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| Titel |
Mixing induced by a propagating normal mode in long term experiments |
| VerfasserIn |
Yvan Dossmann, Florence Pollet, Philippe Odier, Thierry Dauxois |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250154111
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| Publikation (Nr.) |
 EGU/EGU2017-19166.pdf |
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| Zusammenfassung |
| The energy pathways from propagating internal waves to the scales of irreversible mixing in
the ocean are numerous. The triadic resonant instability (TRI) is an intrinsic destabilization
process that can lead to mixing away from topographies. It consists in the destabilization of a
primary internal wave generation leading to the radiation of two secondary waves of lower
frequencies and different wave vectors. In the process, internal wave energy is carried down
to smaller scales.
A previous study focused on the assessment of instantaneous turbulent fluxes fields
associated with the TRI process in laboratory experiments [1].
The present study investigates the integrated impact of mixing processes induced by a
propagative normal mode over long term experiments using a similar setup. Configurations
for which the TRI process is either favored or inhibited are tackled. Optical measurements
using the light attenuation technique allow to follow the internal waves dynamics and the
evolution of the density profile between two runs of one hour typical duration. The
horizontally averaged turbulent diffusivity Kt(z) and the mixing efficiency Γ are
assessed. One finds values up to Kt = 10−6 m2/s and Γ = 11 %, with slightly
larger values in the presence of TRI. The maximum value for Kt is measured at the
position(s) of the maximum shear normal mode shear for both normal modes 1 and
2.
The development of staircases in the density profile is observed after several hours of
forcing. This mechanism can be explained by Phillips’ argument by which sharp interfaces
can form due to vertical variations of the buoyancy flux. The staircases are responsible for
large variations in the vertical distribution of turbulent diffusivity.
These results could help to refine parameterizations of the impact of low order normal
modes in ocean mixing.
Reference :
[1] Dossmann et al. 2016, Mixing by internal waves quantified using combined PIV/PLIF
technique, Experiments in Fluids, 57, 132. |
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