The atmosphere — boundary layer

The boundary layer, also called the atmospheric or planetary boundary layer, is the part of the atmosphere which is directly influenced by the surface.

The characteristics of the boundary layer depend on the underlying surface and the time of day. They vary in two main ways.

• Unstable boundary layers — the surface transfers heat to the atmosphere, usually during the day over land
• Stable boundary layers — the atmosphere transfers heat to the surface, usually during the night over land

Understanding the state of the boundary layer is crucial in forecasting weather conditions at, or near, the surface, such as the formation and dissipation of fog, or extremes of temperature.

Boundary layer processes are also important in assessing air quality and how air pollutants disperse in the atmosphere.