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@ARTICLE{Kaufmann:858221,
      author       = {Kaufmann, Stefan and Voigt, Christiane and Heller, Romy and
                      Jurkat-Witschas, Tina and Krämer, Martina and Rolf,
                      Christian and Zöger, Martin and Giez, Andreas and Buchholz,
                      Bernhard and Ebert, Volker and Thornberry, Troy and
                      Schumann, Ulrich},
      title        = {{I}ntercomparison of midlatitude tropospheric and
                      lower-stratospheric water vapor measurements and comparison
                      to {ECMWF} humidity data},
      journal      = {Atmospheric chemistry and physics},
      volume       = {18},
      number       = {22},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2018-07121},
      pages        = {16729 - 16745},
      year         = {2018},
      abstract     = {Accurate measurement of water vapor in the
                      climate-sensitive region near the tropopause is very
                      challenging. Unexplained systematic discrepancies between
                      measurements at low water vapor mixing ratios made by
                      different instruments on airborne platforms have limited our
                      ability to adequately address a number of relevant
                      scientific questions on the humidity distribution, cloud
                      formation and climate impact in that region. Therefore,
                      during the past decade, the scientific community has
                      undertaken substantial efforts to understand these
                      discrepancies and improve the quality of water vapor
                      measurements. This study presents a comprehensive
                      intercomparison of airborne state-of-the-art in situ
                      hygrometers deployed on board the DLR (German Aerospace
                      Center) research aircraft HALO (High Altitude and LOng Range
                      Research Aircraft) during the Midlatitude CIRRUS (ML-CIRRUS)
                      campaign conducted in 2014 over central Europe. The
                      instrument intercomparison shows that the hygrometer
                      measurements agree within their combined accuracy
                      $(±10 \%$ to $15 \%,$ depending on the humidity
                      regime); total mean values agree within $2.5 \%.$ However,
                      systematic differences on the order of $10 \%$ and up to a
                      maximum of $15 \%$ are found for mixing ratios below 10
                      parts per million (ppm) H2O. A comparison of relative
                      humidity within cirrus clouds does not indicate a systematic
                      instrument bias in either water vapor or temperature
                      measurements in the upper troposphere. Furthermore, in situ
                      measurements are compared to model data from the European
                      Centre for Medium-Range Weather Forecasts (ECMWF) which are
                      interpolated along the ML-CIRRUS flight tracks. We find a
                      mean agreement within $±10 \%$ throughout the troposphere
                      and a significant wet bias in the model on the order of
                      $100 \%$ to $150 \%$ in the stratosphere close to the
                      tropopause. Consistent with previous studies, this analysis
                      indicates that the model deficit is mainly caused by too
                      weak of a humidity gradient at the tropopause},
      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:000451273900002},
      doi          = {10.5194/acp-18-16729-2018},
      url          = {https://juser.fz-juelich.de/record/858221},
}