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Conference Paper

Quantification of global intermittency in stably stratified Ekman flow

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Ansorge,  Cedrick
Max Planck Research Group Turbulent Mixing Processes in the Earth System, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

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Mellado,  Juan-Pedro
Max Planck Research Group Turbulent Mixing Processes in the Earth System, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

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Citation

Ansorge, C., & Mellado, J.-P. (2016). Quantification of global intermittency in stably stratified Ekman flow. In J. Peinke (Ed.), Progress in Turbulence VI: Proceedings of the iTi Conference on Turbulence 2014 (pp. 191-194). Springer International Publishing.


Cite as: https://hdl.handle.net/11858/00-001M-0000-002A-80F6-B
Abstract
In the atmospheric boundary layer, some turbulence-like structures are maintained up to a stable density stratification several times higher than the above-mentioned linear stability analysis predicts. Nonetheless, the cessation of turbulence in such flows exposed to stable density stratification is a well-recognized problem. For non-rotating configurations, namely stably stratified channel- and free-shear flows, it has been shown that this cessation does not occur as an on–off process but is rather a complex transition from a turbulent to a laminar state. When stratification increases gradually, this transition begins with the localized absence of turbulent eddies in an otherwise turbulent flow, and has recently been shown to also occur in stably stratified Ekman flow. This localized absence of turbulence bears a striking resemblance to the absence of turbulence on some or all scales even close to the surface which is sometimes observed in the atmosphere and has been termed Global Intermittency. We propose here a method based on the intermittency factor together with high-pass-filtered flow fields that successfully distinguishes between turbulent and non-turbulent patches in Ekman flow.