Estimation of Turbulent Fluxes Using the Flux-Variance Method over an Alpine Meadow Surface in the Eastern Tibetan Plateau

The flux-variance similarity relation and the vertical transfer of scalars exhibit dissimilarity over different types of surfaces, resulting in different parameterization approaches of relative transport efficiency among scalars to estimate turbulent fluxes using the flux-variance method. We investigated these issues using eddycovariance measurements over an open, homogeneous and flat grassland in the eastern Tibetan Plateau in summer under intermediate hydrological conditions during rainy season. In unstable conditions, the temperature, water vapor, and CO₂ followed the flux-variance similarity relation, but did not show in precisely the same way due to different roles (active or passive) of these scalars. Similarity constants of temperature, water vapor and CO₂ were found to be 1.12, 1.19 and 1.17, respectively. Heat transportation was more efficient than water vapor and CO₂. Based on the estimated sensible heat flux, five parameterization methods of relative transport efficiency of heat to water vapor and CO₂ were examined to estimate latent heat and CO₂ fluxes. The strategy of local determination of flux-variance similarity relation is recommended for the estimation of latent heat and CO₂ fluxes. This approach is better for representing the averaged relative transport efficiency, and technically easier to apply, compared to other more complex ones.