A mixed spectral finite-difference model for neutrally stratified boundary-layer flow over roughness changes and topography

• Published in: Boundary-layer meteorology Vol. 38; no. 3; pp. 273 - 303
• Main Authors: BELJAARS, A. C. M, WALMSLEY, J. L, TAYLOR, P. A
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01-02-1987
• Subjects: Convection, turbulence, diffusion. Boundary layer structure and dynamics; Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; Air flow; Atmospheric boundary layer; Topography; Spectral model; Modeling; Linear model; Finite difference method
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/BF00122448

A linear model for neutral surface-layer flow over complex terrain is presented. The spectral approach in the two horizontal coordinates and the finite-difference method in the vertical combine the simplicity and computational efficiency of linear methods with flexibility for closure schemes of finite-difference methods. This model makes it possible to make high-resolution computations for an arbitrary distribution of surface roughness and topography. Mixing-length and E- epsilon closures are applied to two-dimensional flow above sinusoidal variations in surface roughness, the step-in-roughness problem, and to two-dimensional flow above sinusoidal topography. The main difference between the two closure schemes is found in the shear-stress results. E- epsilon has a more realistic description of the memory effects in length and velocity scales when the surface conditions change. Comparison between three-dimensional model calculations and field data from Askervein Hill shows that, in the outer layer, the advection effects in the shear stress itself are also important. In this layer, an extra equation for the shear stress is needed.