Thomas Wagenhäuser

Goethe University Frankfurt

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Andreas Engel

Goethe University Frankfurt

Tanja Schuck

Goethe University Frankfurt

Timo Keber

Goethe University Frankfurt

Markus Jesswein

Goethe University Frankfurt

Peter Hoor

Johannes Gutenberg University Mainz

Jens‐Uwe Grooß

Forschungszentrum Jülich

E. Atlas

University of Miami

Johannes C. Laube

University of East Anglia

S. A. Montzka

National Oceanic and Atmospheric Administration

D. R. Blake

University of California, Irvine

Cooperative Institutions

Forschungszentrum Jülich

Goethe University Frankfurt

Centre National de la Recherche Scientifique

National Oceanic and Atmospheric Administration

NSF National Center for Atmospheric Research

University of Colorado Boulder

Karlsruhe Institute of Technology

Max Planck Society

University of Bristol

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

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Reply on RC3

Thomas Wagenhäuser

Abstract. Age of stratospheric air is a concept commonly used to evaluate transport timescales in atmospheric models. The mean age can be derived from observations of a single long-lived trace gas species with a known tropospheric trend. Commonly, deriving mean age is based on the assumption that all air enters the stratosphere through the tropical (TR) tropopause. However, in the lowermost stratosphere (LMS) close to the extra-tropical (exTR) tropopause cross tropopause transport needs to be taken into account. We introduce the new exTR-TR method, which considers exTR input into the stratosphere in addition to TR input. We apply the exTR-TR method to in situ SF₆ measurements from three aircraft campaigns (PGS, WISE and SouthTRAC) and compare results to those from the conventional TR-only method. Using the TR-only method, negative mean age values are derived in the LMS close to the tropopause during the WISE campaign in northern hemispheric (NH) fall 2017. Using the new exTR-TR method instead, the number and extent of negative mean age values is reduced. With our new exTR-TR method we are thus able to derive more realistic values of typical transport times in the LMS from in situ SF₆ measurements. Absolute differences between both methods range from 0.3 to 0.4 years among the three campaigns. Interhemispheric differences in mean age are found when comparing seasonally overlapping campaign phases from the PGS and the SouthTRAC campaigns. On average, within the lowest 65 K potential temperature above the tropopause the NH LMS is 0.5 years ± 0.3 years older around March 2016 than the southern hemispheric (SH) LMS around September 2019. The derived differences between results from the exTR-TR method and the TR-only method, as well as interhemispheric differences are higher than the sensitivities of the exTR-TR method to parameter uncertainties, which are estimated to be below 0.22 years for all three campaigns.

Tropopause

Quasi-biennial oscillation

10.5194/egusphere-2022-1197-ac3

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Age of Stratospheric Air: Progress on Processes, Observations, and Long‐Term Trends

Reviews of Geophysics (2024)

Hella Garny Felix Ploeger Marta Ábalos Harald Bönisch Alejandra Castillo

Abstract 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.

10.1029/2023rg000832

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Global seasonal distribution of CH₂Br₂ and CHBr₃ in the upper troposphere and lower stratosphere

Atmospheric chemistry and physics (2022)

Markus Jesswein Rafael P. Fernández Lucas Berná Alfonso Saiz‐Lopez Jens‐Uwe Grooß

