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Volume 18, issue 21 | Copyright

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

Special issue: The Polar Stratosphere in a Changing Climate (POLSTRACC) (ACP/AMT...

Atmos. Chem. Phys., 18, 15643-15667, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Oct 2018

Research article | 30 Oct 2018

Mesoscale fine structure of a tropopause fold over mountains

Wolfgang Woiwode1, Andreas Dörnbrack2, Martina Bramberger2, Felix Friedl-Vallon1, Florian Haenel1, Michael Höpfner1, Sören Johansson1, Erik Kretschmer1, Isabell Krisch3, Thomas Latzko1, Hermann Oelhaf1, Johannes Orphal1, Peter Preusse3, Björn-Martin Sinnhuber1, and Jörn Ungermann3 Wolfgang Woiwode et al.
  • 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 2Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 3Forschungszentrum Jülich, Institute of Energy- and Climate Research, Stratosphere (IEK-7), Jülich, Germany

Abstract. We report airborne remote-sensing observations of a tropopause fold during two crossings of the polar front jet over northern Italy on 12 January 2016. The GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) observations allowed for a simultaneous mapping of temperature, water vapour, and ozone. They revealed deep, dry, and ozone-rich intrusions into the troposphere. The mesoscale fine structures of dry filaments at the cyclonic shear side north of the jet and tongues of moist air entraining tropospheric air into the stratosphere along the anticyclonic shear side south of the jet were clearly resolved by GLORIA observations. Vertically propagating mountain waves with recorded temperature residuals exceeding ±3K were detected above the Apennines. Their presence enhanced gradients of all variables locally in the vicinity of the tropopause. The combination of H2O − O3 correlations with potential temperature reveals an active mixing region and shows clear evidence of troposphere-to-stratosphere and stratosphere-to-troposphere exchange. High-resolution short-term deterministic forecasts of ECMWF's integrated forecast system (IFS) applying GLORIA's observational filter reproduce location, shape, and depth of the tropopause fold very well. The fine structure of the mixing region, however, cannot be reproduced even with the 9km horizontal resolution of the IFS, used here. This case study demonstrates convincingly the capabilities of linear limb-imaging observations to resolve mesoscale fine structures in the upper troposphere and lower stratosphere, validates the high quality of the IFS data, and suggests that mountain wave perturbations have the potential to modulate exchange processes in the vicinity of tropopause folds.

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Short summary
GLORIA observations during two crossings of the polar front jet stream resolve the fine mesoscale structure of a tropopause fold in high detail. Tracer–tracer correlations of H2O and O3 are presented as a function of potential temperature and reveal an active mixing region. Our study confirms conceptual models of tropopause folds, validates the high quality of ECMWF IFS forecasts, and suggests that mountain waves are capable of modulating exchange processes in the vicinity of tropopause folds.
GLORIA observations during two crossings of the polar front jet stream resolve the fine...