VARIABILITY OF SURFACE FLUXES WITHIN A COMPLEX AREA OBSERVED DURING TABLE-92

A data set obtained in a 3 week intensive field experiment called Tsukuba Atmospheric Boundary Layer Experiment (TABLE) 92 allowed some investigation on the heterogeneity of the surface fluxes within a 16 km by 16 km experimental area at and around Tsukuba city, Japan. The area can be characterized by its generally flat topography and by its complex surface land usages. The land covers include crop fields, pine woods and forests, houses or buildings, grass fields, and paddy fields. Five flux stations were installed, in addition to two existing stations, to determine the energy and radiation balance components at each of the major surface types. The analysis of these data made in the present paper has revealed that the spatial variations of surface fluxes were caused by two independent factors. The first one is the non-uniform nature of the incoming solar energy S-d over the area, owing to the inhomogeneous presence of clouds, and the second factor is the variation of the surface cover. The former effect is important only when the sky is partly cloudy. The coefficient of variation for the hourly mean S-d, defined by the ratio of the standard deviation and the mean of S-d measured simultaneously at different stations, was of the order of V = 0.2, whereas the corresponding values of V for the net radiation, latent and sensible heat fluxes owing to the latter effect alone were around V = 0.3-1.0. Thus the variation of the surface cover had a somewhat larger effect on the inhomogeneity of the surface fluxes in the area.