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Planetary Boundary Layer
From SKYbrary Wiki
The lower part of the troposphere which is directly influenced by the surface of the Earth.
Surface friction, terrain, and solar heating all influence, to varying degrees, the part of the atmosphere closest to the surface, causing turbulence, convective activity, and changing wind direction. Above this planetary boundary layer, turbulence is less marked and winds follow the geostrophic flow along Isobars; this part of the atmosphere, where flow is not influenced by the surface, is known as the Free Atmosphere.
The planetary boundary layer can be between 1,000 ft and 10,000 ft in depth depending on the terrain.