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@ARTICLE{Kalicinsky:884901,
      author       = {Kalicinsky, Christoph and Griessbach, Sabine and Spang,
                      Reinhold},
      title        = {{R}adiative transfer simulations and observations of
                      infrared spectra in the presence of polar stratospheric
                      clouds: {D}etection and discrimination of cloud types},
      journal      = {Atmospheric measurement techniques discussions},
      volume       = {144},
      issn         = {1867-8610},
      address      = {Katlenburg-Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2020-03306},
      pages        = {},
      year         = {2020},
      abstract     = {Polar stratospheric clouds (PSCs) play an important role
                      for the spatial and temporal evolution of trace gases inside
                      the polar vortex due to different processes, such as
                      chlorine activation and NOy redistribution. As there are
                      still uncertainties in the representation of PSCs in model
                      simulations, detailed observations of PSCs and information
                      on their type (nitric acid trihydrate (NAT), supercooled
                      ternary solution (STS), and ice) are desirable. The
                      measurements inside PSCs by the airborne infrared limb
                      sounder CRISTA-NF (CRyogenic Infrared Spectrometers and
                      Telescope for the Atmosphere – New Frontiers) during the
                      RECONCILE (Reconciliation of essential process parameters
                      for an enhanced predictability of Arctic stratospheric ozone
                      loss and its climate interactions) aircraft campaign showed
                      a spectral peak at about 816 cm−1. This peak is shifted
                      compared to the peak at about 820 cm−1, which is known to
                      be caused by small NAT particles. To investigate the reason
                      for this spectral difference we performed a large set of
                      radiative transfer simulations of infrared limb emission
                      spectra in the presence of various PSCs (NAT, STS, ice, and
                      mixtures) for the airborne viewing geometry of CRISTA-NF.
                      NAT particles can cause different spectral features in the
                      region 810–820 cm−1. The simulation results show that
                      the appereance of the feature changes with increasing median
                      radius of the NAT particle size distribution from a peak at
                      820 cm−1 to a shifted peak and, finally, to a step-like
                      feature in the spectrum. Based on this behaviour we defined
                      different colour indices to detect PSCs containing NAT
                      particles and to subgroup them into three size regimes:
                      small NAT (≤ 1.0 μm), medium NAT (1.5–4.0 μm), and
                      large NAT (≥ 3.5 μm). Furthermore, we developed a method
                      to detect the bottom altitude of a cloud by using the cloud
                      index (CI), a colour ratio indicating the optical thickness,
                      and the gradient of the CI. Finally, we applied the methods
                      to observations of the CRISTA-NF instrument during one local
                      flight of the RECONCILE aircraft campaign and found STS and
                      medium sized NAT.},
      cin          = {IEK-7 / JSC},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013 / I:(DE-Juel1)JSC-20090406},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244) / 511 - Computational Science
                      and Mathematical Methods (POF3-511)},
      pid          = {G:(DE-HGF)POF3-244 / G:(DE-HGF)POF3-511},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.5194/amt-2020-144},
      url          = {https://juser.fz-juelich.de/record/884901},
}