Micrometeorology and Atmospheric Boundary Layer

Starting with simple definitions and the scope of micrometeorology and the atmospheric planetary boundary layer (PBL), the importance of small-scale turbulent exchange and energy dissipation processes in the PBL to the evolution of local weather and climate is pointed out. The energy budgets of an ‘‘ideal’’ surface and a near-surface canopy layer are briefly described and typical diurnal variations of measured energy fluxes at two (a rural and a suburban) sites are illustrated. Using the conservation equations of thermodynamic energy and moisture, temporal and spatial variations of mean air temperature and specific humidity are described. Diurnal evolutions of potential temperature profiles and the corresponding PBL height are illustrated with some observed data. Typical mean wind profiles in the daytime convective boundary layer (CBL) and the nighttime stable boundary layer (SBL) are also shown and discussed. The strong influence of stability on the PBL height and structure and their diurnal variations are discussed. The widely used flux-profile relations based on the Monin- Obukhov surface-layer similarity theory are presented with a brief discussion of parameterization of surface roughness and fluxes. The statistical description of the PBL turbulence and its commonly used quantitative measures are presented with an illustration of observed time series of turbulence. Some of the better-known similarity theories and scaling of turbulence in the PBL are described. Finally, different types of turbulence closure theories and numerical simulations/models of the PBL are briefly reviewed.