Preprints
https://doi.org/10.5194/egusphere-2024-2117
https://doi.org/10.5194/egusphere-2024-2117
22 Jul 2024
 | 22 Jul 2024

Age of air from ACE-FTS measurements of sulfur hexafluoride

Laura N. Saunders, Kaley A. Walker, Gabriele P. Stiller, Thomas von Clarmann, Florian Haenel, Hella Garny, Harald Bönisch, Chris D. Boone, Ariana E. Castillo, Andreas Engel, Johannes C. Laube, Marianna Linz, Felix Ploeger, David A. Plummer, Eric A. Ray, and Patrick E. Sheese

Abstract. Climate models predict that the Brewer-Dobson Circulation (BDC) will accelerate due to tropospheric warming. This would increase trace gas transport from the tropics to higher latitudes and alter the spatial distribution of greenhouse gases and therefore impact the radiative properties of the atmosphere, resulting in a feedback effect. The stratospheric “age of air”, representing the time since air in the stratosphere exited the troposphere, serves as a diagnostic tool for assessing stratospheric transport. Changes in age of air can therefore indicate changes in the BDC, but detecting these changes requires a long-term observation-based record of age of air. The long-lived trace gas sulfur hexafluoride (SF6) has an increasing concentration in the troposphere and can serve as a clock to derive age of air. However, it is difficult to measure due to its small concentrations, so historically, the availability of age of air datasets derived from SF6 has been limited. Existing datasets include age of air derived from balloon- and aircraft-based measurements from the 1970s to the present and using satellite-based measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) for the 2002–2012 period. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) provides the longest available continuous time series of vertically-resolved SF6 measurements, spanning 2004 to the present. In this study, a new age of air product is derived from the ACE-FTS SF6 dataset. The method is also applied to the MIPAS SF6 dataset. The ACE-FTS product is in good agreement with other observation-based age of air datasets and shows the expected global distribution of age of air values. Two applications of the dataset are then demonstrated: evaluating age of air in a chemistry climate model and calculating the linear trend in age of air in twelve regions within the lower stratospheric midlatitudes (14–20 km, 40–70°) in each hemisphere. All trends are negative and significant to two standard deviations. This is therefore the first observation-based age of air trend study to suggest an acceleration of the shallow branch of the BDC, which transports air poleward in the lower stratosphere, in both hemispheres.

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Laura N. Saunders, Kaley A. Walker, Gabriele P. Stiller, Thomas von Clarmann, Florian Haenel, Hella Garny, Harald Bönisch, Chris D. Boone, Ariana E. Castillo, Andreas Engel, Johannes C. Laube, Marianna Linz, Felix Ploeger, David A. Plummer, Eric A. Ray, and Patrick E. Sheese

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2117', Anonymous Referee #1, 28 Aug 2024
  • RC2: 'Comment on egusphere-2024-2117', Anonymous Referee #2, 14 Sep 2024
Laura N. Saunders, Kaley A. Walker, Gabriele P. Stiller, Thomas von Clarmann, Florian Haenel, Hella Garny, Harald Bönisch, Chris D. Boone, Ariana E. Castillo, Andreas Engel, Johannes C. Laube, Marianna Linz, Felix Ploeger, David A. Plummer, Eric A. Ray, and Patrick E. Sheese
Laura N. Saunders, Kaley A. Walker, Gabriele P. Stiller, Thomas von Clarmann, Florian Haenel, Hella Garny, Harald Bönisch, Chris D. Boone, Ariana E. Castillo, Andreas Engel, Johannes C. Laube, Marianna Linz, Felix Ploeger, David A. Plummer, Eric A. Ray, and Patrick E. Sheese

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Short summary
We present a 17-year stratospheric age of air dataset derived from ACE-FTS satellite measurements of sulfur hexafluoride. This is the longest continuous, global, and vertically resolved age of air time series available to date. In this paper, we show that this dataset agrees well with age of air datasets based on measurements from other instruments. We also present trends in the midlatitude lower stratosphere that indicate changes in the global circulation that are predicted by climate models.