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@ARTICLE{Ren:58510,
      author       = {Ren, C. and MacKenzie, A. R. and Schiller, C. and Shur, G.
                      and Yushkov, V.},
      title        = {{D}iagnosis of processes controlling water vapour in the
                      tropical tropopause layer by a {L}agrangian cirrus model},
      journal      = {Atmospheric chemistry and physics},
      volume       = {7},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {PreJuSER-58510},
      pages        = {5401 - 5413},
      year         = {2007},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {We have developed a Lagrangian air-parcel cirrus model
                      (LACM), to diagnose the processes controlling water in the
                      tropical tropopause layer (TTL). LACM applies parameterised
                      microphysics to air parcel trajectories. The
                      parameterisation includes the homogeneous freezing of
                      aerosol droplets, the growth/sublimation of ice particles,
                      and sedimentation of ice particles, so capturing the main
                      dehydration mechanism for air in the TTL. Rehydration is
                      also considered by resetting the water vapour mixing ratio
                      in an air parcel to the value at the point in the 4-D
                      analysis/forecast data used to generate the trajectories,
                      but only when certain conditions, indicative of convection,
                      are satisfied. The conditions act to restrict rehydration of
                      the Lagrangian air parcels to regions where convective
                      transport of water vapour from below is significant, at
                      least to the extent that the analysis/forecast captures this
                      process. The inclusion of hydration and dehydration
                      mechanisms in LACM results in total water fields near
                      tropical convection that have more of the 'stripy' character
                      of satellite observations of high cloud, than do either the
                      ECMWF analysis or trajectories without microphysics. The
                      mixing ratios of total water in the TTL, measured by a
                      high-altitude aircraft over Brazil (during the TROCCINOX
                      campaign), have been reconstructed by LACM using
                      trajectories generated from ECMWF analysis. Two other
                      Lagrangian reconstructions are also tested: linear
                      interpolation of ECMWF analysed specific humidity onto the
                      aircraft flight track, and instantaneous dehydration to the
                      saturation vapour pressure over ice along trajectories. The
                      reconstructed total water mixing ratios along aircraft
                      flight tracks are compared with observations from the FISH
                      total water hygrometer. Process-oriented analysis shows that
                      modelled cirrus cloud events are responsible for dehydrating
                      the air parcels coming from lower levels, resulting in total
                      water mixing ratios as low as 2 mu mol/mol. Without adding
                      water back to some of the trajectories, the LACM and
                      instantaneous-dehydration reconstructions have a dry bias.
                      The interpolated-ECMWF reconstruction does not suffer this
                      dry bias, because convection in the ECMWF model moistens air
                      parcels dramatically, by pumping moist air upwards. This
                      indicates that the ECMWF model captures the gross features
                      of the rehydration of air in the TTL by convection. Overall,
                      the ECMWF models captures well the exponential decrease in
                      total water mixing ratio with height above 250 hPa, so that
                      all the reconstruction techniques capture more than $75\%$
                      of the standard deviation in the measured total water mixing
                      ratios over the depth of the TTL. By picking up the main
                      contributing processes to dehydration and rehydration in the
                      TTL, LACM reconstructs total water mixing ratios at the top
                      of the TTL, close to the cold point, that are always in
                      substantially better agreement with observations than
                      instantaneous-dehydration reconstructions, and better than
                      the ECMWF analysis for regions of high relative humidity and
                      cloud.},
      keywords     = {J (WoSType)},
      cin          = {ICG-1},
      ddc          = {550},
      cid          = {I:(DE-Juel1)VDB790},
      pnm          = {Atmosphäre und Klima},
      pid          = {G:(DE-Juel1)FUEK406},
      shelfmark    = {Meteorology $\&$ Atmospheric Sciences},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000251239200010},
      doi          = {10.5194/acp-7-5401-2007},
      url          = {https://juser.fz-juelich.de/record/58510},
}