Convective Boundary Layer

The convective boundary layer (CBL) is described, starting with the idealized CBLs associated with near steady-state horizontally homogeneous clear days and convection driven by buoyancy; and then presenting departures from the idealized state. Buoyancy is mainly from surface heating over land, with buoyancy from evaporating water playing a more important role especially over the tropical oceans. The three commonly described layers of the CBL, the surface layer, mixed layer, and entrainment layer, are discussed in terms of profiles of potential temperature, virtual potential temperature, specific humidity, and wind, their vertical transports and variances, and eddy structure, in weak versus stronger winds. Aspects of the evolution of the CBL over land through the day are described, as well as how and when CBLs with clouds resemble the cloudless CBL. Departures from the idealized case are produced from horizontal heterogeneity (nonuniform surfaces or horizontal gradients and advection in the atmosphere) or rapidly evolving surface buoyancy, developing cloudiness, and changes in synoptic forcing.