ENERGY-INERTIAL SCALE INTERACTIONS FOR VELOCITY AND TEMPERATURE IN THE UNSTABLE ATMOSPHERIC SURFACE-LAYER

Triaxial sonic anemometer velocity and temperature measurements were u sed to investigate the local structure of the velocity and temperature fluctuations in the unstable atmospheric surface layer above a grass- covered forest clearing. Despite the existence of a 2/3 power law in t he longitudinal velocity (2 decades) and temperature (1 decade) struct ure functions, local isotropy within the inertial subrange was not att ained by the temperature field, although a near-isotropic state was at tained by the velocity field. It was found that sources of anisotropy were due to interactions between the large-scale and small-scale eddy motion, and due to local velocity-thermal interactions. Statistical me asures were developed and used to quantify these types of interactions . Other types of interactions were also measured but were less signifi cant. The temperature gradient skewness was measured and found to be n on-zero in agreement with other laboratory flow types for inertial sub range scales. Despite these interactions and anisotropy sources in the local temperature field, Obukhov's 1949 hypothesis for the mixed velo city-temperature structure functions was found to be valid. Finally, o ur measurements show that while a 2/3 power-law in the longitudinal ve locity structure function developed at scales comparable to five times the height from the ground surface (z), near-isotropic conditions wer e achieved at scales smaller than z/2.