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Non-orographic gravity waves and turbulence caused by merging jet streams
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  • Wolfgang Woiwode,
  • Andreas Dörnbrack,
  • Markus Geldenhuys,
  • Felix Friedl-Vallon,
  • Andreas Giez,
  • Thomas Gulde,
  • Michael Höpfner,
  • Soeren Johansson,
  • Bernd Kaifler,
  • Anne Kleinert,
  • Lukas Krasauskas,
  • Erik Kretschmer,
  • Guido Maucher,
  • Tom Neubert,
  • Hans Nordmeyer,
  • Christof Piesch,
  • Peter Preusse,
  • Markus Rapp,
  • Martin Riese,
  • Ulrich Schumann,
  • Jörn Ungermann
Wolfgang Woiwode
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)

Corresponding Author:[email protected]

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Andreas Dörnbrack
DLR, Institut für Physik der Atmosphäre
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Markus Geldenhuys
Institute of Energy and Climate Research (IEK-7: Stratosphere), Forschungszentrum Jülich
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Felix Friedl-Vallon
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Andreas Giez
Deutsches Zentrum für Luft- und Raumfahrt
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Thomas Gulde
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Michael Höpfner
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Soeren Johansson
Karlsruhe Institute of Technology
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Bernd Kaifler
Institute of Atmospheric Physics, German Aerospace Center
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Anne Kleinert
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Lukas Krasauskas
Institute of Energy and Climate Research (IEK-7: Stratosphere), Forschungszentrum Jülich
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Erik Kretschmer
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Guido Maucher
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Tom Neubert
Zentralinstitut für Engineering, Elektronik und Analytik-Systeme der Elektronik (ZEA-2), Forschungszentrum Jülich (FZJ)
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Hans Nordmeyer
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Christof Piesch
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT)
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Peter Preusse
Juelich Research Center
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Markus Rapp
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
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Martin Riese
Forschungszentrum Juelich
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Ulrich Schumann
DLR
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Jörn Ungermann
Institute of Energy and Climate Research - Stratosphere (IEK-7), Research Centre Jülich
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Abstract

Jet streams are important sources of non-orographic internal gravity waves and clear air turbulence (CAT). We analyze non-orographic gravity waves and CAT during a merging of the polar front jet stream (PFJ) with the subtropical jet stream (STJ) above the southern Atlantic. Thereby, we use a novel combination of airborne observations covering the meso-scale and turbulent scale in combination with high-resolution deterministic short-term forecasts. Coherent phase fronts stretching along a highly sheared tropopause fold are found in the ECMWF IFS (integrated forecast system) forecasts. During the merging event, the PFJ reverses its direction from antiparallel to parallel with respect to the STJ, going along with strong wind shear and horizontal deformation. Temperature perturbations in limb-imaging and lidar observations onboard the research aircraft HALO in the framework of the SouthTRAC campaign show remarkable agreement with the IFS data. Ten hours earlier, the IFS data show a new “X-shaped” phase line pattern emanating from the sheared tropopause fold. The analysis of tendencies in the IFS wind components shows that these gravity waves are excited by a local body force as the PFJ impinges the STJ. In situ observations of temperature and wind components at 100 Hz confirm upward propagation of the probed portion of the gravity waves. They furthermore reveal embedded episodes of light-to-moderate CAT, Kelvin Helmholtz waves, and indications for partial wave reflection. Patches of low gradient Richardson numbers in the IFS data coincide with episodes where CAT was observed, suggesting that this event was well accessible to turbulence forecasting.