Mixing plays a crucial role on redistributing radiation-actively trace species in the lower stratosphere. In particular, it is potentially the dominant effect for the formation of the extra-tropical transition layer (ExTL). However, various dynamical features can lead to mixing and the role of the small scale dynamics is not yet clear. In the extra-tropics, stratosphere troposphere exchange (STE) occurs frequently during baroclinic life cycles, e.g., in the vicinity of tropopause folds, cut-off lows, or stratospheric streamers. However, how the gravity waves (GWs) contributes to STE and mixing in the lower stratosphere is a research area with many open questions. A series of baroclinic life cycle experiments with the ICOsahedral Non-hydrostatic (ICON) general circulation model have been performed in order to study the impact of gravity waves on the transport and mixing between the upper troposphere and lower stratosphere (UTLS). Dry adiabatic experiments with varying horizontal and vertical resolution allowed to study the GW occurrence in relation to the model grid spacing. Moreover, the effect of varying initial conditions on the emergence of gravity waves is studied. We present analysis of the occurrence of GW in the various life cycles, their dependence on the model grid spacing and the initial conditions. Moreover, we present an analysis on the vertical shear of the horizontal wind associated with gravity waves and the potential for turbulence occurrence as a prerequisite for mixing. The focus of our analysis is the lowermost stratosphere and the effect of gravity wave induced mixing on the formation of the ExTL.

How to cite: Umbarkar, M. and Kunkel, D.: Gravity waves and shear in the lower stratosphere: idealized experiments of baroclinic life cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-633, https://doi.org/10.5194/egusphere-egu24-633, 2024.

Atmospheric moist convection has a considerable influence on the composition of the upper troposphere. Besides the strong effects on the atmospheric moisture budget, the high vertical velocities associated with deep convection lead to a redistribution of air masses, with especially large effects on the concentration of tracers with short atmospheric lifetimes. Even though the importance of convective transport is long known, this process remains a major source of uncertainty.

To diagnose the efficacy of convective tracer transport, we have developed a new modelling tool for simulations in global circulation models that rely on convection parameterisations, namely the convective exchange matrix. The exchange matrix basically links fractional contributions of inflow and outflow between any model level when convection is simulated for a given column. We apply this new tool in the chemistry climate model EMAC (ECHAM5 MESSy Atmospheric Chemistry) in order to characterise the transport of individual convective events. Beyond that, we present long-term statistics on vertical tracer transport into the upper troposphere to highlight the contribution of air masses originated at different heights to the upper tropospheric composition. This also includes the analysis of the regional and global distribution of convective outflow heights of the simulated convective clouds. Finally, we outline a potential application as a support tool for the analysis of upper troposphere aircraft observations in convectively active regions to backtrace the origin of the air masses and their overall contribution to the measured concentrations.

How to cite: Jeske, A., Smoydzin, L., Hoor, P., and Tost, H.: Modelling the changes in the upper tropospheric composition due to convective transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3980, https://doi.org/10.5194/egusphere-egu24-3980, 2024.

Transport in the stratosphere is characterized by upwelling in the tropics and downwelling in the extratropics, and these regions are separated by the so-called turnaround latitudes. In the winter hemisphere, a region of intense wave breaking (the ‘surf zone’) separates the tropics from the polar vortex. In the summer hemisphere, easterly winds do not allow for penetration of planetary waves into the middle and upper stratosphere.

Observational evidence of this global transport circulation comes from the shape of long-lived tracer contours. While the overturning circulation tends to steepen latitudinal gradients of tracers, large-scale stirring by wave breaking leads to quasi-horizontal mixing and thus flattens the gradients. The observed shape of tracer contours results from the combined effects of the two transport processes, and is therefore not trivially related to the turnaround latitudes or mixing diagnostics.

In this study we compare several tracer-based and dynamical-based diagnostics of the tropical width computed both from a CESM1-WACCM model simulation and from satellite observations  and reanalysis data. We find notable differences between the dynamical and tracer metrics particularly in the seasonality, with good correspondence only in the equinox seasons. We also examine the interannual variability and long-term trends.

How to cite: Ivaniha, O., Abalos, M., Calvo, N., S. Shah, K., Davis, S., and Stiller, G.: Diagnosing the dynamical and chemical stratospheric tropical width using model and observational data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20321, https://doi.org/10.5194/egusphere-egu24-20321, 2024.

