Flows of the Near-Surface Boundary Layer

Abstract

Wind shear near the surface is responsible for the entrainment of sand particles, the formation and evolution of aeolian landforms, and the disasters induced by wind-blown sand movement. Therefore, many studies of the wind-blown sand movement are focused on understanding, representing and depicting the characteristics of air flows in the near-surface boundary layer where the wind-blown sand movement mainly takes place. The content of this chapter is arranged as follows. In Sects. 2.1 and 2.2, some basic definitions and equations, including the turbulent model, relevant to the wind-blown sand movement, are introduced in the light of fluid dynamics; Sects. 2.3 and 2.4 provide a brief summary of the characteristics and major observation methods of the atmospheric boundary layer, especially the near-surface boundary layer; Sect. 2.5 gives the basic equations governing air flow and their simplified forms for the near-surface layer and the wind-blown sand movement; Based on field observational results on the surface wind gusts, Sect. 2.6 devotes to the analysis on the statistical characteristics of fluctuating wind fields and resultant saltation activity near the surface, and then to establish two wind velocity prediction models to describe variations of fluctuating wind velocity at different heights and times.