Towards a solution of the closure problem for convective atmospheric boundary-layer turbulence


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Jorg.Hartmann [ at ] awi.de

Abstract

We consider the closure problem for turbulence in the dry convective atmospheric boundary layer (CBL). Transport in the CBL is carried by small scale eddies near the surface and large plumes in the well mixed middle part up to the inversion that separates the CBL from the stably stratified air above. An analytically tractable model based on a multivariate Delta-PDF approach is developed. It is an extension of the model of Gryanik and Hartmann [1] (GH02) that additionally includes a term for background turbulence. Thus an exact solution is derived and all higher order moments (HOMs) are explained by second order moments, correlation coefficients and the skewness. The solution provides a proof of the extended universality hypothesis of GH02 which is the refinement of the Millionshchikov hypothesis (quasi- normality of FOM). This refined hypothesis states that CBL turbulence can be considered as result of a linear interpolation between the Gaussian and the very skewed turbulence regimes. Although the extended universality hypothesis was confirmed by results of field measurements, LES and DNS simulations (see e.g. [2-4]), several questions remained unexplained. These are now answered by the new model including the reasons of the universality of the functional form of the HOMs, the significant scatter of the values of the coefficients and the source of the magic of the linear interpolation. Finally, the closures 61 predicted by the model are tested against measurements and LES data. Some of the other issues of CBL turbulence, e.g. familiar kurtosis-skewness relationships and relation of area coverage parameters of plumes (so called filling factors) with HOM will be discussed also.



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Conference (Talk)
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Not peer-reviewed
Publication Status
Published
Event Details
Turbulent Mixing and Beyond, Sixth International Conference, Tenth Anniversary Program, 14 Aug 2017 - 18 Aug 2017, The Abdus Salam International Centre for Theoretical Physics Trieste, Italy.
Eprint ID
45586
Cite as
Gryanik, V. and Hartmann, J. (2017): Towards a solution of the closure problem for convective atmospheric boundary-layer turbulence , Turbulent Mixing and Beyond, Sixth International Conference, Tenth Anniversary Program, The Abdus Salam International Centre for Theoretical Physics Trieste, Italy, 14 August 2017 - 18 August 2017 .


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