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Dynamics and chemistry of the upper troposphere and lower stratosphere (UTLS)

The composition of the upper troposphere and the lower stratosphere (UTLS) plays a key role in the climate system. Our understanding of the interactions between dynamics, chemistry and climate in this region is rapidly advancing thanks to both observational and modelling studies. In this session we invite studies of dynamical, transport and chemical processes determining the variability and long-term trends in the composition of the UTLS, and related impacts on radiation and dynamics. This particularly includes studies of upper and middle stratospheric as well as of tropospheric dynamics and chemistry affecting the UTLS. We encourage studies bringing together recent in situ and/or remote sensing observations and model simulations of different complexity (e.g., comprehensive climate models, chemistry transport models, idealized and conceptual models).

Convener: Felix Ploeger | Co-conveners: Tanja Schuck, Hella Garny, Harald Boenisch, Daniel Kunkel
| Tue, 24 May, 08:30–11:50 (CEST), 13:20–14:50 (CEST)
Room 0.11/12

Tue, 24 May, 08:30–10:00

Chairperson: Felix Ploeger

Stratospheric circulation

Gabriel Chiodo and Marina Friedel

The important role of stratospheric feedbacks for the climate system – most notably how the ozone layer responds to anthropogenic forcings, and how that response then feeds back on the climate itself – remains largely unexplored, apart from the effects associated with gases regulated by the Montreal Protocol. This is because, to date, most models participating to CMIP inter-comparisons do not account for the complex interplay between stratospheric composition, dynamics and radiation. Here, we are providing a review of recent work highlighting the importance of such interplay on a broad range of time-scales, encompassing short-term variability to long-term climate change. First, we will show that increasing carbon dioxide levels lead to substantial changes in the ozone layer, and that these changes have a substantial effect on the circulation response to that forcing in both hemispheres (Chiodo & Polvani 2017; 2019). Then, we will review recent work on stratospheric water vapor (SWV) feedbacks under global warming, showing contrasting results concerning the effects on surface climate. Lastly, we will explore the connection between Arctic ozone and surface climate, highlighting the impacts of springtime ozone depletion on surface climate, and the sizable contribution of ozone feedbacks. Such findings demonstrate that stratospheric composition feedbacks play a key role in shaping climate response to anthropogenic forcings and stratosphere-troposphere coupling, both via radiative and dynamical processes. However, the coupling between ozone, SWV and climate is still subject to large uncertainties. We will discuss sources of uncertainty and model limitations, and implications for CMIP6.

How to cite: Chiodo, G. and Friedel, M.: Stratospheric composition feedbacks in a changing climate: a review, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11951, https://doi.org/10.5194/egusphere-egu22-11951, 2022.

Petr Šácha and Radek Zajíček

The meridional overturning mass circulation in the middle atmosphere, i.e. the Brewer- Dobson circulation (BDC), was first discovered before decades based on the distribution of trace gases and a basic analytical concept of BDC has been derived using the transformed Eulerian mean equations. Since then, BDC is usually defined as consisting of a diffusive part, and an advective, residual mean circulation.

Climate model simulations robustly show that the advective BDC part accelerates in connection to the greenhouse gas induced climate change and this acceleration dominates the middle atmospheric changes in climate model projections. A prominent quantity that is being studied as a proxy for advective BDC changes is the net tropical upwelling across the 70 hPa, which measures the amount of mass advected by residual circulation to the stratosphere and upwards.

Another robust aspect of the changes in greenhouse gas concentrations is the changing structure of the atmosphere across layers. Particularly, it was debated whether the increasing BDC is not driven by the vertical shift of the circulation. In our research, we give a complete and definitive answer to this question. We developed an analytical method that allows us to attribute the changes in tropical upwelling to kinematic causative factors such as increasing residual mean vertical mass flux, vertical shift of the circulation and for the first time, changes in width of the upwelling region and changing curvature of the 70hPa level. Our results demonstrate that this is the complete set of kinematic factors influencing the net upwelling and that all of these factors are important contributions to the net upwelling change.


How to cite: Šácha, P. and Zajíček, R.: Is the Brewer-Dobson circulation increasing or moving upward? A definitive answer., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7565, https://doi.org/10.5194/egusphere-egu22-7565, 2022.

Edward Charlesworth et al.

Both theory and climate model results suggest that the Brewer-Dobson circulation should strengthen with increasing greenhouse gas concentrations. Can this be confirmed by observations?

Directly measuring the circulation strength is not possible, so verification of this sensitivity has been limited to inferences from observations of long-lived chemicals. These methods, however, are complex and accumulation of the data required for them is difficult. Meanwhile, ozone observations are available from multiple sources spanning decades, but have only been applied to qualitative study of the stratospheric circulation, until now.

In this work, we present a new quantity - effective upwelling - which can be derived from ozone observations by a simple calculation. We then show that effective upwelling anomalies can be an effective proxy for residual circulation (i.e. TEM) upwelling. We present a comparison of TEM upwelling and effective upwelling calculated from CCMI model data to show the validity of the method, and follow this by presenting seasonal cycles, trends, and variability of effective upwelling as calculated by satellite observations.

How to cite: Charlesworth, E., Diallo, M., Plöger, F., Birner, T., and Jöckel, P.: A Method for Estimating the Evolution of Brewer-Dobson Circulation Upwelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8311, https://doi.org/10.5194/egusphere-egu22-8311, 2022.

Daniele Minganti et al.

The Brewer-Dobson Circulation (BDC) determines the distribution of long-lived tracers in the stratosphere; therefore, their changes can be used to diagnose changes in the BDC. We investigate decadal (2005-2018) trends of nitrous oxide (N2O) stratospheric columns (12-40 km) as measured by four Fourier transform infrared (FTIR) ground-based instruments and by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), and compare them with simulations by two models: a chemistry-transport model (CTM) driven by four different reanalyses, and the Whole Atmosphere Chemistry-Climate Model (WACCM). The limited sensitivity of the FTIR instruments can hide negative N2O trends in the mid-stratosphere because of the large increase in the lowermost stratosphere. When applying the ACE-FTS sampling on model datasets, the reanalyses by the European Centre for Medium Range Weather Forecast (ECMWF) compare best with ACE-FTS, but the N2O trends are consistently exaggerated. Model sensitivity tests show that while decadal N2O trends reflect changes in transport, these trends are less significant in the northern extratropics due to the larger variability of transport over timescales shorter than two years in that region. We further investigate the N2O Transformed Eulerian Mean (TEM) budget in three model datasets. The TEM analysis shows that enhanced advection affects the stratospheric N2O trends more than changes in mixing. While no ideal observational dataset currently exists, this model study of N2O trends still provides new insights about the BDC and its changes thanks to relevant sensitivity tests and the TEM analysis.

