Atmospheric Boundary Layer

(or friction layer, planetary boundary layer), the air layer adjacent to the earth’s surface. Because of the intense turbulent mixing that occurs in it, its properties are determined primarily by the thermal and dynamic influence of the underlying surface. The thickness of the layer ranges from 300—400 m to 1-2 km. The greater the roughness of the underlying surface and the more intense the turbulence, the greater the thickness. For this reason, the thickness increases with increasing wind speed and decreasing thermal stability of the atmosphere. Transfer of heat and moisture between the earth’s surface and the free atmosphere lying above the layer is accomplished through the layer. The layer is characterized by an especially high level of contamination by dust and condensation products. Up to an altitude of 100 m wind speed within the layer increases approximately in proportion to the logarithm of the altitude; above 100 m it increases more and more slowly.