Comparison of aerodynamic and radiometric surface temperature using precision weighing lysimeters

摘要

Radiometric surface temperature (T_s) is commonly used as a surrogate for aerodynamic temperature (T_o) in computing the sensible heat flux term (H) in the energy balance. However, these temperatures may differ by several degrees, leading to possible errors (especially for large H) and their relationship is not well known. Previous researchers have established empirical and semi-empirical parameterizations of the radiometric roughness length (Z_(or)) or some related form (e.g., kB_r~(-1) = ln[Z_(om)/Z_(or)], where Z_(om) is the momentum roughness length). In this paper, we estimated T_o - T_a (where T_a is air temperature at 2 m height) and z_(or) using large, precision weighing lysimeters planted with irrigated alfalfa, irrigated and dryland cotton, and dryland grain sorghum. T_s was measured by infrared thermometers mounted over the lysimeters. No apparent relations were found between (T_o - T_a) and (T_s - T_a) or between Z_(or) (in the kB_r~(-1) form) and meteorological variables or leaf area index (LAI). The kB_r~(-1) parameter appeared to be most influenced by the different surface roughness of each crop type. Using constant kB_r~(-1) values established for each type of surface, the energy balance model showed reasonable agreement with H and LE derived from lysimeter measurements.