Estimation of Bulk Transfer Coefficient and Surface Moisture Availability on a Sorghum Field in Sand Dune

The bulk transfer method combined with the heat balance equation of the surface requires the bulk transfer coefficient for sensible heat flux C_HU and the surface moisture availability β (evapotranspiration efficiency) to evaluate the surface temperature T_s, sensible heat flux H and latent heat flux lE, respectively. This paper examines relations between these coefficients and various factors (soil moisture content, solar radiation). Meteorological observations on a sorghum field in Tottori sand dune were carried out for 6-28 August, 1994. Significant results of the observations are the followings: 1) The value of bulk transfer coefficient varied with the atmospheric stability. 2) The value of β increased with increasing solar radiation, and tended to a constant value (β=0.35) when the solar radiation exceeded about 600 Wm^-2. 3) The value of β increased according to the soil moisture content. Observations of T_s, H and lE were compared with the simulations with the single source model (Kondo and Watanabe, 1992). This model simulates well the observed values of the daily mean of T_s, H and lE within an error of about±20 Wm^-2,±20 Wm^-2 and ±1.1°C, respectively.