There are two major pathways for the air in the tropical tropopause Layer (TTL) transport into the stratosphere: overshooting convection and slow large-scale updrafts. Here we present further evidence of the latter pathway, the large-scale slow upwelling over the Tropical Western Pacific (TWP) region. The TWP region is known for its coldest tropopause, considered to be the region where water vapour is freeze-dried to a minimum value based on saturated vapour pressure before it eventually enters the stratosphere through a slow ascent. During this process, persistent subvisible cirrus clouds (SVC) with an optical thickness of less than 0.3 are formed in the region and the presence of SVC is taken as an indication of transport into the stratosphere. An important consequence of the slow upwelling pathway over the TWP region is the vertical transport of trace constituents. This pathway will cause the trace gases to transport into the stratosphere and therefore affect the composition of the stratospheric air (Müller et al., 2023; Rex et al., 2014).  

Motivated by this, we used ground-based COMpact Cloud-Aerosol Lidar (COMCAL) observations in Koror, Palau (7.34°N, 134.47°E, in the heart of the Pacific warm pool) and combined trajectory model simulations by Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) to study the transport pathway, with a special focus on this slow large-scale updrafts over this key region. 

We present measurements of cirrus clouds by the gound-based COMCAL Lidar from 2018 to 2022. The annual cycle shows that cloud layer height peaks with the highest Cold Point Tropopause (CPT) in NH winter and reaches its minimum with the lowest CPT in NH summer.  Compared with similar cirrus cloud measurements obtained in other tropical sites, our measurements reveal that cirrus clouds detected over TWP are the coldest and highest. The prevalence of the coldest cirrus cloud layer detected over Palau corresponds to the cold trap, a region of exceptionally cold air, in UTLS over the TWP region. In order to build the relationship between the transport path in the UTLS region and measurements, we conducted trajectory analysis by HYSPLIT model simulations based on cirrus cloud layer measurements. Our measurements and analysis of trajectories reveal that only in winter with high supersaturation at the altitude where the SVCs are detected, the air masses are further dehydrated and slowly ascend into the stratosphere. This sheds light on the pathway of slow ascend of the tropospheric air entering into the stratosphere during the NH winter over the TWP region.

Reference:

K. Müller, I. Wohltmann, P. von der Gathen, and M. Rex, “Air mass transport to the tropical west pacific troposphere inferred from ozone and relative humidity balloon observations above palau,” EGUsphere, vol. 2023, pp. 1–37, 2023.
M. Rex, I. Wohltmann, T. Ridder, R. Lehmann, K. Rosenlof, P. Wennberg, D. Weisenstein, J. Notholt, K. Krüger, V. Mohr, and S. Tegtmeier, “A tropical west pacific oh minimum and implications for stratospheric composition,” Atmos. Chem. Phys., vol. 14, no. 9, pp. 4827–4841, 2014. 

How to cite: Sun, X., Palm, M., and Notholt, J.: Exploring the Slow Large-scale updraft Pathway into the Stratosphere over the Tropical Western Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10103, https://doi.org/10.5194/egusphere-egu24-10103, 2024.

The summertime Asian Monsoon (AM) is the single most important contributor to water vapor in the UTLS and overworld stratosphere. Much of that water comes from sublimating ice, but the life cycle of the condensate lofted by overshooting convection is not well understood. We report here on insights into that life cycle derived from the first in-situ measurements of water vapor isotopic composition over the Asian Monsoon. The Chicago Water Isotope Spectrometer (ChiWIS) flew on high-altitude aircraft in the monsoon center during the StratoClim (2017) campaign out of Nepal, and in monsoon outflow during ACCLIP (2022) out of South Korea. Both campaigns sampled a broad range of convective and post-convective conditions, letting us trace how convective ice sublimates, reforms, and leaves behind characteristic isotopic signatures. We use isotopic models, along with TRACZILLA backtrajectories and convective interactions derived from cloud-top products, to follow the evolving isotopic composition along flight paths in both campaigns. Results support the wide diversity of isotopic enhancement seen in both campaigns and show how temperature cycles downstream of convective events modify environmental isotopic compositions.

How to cite: Clouser, B., KleinStern, C., Singer, C., Sarkozy, L., Khaykin, S., Lykov, A., Viciani, S., Bianchini, G., D'Amato, F., Homeyer, C., Legras, B., Wienhold, F., and Moyer, E.: Microphysical Modeling of Water Isotopic Composition in the Asian Summer Monsoon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16002, https://doi.org/10.5194/egusphere-egu24-16002, 2024.

Stratospheric water vapor (SWV) plays an important role in Earth's climate. For example, variations in SWV levels can feedback onto global temperatures and climate patterns. However, projections of future changes in SWV still pose a difficult challenge for global climate models, mainly due to their dependence on a variety of highly uncertain factors ranging from chemical reactions to changes in the tropospheric and stratospheric circulation (Charlesworth et al. 2023).

