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@ARTICLE{Dietmller:841713,
      author       = {Dietmüller, S. and Garny, H. and Ploeger, Felix and
                      Jöckel, P. and Duy, C.},
      title        = {{E}ffects of mixing on resolved and unresolved scales on
                      stratospheric age of air},
      journal      = {Atmospheric chemistry and physics},
      volume       = {17},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2018-00021},
      pages        = {7703-7719},
      year         = {2017},
      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
                      (ECHAM/MESSy Atmospheric Chemistry) and the Chemical
                      Lagrangian Model of the Stratosphere (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.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244)},
      pid          = {G:(DE-HGF)POF3-244},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000404403900003},
      doi          = {10.5194/acp-17-7703-2017},
      url          = {https://juser.fz-juelich.de/record/841713},
}