Atmospheric Boundary Layer

Donald H. Lenschow

THE ATMOSPHERIC BOUNDARY LAYER (ABL) is the bottom layer of the atmosphere. Its defining characteristic is that it interacts with the Earth's surface on a time scale of a few hours or less. Therefore, all constituents emitted at or near the surface rapidly diffuse throughout the ABL. This rapid interaction is a direct result of turbulence, which is an essential feature of the ABL. Over land, its depth can vary from a few miles in the daytime to a few dekameters at night. The atmosphere near the earths surface is almost always turbulent; that is, the air is continually undergoing seemingly random motions, in addition to whatever wind may exist. The sources of turbulence are wind shear (the change in wind speed and direction with height) and convection (motions driven by air density differences resulting from surface heating or latent heating from water phase changes). Defining characteristics of turbulence are ...

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