Preprints
https://doi.org/10.5194/egusphere-2024-2208
https://doi.org/10.5194/egusphere-2024-2208
23 Jul 2024
 | 23 Jul 2024

Multi-model assessment of climatologies in the upper troposphere–lower stratosphere using the IAGOS data

Yann Cohen, Didier Hauglustaine, Nicolas Bellouin, Marianne Tronstad Lund, Sigrun Matthes, Agnieszka Skowron, Robin Thor, Ulrich Bundke, Andreas Petzold, Susanne Rohs, Valérie Thouret, Andreas Zahn, and Helmut Ziereis

Abstract. The evaluation of global chemistry-climate/transport models in the upper troposphere – lower stratosphere (UTLS) is a important step towards a better understanding of the chemical composition near the tropopause, and therefore towards a more accurate assessment of the impact of NOx emissions in this region of the atmosphere, notably by subsonic aviation. For this purpose, the current study focuses on an evaluation of long-term simulations from five global models based on in-situ measurements on board passenger aircraft (IAGOS). Most simulations span over the 1995–2017 time period, and follow a common protocol among the models. The assessment focuses on climatological averages of ozone (O3), water vapour (H2O), carbon monoxide (CO), and reactive nitrogen compounds (NOy). In the extra-tropics, the models reproduce the seasonality of ozone, water vapour and NOy in both the upper troposphere (UT) and the lowermost stratosphere (LS), but none of them reproduces the CO springtime maximum in the UT. The tropospheric tracers (CO and H2O) tend to be underestimated by the models, which is consistent with an overestimation of the cross-tropopause exchange, but does not exclude other factors as an underestimation of CO emissions, an underestimation of transport from the surface, or an overestimated CO oxidation by the hydroxyl radical (OH). Ozone is systematically overestimated in the UT by most models, and the NOx background appears as the main contributor to the ozone variability across the models. The partitioning between NOy species changes drastically across the models, and acts as a source of uncertainty on the NOx mixing ratio and on its impacts on atmospheric composition and particularly on the response to aviation NOx emissions. However, independently on the mean biases, we highlight some well-reproduced geographical and seasonal distributions, as the ITCZ seasonal shifts above Africa, the upper-tropospheric H2O maximum in the Asian summer monsoon, and the extratropical ozone (H2O) in the LS (UT) that show a high correlation with the observations. These features are encouraging regarding the simulated dynamics in both the troposphere and the stratosphere. The current study confirms the importance of an accurate separation between the UT and LS using a dynamical tracer for model results evaluation but also for model intercomparisons.

Competing interests: At least one of the co-authors is a member of the editorial board of Atmospheric Chemistry and Physics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
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Journal article(s) based on this preprint

12 Jun 2025
Evaluation of O3, H2O, CO, and NOy climatologies simulated by four global models in the upper troposphere–lower stratosphere with IAGOS measurements
Yann Cohen, Didier Hauglustaine, Nicolas Bellouin, Marianne Tronstad Lund, Sigrun Matthes, Agnieszka Skowron, Robin Thor, Ulrich Bundke, Andreas Petzold, Susanne Rohs, Valérie Thouret, Andreas Zahn, and Helmut Ziereis
Atmos. Chem. Phys., 25, 5793–5836, https://doi.org/10.5194/acp-25-5793-2025,https://doi.org/10.5194/acp-25-5793-2025, 2025
Short summary
Yann Cohen, Didier Hauglustaine, Nicolas Bellouin, Marianne Tronstad Lund, Sigrun Matthes, Agnieszka Skowron, Robin Thor, Ulrich Bundke, Andreas Petzold, Susanne Rohs, Valérie Thouret, Andreas Zahn, and Helmut Ziereis

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2208', Anonymous Referee #1, 17 Aug 2024
  • RC2: 'Comment on egusphere-2024-2208', Anonymous Referee #2, 03 Sep 2024

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2208', Anonymous Referee #1, 17 Aug 2024
  • RC2: 'Comment on egusphere-2024-2208', Anonymous Referee #2, 03 Sep 2024

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Yann Cohen on behalf of the Authors (13 Feb 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (14 Feb 2025) by Jianzhong Ma
ED: Publish subject to minor revisions (review by editor) (26 Feb 2025) by Jianzhong Ma
AR by Yann Cohen on behalf of the Authors (03 Mar 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (05 Mar 2025) by Jianzhong Ma
AR by Yann Cohen on behalf of the Authors (07 Mar 2025)  Manuscript 

Journal article(s) based on this preprint

12 Jun 2025
Evaluation of O3, H2O, CO, and NOy climatologies simulated by four global models in the upper troposphere–lower stratosphere with IAGOS measurements
Yann Cohen, Didier Hauglustaine, Nicolas Bellouin, Marianne Tronstad Lund, Sigrun Matthes, Agnieszka Skowron, Robin Thor, Ulrich Bundke, Andreas Petzold, Susanne Rohs, Valérie Thouret, Andreas Zahn, and Helmut Ziereis
Atmos. Chem. Phys., 25, 5793–5836, https://doi.org/10.5194/acp-25-5793-2025,https://doi.org/10.5194/acp-25-5793-2025, 2025
Short summary
Yann Cohen, Didier Hauglustaine, Nicolas Bellouin, Marianne Tronstad Lund, Sigrun Matthes, Agnieszka Skowron, Robin Thor, Ulrich Bundke, Andreas Petzold, Susanne Rohs, Valérie Thouret, Andreas Zahn, and Helmut Ziereis

Data sets

IAGOS time series D. Boulanger, R. Blot, U. Bundke, C. Gerbig, M. Hermann, P. Nédélec, S. Rohs, and H. Ziereis https://doi.org/10.25326/06

Model code and software

Interpol-IAGOS Yann Cohen, Valérie Thouret, Virginie Marécal, and Béatrice Josse https://doi.org/10.25326/81

Yann Cohen, Didier Hauglustaine, Nicolas Bellouin, Marianne Tronstad Lund, Sigrun Matthes, Agnieszka Skowron, Robin Thor, Ulrich Bundke, Andreas Petzold, Susanne Rohs, Valérie Thouret, Andreas Zahn, and Helmut Ziereis

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Latest update: 12 Jun 2025
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Short summary
The chemical composition of the atmosphere near the tropopause is a key parameter for evaluating the climate impact of subsonic aviation pollutants. This study uses in-situ data on board passenger aircraft to assess the ability of 5 chemistry-climate models to reproduce (bi-)decadal climatologies in ozone, carbon monoxide, water vapour, and reactive nitrogen in this region. The models reproduce well the very distinct ozone seasonality in the upper troposphere and in the lower stratosphere.
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