Age of stratospheric air is a well established metric for the stratospheric transport circulation. Rooted in a robust theoretical framework, this approach offers the benefit of being deducible from observations of trace gases. Given potential climate-induced changes, observational constraints on stratospheric circulation are crucial. In the past two decades, scientific progress has been made in three main areas: (a) Enhanced process understanding and the development of process diagnostics led to better quantification of individual transport processes from observations and to a better understanding of model deficits. (b) The global age of air climatology is now well constrained by observations thanks to improved quality and quantity of data, including global satellite data, and through improved and consistent age calculation methods. (c) It is well established and understood that global models predict a decrease in age, that is, an accelerating stratospheric circulation, in response to forcing by greenhouse gases and ozone depleting substances. Observational records now confirm long-term forced trends in mean age in the lower stratosphere. However, in the mid-stratosphere, uncertainties in observational records are too large to confirm or disprove the model predictions. Continuous monitoring of stratospheric trace gases and further improved methods to derive age from those tracers will be crucial to better constrain variability and long-term trends from observations. Future work on mean age as a metric for stratospheric transport will be important due to its potential to enhance the understanding of stratospheric composition changes, address climate model biases, and assess the impacts of proposed climate geoengineering methods.
How to cite: Garny, H. and the Age of Air ISSI Team: A review on Age of Stratospheric Air: Progress on Processes, Observations, and Long-Term Trends, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6029, https://doi.org/10.5194/egusphere-egu25-6029, 2025.
The tropopause is a sensitive indicator of both radiative and dynamic changes in the atmospheric climate system. This study presents an analysis of lapse-rate tropopause (LRT) trends using remote-sensing satellite data for the period 2002-2023. The evaluation of trends is performed using GNSS radio occultation satellite measurements, which are particularly well suited for observing the temperature in the tropopause region with high vertical resolution and global coverage. In addition, GNSS radio occultation provides long-term stable measurements that allow robust detection of tropopause trends. Our results indicate pronounced zonal and meridional variations in LRT temperature trends, with certain regions exhibiting significant warming while others show no substantial trends. In particular, the tropics show LRT warming but no trend in LRT height. Additionally, we observe distinct seasonal patterns of trends in LRT temperature and height, with particularly pronounced trends in the Pacific region in the Northern Hemisphere winter. A spatially and seasonally resolved view of LRT trends is thus required for a complete picture of the changes in the tropopause region.
How to cite: Ladstädter, F., Stocker, M., Scher, S., and Steiner, A. K.: Observed zonally and meridionally resolved trends in lapse rate tropopause temperature and height over the past two decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19003, https://doi.org/10.5194/egusphere-egu25-19003, 2025.
The tropical tropopause layer (TTL) serves as a crucial boundary for air exchange between the troposphere and stratosphere, influencing the chemical composition and radiative balance of the lower stratosphere. Specifically, the cold-point tropopause, where air parcels undergo final dehydration, plays a key role in determining stratospheric water vapor content, which has significant implications for the global energy budget.
Our research utilizes Global Navigation Satellite System – Radio Occultation (GNSS-RO) and radiosonde data to investigate long-term changes in cold-point temperature and their impact on water vapor trends. We present evidence of a shift from pre-2000 cooling to post-2000 warming in TTL and lower stratospheric temperatures. Between 2002 and 2023, the cold point exhibits significant warming trends, reaching up to 0.7 K per decade during boreal winter and spring, with pronounced longitudinal asymmetries. These trends are strongest over the Atlantic and weakest over the central Pacific and are anti-correlated with upper tropospheric temperature trends. Our analysis shows a decrease in the seasonal cycle of cold-point temperature by ∼7%, driving a corresponding reduction of 6% in the seasonal cycle of water vapor at 100 hPa. This decrease of the water vapor seasonal cycle is transported upwards weakening the amplitude of the well-known stratospheric tape recorder signal.
Our findings are reproduced by reanalysis data (ERA5, JRA-55, MERRA-2), which accurately capture the spatial and seasonal variations in temperature trends. The reanalyses also highlight an important connection between TTL temperatures and tropical upwelling with a pre-2000 increase in tropical upwelling consistent with observed cold-point cooling and a post-2000 decrease in upwelling consistent with observed cold-point warming.
How to cite: Zolghadrshojaee, M., Tegtmeier, S., M. Davis, S., Pilch Kedzierski, R., and Haimberger, L.: Variability and long-term changes in tropical cold-point temperature, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-59, https://doi.org/10.5194/egusphere-egu25-59, 2025.
The mass of the lowermost stratosphere (LMS) is an important characteristic of the thermodynamic structure of the lower stratosphere. From a scientific perspective, long-term LMS mass changes illustrate the combined effect of tropopause pressure trends, tropical width trends and temperature changes in the tropical tropopause region. Further, understanding LMS mass trends can improve our knowledge of lower stratospheric ozone and water vapor trends that, despite their radiative importance, are still insufficiently understood. From a technical perspective, comparing LMS mass trends across reanalyses reveals consistencies and discrepancies between the data sets.
We examine long term trends in LMS mass using five modern reanalyses – ERA5, ERA-Interim, MERRA-2, JRA-55 and JRA3Q – for the time period 1979–2019. The focus is on changes after the year 1998, marking the anticipated beginning of stratospheric ozone recovery. The trend analysis is performed with a dynamic linear regression model (DLM).
All reanalyses consistently show decreasing tropopause pressure in the tropics and the Northern Hemisphere (NH) extratropics. This is reflected in a robust LMS mass decrease in the NH when a fixed isentrope of 380K is used as upper boundary, i.e. to approximate the tropical tropopause. However, we show that a fixed isentrope is an inadequate approximation of the upper LMS boundary for long-term studies, as the tropical tropopause also exhibits a trend. Therefore, we propose dynamically varying upper boundaries linked to the tropical tropopause potential temperature, accounting for this trend. In ERA5, ERA-Interim and MERRA-2, the dynamical upper boundaries are able to partly compensate for the tropopause rise in the NH. In contrast, the LMS mass decrease in the NH is enhanced by the dynamical upper boundaries in JRA-55 and JRA3Q. This is due to opposing absolute temperature trends in the tropical tropopause region across the reanalyses.
How to cite: Weyland, F., Hoor, P., Kunkel, D., Birner, T., Turhal, K., and Plöger, F.: Long-term Changes in the Thermodynamic Structure and the Mass of the Lowermost Stratosphere Comparing Five Modern Reanalyses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19101, https://doi.org/10.5194/egusphere-egu25-19101, 2025.
The atmospheric temperature and moisture profiles have changed given the rapid increases in the sea surface temperature in the past decades. This has implications for the stability of the atmosphere and therefore for the frequency, intensity and other characteristics of atmospheric moist convection and convective transport of water vapour and trace species. The latter is of high relevance to the composition of the upper troposphere and lower stratosphere.
We performed a historical simulation with the global chemistry climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) from 1979 to 2020 and investigated the changes in convective properties and transport. Within EMAC, the convective exchange matrix is applied to quantify and track the convective transport. This tool connects the transport of air masses between all model levels due to convection and enables the analysis of convective transport features and their changes disentangled from other processes.
Deep convection is reaching higher in the decade from 2011 to 2020 in comparison to 1980 to 1989. This is strongly correlated with an increase in the tropopause height. Thereby, the convective mass fluxes increased in the upper troposphere, but the overall strength of the convection did not change. Deep convection occurs less frequently in the more recent period. This leads in total to a decrease in the transport from the boundary air to the upper troposphere on average from 2011 to 2020 compared to the reference period at the beginning of the simulation time. We will present these trends and their dependence on the choice of the convection parameterisation and the nudging of the meteorological conditions.
How to cite: Jeske, A. and Tost, H.: Changes in the convective transport into the upper troposphere due to climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2225, https://doi.org/10.5194/egusphere-egu25-2225, 2025.
Reducing methane emissions is critical for restricting global surface temperature increases. However, methane also influences stratospheric ozone, and its recovery, via chemical and radiative processes. Using the state-of-the-art methane emission-driven capability in the fully coupled United Kingdom Earth System Model (UKESM), we examine the impact of methane emission reductions and methane removal of varying magnitude and timing on stratospheric ozone recovery in the 21st Century under climate scenarios with high (SSP3-7.0) and low (SSP1-2.6) surface warming. Despite beneficial reductions to surface temperatures and surface ozone, reducing methane emissions slows, and in some cases even prevents, the recovery of total column ozone (TCO). This is driven by reduced ozone production in the troposphere and lower stratosphere and by increased destruction in the mid and upper stratosphere by compounds derived from nitrous oxide (N2O) and halocarbons. This suggests that for methane emission reductions to be universally beneficial, they must be accompanied by continued efforts to reduce emissions of N2O and halocarbons.
How to cite: Weber, J., Wright, M., Collins, B., Shine, K., O'Connor, F., Folberth, G., Griffiths, P., and Abernethy, S.: CH4 emission reductions and removal slow stratospheric O3 recovery and highlight importance of chlorine and N2O mitigation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6351, https://doi.org/10.5194/egusphere-egu25-6351, 2025.
The characterization of the stratosphere-troposphere exchange (STE) is fundamental to its role in the global atmospheric budget of chemical constituents. The troposphere-to-stratosphere transport can inject anthropogenic pollutants from the Earth’s surface into the stratosphere, changing its chemical composition and influencing the radiative processes. For instance, the Asian Tropopause Aerosol Layer, with a main known pathway via the Asian summer monsoon, has been shown to have a radiative cooling effect on the surface. Here we propose a previously underreported potential pathway contributing to STE via tropical cyclones, typhoons in particular. We focus on one episode of a typhoon crossing over the Philippines, which is located in the highly polluted Eastern Asia-Western Pacific region. A case study for typhoon Molave (2020), combining a Lagrangian modeling tool with the Weather Research and Forecasting model (FLEXPART-WRF), demonstrates that the typhoon can result in rapid transport of pollutants from the surface to the upper troposphere-lower stratosphere (UTLS) region, inducing strong STE. Using a Lagrangian model, it has been possible to characterize the intensity of the air intrusion from the boundary layer to the free troposphere and stratosphere by computing their residence times. Furthermore, we try to disentangle the role of convection, orographic lifting, and gravity waves inducing this type of rapid transport. Overall, our study indicates that typhoon episodes can play an important, intermittent and previously insufficiently considered role in STE, influencing emerging topics of the highest importance such as the long-range dispersion of microplastics.
How to cite: Martina, M., Villalba Pradas, A., and Šácha, P.: Stratosphere-Troposphere Exchange during a Typhoon event: A Lagrangian approach., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4817, https://doi.org/10.5194/egusphere-egu25-4817, 2025.
Understanding air mass sources and transport pathways in the Tropical Western Pacific (TWP) is crucial for determining the origins of atmospheric constituents in the stratosphere. This study uses lidar and ballon observations in Koror, Palau, and trajectory simulations to study the upward transport pathway over the TWP in the upper troposphere and lower stratosphere (UTLS). During northern hemisphere winter, the region experiences the highest relative humidity with respect to ice (RHi) and the lowest temperatures (<185 K) at 16–18 km, and is called the "cold trap". These conditions lead to water vapor condensation, forming thin cirrus clouds. Latent heat released during cloud formation drives the ascent of air masses.
