20 Jun 2022
20 Jun 2022
Status: this preprint is open for discussion.

On the impact of Himalaya-induced gravity waves on the polar vortex, Rossby wave activity and ozone

Ales Kuchar1, Petr Sacha2,3, Roland Eichinger2,4, Christoph Jacobi1, Petr Pisoft2, and Harald Rieder3 Ales Kuchar et al.
  • 1Institute for Meteorology, Leipzig University, 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
  • 4Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. The instability of the Northern Hemisphere polar vortex is mainly caused by the breaking of planetary-scale (Rossby) waves (RWs). However, gravity waves (GWs) may also play an important role in polar vortex preconditioning before breakdown events. Moreover, GWs affect dynamics in the stratosphere by altering the upward propagation of RWs at short time scales and therefore indirectly influence polar vortex stability. Due to the coarse spatial resolution of global chemistry-climate models, current efforts in climate research rely on simulations where the majority of the GW spectrum is parameterized. In the present study, we apply a recently developed method for detecting strong orographic gravity wave (OGW) drag events in the lower stratosphere above the Himalayas. For this, we use a specified dynamics simulation of the chemistry-climate model CMAM (Canadian Middle Atmosphere Model) spanning the period 1979–2010. We show that strong OGW drag events above the Himalayas are associated with anomalously increased upward RW propagation in the stratosphere. This, in turn, is associated with an increase of the refractive index in the mid-latitude lower stratosphere, a region where the OGW drag dominates. Our results also illustrate that OGW strong events have the potential to alter ozone variability via changes of mixing in the surf zone and advection from lower latitudes. Altogether, we detail a preconditioning process of the polar vortex morphology by GWs above the Himalayas and how this relates to the proximity to polar vortex breakdown.

Ales Kuchar et al.

Status: open (until 01 Aug 2022)

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Ales Kuchar et al.


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Short summary
We focus on the impact of small-scale orographic gravity waves (OGWs) above the Himalayas. The interaction of GWs with the large-scale circulation in the stratosphere is not still well understood and can have implications on climate projections. We use a chemistry-climate model to show that these strong OGW events are associated with anomalously increased upward planetary-scale waves and in turn affect the circumpolar circulation and have the potential to alter ozone variability as well.