Neutral planetary boundary layer above a nonhomogeneous surface

Abstract

Theoretical analyses of the atmospheric boundary layer are generally based on the assumptions of stationarity and horizontal homogeneity, which permit one to neglect the inertial terms in equations of motion. The importance of these terms is examined for the case where slight inhomogeneities may cause small but monotonic changes of surface shear in the direction of flow. Considering several models of the neutral barotropic Ekman layer, it is shown that horizontal gradient in the friction velocity of as small as one cm/sec per ten kilometers could make the wind hodograph deviate significantly from that for the homogeneous case. Significant deviations from the logarithmic profile in the surface layer, on the other hand, would occur for horizontal gradients of at least an order of magnitude greater. Thus, the practical criteria for assuming homogeneity may be far more strict and difficult to satisfy for the outer layer than these are for the surface layer.