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| Titel |
Turbulence closure: turbulence, waves and the wave-turbulence transition – Part 1: Vanishing mean shear |
| VerfasserIn |
H. Z. Baumert, H. Peters |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 5, no. 1 ; Nr. 5, no. 1 (2009-03-06), S.47-58 |
| Datensatznummer |
250002264
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| Publikation (Nr.) |
 copernicus.org/os-5-47-2009.pdf |
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| Zusammenfassung |
This paper extends a turbulence closure-like model for stably stratified
flows into a new dynamic domain in which turbulence is generated by internal
gravity waves rather than mean shear. The model turbulent kinetic energy
(TKE, K) balance, its first equation, incorporates a term for the energy
transfer from internal waves to turbulence. This energy source is in addition
to the traditional shear production. The second variable of the new
two-equation model is the turbulent enstrophy (Ω). Compared to the
traditional shear-only case, the Ω-equation is modified to account for
the effect of the waves on the turbulence time and space scales. This
modification is based on the assumption of a non-zero constant flux
Richardson number in the limit of vanishing mean shear when turbulence is
produced exclusively by internal waves. This paper is part 1 of a continuing
theoretical development. It accounts for mean shear- and internal wave-driven
mixing only in the two limits of mean shear and no waves and waves but no
mean shear, respectively.
The new model reproduces the wave-turbulence transition analyzed by D'Asaro
and Lien (2000b). At small energy density E of the internal wave field, the
turbulent dissipation rate (ε) scales like
ε~E2. This is what is observed in the deep sea. With
increasing E, after the wave-turbulence transition has been passed, the
scaling changes to ε~E1. This is observed, for example, in
the highly energetic tidal flow near a sill in Knight Inlet. The new model
further exhibits a turbulent length scale proportional to the Ozmidov scale,
as observed in the ocean, and predicts the ratio between the turbulent Thorpe
and Ozmidov length scales well within the range observed in the ocean. |
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