Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2016-1144
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
23 Jan 2017
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Effects of mixing on resolved and unresolved scales on stratospheric age of air
Simone Dietmüller1, Hella Garny1, Felix Plöger2, Patrick Jöckel1, and Cai Duy1 1Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
2Institute of Energy and Climate Research (IEK-7), Forschungszentrum Jülich GmbH, Jülich, Germany
Abstract. Mean age of air (AoA) is a widely used metric to describe the transport along the Brewer-Dobson circulation. We seek to untangle the effects of different processes on the simulation of AoA, using the chemistry-climate model EMAC and the Lagrangian chemistry transport model CLaMS. Here, the effects of residual transport and two-way mixing on AoA are calculated. To do so, we calculate the residual circulation transit time (RCTT). The difference of AoA and RCTT is defined as aging by mixing. However, as diffusion is also included in this difference, we further use a method to directly calculate aging by mixing on resolved scales. Comparing these two methods of calculating aging by mixing allows for separating the effect of unresolved aging by mixing (which we term "aging by diffusion" in the following) in EMAC and CLaMS. We find that diffusion impacts AoA by making air older, but its contribution plays a minor role (order of 10 %) in all simulations. However, due to the different advection schemes of the two models, aging by diffusion has a larger effect on AoA and mixing efficiency in EMAC, compared to CLaMS. Regarding the trends in AoA, in CLaMS the AoA trend is negative throughout the stratosphere except in the northern hemisphere middle stratosphere, consistent with observations. This slight positive trend is neither reproduced in a free-running nor in a nudged simulation with EMAC – in both simulations the AoA trend is negative throughout the stratosphere. Trends in AoA are mainly driven by the contributions of RCTT and aging by mixing, whereas the contribution of aging by diffusion plays a minor role.

Citation: Dietmüller, S., Garny, H., Plöger, F., Jöckel, P., and Duy, C.: Effects of mixing on resolved and unresolved scales on stratospheric age of air, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2016-1144, in review, 2017.
Simone Dietmüller et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Anonymous Review of Dietmüller et al.', Anonymous Referee #2, 13 Feb 2017 Printer-friendly Version 
AC1: 'Reply to Referee #2', Simone Dietmüller, 24 Apr 2017 Printer-friendly Version Supplement 
 
RC2: 'Review of Dietmuller et al', Eric Ray, 21 Feb 2017 Printer-friendly Version 
AC2: 'Reply to E. Ray', Simone Dietmüller, 24 Apr 2017 Printer-friendly Version Supplement 
Simone Dietmüller et al.
Simone Dietmüller et al.

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