Diverse factors lead to significant variations in SWV projections among CMIP6 climate models (Keeble et al., 2021). To tackle this issue, we aim to narrow down and comprehend model uncertainty in SWV projections by employing advanced, explainable machine learning (XML) frameworks. We build on recent work by Nowack et al. (2023) who used a linear XML approach to infer historical relationships between atmospheric temperature patterns and tropical lower SWV. Across CMIP models, they demonstrated that these relationships also hold under strong greenhouse gas forcing scenarios, opening up a direct link between present-day observations and future projections.

However, Nowack et al.'s work highlighted the challenge of interpreting the patterns learned by the statistical model. In this presentation, our goal is to decode these patterns, relating them to key physical mechanisms. Additionally, we aim to validate the reliability of prominent features from observations by testing equivalent patterns in selected climate models over longer timescales. To achieve this, we'll utilize advanced non-linear XML techniques like SHAP values combined with regression-tree methods to estimate feature importance.

The outcomes stress the importance of local temperature patterns near the targeted level in estimating SWV. Additionally, the impact of a two-month lag stands out comparing to one- and zero-month lags. Although CMIP dataset training period aligned with observations seems consistent, it varies across models. A longer training period results in a more stable and robust training pattern.

References:

Charlesworth, E., Plöger, F., Birner, T. et al. Stratospheric water vapor affecting atmospheric circulation. Nat Commun 14, 3925 (2023). https://doi.org/10.1038/s41467-023-39559-2

Keeble, J., Hassler, B., et al. Evaluating stratospheric ozone and water vapour changes in CMIP6 models from 1850 to 2100. Atmospheric Chemistry and Physics, 21(6), 5015-5061 (2021). https://doi.org/10.5194/acp-21-5015-2021

Nowack, P., Ceppi, P., Davis, S.M. et al. Response of stratospheric water vapour to warming constrained by satellite observations. Nat. Geosci. 16, 577–583 (2023). https://doi.org/10.1038/s41561-023-01183-6

How to cite: Amiramjadi, M. and Nowack, P.: Observational constraints on uncertainties in stratospheric water vapour projections: how to open the black-box with explainable machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17783, https://doi.org/10.5194/egusphere-egu24-17783, 2024.

The abundance of water vapor (H₂O) in the upper troposphere-lower stratosphere (UTLS) plays a critical role for the Earth's radiative balance. Yet, accurate measurements of H₂O in the UTLS are still very demanding, and lack sufficient spatial and temporal coverage. Therefore, frequent and long-term measurements with high precision and vertical resolution, as provided by balloon-borne instruments, are required. Furthermore, large discrepancies were often found between different measuring techniques, both in the field and in laboratory settings, indicating the difficulty of reliable H₂O measurements at the low concentrations of the UTLS.

Within the GCOS-funded Swiss H₂O-Hub project, we aim to address this challenge by continuously optimizing and validating the performances of two novel balloon-borne hygrometers, while exploiting their complementarity and vertical overlap with remote sensing techniques. Particularly, the balloon-borne laser spectrometer for UTLS water research ("ALBATROSS") [1,2], based on mid-IR laser absorption spectroscopy, and the Peltier-cooled frostpoint hygrometer (PCFH) [3], based on the chilled-mirror principle, are operated jointly with remote sensing measurements by the Raman lidar for meteorological observations (RALMO) [4] and the middle atmospheric water vapor radiometer (MIAWARA) [5]. The altitude coverages of RALMO (troposphere) and MIAWARA (stratosphere and mesosphere) offer two valuable overlap regions for the UTLS measurements by ALBATROSS and PCFH, while all together this set of instruments provides the unique possibility to monitor the altitude-resolved H₂O profile from ground to space.

Here we report on the results of the first measurement campaign of the project, conducted in summer 2023 at the MeteoSwiss Observatory Payerne. This included in total 7 balloon soundings with PCFH and ALBATROSS, along with simultaneous retrievals by RALMO and MIAWARA. All balloon-borne payloads were accompanied by a Vaisala RS41 radiosonde and a cryogenic frostpoint hygrometer (CFH) instrument as a reference. The data show very good agreement between the different techniques in the upper troposphere, and some limitations in the lower stratosphere. This is a promising result in the context of the ongoing reconception of the CFH method owing to its use of fluoroform (HFC-23) as cooling agent, which must be phased out due to its high global warming potential. Additionally, the MIAWARA measurements revealed the signature of the Hunga Tonga-Hunga Ha'apai volcanic eruption on H₂O in the upper stratosphere and mesosphere.

