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@ARTICLE{Petzold:884280,
      author       = {Petzold, Andreas and Neis, Patrick and Rütimann, Mihal and
                      Rohs, Susanne and Berkes, Florian and Smit, Herman G. J. and
                      Krämer, Martina and Spelten, Nicole and Spichtinger, Peter
                      and Nédélec, Philippe and Wahner, Andreas},
      title        = {{I}ce-supersaturated air masses in the northern
                      mid-latitudes from regular in situ observations by passenger
                      aircraft: vertical distribution, seasonality and
                      tropospheric fingerprint},
      journal      = {Atmospheric chemistry and physics},
      volume       = {20},
      number       = {13},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2020-03172},
      pages        = {8157 - 8179},
      year         = {2020},
      abstract     = {The vertical distribution and seasonal variation of water
                      vapour volume mixing ratio (H2O VMR), of relative humidity
                      with respect to ice (RHice) and particularly of regions with
                      ice-supersaturated air masses (ISSRs) in the extratropical
                      upper troposphere and lowermost stratosphere are
                      investigated at northern mid-latitudes over the eastern
                      North American, North Atlantic and European regions for the
                      period 1995 to 2010. Observation data originate from regular
                      and continuous long-term measurements on board instrumented
                      passenger aircraft in the framework of the European research
                      programme MOZAIC (1994–2010), which continues as the
                      European research infrastructure IAGOS (from 2011). Data
                      used in our study result from collocated observations of O3
                      VMR, RHice and temperature, as well as H2O VMR deduced from
                      RHice and temperature data. The in situ observations of H2O
                      VMR and RHice with a vertical resolution of 30 hPa
                      (< 750 m at the extratropical tropopause level) and a
                      horizontal resolution of 1 km resolve detailed features of
                      the distribution of water vapour and ice-supersaturated air
                      relative to the thermal tropopause, including their seasonal
                      and regional variability and chemical signatures at various
                      distances from the tropopause layer. Annual cycles of the
                      investigated properties document the highest H2O VMR and
                      temperatures above the thermal tropopause in the summer
                      months, whereas RHice above the thermal tropopause remains
                      almost constant in the course of the year. Over all
                      investigated regions, upper tropospheric air masses close to
                      the tropopause level are nearly saturated with respect to
                      ice and contain a significant fraction of ISSRs with a
                      distinct seasonal cycle of minimum values in summer
                      $(30 \%$ over the ocean, $20 \%–25 \%$ over land)
                      and maximum values in late winter $(35 \%–40 \%$ over
                      both land and ocean). Above the thermal tropopause, ISSRs
                      are occasionally observed with an occurrence probability of
                      $1.5 ± 1.1 \%,$ whereas above the dynamical
                      tropopause at 2 PVU (PVU: potential vorticity unit), the
                      occurrence probability increases 4-fold to
                      $8.4 ± 4.4 \%.$ In both coordinate systems related to
                      tropopause height (TPH), the ISSR occurrence probabilities
                      drop to values below $1 \%$ for the next higher air mass
                      layer with pressure levels p < pTPH−15 hPa. For both
                      tropopause definitions, the tropospheric nature or
                      fingerprint, based on O3 VMR, indicates the continuing
                      tropospheric influence on ISSRs inside and above the
                      respective tropopause layer. For the non-ISSRs, however, the
                      stratospheric nature is clearly visible above the thermal
                      tropopause, whereas above the dynamical tropopause the air
                      masses show a still substantial tropospheric influence. For
                      all three regions, seasonal deviations from the long-term
                      annual cycle of ISSR occurrence show no significant trends
                      over the observation period of 15 years, whereas a
                      statistically significant correlation between the North
                      Atlantic Oscillation (NAO) index and the deviation of ISSR
                      occurrence from the long-term average is observed for the
                      North Atlantic region but not for the eastern North American
                      and European regions.},
      cin          = {IEK-7 / IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013 / I:(DE-Juel1)IEK-8-20101013},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244) / 243 - Tropospheric trace
                      substances and their transformation processes (POF3-243)},
      pid          = {G:(DE-HGF)POF3-244 / G:(DE-HGF)POF3-243},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000550825000001},
      doi          = {10.5194/acp-20-8157-2020},
      url          = {https://juser.fz-juelich.de/record/884280},
}