Measurement and estimation of the aerodynamic resistance

Abstract

Using two methods of eddy correlation system and evaporation pan to measure respectively the aerodynamic resistance over bare soil surface and maize field, this paper analyses the diurnal variation of the aerodynamic resistance and its relationship with wind speed. Based on direct measurements by eddy correlation system, an evaluation of the aerodynamic resistance models is made. These models include Thom model, Verma-Ronsenberg model, Monteith-Hatfield model, XieXianqun model, Mahrt-Ek model, Choudhury-1 model and Choudhury-2 model. The results show that: the distribution of the aerodynamic resistance takes a "U" type in the daytime and inverse "V" type at night. The aerodynamic resistance is a power function of wind speed. The aerodynamic resistances measured by eddy correlation system are in agreement with those measured by evaporation pan, but big differences occur when the evaporation rate is very small at night or rainy day. Choudhury-1 model, XieXianqun model and Thom model give the better agreement with the measurements by eddy correlation system both over bare soil surface and the maize field, while Mahrt-Ek Model and Monteith-Hatfield model perform worse.