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| Titel |
Structuring of turbulence and its impact on basic features of Ekman boundary layers |
| VerfasserIn |
I. Esau, R. Davy, S. Outten, S. Tyuryakov, S. Zilitinkevich |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 20, no. 4 ; Nr. 20, no. 4 (2013-08-22), S.589-604 |
| Datensatznummer |
250086043
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| Publikation (Nr.) |
 copernicus.org/npg-20-589-2013.pdf |
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| Zusammenfassung |
| The turbulent Ekman boundary layer (EBL) has been studied in a large number of
theoretical, laboratory and modeling works since F. Nansen's observations
during the Norwegian Polar Expedition 1893–1896. Nevertheless, the proposed
analytical models, analysis of the EBL instabilities, and turbulence-resolving
numerical simulations are not fully consistent. In particular, the role of
turbulence self-organization into longitudinal roll vortices in the EBL and
its dependence on the meridional component of the Coriolis force remain
unclear. A new set of large-eddy simulations (LES) are presented in this study.
LES were performed for eight different latitudes (from 1° N to
90° N) in the domain spanning 144 km in the meridional
direction. Geostrophic winds from the west and from the east were used to
drive the development of EBL turbulence. The emergence and growth of longitudinal
rolls in the EBL was simulated. The simulated rolls are in good agreement
with EBL stability analysis given in Dubos et al. (2008). The destruction of
rolls in the westerly flow at low latitude was observed in simulations, which
agrees well with the action of secondary instability on the rolls in the EBL.
This study quantifies the effect of the meridional component of the Coriolis
force and the effect of rolls in the EBL on the internal EBL parameters such
as friction velocity, cross-isobaric angle, parameters of the EBL depth and
resistance laws. A large impact of the roll development or destruction is
found. The depth of the EBL in the westerly flow is about five times less
than it is in the easterly flow at low latitudes. The EBL parameters, which
depend on the depth, also exhibit large difference in these two types of
the EBL. Thus, this study supports the need to include the horizontal
component of the Coriolis force into theoretical constructions and
parameterizations of the boundary layer in models. |
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