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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-21
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-21
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 May 2020

Submitted as: research article | 13 May 2020

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This preprint is currently under review for the journal WCD.

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Ales Kuchar1, Petr Sacha2,3, Roland Eichinger4,5, Christoph Jacobi1, Petr Pisoft2, and Harald E. Rieder3 Ales Kuchar et al.
  • 1Institute for Meteorology, Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 2Department of Atmospheric Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
  • 3Institute of Meteorology and Climatology, University of Natural Resources and Life Sciences, Vienna (BOKU), Gregor-Mendel-Strasse 33, 1180 Vienna, Austria
  • 4Meteorological Institute, Ludwig-Maximilians-University (LMU), Munich, Germany
  • 5Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called OGW hotspot regions have been shown to exert a large impact on the total wave forcing, in particular in the lower stratosphere (LS). Motivated by this we investigate the asymmetrical distribution of the three-dimensional OGW drag (OGWD) for selected hotspot regions in the specified dynamics simulation of the chemistry-climate model CMAM (Canadian Middle Atmosphere Model) for the period 1979–2010. As an evaluation, we first compare zonal mean OGW fluxes and GW drag (GWD) of the model simulation with observations and reanalyses in the northern hemisphere. We find an overestimation of GW momentum fluxes and GWD in the model's LS, presumably attributable to the GW parameterizations which are tuned to correctly represent the dynamics of the southern hemisphere. In the following, we define three hotspot regions which are of particular interest for OGW studies, namely the Himalayas, the Rocky Mountains and East Asia. The GW drags in these hotspot regions emerge as strongly intermittent, a result that can also quantitatively be corroborated with observational studies. Moreover, a peak-detection algorithm is applied to capture the intermittent and zonally asymmetric character of OGWs breaking in the LS and to assess composites for the three hotspot regions. This shows that LS peak OGW events can have opposing effects on the upper stratosphere and mesosphere depending on the hotspot region. Our analysis constitutes a new method for studying the intermittency of OGWs, thereby facilitating a new possibility to assess the effect of particular OGW hotspot regions on middle atmospheric dynamics.

Ales Kuchar et al.

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Ales Kuchar et al.

Data sets

Accompanying data to "On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics" A. Kuchar https://doi.org/10.17632/j3hj7f9t67.1

Model code and software

kuchaale/wcd_2020: First release of my WCD code repository A. Kuchar https://doi.org/10.5281/zenodo.3780102

Ales Kuchar et al.

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Latest update: 07 Jul 2020
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Short summary
Our study focuses on the impact of topographic structures such as Himalayas and Rocky mountains, so-called orographic gravity-wave hotspots. These hotspots play an important role in the dynamics of the middle atmosphere, in particular in the lower stratosphere. We study intermittency and zonally asymmetric character of these hotspots and their effects on the upper stratosphere and mesosphere using a new detection method in various modeling and observational datasets.
Our study focuses on the impact of topographic structures such as Himalayas and Rocky mountains,...
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