MEASUREMENTS OF TURBULENT FLUXES AND MODEL SIMULATION OF MICROMETEOROLOGY IN A WHEAT FIELD AT ZHANGYE OASIS

Simultaneous measurements of water vapor, sensible heat, carbon dioxid e and momentum fluxes were made above and within plant canopies of a w heat field at Zhangye oasis in June, 1992, using the eddy correlation method. The diurnal variations of energy and carbon dioxide budget com ponents and related meteorological parameters were obtained. Vertical fluxes of water vapor, sensible heat and carbon dioxide above plant ca nopies were predominant, compared with the fluxes at the middle layer of the plant canopy. This implies that, in the daytime, the upper part of dense plant canopies (LAI = 5) was an active source region of wate r vapor as well as an active sink region of carbon dioxide. A moderate and steady wind from the surrounding warmer desert and Gobi areas inc reased an upward water vapor flux and caused a significant downward se nsible heat flux above plant canopies; these phenomena are the so-call ed oasis effects peculiar to the arid region. The diurnal variations o f turbulent fluxes and related quantities observed in a wheat field we re compared with the results of Goudriaan's simulation model. The mode l simulates well some primary characteristics of wheat crop micrometeo rology; large loss of latent heat in upper parts of plant canopies, an d a significant downward sensible heat flux under moderate wind speed conditions.