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Characterizing the subsiding shell of shallow cumulus with Doppler lidar
  • +4
  • Ulrich Löhnert,
  • fanyang,
  • Kevin Sanchez,
  • minttu.tuononen,
  • crewell,
  • mcmichael,
  • vogelmann
Ulrich Löhnert
University of Cologne
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Kevin Sanchez
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minttu.tuononen
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Abstract

Recent LES modelling and in-situ observations sugggest that upward mass flux into shallow cumulus is compensated by relatively narrow regions of stronger downdrafts in close proximity to the outer cloud boundaries, the so-called subsiding shell. This is in contrast to the classical view that mass flux into the cloud is compensated uniformly through weak downdrafts in the clear sky regions between the clouds. This study shows a statistical analysis of the subsiding shell of typical shallow cumulus clouds observed at the Souther Great Plains site of the US DOE Atmospheric Radiation Measurement facility by means of Dopple lidar. Although the measurement set up of the ground-based systems allows only vertically pointing observations of overpassing clouds, it is shown that this ground-based remote sensing technology can come to the following conclusions:  1.) the exitstence of a subsiding shell at the lateral edges of shallow culumuls clouds is confirmend, 2.) The subsiding shell is on average Xm wide and depends mainly on .. 3.) The front edge of an overpassing cloud shows stronger updrafts, whereas the back end a more pronounced subsiding shell ... These results make clear that Doppler lidar can deliver valuable insight into the coupling of cloud thermodynamics, dynamics and microphysics - processes that are essential to correctly resolved by models, especially in the Tropics where shallow cumulus plays asignificant role not only for the water cycle, but also the climate relavant cloud-radiation interaction.