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| Titel |
Gravity wave generation from jets and fronts: idealized and real-case simulations |
| VerfasserIn |
Riwal Plougonven, Antonin Arsac, Albert Hertzog, Lionel Guez, François Vial |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040954
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| Zusammenfassung |
| The generation of gravity waves from jets and fronts remains an outstanding issue in the
dynamics of the atmosphere. It is important to explain and quantify this emission because of
the several impacts of these waves, in particular the induced momentum fluxes towards the
middle atmosphere, and their contribution to turbulence and mixing, e.g. in the region of the
tropopause. Yet, the mechanisms at the origin of these waves have been difficult to identify,
the fundamental reason for this being the separation between the time scales of balanced
motions and gravity waves.
Recent simulations of idealized baroclinic life cycles and of dipoles have provided
insights into the mechanisms determining the characteristics and the amplitude of gravity
waves emitted by jets. It has been shown in particular that the environmental strain and shear
play a crucial role in determining the characteristics and location of the emitted
waves, emphasizing jet exit regions for the appearance of coherent low-frequency
waves. It has also been shown how advection of relatively small-scales allow to
overcome the separation of time scales alluded to above. Recent results, remaining
open questions and ongoing work on these idealized simulations will be briefly
summarized.
Nevertheless, unavoidable shortcomings of such idealized simulations include the
sensitivity of the emitted waves to model setup (resolution, diffusion, parameterizations) and
uncertainty regarding the realism of this aspect of the simulations. Hence, it is necessary to
compare simulations with observations in order to assess their relevance.
Such comparison has been undertaken using the dataset from the Vorcore campaign
(Sept. 2005 - Feb. 2006, Hertzog, J. Atmos. Ocean. Techno. 2007) during which 27
superpressure balloons drifted as quasi-Lagrangian tracers in the lower stratosphere above
Antarctica and the Southern Ocean. High-resolution simulations (dx = 20Â km) have
been carried out using the Weather Research and Forecast model for nearly two
months. The realism of the simulated gravity waves is established based on systematic
comparison with the observations and on case studies. The simulations are then used
to quantify the importance and characteristics of gravity waves emitted from jets
and fronts above the Southern Ocean. In particular, application of results from the
idealized simulations to real cases, with a check provided by observations, will be
discussed. |
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