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| Titel |
Gravity Wave Emission by Spontaneous Imbalance of Baroclinic Waves in the Continuously Stratified Rotating Annulus |
| VerfasserIn |
S. Borchert, U. Achatz, F. Rieper, M. D. Fruman |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060760
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| Zusammenfassung |
| We use a numerical model of the classic differentially heated rotating annulus experiment to
study the spontaneous emission of gravity waves (GWs) from jet stream imbalances, which is
a major source of these waves in the atmosphere for which no satisfactory parameterization
exists. Atmospheric observations are the main tool for the testing and verification of
theoretical concepts but have their limitations. Given their specific potential for yielding
reproducible data and for studying process dependence on external system parameters,
laboratory experiments are an invaluable complementary tool. Experiments with a rotating
annulus exhibiting a jet modulated by large-scale waves due to baroclinic instability have
already been used to study GWs: Williams et al (2008) observed spontaneously emitted
interfacial GWs in a two-layer flow, and Jacoby et al (2011) detected GWs emitted from
boundary-layer instabilities in a differentially heated rotating annulus. Employing a new
finite-volume code for the numerical simulation of a continuously stratified liquid in a
differentially heated rotating annulus, we here investigate whether such an experiment
might be useful for studies of spontaneous imbalance. A major problem was the
identification of experimental parameters yielding an atmosphere-like regime where the
Brunt-Vaisala frequency is larger than the inertial frequency, so that energy transport by the
lowest-frequency waves is predominantly horizontal while high-frequency GWs
transport energy vertically. We show that this is indeed the case for a wide and shallow
annulus with relatively large temperature difference between the inner and outer
cylinder walls. We also show that this set-up yields a conspicuous signal in the
horizontal divergence field close to the meandering jet. Various analyses support the
notion that this signal is predominantly due to GWs superposed on a geostrophic
flow.
Jacoby, T. N. L., Read, P. L., Williams, P. D. and Young, R. M. B., 2011: Generation of
inertia-gravity waves in the rotating thermal annulus by a localised boundary layer instability.
Geophys. Astrophys. Fluid Dyn., 105, 161-181. doi:10.1080/03091929.2011.560151
Williams, P. D., Haine, T. W. N. and Read, P. L., 2008: Inertia-gravity waves emitted from
balanced flow: observations, properties, and consequences. J. Atmos. Sci., 65, 3543-3556.
doi:10.1175/2008JAS2480.1 |
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