Further measurement campaigns, planned for the upcoming years, will allow to refine the performances of all instruments under UTLS conditions, as well as to continue monitoring the interannual variability and trends in upper air H₂O over Switzerland.

[1] Graf et al., Atmos. Meas. Tech., 14, 1365–1378, 2021.

[2] Brunamonti et al., Atmos. Meas. Tech., 16, 4391–4407, 2023.

[3] Jorge, Diss. ETH No. 26352, 2019.

[4] Dinoev et al., Atmos. Meas. Tech., 6, 1329–1346, 2013.

[5] Straub et al., Atmos. Meas. Tech., 3, 1271–1285, 2010.

How to cite: Brunamonti, S., Poltera, Y., Wienhold, F., Romanens, G., Martucci, G., Bell, A., Filinis, A., Matthey, R., Murk, A., Haefele, A., Peter, T., Emmenegger, L., Tuzson, B., and Stober, G.: Altitude-resolved measurements of water vapor from ground to space: the Swiss H2O-Hub , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7994, https://doi.org/10.5194/egusphere-egu24-7994, 2024.

Water vapor (H₂O) is a key trace gas in the upper troposphere (UT) and lowermost stratosphere (LMS) because it plays a crucial role in the Earth’s climate. However, accurate knowledge of the amount of H₂O in this region is still insufficient due to the difficulty and lack of in-situ and space-borne measurements. This study presents a new methodology to compile H₂O climatologies for the LMS from simple, extensive measurements aboard passenger aircraft between 1994 and now within the IAGOS infrastructure covering in the extratropical UT/LMS.

To this end, a statistical comparison of mean H₂O in sampling bins of air relative to the tropopause is performed between a dataset from ≈60.000 flights applying the IAGOS-MOZAIC and -CORE simple sensor and a dataset of only ≈500 flights using the more sophisticated IAGOS-CARIBIC instrument. We find good agreement in the UT, but a systematic positive bias in the simple measurements in the LMS. To account for this bias, mean water vapor values of the simple sensor are adjusted to the sophisticated observations based on a new statistical approach. After applying this new method, the LMS water vapor measurements are in good agreement. The extensive H₂O dataset from the simple IAGOS sensor can now be used to produce highly resolved water vapor climatologies for the climatically sensitive LMS region. With the adjusted IAGOS H₂O data, water vapor transport processes and (de-)hydration of air masses in the extratropical UT/LMS are analysed through backward trajectories and microphysical CLaMS-ICE simulations.

How to cite: Konjari, P., Rolf, C., Krämer, M., Rohs, S., Li, Y., Bönisch, H., Zahn, A., and Petzold, A.: Water vapor variability in the extratropical UTLS from combined passenger and reasearch aircraft measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7752, https://doi.org/10.5194/egusphere-egu24-7752, 2024.

The June 1991 Pinatubo and January 2022 Hunga Tonga-Hunga Ha’apai (HTHH) are the two most explosive tropical volcanic eruptions in 30 years. The two, one with high sulfur dioxide (SO₂) emission and the other high water vapour (H₂O) emission, provide two different paradigm cases to understand the post-eruption tropical transport. Here we use the VolMIP short-term climate-response experiments with the UK Earth System Model (UKESM1) to explore the post-eruption tropical H₂O transport after a high-SO₂ case.

Aerosol-absorptive heating causes peak SWV increases of 17% (~1 ppmv) and 10% (0.5 ppmv) at 100 hPa and 50 hPa, at ~18 months and ~23 months post-eruption, respectively. The main SWV increase occurs only after the descending aerosol heating reaches the tropopause, suggesting a key role for aerosol microphysical processes (sedimentation rate). This increase is strongly modulated by ENSO variability. With a consistent biased Quai-Biannual Oscillation (QBO) towards the westerly phase, tropical upwelling under different ENSO conditions strongly mediates this effect.

We will also discuss the observed tropical H₂O entry after HTHH eruption. With a triple-dip La Niña background and the strong H₂O-induced cooling in the lower stratosphere, the tropical H₂O transport through 2022/23 is dominated by the volcanic forcing and the sea surface temperature. An up-to-date observation from satellite data is used for analysing this unique HTHH volcanic forcing, while future modelling is needed for a tangible impact.

How to cite: Zhou, X., Zhang, W., Mann, G., Feng, W., Dhomse, S., and Chipperfield, M.: Post-eruption tropical water vapour transport: Pinatubo and Hunga Tonga-Hunga Ha’apai, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9179, https://doi.org/10.5194/egusphere-egu24-9179, 2024.