Abstract. Bromine released from the decomposition of short-lived brominated source gases contributes as a sink of ozone in the lower stratosphere. The two major contributors are CH2Br2 and CHBr3. In this study, we investigate the global seasonal distribution of these two substances, based on four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission. Observations of CH2Br2 in the free and upper troposphere indicate a pronounced seasonality in both hemispheres, with slightly larger mixing ratios in the Northern Hemisphere (NH). Compared to CH2Br2, CHBr3 in these regions shows larger variability and less clear seasonality, presenting larger mixing ratios in winter and autumn in NH midlatitudes to high latitudes. The lowermost stratosphere of SH and NH shows a very similar distribution of CH2Br2 in hemispheric spring with differences well below 0.1 ppt, while the differences in hemispheric autumn are much larger with substantially smaller values in the SH than in the NH. This suggests that transport processes may be different in both hemispheric autumn seasons, which implies that the influx of tropospheric air (“flushing”) into the NH lowermost stratosphere is more efficient than in the SH. The observations of CHBr3 support the suggestion, with a steeper vertical gradient in the upper troposphere and lower stratosphere in SH autumn than in NH autumn. However, the SH database is insufficient to quantify this difference. We further compare the observations to model estimates of TOMCAT (Toulouse Off-line Model of Chemistry And Transport) and CAM-Chem (Community Atmosphere Model with Chemistry, version 4), both using the same emission inventory of Ordóñez et al. (2012). The pronounced tropospheric seasonality of CH2Br2 in the SH is not reproduced by the models, presumably due to erroneous seasonal emissions or atmospheric photochemical decomposition efficiencies. In contrast, model simulations of CHBr3 show a pronounced seasonality in both hemispheres, which is not confirmed by observations. The distributions of both species in the lowermost stratosphere of the Northern and Southern hemispheres are overall well captured by the models with the exception of southern hemispheric autumn, where both models present a bias that maximizes in the lowest 40 K above the tropopause, with considerably lower mixing ratios in the observations. Thus, both models reproduce equivalent flushing in both hemispheres, which is not confirmed by the limited available observations. Our study emphasizes the need for more extensive observations in the SH to fully understand the impact of CH2Br2 and CHBr3 on lowermost-stratospheric ozone loss and to help constrain emissions.

Seasonality

Middle latitudes

Sink (geography)

Mixing ratio

10.5194/acp-22-15049-2022

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Global seasonal distribution of CH₂Br₂ and CHBr₃ in the upper troposphere and lower stratosphere

Markus Jesswein Rafael P. Fernández Lucas Berná Alfonso Saiz‐Lopez Jens‐Uwe Grooß

Abstract. Bromine released from the decomposition of short-lived brominated source gases contributes as a sink of ozone in the lower stratosphere. The two major contributors are CH2Br2 and CHBr3. In this study, we investigate the global seasonal distribution of these two substances, based on four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission. Observations of CH2Br2 in the free and upper troposphere indicate a pronounced seasonality in both hemispheres, with slightly larger mixing ratios in the Northern Hemisphere (NH). Compared to CH2Br2, CHBr3 in these regions shows larger variability and less clear seasonality, presenting larger mixing ratios in winter and autumn in NH mid to high latitudes. A clear CH2Br2 maximum is observed in the NH during autumn with a less pronounced similar feature in the Southern Hemisphere (SH). This suggests that transport processes may be different in both hemispheric autumn seasons, which implies that the influx of tropospheric air ("flushing") into the NH lowermost stratosphere is more efficient than in the SH. However, the SH database is insufficient to quantify this difference. We further compare the observations to model estimates of TOMCAT and CAM-Chem, both using the same emission inventory. The pronounced tropospheric seasonality of CH2Br2 in the SH is not reproduced by the models, presumably due to erroneous seasonal emissions or atmospheric photochemical decomposition efficiencies. In contrast, model simulations of CHBr3 show a pronounced seasonality in both hemispheres, which are not confirmed by observations. The distributions of both species in the lowermost stratosphere of the Northern and Southern Hemispheres are overall well captured by the models with the exception of southern hemispheric autumn, where both models present a bias that maximizes in the lowest 40 K above the tropopause, with considerably lower mixing ratios in the observations. Thus, both models reproduce equivalent "flushing" in both hemispheres, which is not confirmed by the available observations. Our study emphasises the need for more extensive 20 observations in the SH to fully understand the impact of CH2Br2 and CHBr3 on lowermost stratospheric ozone loss and to help constraining emissions.

