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Volume 17, issue 24 | Copyright

Special issue: Sources, propagation, dissipation and impact of gravity waves...

Atmos. Chem. Phys., 17, 14853-14869, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Dec 2017

Research article | 14 Dec 2017

Mountain waves modulate the water vapor distribution in the UTLS

Romy Heller1, Christiane Voigt1,2, Stuart Beaton3, Andreas Dörnbrack1, Andreas Giez4, Stefan Kaufmann1, Christian Mallaun4, Hans Schlager1, Johannes Wagner1, Kate Young3, and Markus Rapp1,5 Romy Heller et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 2Johannes-Gutenberg-Universität Mainz, Institut für Physik der Atmosphäre, Mainz, Germany
  • 3National Center for Atmospheric Research, Boulder, Colorado, USA
  • 4Deutsches Zentrum für Luft- und Raumfahrt, Flugexperimente, Oberpfaffenhofen, Germany
  • 5Ludwig-Maximillians-Universität München, Meteorologisches Institut München, Munich, Germany

Abstract. The water vapor distribution in the upper troposphere–lower stratosphere (UTLS) region has a strong impact on the atmospheric radiation budget. Transport and mixing processes on different scales mainly determine the water vapor concentration in the UTLS. Here, we investigate the effect of mountain waves on the vertical transport and mixing of water vapor. For this purpose we analyze measurements of water vapor and meteorological parameters recorded by the DLR Falcon and NSF/NCAR Gulfstream V research aircraft taken during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) in New Zealand. By combining different methods, we develop a new approach to quantify location, direction and irreversibility of the water vapor transport during a strong mountain wave event on 4 July 2014. A large positive vertical water vapor flux is detected above the Southern Alps extending from the troposphere to the stratosphere in the altitude range between 7.7 and 13.0km. Wavelet analysis for the 8.9km altitude level shows that the enhanced upward water vapor transport above the mountains is caused by mountain waves with horizontal wavelengths between 22 and 60km. A downward transport of water vapor with 22km wavelength is observed in the lee-side of the mountain ridge. While it is a priori not clear whether the observed fluxes are irreversible, low Richardson numbers derived from dropsonde data indicate enhanced turbulence in the tropopause region related to the mountain wave event. Together with the analysis of the water vapor to ozone correlation, we find indications for vertical transport followed by irreversible mixing of water vapor.

For our case study, we further estimate greater than 1Wm−2 radiative forcing by the increased water vapor concentrations in the UTLS above the Southern Alps of New Zealand, resulting from mountain waves relative to unperturbed conditions. Hence, mountain waves have a great potential to affect the water vapor distribution in the UTLS. Our regional study may motivate further investigations of the global effects of mountain waves on the UTLS water vapor distributions and its radiative effects.

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