Abstract
Spatial distributions of the downward radiation and the snowmelt rates on a forest floor were calculated under the meteorological conditions in the snowmelt period using estimated three dimensional distributions of the foliage density at a sparse and a dense forest sites with and without leaves. Using the calculated spatial distributions, we evaluated the spatial representativeness of the daily downward radiation and that of the daily snowmelt rates measured at anywhere on the forest floors. The global solar radiation didn't represent the spatial average. The downward long-wave radiation represented the spatial average. The snowmelt rates showed good representativeness except in the leaved sparse forest. The calculated distributions also showed the following results. The spatial variations of the snowmelt rates were small in spite of the large spatial variations of the global radiation on the forest floors. The cause was the high albedo of snow surface and the reverse correlation of the spatial variation between the global radiation and the downward long-wave radiation on the forest floors. The standard deviations of the spatial distributions of the downward radiation and the snowmelt rates on the forest floors depended on that of the foliage density. Moreover the representativeness of the hourly downward long-wave radiation measured at anywhere on the forest floors were discussed under the more wide meteorological conditions. The hourly value represented the spatial average except on the leaved sparse forest floor. The value on the leaved sparse forest floor had the representativeness when the apparent air emissivity was over 0.7.