A case study in December 2018 shows a subvisible cirrus cloud layer (optical depth < 0.03) measured by lidar, coinciding with high supersaturation (RHi > 150%) observed by radiosonde. Trajectories initiated from the cloud layers confirm that air masses ascend slowly from the troposphere into the stratosphere primarily during northern hemisphere winter. In contrast, lidar measurements show similar cloud layers during a summer case (August 2022) with warmer temperatures and drier conditions, where air descends after cloud formation indicated by the forward trajectory. Among all cirrus clouds observed in December and August, 46% of air masses rise above 380 K after cloud formation in December, compared to only 5% in August, possibly influenced by the Asian summer monsoon. These findings underscore the importance of the cold trap in driving air mass transport and water vapor transformations in the UTLS.
How to cite: Sun, X., Müller, K., Palm, M., Ritter, C., Ji, D., Röpke, T. B., and Notholt, J.: Evidence of Tropospheric Uplift into the Stratosphere via the Tropical Western Pacific Cold Trap, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8559, https://doi.org/10.5194/egusphere-egu25-8559, 2025.
The Tropical Tropopause Layer (TTL) is a gateway for momentum fluxes and atmospheric components to the global stratosphere. The dynamical processes in the TTL remain challenging to characterize, particularly at turbulent length scales, and are still poorly understood. Current estimates of turbulence frequency and intensity vary considerably between observations in this region, although they are crucial for designing efficient and accurate model parameterizations.
Quasi-Lagrangian in situ measurements of thermodynamic parameters and GPS are obtained from STRATEOLE-2 long-duration balloons drifting at isopycnal level around 20 km altitude during several months over the equator. The balloons' vertical oscillations around their density equilibrium position in a stratified environment allow us to estimate local vertical gradients in temperature, pressure and winds. From these estimates we evaluate Richardson numbers, which enable us to characterize the flow as turbulent or laminar during each flight, and thus to estimate turbulent fractions.
Various methods were tested to evaluate local gradient estimates that can be applied directly to the detection of turbulent episodes. For example, using the envelope defined by the local extrema of the time series, we estimate instantaneous local gradients from the ratio of the variables amplitude to the vertical displacement amplitude. This approach enables the reconstruction of temperature and wind increments time series. By calculating correlations between observed and reconstructed increments, we show that our gradients are quite consistent, especially for shear winds estimates.
We deduce the turbulent fraction from the ratio of the mean lifetime of turbulent episodes to the mean interval between two successive ones. Additionally, we describe the distribution of these estimates.
How to cite: Juge, F., Wilson, R., and Hertzog, A.: Turbulent fractions in the Tropical Tropopause Layer using STRATEOLE-2 long-duration balloon measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18470, https://doi.org/10.5194/egusphere-egu25-18470, 2025.
The extratropical transition layer of (ExTL) has been recognized about 20 years ago as part of the upper troposphere / lower stratosphere (UTLS) of the extratropics, which shows the chemical characteristics of both, the stratosphere and the troposphere. Its composition is to a large extent dominated by rapid transient small scale dynamical processes, driven by mid-latitude synoptics. The dynamical processes may include frontal uplift and shear at the tropopause , convection and gravity wave breaking, all in sum leading to turbulence and mixing. As a result gradients of tracer, moisture, and aerosol are highly perturbed on small scales and cross tropopause exchange may occur.
Here we report on a novel measurement approach during June 2024 with a double platform airborne approach targeting small scale variability in the UTLS. This allowed for simultaneous measurements of ozone, humidity and aerosol size distribution on two platforms, which provide information on the vertical gradients of these quantities. The gradients of ozone and aerosol number concentration show a surprisingly high variability in the UTLS and at the tropopause highlighting the importance of small scale processes for the composition of the tropopause region. The measurements were complemented by surface-based and balloon-borne observations at one surface site and comprehensive forecasts including forward trajectories based on ICON forecast data as well as ECMWF forecast data.
We will present highlights from the mission including convective overshoots deep into the LMS at high latitudes, probing of convective outflow and mixing at the tropopause, as well as cirrus occurrence in the stratosphere.
The mission was a central part of the collaborative research center TPChange (The tropopause region in a changing atmosphere).
How to cite: Hoor, P. and the The TPEx team: Fine scale structure of the tropopause region as measured during the TPEx mission, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9313, https://doi.org/10.5194/egusphere-egu25-9313, 2025.
Convective overshoot can result in irreversible mixing of air from the troposphere into the stratosphere, thereby influencing the radiation balance of this climate-sensitive region by altering greenhouse gas concentrations, particularly water vapor, and inducing ice and aerosol particles into the stratosphere. This study examines the cloud microphysical properties and trace gas signatures associated with a convective overshoot event observed during the TPex (TropoPause composition gradients and mixing Experiment) campaign in June 2024 over southern Sweden. While recent investigations have predominantly focused on convective overshoots related to air masses of (sub)tropical origin, this particular event took place during a cold air outbreak characterized by low tropopause altitudes (9 km; with temperatures around -55°C).
For the study, microphysical data collected in-situ during Tpex aboard a Learjet by NIXE-CAPS (New Ice eXpEriment - Cloud and Aerosol Particle Spectrometer) and trace gas measurements, including water vapor and ozone, were utilized. The findings reveal that ice particles were transported into the lower stratosphere, up to 1.5 km above the tropopause. At this altitude, a pronounced stratospheric ozone concentration of approximately 800 ppbv and a notable tropospheric water vapor concentration (~40 ppmv) were recorded, the latter being twice as high as background levels at the same height. This substantial injection of tropospheric air was linked to gravity wave breaking, and subsequently irreversible mixing near the overshooting top.
To gain deeper insight into the development of the overshoot, a forward trajectory analysis was conducted, and the evolution of cloud ice microphysical properties along the trajectories was simulated using the CLaMS (Chemical Lagrangian Model of the Stratosphere) model.
How to cite: Konjari, P., Rolf, C., Krämer, M., Afchine, A., Spelten, N., Emig, N., Joppe, P., Bozem, H., and Hoor, P.: Microphysical properties and trace gas signatures of a convective overshoot observed over Sweden during the TPex campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16726, https://doi.org/10.5194/egusphere-egu25-16726, 2025.
The paper discusses multiscale dynamical processes shaping a mixing line in the upper troposphere/lower stratosphere (UTLS). It focuses on aircraft observations above southern Scandinavia during a mountain wave event and how they can be analyzed based on dynamic variables and the trace gases N2O and CO. This study aims to identify the irreversible component of the stratosphere-troposphere exchange. It was shown that the overall shape of the mixing line is determined by the large-scale and mesoscale atmospheric conditions in the UTLS. Especially, the wide range of Θ values along the flight tracks causes a compact, almost linear tracer-tracer relation between N2O and CO. Only motion components with scales less than 4 km lead to the observed scattering along the mixing line. The anisotropic and patchy nature of the observed turbulence is responsible for this scatter in N2O and CO. The turbulence analysis reveals different scaling laws for the power spectra upstream, over the ridge and downstream of the mountains that lead to energy dissipation and irreversible mixing. The study suggests that turbulence dynamics may follow a cycle starting with 3D homogeneous isentropic turbulence upstream, transitioning to anisotropic turbulence over the ridge and further downstream. This transition is attributed to an interplay between turbulent eddies and internal gravity waves.
How to cite: Dörnbrack, A., Hoor, P., Rodriguez Imazio, P., and Lachnitt, H.-C.: Multiscale Dynamical Processes Shaping a Mixing Line, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7145, https://doi.org/10.5194/egusphere-egu25-7145, 2025.
Aircraft measurement campaigns such as IAGOS-CARIBIC and HALO missions are invaluable sources of long-lived trace gas observations in the extratropical Upper Troposphere and Lower Stratosphere (exUTLS). The simultaneous measurement of multiple substances enables a comprehensive characterisation of sampled air masses.
To contextualize these observations, the use of dynamic coordinate systems - where measurements are for example presented relative to the tropopause - is highly beneficial. The tropopause itself can be defined from several perspectives, including differences in chemical composition, dynamical parameters, or temperature gradients between the troposphere and stratosphere.
In this study, we examine how different tropopause definitions influence the climatology of long-lived tracer substance observations. We investigate how effective filtering of tropospheric and stratospheric air masses can homogenise measurements of long-lived tracers and therefore decouple atmospheric dynamics from long-term trends and seasonalities. Meteorological parameters used in this analysis are obtained from ERA5 reanalysis data sets, which have been subsampled along the flight tracks.
Our findings indicate that the thermal tropopause results in larger variability in bins around the tropopause. Different potential-vorticity thresholds result in vertically displaced distributions but similar trends around the tropopause. Chemical tropopauses, while effective in differentiating between the troposphere and stratosphere, show significant limitations in their sensitivity towards the surface.
How to cite: Bauchinger, S., Schuck, T., Zahn, A., Bönisch, H., Lachnitt, H.-C., and Engel, A.: Evaluating the impact of tropopause definitions on long-lived tracer distributions in the exUTLS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2797, https://doi.org/10.5194/egusphere-egu25-2797, 2025.
The composition of the upper troposphere is determined by both the tropospheric transport times causing near surface air to be transported away from the emission sources as well as the dynamics of the atmosphere, including exchange with the stratosphere. Atmospheric convection and the associated tracer transport lead to rapid mixing of air masses given the strong up- and downdrafts in convective clouds, both in the tropics and the midlatitudes.
However, determining the impact of convection on a sampled air mass is rather difficult from an experimental point of view, as the mixing ratios of short lived compounds can originate from one individual or several convective mixing events. For that purpose, we use global simulation results using parameterised convection and driven by re-analysis data for the period of the SOUTHTRAC campaign.
We sample the output from the convective exchange matrix, i.e., a novel diagnostic for convective transport, on backward trajectories for aircraft measurements and therefore can identify the contribution of near surface air to the UTLS composition. Additionally, we analyse the time evolution of the air mass and the convective events to estimate the contribution of observed trace gases to the total composition in an temporally integrated point of view, which allows to also estimate the chemical degradation of compounds given their individual chemical lifetimes. Overall, this study which is within the framework of the TPChange project, consequently leads to a better understanding of the composition of the upper troposphere and potential injections into the lower stratosphere.
How to cite: Tost, H., Jeske, A., Smoydzin, L., and Hoor, P.: Tracking air mass history with respect to convective mixing - a SOUTHTRAC example, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9737, https://doi.org/10.5194/egusphere-egu25-9737, 2025.
Public attention has been captured by urban pollution and wildfire smoke plumes and their adverse impacts on air quality and public health even far downstream of their origin. Downwind impacts depend on the rate at which these plumes dissipate. However, quantifying this rate using chemical transport models has proven difficult because numerical diffusion systematically overestimates plume dilution. This bias affects our understanding of non-linear chemistry, chemistry-climate coupling, as well as surface impacts. We therefore seek to constrain the rate at which an emitted mass of pollutant is diluted in the upper troposphere, by combining observations with model simulations.
