Variation of the beta coefficient in the relaxed eddy accumulation method

Increased usage of the conditional sampling techniques of the relaxed eddy accumulation method of measuring trace gas fluxes from vegetation raises questions as to the physical meaning of the beta factor. Using sensible heat flux data to calculate beta by comparison of the eddy covariance and conditional sampling algorithms suggests a mean value of 0.56. A theoretical approach based on the Gram-Charlier distribution is shown to need cross product terms up to the 4th order to provide a good description of beta by taking into account the skewness and flatness of the distributions of the components of wind velocity and scalars. This description also shows that beta is not constant but will vary with turbulence characteristics in time and space. Values of beta for scalar and momentum fluxes are shown to vary over a typical range of 0.40 to 0.63.