Wavelet analysis of multi-scale properties of turbulent fluxes above a forest

Multi-scale properties in down-gradient and counter-gradient contributions to turbulent fluxes of sensible heat and CO2, with the WPL correction for density effect (Webb, Pearman and Leuning, 1980) applied to wavelet cospectra, are analyzed using the wavelet transform. Eddy-covariance data measured above a forest at the Aiken AmeriFlux Site located at the US Department of Energy's Savannah River Site in daytime weakly unstable atmospheric conditions during Feb-Mar, 2011 are used. Results reveal that the occurrence and intensity of upward and downward events in wavelet cospectra, and the upward and downward global wavelet cospectra, are scale-dependent. The dominant one of upward and downward components, that is consistent with the direction of the fluxes, possesses higher occurrence and intensity at larger scales than at small scales. Opposite scale properties are observed for the minor component. The peak of the main component of the wavelet cospectra is at larger scales of 30-40 s than the peak of intensity at about 20 s.