The Planetary Boundary Layer

The dynamics associated with atmospheric interactions with Earth's surface and the production of boundary layers are considered. Reynolds averaging is introduced and used to identify turbulent fluxes that alter a mean atmospheric profile. Turbulent kinetic energy (TKE) is defined, and the role of buoyancy and momentum fluxes in the evolution of TKE is examined. Approximations to the TKE and boundary layer representation are discussed, including flux–gradient ( K ) theory, the mixing length hypothesis, and the Ekman layer. The physical processes whereby circulations spin down through Ekman layers is discussed in detail.