An objective method for determining principal time scales of coherent eddy structures using orthonormal wavelets

Abstract

A new, parameter-free method, based on orthonormal wavelet expansions is proposed for calculating the principal time scale of coherent structures in atmospheric surface layer measurements. These organized events play an important role in the exchange of heat, mass, and momentum between the land and the atmosphere. This global technique decomposes the energy contribution at each scale into organized and random eddy motion. The method is demonstrated on vertical wind velocity measurements above bare and vegetated surfaces. It is found to give nearly identical results to a local thresholding approach developed for signal de-noising that assigns the wavelet coecients to organized and random motion. The eect of applying anti-and/or near-symmetrical wavelet basis functions is also investigated. Ó

Identification of relationship between sunspots and natural runoff in the Yellow River based on discrete wavelet analysis

“…Recently, wavelet methods essentially were used in order to identify coherent convective storm structures and to characterize their temporal variability (Szilagyi, Parlange, Katul, & Albertson, 1999), to explain the nonstationarity of karstic watersheds (Labat et al, 2000a(Labat et al, , 2000b. Chou and Wang (2002) applied discrete wavelet transform to decompose and compress the unit hydrograph.…”

Atmospheric stability effect on subgrid-scale physics for large-eddy simulation

“…In turbulent boundary-layer ows, coherent structures are associated with the sweep/ ejection nature of the¯ow, and their presence in the atmospheric surface layer is easily identi®ed through ramps in the measured temperature signal [15,16,22,23,50,53,54,58]. Such coherent motions are well known to be responsible for a very important fraction (75% and more) of the total turbulent¯uxes [15], and therefore it is important that SGS models used in LES of the ABL capture the relationship between the coherent structures and the dynamics of the non-resolved scales.…”

Orthogonal wavelet analysis of counter gradient transport phenomena in turbulent asymmetric channel flow

“…Different methods give different results about the principal scale of coherent structures, including maximal energy method [17], energy method by Liandrat et al [18], energy method by Farge [7] and de-noising method by Szilagyi et al [19]. The energy methods adopt a continuous wavelet while the de-noising method adopts a discrete wavelet.…”

“…Velocity-velocity (u-v) correlations method to evaluate the contribution of coherent structures on different scales, Szilagyi et al[19] adopted the maximal value of difference between p m in (11) and p wn m (for white noise) as the principal scale of coherent structures.…”