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- Title
A method to determine the characteristic time‐scales of quasi‐isotropic surface‐layer turbulence over complex terrain: A case‐study in the Adige Valley (Italian Alps).
- Authors
Falocchi, Marco; Giovannini, Lorenzo; de Franceschi, Massimiliano; Zardi, Dino
- Abstract
The present paper provides a method to identify the appropriate time‐scales at which turbulence components behave quasi‐isotropically. In particular, the scales are identified on the basis of an analysis of anisotropic turbulence in the spectral domain. The definition of the spectral anisotropic tensor in terms of ogive functions, rather than of (co)spectra, allows for the evaluation of the overall degree of isotropy associated with time‐scales smaller than a given one. In this way, the time‐scale separating isotropic from anisotropic turbulence is related to the frequency at which the degree of isotropy meets a threshold value, representative of quasi‐isotropic turbulence. The procedure is tested on a dataset of wind speed components and sonic temperature collected on the floor of the Adige Valley (northeastern Italian Alps), which is adopted as a case‐study. Finally, the suitability of the estimated time‐scales is assessed in the framework of the Monin–Obukhov Similarity Theory by evaluating the agreement of the dimensionless standard deviations with the similarity functions. Especially over complex terrain, disentangling terrain effects from more intrinsic turbulence properties requires a proper identification and separation of the low‐frequency components from the smaller‐scale properties. This article proposes a method to estimate the time‐scales of surface‐layer turbulence from the analysis of the spectral distribution of the degree of isotropy. The procedure is applied on a dataset collected in complex terrain and tested by evaluating the agreement of second‐order statistical moments of turbulent variables on similarity functions.
- Subjects
WIND speed; TURBULENCE
- Publication
Quarterly Journal of the Royal Meteorological Society, 2019, Vol 145, Issue 719, p495
- ISSN
0035-9009
- Publication type
Article
- DOI
10.1002/qj.3444