The Asian summer monsoon is linked to deep convection over the Indian subcontinent and to an anticyclonic flow that extends from the upper troposphere into the lower stratosphere region. This allows both gas-phase aerosol precursors and aerosol particles from surface sources to reach the stratosphere. The horizontal transport out of the Asian monsoon anticyclone towards the extratropical lower stratosphere of the Northern Hemisphere is the focus of this study.

We present an annual record of Lidar observations at AWIPEV in Ny-Ålesund. The data record is free from obvious layers like polar stratospheric clouds, volcanic eruptions or forest fires. Nevertheless, the lower stratosphere reveals an annual cycle with lower backscatter values in winter and spring and higher backscatter values in summer and autumn. The Lidar measurements have been linked to backward trajectory calculations and simulations of artificial surface origin tracers with the three-dimensional Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations show that air masses observed above Ny-Ålesund have been transported from surface sources in Asia into the Arctic lower stratosphere. Thus, the increased backscatter values during summer and autumn can be explained by transport of aerosol particles from the Asian summer monsoon into the Arctic lower stratosphere.

How to cite: Tritscher, I., Graßl, S., Ritter, C., and Vogel, B.: Aerosol Transport from the Asian Summer Monsoon into the Arctic Lower Stratosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8648, https://doi.org/10.5194/egusphere-egu24-8648, 2024.

Convective processes play a critical role in the atmosphere’s energy balance. In high updraft regimes, turbulent and diabatic processes redistribute moisture, heat, and aerosols, which lead to cloud formation affecting the radiation budget of the atmosphere.

During the HALO airborne CIRRUS-HL mission in summer 2021, the outflow of a convective system over Northern Italy was probed at different altitudes. The system had an overshooting top accompanied by lightning and icing conditions. A suit of in-situ (aerosol, cloud probes, trace gases) and remote sensing (Lidar) instruments deployed on the research aircraft HALO combined with satellite observations  provided the opportunity to investigate the system from different perspectives.

The in-situ H₂O -O₃ correlation revealed unexpected insights in the extra-tropical tropopause transition layer (exTL), characterized by enhanced water vapor  and ice crystal number in the exTL. The convective system penetrated into the exTL with O₃ up to 450ppb. In contrast, the CO -O₃ correlation shows minor influence, indicating that this convection event was little impacted by large scale mixing processes.

The potential temperature around the upper cloud edge ranged from 330K to 350K. At higher potential temperatures (377-392K) no H₂O enhancements were observed. Nevertheless, the irreversible injection of water vapor could lead to transport of moisture into the lower stratosphere in the following hours and days downwind of the system.

Within the upper cloud part and in the vicinity of the cloud, water vapor and ice crystals are enhanced in comparison to the undisturbed surrounding, as visible in the Lidar curtain. Both, water vapor and ice crystals influence the hydration and dehydration of the exTL. While larger ice crystals sediment, smaller ice crystals may sublimate and contributing to a locally enhanced water vapor budget. Our measurements show, that strong convective systems can act as a potential moisture source of the lowermost stratosphere.  

How to cite: Tomsche, L., de la Torre Castro, E., Dischl, R., Hahn, V., Harlaß, T., Jurkat-Witschas, T., Kaufmann, S., Krüger, K., Marsing, A., Mayer, J., Obersteiner, F., Roiger, A., Wirth, M., Zahn, A., Zöger, M., and Voigt, C.: Injection of water vapor into the stratosphere in a convective system above Europe – a measurement perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9974, https://doi.org/10.5194/egusphere-egu24-9974, 2024.

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is a limb-imaging Fourier-Transform spectrometer (iFTS) providing mid-infrared spectra with high spectral sampling (0.0625 cm^-1 in the wavelength range 780-1400 cm^-1). GLORIA, a demonstrator for the Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT, one of the remaining two candidates for the ESA Earth Explorer 11 mission) was deployed on the Russian M55 Geophysica and is still being deployed on HALO, the German high-altitude research aircraft. In order to enhance the vertical range of GLORIA to observations in the middle stratosphere albeit still reaching down to the middle troposphere, the instrument was adapted to measurements from stratospheric balloon platforms. GLORIA-B performed its first flight from Kiruna (northern Sweden) in August 2021 and its second flight from Timmins (Ontario/Canada) in August 2022 in the framework of the EU Research Infrastructure HEMERA.

The objectives of GLORIA-B observations for these campaigns have been its technical qualification and the provision of a first imaging hyperspectral limb-emission dataset from 5 to 36 km altitude. Further, scientific objectives, which are, amongst many others, the diurnal evolution of photochemically active species belonging to the nitrogen (e.g. N₂O₅, NO₂), chlorine (e.g. ClONO₂), and bromine (BrONO₂) families are discussed.

