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@ARTICLE{Li:1005593,
      author       = {Li, Yun and Krämer, Martina and Mahnke, Christoph and
                      Rohs, Susanne and Bundke, Ulrich and Spelten, Nicole and
                      Dekoutsidis, Georgios and Gross, Silke and Voigt, Christiane
                      and Schumann, Ulrich and Petzold, Andreas},
      title        = {{U}pper-tropospheric slightly ice-subsaturated regions:
                      frequency of occurrence and statistical evidence for the
                      appearance of contrail cirrus},
      journal      = {Atmospheric chemistry and physics},
      volume       = {23},
      number       = {3},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2023-01552},
      pages        = {2251-2271},
      year         = {2023},
      abstract     = {Microphysical, optical, and environmental properties of
                      contrail cirrus and natural cirrus were investigated by
                      applying a new, statistically based contrail-cirrus
                      separation method to 14.7 h of cirrus cloud measurements
                      (sampling frequency 1 Hz, max. similar to 290 m s(-1), total
                      length of sampled in-cloud space similar to 15 000 km)
                      during the airborne campaign ML-CIRRUS in central Europe and
                      the northeast Atlantic flight corridor in spring 2014. We
                      find that pure contrail cirrus appears frequently at the
                      aircraft cruising altitude (CA) range with ambient pressure
                      varying from 200 to 245 hPa. It exhibits a higher median ice
                      particle number concentration (N-ice), a smaller median mass
                      mean radius (R-ice), and lower median ice water content
                      (IWC) (median: Nice=0.045 cm(-3), R-ice=16.6 mu m, IWC = 3.5
                      ppmv), and it is optically thinner (median extinction
                      coefficient Ext = similar to 0.056 km(-1)) than the cirrus
                      mixture of contrail cirrus, natural in situ-origin and
                      liquid-origin cirrus found around the CA range (median:
                      N-ice=0.038 cm(-3), R-ice=24.1 mu m, IWC = 8.3 ppmv, Ext
                      =similar to 0.096 km(-1)). The lowest and thickest cirrus,
                      consisting of a few large ice particles, are identified as
                      pure natural liquid-origin cirrus (median: N-ice=0.018
                      cm(-3), R-ice=42.4 mu m, IWC = 21.7 ppmv, Ext = similar to
                      0.137 km(-1)). Furthermore, we observe that, in particular,
                      contrail cirrus occurs more often in slightly
                      ice-subsaturated instead of merely ice-saturated to
                      supersaturated air as often assumed, thus indicating the
                      possibility of enlarged contrail cirrus existence regions.
                      The enlargement is estimated, based on IAGOS long-term
                      observations of relative humidity with respect to ice
                      (RHice) aboard passenger aircraft, to be approximately 10
                      $\%$ for Europe and the North Atlantic region, with the
                      RHice threshold for contrail cirrus existence decreased from
                      100 $\%$ to 90 $\%$ RHice and a 4 h lifetime of contrail
                      cirrus in slight ice subsaturation assumed. This increase
                      may not only lead to a non-negligible change in contrail
                      cirrus coverage and radiative forcing, but also affect the
                      mitigation strategies of reducing contrails by rerouting
                      flights.},
      cin          = {IEK-7 / IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013 / I:(DE-Juel1)IEK-8-20101013},
      pnm          = {2112 - Climate Feedbacks (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2112},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000938012500001},
      doi          = {10.5194/acp-23-2251-2023},
      url          = {https://juser.fz-juelich.de/record/1005593},
}