The first step towards our goal is to track plumes in satellite retrievals. The task is daunting: plumes deform, split, and merge, and are at times obscured by clouds or simply out of satellites' sight. In addition, the standard practice of defining plumes as regions with pollutant concentrations greater than a preset threshold is rendered ineffective by the very dilution we aim to quantify: the threshold should change over time to reflect plume dilution, but at what rate?
To address these issues, we propose a new plume definition that incorporates both pollutant ('chemical') data and meteorological ('dynamical') data. Our approach views a plume as a collection of pollutant-enriched air masses, where each air mass is a region bounded by dynamical barriers. Because dilution is slow across such barriers, the envelope of the 'chemical-dynamical' plumes thus defined provides a spatial constraint on dilution processes. By tracking ‘chemical-dynamical’ plumes over time using Lagrangian tools, we aim to more accurately define the volume relevant to quantifying the dilution of the pollutant mass.
We present a proof of concept for our approach using simulated carbon monoxide and meteorological fields archived from the GEOS Chemical Forecast system. We show that our plume-tracking method a) reduces sensitivity to the choice of pollutant concentration threshold to define plumes, and b) can overcome the coverage limitations of pollutant data retrieved by satellite instruments. Overall, our new method represents a promising step towards quantifying tracer dilution using observations as a primary source of information.
How to cite: Rivoire, L., Eastham, S., Fiore, A., Curbelo, J., Palmo, J., and Finkel, J.: A new method to quantify tracer dispersion in the upper troposphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14762, https://doi.org/10.5194/egusphere-egu25-14762, 2025.
It is well established that the drastic ozone loss in the Antarctic stratosphere, commonly known as the ozone hole, is caused by gas-phase and heterogeneous processes. Chemistry models generally reproduce observed ozone depletion reasonable well. However, models have been unable to reproduce observations of rapid HCl loss at the beginning of the polar winter. Here we examine the impact of the heterogeneous reaction between Cl2O2 and HCl to form HOOCl and its subsequent photolysis on chlorine compounds. A chemical mechanism with these reactions added is able to clearly better reproduce the observed temporal development of the chlorine compounds HCl, ClONO2, ClO, and HOCl in the polar vortex lower stratosphere. The proposed chemical mechanism does moderately increase the chemical ozone column depletion, about 10\% in the lower stratospheric vortex core in September. Laboratory measurements of the proposed reactions are needed to confirm this mechanism.
How to cite: Grooß, J.-U., Müller, R., Crowley, J. N., and Hegglin, M. I.: A chemical mechanism explaining the observed wintertime HCl in the Antarctic vortex, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6597, https://doi.org/10.5194/egusphere-egu25-6597, 2025.
Ice supersaturated regions (ISSRs) are area in the upper troposphere and lower stratosphere (UTLS) where relative humidity (RH) with respect to ice exceeds 100%. These regions are critical for the formation of cirrus clouds and contrails. While the impact of ISSRs on the planetary radiation balance is small to negligible, the thin cirrus clouds and aircraft induced contrail cirrus formed within them have a large radiative impact. Understanding the characteristics of ISSRs, including their geometry and seasonal variability, is essential for improving atmospheric models. While ISSR path-length statistics have been studied, their geometric properties, particularly fractal characteristics, and their seasonal variability remain largely unexplored.
We identify ISSRs using ERA5 reanalysis data spanning from 2010 to 2020 at three pressure levels. An area-perimeter method is employed to compute fractal dimensions. The results reveal slopes equaling fractal dimensions with high coefficients of determination, strongly suggesting that ISSRs in the UTLS exhibit fractal behavior. A seasonal cycle in both dimension and total count of observed ISSRs was verified on both hemispheres. We hypothesize that this is caused by the seasonal variation of convective and frontal activity.
We further analyzed the latitudinal and longitudinal spans of ISSRs and the path lengths of modeled flights along common IAGOS flight routes. The results of the latitudinal and longitudinal spans suggest two distinct formation processes for ISSRs.
How to cite: Schuh, H., Spichtinger, P., and Reutter, P.: Fractal Characteristics and Seasonal Variations of Ice-SupersaturatedRegions (ISSRs) in the Tropopause Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16298, https://doi.org/10.5194/egusphere-egu25-16298, 2025.
Aircraft engines emit aerosols and aerosol precursor gases, mostly black carbon (soot) and sulfur dioxide, which remain longer in the atmosphere than aerosols emitted at the surface. Long-range transport during that long residence time means that aviation aerosols may interact with clouds far from the main flight corridors. The radiative forcing of interactions between aviation aerosols and clouds is so uncertain that even its uncertain range is unknown. Its quantification relies on climate models, where aerosol concentrations and long-range vertical and horizontal transport are strongly affected by wet scavenging, which can be parameterized in different ways with several tunable parameters. One could assume that the representation of wet scavenging is of secondary importance for the simulated residence time of aviation aerosols, because they are emitted high above precipitating clouds. In this work, we use the LMDZ-OR-INCA climate model to investigate the impact of three different scavenging parameterizations on total and aviation aerosol distributions, using regional and seasonal vertical profiles measured during the ATom and HIPPO airborne campaigns to evaluate the performances of the different parameterizations. Results confirm that the residence time and the mass budgets of black-carbon, sulfates and nitrates from all sources are significantly influenced by the scavenging scheme. Moreover, the skill of a scavenging parameterization to simulate vertical aerosol concentration profiles depends on geographical location, altitude and season, although no parametrizations are consistently better than the others. Unexpectedly, the scavenging parameterizations also affect aviation aerosol concentrations at flight cruise levels: although scavenging rates are small, residence time are long so differences accumulate. Near-surface aerosol concentrations, which are mainly due to Landing and Take-off Operations (LTO), are also affected by the choice of a wet scavenging parameterization. Results suggest it may be possible to design a new scavenging routine for LMDZ-OR-INCA model to better represent the long-range transport of aviation aerosols and reduce uncertainties in aviation aerosol-cloud interaction radiative forcing.
How to cite: Février, N., Hauglustaine, D., and Bellouin, N.: Importance of the representation of aerosol wet scavenging for aviation aerosol transport, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20209, https://doi.org/10.5194/egusphere-egu25-20209, 2025.
Recent increases in global anthropogenic ammonia emissions have yet to be fully quantified in terms of impacts on atmospheric particle formation, cloud microphysical properties, and climate. We employ the EMAC global climate-chemistry model, including recently published multi-component new particle formation (NPF) parameterisations from the CERN CLOUD experiment, to investigate the impact of anthropogenic ammonia on upper tropospheric processes. Our simulations show that convective transport significantly enhances ammonia-driven NPF and particle growth at these altitudes, leading to an average increase in particle number concentrations by up to 2000 cm⁻³ and a doubling of cloud condensation nuclei (CCN) concentrations over regions with high ammonia emissions. In simulations without anthropogenic ammonia, aerosol composition in the upper troposphere is dominated by sulphate and organic species rather than ammonium nitrate. Furthermore, anthropogenic ammonia emissions contribute to an increase in aerosol optical depth by up to 90%, producing a pronounced radiative forcing pattern: cooling in the Northern Hemisphere and warming in the Southern Hemisphere. These results underscore the critical role of ammonia emissions in aerosol composition in the upper troposphere and the global radiative forcing of climate.
How to cite: Xenofontos, C.: Anthropogenic Ammonia's Impact on Upper Tropospheric Aerosol Composition and Climate Forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6744, https://doi.org/10.5194/egusphere-egu25-6744, 2025.
A consistent result of climate model simulations is the moistening of the stratosphere. Many models show their strongest changes in stratospheric water vapor in the extratropical lowermost stratosphere, a change which could have substantial climate feedbacks (e.g. Banerjee et al. 2019).
However, models are also heavily wet-biased in this region when compared to observations (Keeble et al. 2020), presenting some uncertainty on the robustness of these model results. In this study, we examine this wet bias, showing that it is consistent across various models. We present the results of applying a fully-Lagrangian transport scheme (CLaMS) within the EMAC climate model, showing that water vapor distributions from the modified model are very similar to observations.
Addionally, we describe the sensitivity of the atmospheric circulation in the stratosphere and troposphere to the abundance of water vapor in the lowermost stratosphere, including the mechanism by which this occurs, and show that the related effects on atmospheric circulation are of similar magnitude as climate change effects.
How to cite: Charlesworth, E. and Plöger, F.: Stratospheric Water Vapor Affecting Atmospheric Circulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19950, https://doi.org/10.5194/egusphere-egu25-19950, 2025.
High-explosivity volcanic eruptions and extreme-intensity fires can inject pollutants into the upper troposphere and stratosphere (UTS), generating persistent disturbances of its composition and of the stratospheric aerosol layer, affecting the radiative balance and the climate system on a global scale.
We focus on two recent events, the largest known plume generated by a forest fire on 2020 new year in Australia (AF) with an amplitude comparable to a large volcanic eruption and the Hunga submarine eruption in January 2022, which has generated the largest stratospheric disturbance since the Pinatubo eruption. Its plume has been exceptional by its altitude reach 58 km and the massive injection of water vapour (10% instantaneous increase in the stratosphere).
In both cases, we take advantage of the large number and diversity of spaceborne instruments to analyze and revisit the properties of the stratospheric plumes, in particular the role of confinement in mesoscale structures dynamically induced from the radiative forcing. In the case of the AF, rising anticyclonic smoke vortices were formed by shortwave absorption and maintained compact for several months during which the confinement maintained the high concentration in aerosol and an anomalous chemical composition with a persisting moist air depleted in ozone. The ozone anomaly in the ozone column is also partly dynamical due to the fast rising motion of the vortices when they cruise in the high latitude summer stratosphere. In the case of the Hunga eruption, condensing water vapour was first essential to get rid of most of the ashes during the first hours following the eruption. The strong emission of the remaining water vapour in the stratosphere generated a pair of rapidly descending structures, also anticyclonic, that eventually broke after about a couple of weeks but were essential in maintaining a confinement able to convert SO2 to sulfates at an unprecedented rate. Such compact structures are in fact expected in any plume submitted to localized internal warming or cooling. The confinement process is discussed in relation with the various estimates of SO2 and sulfate, in particular a mesoscale resolving product with IASI which shows the fast conversion to sulfate in mesoscale structures. The longer-term impact is diagnosed with SAGE III, showing how the rapid growth led to larger than usual aerosols with a sharper distribution, differing from other eruptions and providing large radiative impact in spite of the relatively small amount of emitted SO2. In passing, these unusual characters are the main reason of the dispersion of measurements of limb scattered instruments for this event. We show on the contrary that the SAGE III measurements are in very good agreements with the CALIOP estimates of extinctions for the isolated plume.
How to cite: Legras, B., Podglajen, A., Duchamp, C., Sellitto, P., Siddans, R., Carboni, E., and Belhadji, R.: The role of mesoscale structures in the disturbance of the stratosphere by two major events in 2020 and 2022, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13614, https://doi.org/10.5194/egusphere-egu25-13614, 2025.
