elevated carbon monoxide levels as effectively as the spectral clustering method.

This study examines how Asian Summer Monsoon (ASM) outflow perturbs the chemical composition of background aerosol in the extratropical lower stratosphere (ExLS). We analyze the summer-to-autumn transition in aerosol chemical composition using in-situ measurements from the ERICA instrument acquired during the PHILEAS aircraft campaign in August-September 2023 over the North Pacific, Alaska, northern Canada, and northern Europe. We observe an enrichment of ammonium and nitrate aerosol in the ExLS background air masses from summer to autumn, particularly at potential temperatures above 370 K (∼ 13 km). Concurrently, the fraction of NO ⁺ -rich particles in the ExLS increases from August to September 2023. The corresponding mass spectra indicate internally mixed particles containing nitrate, sulfate, ammonium, and organic matter. Simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) show this seasonal transition is associated with the intrusion of relatively young air masses (<3.5 months old) originating from South Asia and the western Pacific into the ExLS, especially in autumn. These particles persist in the lower stratosphere for weeks up to months and undergo chemical aging. This aging is reflected by an observed increasing oxidative degree of organic matter, a decreasing nitrate-to-sulfate ratio, and an increasing ammonium-to-nitrate ratio, suggesting progressive sulfate incorporation and particle nitrate depletion. Overall, our results demonstrate that the ASM outflow can substantially shape ExLS background aerosol composition through the convective uplift, subsequent transport, and aging of ammonium- and nitrate-rich air masses from polluted surface regions, with important implications for stratospheric heterogeneous chemistry and aerosol-climate interactions.

Mixing of air between compartments of the atmosphere is fundamental to atmospheric composition. Such mixing is commonly studied using tracer-tracer correlations. We generalize this approach by statistical classification methods using several tracers to quantify mixing. This paper presents a matching flight-experiment of a filament of Asian monsoon air in the Upper Troposphere/Lower Stratosphere (UTLS) off the Alaskan coast by two flights of the High Altitude and Long Range research aircraft (HALO) conducted during the “Probing High Latitude Export of air from the Asian Summer Monsoon (PHILEAS)” campaign. The 3-D structure of the filament was revealed by tomographic observations by the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) of five trace species. The observed tracer mixing ratios show evidence for a tropopause folding linked to a Rossby wave breaking event. Using a Gaussian mixture model to cluster our observations by similarity we identify five classes of air masses: tropospheric air (both continental and maritime), Asian Summer Monsoon outflow (ASMO), mixed air and stratospheric air. Trajectory calculations are carried out to identify air masses which are observed in both flights. The unique 3-D observations allow us to reveal the spatial structure of the mixing processes. Particularly, mixing of ASMO air directly with stratospheric air and into the UTLS are shown. Comparing the classification to simulated artificial surface-origin tracers in the Chemical Lagrangian Model of the Stratosphere (CLaMS), we find strong evidence for distinctly correlated air masses to originate within different source regions within the Asian monsoon region.