How to cite: Minganti, D., Chabrillat, S., Errera, Q., Prignon, M., Kinnison, D., Garcia, R., Abalos, M., Alsing, J., Schneider, M., Smale, D., Jones, N., and Mahieu, E.: N2O rate of change as a diagnostic of the Brewer-Dobson Circulation in the stratosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10086, https://doi.org/10.5194/egusphere-egu22-10086, 2022.

Thierry Dudok de Wit and Gisèle Krysztofiak and the N2O MTMS in situ Team

Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere and is now considered as the most important depleting source gas of stratospheric ozone (O3). Its sources are both natural and anthropogenic, mainly as an unintended by-product of human food production activities. Scientifically, a major issue is the identification and quantification of trends in the N2O concentration from the middle troposphere to the middle stratosphere (MTMS) by in-situ and remote sensing observations due to the paucity of measurements. To address the temporal variability of N2O, we assembled the first comprehensive dataset for in-situ and remote sensing N2O concentrations from 1987 to 2018, based on aircraft and balloon measurements in the MTMS. Using statistical methods, we quality-controlled all the measurements to exclude outliers and particular dynamic cases (tropospheric intrusion, stratospheric descent). This allowed us to determine N2O trends in the MTMS, based on selected observations during the period 1987-2018. This consistent dataset was also used to study the N2O seasonal cycle in order to investigate the relationship with its emission sources through zonal means and atmospheric dynamic. The results show a long-term (30 years) increase in global N2O concentration in the MTMS with an average of 0.89 ± 0.09 ppb/yr in the troposphere and 0.95 ± 0.13 ppb/yr in the stratosphere, consistent with 0.80 ppb/yr derived from ground measurements and ACE-FTS satellite measurements.

How to cite: Dudok de Wit, T. and Krysztofiak, G. and the N2O MTMS in situ Team: N2O temporal variability from the middle troposphere to the middle stratosphere based on airborne and balloon-borne observations during the period 1987-2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9807, https://doi.org/10.5194/egusphere-egu22-9807, 2022.

Stratospheric circulation - Discussion

Stratospheric smoke

Bernard Legras et al.

Ascending persistent smoke mesoscale anticyclonic vortices have been recently discovered in the mid-latitude stratosphere after several large wildfires. Such vortices can survive up to three months are rising to top altitudes between 20 and 36 km distributing aerosols along their way. They are also associated with a mini ozone hole.  We will survey these observations from active and passive satellite instruments and the reconstruction of vortices by assimilation of the signature left in the ozone and temperature measurements. We will show in particular how the temperature dipole associated with the vortices is retrieved from the GPS-RO occultation and reproduced by the assimilation and describe a remarkable case of superimposition during the crossing of two vortices.  

We will then describe our current understanding of the dynamics and stability of such structures where the radiative heating by solar absorption on the black carbon is the key forcing and where long wave radiative transfer provide a damping and diffusive effect. We will discuss the similarities and differences between simulations representing and full dynamics and the analysis that relies only on the  temperature information. A simplified 1D-model will be used as a tool for interpretation and sensitivity studies.

How to cite: Legras, B., Podglajen, A., Sellitto, P., Lestrelin, H., Reboud, J., Doc, J., and Lapeyre, G.: Ascending smoke vortices in the stratosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5972, https://doi.org/10.5194/egusphere-egu22-5972, 2022.

Sergey Khaykin et al.

The Australian bushfires of 2019/20 caused a massive injection of combustion products into the stratosphere that led to a persistent planetary-scale perturbation of all stratospheric climate-relevant variables. This extreme event enabled study of a striking atmospheric phenomenon, the smoke-charged vortex (SCV) – a persistent synoptic-scale anticyclone, which acts to confine the carbon-rich aerosol clouds during their solar-driven rise. This way, highly-concentrated absorbing aerosols are lofted above 30 km, which prolongs their stratospheric residence time and radiative effects.  Here, we use lidar observations at Lauder, New Zealand together with high-resolution radiosonde data and ozone soundings as well as satellite observations (CALIPSO, MLS, TROPOMI) and ERA5 reanalysis to characterize the optical, chemical and thermodynamical properties of a matured 7-km-tall SCV during its transfer over the South Island at 27 km altitude. The gaseous composition of the SCV was characterized by strongly enhanced water vapour and depleted ozone concentrations, leading to a synoptic-scale ozone hole with the total column reduced by up to 20%. The lidar measurements reveal a characteristic bottom-side elongation of the smoke bubble – a tail of aerosols extending over hundreds of kilometers and rotating together with the main body.

 Using long-term ground-based lidar and satellite measurement records, we show that monthly-mean stratospheric aerosol optical depth in early 2020 was highest since the major eruption of Mt. Pinatubo in 1991. With that, the removal of smoke aerosol from the stratosphere took longer than one year.  

How to cite: Khaykin, S., Querel, R., Liley, B., Sakai, T., Uchino, O., Morino, I., Godin-Beekmann, S., Hauchecorne, A., and Legras, B.: Australian smoke-charged vortex observations above New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5597, https://doi.org/10.5194/egusphere-egu22-5597, 2022.

Leehi Magaritz Ronen and Shira Raveh-Rubin

The extensive wildfires during December 2019 – January 2020 in South-East Australia released a mass of smoke into the stratosphere comparable to large volcanic eruptions. The smoke was observed throughout the southern hemisphere stratosphere months after the fires. Pyrocumulunimbus clouds (pyCb) are commonly presented as the main mechanism able to transport wildfire smoke across the tropopause into the stratosphere and were assumed as the driving mechanism also in this case. However, the smoke only appeared in the higher stratospheric levels downstream of the fires in the central south Pacific. Furthermore, there is indication that  pyCb were not active when the smoke was first seen in satellite images.  

In this study, using Lagrangian airmass trajectory analysis together with satellite observations we are able to fill the gap and identify the pathway of the smoke, its entry point into the upper levels and the mechanism that allows the smoke to enter the stratosphere. We find that the transitioning tropical cyclone Sarai merged with an extratropical cyclone to form a troposphere-wide cyclonic system, with a deep potential vorticity cutoff above it. Initially, the smoke traveled in the isentropic layer between 340 and 350 °K, just below the tropopause. Having reached the cyclone, the smoke changed direction, circulated around the low and entered the stratosphere through a dip in the tropopause height within the cutoff.

The cyclonic system described in this case study is not uncommon in these regions, possibly underlining the importance of this mechanism for troposphere-to-stratosphere exchange.

How to cite: Magaritz Ronen, L. and Raveh-Rubin, S.: Wildfire Smoke Highlights Troposphere-to-Stratosphere Pathway, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-771, https://doi.org/10.5194/egusphere-egu22-771, 2022.

Aurélien Podglajen et al.

