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@ARTICLE{Konopka:280097,
      author       = {Konopka, Paul and Ploeger, Felix and Tao, Mengchu and
                      Birner, Thomas and Riese, Martin},
      title        = {{H}emispheric asymmetries and seasonality of mean age of
                      air in the lower stratosphere: {D}eep versus shallow branch
                      of the {B}rewer-{D}obson circulation},
      journal      = {Journal of geophysical research / Atmospheres},
      volume       = {120},
      number       = {5},
      issn         = {2169-897X},
      address      = {Hoboken, NJ},
      publisher    = {Wiley},
      reportid     = {FZJ-2015-07844},
      pages        = {2053 - 2066},
      year         = {2015},
      abstract     = {Based on multiannual simulations with the Chemical
                      Lagrangian Model of the Stratosphere, (CLaMS) driven by
                      ECMWF ERA-Interim reanalysis, we discuss hemispheric
                      asymmetries and the seasonality of the mean age of air (AoA)
                      in the lower stratosphere. First, the planetary wave forcing
                      of the Brewer-Dobson circulation is quantified in terms of
                      Eliassen Palm flux divergence calculated by using the
                      isentropic coordinate θ. While the forcing of the deep
                      branch at θ = 1000 K (around 10 hPa) has a clear maximum in
                      each hemisphere during the respective winter, the shallow
                      branch of the Brewer-Dobson circulation, i.e., between 100
                      and 70 hPa (380 < θ < 420 K), shows almost opposite
                      seasonality in both hemispheres with a pronounced minimum
                      between June and September in the Southern Hemisphere.
                      Second, we decompose the time-tendency of AoA into the
                      contributions of the residual circulation and of eddy mixing
                      by analyzing the zonally averaged tracer continuity
                      equation. In the tropical lower stratosphere between ±30°,
                      the air becomes younger during boreal winter and older
                      during boreal summer. During boreal winter, the decrease of
                      AoA due to tropical upwelling outweighs aging by isentropic
                      mixing. In contrast, weaker isentropic mixing outweighs an
                      even weaker upwelling in boreal summer and fall making the
                      air older during these seasons. Poleward of 60°, the deep
                      branch locally increases AoA and eddy mixing locally
                      decreases AoA with the strongest net decrease during spring.
                      Eddy mixing in the Northern Hemisphere outweighs that in the
                      Southern Hemisphere throughout the year.},
      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) / HITEC - Helmholtz
                      Interdisciplinary Doctoral Training in Energy and Climate
                      Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF3-244 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000351678100026},
      doi          = {10.1002/2014JD022429},
      url          = {https://juser.fz-juelich.de/record/280097},
}