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The Coriolis effect on coherent structures in planetary boundary layers
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
2003 (English)In: Journal of turbulence, ISSN 1468-5248, Vol. 4, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

Coherent structures are often visible in atmospheric boundary layers as convective clouds and irregular fog. Large eddy simulations (LES) provide data to study the coherent structures by means of multivariate methods of statistical analysis. One of such methods is a proper orthogonal decomposition (POD). A POD can isolate most energetic three-dimensional structures in turbulent boundary layers. Coherent structures in planetary boundary layers (PBLs) were found to be inherently different from those in laboratory boundary layers without background rotation. This study attributes the differences to an interaction between the vorticity of coherent structures and the constant background vorticity of the planet rotation. LES of neutrally stratified PBLs clearly show the Coriolis force effect. The Coriolis effect supports vortices with vorticity parallel to the planetary vorticity. Simultaneously, the Coriolis effect destroys vortices with vorticity counter-parallel to the planetary vorticity. Convective PBLs show an interplay of vorticities of shear- and buoyancy-induced coherent structures. The Coriolis effect is less important in convective PBLs in comparison with neutral PBLs. The horizontal and vertical components of the Coriolis force act in essentially different ways. The vertical component mainly damps the coherent structures. It also turns the structures relative to the geostrophic wind. The horizontal component mainly makes the structures asymmetrical.

Place, publisher, year, edition, pages
2003. Vol. 4, 1-10 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-90147DOI: 10.1088/1468-5248/4/1/017OAI: oai:DiVA.org:uu-90147DiVA: diva2:162386
Available from: 2003-02-19 Created: 2003-02-19 Last updated: 2013-06-14Bibliographically approved
In thesis
1. Large Eddy Simulation of Non-Local Turbulence and Integral Measures of Atmospheric Boundary Layers
Open this publication in new window or tab >>Large Eddy Simulation of Non-Local Turbulence and Integral Measures of Atmospheric Boundary Layers
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A new large eddy simulation (LES) code is developed and used to investigate non-local features of turbulent planetary boundary layers (PBLs). The LES code is based on filtered Navier-Stokes equations, which describe motions of incompressible, Boussinesq fluid at high Reynolds numbers. The code computes directly large-scale, non-universal turbulence in the PBL whereas small-scale, universal turbulence is parameterized by a dynamic mixed subgrid closure. The LES code is thoroughly tested against high quality laboratory and field data.

This study addresses non-local properties of turbulence which emphasis on the stable stratification. Its basic results are as follows. The flow stability in PBLs is generally caused by two mechanisms: the negative buoyancy force (in the stable density stratification) and the Coriolis force (in the rotating system). The latter stabilizes the flow if the earth’s vorticity and the turbulent vorticity are anti-parallel. The Coriolis force stability suppresses large-scale turbulence and makes large eddies asymmetric. The density stratification suppresses vertical scales of turbulence. Joint actions of the Coriolis and the buoyancy forces result in a more complex behavior of turbulence. Particularly, the layers of vigorous turbulence may appear in the course of development of low-level jets in baroclinic atmosphere.

Non-local effects determine integral measures of PBLs, first of all the PBL depth. This study clearly demonstrates its pronounced dependences on the Coriolis parameter, the Kazanski-Monin internal stability parameter, and newly introduced imposed-stability and baroclinicity parameters. An LES database is created and used to validate an advanced PBL-depth formulation. LES support the idea that PBLs interact with the stably stratified free flow through the radiation of gravity waves, excited by large turbulent eddies at the interface.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 30 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 800
Meteorology, Planetary boundary layers, large eddy simulations, non-local turbulence, Meteorologi
National Category
Meteorology and Atmospheric Sciences
Research subject
urn:nbn:se:uu:diva-3321 (URN)91-554-5519-0 (ISBN)
Public defence
2003-03-24, Axel Hambergsalen, Geocentrum, Uppsala, 10:00
Available from: 2003-02-19 Created: 2003-02-19Bibliographically approved

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