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| Titel |
Mixed layer deepening by Langmuir circulation |
| VerfasserIn |
J.-B. Flór, E. J. Hopfinger, E. Guyez |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027966
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| Zusammenfassung |
| Mixed layer deepening has important consequences for general ocean circulation and climate
models, as well as for the dynamics of lakes and reservoirs. Among the various
surface-induced mixing processes such as shear, convection and precipitation, a mechanism
that has drawn increasing interest is Langmuir circulation. Though Langmuir circulation
occurs in the mixing layers of oceans and lakes for relatively low wind speeds, its
relevance to mixed layer deepening is still an open question. In order to estimate
the contribution to mixing in the upper layer of oceans and lakes by Langmuir
vortex-cells relative to shear-induced mixing, we employ results on entrainment rate
obtained from laboratory experiments with Taylor vortex cells. New information about
mixing by horizontal vortices like langmuir vortices has been obtained from recent
experimental results by Guyez et al. (J. Fluid Mech. 2007) on mixing across a density
interface by turbulent Taylor vortices in a Taylor-Couette flow. Using the analogy
between these vortex cells and Langmuir vortices, we relate the vortex flow and
the shear across the mixed layer to a surface friction-velocity u* and show that
up to a Richardson number of Ri* - 50, layer deepening is predominantly by
shear-generated turbulence, whereas for Ri* > 50 the contribution by coherent
Langmuir cells is of increasing importance and dominates, since there is no critical
Froude-number criterion for the arrest of mixing by Langmuir cells. These results
confirm observations in that shear-generated turbulence dominates during initial
layer deepening under relatively weak buoyancy effects, and that subsequently
Langmuir-cell mixing is of equal importance or even dominate mixed layer deepening. |
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