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@ARTICLE{Kalicinsky:891060,
      author       = {Kalicinsky, Christoph and Griessbach, Sabine and Spang,
                      Reinhold},
      title        = {{A} new method to detect and classify polar stratospheric
                      nitric acid trihydrate clouds derived from radiative
                      transfer simulations and its first application to airborne
                      infrared limb emission observations},
      journal      = {Atmospheric measurement techniques},
      volume       = {14},
      number       = {3},
      issn         = {1867-8548},
      address      = {Katlenburg-Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2021-01343},
      pages        = {1893 - 1915},
      year         = {2021},
      abstract     = {Polar stratospheric clouds (PSCs) play an important role in
                      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 made by the CRISTA-NF (CRyogenic
                      Infrared Spectrometers and Telescope for the Atmosphere –
                      New Frontiers) airborne infrared limb sounder 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 with the known peak at about 820 cm−1, which is
                      recognised as being caused by the emission of radiation 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
                      810–820 cm−1 region. The simulation results show that
                      the appearance of the feature changes with an 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, caused by the increasing
                      contribution of scattering to the total extinction. Based on
                      the appearance of the spectral feature, we defined different
                      colour indices to detect PSCs containing NAT particles and
                      to subgroup them into three size regimes under the
                      assumption of spherical particles: 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 vertical 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          = {211 - Die Atmosphäre im globalen Wandel (POF4-211) / 5111
                      - Domain-Specific Simulation $\&$ Data Life Cycle Labs
                      (SDLs) and Research Groups (POF4-511)},
      pid          = {G:(DE-HGF)POF4-211 / G:(DE-HGF)POF4-5111},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000627575900001},
      doi          = {10.5194/amt-14-1893-2021},
      url          = {https://juser.fz-juelich.de/record/891060},
}