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| Titel |
Wave-attractors and mean flow in a spherical shell due to time-modulated rotation |
| VerfasserIn |
Sandy Koch, Uwe Harlander, Christoph Egbers |
| 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 |
250041661
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| Zusammenfassung |
| In geophysical fluids, such as the atmosphere, the oceans or the liquid core of the
earth, periodic flows can be found on all scales. For planetary scales, such flows are
caused by tidal forces which initiate waves of smaller scales. In rotating systems,
inertial waves play a decisive role. These waves are the result of a subtle interplay
between inertial and Coriolis forces. In case of multiple reflections, e.g. on the
curved boundaries of a spherical shell, wave rays follow certain orbits [1,2], called
wave-attractors. Generally they point to internal boundary layers that are detached from the
boundaries. Inertial waves also generate mean flows [3]. Wave-attractor related internal
boundary layers have been studied experimentally since about 10 years. However, no
experiment has been realized for spherical geometry. Previous experimental studies of
wave-attractors were performed in a rotating box [1], or a rotating cylindrical gap
[4].
In contrast, we suggest to conduct a laboratory experiment that consists of two
co-rotating and concentric spherical shells. The rotation of the shell is varied in
form of a sinus curve forcing the particles to be deflected from their rest position.
Coriolis forces drive particles back to their initial position where they overshoot due to
inertia. This mechanism gives rise to oscillations called inertial waves. Tilgner [3,5]
showed in his numerical investigations that in fast rotating spherical shells attractors
occur and also two attractors can coexist for certain frequencies. In addition, he
showed that decreasing the radius of the inner sphere, the number of attractors is also
decreasing. Later, he showed that a zonal flow can be excited by an interaction of inertial
waves.
For comparison with the numerical investigation we specify different visualization and
measurement techniques. Wave-attractors can be identified by velocity, kinetic energy or
vorticity. Longtime-LDA measurements can determine whether a wave driven mean flow
arise.
References
L.R.M. Maas, J. Fluid Mech. 437, 13-28, 2001
U. Harlander und L.R.M.Maas, Dynamics of Atmospheres and Oceans 44, 1-28,
2007
A. Tilgner, Phys. Rev. Letters 99,194501, 2007
Swart, A., L.R.M. Maas, U. Harlander, and A. Manders, Dynamics of
Atmospheres and Oceans, doi: 10.1016/j.dynatmoce.2009.08.003 , 2009
A. Tilgner, Phys. Rev. Vol. 59, No. 2, 1997 |
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