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@ARTICLE{Jorge:884900,
      author       = {Jorge, Teresa and Brunamonti, Simone and Poltera, Yann and
                      Wienhold, Frank G. and Luo, Bei P. and Oelsner, Peter and
                      Hanumanthu, Sreeharsha and Sing, Bhupendra B. and Körner,
                      Susanne and Dirksen, Ruud and Naja, Manish and Fadnavis,
                      Suvarna and Peter, Thomas},
      title        = {{U}nderstanding cryogenic frost point hygrometer
                      measurements after contamination by mixed-phase clouds},
      journal      = {Atmospheric measurement techniques},
      volume       = {-},
      issn         = {1867-1381},
      address      = {Katlenburg-Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2020-03305},
      pages        = {-},
      year         = {2020},
      abstract     = {Abstract. Balloon-borne water vapour measurements in the
                      (sub)tropical upper troposphere and lower stratosphere
                      (UTLS) by means of frost point hygrometers provide important
                      information on air chemistry and climate. However, the risk
                      of contamination from sublimating hydrometeors collected by
                      the intake tube may render these measurements difficult,
                      particularly after crossing low clouds containing
                      supercooled droplets. A large set of measurements during the
                      2016–2017 StratoClim balloon campaigns at the southern
                      slopes of the Himalayas allows us to perform an in-depth
                      analysis of this type of contamination. We investigate the
                      efficiency of wall-contact and freezing of supercooled
                      droplets in the intake tube and the subsequent sublimation
                      in the UTLS using Computational Fluid Dynamics (CFD). We
                      find that the airflow can enter the intake tube with
                      impingement angles up to 60°, owing to the pendulum motion
                      of the payload. Supercooled droplets with radii > 70 μm, as
                      they frequently occur in mid-tropospheric clouds, typically
                      undergo contact freezing when entering the intake tube,
                      whereas only about 50 $\%$ of droplets with 10 μm radius
                      freeze, and droplets 100 ppmv) in the stratosphere.
                      Furthermore, we use CFD to differentiate between
                      stratospheric water vapour contamination by an icy intake
                      tube and contamination caused by outgassing from the balloon
                      and payload, revealing that the latter starts playing a role
                      only at high altitudes (p},
      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},
      doi          = {10.5194/amt-2020-176},
      url          = {https://juser.fz-juelich.de/record/884900},
}