Anticyclonically-trapped plumes were discovered following the unprecedented 2020 Australian fires, which saw the rise of a 1,000-km diameter, 6-km deep bubble of tropospheric air enriched in combustion products from 19 to 35 km asl over 3 months. Since then, a number of previous occurrences has been reported, notably in the aftermath of the 2017 Canadian fires. Lifted by solar heating from black carbon aerosols, the long-lived anticyclonic plumes are characterized by a joint upward motion of plume material and anticyclonic potential vorticity (PV).  These newly discovered objects raise fundamental questions from a dynamical standpoint. In particular, although the similar evolution of tracers and PV is a well-known property of quasi-adiabatic flows, it has no reason to hold in the presence of diabatic heating. Hence, there is seemingly a contradiction between the observed preservation of the low PV-aerosol-tracer relationship over time and fundamental properties of PV in this diabatically-forced flow.

In this presentation, we propose a conceptual model for the formation and evolution of smoked-charged anticyclones. The mechanisms at play will first be illustrated using idealized numerical simulations with the Weather Research and Forecast (WRF) model where we explore for the first time the flow response to a Lagrangian tracer locally heating the atmosphere. We will then analyze key features of the observed anticyclonic structures reproduced by the model, including the maintenance of the anticyclonic tracer bubble along its ascent, the formation of a tracer front at its top and of a tail at its lower bound, and a very low, almost-vanishing PV within the vortex. Finally, we will discuss some implications of our findings, in particular regarding the dynamical conditions favoring the formation and maintenance of such structures.

How to cite: Podglajen, A., Legras, B., Lapeyre, G., and Plougonven, R.: Dynamics of ascending smoke-charged anticyclones , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5854, https://doi.org/10.5194/egusphere-egu22-5854, 2022.

Stratospheric smoke - Discussion

Tue, 24 May, 10:20–11:50

Chairperson: Peter Hoor

Water vapour

Paul Konopka et al.

The significant climate feedback of stratospheric water vapor (SWV) necessitates quantification of changes in the SWV budget. Model simulations driven by the newest ECMWF reanalysis ERA5,  satellite observations from the Microwave Limb Sounder (MLS) and in-situ frost point hygrometer observations from Boulder consistently show substantial stratospheric moistening  after the year 2000, following a drop in water vapor at the turn of the millenium.  The time evolution of the simulated SWV anomalies is in excellent agreement with that derived from MLS.  We find strong positive SVW trends in the Northern Hemisphere and weakly negative trends over the South Pole, mainly during austral winter. Moistening of the tropical stratosphere after 2000 occurs mainly during late boreal winter/spring, reaches values of ∼0.2 ppm/decade, is well correlated with a warming of the cold point tropopause by ∼0.4 K/decade and is partially caused by volcanic eruptions and ENSO.

How to cite: Konopka, P., Tao, M., Ploeger, F., Hurst, D. F., Santee, M. L., and Riese, M.: Stratospheric moistening after 2000, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2301, https://doi.org/10.5194/egusphere-egu22-2301, 2022.

Konstantin Krueger et al.

Current NWP analyses and reanalyses are known to possess a moist bias in the lower stratosphere of the mid-latitudes [1]. An accurate representation of water vapor in the extratropical upper troposphere and lower stratosphere (UTLS), however, is crucial to correctly predict weather but also when climate models are verified against reanalysis products. This presentation uses a unique airborne multi-campaign water vapor profile data set to better characterize the vertical structure of this bias and to investigate its connection to mixing processes.

Highly-resolved water vapor profiles have been recorded with the differential absorption lidar (DIAL) WALES onboard the research aircraft HALO on various field campaigns since 2013. The high-resolution humidity profiles along the flight path provide high data availability across the entire UTLS in cloud-free situations. We analyzed mid-latitude data from more than 40 flights over the Northern Atlantic and Europe that cover a broad spectrum of synoptic situations and different seasons.

This comprehensive data set is used for a comparison with the European Centre for Medium-Range Weather Forecast’s (ECMWF) ERA5 reanalysis. First, we show an example specific humidity distribution along a cross-section in the surrounding of an extratropical cyclone. The comparison to ERA5 indicates the largest positive and negative deviations in the UT, but on average no systematic differences. In contrast, we find a coherent layer of strongly overestimated humidity above the thermal tropopause (TP) persisting along the whole flight path. Second, the vertical structure of deviations is verified for all flights. On average, deviations in the UT are relatively weak (+15%) and the minimum bias (+10%) is found at the thermal tropopause. Above the TP, within a layer of 1-1.5 km the bias rapidly increases up to a maximum of +52% while it decreases again to 15-20 % by 4 km. Although the shape of the vertical structure is similar for each flight, variations of the moist bias are observed for different seasons. For instance, the overestimation in summer is more than twice as high as for autumn observations.

A possible explanation for this systematic moist bias is overestimation of mixing of water vapor into the LS. During one field campaign, WALES additionally observed ozone profiles which allow a classification of the observations into tropospheric, stratospheric and mixed air using H2O-O3 correlations in tracer-tracer space [2]. We demonstrate that the bias is particularly increased in air that was mixed in its history which indicates that mixing processes are not sufficiently well represented by ERA5.



[1]Bland, J., Gray, S., Methven, J. and Forbes, R.: Characterising the extratropical near-tropopause analysis humidity biases and their radiative effects on temperature forecasts, Q.J.R. Met. Soc., 147(741), 3878-3898, https://doi.org/10.1002/qj.4150, 2021.

[2]Schäfler, A., Fix, A., and Wirth, M.: Mixing at the extratropical tropopause as characterized by collocated airborne H2O and O3 lidar observations, Atmos. Chem. Phys., 21, 5217–5234, https://doi.org/10.5194/acp-21-5217-2021, 2021.


How to cite: Krueger, K., Schaefler, A., Craig, G., Weissmann, M., and Wirth, M.: Vertical structure of the lower-stratospheric moist bias in ERA5 reanalyses and its relation to mixing processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2281, https://doi.org/10.5194/egusphere-egu22-2281, 2022.

Prashant Singh and Bodo Ahrens

We investigate the deep convection activity over the Himalayan Mountain (HM) and Tibetan Plateau (TP) using long-term lightning and precipitation data sets.  The observational data suggest that lightning activity during the months of May & June is greater in comparison with the rest of the year. Since lightning events are treated as a signature of deep convection, those periods can be classified as deep convective periods. In addition, Easter HM shows high deep convection activity during March-April and Western HM during September-October. The Southern TP faces maximum disturbance during June-August mainly during afternoon hours 12:00-16:00 Local Time (LT). Whereas over Eastern and Western HM region peak hours are between 22:00-04:00 LT and 15:00-20:00 LT, and Central HM peaks are between 14:00-19:00 LT. We further report the relation between changing planetary boundary layer (PBL) and water vapor (WV) transport during deep convection events at seasonal and diurnal scales over TP and HM.

