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 e asily be described for modelling and remote sensing purposes by means of th e thermal roughness length (z(ot)) This roughness length is usually express ed relative to the roughness length for wind speed (z(ou)): kB(-1) = In(z(o u)/z(ot)). In the past, the kB(-1) factor has been taken as a constant havi ng a value of ca. 2 in the case of homogeneous canopies. There is some theo retical evidence that kB(-1) should depend on friction velocity (u(*)) or r oughness Reynolds number (Re-o). In this study, previously published barley and pasture data were re-evaluated. It was shown that the reciprocal of St anton number, which is a part of kB(-1), could be expressed commonly for bo th 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 Elsev ier Science B.V. All rights reserved.