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@ARTICLE{Ploeger:909803,
      author       = {Ploeger, Felix and Garny, Hella},
      title        = {{H}emispheric asymmetries in recent changes in the
                      stratospheric circulation},
      journal      = {Atmospheric chemistry and physics},
      volume       = {22},
      number       = {8},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2022-03424},
      pages        = {5559 - 5576},
      year         = {2022},
      abstract     = {The expected effect of ozone recovery on the stratospheric
                      Brewer–Dobson circulation (BDC) is a slow-down, strongest
                      in the Southern Hemisphere (SH). In contrast, the BDC has
                      been found to weaken more strongly in the Northern
                      Hemisphere (NH) relative to the SH in recent decades,
                      inducing substantial effects on chemical composition. We
                      investigate hemispheric asymmetries in BDC changes since
                      about 2000 in simulations with the Chemical Lagrangian Model
                      of the Stratosphere (CLaMS) driven with different reanalyses
                      (ERA5, ERA-Interim, JRA-55, MERRA-2) and contrast those to
                      free-running climate model simulations. We find that
                      age-of-air increases robustly in the NH stratosphere
                      relative to the SH in all reanalyses. Related nitrous oxide
                      changes agree well between reanalysis-driven simulations and
                      satellite measurements, providing observational evidence for
                      the hemispheric asymmetry in BDC changes. We show that the
                      composition changes in reanalyses are caused by structural
                      residual-circulation changes related to an upward shift and
                      strengthening of the deep BDC branch, resulting in longer
                      transit times, and a downward shift and weakening shallow
                      branch in the NH relative to the SH. Although climate model
                      simulations show that ozone recovery will lead to overall
                      reduced circulation and age-of-air trends, the
                      hemispherically asymmetric signal in circulation trends is
                      small compared to internal variability. Therefore, observed
                      circulation trends over the recent past are not in
                      contradiction to expectations from climate models.
                      Furthermore, the hemispheric asymmetry in BDC trends
                      imprints on the composition of the lower stratosphere, and
                      the signal might propagate into the troposphere, potentially
                      affecting composition down to the surface.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {2112 - Climate Feedbacks (POF4-211) / 2B3 - ESM (CTA - CCA)
                      (POF4-2B3) / DFG project 428312742 - TRR 301: Die
                      Tropopausenregion in einer Atmosphäre im Wandel},
      pid          = {G:(DE-HGF)POF4-2112 / G:(DE-HGF)POF4-2B3 /
                      G:(GEPRIS)428312742},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000787778000001},
      doi          = {10.5194/acp-22-5559-2022},
      url          = {https://juser.fz-juelich.de/record/909803},
}