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

A new, parameter-free method, based on orthonormal wavelet expansions is pr oposed for calculating the principal time scale of coherent structures in a tmospheric surface layer measurements. These organized events play an impor tant 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 demonstrat ed on vertical wind velocity measurements above bare and vegetated surfaces . It is found to give nearly identical results to a local thresholding appr oach developed for signal de-noising that assigns the wavelet coefficients to organized and random motion. The effect of applying anti- and/or near-sy mmetrical wavelet basis functions is also investigated. (C) 1999 Elsevier S cience Limited. All rights reserved.