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   -> Volume 4, Issue 2

Preprint: Partitioning eddy motion using Lorentz wavelet filtering
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Brani Vidakovic

PostPosted: Mon Dec 02, 2002 5:42 pm    
Subject: Preprint: Partitioning eddy motion using Lorentz wavelet filtering
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Preprint: Partitioning eddy motion using Lorentz wavelet filtering

Preprint available:

The partitioning of attached and detached eddy motion in the
atmospheric surface layer using Lorentz wavelet filtering

By Gabriel Katul and Brani Vidakovic

via anonymous ftp:
-rw-r--r-- 1 119 33 1996900 Feb 9 10:40
-rw-r--r-- 1 119 33 574818 Feb 9 10:41


Townsend's (1976) attached eddy hypothesis states that the
turbulent structure in the constant stress layer can be decomposed
into attached and detached eddy motion. This paper
proposes and tests methodology for
separating the attached and detached eddy motion from time series
measurements of velocity and temperature.
The proposed methodology is based on the time-frequency
localization and filtering capabilities of the orthonormal wavelet
transforms. Using a relative entropy statistical measure, the
optimal wavelet basis is identified first. The turbulence time
series measurements are then transformed into the wavelet domain
where the contribution of specific events in the time-frequency
domain are identified. The filtering scheme utilizes a recently
constructed Lorentz thresholding methodology that successfully
eliminated all wavelet coefficients associated with the detached
eddy motion. While this filtering scheme lacks the compression
efficiency of the classical Donoho and Johnstone's universal
thresholding model, it conserves the higher-order statistics and
important turbulence interactions related to the Reynolds stresses.
Following the filtering scheme, the attached eddy motion time
series is re-constructed by an inverse wavelet transform of the
non-zero wavelet coefficients. The proposed partitioning
methodology for attached and detached eddy motion is tested using
$56 Hz$ triaxial sonic anemometer velocity and temperature
measurements above a uniform dry lake bed in Owens valley,
California, for a wide range of atmospheric stability conditions.
Validation that the wavelet filtered time series represented the
attached eddy motion is also discussed in the context of
conservation of turbulence energy and surface fluxes.
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