The tropical Cold-point tropopause temperature (CPT) is a prominent climate variable: it effectively controls the amount of water vapor entering the stratosphere by freeze-drying the air masses that cross through the tropopause near the equator.
GNSS radio-occultation measurements (GNSS-RO) provide global coverage of temperature profiles with high vertical resolution, making possible the monitoring of the CPT evolution outside of the few tropical regions covered by radiosondes. Reanalyses are all known to have a modeled CPT that is on average too warm, compared to GNSS-RO measurements. The reanalysis warm CPT biases maximize near the Equator, hinting at a possible role of equatorial waves.
Observed equatorial CPT shows spectral peaks coinciding with equatorial wave dispersion curves, i.e. it is modulated by the equatorial waves that propagate through the equatorial tropopause. However, to date the warm biases in reanalysis CPT have only been studied from a systematic and zonal-mean perspective, without accounting for equatorial wave presence.
In the present study, we bridge this gap by showing how the reanalysis warm CPT bias varies relative to the phase of equatorial waves. Reanalysis datasets (ERA5, ERA-Interim, JRA55, CFSR and MERRA-2, all with CPT from model levels) are inter-compared to multi-mission GNSS-RO for the years 2007-2018. Equatorial waves are filtered from a 5° x 5° daily grid – the best resolution that GNSS-RO data density permits reliably for 2007-2018 – onto which the reanalyses CPTs are interpolated for a 1-to-1 comparison.
A common feature among all reanalysis datasets is as follows: within an equatorial wave’s cold phase, reanalysis CPT biases markedly increase – sometimes by over 1K on top of the average warm bias. The opposite happens within the warm phase of the wave: the bias decreases. This can be explained by the stronger vertical temperature gradients around the colder equatorial CPTs, and the atmospheric models of the reanalyses increasingly struggling there.
There is an important caveat to the above: a time-space scale-dependence, where smaller-scale and faster equatorial waves modulate CPT reanalysis bias more. Mixed Rossby-Gravity waves show this behavior most clearly, Kelvin waves about half the magnitude, and equatorial Rossby wave modulation of CPT reanalysis bias is even weaker but still apparent. In contrast, the large-scale and slow-moving MJO does not show any of this bias modulation.
Current work is on validating Inertia-Gravity wave results which may contain significant proportions of noise. Analysis of assimilation increments of CPT in the reanalyses shows data assimilation cooling the modeled CPT – enhancing the gradients around it – in all datasets.
How to cite: Pilch Kedzierski, R., Davis, S., Tegtmeier, S., Wargan, K., and Weissmann, M.: Cold-point tropopause temperature bias modulated by equatorial waves: a reanalysis intercomparison, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8747, https://doi.org/10.5194/egusphere-egu25-8747, 2025.
Turbulence was responsible for 71% of all weather-related aviation accidents and incidents in the US between 2000–2011 [1], leading to structural damage, injuries, and US$200 million in unforeseen costs for airlines each year [2]. With only 14% of turbulence encounters being attributable to convection [3], clear-air turbulence (CAT) is a leading cause of these encounters and thus poses a major risk to travellers.
A variety of dynamical mechanisms can be responsible for CAT, including shear instabilities, inertial instabilities, and gravity waves; however, differentiating between the distinct roles of each mechanism when more than one is present remains difficult. In fact, it is the precise evolution of these atmospheric instabilities and waves, and their potential for generating CAT, which remain uncertain in our current scientific understanding.
In this study, we investigate the relationship between CAT and gravity waves, with a specific focus on tracking the formation of these waves around regions of inertial instability. Previously, [4] showed the emission of inertia–gravity waves following the release of inertial instability using idealised model simulations. Here, we use the WRF model to consider some real-world examples of where regions of low potential vorticity (PV) in the vicinity of the jet stream are associated with inertia–gravity waves. We track the waves as they propagate and investigate whether the causal link found by Thompson and Schultz can be observed in more realistic simulations.
We present results from several case studies exhibiting this behaviour, identifying the sources of the gravity waves observed in simulations. The characteristics of these waves will be compared to those in the idealised model simulations, and gravity-wave parameters will be calculated. Finally, we widen our analysis by examining the broader upstream pattern that contributes to the development of the initial inertial instabilities and explore the different regimes under which these phenomena occur.
References:
[1] Gultepe, I. et al. (2019), "A review of high impact weather for aviation meteorology." Pure and Applied Geophysics, 176, pp.1869–1921.
[2] Williams, J. K. (2014), "Using random forests to diagnose aviation turbulence." Machine Learning, 95, pp.51-70.
[3] Meneguz, E., Wells, H. and Turp, D. (2016), "An automated system to quantify aircraft encounters with convectively induced turbulence over Europe and the Northeast Atlantic." Journal of Applied Meteorology and Climatology, 55(5), pp.1077-1089.
[4] Thompson, C. F. and Schultz, D. M. (2021), "The release of inertial instability near an idealized zonal jet." Geophysical Research Letters, 48(14), e2021GL092649.
How to cite: Banyard, T. P., Schultz, D. M., Vaughan, G., Burgess, B. H., Kaluza, T., and Williams, P. D.: A Source of Clear-Air Turbulence? Tracking Gravity Wave Formation in Inertially Unstable Regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19191, https://doi.org/10.5194/egusphere-egu25-19191, 2025.
Dichloromethane (CH2Cl2) is known to be emitted by industrial processes and suspected to be capable of delaying the recovery of the stratospheric ozone layer significantly. A rapid rise of its global emissions over the last decades, with the majority being located in East and South East Asia, is documented in the literature. We present unique observations of CH2Cl2-rich air masses over the North Pacific, Canada and Alaska by the infrared limb imager GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere). During the boreal summer of 2023, GLORIA was deployed aboard the German research aircraft HALO (High Altitude and LOng Range Research Aircraft) in the framework of the PHILEAS campaign (Probing High Latitude Export of Air from the Asian Summer Monsoon). Two-dimensional vertical cross-sections of CH2Cl2 derived from GLORIA observations in August and September 2023 show large plumes with high mixing ratios of typically up to ~300 pptv far away from their anticipated source regions. Up to 450 pptv are observed locally, which corresponds to ~700% of the northern hemispheric background in that season. Air masses with high CH2Cl2 mixing ratios are detected in the free troposphere and moderately enhanced mixing ratios are observed partly also in the tropopause region. Using backward trajectories and simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS), the transport pathways and timescales of the observed air masses are analysed. Our analysis suggests that East Asia is a major source region of the observed air masses. Together with the model data and in situ observations by HAGAR-V (High Altitude Gas AnalyzeR-V) and GhOST (Gas chromatograph for Observational Studies using Tracers), the GLORIA observations provide new insights into the long-range transport of CH2Cl2-rich airmasses from the Asian Summer Monsoon region. GLORIA is an airborne demonstrator for the ESA Earth Explorer 11 candidate CAIRT (Changing-Atmosphere Infra-Red Tomography explorer), which is currently in the final selection round and would provide new opportunities to study a multitude of ozone- and climate-relevant trace species continuously.
How to cite: Woiwode, W., Grooß, J.-U., Lauther, V., Johansson, S., Ungermann, J., Neubert, T., Engel, A., Hoor, P., and Riese, M. and the GLORIA, CLaMS, HAGAR, and GhOST Teams: Two-dimensional observations of dichloromethane-rich air masses transported from the Asian summer monsoon region across the North Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12886, https://doi.org/10.5194/egusphere-egu25-12886, 2025.
Definition of the boundaries of the Asian summer monsoon anticyclone (ASMA) is a known challenge that highly impacts the information about the anticyclone's behavior and affects the study of its interannual variability. We present a novel method based on the absolute vortex moments that defines the ASMA boundaries by solving an optimization problem. The results show climatology (1980–2023), interannual variability, start and end dates range and the duration of the anticyclone peak phase calculated with help of the defined method. In addition, three individual years – 2017, 2022 and 2023 are highlighted during which StratoClim, ACCLIP and PHILEAS campaigns took place respectively. The interannual analysis is based on the anticyclone's centroid latitude and longitude, excess kurtosis, angle, aspect ratio and using 4 isentropic surfaces: 350, 370, 390 and 410K. The work determined correlation of the centroid position of the anticyclone with a set of month lag ENSO considering the whole year equatorial pacific sea surface temperature anomalies (DJF–NDJ) using ONI index. The ASMA centroid latitude is negatively correlated with 5-month lag ENSO ( ∼ -0.6) when the anticyclone is still in its formation phase and then the correlation starts to decline when the anticyclone enters its peak phase.
How to cite: Kachula, O., Vogel, B., and Günther, G.: Interannual variability of the Asian Summer Monsoon Anticyclone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3216, https://doi.org/10.5194/egusphere-egu25-3216, 2025.
Motivated by the limited knowledge of how much the extratropical UTLS region is influenced by the Asian summer monsoon (ASM) outflow, we conducted the aircraft-based mission PHILEAS (Probing High Latitude Export of air from the Asian Summer Monsoon). The mission took place in August/September 2023, operating from Oberpfaffenhofen (Germany) and Anchorage (Alaska). The research aircraft HALO was equipped with a comprehensive suite of in-situ and remote-sensing instruments for aerosol and gas analysis.
We performed vertically-resolved submicron aerosol composition measurements up to a potential temperature of 400 K (~14.5 km altitude) by using the ERICA aerosol mass spectrometer. Our analysis identifies particulate ammonium nitrate and organic compounds as prevalent throughout the extratropical lower stratosphere. The mass concentrations are comparable to those in remote continental regions. The presence of this pollution aerosol is linked to the ASM convection, followed by subsequent isentropic northward transport in the stratosphere. Global simulations with the ECHAM/MESSy Atmospheric Chemistry model (EMAC) suggest that this transport pathway persists from July to September and recurs annually. Even after the ASM dissipates in September, the particulate ammonium remains widespread in the stratosphere, with broad implications for stratospheric aerosol composition and heterogeneous chemistry.
How to cite: Köllner, F. and Eppers, O. and the PHILEAS team: Widespread influence of aerosol from the Asian summer monsoon throughout the extratropical lower stratosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13843, https://doi.org/10.5194/egusphere-egu25-13843, 2025.
Water vapor in the Upper Troposphere and Lower Stratosphere (UTLS) plays a crucial role in climate feedback by influencing radiation, chemistry, and atmospheric dynamics. The amount of water vapor entering the stratosphere is sensitive to cold point temperatures (CPT), making Northern Hemisphere summer monsoons more favorable for transporting water vapor into the stratosphere. This study uses a Lagrangian method to reconstruct water vapor over the Asian (ASM) and North American (NAM) monsoons, investigating their contributions to stratospheric water vapor. The Lagrangian method tracks air parcels and identifies the coldest temperature along each trajectory, contrasting with local methods that rely on vertical temperature profiles. The reconstructed water vapor fields are validated against satellite observations from SAGE III/ISS and NASA’s Aura MLS. SAGE III/ISS shows stronger moisture enhancements than MLS, but both datasets reveal similar water vapor anomalies within the ASM and NAM anticyclones. Although the Lagrangian method is dry-biased compared to observations, it effectively reconstructs UTLS water vapor (correlation coefficient ~0.75), capturing moist anomalies in the ASM but performing less well in the NAM. Our analysis shows that, rather than local conditions, large-scale cold point tropopause temperatures in the vicinity of the monsoons primarily drive the moisture anomalies, with NAM water vapor significantly influenced by long-range transport from South Asia. Some convection-related processes, such as east-west shifts within the ASM, are not fully captured due to unresolved temperature variability in ERA5 and missing ice microphysics. Despite biases and computational challenges, the Lagrangian method provides valuable insights into UTLS water vapor transport.
