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The Convective Boundary layer (CBL), also known as the daytime Planetary boundary layer, is the part of the atmosphere most directly affected by solar heating of the earth's surface. This layer extends from the earth surface to a capping inversion that typically locates at a height of 1–2 km by midafternoon over land. Below the capping inversion (10-60% of CBL depth, also called entrainment zone in the daytime), CBL is divided into two sub-layers: mixed layer (35-80% of CBL depth) and surface layer (5-10% of CBL depth). The mixed layer, the major part of CBL, has a nearly constant distribution of quantities such as potential temperature, wind speed, moisture and pollutant concentration because of strong buoyancy generated convective turbulent mixing. Parameterization of turbulent transport is used to simulate the vertical profiles and temporal variation of quantities of interest, because of the randomness and the unknown physics of turbulence. However, turbulence in the mixed layer is not completely random, but is often organized into identifiable structures such as thermals and plumes in the CBL. Simulation of these large eddies is quite different from simulation of smaller eddies generated by local shears in the surface layer. Non-local property of the large eddies should be accounted for in the parameterization. ==Mean Characteristics== The mean characteristics of the three layers of the CBL are as follows. (1) The Surface layer is a very shallow region close to the ground (bottom 5 to 10% of CBL). It is characterized by a superadiabatic lapse rate, moisture decrease with height and strong wind shear.〔 Almost all wind shear and all the potential temperature gradient in the CBL are confined in the surface layer. (2) The Mixed layer composing the middle 35 to 80% of CBL〔 is characterized by conserved variables such as potential temperature, wind speed and moisture. (3) The Entrainment zone (or Capping inversion) can be quite thick, averaging about 40% of the depth of the CBL. It is the region of statically stable air at the top of the mixed layer, where there is entrainment of free atmosphere air downward and overshooting thermals upward.〔 Potential temperature, wind speed has a sharp increase across the capping inversion, while moisture has a sharp decrease. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Convective Boundary Layer」の詳細全文を読む スポンサード リンク
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