How representative are local measurements of the surface shear stress for regional values?

Abstract

Local values of surface shear stress measured by eddy correlation devices were compared to regional ones generated by Monin–Obukhov similarity (MOS) theory in the atmospheric surface layer over the cooperative atmosphere–surface exchange study (CASES) area in eastern Kansas. For this comparison, minisodar average wind speed profiles were used to implement MOS. The local surface shear stress values were found to be representative of the regional ones only under free convective conditions. For weak to strongly neutral atmospheric conditions, regional values of the surface shear stress were underpredicted by a factor of two by the locally measured ones. Empirical interpolation equations are proposed to describe the relationship in the intermediate range. The surface roughness values of 0.12 and 0.40 m, respectively, were determined for the two locations of the minisodar sounders by regional analysis of their mean wind speed measurements under neutral atmospheric conditions. The roughness values found in this present study compared well to past investigations conducted in this region. Minisodar roughness values were found in this present study to be a good alternative to radiosonde determined ones.