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@ARTICLE{Weigel:823856,
      author       = {Weigel, Ralf and Spichtinger, Peter and Mahnke, Christoph
                      and Klingebiel, Marcus and Afchine, Armin and Petzold,
                      Andreas and Krämer, Martina and Costa, Anja and Molleker,
                      Sergej and Reutter, Philipp and Szakáll, Miklós and Port,
                      Max and Grulich, Lucas and Jurkat, Tina and Minikin, Andreas
                      and Borrmann, Stephan},
      title        = {{T}hermodynamic correction of particle concentrations
                      measured by underwing probes on fast-flying aircraft},
      journal      = {Atmospheric measurement techniques},
      volume       = {9},
      number       = {10},
      issn         = {1867-8548},
      address      = {Katlenburg-Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2016-06496},
      pages        = {5135 - 5162},
      year         = {2016},
      abstract     = {Particle concentration measurements with underwing probes
                      on aircraft are impacted by air compression upstream of the
                      instrument body as a function of flight velocity. In
                      particular, for fast-flying aircraft the necessity arises to
                      account for compression of the air sample volume. Hence, a
                      correction procedure is needed to invert measured particle
                      number concentrations to ambient conditions that is commonly
                      applicable to different instruments to gain comparable
                      results. In the compression region where the detection of
                      particles occurs (i.e. under factual measurement
                      conditions), pressure and temperature of the air sample are
                      increased compared to ambient (undisturbed) conditions in
                      certain distance away from the aircraft. Conventional
                      procedures for scaling the measured number densities to
                      ambient conditions presume that the air volume probed per
                      time interval is determined by the aircraft speed (true air
                      speed, TAS). However, particle imaging instruments equipped
                      with pitot tubes measuring the probe air speed (PAS) of each
                      underwing probe reveal PAS values systematically below those
                      of the TAS. We conclude that the deviation between PAS and
                      TAS is mainly caused by the compression of the probed air
                      sample. From measurements during two missions in 2014 with
                      the German Gulfstream G-550 (HALO – High Altitude LOng
                      range) research aircraft we develop a procedure to correct
                      the measured particle concentration to ambient conditions
                      using a thermodynamic approach. With the provided equation,
                      the corresponding concentration correction factor ξ is
                      applicable to the high-frequency measurements of the
                      underwing probes, each of which is equipped with its own air
                      speed sensor (e.g. a pitot tube). ξ values of 1 to 0.85 are
                      calculated for air speeds (i.e. TAS) between 60 and
                      250 m s−1. For different instruments at individual
                      wing position the calculated ξ values exhibit strong
                      consistency, which allows for a parameterisation of ξ as a
                      function of TAS for the current HALO underwing probe
                      configuration. The ability of cloud particles to adopt
                      changes of air speed between ambient and measurement
                      conditions depends on the cloud particles' inertia as a
                      function of particle size (diameter Dp). The suggested
                      inertia correction factor μ (Dp) for liquid cloud drops
                      ranges between 1 (for Dp < 70 µm) and 0.8 (for
                      100 µm < Dp < 225 µm) but it needs to be
                      applied carefully with respect to the particles' phase and
                      nature. The correction of measured concentration by both
                      factors, ξ and μ (Dp), yields higher ambient particle
                      concentration by about $10–25 \%$ compared to
                      conventional procedures – an improvement which can be
                      considered as significant for many research applications.
                      The calculated ξ values are specifically related to the
                      considered HALO underwing probe arrangement and may differ
                      for other aircraft. Moreover, suggested corrections may not
                      cover all impacts originating from high flight velocities
                      and from interferences between the instruments and e.g. the
                      aircraft wings and/or fuselage. Consequently, it is
                      important that PAS (as a function of TAS) is individually
                      measured by each probe deployed underneath the wings of a
                      fast-flying aircraft.},
      cin          = {IEK-7 / IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013 / I:(DE-Juel1)IEK-8-20101013},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244) / 243 - Tropospheric trace
                      substances and their transformation processes (POF3-243) /
                      HITEC - Helmholtz Interdisciplinary Doctoral Training in
                      Energy and Climate Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF3-244 / G:(DE-HGF)POF3-243 /
                      G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000386666200001},
      doi          = {10.5194/amt-9-5135-2016},
      url          = {https://juser.fz-juelich.de/record/823856},
}