The budget equations of turbulent kinetic energy and shear stress contain interaction terms of velocity-pressure and velocity-pressure gradient. These terms were estimated in the surface layer using the air pressure observed at the surface and wind velocity components over plant canopies. The magnitude of the pressure interaction terms was significantly large; it was not negligible compared with the production terms in each budget equation. The present results obtained over a rough surface also confirmed previous results that pressure terms play an important role in the turbulent kinetic energy budgets and the shear stress budget. The height dependency of nondimensional pressure terms versus (z -d)/z,, was not clear.

An experiment was conducted to study turbulent transport processes of scalar quantities within and above a rice plant canopy. A sonic anemometer-thermometer and a Lyman-z humidiometer were used to measure the turbulent fluxes of sensible and latent heat and related turbulence statistics within a paddy field. The sensible and latent heat fluxes measured at two heights within and above the plant canopy showed that the upper layer ofthis plant canopy was an active source region and that the source strength of sensible and latent heat depended on the solar radiation and physiology of rice plants. Analysis ofjoint probability distributions of w and T and of w and 4 within this plant canopy showed that downdrafts were remarkably efficient for upward transport of sensible and latent heat in the daytime. The vertical fluxes of temperature and humidity variance were also divergent from the upper layer of plant canopies. The power spectra of temperature and humidity within the plant canopy decreased rapidly in the high frequency range, compared with the -2/3 law relationship of nS(n) vs log n observed above plant canopies.

Temperature fluctuations in the stable air layer before and after sunset were measured at 4 heights within and above a wheat field. Large positive temperature fluctuations were frequently observed within the plant canopy. The standard deviations, skewness factors and flatness factors of temperature fluctuations within the canopy showed peculiar time variations, having remarkable positive skewness factors. The occurrence of large positive temperature fluctuations was probably related to the difference of temperature gradients below and above the observation height, i.e., these fluctuations frequently occurred when the temperature gradient above the observation height was greater than that below the observation height. Furthermore, the vertical mixing associated with the penetration of downdrafts from the air layer above the canopy was requisite for the occurrence of the phenomenon.

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