Analysis of Land Surface Heat Fluxes Using the Orthonormal Wavelet Approach

Heat fluxes under unstable atmospheric conditions are measured and analyzed using orthonormal wavelet expansions. Both wavelet and Fourier power spectra display a −1 power law that can be derived from dimensional arguments for latent and sensible heat flux in the turbulent production subrange. The wavelet expansion is used to investigate the spatial structure of the heat fluxes for those scales that exhibit a −1 power law. Dimensionless statistical measures which provide spatial information at different scales are developed and applied to the sensible and latent heat flux measurements. Deviations from Gaussian statistics were observed at the turbulent production subrange. The large flux events (both positive and negative) in the heat flux signals contribute directly to the energy and spatial structure of the −1 power law. The wavelet transform is used to identify the scale of turbulent action directly responsible for the tails observed in the horizontal gradient probability density function of both heat fluxes.