Preprints
https://doi.org/10.5194/acp-2021-934
https://doi.org/10.5194/acp-2021-934
 
25 Nov 2021
25 Nov 2021
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Estimating Brewer-Dobson circulation trends from changes in stratospheric water vapour and methane

Liubov Poshyvailo-Strube1,2,3, Rolf Müller1, Stephan Fueglistaler4,5, Michaela I. Hegglin7, Johannes C. Laube1, C. Michael Volk6, and Felix Ploeger1,6 Liubov Poshyvailo-Strube et al.
  • 1Institute of Energy and Climate Research: Stratosphere (IEK-7), Forschungszentrum Jülich, Jülich, Germany
  • 2Institute of Bio- and Geosciences: Agrosphere (IBG-3) Forschungszentrum Jülich, Jülich, Germany
  • 3Centre for High-Performance Scientific Computing in Terrestrial Systems (HPSC TerrSys), Geoverbund ABC/J, Jülich, Germany
  • 4Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA
  • 5Department of Geosciences, Princeton University, Princeton, NJ, USA
  • 6University of Wuppertal, Institute for Atmospheric and Environmental Research, Wuppertal, Germany
  • 7Department of Meteorology, University of Reading, Reading, UK

Abstract. The stratospheric meridional overturning circulation, also referred to as the Brewer-Dobson circulation (BDC), controls the composition of the stratosphere, which, in turn, affects radiation and climate. As the BDC cannot be directly measured, one has to infer its strength and trends indirectly. For instance, trace gas measurements allow the calculation of average transit times.

Satellite measurements provide information on the distributions of trace gases for the entire stratosphere, with measurements of particularly long and dense coverage available for stratospheric water vapour (H2O). Although chemical processes and boundary conditions confound interpretation, the influence of CH4 oxidation on H2O is relatively straightforward, and thus H2O is an appealing tracer for transport analysis despite these caveats. In this work, we explore how mean age of air trends can be estimated from the combination of stratospheric H2O and CH4 data. We carry out different sensitivity studies with the Chemical Lagrangian Model of the Stratosphere (CLaMS) and focus on the analysis of the periods of 1990–2006 and 1990–2017. In particular, we assess the methodological uncertainties related to the two commonly-used approximations of (i) instantaneous stratospheric entry mixing ratio propagation, and (ii) constant correlation between mean age and the fractional release factor of methane.

Our results show that the estimated mean age of air trends from the combination of observed stratospheric H2O and CH4 changes may be significantly affected by the assumed approximations. Depending on the investigated stratospheric region and the considered period, the error in estimated mean age of air decadal trends can be large – the discrepancies are up to 10 % per decade or even more at the lower stratosphere. For particular periods, the errors from the two approximations can lead to opposite effects, which may even cancel out. Finally, we propose an improvement to the approximation method by using an idealised age spectrum to propagate stratospheric entry mixing ratios. The findings of this work can be used for improving and assessing the uncertainties in stratospheric BDC trend estimation from global satellite measurements.

Liubov Poshyvailo-Strube et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-934', Anonymous Referee #1, 14 Dec 2021
  • RC2: 'Comment on acp-2021-934', Anonymous Referee #2, 30 Dec 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-934', Anonymous Referee #1, 14 Dec 2021
  • RC2: 'Comment on acp-2021-934', Anonymous Referee #2, 30 Dec 2021

Liubov Poshyvailo-Strube et al.

Liubov Poshyvailo-Strube et al.

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Short summary
The stratospheric meridional overturning circulation, also referred to as the Brewer-Dobson circulation (BDC), controls the composition of the stratosphere, which, in turn, affects radiation and climate. As the BDC cannot be directly measured, one has to infer its strength and trends indirectly. In the scope of this paper, we explore in the “model world” how mean age of air trends can be estimated from the combination of stratospheric water vapour and methane data.
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