Preprints
https://doi.org/10.5194/egusphere-2024-1736
https://doi.org/10.5194/egusphere-2024-1736
18 Jul 2024
 | 18 Jul 2024

Hemispheric asymmetry in recent stratospheric age of air changes

Kimberlee Dube, Susann Tegtmeier, Felix Ploeger, and Kaley A. Walker

Abstract. Many stratospheric trace gases, including O3, HCl, and NOy, have opposing trends in the Southern Hemisphere (SH) compared to the Northern Hemisphere (NH) during the last two decades. Some of this difference is due to hemispherically asymmetric changes in the rate of transport by the Brewer-Dobson Circulation (BDC), and some is due to ozone depletion and recovery. The mean Age of Air (AoA) is a common proxy for the transport rate by the BDC in models, however it cannot be directly measured. We use observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) along with results from the Chemical Lagrangian Model of the Stratosphere (CLaMS) to derive AoA anomalies and AoA trends. The AoA is derived using observations of N2O, CH4, and CFC-12, all long-lived trace gases with tropospheric sources. We also consider CLaMS simulations driven with four different reanalyses (ERA5, ERA-Interim, JRA-55, MERRA-2). We find that, irrespective of which trace gas or reanalysis is used, air in the NH aged by up to 0.3 years/decade relative to the SH over 2004–2017. The maximum hemispheric difference in aging occurs in the middle stratosphere, near 30 hPa (~24 km). We also show that the aging rate in the NH becomes smaller when the analysis is extended to 2021. The observed aging in the NH middle stratosphere contradicts model predictions of a decrease in stratospheric AoA in response to rising atmospheric greenhouse gas levels. However, the smaller aging rate during 2004–2021 compared to 2004–2017 provides some evidence that the NH aging is impacted by decadal variability and the limited length of the observation period.

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Journal article(s) based on this preprint

31 Jan 2025
Hemispheric asymmetry in recent stratospheric age of air changes
Kimberlee Dubé, Susann Tegtmeier, Felix Ploeger, and Kaley A. Walker
Atmos. Chem. Phys., 25, 1433–1447, https://doi.org/10.5194/acp-25-1433-2025,https://doi.org/10.5194/acp-25-1433-2025, 2025
Short summary
Kimberlee Dube, Susann Tegtmeier, Felix Ploeger, and Kaley A. Walker

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Very good paper - please clarify methodology and expand discussion', Simon Chabrillat, 23 Aug 2024
    • RC2: 'Excellent progress on this topic', Thomas Wagenhäuser, 12 Sep 2024
  • AC1: 'Comment on egusphere-2024-1736', Kimberlee Dubé, 21 Oct 2024

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Very good paper - please clarify methodology and expand discussion', Simon Chabrillat, 23 Aug 2024
    • RC2: 'Excellent progress on this topic', Thomas Wagenhäuser, 12 Sep 2024
  • AC1: 'Comment on egusphere-2024-1736', Kimberlee Dubé, 21 Oct 2024

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Kimberlee Dubé on behalf of the Authors (21 Oct 2024)  Author's response   Author's tracked changes   Manuscript 
ED: Publish subject to minor revisions (review by editor) (18 Nov 2024) by Beatriz Monge-Sanz
AR by Kimberlee Dubé on behalf of the Authors (26 Nov 2024)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (11 Dec 2024) by Beatriz Monge-Sanz
AR by Kimberlee Dubé on behalf of the Authors (11 Dec 2024)  Manuscript 

Journal article(s) based on this preprint

31 Jan 2025
Hemispheric asymmetry in recent stratospheric age of air changes
Kimberlee Dubé, Susann Tegtmeier, Felix Ploeger, and Kaley A. Walker
Atmos. Chem. Phys., 25, 1433–1447, https://doi.org/10.5194/acp-25-1433-2025,https://doi.org/10.5194/acp-25-1433-2025, 2025
Short summary
Kimberlee Dube, Susann Tegtmeier, Felix Ploeger, and Kaley A. Walker
Kimberlee Dube, Susann Tegtmeier, Felix Ploeger, and Kaley A. Walker

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Short summary
The transport rate of air in the stratosphere has changed in response to human emissions of greenhouse gases and ozone depleting substances. This transport rate can be approximated using measurements of long-lived traces gases. We use observations and model results to derive anomalies and trends in the mean rate of stratospheric air transport. We find that air in the northern hemisphere aged by up to 0.3 years/decade relative to air in the southern hemisphere over 2004–2017.