In this contribution we demonstrate the performance of GLORIA-B with regard to level-2 data of the flight in August 2021, 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 long-lived tracer comparisons to accompanying in-situ datasets. In addition, diurnal variations of photochemically active gases are compared to simulations of the chemistry climate model EMAC. Calculations largely reproduce the temporal variations of the species observed by GLORIA-B.

How to cite: Wetzel, G., Johansson, S., Friedl-Vallon, F., Höpfner, M., Catoire, V., Engel, A., Gulde, T., Jacquet, P., Kirner, O., Kleinert, A., Kretschmer, E., Laube, J., Maucher, G., Neubert, T., Nordmeyer, H., Piesch, C., Preusse, P., Schuck, T., Ungermann, J., and Woiwode, W.: Stratospheric and upper tropospheric measurements of long-lived tracers and photochemically active species of the nitrogen, chlorine, and bromine families with GLORIA-B, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1519, https://doi.org/10.5194/egusphere-egu24-1519, 2024.

The Southern Hemisphere has long been underrepresented in high altitude in situ trace gas measurements. This leads to significant uncertainties in understanding and predicting their effects on stratospheric chemistry and circulation. In a pioneering effort, a balloon campaign took place in Beaufort West (32.3540 ˚S, 22.5833˚E) in early 2023, the first of its kind in South Africa. Two different sensor packages were launched during six balloon flights and reached altitudes up to 33 km. These balloon flights provided unique measurements of key atmospheric constituents, including water vapor, ozone, CO2, CH4, CO, SF6, and various ozone depleting substances.

Here, we present an overview of these findings, along with a comparison with similar data from the Northern Hemisphere, and with data from the Chemical Lagrangian Model of the Stratosphere (CLaMS). A first notable result revealed the sampling of tropical air masses with unusually low water vapor mixing ratios [2.1 ppmv] around the upper troposphere and lower stratosphere (UTLS) region. A follow-up campaign is planned for 2024 to further enrich the dataset and enhance insights into stratosphere-troposphere exchange dynamics.

How to cite: Blazaki, K., Rolf, C., Laube, J., Ploeger, F., Voet, F., Geldenhuys, M., Mkololo, T., Labuschagne, C., and Labuschagne, P.: Trace gas balloon borne in situ measurements in the Southern Hemisphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16047, https://doi.org/10.5194/egusphere-egu24-16047, 2024.

The Hunga Tonga-Hunga Ha'apai (HTHH) volcanic eruption on January 15th 2022 injected unprecedented amounts of H₂O as well as modest amounts of aerosol precursor sulfur dioxide into the stratosphere. Satellite observations have shown strong stratospheric cooling and circulation changes throughout 2022. Large ozone reduction in the Southern Hemisphere wintertime midlatitudes and springtime Antarctic ozone losses are also observed. In addition, a chemistry-climate model (WACCM) can track the evolving HTHH plumes and capture observed responses to the volcanic eruption till the end of 2023. We will present a comprehensive update regarding the perturbations in stratospheric composition and their effects on large-scale circulation since the HTHH eruption. We will also examine the longer-term evolution of HTHH H₂O burden and will quantify the contributions of polar dehydration, stratosphere-troposphere exchange of mass, and chemical process.

How to cite: Wang, X., Randel, W., Yu, W., Zhu, Y., and Zhang, J.: An update on the perturbations in stratospheric composition and climate following the Hunga Tonga-Hunga Ha'apai volcanic eruption, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14118, https://doi.org/10.5194/egusphere-egu24-14118, 2024.

We present trace gas and aerosol measurements obtained by the airborne infrared imaging limb sounder GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) that has been operated onboard HALO (High Altitude and Long Range Research Aircraft) during the PHILEAS campaign (Probing High Latitude Export of air from the Asian Summer Monsoon ; August-September 2023). We measured outflow from the Asian Monsoon above the North Pacific, and the Mediterranean, as well as pollution plumes from biomass burning events in North America. In this contribution, we present retrieval results of ammonia (NH₃), solid ammonium nitrate and other pollution trace gases (e.g. PAN) as two-dimensional distributions with high vertical resolution, derived from GLORIA observations in the UTLS (Upper Troposphere Lower Stratosphere).

Our GLORIA observations reveal considerable abundances of solid ammonium nitrate, which is connected to the Asian Monsoon, in the lower stratosphere outside the Asian Monsoon Anticyclone. Measurements from a previous airborne campaign within the Asian Monsoon (StratoClim 2017) showed large enhancements of NH₃ (precursor of ammonium nitrate), and solid ammonium nitrate in the Asian Monsoon upper troposphere.

