Turbulent energy dissipation rates and exchange processes above a non‐homogeneous surface

Abstract

SUMMARYEnergy dissipation rates and the eddy fluxes of sensible heat, momentum, and total kinetic energy have been measured above a non-homogeneous surface. Calculations were made from simultaneous observations of fluctuations in air temperature and the orthogonal components of wind velocity at heights of 16 m and 40 m. In all thermal stratifications, dissipation rates given by the Kolmogoroff structure function are in close agreement with direct measurements of the energy extracted from the mean flow. During stable stratification, energy losses due to work done against gravity and to the divergence of the vertical flux of turbulent kinetic energy are nearly an order of magnitude smaller than the dissipation. In unstable stratification, energy losses due to the flux divergence are of the same order as the dissipation and are approximately three times larger than the energy produced by buoyancy. Estimates ofthevertical heat flux from the Obukhov structure function compare favourably with directly-measured fluxes if the constant in the structure function is assigned a value of 0.7 in lapse conditions and a value of 1.6 in inversion conditions. The measurements also show that the ratio of the diffusivities of heat and momentum at a height of 16 m is significantly greater than unity in unstable stratification and significantly less than unity in stable stratification. Finally, the new measurements of dissipation rate are shown to be consistent with values obtained in previous studies.

The drag coefficient as determined by the dissipation method and its relation to intermittent convection in the surface layer

“…The third term, +D, represents transport due to the vertical divergences of the vertical flux of turbulent kinetic energy and work done by pressure fluctuations. The relative magnitudes and signs of the terms represented in (5) have been investigated by a number of workers (Record and Cramer, 1966;Fichtl and McVehil, 1970;McBean et al, 1971;Wyngaard and CotC, 1971;Garratt, 1972). The results of these studies have not been unanimous or conclusive, primarily due to the difficulty in evaluating #D. The flux divergence contains a third moment and the instrumental di~culties that the measurement of static pressure presents have left pressure transport to guesswork until only recently.…”

Vertical transport of turbulent kinetic energy in the surface layer over a paddy field

“…Since Panofsky (1962) indicated that the divergence of turbulent kinetic energy flux was important in the energy budget of the atmospheric boundary layer, direct measurements of this flux have been made by several researchers (e.g., Record and Cramer, 1966;Maitani and Mitsuta, 1967;. Recently, McBean and Elliott (1975) discussed the stability dependence of normalized kinetic energy flux using their observational results as well as those from other studies (Wyngaard and CotC, 1971;Garratt 1972;Banke and Smith, 1973).…”

Turbulent kinetic energy in the atmospheric surface layer during the summer monsoon

“…(a) Panofsky (1962) and Record & Cramer (1966) reported TKE evolution in the ASL and showed that the divergence of TKE flux was important under steady-state conditions. Busch & Panofsky (1968) in their spectral study of atmospheric turbulence contested the importance of divergence of TKE flux and showed that dissipation compensates shear and buoyancy productions.…”