How to cite: Singh, P. and Ahrens, B.: Spatial and temporal analysis of deep convection activity over Tibetan plateau and the Himalayan Mountain region., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5340, https://doi.org/10.5194/egusphere-egu22-5340, 2022.

Susanne Rohs et al.

The European research infrastructure IAGOS (In-Service Aircraft for a Global Observing System; www.iagos.org) and its predecessor MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) is a global observation system for atmospheric composition by deploying autonomous instruments aboard a fleet of commercial passenger aircraft. The combined time series spans now more than 25 years and is comprised of more than 60000 flights.  This makes it ideally suited for atmospheric research on a statistical basis.

Previous results, investigating the MOZAIC period, have already given insights into the seasonal and regional variability of the Relative Humidity (RH) distribution and the regions with ice-supersaturated air masses (ISSR). Thereby, significant ISSR occurrence exists in the Ex-UTLS (Petzold et al., ACP, 2020, doi.org/10.5194/acp-20-8157-2020), a region in which the distribution of water vapour shows a large spatial and temporal variability.

In the present study, we extend this study by using the combined time series from 1996 to 2020 for the long-term characterization of RH distribution in the Ex-UTLS. We will focus on comparing the distribution of RH for different years and seasons and analyzing the time series for potential long term trends.

How to cite: Rohs, S., Smit, H., Bundke, U., Kennert, M., Blomel, T., Gläser, J., and Petzold, A.: Relative Humidity (RH) distribution in the extratropical upper troposphere and lowermost stratosphere: Long-term evolution derived from in-situ observations of the combined IAGOS and MOZAIC time series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3789, https://doi.org/10.5194/egusphere-egu22-3789, 2022.

Patrick Konjari et al.

Water vapor in the upper troposphere and lower stratosphere (UTLS) plays an important role in the climate system. In order to investigate processes affecting water vapor in the UTLS, accurate in-situ measurements are of particular importance in this region. In this work, in-situ airborne measurements from passenger as well as from research aircrafts are utilized. Different measurement campaigns are aggregated in a combined data set named JULIA (JÜLich In-situ Airborne Data Base). JULIA uses measurements from advanced airborne instrumentation (e.g. water vapor, cloud particle radius and concentration) that were taken during more than 500 flights or balloon launches in the period 1996-2021 on different locations around the globe. Measurements from passenger aircrafts are provided by the IAGOS-MOZAIC (1994-2014) and IAGOS-CORE (2011-today) data sets (later I-M/C), with a total of more than 60.000 flights.

In this study, statistics of the UTLS water vapor distribution are investigated by combining the advantage of a large number of measurements (I-M/C) with the more advanced campaign measurements (JULIA). Therefore, a comparison of JULIA and I-M/C is performed in a climatological manner. In order to reduce the natural dynamical variability in both data sets, the water vapor distribution is analyzed vertically relative to the thermal tropopause and horizontally in equivalent latitude coordinates. In the UT, JULIA and I-M/C water vapor measurements were found to be in good accordance. In the LS however, I-M/C overestimates the very low stratospheric water vapor concentrations, with a wet bias of approximately 10 ppmv for values of less than 7 ppmv. Despite this bias, I-M/C observations better resolve the seasonality of water vapor in the UTLS than JULIA. A correction of low water vapor amounts is applied and the resulting data provide more accurate water vapor values combined with the better resolution of I-M/C. This combined data set is used to present seasonal climatologies of the vertical resolved water vapor variability in the UTLS. This residual water vapor variability can be linked to transport processes around the tropopause, which are not resolved by meteorological reanalyses.



This study is funded by the SFB 'The Tropopause Region in a Changing Atmosphere' (DFG TRR 301) project 'Large Scale Variations of Water Vapor and Ice Supersaturated Regions'.

How to cite: Konjari, P., Krämer, M., Brast, N., Reutter, P., Petzold, A., Rohs, S., and Rolf, C.: UTLS Water Vapor Climatologies derived from combined In-Situ Passenger and Research Aircraft Measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9841, https://doi.org/10.5194/egusphere-egu22-9841, 2022.

Nils Brast et al.

With their frequent abundance in the tropopause region, cirrus clouds and their potential formation regions, the so-called ice-supersaturated regions (ISSRs), may have a significant impact on the tropopause structure by diabatic processes that result from latent heating, driven by phase transitions and interaction with radiation. This may lead to an alteration of the structure of potiential vorticity(PV), leading to changes of large scale dynamics and the stratosphere-to-troposphere exchange.
One of the most important long-term in-situ data set to study water vapor content at the tropopause level is provided by the European Research Infrastructure 'In-service Aircraft for a Global Overserving System' (IAGOS) (Petzold et al., 2020). Along the flight tracks of commercial passenger aircrafts, atmospheric state parameters and chemical properties of the surrounding air are recorded by compact instrument packages. In general, the cruising altitude of these aircraft ranges between 9 and 13 km, making this data set especially viable for studies of the upper troposphere/lowermost stratosphere (UTLS). However, due to the sparsity of these measurements, IAGOS on its own cannot provide three-dimensional water vapour fields with a high temporal resolution in the UTLS region, which are necessary to gain a deeper understanding of the cirrus cloud life cycle. Instead, we use these measurements to evaluate the quality of the well-known ERA-5 data set with regards to e.g. a seasonal cycle of the vertical distribution of water mixing ratio, the relative humidity and the fraction of ice-supersaturated regions. Additionally, the benefit of the higher resolution of ERA-5 over its predecessor ERA-Interim will be quantified.

How to cite: Brast, N., Reutter, P., and Spichtinger, P.: Evaluation of ERA-5 reanalysis data with respect to the humidity in the UTLS region, using the in-situ data set IAGOS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8421, https://doi.org/10.5194/egusphere-egu22-8421, 2022.

Water vapour - Discussion

UTLS composition

Doug Kinnison et al.

The role of the Asian Summer Monsoon (ASM) on influencing the chemical composition of the upper troposphere and lower stratosphere (UTLS) will be examined using the recently developed three-dimensional MUlti-Scale Infrastructure for Chemistry & Aerosols (MUSICA) chemistry-climate model. MUSICA uses a Spectral Element dynamical core, with an ASM regional refinement (RR) option where the horizontal resolution is increased from ~1.0 º to ~0.25º and the vertical resolution is ~500m in the UTLS. For this study, the specified dynamics option is applied where the temperature, zonal and meridional winds from the NASA Goddard Earth Observing System version 5 (GEOS5) data assimilation model are used to drive the physical parameterization controlling boundary layer exchanges, advective and convective transport, and the hydrological cycle. MUSICA includes fully interactive chemistry with ~240 chemical species and over 500 chemical reactions along with the representation of sulfate, primary and aged black carbon, primary and secondary organic, sea salt, and dust aerosols. This model study will examine the magnitude and variability of ozone precursors (e.g., VOCs, NOx, and CO) and halogen ozone depleting substances in the ASM UTLS outflow region for the 2017 through 2021 boreal summer seasons. The interannual influences of the ASM chemical emissions on UTLS oxidizing capacity and odd-oxygen loss processes will be quantified. The results from this model study will address the main hypothesis of the Asian summer monsoon Chemical and Climate Impact Project (ACCLIP), namely that the western Pacific is a significant pathway for reactive chemical pollutants and climate-relevant emissions from the ASM to enter the global UTLS. ACCLIP is an NSF/NASA supported airborne mission that will based from Osan, South Korea in July/August 2022.

