Three separate studies concerning flow over inhomogeneous terrain are presented. Two-dimensional nonlinear models were constructed and then integrated numerically. In the first study, the atmospheric boundary layer flow over terrain with a discontinuous variation in roughness was studied. A time dependent numerical model, using Blackadar's expression of mixing length and assuming no dynamic pressure effect and no vertical displacement of the zero velocity level at the lower boundary, was integrated until a steady-state situation was reached. The results agree with earlier theoretical work of Panofsky and Townsend and also with observations by Sterns and Lettau. The second study represents an attempt to solve a problem similar to the one just described using a steady-state model. An iterative method for solving the equations was derived. In addition, the dynamic pressure effect was also incorporated. The results show satisfactory agreement with those of Panofsky and Townsend. It is found that the dynamic pressure effect causes an apparent horizontal smoothing of the motion field. In the third study, the effect of an isolated hot surface (10 km wide) on the motion and temperature field is investigated. The model is time dependent and is based primarily on a sea breeze model by Estoque. As expected, the results show that the intensity of the upward motions which are induced is inversely proportional to the strength of the prevailing flow. The perturbations in both the temperature and velocity fields extend to several tens of kilometers downwind of the hot surface.

A two-dimensional time dependent numerical model of the atmospheric boundary layer is formulated and used to investigate various characteristics of air motion when a change occurs in roughness and/or temperature characteristics of the underlying surface. The integrations have been carried out for steady-state situations also. The model incorporates the effects of penetrative convection, diabatic influence associated with small-scale eddy diffusion, and pressure effects induced by horizontal nonuniformity of terrain in temperature and roughness. The results show that warm surfaces do not necessarily increase the height of internal boundary layers in the vicinity of surface discontinuity. The effects of discontinuity are quite appreciable at large fetches downwind from the discontinuity. (Author).

This book offers a comprehensive review of our current understanding of the planetary boundary layer, particularly the turbulent exchanges of momentum, heat and passive scalars between the surface of the Earth and the atmosphere. It presents and discusses the observations and the theory of the turbulent boundary layer, both for homogeneous and more realistic heterogeneous surface conditions, as well as the dispersion of tracers. Lastly it addresses the main problems arising due to turbulence in weather, climate and atmospheric composition numerical models. Written for postgraduate and advanced undergraduate-level students and atmospheric researchers, it is also of interest to anyone wanting to understand the findings and obtain an update on problems that have yet to be solved.