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12,688,000 Yen (FY1998; 4,222,000 Yen)
This sub-theme is aiming at a development of a relevant parameterization for the exchange process between a forest ecosystem and the atmosphere.
To obtain basic data for the parameterization, a long-term tower observation of the energy exchange between a forest and the atmosphere has been continuously conducted over a deciduous broad-leaf forest in Kawagoe, Japan. The observation also covers microclimate within the forest, soil moisture and temperature, leaf area, etc. , as controlling environments. To keep quality of data, the maintenance of instruments was made carefully, and many different techniques were adopted in parallel for each measurement. The observed results show that the albedo and each component of the energy budget of the forest exhibit clear seasonal variation, correlating well with the seasonal change in the leaf area index. A proper consideration of the phenological cycle is hence necessary for a parameterization of the energy exchange over a deciduous forest.
Applying a simple canopy model to the obtained data, the evaporation efficiency of the forest (the most important parameter to model the energy budget) was estimated. The results show that the value of evaporation efficiency has seasonal and diurnal variations. The seasonal variation is induced by the phenological change in the tree activity, and the diurnal variation comes from the stomatal regulation which responds to the meteorological condition. As the first step of the parameterization, the dependency of evaporation efficiency to the meteorological condition was modeled simply with the solar radiation and the evaporative demand (expressed in terms of the potential evaporation rate) of the atmosphere. The diurnal variation of energy budget of the forest was then successfully simulated using this parameterization.
Land-surface process, Forest, Energy budget, Long-term observation, Parameterization