ABSTRACT
The troposphere is often divided in two layers: the boundary layer (BL) and the free atmosphere. The BL corresponds to the turbulent region where the surface has a direct influence. The understanding of the phenomenology that occurs in the atmospheric BL has relevance in many domains, including the dispersion of pollutants, the forecast of temperature, moisture, and wind near the surface, and the processes of cloud and storm formation. Nonlocal approaches were inspired by the observation of many thermals that make an ascent almost without lateral mixing, transporting air at significant distances in the boundary layer, a picture of the flow that is consistent with the analysis of cloud images. The BL top-entrainment process is related to the penetration of free-atmosphere air into the convective boundary layer, enhancing the growth of the BL and playing a key role in its structure.
