Dissipation methods, Taylor's hypothesis, and stability correction functions in the atmospheric surface layer

Abstract

The traditional dissipation method and the new approaches suggested by Albertson et al. [1996] and Hsieh et al. [1996] to estimate momentum and heat fluxes were compared using velocity and temperature measurements in the atmospheric surface layer. These measurements were carried out above two different sites (grass and bare soil) over a wide range of atmospheric stability and turbulent intensity conditions. Taylor's hypothesis, flux divergence terms, and stability correction functions which play important roles in the dissipation methods were also evaluated. In highly turbulent intensity flows, deviations from Taylor's hypothesis may cause some errors in estimating dissipation rates and subsequent fluxes. Wyngaard and Clifford [1977] proposed a model to interpret the influence of departures from Taylor's hypothesis. In this study we evaluate this influence in the inertial subrange and discuss the usefulness of Wyngaard and Clifford's model in practice. We also found the flux divergence term in the temperature variance budget equation to be significant, relative to the production term in unstable conditions. Our measurements showed that discarding the flux divergence term resulted in systematic underpredictions of the sensible heat flux by the dissipation methods. The proposed dissipation method by Hsieh et al. [1996] for estimating sensible heat flux was extended to momentum flux, and its implications for stability correction functions were discussed. Good agreement between eddy correlation measured and predicted sensible heat fluxes by the methods of Albertson et al. [1997] and Hsieh et al. [1996] was noted.