How to cite: Kinnison, D., Zhang, J., Honomichl, S., Smith, W., Pan, L., Tilmes, S., Zhu, Y., Emmons, L., and Saiz-Lopez, A.: Influence of the Asian Summer Monsoon on the Chemical Composition of the Upper Troposphere and Lower Stratosphere using the MUSICA Regionally Refined Chemistry Climate Model , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6619, https://doi.org/10.5194/egusphere-egu22-6619, 2022.

Linda Smoydzin and Peter Hoor

By analysing the global distribution of the highest 2% of daily CO mixing ratios at 400hPa derived from the MOPITT satellite instrument for 20 years (2000-2019), we detect very regularly regions with very high CO values (i.e. mixing ratios belonging to the globally highest 2%) over the remote northern hemispheric (NH) Pacific. Such events of elevated CO over the upper tropospheric NH-Pacific occur throughout the year, with a surprisingly high regularity and frequency (70% of all days during winter, 80% respectively during spring).

During winter, most of these pollution events are detected over the north-eastern and central NH-Pacific, during spring over the central NH-Pacific and during summer over the western NH-Pacific. We detect most pollution events during spring. To link each individual pollution event detected by the 2% filtering method with a specific CO source region, we performed trajectory calculations using MPTRAC, a lagrangian transport model. To analyse transport pathways and uplift mechanisms we combine MOPITT data, the trajectory calculations and ERA-Interim reanalysis data. It becomes apparent, that air masses from China being lifted along a frontal system into the free troposphere are the major CO source throughout the year. The contribution of other source regions and uplift mechanisms shows a strong seasonal cycle: NE-Asia in relation with upward transport of air masses in the warm conveyor belt of a midlatitude cyclone is a significant CO-source region during winter, spring and summer while India is an important source region mainly during spring and summer and SE-Asia mainly during spring.

How to cite: Smoydzin, L. and Hoor, P.: Contribution of Asian emissions to upper tropospheric CO over theremote Pacific, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11050, https://doi.org/10.5194/egusphere-egu22-11050, 2022.

Thibaut Lebourgeois et al.

IAGOS (www.iagos.org) is a European research infrastructure using commercial aircraft to measure the atmospheric composition. In particular, IAGOS provides regular carbon monoxide (CO) data since December 2001. In this study we use eighteen years of available data (from 2002 to 2019) to investigate CO anomalies throughout the entire flight i.e. vertical profiles over airports and upper troposphere/lower stratosphere (UTLS) at cruise altitude.

IAGOS flight track is divided into four distinctive vertical groups: boundary layer, middle troposphere, upper troposphere and lower stratosphere. The entire IAGOS data set has been split in 18 regions according to the geographical variability (e.g. continents over northern mid-latitudes, tropics, etc ...) and the different seasonal cycles of CO. CO anomalies are defined as air masses with CO mixing ratios above the 95th/99th percentile of the regional/seasonal/vertical distribution. This unique data set allows us to look at the variety of CO anomalies between regions and seasons.

Soft-io module which couples emission inventories and Lagrangian modelling along IAGOS flight track is used to quantify in which proportion those anomalies are linked to biomass burning and anthropogenic emissions.

The origin of those events presents high seasonal discrepancies (drought season and cold season) but also inter-annual variabilities. Anomalies coming from anthropogenic sources hit the most heavily on the lower part of the atmosphere of densely populated areas. However, none of the region, whatever the altitude range, are spared by anthropogenic pollution. Anomalies coming from biomass burning present large regional variability caused by weather conditions and biomass differences. We quantified these local and temporal variabilities to better understand processes affecting CO anomalies in the troposphere and UTLS.

How to cite: Lebourgeois, T., Sauvage, B., Wolff, P., Josse, B., Marecal, V., and Thouret, V.: Seasonal and regional characteristics of carbon monoxide anomalies as seen by IAGOS between 2002 and 2019:, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7022, https://doi.org/10.5194/egusphere-egu22-7022, 2022.

Christine Borchers et al.

The chemical composition of the upper troposphere and lower stratosphere (UTLS) region plays a major role in Earth’s climate. Therefore, it is important to learn more about the transport mechanism of secondary organic aerosols (SOA) and their precursors into the UTLS region. One fast way of transport from the boundary layer to the upper troposphere is the deep convection. Organic vapors and particles, which get dissolved in cloud droplets, can take different pathways if the droplets freeze during the transport to the UTLS. Freezing occurs via different processes, for example riming which describes the freezing of supercooled liquid droplets upon the collision with ice crystals. During the riming the organic compounds could either revolatilise in the mixed zone of clouds or stay in the particles and get washed-out by precipitation or get transported to high altitudes and may revolatilise there if the cloud droplets sublimate. This partitioning between the ice and gas phase is given by the so-called retention coefficients.

Riming experiments in the worldwide unique vertical wind tunnel facility of the Johannes Gutenberg University of Mainz were carried out to derive retention coefficients for pinonoic and pinic acid. Both substances are formed during the monoterpene oxidation and represent SOA constituents.  The simulated conditions were close to those prevailing in the mixed phase zone in convective clouds where riming is the predominant growth mechanism of ice particles. Artificial ice particles were captively floated at their approximate terminal velocity and exposed to a cloud of supercooled droplets containing the substance of interest. The cloud had liquid water contents between 1 and 3 g m-3 and temperatures ranging from -12 to -2 °C representing dry and wet growth conditions. From the concentrations of the substances before and after riming the retention coefficients for pinonic acid or pinic acid were obtained and compared to retention parameterizations available in literature.

How to cite: Borchers, C., Dörholt, K., Theis, A., Vogel, A. L., and Hoffmann, T.: Retention of secondary organic aerosols during riming experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8352, https://doi.org/10.5194/egusphere-egu22-8352, 2022.

UTLS composition - Discussion

Tue, 24 May, 13:20–14:50

Chairperson: Harald Boenisch

Meike Rotermund et al.