Further, GLORIA measured UTLS air masses heavily influenced by biomass burning during PHILEAS. Due to the ability of GLORIA to measure pollution trace gases with different atmospheric life times, we are able to estimate the age of individual plumes, based on their chemical composition. As an example, we show measurements from a PHILEAS flight, influenced by aged and fresh pollution.

In a first analysis, we compare our measurements with atmospheric models to examine air mass origins. In particular, we use artificial tracers calculated by the ICON-ART (ICOsahedral Nonhydrostatic - Aerosol and Reactive Trace gases), one of the models that was also used in forecast configuration for flight planning.

How to cite: Johansson, S., Wetzel, G., Höpfner, M., Braesicke, P., Friedl-Vallon, F., Glatthor, N., Kleinert, A., Neubert, T., Preusse, P., Riese, M., Sinnhuber, B.-M., Ungermann, J., and Versick, S. and the the GLORIA team: Ammonium nitrate and biomass burning pollution in the UTLS: First results from GLORIA airborne measurements of Asian Monsoon outflow during the PHILEAS campaign 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9585, https://doi.org/10.5194/egusphere-egu24-9585, 2024.

Ammonia emissions in south-east Asia are a significant contributor to air pollution. This pollution, through convective transport by the Asian monsoon anticyclone, can initiate new particle formation events in the upper troposphere and the development of the Asian Tropopause Aerosol Layer (ATAL). Despite the acknowledged influence of ammonia emissions and particulate ammonium on upper tropospheric air pollution and cloud formation, a comprehensive understanding of the ATAL remains limited. A substantial knowledge gap persists regarding its origin, maintenance, chemical composition, and the climatic implications of these factors. We use the EMAC chemistry-climate model to study the influence of ammonia emissions on nucleation mechanisms contributing to the development of the ATAL. Through the integration of observational data with model simulations and the application of parameterisations from the CERN CLOUD experiment, we investigate the conditions sustaining the ATAL and explore its climatic implications. The findings suggest that ammonia emissions enhance nucleation rates in the ATAL, resulting in up to 70% increases in cloud condensation nuclei (CCN) concentrations. A diurnal cycle analysis reveals that these new particle formation mechanisms mostly occur during daylight after convection events uplifting precursor gases. Our findings enhance the understanding of the impact of anthropogenic emissions on CCN formation processes and their implications for climate in the regions characterised by high ammonia emissions.

How to cite: Xenofontos, C., Kohl, M., Pozzer, A., Lelieveld, J., and Christoudias, T.: Modelling the Impact of Ammonia Emissions on New Particle Formation in the Asian Monsoon Upper Troposphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2061, https://doi.org/10.5194/egusphere-egu24-2061, 2024.

The Asian tropopause aerosol layer (ATAL) was thicker than other regions at the same latitude due to the strong confinement effect of the Asian summer monsoon anticyclone. The size distribution of the particles remains unknown and requires further investigation. Aerosol profiles were measured by balloon-borne sensors (Cobald, POPS) launched from Lhasa (29.66 °N, 91.14 °E), Golmud (36.48 °N, 94.93 °E), and Kunming (25.01 °N, 102.65 °E) China, from 2019 to 2022 over the Tibetan Plateau at the part of the SWOP (Sounding Water vapor, Ozone, and Particle) campaign. The measurements combined with backward trajectories show that the volcano Raikoke (48°N, 153°E) in June 2019 and the dust storm in March 2021 over the Taklamakan desert have significantly impacted on the aerosol layer in the upper troposphere and lower stratosphere (UTLS). The backscatter ratio at wavelength 455 nm of the volcanic plume and dust storm was higher than the ATAL. The particle number density in the volcanic plume is 30 cm^-3, higher than the ATAL and dust storm (10 cm^-3) in the lower stratosphere, with particle diameters centered around 0.42-3.4 μm. In contrast, the dust storm has a high density of up to 100 cm^-3 in the upper troposphere with particle diameters less than 0.42 μm.

How to cite: Li, D., Bian, J., and Bai, Z.: Aerosol perturbation in the UTLS region over the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7205, https://doi.org/10.5194/egusphere-egu24-7205, 2024.

