 |
| Titel |
Impact of viscous boundary layers on the emission of lee-waves |
| VerfasserIn |
Antoine Renaud, Antoine Venaille, Freddy Bouchet |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250153842
|
| Publikation (Nr.) |
 EGU/EGU2017-18871.pdf |
|
|
|
|
|
| Zusammenfassung |
| Oceans large-scale structures such as jets and vortices can lose their energy into small-scale
turbulence. Understanding the physical mechanisms underlying those energy transfers
remains a major theoretical challenge. Here we propose an approach that shed new light
on the role of bottom topography in this problem. At a linear level, one efficient
way of extracting energy and momentum from the mean-flow above topography
undulations is the radiation of lee-waves. The generated lee-waves are well described
by inviscid theory which gives a prediction for the energy-loss rate at short time
[1].
Using a quasi-linear approach we describe the feedback of waves on the mean-flow occurring
mostly close to the bottom topography. This can thereafter impact the lee-waves radiation and
thus modify the energy-loss rate for the mean-flow. In this work, we consider the Boussinesq
equations with periodic boundary conditions in the zonal direction. Taking advantage of this
idealized geometry, we apply zonally-symmetric wave-mean interaction theory [2,3]. The
novelty of our work is to discuss the crucial role of dissipative effects, such as molecular
or turbulent viscosities, together with the importance of the boundary conditions
(free-slip vs no-slip). We provide explicite computations in the case of the free
evolution of an initially barotropic flow above a sinusoidal topography with free-slip
bottom boundary condition. We show how the existence of the boundary layer for the
wave-field can enhance the streaming close to the topography. This leads to the
emergence of boundary layer for the mean-flow impacting the energy-loss rate
through lee-wave emissions. Our results are compared against direct numerical
simulations using the MIT general circulation model and are found to be in good
agreement.
References
[1] S.L. Smith, W.R. Young, Conversion of the Barotropic Tide, JPhysOcean 2002
[2] 0. Bühler, Waves and Mean Flows, second edition, Cambridge university press
2014
[3] J. Muraschko et al, On the application of WKB theory for the simulation of the
weakly nonlinear dynamics of gravity waves, Q. J. R. Meteorol. Soc. 2013 |
|
|
|
|
|
|