Surface heterogeneity and vertical structure of the boundary layer

The concepts of vertical structure of the boundary layer over homogeneous surfaces are discussed, including the roughness sublayer, surface layer (inertial layer) and outer layer. As an interpretive literature survey, the vertical depth of the influence of surface heterogeneity, relative to such vertical structure, is examined in terms of blending height theory, convective boundary-layer scaling and internal boundary-layer theory. These concepts are examined with data over different surface types. The rich variety of types of surface heterogeneity and background flow preclude description of their influence on the boundary layer by one single approach. Nonetheless, new scaling arguments offer promise for convective conditions. Internal boundary layers are found to form only in certain situations and even then may exhibit more diffuse vertical structure compared to the textbook internal boundary layer. New scaling arguments are developed to describe the potential for internal boundary-layer development in flow of warm air over a cooler surface. These arguments explain some aspects of the observations but remain incomplete.