The Asian Monsoon Anticyclone (AMA) is of global importance because of its role in transporting pollutants over long distances through dynamic processes such as eddy shedding. Its impact extends beyond the Asian region to Europe and North America. To study the composition of the extratropical Upper Troposphere and Lower Stratosphere (UTLS) under the influence of the export of AMA air masses, airborne measurements were conducted on board the research aircraft HALO from Anchorage (Alaska) in August/September 2023.
Our instrument ERICA (ERC Instrument for the Chemical composition of Aerosols) was a part of this mission, with the objective to analyze the chemical composition of particles in the outflow region of the AMA. ERICA combines the aerosol mass spectrometer ERICA-AMS, which is designed for bulk measurements of aerosol particles, and the single-particle mass spectrometer ERICA-LAMS.
The objective of our study was to determine whether aerosol particles are transported from the AMA into the extratropical UTLS region. Measurements of methane and dichloromethane were employed to identify air masses originating from the AMA. To distinguish between the tropospheric and stratospheric air masses, ozone and nitrous oxide were utilized. Our results demonstrate that UTLS air masses exhibit elevated concentrations of ammonium, nitrate and organic matter based on ERICA-AMS data, along with enhanced methane and dichloromethane mixing ratios. These results are consistent with previous high-altitude measurements in the center of the AMA, showing the presence of enhanced ammonium nitrate and organic particle concentrations (Appel et al., 2022). These findings lead to the conclusion that particles from the AMA were transported from the center of the AMA into the extratropical UTLS region. Initial data analysis suggests a quasi-horizontal isentropic transport of these particles from subtropical to extratropical regions.

How to cite: Ekinci, F., Köllner, F., Eppers, O., Appel, O., Brauner, P., Dragoneas, A., Molleker, S., Lauther, V., Volk, C. M., Hoor, P., Schneider, J., and Borrmann, S.: Transport of ammonium nitrate and organic aerosol into the extratropical stratosphere associated with the Asian monsoon outflow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9406, https://doi.org/10.5194/egusphere-egu24-9406, 2024.

The UTLS (upper troposphere and lower stratosphere) is a region relevant for weather and climate forecasts as well as for chemical aspects in the troposphere and stratosphere. For these reasons many observations have been conducted in recent years. Comparing data of different measurement campaigns is sometimes a bit difficult, especially for the supporting model data. Often, different model types or grid widths are used or one variable is missing or calculated with different methods.

The main goal of this work is to create a dataset of multiple measurement campaigns with consistent meteorological parameters and supporting analysis.

In a first step, we use ERA5 (European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5) data with a horizontal grid width of 1° and a time resolution of 6 hours as well as CLaMS (Chemical Lagrangian Model of the Stratosphere) data. In a second step, we also use ERA5 data with a time resolution of 1 hour and a horizontal grid width of 0.3°.The dataset contains several native and derived meteorological (e.g., potential vorticity, equivalent latitude) variables and tropopause diagnostics (e.g., height of laps rate and several dynamical tropopauses) from ERA5. To include information on transport and time scales artificial regional tracers (e.g., O₃, CO) and age spectrum variables (e.g., E90 tracer, mean age) from CLaMS are used. The interpolation is carried out for multiple campaigns i.e., for several airborne and balloon campaigns on different platforms.

To introduce the dataset, we also present a few possible application examples in relation to the distribution of trace gases and other species. Furthermore, we present comparisons of different model data and measurement data.

How to cite: Lachnitt, H.-C., Plöger, F., Kunkel, D., and Hoor, P. and the Campaign PI’s: Observational data synthesis (TPChange Central Project Z01), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16776, https://doi.org/10.5194/egusphere-egu24-16776, 2024.

Turbulence in the tropical stratosphere affects the vertical transport of aerosols and gases, with implications for global atmospheric chemistry and the radiative budget of the Earth. However, it is unresolved in global models of the atmosphere, and turbulence parameterizations have not been evaluated within this region. Observational estimates of vertical mixing, including turbulent mixing, in the tropical stratosphere vary widely. We use two decades of high vertical resolution (10 m) radiosonde data from three near-equatorial sites in the tropical West Pacific to quantify the occurrence of stratospheric turbulent layers of at least 200 m thickness, and investigate its temporal and spatial variability, using subcritical Richardson number as a proxy for turbulence. Our estimates of upper tropospheric and lower stratospheric turbulence frequency agree well with published estimates from aircraft data in the same region. We find that stratospheric turbulence typically occurs within downward propagating Kelvin waves, and is most common (3.3% occurrence) right before the quasi biennial oscillation (QBO) phase switches from negative to positive, which coincides with a maximum in Kelvin wave activity. It is least common (0.3% occurrence) during the negative phase of the QBO. Thus, the frequency of tropical stratospheric turbulence varies over a factor of ten depending on the phase of the QBO.

How to cite: Atlas, R., Podglajen, A., and Wilson, R.: Turbulence in the tropical stratosphere, Kelvin waves, and the quasi-biennial oscillation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14999, https://doi.org/10.5194/egusphere-egu24-14999, 2024.