We report on measurements of organic, inorganic and total bromine (Brtot) in the upper troposphere and lower stratosphere (UTLS) over southern Argentina and surroundings extending down to the Antarctic Peninsula in September and November of 2019. These measurements were recorded from the German High Altitude and LOng range research aircraft (HALO) as part of the Transport and Composition of the Southern Hemisphere UTLS (SouthTRAC) research campaign. Brtot is inferred from measured total organic bromine (Brorg), i.e., the sum of bromine contained in CH3Br, the halons and the major very short-lived brominated species, added to inorganic bromine (Bryinorg), evaluated from measured BrO and photochemical modelling. Lagrangian transport modelling as well as in situ measured transport (CO and N­­2O) and air mass lag-time (SF6) tracers are used to identify air mass transport pathways into the UTLS and indicate the likely origins of bromine-rich air masses reaching the Southern Hemisphere (SH) lower stratosphere. Additionally, the SH bromine volume mixing ratios are compared with previous measurements from fall 2017 observed in the Northern Hemisphere as part of the Wave-driven ISentropic Exchange (WISE) research campaign, and the long term trend in stratospheric bromine.

How to cite: Rotermund, M., Engel, A., Grooß, J.-U., Hoor, P., Jesswein, M., Kluge, F., Schuck, T., Vogel, B., Wagenhäuser, T., Weyland, B., Zahn, A., and Pfeilsticker, K.: Organic, inorganic and total bromine measurements around the extratropical tropopause and lowermost stratosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9685, https://doi.org/10.5194/egusphere-egu22-9685, 2022.

Pratik Rao et al.

Aviation contributes to 3.5% of anthropogenic climate change in terms of Effective Radiative Forcing (ERF) and 5% in terms of temperature change. Aviation climate impact is expected to increase rapidly due to the growth of air transport sector in most regions of the world and the effects of the COVID-19 pandemic are expected to only have a temporary effect on this growth. While efforts have been made to curb CO2 emissions, non-CO2 effects that are at least equally significant according to recent research, require more attention. The EU Horizon 2020 project ClimOp considers a comprehensive approach to tackling the climate impact of aviation using novel operational measures. One such measure is climate-optimised flight planning, where small deviations can be made in aircraft trajectories to minimise their overall climate impact. Algorithmic Climate Change Functions (aCCFs) are used to estimate the climate impact of local non-CO2 effects such as nitrogen oxide (NOx) emissions (via ozone (O3) formation and methane (CH4) depletion), aviation water vapour (H2O) and contrails using weather variables directly as inputs. By using these functions in an air traffic optimisation module, climate sensitive regions are detected and avoided leading to climate-optimised trajectories. Here, we focus specifically on evaluating the effectiveness of reducing the aviation NOx induced climate impact via O3 formation, using only O3 aCCFs for the optimisation strategy. This is achieved using the chemistry climate model EMAC (ECHAM5/MESSy) and various submodels. A summer and winter day, characterised by high spatial variability of O3 aCCFs are selected, following which, air traffic over the European airspace is optimised with respect to climate as well as operating cost. The air traffic is laterally and vertically optimised separately to enable an evaluation of the horizontal and vertical pattern of O3 aCCFs. It is shown that despite the significant impact of the synoptic situation on the transport of emitted NOx, the climate-optimised flights lead to lower O3 Radiative Forcing (RF) compared to the cost-optimised flights. The study finds that while O3 aCCFs can reduce the climate impact, there are certain discrepancies in the prediction of O3 impact from aviation NOx emissions, as seen for the selected summer day. Although the aCCFs concept is a rough simplification in predicting future pathways of emissions and subsequent climate impact, we could show that it enables a reasonable first estimate. Further research is required to better describe the aCCFs allowing an improved estimate in O3-RF reduction for optimisation approaches.

How to cite: Rao, P., Yin, F., Grewe, V., Yamashita, H., Jöckel, P., Matthes, S., Mertens, M., and Frömming, C.: The analysis of the climate mitigation potential in terms of O3-Radiative Forcing from aviation NOx using O3 algorithmic climate change functions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3496, https://doi.org/10.5194/egusphere-egu22-3496, 2022.

Christoph Mahnke et al.

The impact of aviation on atmospheric aerosol, its processing, and its effects on climate is still associated with large uncertainties. We identified aircraft exhaust plumes observed during flights of the IAGOS-CARIBIC Flying Laboratory and performed a dedicated analysis of the aviation related atmospheric aerosol properties.

The European Research Infrastructure IAGOS (www.iagos.org) is using in-service aircraft as observation platforms, equipped with instrumentation for measuring gaseous species, aerosols, and cloud particles. From July 2018 to March 2020 the IAGOS-CARIBIC Flying Laboratory (equipped with 15 scientific instruments) conducted 42 operational flights aboard a Lufthansa Airbus A340-600 passenger aircraft. These flights covered routes between Munich (Germany) and destinations in North America, South Africa, and East Asia.

The IAGOS-CARIBIC data set resulting from these flights includes a wide variety of aerosol and trace gas measurements, which could be fully synchronised for a subset of 36 flights. An algorithm was developed and implemented to automatically identify unique aircraft exhaust plumes based on the 1 Hz resolved NOy and aerosol data sets. For the years 2018 to 2020, the algorithm detected about 1100 unique aircraft exhaust plumes. These exhaust plumes were further categorised as tropospheric (37 %) and stratospheric (63 %) as well as in-cloud (12 %) and clear sky (82 %) conditions, providing a solid statistical bases and global insight into the impact of aviation on aerosol and trace gas properties. For each plume the measured parameters were further divided into their respective background and plume excess values.

The analysis of the plume excess characteristics (e.g., in terms of the fraction of accumulation mode particles or the non-volatile aerosol fraction) shows that the aerosol properties inside the plume are independent from their background environment in the upper troposphere, the tropopause region, and the lowermost stratosphere. This would allow a parameterization of the plume aerosol properties independent of the flight altitude. Furthermore, we discuss the evolution of the aerosols aging/processing for the encountered aircraft exhaust plumes.

Acknowledgments: Part of this study is funded by the ACACIA project (EU Grant Agreement Number 875036). We thank all members of IAGOS-CARIBIC, in particular Deutsche Lufthansa and Lufthansa Technik for enabling the IAGOS-CARIBIC observatory. The German Federal Ministry of Education and Research (BMBF) is acknowledged for financing the instruments operation and data analysis as part of the joint project IAGOS-D under grants 01LK1301A and 01LK1301C.

How to cite: Mahnke, C., Gomes, R., Bundke, U., Berg, M., Ziereis, H., Sharma, M., Righi, M., Hendricks, J., Zahn, A., and Petzold, A.: Properties and processing of aviation induced aerosol within the UTLS observed from the IAGOS-CARIBIC Flying Laboratory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-908, https://doi.org/10.5194/egusphere-egu22-908, 2022.

Yann Cohen et al.

A wide variety of observation data sets are used to assess long-term simulations provided by chemistry-climate models (CCMs) and chemistry-transport models (CTMs). However, the upper troposphere – lower stratosphere (UTLS) is hardly assessed in the models because of uncertainties in remote measurements, a limited area for balloon-borne observations and a limited period for aircraft campaigns. Observations performed in the framework of the IAGOS program (In-service Aircraft for a Global Observing System) combine the advantages of in situ measurements in the UTLS with an almost global-scale area, a ~20-year monitoring period and a high sampling frequency. Few model assessments have been made using the IAGOS database, and none of them involved the whole cruise data set.

