planetary boundary layer (PBL)

A layer of air in contact with the Earth's surface, subject to its influence, and located below the free atmosphere. Motions within it are strongly influenced by friction with that surface. Its thickness is variable, ranging between 500 and 1000 meters, although some authors place its upper limit at 1500 m of altitude. Its lowest part is a turbulent layer, while above it lies the Ekman or friction layer, where the influence of friction decreases rapidly with height. The planetary boundary layer (PBL) receives various names, such as mixing layer, convective layer, mechanical layer, or atmospheric boundary layer. It is common to refer to it by the acronym given in the text, or its English equivalents (PBL [Planetary Boundary Layer], ABL [Atmospheric Boundary Layer], CBL [Convective Boundary Layer], ML [Mixed Layer]...).