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@PHDTHESIS{Gensch:2112,
      author       = {Gensch, Iulia},
      title        = {{W}ater and nitric acid in cirrus clouds:microphysical
                      kinetical modeling and a closure to field observations},
      volume       = {4286},
      school       = {Univ. Wuppertal},
      type         = {Dr. (Univ.)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-2112, Juel-4286},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {IX, 105 p.},
      year         = {2008},
      note         = {Record converted from VDB: 12.11.2012; Wuppertal, Univ.,
                      Diss., 2008},
      abstract     = {Upper tropospheric relative humidities over ice
                      (RH$_{ice}$) of up to 200\% have been reported frequently in
                      recent times. This unexpectedly high supersaturation out-
                      and inside of cold cirrus clouds may have significant impact
                      on the Earth’s climate. In the first case, clear sky
                      supersaturation could be justified when the critical
                      supersaturation for ice cloud formation is higher than until
                      now assumed. This would lead to a decrease in high cloud
                      cover and thus impact on the radiation budget. In the second
                      case, high supersaturation inside of cirrus clouds could
                      suggest the existence of unknown microphysical and radiative
                      properties with consequences for climate and the vertical
                      redistribution of water and nitric acid. Peter et al. (2006)
                      summarized possible reasons for the observed supersaturation
                      in a ’supersaturation puzzle’, calling into question
                      whether this puzzle can be solved by solely using the
                      conventional ice cloud microphysics. Another important
                      question raised in this study is whether the supersaturation
                      may result from uncertainties or flaws in the water
                      measurements. The aim of this PhD thesis is to puzzle out
                      these questions. Therefore upper tropospheric field
                      observations are simulated with an adequate conventional
                      kinetic model in order to analyze the origin and persistence
                      of high ice supersaturation, particularly inside cold cirrus
                      clouds. The proposed $\underline{M}$odel for
                      $\underline{A}$erosol and $\underline{I}$ce
                      $\underline{D}$ynamics (MAID) handles widely aerosol and ice
                      microphysics, including: gas-diffusive particle growth and
                      evaporation, homogeneous and heterogeneous ice nucleation,
                      water vapor deposition and nitric acid uptake on growing ice
                      crystal. Special emphasis of MAID is the exact balancing of
                      chemical species among different physical states. MAID is
                      validated here, based on observations during the field
                      campaign POLSTAR–1 1997 (Polar Stratospheric Aerosol
                      Experiment). Further, a detailed analysis of cirrus cloud
                      observations during CR-AVE 2006, the tropical Costa Rica –
                      Aura Validation Experiment, is performed with MAID. The
                      model is initialized with different aerosol properties,
                      water mixing ratios, accommodation factors of water on ice
                      and amplitudes of mesoscale temperature fluctuations. A
                      notable feature here is to vary the freezing mechanism in
                      the simulations. The model results indicate high sensitivity
                      of the cloud microphysical evolution to the freezing
                      pathway. The ice microphysics, as well as the partitioning
                      of water and nitric acid inside the cloud derived from all
                      sensitivity studies are compared at last with the the
                      microphysical and chemical in-situ observations, to
                      determine the most probable constellation of initial
                      conditions and processes that led to the very cold,
                      sub-visible tropical cirrus cloud observed during CR–AVE.
                      The best agreement between model results and measurements is
                      given when the cirrus cloud forms heterogeneously, with
                      total accommodation of water on ice. By varying the freezing
                      pathway, the accommodation factor of water on ice, or the
                      amount of available water, clouds with completely different
                      microphysical properties form. As a summary, this work
                      demonstrates that it is possible to simulate significant
                      supersaturation inside cold cirrus (T<200 K) with
                      conventional microphysics when assuming heterogeneous ice
                      nucleation as the freezing mechanism. Thus, heterogeneous
                      freezing appears to be an important pathway for cold cirrus
                      cloud formation. More generally, a freezing mechanism
                      producing low number densities of ice crystals could explain
                      the frequent high supersaturation inside cirrus clouds
                      observed in this temperature range.},
      cin          = {ICG-1},
      cid          = {I:(DE-Juel1)VDB790},
      pnm          = {Atmosphäre und Klima},
      pid          = {G:(DE-Juel1)FUEK406},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/2112},
}