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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-15
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-15
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 30 Jan 2019

Regular paper | 30 Jan 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

Nadja Samtleben1, Christoph Jacobi1, Petr Pišoft3, Petr Šácha2,3,4, and Aleš Kuchař3 Nadja Samtleben et al.
  • 1Institute for Meteorology, Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 2Institute for Meteorology, Universität für Bodenkultur Wien, Gregor-Mendel-Straße 33, 1180 Vienna, Austria
  • 3Department of Atmospheric Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
  • 4EPhysLab, Faculty of Sciences, Universidade de Vigo, Campus As Lagoas, s/n, 32004 Ourense, Spain

Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, global circulation model. To this end, for the hotspot region we selected a fixed longitude range in the East Asian region (120° E–170° E) and a latitude range from 22.5° N–52.5° N between 18 km and 30 km, which was then shifted northward in steps of 5°. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) 1 activity in the upper stratosphere/lower mesosphere, i.e. less SPWs 1 are propagating upwards. These GW hotspots are leading to a negative refractive index inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected with an increased zonal mean zonal wind at lower latitudes. This in turn decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability which generates SPWs 1 in the polar region, where we observe a strong positive Eliassen-Palm (EP) divergence. Thus, the EP flux is increasing towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes) where the SPWs 1 are breaking and the zonal mean zonal wind is decreasing. Thus, the local GW forcing is leading to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere by GW hotspots which are located northward of 50° N is negligible because the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

Nadja Samtleben et al.
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Nadja Samtleben et al.
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Short summary
Simulations of locally breaking gravity wave hotspots in the stratosphere show a suppression of wave propagation at midlatitudes leading to a displacement of the polar vortex towards lower latitudes. This effect is highly depending on the position of the artificial gravity wave forcing. It is strongest (weakest) for hotspots at lower to middle latitudes (higher latitudes).
Simulations of locally breaking gravity wave hotspots in the stratosphere show a suppression of...
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