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@ARTICLE{Kunkel:889267,
      author       = {Kunkel, Daniel and Hoor, Peter and Kaluza, Thorsten and
                      Ungermann, Jörn and Kluschat, Björn and Giez, Andreas and
                      Lachnitt, Hans-Christoph and Kaufmann, Martin and Riese,
                      Martin},
      title        = {{E}vidence of small-scale quasi-isentropic mixing in ridges
                      of extratropical baroclinic waves},
      journal      = {Atmospheric chemistry and physics},
      volume       = {19},
      number       = {19},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2021-00172},
      pages        = {12607 - 12630},
      year         = {2019},
      abstract     = {Stratosphere–troposphere exchange within extratropical
                      cyclones provides the potential for anthropogenic and
                      natural surface emissions to rapidly reach the stratosphere
                      as well as for ozone from the stratosphere to penetrate deep
                      into the troposphere, even down into the boundary layer. The
                      efficiency of this process directly influences the surface
                      climate, the chemistry in the stratosphere, the chemical
                      composition of the extratropical transition layer, and
                      surface pollution levels. Here, we present evidence for a
                      mixing process within extratropical cyclones which has
                      gained only a small amount of attention so far and which
                      fosters the transport of tropospheric air masses into the
                      stratosphere in ridges of baroclinic waves. We analyzed
                      airborne measurement data from a research flight of the WISE
                      (Wave-driven ISentropic Exchange) campaign over the North
                      Atlantic in autumn 2017, supported by forecasts from a
                      numerical weather prediction model and trajectory
                      calculations. Further detailed process understanding is
                      obtained from experiments of idealized baroclinic life
                      cycles. The major outcome of this analysis is that air
                      masses mix in the region of the tropopause and potentially
                      enter the stratosphere in ridges of baroclinic waves at the
                      anticyclonic side of the jet without changing their
                      potential temperature drastically. This quasi-isentropic
                      exchange occurs above the outflow of warm conveyor belts, in
                      regions which exhibit enhanced static stability in the lower
                      stratosphere and a Kelvin–Helmholtz instability across the
                      tropopause. The enhanced static stability is related to
                      radiative cooling below the tropopause and the presence of
                      small-scale waves. The Kelvin–Helmholtz instability is
                      related to vertical shear of the horizontal wind associated
                      with small-scale waves at the upper edge of the jet stream.
                      The instability leads to the occurrence of turbulence and
                      consequent mixing of trace gases in the tropopause region.
                      While the overall relevance of this process has yet to be
                      assessed, it has the potential to significantly modify the
                      chemical composition of the extratropical transition layer
                      in the lowermost stratosphere in regions which have
                      previously gained a small amount of attention in terms of
                      mixing in baroclinic waves.},
      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:000489689500005},
      doi          = {10.5194/acp-19-12607-2019},
      url          = {https://juser.fz-juelich.de/record/889267},
}