How to cite: Wang, H., Park, M., Tao, M., Peña-Ortiz, C., Pilar Plaza, N., Ploeger, F., and Konopka, P.: Understanding Boreal Summer UTLS Water Vapor Variations in Monsoon Regions: A Lagrangian Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3680, https://doi.org/10.5194/egusphere-egu25-3680, 2025.
The CATRINE (Carbon Atmospheric Tracer Research to Improve Numerics and Evaluation) project, financed by the European Union, is a ground-breaking initiative aiming at improving the accuracy and dependability of atmospheric tracer transport models. The European Centre for Medium-Range Weather Forecasts (ECMWF) coordinates CATRINE, which brings together an interdisciplinary team of atmospheric scientists, climate researchers, and computational modelers to address significant challenges in emissions monitoring and carbon cycle knowledge. This investigation focuses on high-resolution global simulations of key atmospheric constituents—carbon dioxide (CO₂), methane (CH₄), and carbon monoxide (CO)—using two state-of-the-art numerical frameworks: the ICOsahedral Nonhydrostatic Atmospheric Model with aerosol and reactive trace gas capabilities (ICON-ART) and the Integrated Forecasting System (IFS) to advance our understanding of trace gas transport dynamics and improve numerical modelling techniques.
The study implements sophisticated modelling approaches within both frameworks, leveraging ICON-ART's innovative unstructured triangular grid system based on a spherical icosahedron, which facilitates flexible grid refinement and incorporates a height-based terrain-following coordinate system with smooth level vertical coordinate implementation. The ART module, coupled online with ICON, enables detailed simulation of aerosols and trace gases, encompassing their emissions, transport, and removal processes throughout the troposphere and stratosphere. In parallel, the investigation examines the IFS framework, renowned for its global numerical weather prediction capabilities, as well as atmospheric composition/air quality monitoring and prediction as part of the Copernicus Atmosphere Monitoring Service (CAMS).
The methodology employs high-resolution global simulations focused on trace gas transport processes, with particular emphasis on the upper troposphere/lower stratosphere (UTLS) region. The validation framework integrates observational data from the DCOTSS (Dynamics and Chemistry of the Summer Stratosphere) flight campaigns to evaluate model performance across various atmospheric phenomena. Also, the analysis examines deep convective overshooting event as characteristic cases where rapid vertical transport significantly modifies UTLS composition, altering mixing ratios of CO₂, CH₄, CO, and other trace species. Statistical analyses quantify model performance in representing these complex transport processes and their effects on atmospheric composition across multiple spatial and temporal scales.
The comparative analysis reveals distinct characteristics in how ICON-ART and IFS represent transport processes, particularly during deep convective events and associated overshooting phenomena. These findings contribute substantial methodological advances to atmospheric sciences, with direct implications for improving our understanding of UTLS dynamics, enhancing emissions monitoring capabilities, and supporting more accurate climate change assessments. The research establishes a comprehensive framework for future investigations of atmospheric transport processes, particularly in regions of complex dynamical interactions such as the UTLS region.
How to cite: Qor-el-aine, A., Versick, S., and Agusti-Panareda, A.: Comparative Analysis of Transport Trace Gases in High-Resolution Simulations from ICON-ART and IFS Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7998, https://doi.org/10.5194/egusphere-egu25-7998, 2025.
Polar stratospheric clouds (PSCs) play a fundamental role in depleting stratospheric ozone. Heterogeneous reactions on their surfaces increase the concentration of active chlorine, which can catalytically destroy ozone and prolong ozone depletion by denitrifying and dehydrating the stratosphere. However, parametrisations of PSC formation is poorly included in global chemistry-climate models due to the complexity of the microphysical processes involved in PSC particle formation. This limits our ability to project the future recovery of the stratospheric ozone and the resulting climate impacts.
In this work, the representation of PSCs in the UK Earth System Model (UKESM) has been improved by refining the particle formation schemes to 1) kinetically determine the growth of nitric acid trihydrate particles rather than using a thermodynamic assumption, and 2) include the growth of supercooled ternary solution particles through the uptake of nitric acid rather than using a sulphate aerosol climatology. To validate these changes, the simulated PSCs are converted into optical properties and evaluated against satellite data. Here, a comparison of the results from the new PSC scheme in the UKESM with the observations from the satellite-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is presented. Whether the changes to the formation parameterisation improve the model’s ability to accurately simulate PSCs both temporally and spatially in the Northern and Southern hemisphere is assessed and the effect on stratospheric denitrification in the model is examined.
How to cite: Sangha, I., Orr, A., Abraham, L., Lu, H., Pitts, M., Poole, L., and Weimer, M.: Comparing simulated polar stratospheric clouds in the UKESM with CALIOP satellite data , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-610, https://doi.org/10.5194/egusphere-egu25-610, 2025.
Methane (CH4) ranks as the second most significant anthropogenic greenhouse gas following carbon dioxide (CO2). It originates from a wide range of surface sources and subsequently enters the stratosphere through the tropical tropopause. In line with the observed positive trend in tropospheric CH4, stratospheric CH4 has shown an overall increase in the long-term trend. However, contrary to the continuous increase in tropospheric CH4, stratospheric CH4 exhibits a temporal decrease in the Northern Hemisphere middle to upper stratosphere during short-time periods. This study investigates the causes behind the decreasing trend of stratospheric CH4 in the Northern Hemisphere from 1991 to 2000. We find that the extreme decrease of stratospheric CH4 from July 1994 to May 1997 contributes to the overall decreasing trend of CH4 from 1991 to 2000. This extreme decrease is attributed to the weakened meridional component of the residual circulation. The weakened meridional component attenuates the transport of CH4-rich air from the low-latitude lower stratosphere to the mid-latitude middle and upper stratosphere, leading to the observed decrease in CH4. It is further found that the smallest SST gradient in the North Pacific and adjacent regions is identified as a significant factor contributing to the weakened residual circulation and the decrease in CH4. Simulations by a chemistry-climate model support the results.
How to cite: Han, Y., Li, S., Tan, X., Guo, W., Feng, W., Li, X., Wang, F., and Xie, F.: Impact of the 1994–1997 Temporary Decrease in Northern Hemisphere Stratospheric Methane on the 1990s Methane Trend, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1407, https://doi.org/10.5194/egusphere-egu25-1407, 2025.
Changes in stratospheric water vapor and other constituents have important radiative and chemical impacts on climate. Here, we use Aura Microwave Limb Sounder (MLS) satellite observations and five meteorological and composition-focused reanalyses to examine covariations of water vapor, ozone, and carbon monoxide (CO) within the dynamical and thermodynamic environment of the tropopause layer (147–68 hPa) above the Asian summer monsoon (ASM). All reanalyses capture the thermal environment near the tropopause well and largely capture the climatological distributions and seasonal cycles of water vapor, along with the seasonal ‘ozone valley’ and convective enhancement of CO above the monsoon. The primary balance is between advective hydration and cold trap dehydration near the cold point; however, data assimilation effects are of the same order as the leading balance and therefore cannot be neglected. Applying principal component analysis to both vertical and horizontal variations of water vapor, we identify three leading modes of deseasonalized variability. The first mode, which consists of regional-scale moist or dry anomalies on the interannual scale, is decomposed into a linear trend over 2005–2021 and detrended interannual variability. The spatial pattern and sign of the linear trend in tropopause-layer water vapor over this period differ between Aura MLS and the reanalyses despite a consistent increasing trend. Signatures of interannual variability are otherwise largely consistent, except for ozone in the Japanese Reanalysis for Three-Quarters of a Century (JRA-3Q), which assimilates only total column ozone. Detrended interannual variability in water vapor can be attributed mainly to the pre-monsoon influence of the quasi-biennial oscillation. The second mode features dry or moist anomalies centered in the northeastern and southwestern quadrants of the anticyclone coupled with weaker opposing anomalies in the southeast, while the third mode features a horizontal dipole oriented east-to-west. The second and third modes vary on subseasonal scales and often occur in quadrature, representing the propagation of quasi-biweekly waves across the monsoon domain. The overall consistency between Aura MLS and reanalysis-derived modes of variability in UTLS water vapor in this region is a promising sign that atmospheric reanalyses are increasingly able to capture the processes controlling water vapor near the tropopause.
How to cite: Zhang, S. and Wright, J. S.: Mechanistic evaluation of reanalysis composition and circulation in the Asian monsoon tropopause layer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1676, https://doi.org/10.5194/egusphere-egu25-1676, 2025.
Substantial methane (CH4) emissions in Asia are efficiently transported to the upper troposphere through the monsoon dynamical system, which forms a remarkable seasonal CH4 enhancement in the upper troposphere. Using a chemical transport model GEOS-Chem driven by surface optimized CH4 flux, the CH4 enhancement over the Asian monsoon region is explored as a combined effect of the monsoon dynamical system and regionally increased emissions during late monsoon season. The spatial distributions of CH4 at the upper troposphere show strong subseasonal variability, which is closely tied to the east-west oscillation of Asian monsoon anticyclone (AMA). Besides, the AMA patterns influence the vertical structure of methane. The AMA center around 80°E favors the upward transport from north India and Bangladesh while the AMA center around 105°E favors the source from southwest China transported to the upper troposphere. The AMA center over the Iranian Plateau suppresses the vertical transport and favors the horizontal redistribution. According to our model sensitivity study, the differences in the upper tropospheric CH4 anomalies caused by large-scale circulation is 1-2 times of that caused by regional surface emissions. Our research highlights the complex interaction between monsoon dynamics and surface emissions to determine the upper tropospheric methane.
How to cite: Tao, M., Zhu, S., Cai, Z., Liu, Y., Feng, L., Pubu, S., Yu, Z., and Cao, J.: Significant Response of Methane in the Upper Troposphere to Subseasonal Variability of the Asian Monsoon Anticyclone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2047, https://doi.org/10.5194/egusphere-egu25-2047, 2025.
The Asian summer monsoon (ASM) is one of the most important events of the northern winter hemisphere. It represents an effective pathway of tropospheric air originating from the south-Asian continent into the upper troposphere (UT), which is to date only partially understood and quantified.
Through Rossby wave breaking events large filaments of ASM air are transported westward into the mid-latitudes, where they are mixed into the lower stratosphere (LS). The composition of the UTLS, especially with respect to radiatively active trace gas species, is a key factor for the global climate, which the ASM affects directly.