Cohen et al. (2021, GMD) proposed a method to project all the IAGOS data onto a model monthly grid, in order to make them ready for assessing global climatologies and seasonal cycles above several well-sampled regions in the North Hemisphere. This work has been extended to a daily resolution for an accurate separation between the upper troposphere and the lower stratosphere, and to other chemical species. In this study, we apply this method to a set of simulations generated by the following CTMs or CCMs: Oslo-CTM3, MOZART3, EMAC, UKESM, and LMDZ-OR-INCA, all involved into the ACACIA European Union program (Advancing the Science for Aviation and Climate) that focuses on the climate impact of the subsonic aviation emissions. The runs are generated following a common protocol, notably regarding the boundary conditions (e.g. emission inventories) and the chemical configurations, the latter including gaseous tropospheric and stratospheric chemistry, and heterogeneous chemistry. The multi-model assessment concerns the 1994 – 2017 period, and focuses on ozone, carbon monoxide, water vapour and reactive nitrogen (NOy) fields.

How to cite: Cohen, Y., Hauglustaine, D., Bellouin, N., Lund, M. T., Matthes, S., Petzold, A., Rohs, S., Skowron, A., Thouret, V., and Ziereis, H.: A multi-model assessment of atmospheric composition in the UTLS with the IAGOS database, in the frame of the ACACIA EU project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11424, https://doi.org/10.5194/egusphere-egu22-11424, 2022.

Jan Clemens et al.

Air mass transport within the summertime Asian monsoon circulation provides a major source of anthropogenic pollution for the upper troposphere and lower stratosphere (UTLS). In our study, we investigate the quasi-horizontal transport of airmasses from the Asian summer monsoon anticyclone (ASMA) into the extratropical lower stratosphere and their chemical evolution. For that reason, we developed a method to identify and track the air masses exported from the monsoon. This method is based on the anomalously low potential vorticity (PV) of these air masses (tropospheric low–PV cutoffs) compared to the lower-stratosphere, and uses trajectory calculations and chemical fields from the Chemical Lagrangian Model of the Stratosphere (CLaMS). The results show evidence for frequent summertime transport from the monsoon anticyclone to mid-latitudes over the North Pacific, even reaching high latitude regions of Siberia and Alaska. Particularly, the most promising region and time for measurements of transported anticyclonic air masses that cross the tropopause, is the North Pacific from July to August. Most of the low–PV cutoffs related to air masses exported from the ASMA have lifetimes shorter than one week (about 90%) and sizes smaller than 1 percent of the northern hemisphere (NH) area. The chemical composition of these air masses is characterised by carbon monoxide, ozone and water vapour mixing ratios at an intermediate range between values typical for the monsoon anticyclone and the lower-stratosphere. The chemical evolution during transport within these low–PV cutoffs shows a gradual change from characteristics of the monsoon anticyclone to characteristics of the lower stratospheric background during about one week, indicating continuous mixing with the background atmosphere.

How to cite: Clemens, J., Ploeger, F., Konopka, P., Portmann, R., Sprenger, M., and Wernli, H.: Characterization of transport from the Asian summer monsoon anticyclone into the UTLS via shedding of low-potential vorticity cutoffs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1443, https://doi.org/10.5194/egusphere-egu22-1443, 2022.

UTLS composition - Discussion

Tropopause structure and dynamics

Peter Hoor et al.

The extratropical transition layer or ExTL has been recognized about 20 years ago as part of the upper troposphere / lower stratosphere (UTLS) of the extratropics. This region encompasses the tropopause and shows the chemical characteristics of both, the stratosphere and the troposphere. Tracer-tracer correlations show this ambiguous chemical character as the integral effect of numerous different processes contributing to transport and subsequent mixing. The ExTL exhibits a chemical composition which is remarkably distinct from the deeper lowermost stratosphere. The ExTL roughly extends 2 km (or 30K potential temperature) above the local (dynamical) tropopause. Notably the ExTL has been identified with only a weak seasonality (if at all) being a persistent feature at the extratropical tropopause all year round.

Various dynamical processes have been recognized to contribute to the chemical composition of the ExTL such as larger scale processes related to stirring and mixing at the jets as well as smaller scale processes such as overshooting convection, gravity wave induced turbulence and radiatively induced diabatics at the tropopause. The sum of these processes does not only affect the tropopause sharpness (i.e. the tropopause inversion layer TIL) but also contributes to the surprisingly distinct composition of the ExTL. This is a direct result of the short time scales of cross tropopause transport and mixing compared to the lowermost stratosphere beyond the ExTL where longer time scales prevail. However, a dynamical process based explanation for the upper bound of the ExTL is yet missing.

Most recent analysis of ERA5 reanalysis data provides strong indication that vertical shear is a key feature for maintaining the ExTL over the whole year. The results show that transient shear processes are a common feature of the tropopause region with a vertical extent of 2km (or 30 K in potential temperature units) around the tropopause. Here, they constitute a persistent potential cause of dynamical instability, which may lead to turbulence and mixing and thus the observed chemical distinctness and extent of the ExTL.

How to cite: Hoor, P., Kaluza, T., Kunkel, D., Lachnitt, H.-C., Amelie, M., Bense, V., Bozem, H., and Joppe, P.: Revisiting the ExTL: From tracer correlations to dynamical processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5886, https://doi.org/10.5194/egusphere-egu22-5886, 2022.

Lars Hoffmann and Reinhold Spang

The tropopause layer plays a key role in manifold processes in atmospheric chemistry and physics. Here we compare the representation and characteristics of the lapse rate tropopause according to the definition of the World Meteorological Organization (WMO) as estimated from European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data.

Our study is based on ten-year records (2009 to 2018) of ECMWF's state-of-the-art reanalysis ERA5 and its predecessor ERA-Interim. The intercomparison reveals notable differences between ERA5 and ERA-Interim tropopause data, in particular on small spatiotemporal scales. The monthly mean differences of ERA5 minus ERA-Interim tropopause heights vary between -300 m at the transition from the tropics to the extratropics (near 30°S and 30°N) to 150 m around the equator. Mean tropopause temperatures are mostly lower in ERA5 than in ERA-Interim, with a maximum difference of up to -1.5 K in the tropics. Monthly standard deviations of tropopause heights of ERA5 are up to 350 m or 60 % larger than for ERA-Interim. Monthly standard deviations of tropopause temperatures of ERA5 exceed those of ERA-Interim by up to 1.5 K or 30 %. The occurrence frequencies of double tropopause events in ERA5 exceed those of ERA-Interim by up to 25 percentage points at mid latitudes.

