The evaporation rate was derived from the energy balance equation and compared with a calculated potential evaporation rate. In some cases marked differences were observed. The experimental and data processing systems are described.Ĭo-spectra for momentum and heat fluxes were obtained and compared with those found by other investigators. Wind velocity components were determined with three hot-wire anemometers, the temperature with a rapid resistance thermometer. Fluxes of heat and momentum are measured by the eddy-correlation method at a height of 1 m. The experimental site is described it is considered to be representative for large grassland areas in Western Europe. Measurements of the terms in the energy balance of grassland, with the exception of the evaporative flux, were performed. This paper is a first report on a programme aimed at recording continuously heat and vapour fluxes close to the earth's surface. This implied that the intercepted precipitation evaporated more rapidly than would be predicted by either method. 7 times as great as that of the canopy that was not wet. The rate of the evapotranspiration from the wet canopy was 1. Advection was considered the source of additional energy for increasing the evapotranspiration. Such a phenomenon was observed often during rainy periods. In the latter case, the evapotranspiration exceeded the net radiation. When the canopy was wet, the estimated evapotranspiration consumed 74 percent (heat budget) and 109 percent (Monteith) of the net radiation. As the total amount of precipitation intercepted by the trees was 28.60 mm, it was shown that the evaporation of intercepted precipitation was between 30 and 40 percent of the evapotranspiration calculated by either method. Furthermore, the ratios of the evapotranspiration by both methods to the evaporation from an evaporation pan were 0.60 and 0.81 respectively. This corresponded to approximately 54 percent and 73 percent respectively of the measured net radiation during the same. et Z.) stand was measured by the heat budget method and by Monteith's equation for a period of 28 days in May and June 1980. The evapotranspiration from a Hinoki (Chamaecyparis obtusa S.
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