Transient tropopause waves

Vortragender: Andreas Dörnbrack (DLR, Deutsches Zentrum für Luft- und Raumfahrt)

Flight-level airborne observations have often detected gravity waves with horizontal wavelengths λx≲10km near the tropopause. Here, in situ and remote sensing aircraft data of these short gravity waves trapped along tropopause inversion layer and collected during a mountain-wave event over southern Scandinavia are analyzed to quantify their spectral energy and energy fluxes and to identify nonstationary modes. A series of three-dimensional numerical simulations are performed to explain the origin of these transient wave modes and to investigate the parameters on which they depend. It turns out that mountain-wave breaking in the middle atmosphere and the subsequent modification of the stratospheric flow are the key factors for the occurrence of trapped modes with λx≲10km. In particular, the intermittent and periodic breaking of mountain waves in the lower stratosphere forms a wave duct directly above the tropopause, in which the short gravity waves are trapped. The characteristics of the trapped, downstream-propagating waves are mainly controlled by the sharpness of the tropopause inversion layer. It could be demonstrated that different settings for optimizing the numerical solver have a significantly smaller influence on the solutions.

Das Kolloquium wird in Zusammenarbeit mit dem Forschungsverbund VINAR und der GeoSphere Austria (früher ZAMG) durchgeführt.

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