Dependence of kB-1 factor on roughness Reynolds number for barley and pasture

One of the surface energy balance components, the sensible heat flux, can easily be described for modelling and remote sensing purposes by means of the thermal roughness length (z(ot)) This roughness length is usually expressed relative to the roughness length for wind speed (z(ou)): kB(-1) = In(z(ou)/z(ot)). In the past, the kB(-1) factor has been taken as a constant having a value of ca. 2 in the case of homogeneous canopies. There is some theoretical evidence that kB(-1) should depend on friction velocity (u(*)) or roughness Reynolds number (Re-o). In this study, previously published barley and pasture data were re-evaluated. It was shown that the reciprocal of Stanton number, which is a part of kB(-1), could be expressed commonly for both surfaces. The re-evaluated kB(-1) factor took the form: kB(-1) = 0.37Re(o)(0.3)-(1.2 or 1.9) (for barley and pasture, respectively). (C) 2001 Elsevier Science B.V. All rights reserved.