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@PHDTHESIS{Rolf:151817,
      author       = {Rolf, Christian},
      title        = {{L}idar observations of natural and volcanic-ash-induced
                      cirrus clouds},
      volume       = {163},
      school       = {Universität Wuppertal},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2014-01691},
      isbn         = {978-3-89336-847-1},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {124 p.},
      year         = {2013},
      note         = {Dissertation, Universität Wuppertal, 2012},
      abstract     = {Cirrus clouds - which consist solely of ice particles -
                      influence the Earth’s radiation budget and thus the
                      climate system since they scatter the incoming solar
                      radiation (cooling effect) and absorb the outgoing radiation
                      of the Earth (warming effect). However, this influence has
                      not yet been quantified. The purpose of this thesis is to
                      extend our knowledge about cirrus with the help of lidar
                      measurements in combination with model simulations. In the
                      first part, observations of cirrus clouds made with a
                      backscatter lidar over Jülich are presented, focusing on
                      obtaining a representative cirrus climatology. The cirrus
                      clouds are evaluated with a temporal average extinction
                      profile by considering a multiple scattering correction. By
                      using additional meteorological data, the climatological
                      observations are analyzed under macrophysical, radiative,
                      and microphysical aspects and considered to be
                      representative in comparison to other mid-latitude lidar
                      climatologies. Most of the observed cirrus clouds were
                      generated due to synoptic weather patterns (e.g. frontal
                      systems), showing a large vertical thickness of about 2.2 km
                      and occurring mostly directly below the tropopause. Mean and
                      median values of optical depth are found to be around 0.28
                      and 0.12 (range: 0.002 - 3), respectively. The most
                      frequently observed ice water content (IWC) was found to be
                      6 ppmv (range: 0.01 - 400 ppmv). The lowest detected IWC
                      values from aircraft in situ measurements (∼ 0.01 ppmv)
                      are confirmed by the lidar observations. This result is of
                      importance, since up to now it has been unclear whether in
                      situ aircraft instruments were able to detect the thinnest
                      cirrus clouds. In the second part of the thesis,
                      heterogeneous ice formation induced by volcanic ash from the
                      Eyjafjallajökull volcano eruption in April 2010 is
                      investigated based on a lidar observation of an ash-induced
                      cirrus cloud in combination with model simulations along air
                      mass trajectories. The microphysical properties of the
                      cirrus cloud can only be represented by the microphysical
                      model simulations on the assumption of an enhanced number of
                      efficient ice nuclei (IN) originating from the volcanic
                      eruption. The IN concentration determined by lidar
                      measurements directly before and after cirrus cloud
                      occurrence implies a value of around 0.1 cm$^{−3}$ (in
                      comparison to normal IN conditions of 0.01 cm$^{−3}$).
                      This leads to a cirrus cloud with rather small ice crystals
                      having a mean radius of 12 μm and a modification of the ice
                      particle number (0.08 cm$^{−3}$ instead of 3 ·
                      10$^{−4}$ cm$^{−3}$ under normal IN conditions). The
                      effectiveness of IN was estimated by the microphysical model
                      and the backward trajectories based on ECMWF data,
                      establishing a freezing threshold of around 105 \% relative
                      humidity with respect to ice in a temperature range from -45
                      to −55$^{\circ}$C. Only these highly efficient IN made the
                      formation of the cirrus cloud in a slightly supersaturated
                      environment possible. With the help of this case study, the
                      possible influence of IN on the appearance and microphysical
                      - and thus radiative - properties of cirrus clouds was
                      demonstrated. From an additional set of idealized model
                      simulations it can be concluded that the microphysical and
                      thus optical properties of cirrus clouds are affected for
                      the complete range of atmospheric conditions in the presence
                      of a high number of IN.},
      keywords     = {Dissertation (GND)},
      cin          = {IEK-7},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {234 - Composition and Dynamics of the Upper Troposphere and
                      Stratosphere (POF2-234)},
      pid          = {G:(DE-HGF)POF2-234},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/151817},
}