During the PHILEAS (Probing High Latitude Export of Air from the Asian Summer Monsoon) campaign in later summer 2023 a filament of ASM outflow was measured with the airborne limb imager GLORIA on board the German research aircraft HALO on two consecutive days. The edge of the filament was imaged in 3-D during the first flight and its outflow based on CLaMS trajectory calculations was revisited inside a second 3-D retrieval on the following day. The chemical composition of the filamented air was measured in the five different trace gas species water vapor, ozone, peroxyacetyl nitrate (PAN), nitric acid and carbon tetrachloride with unprecedented 3-D spatial resolution unique to the GLORIA instrument. The filament contains a strong tropopause fold, which perturbs its dynamical structure.
We present the tomographic retrievals of the matching flights. We are able to identify the different types of air from their chemical composition using a novel classification method based on mixture models, and are able to resolve the spatial structure of both the filament and the mixing process on the mesoscale. By revisiting the outflow of the filament we are able to directly measure the change in chemical composition and are able to determine and quantify the different possible pathways during mixing. We are able to uniquely link the different types of air to different regions of origin.
GLORIA is an airborne demonstrator for the European Space Agency Earth Explorer 11 candidate CAIRT, currently selected for Phase A. GLORIA observations offer an outlook on how exploring global processes in the UTLS would be possible using CAIRT.
How to cite: Kaumanns, J. and the GLORIA Team: Analysing mixing processes in tomographically imaged filaments of Asian Monsoon outflow during the PHILEAS campaign using computer vision, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4335, https://doi.org/10.5194/egusphere-egu25-4335, 2025.
Small changes in the equilibrium between water vapor and cirrus clouds in the upper troposphere and lower stratosphere (UTLS) can strongly influence atmospheric radiative forcing. Relative humidity with respect to ice (RHice) is a key parameter governing the formation and life cycle of cirrus clouds.
We present RHice measurements in the UTLS over the North Sea and Germany during the TPEx Learjet campaign (7–20 June 2024), conducted from Hohn, Germany, as part of the TPChange research program. Two IAGOS capacitive hygrometers (ICHs) were deployed: one mounted on the Learjet fuselage and the other on an AIRTOSS (AIRcraft Towed Sensor Shuttle) trailing approximately 70–180 m below the aircraft. This setup enabled the resolution of fine vertical structures of RHice that cannot be captured by weather and climate models.
By combining ICH RHice measurements with ECMWF ERA5 cloud ice water content along flight paths, we distinguish between cirrus and non-cirrus conditions, corroborated by the NIXE cloud probe onboard. Additionally, we examine the fine vertical structure of RHice across the extratropical tropopause and its relationship with cirrus clouds. These findings enhance our understanding of cirrus cloud occurrence and variability in this sensitive region, providing valuable insights for improving their representation in climate models.
How to cite: Li, Y., Rohs, S., Afchine, A., Spelten, N., Rolf, C., Emig, N., Bozem, H., Hoor, P., Schell, D., and Petzold, A.: Vertical Variability of Relative Humidity and Its Relation to Cirrus Clouds in the Extratropical UTLS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6027, https://doi.org/10.5194/egusphere-egu25-6027, 2025.
The extratropical transition layer (ExTL), located above the extratropical tropopause, is an atmospheric region characterized by vertical gradients in atmospheric composition, transitioning between tropospheric and deeper stratospheric properties. Since the tropopause constitutes a mixing barrier under adiabatic conditions, the existence of the ExTL is evidence of diabatic processes influencing this atmospheric region.
Although not usually thought to occur above the tropopause, cirrus clouds can be the cause of diabatic processes via radiative and latent (microphysical) effects. Here we present two cases of cirrus occurrence above the extratropical tropopause captured during the AIRTOSS-ICE (2013) and TPEx (2024) campaigns. The observational data include simultaneous in situ measurements on two platforms in different altitudes, allowing for the calculation of vertical gradients of potential temperature (static stability) and other quantities. The measurements are supported by ERA5 reanalysis data as well as Lagrangian analyses of ICON (Icosahedral Nonhydrostatic) model simulations which yield contributions from different diabatic processes to the evolution of air masses.
The results of the AIRTOSS-ICE case suggest long residence times of the cirrus in stratospheric air as well as substantial differences in static stability between in- and outside the cirrus. The second case confirms the earlier observations and extends the simultaneous in situ measurements to ozone mixing ratios. Our findings underline the importance of diabatic cloud processes for the thermodynamic structure of the ExTL and potential cross tropopause exchange.
How to cite: Emig, N., Afchine, A., Bozem, H., Chau, C. H., Hoor, P., Joppe, P., Kunkel, D., Lachnitt, H.-C., Li, Y., Miltenberger, A., and Schneider, J.: Cirrus related diabatic processes and impact on ExTL structure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8181, https://doi.org/10.5194/egusphere-egu25-8181, 2025.
Deep convection plays a crucial role in atmospheric transport, yet the associated vertical transport characteristics and timescales remain insufficiently understood. This study investigates the transport dynamics of tropical deep convection by analyzing two key timescales: transit time, the average duration for chemical species to travel from the boundary layer to the upper troposphere, and turnover time, the average residence time of chemical species in the upper troposphere. The transit time considers the parcel taken through different pathways, represented mathematically by the Green function. This calculation requires integrating over all possible pathways and times, adding complexity. In contrast, the turnover time is derived from a more straightforward mass-balance approach, depending solely on the difference in mixing ratios between the upper troposphere and the boundary layer. Using observations from the CONvective TRansport of Active Species in the Tropics (CONTRAST) experiment conducted from January to February 2014, this study estimated transit and turnover times by analyzing mixing ratio differences of trace gaseous species between the boundary layer and the upper troposphere in relation to their atmospheric lifetimes. The mean transit time was determined to be 8.4 days, while the mean turnover time was 9.3 days, indicating a remarkable similarity despite their distinct physical interpretations. This close correspondence suggests a robust consistency between the efficiency of vertical transport and upper-tropospheric residence characteristics of species within deep convective systems. These findings might indicate the simpler mass-balance residence time could be applied to represent the convection processes and offer a foundation for quantifying the impact of chemical species on the warming efficiency through convective transport.
How to cite: Wang, C.-W., Luo, Z. J., and Hung, H.-M.: Understanding Convective Transport Through Transit and Turnover Timescales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8337, https://doi.org/10.5194/egusphere-egu25-8337, 2025.
The increasing severity and duration of forest fire seasons, exemplified by the Canadian fires of 2017 (Pacific Northwest Event) and the Australian fires of 2019-2020 (Australian New Year's event), have highlighted the significant impact of these events on the stratosphere. Through intense pyrocumulonimbus activity, these fires injected large quantities of gases, biomass burning products, and other pollutants into the stratosphere. During both fires, a unique phenomenon was observed, i.e. the formation of vortex structures in the stratosphere.
Theses vortex structures confined the injected mixture of gases and aerosols, transporting them over weeks in the case of the Canadian fires and months for the Australian fires. These vortices caused localized disturbances in stratospheric chemical composition and triggered specific chemical reactions.
This study focuses on the localized impact created by these vortices, particularly their role in ozone depletion. By confining and transporting biomass combustion products, these vortex structures created conditions for unique chemistry. Data from the Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) revealed substantial increases in water vapor and biomass burning tracers, including CO, CH₃Cl, HCN, and CH₃OH. Simultaneously, significant depletions were observed in critical stratospheric reservoirs such as HNO₃, ClONO₂, and HCl. This was accompanied by a marked decrease in ozone mixing ratios with respect to unperturbed conditions, initially associated with injection of ozone-poor tropospheric air but maintained throughout the course of the vortices, questioning about the occurrence of potential ozone destruction through heterogeneous chemical processes, even if no direct evidence of chlorine activation is observed.
Similarities in the chemical content are clearly highlighted for these two events. While this analysis sheds light on the impact of these vortices on stratospheric chemistry, further investigations are necessary to explore the role of organic compounds in the observed ozone depletion and to better understand the broader implications of increasingly severe wildfire events on atmospheric composition and dynamics.
How to cite: Vieille, L., Jégou, F., Berthet, G., Duchamp, C., and Legras, B.: Observed perturbation of stratospheric chemical composition caused by wildfires smoke vortices, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10043, https://doi.org/10.5194/egusphere-egu25-10043, 2025.
Atmospheric gravity waves (GWs) play a crucial role in the dynamics of the middle atmosphere, transporting energy and momentum and substantially influencing the atmospheric energy budget. In the upper troposphere and lower stratosphere (UTLS), the composition is shaped by horizontal transport, vertical transport associated with convective systems and warm conveyor belts (WCBs), as well as turbulent mixing. GWs can drive cross-isentropic fluxes of trace gases through turbulence generation; however, their role in enhancing shear and turbulent mixing within the extratropical transition layer (ExTL) remains poorly understood.
This study investigates the characteristics and dynamics of GWs generated near an extratropical cyclone using observations from the WISE (Wave-driven ISentropic Exchange) campaign over the North Atlantic on 23 September 2017, supported by ERA-Interim and ERA5 reanalysis data. Additionally, convection-permitting simulations with the ICOsahedral Non-hydrostatic (ICON) model were conducted on a global and two higher resolution nested domains. The tracer observations reveal fine scale structures around the tropopause which are embedded in a region affected by the WCB ascent, inertia gravity waves, a mesoscale modifications in the tropopause structure.
These GWs propagate through highly sheared flows above the jet stream, perturbing background wind shear and static stability, creating conditions conducive to turbulent mixing in the lowermost stratosphere (LMS). The observed significant correlation between GW-induced absolute momentum flux and enhanced small-scale shear confirms their role in driving potential turbulence and facilitating trace gas exchange in the lower stratosphere. Bands of low Richardson number, indicative of potential turbulence, suggest regions prone to clear air turbulence (CAT).
Our findings underscore the critical role of GWs in enhancing vertical wind shear and facilitating turbulent mixing in the LMS, thereby contributing to the formation of the ExTL. These results highlight the necessity of accurately representing GWs in atmospheric models to improve predictions of clear-air turbulence and associated mixing in the UTLS.
How to cite: Umbarkar, M., Hoor, P., Schwenk, C., Miltenberger, A., Kaluza, T., Lachnitt, H.-C., and Kunkel, D.: Evidence of gravity wave contribution to vertical shear and mixing in the lower stratosphere: a WISE case study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11148, https://doi.org/10.5194/egusphere-egu25-11148, 2025.
Stratospheric aerosols have long been known to directly impact ozone concentrations through heterogeneous chemistry involving halogen and nitrogen oxide species. While these aerosols are commonly assumed to consist entirely of sulfate, measurements have revealed a significant organic fraction in the ambient lower stratosphere. Additionally, wildfires like the 2019-2020 Australian wildfires have injected large quantities of organic aerosol (OA) and gas-phase organics into the stratosphere. Satellite observations following the Australian wildfires found that chlorine species were markedly perturbed, and ozone loss had occurred. These perturbations cannot be explained based on the heterogeneous chemistry of sulfate aerosol, demonstrating the need for an improved understanding of stratospheric aerosol heterogeneous chemistry. Despite the widespread presence of OA in the stratosphere, virtually no laboratory experiments have been performed to constrain the interaction of OA with halogen and nitrogen oxide species under stratospheric conditions. The uptake of HCl to OA is particularly important because it is a possible loss pathway of Cly and a precursor to the chlorine activation reaction of ClONO2 + HCl. Here I present the development of an aerosol flow reactor to study the uptake of HCl to OA proxies to improve our understanding of stratospheric chlorine and, by extension, ozone chemistry.
