Definition

The Planetary Boundary Layer (PBL) is the lowest part of the troposphere which is subject to direct earth-atmosphere influence because of its proximity to the surface of the earth. It is sometimes referred to as the Atmospheric Boundary Layer (ABL).

Description

Surface friction, terrain and solar heating all influence, to varying degrees, that part of the atmosphere closest to the surface, leading to mechanical turbulence, convective activity and variation in wind direction and speed.

Air is a poor conductor of energy - which in Meteorology is basically in the form of heat. However, at levels near the surface of the Earth, solar heating and terrestrial cooling do affect the temperature of the air immediately above the Earth's surface. On hot summer days, for example, intense heating of the Earth's surface warms the air above said surface, which in turn changes the stability of the air.