Low‐frequency processes and turbulence structure in a perturbed boundary layer

An analysis of the turbulence structure in a perturbed boundary layer and in low‐wind regimes is presented. The study is based on 15 months of continuous wind and turbulence measurements gathered, within the framework of the Urban Turbulence Project, at three levels (5, 9 and 25 m) on a mast located...

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Bibliographic Details
Published in:Quarterly journal of the Royal Meteorological Society 2013-04, Vol.139 (673), p.1059-1072
Main Authors: Mortarini, L., Ferrero, E., Falabino, S., Trini Castelli, S., Richiardone, R., Anfossi, D.
Format: Article
Language:English
Subjects:
Autocorrelation functions
Boundary layer
Earth, ocean, space
Exact sciences and technology
External geophysics
Fluid dynamics
Fluid flow
low wind
Meteorology
Parametrization
perturbed boundary layer
Physics of the high neutral atmosphere
Statistics
Turbulence
turbulence structure
Turbulent flow
urban turbulence
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Summary:An analysis of the turbulence structure in a perturbed boundary layer and in low‐wind regimes is presented. The study is based on 15 months of continuous wind and turbulence measurements gathered, within the framework of the Urban Turbulence Project, at three levels (5, 9 and 25 m) on a mast located in the outskirts of the city of Turin (Italy). The aim of the work is to investigate low‐frequency processes in a perturbed boundary‐layer. In fact, the urban canopy and the heat island, together with frequent low‐wind conditions, interact with and modify the turbulence structure. In order to investigate this modification, the velocity Eulerian autocorrelation functions together with both the Eulerian and Lagrangian time‐scales are shown and compared with the classical theory. The comparisons show that in low‐wind cases the velocity autocorrelation functions are not simply exponential but present an oscillating behaviour. A method of normalization is proposed together with an analysis on the applicability of this function. The estimated Lagrangian time‐scales are compared with two widely used parametrizations. It is found that the presence of the urban fabric influences the turbulence time‐scales and suggests the development of new parametrizations. Finally, higher‐order statistics are evaluated and the relationship between higher‐order and lower‐order moments are analysed, pointing out the effects due to the urban environment. Copyright © 2012 Royal Meteorological Society
ISSN:0035-9009
1477-870X
DOI:10.1002/qj.2015