How to cite: Pedersen, C., Verbart, D., and Keutsch, F.: Towards Measuring the Uptake of HCl to Organic Aerosol Proxies Under Stratospheric Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12700, https://doi.org/10.5194/egusphere-egu25-12700, 2025.
The Upper Troposphere/Lower Stratosphere (UT/LS) above the Tropical West Pacific (TWP) is an important pathway into the global stratosphere, influencing stratospheric chemistry and atmospheric dynamics overall. Its composition and dynamics are subject to both seasonal and inter-annual variations like El Niño Southern Oscillation (ENSO). We have studied the effects of ENSO on the composition and transport dynamics of the UT/LS using the variables ozone and relative humidity over ice (RHi). The analysis is based on measurements, made at the Palau Atmospheric Observatory (PAO) from 2016 until 2024 using ECC ozone sondes with Vaisala RS92/RS41 radiosondes (Müller et al., 2024a). The PAO is located on the island-state of Palau (7.3° N, 134.5° E); in the tropical warm pool and is part of the Southern Hemisphere ADditional OZone (SHADOZ) network.
We found that the UT/LS (14-18.5 km) tends to be drier and more ozone-rich during El Niño, compared to La Niña. During El Niño the ascending branch of the Walker Circulation is weakened, resulting in the suppression of local convection and thus less uplift of humid, ozone poor air-masses and accumulation of ozone in the UT/LS. Using Lagrangian-Backtrajectories, calculated with the Lagrangian Chemistry and Transport Model ATLAS (Wohltmann et al., 2009; Wohltmann et al., 2019) we further identified where the air-parcels were last mixed in a convective cell on their way to Palau. We found that under El Niño conditions, during winter and spring the distribution for this point of last mixing shifts eastward with the ascending branch of the Walker Circulation. This is in contrast to summer and autumn, where the point of last mixing distribution shifts northward, with the transport path taking an anticyclonic route from Asia to Palau, indicating the dominant influence of the Asian-Summer-Monsoon (ASM) over the typical El Niño pattern.
We conclude that ENSO is an important mode of variability for the composition and transport dynamics of the UT/LS. However, the seasonal differences for El Niño conditions highlight the importance of the ASM in this region during summer and autumn.
How to cite: Röpke, T., Müller, K., Wohltmann, I., and Rex, M.: How ENSO affects ozone, RHi and transport dynamics at the UTLS above Palau and the Tropical West Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13178, https://doi.org/10.5194/egusphere-egu25-13178, 2025.
The Earth's radiation budget could be affected by the distribution of the chemical composition in the upper troposphere/lower stratosphere (UTLS). Bi-directional stratosphere-troposphere exchange is one of the processes affecting the UTLS chemistry. This exchange could be e.g., facilitated by clear air turbulence (CAT), as it leads to diabatic mixing of chemical tracers between stratosphere and troposphere. Chemistry climate models usually ignore such small scale processes. In order to examine its importance, we developed a new submodel CAT for the climate chemistry model EMAC to parameterize the turbulent tracer mixing in the UTLS. The mixing scheme uses a 2-layer mixing algorithm based on turbulence diagnostics including the widely used Ellrod index and a newly introduced MoCATI. The model results show that the new mixing scheme could lead to a significant difference of the UTLS radiative active tracer gases in a climatological time scale. We also compared the results of the CAT submodel in EMAC with the turbulent mixing scheme of the non-hydrostatic regional model COSMO to investigate the impact of the turbulent mixing on a smaller spatial and temporal scale. The result shows that the new scheme could mix tracer significantly near the tropopause as the COSMO mixing scheme. The implementation of the new CAT submodel could allow further research on the long term climatic impact of turbulent mixing in the UTLS such as radiative budget or ozone destructive substances.
How to cite: Chau, C. H., Hoor, P., and Tost, H.: Clear air turbulence induced tracer mixing in the UTLS using Chemistry-Climate Model EMAC, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13848, https://doi.org/10.5194/egusphere-egu25-13848, 2025.
The chemical composition, especially of aerosol particles, in the extratropical upper troposphere and lower stratosphere (exUTLS) plays a crucial role in the radiation budget of the atmosphere. This composition is affected by large-scale dynamics in the stratosphere and troposphere, and additionally by small-scale processes. The effects of aerosol particle number concentration as well as the chemical composition in the extratropical lowermost stratosphere (exLMS) are a major research topic in recent years. The measurements presented in this study were taken during the TPEx campaign (Tropopause composition gradients and mixing Experiment) in summer 2024 over the North Sea and northern Germany. In addition to aerosol and trace gas measurements taken on the main platform, a Learjet 35A, we make use of partly redundant aerosol and trace gas measurements on a fully automated sensor shuttle towed by the aircraft (TOSS; towed sensor shuttle), which yield information about the vertical distribution of the measured quantities. The aim of this study is to describe the process of warm conveyor belt (WCB) uplift as source for aerosol particles in the exLMS. Although WCBs are typically associated with cloud formation and efficient precipitation formation, we were able to observe transported aerosol originating at lower altitudes in the outflow. In more detail, we present the observation of a small-scale streamer of polluted biomass burning (BB) air masses which most probably originate from forest fires over Canada. Trajectory analyses indicate that the aerosol is transported within the lowest 2 km above the surface across the Atlantic towards Europe where it undergoes the moist uplift and consequent mixing into the exLMS. The TOSS below the aircraft allows for obtaining in-situ temperature gradients over a vertical scale of 200 m. In particular potential temperature gradients show a change, presumably caused by a potential radiative warming effect of the observed BB aerosol. We compared this observation with a 1D-radiation simulation, for which the measured chemical composition as well as the size distribution of the aerosol particles were used as input parameters.
How to cite: Joppe, P., Schneider, J., Wilsch, J., Bozem, H., Breuninger, A., Curtius, J., Emig, N., Hoor, P., Kunkel, D., Lachnitt, H.-C., Kurth, I., Li, Y., Miltenberger, A., Richter, S., Rolf, C., Schwenk, C., Spelten, N., Tost, H., Vogel, A., and Borrmann, S.: Observation of biomass burning aerosol from Canada in a warm conveyor belt outflow event over Europe during TPEx, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15106, https://doi.org/10.5194/egusphere-egu25-15106, 2025.
The Asian tropopause aerosol layer (ATAL) is a feature occurring within the anticyclone of the Asian summer monsoon in the UTLS region between 13 and 18 km. This aerosol layer can have significant implications for the Earth’s radiative budget (Vernier et al., 2015) and the chemistry of the stratosphere depending on its chemical composition. So far, ammonium nitrate, organics and sulfate have been identified as the main particle compounds found in the ATAL (Appel et al., 2022). High emissions of ammonia in northern India play a crucial role for the formation of ammonium nitrate in the ATAL (Höpfner et al., 2019). However, the effect of different origin regions on the chemical composition of the ATAL remains unclear.
Here, we present a comparison between aircraft-based measurements above India and Nepal during the StratoClim campaign in summer 2017 and above the Western Pacific during the ACCLIP campaign in summer 2022. For both airborne missions, the chemical composition of aerosol particles was measured using the hybrid aerosol mass spectrometer ERICA (ERC instrument for chemical composition of aerosols; Hünig et al., 2022; Dragoneas et al., 2022). In addition, the air mass origin was determined based on kinematic backward trajectories combined with satellite-derived convective cloud top altitudes.
Our results from the non-refractory particle composition measurements reveal a larger contribution of organics and sulfate and less ammonium nitrate mass fractions during the ACCLIP mission compared to the StratoClim measurements. Combining the ERICA results and the trajectory-based product of air mass history, the differences could be explained by a large contribution from east Asian sources. In 2022, the monsoon anticyclone extended further to the northeast compared to the climatological mean. Thus, our results suggest the convection above eastern China with high emissions of SO2 and volatile organic compounds as driver of the observed changes in the ATAL composition.
References:
Appel, O., Köllner, F., Dragoneas, A., et al.: Chemical analysis of the Asian tropopause aerosol layer (ATAL) with emphasis on secondary aerosol particles using aircraft-based in situ aerosol mass spectrometry, Atmos. Chem. Phys., 22, 13607–13630, https://doi.org/10.5194/acp-22-13607-2022, 2022.
Dragoneas, A., Molleker, S., Appel, O., et al.: The realization of autonomous, aircraft-based, real-time aerosol mass spectrometry in the upper troposphere and lower stratosphere, Atmos. Meas. Tech., 15, 5719–5742, https://doi.org/10.5194/amt-15-5719-2022, 2022.
Höpfner, M., Ungermann, J., Borrmann, S. et al.: Ammonium nitrate particles formed in upper troposphere from ground ammonia sources during Asian monsoons. Nat. Geosci., 12, 608–612, https://doi.org/10.1038/s41561-019-0385-8, 2019.
Hünig, A., Appel, O., Dragoneas, A., et al.: Design, characterization, and first field deployment of a novel aircraft-based aerosol mass spectrometer combining the laser ablation and flash vaporization techniques, Atmos. Meas. Tech., 15, 2889–2921, https://doi.org/10.5194/amt-15-2889-2022, 2022.
Vernier, J. -P., Fairlie, T. D., Natarajan, M., et al.: Increase in upper tropospheric and lower stratospheric aerosol levels and its potential connection with Asian pollution. J. Geophys. Res. Atmos., 120: 1608–1619. doi: 10.1002/2014JD022372, 2015.
How to cite: Eppers, O., Köllner, F., Appel, O., Brauner, P., Ekinci, F., Molleker, S., Dragoneas, A., Smith, W., Ueyama, R., Bucci, S., Legras, B., Williamson, C., Schneider, J., and Borrmann, S.: Influence of convection over East Asia on the chemical composition of the Asian Tropopause Aerosol Layer inferred from airborne aerosol mass spectrometry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15894, https://doi.org/10.5194/egusphere-egu25-15894, 2025.
The current state of knowledge about the occurrence of turbulence in the upper troposphere and lower stratosphere (UTLS) is linked to our understanding of the underlying atmospheric instabilities, the reliability of diagnostics for identifying them in gridded numerical model data, and the availability of measurements to validate the theoretical approach. Although advances in observational coverage and model resolution have led to ongoing reevaluation of the predictive accuracy of turbulence diagnostics, their climatological characteristics, and the alignment with measurement-based climatologies, these aspects are seldom examined together within individual studies using the same datasets. This separation has left room for the interpretation of model-based turbulence maps as a key source for turbulence statistics in the free atmosphere.
