利用繫留探空氣球及渦流協變性系統於都會區，水稻田及混合區域推估地表粗糙度及Bowen ratio之觀測

Abstract

The similarity theory of the ASL in conjunction with the energy budget equation of land surface under unstable atmospheric conditions was used to determine the aerodynamic roughness lengths for two urban areas and three rice paddies mixed with buildings over a complex terrain in central Taiwan. At each of the sites, surface net radiation, ground heat flux and vertical profiles of wind speed, temperature and humidity within the atmospheric surface layer (ASL) were measured. Over the Taichung urban area, the roughness was determined to be 2.1 m with a zero-plane displacement height of 35 m. Over the Caotun urban area, the roughness was determined to be 1.2 m with a zero-plane displacement height of 11 m. Over the two mixed farmlands, the roughness values were determined to be 0.2 - 0.5 m and over the homogeneous rice paddy in Wufeng, the roughness values were determined to be 0.032 m that close to the values (0.008 – 0.02 m) for homogeneous rice paddies reported in the literature. A preliminary relationship for estimating roughness value as a function of residential fraction, farmland fraction and building height (or population density) is derived. The observations show that during the daytime, the mean height range of the ASL was 30<(z-d0)/z0<106 and the fingerprint areas extended 1.5 km upwind from the three profile sites. During the day, the energy balance ratio measured by an Eddy Covariance (EC) system is found to be 94% after considering the photosynthetic and local advected heat fluxes. The observations by the EC system suggest that the Bowen ratio was about 0.16 during the daytime. Albedo is estimated as 0.1 according to the solar radiation and the reflected show-wave radiation. The EC system also measured the daytime absorbed CO2 flux at 1.2 mg m-2 s-1 and nighttime respiration rate at 0.12 mg m-2 s-1. Relationships of CO2 flux as functions of net solar radiation, air temperature and leaf area index are derived. The diurnal pattern of the canopy resistance for evapotranspiration is found to be a U shape with the minimum value at 42 s m-1 around noon of the rice paddy. A relationship of canopy resistance related to net solar radiation and leaf area index is derived with a correlation coefficient of 0.78.