Seasonality

Mixing ratio

10.5194/acp-2022-472

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Supplementary material to "Mean age from observations in the lowermost stratosphere: an improved method and interhemispheric differences"

Thomas Wagenhäuser Markus Jesswein Timo Keber Tanja Schuck Andreas Engel

10.5194/egusphere-2022-1197-supplement

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Organic, inorganic and total bromine measurements around the extratropical tropopause and lowermost stratosphere

Meike Rotermund Andreas Engel Jens‐Uwe Grooß Peter Hoor Markus Jesswein

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 N&#173;&#173;2O) 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.

10.5194/egusphere-egu22-9685

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Comment on egusphere-2023-1824

Tanja Schuck Johannes Degen E. J. Hintsa Peter Hoor Markus Jesswein

Abstract. Anthropogenic trace gases often exhibit interhemispheric gradients because of larger emissions in the northern hemisphere. Depending on a tracer's emission pattern and sink processes, trace gas observations can thus be used to investigate interhemispheric transport in the atmosphere. Vice versa, understanding interhemispheric transport is important for interpreting spatial tracer distributions and for inferring emissions. We combine several datasets from the upper troposphere (UT) to investigate the interhemispheric gradient of sulfur hexafluoride (SF₆) covering latitudes from ~80° N to~60° S: canister sampling based measurements from the IAGOS-CARIBIC infrastructure and data from the in-flight gas chromatography instruments GhOST and UCATS. The interhemispheric gradient of SF₆ in the UT is found to be weaker than near the surface. Using the concept of a lag time removes the increasing trend from the time series. At the most southern latitudes, a lag time of over 1 year with respect to the northern mid-latitude surface is derived, and lag times decrease over the period 2006–2020 in the tropics and in the southern hemisphere. Observations are compared to results from the two-dimensional AGAGE 12-box model. Based on EDGAR 7 emissions, fair agreement of lag times is obtained for the northern hemisphere, but southern hemispheric air appears too "old". This is consistent with earlier findings that transport from the northern extra-tropics into the tropics is too slow in many models. The influence of the emission scenario and the model transport scheme are evaluated in sensitivity runs. It is found that EDGAR 7 underestimates emissions of SF₆ globally and in the southern hemisphere, whereas northern extra-tropical emissions seem overestimated. Faster southward transport from the northern extra-tropics would be needed in the model, but transport from the southern tropics into the southern extra-tropics appears too fast.

TRACER

Sink (geography)

Trace gas

10.5194/egusphere-2023-1824-rc1

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Supplementary material to "The interhemispheric gradient of SF₆ in the upper troposphere"

Tanja Schuck Johannes Degen E. J. Hintsa Peter Hoor Markus Jesswein

10.5194/egusphere-2023-1824-supplement

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SF6 and CFC-12 measurements and mean age along HALO flight tracks during PGS, WISE and SouthTRAC

Zenodo (CERN European Organization for Nuclear Research) (2022)

Thomas Wagenhäuser Markus Jesswein Timo Keber Tanja Schuck Andreas Engel

This dataset belongs to the paper " Mean age from observations in the lowermost stratosphere: an improved method and interhemispheric differences", submitted to ACP in 2022. It contains SF₆ and CFC-12 measurements from the GhOST instrument (ECD-Channel), mean age calculated using the conventional TR-only method (mA_fit), mean age calculated using the extended exTR-TR method (mA_fit_fracts) and flight track information (delta theta, equivalent latitude, latitude, longitude in csv format for the three aircraft campaigns PGS (PGS_age.csv), WISE (WISE_age.csv) and SouthTRAC (ST_age.csv). Mean age values have not been corrected for mesospheric loss of SF₆. The Python code tools for reproducing mean age calculations are available at

https://doi.org/10.5281/zenodo.7267114

https://doi.org/10.5281/zenodo.7267203

10.5281/zenodo.7275822

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Citations (7)

Reply on RC1

Thomas Wagenhäuser

Tropopause

Quasi-biennial oscillation

10.5194/egusphere-2022-1197-ac1

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