We present a climatology of upper tropospheric relativ turbulence frequency maps from several hundred million automated EDR turbulence reports from commercial aircraft between January 2017 and September 2024, made available by the NOAA MADIS ACARS (National Oceanic and Atmospheric Administration – Meteorological Assimilation Data Ingest System – Aircraft Communications Addressing and Reporting System) archive. Sampling biasses in the archived data are taken into account by analyzing only consistently reported turbulence intensities along regularly sampled flight tracks.
The relative frequency maps of observed turbulence indicate distinct large-scale maxima over the northern hemisphere winter storm tracks, whereas North America exhibits minimum turbulence frequencies across broad areas. Additional maxima are evident along tropical flight routes over the Atlantic and Pacific. The 99th percentile of the Richardson number derived from ERA5 reanalysis data as one key diagnostic shows good agreement with the measurements on seasonal scales, whereas the Ti1 index indicates a distinct northward shift of the storm track maxima as the predominant feature. Linking the seasonal signals with the local forecast precision and probability of detection shows high variability across all longitudes and latitudes, which resolves the apparent contradiction between highest-ranking overall classification skill of the Ti1 index and low agreement with observations on seasonal timescales.
How to cite: Kaluza, T., Williams, P., Schultz, D., Vaughan, G., and Banyard, T.: How representative are turbulence diagnostic statistics on seasonal time scales?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18146, https://doi.org/10.5194/egusphere-egu25-18146, 2025.
We present a new retrieval protocol for chilled mirror hygrometer measurements under rapidly changing humidity conditions that enables balloon-borne frost point measurements in the upper troposphere/lower stratosphere of unprecedented accuracy. Chilled mirror hygrometers measure the frost point (or dew point) of air by quantifying the degree of saturation of the air with respect to the condensed phases of water (ice or liquid water). To this end, they attempt to determine the thermodynamic equilibrium of the condensate with the vapor phase by measuring the mirror reflectance, which changes with the thickness of the condensate. In the rapidly changing environment along the balloon trajectory, however, the adjustment of the mirror temperature to the new equilibrium point leads to frequent, damped overshoots or non-equilibrium errors. For the Cryogenic Frost Point Hygrometer (CFH), a balloon-borne chilled mirror instrument of reference quality, we (i) identify points in time along the balloon trajectory when the mirror is in true equilibrium with the gas phase, which we term ‘Golden Points’, and (ii) correct the measurements for non-equilibrium conditions between these Golden Points. For (i), we identify the points where the mirror reflectance assumes an extreme value, i.e. a maximum or a minimum. At these extreme points, the CFH mirror temperature represents the frost point with an accuracy better than 0.2 K (resulting from the uncertainties of the mirror temperature sensor and the precise timing of the Golden Points along the sounding profile). These accurately determined frost points can be used to detect and correct offsets, biases and time-lag errors in other humidity sensors flown together with CFH on the same balloon payload, such as the thin-film capacitive hygrometer of the Vaisala RS41 radiosonde. In the middle stratosphere (~ 28 km), a frost point uncertainty of 0.2 K corresponds to < 4 % uncertainty (2-σ) in H2O mixing ratio which includes the 0.3 hPa uncertainty of the RS41 radiosonde GPS-based pressure measurement. At lower altitudes, the uncertainty is even less. For (ii), we compute the time-derivative of the mirror reflectance, which is proportional to the non-equilibrium error. The proportionality factor is related to a property of the mirror condensate, which we term ‘morphological sensitivity’, and allows correction of the CFH non-equilibrium data. The sensitivity constant is determined using an a-priori reference, such as the RS41 radiosonde humidity measurements after they have been time-lag and bias-corrected by means of (i), or the Golden Points interpolation in situations where Golden Points occur frequently enough (< 50 m) and the non-equilibrium error between Golden Points is large enough (> 0.5 K). This procedure paves the way for H2O mixing ratio and relative humidity observations of unprecedented accuracy (< 4 % at 250 m vertical resolution) in the UT/LS. We showcase this novel measurement strategy and design philosophy on chilled mirror hygrometers with low global warming potential coolant, DIA-CFH (i.e., CFH using a mixture of dry ice and alcohol as coolant) and PCFH (thermoelectric coolant), flown in 2023-2024 over the central European alpine region as part of the Swiss H2O Hub project.
How to cite: Poltera, Y., Luo, B., Wienhold, F. G., and Peter, T.: Observations of water vapor in the UT/LS of unprecedented accuracy with non-equilibrium corrected frost point hygrometers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19811, https://doi.org/10.5194/egusphere-egu25-19811, 2025.
Understanding the interaction between freezing processes and the vertical movement of trace gases into the upper atmosphere during intense convection is essential for analyzing the distribution of aerosol precursors and their impact on the climate. We conducted experimental studies in a cold room with freely suspended raindrops (2 mm diameter) using an acoustic levitation setup. For the first time, we examined how freezing affects the retention of organic species, using silver iodide as the ice nucleating agent. Through quantitative chemical analysis, we calculated the retention coefficient, which represents the proportion of a chemical species that remains in the ice phase relative to its concentration prior to freezing. We measured the retention coefficients of nitric acid, formic acid, acetic acid, and 2-nitrophenol as individual compounds, as well as in binary and complex mixtures. Our findings indicate that physical properties have a greater influence on overall retention than chemical properties in the case of the larger raindrops we studied. Therefore, nearly all substances are completely retained during the freezing process in rain-sized drops, even those with low Henry’s law constants. An ice shell forms within 4.8 milliseconds after freezing begins, and this ice shell formation is the key factor preventing the expulsion of dissolved substances from the drop.
How to cite: Gautam, M., Seymore, J., Hey, M., Theis, A., Diehl, K., Bormann, S., Mitra, S. K., and Szakáll, M.: Retention During Freezing of Raindrops, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7476, https://doi.org/10.5194/egusphere-egu25-7476, 2025.
We will present the Stratosphere Troposphere Response using Infrared Vertically-resolved light Explorer (STRIVE) mission concept, which was recently selected for a competitive Phase A Concept Study within NASA's 2023 Earth System Explorers Program. STRIVE fills a critical need for high vertical resolution profiles of temperature, ozone, trace gases, and aerosols in the upper troposphere and stratosphere with near-global horizontal sampling. The goal of STRIVE is to understand the processes controlling the composition and dynamics of the upper troposphere and stratosphere, thus constraining their critical influence on the predictability of weather, climate, the ozone layer, and air quality.
STRIVE will carry two synergistic instruments: a limb-scanning imaging Dyson spectrometer retrieving profiles of temperature, trace gas concentrations, aerosol extinction, and cloud properties during day and night; and a dual-spectral multi-directional limb profiling radiometer retrieving detailed aerosol properties during day. STRIVE will measure infrared radiation emitted and scattered from the atmospheric limb to provide profiles of temperature, O3, H2O, CH4, N2O, CFCs, CO, NO2, HNO3, ClONO2, N2O5, HCN, cloud top height, polar stratospheric clouds, and aerosol properties with fine vertical resolution (1 km) and unparalleled horizontal sampling (>400,000 profiles each day). STRIVE has the novel ability to resolve small-scale vertical structures of atmospheric composition and temperature, enabling new insights into the processes of troposphere-stratosphere interactions. STRIVE will provide unique observations necessary to inform and evaluate next-generation global Earth system models in the upper troposphere and stratosphere.
How to cite: Jaeglé, L., Wang, J., Oman, L., and DeLand, M. and the STRIVE Science Team: The STRIVE Earth System Explorer Mission Concept, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7598, https://doi.org/10.5194/egusphere-egu25-7598, 2025.
Stratospheric aerosols play a critical role in the chemistry of the atmosphere and the climate through heterogeneous chemistry and radiative forcing. While sulfate aerosols in the stratosphere are relatively well-studied, the organic component of stratospheric aerosols remain poorly understood, despite their potential to impact climate and chemistry.
The Stratospheric Aerosol processes, Budget, and Radiative Effects (SABRE) 2023 campaign employed high-altitude aircraft (WB-57) with a payload designed to better characterize stratospheric aerosols. We used a cascade impactor (Mini-MOUDI 135, MSP) to collect aerosol particles between 0.18-3.2 μm aerodynamic diameter for offline analysis. Here we highlight the effectiveness of Computer-Controlled Scanning Electron Microscopy with Energy Dispersive X-ray (CCSEM-EDX) and Scanning Transmission X-ray microscopy paired with near-edge X-ray absorption fine structure (STXM-NEXAFS) to determine stratospheric aerosol composition and morphology. These properties can help constrain aerosol effects on radiative forcing and ozone chemistry. CCSEM-EDX is used to analyze the morphological and elemental properties of atmospheric aerosols on the single particle basis. STXM-NEXAFS uses carbon K-edge spectra to categorize individual stratospheric aerosols into organic carbon, elemental carbon, and inorganic content, which can be used to investigate the mixing state, morphology, and carbon functional group distribution. Preliminary findings from nanospray Desorption Electrospray Ionization (nano-DESI) further reveal molecular-level organic aerosol composition. We show comparative analysis across multiple flights, distinguishing between polar vortex and non-polar vortex air. Finally, we explore the implications of these findings for assessing the chemical and radiative properties of stratospheric aerosols, advancing our understanding of their role in Earth’s atmosphere.
How to cite: Abou-Rizk, S., Li, Y., Cheng, Z., China, S., Lai, Z., Mansoura, X., Vandergrift, G., Lata, N. N., Rahman, A., Thornberry, T., Dykema, J., and Keutsch, F.: The Organic Contribution to Stratospheric Aerosol Particles Collected during the SABRE 2023 Campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20453, https://doi.org/10.5194/egusphere-egu25-20453, 2025.
How to cite: Kult-Herdin, J., Rieder, H., and Kuchar, A.: Are springtime Arctic ozone concentrations predictable from wintertime observations?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10853, https://doi.org/10.5194/egusphere-egu25-10853, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot 5
EGU25-15068 | ECS | Posters virtual | VPS3
Stratospheric Circulation in the Southern Hemisphere: links to tropical winds, ozone and Hunga EruptionWed, 30 Apr, 14:00–15:45 (CEST) | vP5.12
The Southern Hemisphere (SH) stratosphere circulation can be organized around the development of the low-latitude jet (LLJ) in the upper stratosphere during winter months. The LLJ is associated with weak planetary wave activity, reduced residual circulation, and connections to westerly anomalies of the middle and upper stratosphere during early and mid-winter. The 2022 Hunga eruption coinciding with an anomalously strong LLJ year. Additionally, the LLJ is linked to a persistent, strong polar vortex in the lower stratosphere during October–December. This strong vortex, primarily driven by dynamical processes in winter, is further associated with enhanced ozone losses in spring, with ozone feedback reinforcing the vortex as sunlight returns in October.
How to cite: Wang, X., Yu, W., Randel, W., and Garcia, R.: Stratospheric Circulation in the Southern Hemisphere: links to tropical winds, ozone and Hunga Eruption, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15068, https://doi.org/10.5194/egusphere-egu25-15068, 2025.
Additional speaker
- Peter Hoor, Johannes Gutenberg University Mainz, Germany