LATENT AND SENSIBLE HEAT-FLUX PREDICTIONS FROM A UNIFORM PINE FOREST USING SURFACE RENEWAL AND FLUX VARIANCE METHODS

A surface renewal model that links organized eddy motion to the latent and sensible heat fluxes is tested with eddy correlation measurements carried out in a 13 m tall uniform Loblolly pine plantation in Duke F orest, Durham, North Carolina. The surface renewal model is based on t he occurance of ramp-like patterns in the scalar concentration measure ments. To extract such ramp-like patterns from Eulerian scalar concent ration measurements, a newly proposed time-frequency filtering scheme is developed and tested. The time-domain filtering is carried out usin g compactly-supported orthonormal wavelets in conjunction with the ''U niversal Wavelet Thresholding'' approach of Donoho and Johnstone, whil e the frequency filtering is carried out by a band-pass sine filter ce ntered around the ramp-occurrence Frequency as proposed by other studi es. The method was separately tested for heat and water vapour with go od agreement between eddy correlation flux measurements and model pred ictions. The usefulness of the flux-variance method to predict sensibl e and latent heat fluxes is also considered. Our measurements suggest that the simple flux-variance method reproduces the measured heat and momentum fluxes despite the fact that the variances were measured with in the roughness sublayer and not in the surface layer. Central to the predictions of water vapour fluxes using the flux-variance approach i s the similarity between heat and water vapour transport by the turbul ent air flow. This assumption is also investigated for this uniform fo rest terrain.