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@ARTICLE{Groo:849790,
      author       = {Grooß, Jens-Uwe and Müller, Rolf and Spang, Reinhold and
                      Tritscher, Ines and Wegner, Tobias and Chipperfield, Martyn
                      P. and Feng, Wuhu and Kinnison, Douglas E. and Madronich,
                      Sasha},
      title        = {{O}n the discrepancy of {HC}l processing in the core of the
                      wintertime polar vortices},
      journal      = {Atmospheric chemistry and physics},
      volume       = {18},
      number       = {12},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2018-03902},
      pages        = {8647 - 8666},
      year         = {2018},
      abstract     = {More than 3 decades after the discovery of the ozone hole,
                      the processes involved in its formation are believed to be
                      understood in great detail. Current state-of-the-art models
                      can reproduce the observed chemical composition in the
                      springtime polar stratosphere, especially regarding the
                      quantification of halogen-catalysed ozone loss. However, we
                      report here on a discrepancy between simulations and
                      observations during the less-well-studied period of the
                      onset of chlorine activation. During this period, which in
                      the Antarctic is between May and July, model simulations
                      significantly overestimate HCl, one of the key chemical
                      species, inside the polar vortex during polar night. This
                      HCl discrepancy is also observed in the Arctic. The
                      discrepancy exists in different models to varying extents;
                      here, we discuss three independent ones, the Chemical
                      Lagrangian Model of the Stratosphere (CLaMS) as well as the
                      Eulerian models SD-WACCM (the specified dynamics version of
                      the Whole Atmosphere Community Climate Model) and
                      TOMCAT/SLIMCAT. The HCl discrepancy points to some unknown
                      process in the formulation of stratospheric chemistry that
                      is currently not represented in the models.We characterise
                      the HCl discrepancy in space and time for the Lagrangian
                      chemistry–transport model CLaMS, in which HCl in the polar
                      vortex core stays about constant from June to August in the
                      Antarctic, while the observations indicate a continuous HCl
                      decrease over this period. The somewhat smaller
                      discrepancies in the Eulerian models SD-WACCM and
                      TOMCAT/SLIMCAT are also presented. Numerical diffusion in
                      the transport scheme of the Eulerian models is identified to
                      be a likely cause for the inter-model differences. Although
                      the missing process has not yet been identified, we
                      investigate different hypotheses on the basis of the
                      characteristics of the discrepancy. An underestimated HCl
                      uptake into the polar stratospheric cloud (PSC) particles
                      that consist mainly of H2O and HNO3 cannot explain it due to
                      the temperature correlation of the discrepancy. Also, a
                      direct photolysis of particulate HNO3 does not resolve the
                      discrepancy since it would also cause changes in chlorine
                      chemistry in late winter which are not observed. The
                      ionisation caused by galactic cosmic rays provides an
                      additional NOx and HOx source that can explain only about
                      $20\%$ of the discrepancy. However, the model simulations
                      show that a hypothetical decomposition of particulate HNO3
                      by some other process not dependent on the solar elevation,
                      e.g. involving galactic cosmic rays, may be a possible
                      mechanism to resolve the HCl discrepancy. Since the
                      discrepancy reported here occurs during the beginning of the
                      chlorine activation period, where the ozone loss rates are
                      small, there is only a minor impact of about $2\%$ on the
                      overall ozone column loss over the course of Antarctic
                      winter and spring.},
      cin          = {IEK-7 / JARA-HPC},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013 / $I:(DE-82)080012_20140620$},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244) / Chemisches Lagrangesches
                      Modell der Stratosphäre (CLaMS) $(jicg11_20090701)$},
      pid          = {G:(DE-HGF)POF3-244 / $G:(DE-Juel1)jicg11_20090701$},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000435651200002},
      doi          = {10.5194/acp-18-8647-2018},
      url          = {https://juser.fz-juelich.de/record/849790},
}