The above figure shows the typical diurnal evolution of the BL in high-pressure regions (i.e., without the development
of deep cumulus convection and much effect of vertical lifting).
· At and shortly after sunrise, surface heating causes turbulent eddies to develop, producing a mixed layer whose depth
grows to a maximum depth in late morning. In this mixed layer, potential temperature and water vapor mixing ratio are
nearly uniform.
· At the sunset, the deep surface cooling creates a stable (nocturnal) boundary layer, above which is a residual layer,
basically the leftover part of the daytime mixed layer
· At all time, near the surface is a thin surface layer in which the vertical fluxes are nearly constant. It is also called
constant-flux layer.