We attribute the differences between the ERA5 and ERA-Interim tropopause data and the larger, more realistic variability of ERA5 to improved spatiotemporal resolution and better representation of geophysical processes in the forecast model as well as improvements in the data assimilation scheme and the utilization of additional observations in ERA5. The improved spatiotemporal resolution of ERA5 allows for a better representation of mesoscale features, in particular of gravity waves, which affect the temperature profiles in the upper troposphere and lower stratosphere and thus the tropopause height estimates.

We evaluated the quality of the ERA5 and ERA-Interim reanalysis tropopause data by comparisons with COSMIC and MetOp Global Positioning System (GPS) satellite observations as well as high-resolution radiosonde profiles. The comparison indicates an uncertainty of the first tropopause for ERA5 (ERA-Interim) of about ±150 m to ±200 m (±250 m) based on radiosonde data and ±120 m to ±150 m (±170 m to ±200 m) based on the coarser resolution GPS data at different latitudes. Consequently, ERA5 will provide more accurate information than ERA-Interim for future tropopause-related studies.

How to cite: Hoffmann, L. and Spang, R.: An assessment of tropopause characteristics of the ERA5 and ERA-Interim meteorological reanalyses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13211, https://doi.org/10.5194/egusphere-egu22-13211, 2022.

Louis Rivoire et al.

Tropopause folds are documented to be frequent occurrences in the vicinity of the polar and subtropical jets. The rapidly changing nature of the folds and their complex fine scale structure make quantifying the associated cross-tropopause transport a significant challenge. To date, observational data sets do not provide sufficient coverage or resolution to easily overcome this challenge. In addition, ground-based observations are only representative of local processes or extreme events and do not directly inform global behavior. As a result, cross-tropopause transport estimates have relied on global models and reanalyses. However, observational evidence suggests that such models are prone to errors in both the occurrence frequency of tropopause folds and the amount of transport they generate individually. These limitations serve as the basis for our work, and we focus on a new framework to quantify the occurrence frequency of tropopause folds.


Existing literature provides various methods to quantify the occurrence frequency of tropopause folds, with some using Lagrangian parcel trajectories and others using tracer-like quantities and dynamical proxies for transport. Results vary greatly in distribution and in amplitude. Overall, because tropopause folds are associated with jet streams, a central problem lies in tracking said jet streams. Existing jet tracking algorithms tend to be complex, computationally expensive, and rely on a variety of ad hoc parameters and thresholds that are based on current climatologies (such as a minimum wind speed threshold). Consequently, these algorithms produce outputs that are sensitive to arbitrary choices and that are not well suited for climate studies.


We develop a jet tracking algorithm with two central improvements:

1) it includes temporal information about the evolution of features of interest, by using a time-integrated variable that provides information about parcel transport;

2) it minimizes the use of ad hoc parameters by defining jet features qualitatively, i.e., as spatially and temporally coherent local maxima in parcel transport;

By including temporal information, we are able to track dynamically relevant features, which is a substantial improvement over existing algorithms that use instantaneous meteorological fields. We present a comparison of the jet stream features identified by our algorithm versus existing ones. We also use the output of our algorithm as a jet-relative coordinate system, which allows us to identify tropopause folding events in global data sets, and to quantify their occurrence frequency.

How to cite: Rivoire, L., Linz, M., Curbelo, J., and Golja, C.: An improved jet-relative coordinate system for the detection of tropopause folds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8959, https://doi.org/10.5194/egusphere-egu22-8959, 2022.

Thorsten Kaluza et al.

The tropopause is often concieved as a quasi-two-dimensional surface which marks the border between the troposphere to the stratosphere. The transition of chemical trace gas characteristics along with the ambiguity of different tropopause definitions however gives rise to a perception of the tropopause as a three-dimensional transition layer. The transition of the chemical composition is associated with the occurrence of distinct dynamical processes at the interface between troposphere and stratosphere. These processes foster cross-tropopause exchange and mixing around the tropopause which in turn is thought to create the chemical transition across the tropopause. A variety of diabatic processes have been proposed and analysed in this context, i.e., convective overshooting and injection of tropospheric air into the stratosphere, radiatively induced potential vorticity modification along with a modulation of the tropopause altitude and stratosphere-troposphere-exchange, and the occurrence of flow instabilities and turbulence. The overall significance of individual processes concerning the formation and maintenance of the all year existing and chemically defined extratropical transition layer remains an open research question.

This study aims to shed new light onto this question. For this an analysis is presented over the time period of two winter seasons. The goal is to obtain a tropopause relative vertical distribution of turbulence across the tropopause over the North Atlantic. A total of 1.5 million automated EDR reports from commercial aircrafts have been analysed to identify the occurrence of turbulence in the UTLS. This data is complemented by ERA5 reanalysis data to put the EDR reports into the tropopause relative coordinate system. From ERA5 several other turbulence indicators and diagnostics are calculated and will be presented to ultimately explain the vertical extent of the transition layer around the tropopause.

How to cite: Kaluza, T., Hoor, P., and Kunkel, D.: Analysis of turbulence from EDR reports and ERA5 in the UTLS over the North Atlantic during winter in a tropopause-relative framework, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3606, https://doi.org/10.5194/egusphere-egu22-3606, 2022.

Priyanka Ghosh et al.

We explore the spectral characteristics of the horizontal and vertical wind fluctuations, in the troposphere and lower stratosphere, using the Middle Atmosphere Alomar Radar System (MAARSY) during the years 2017-2020 over Andøya, Norway (69.30°N, 16.04°E). The power spectral density covers a broad frequency range of 3.5 d-1 > f > 1 h-1. The power spectra are categorized in different ranges: two frequency ranges (lower and higher than (13 h)-1), four altitude ranges (lower troposphere, middle troposphere, tropopause region, and lower stratosphere), and four seasons (spring, summer, autumn, and winter). We investigated the power-law S(f) ∝ fβ through a least-squares regression. Our results demonstrate that (i) the spectra of the horizontal winds follow a power-law with slopes of about β = -5/3 (at high-frequency), and β = -2 (at low-frequency), respectively, and the slope steepens vertically around the tropopause and seasonally during the summer, and (ii) the slope β in the vertical wind is shallow β > -1, which flattens with altitude. The momentum flux and vertical wind variance exhibit seasonal and altitudinal variations, both of which minimize in summer and maximize at the lower troposphere. The probable reason for such variation will be discussed in the presentation.



How to cite: Ghosh, P., He, M., Latteck, R., Renkwitz, T., Avsarkisov, V., Zecha, M., and Chau, J. L.: Statistical characteristics of wind fluctuations in the troposphere and lower stratosphere over Andøya, Norway (69.30°N, 16.04°E) revealed by MAARSY, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2952, https://doi.org/10.5194/egusphere-egu22-2952, 2022.

Tropopause structure and dynamics - Discussion