13. The Height of the Atmospheric Planetary Boundary layer: State of the Art and New Development

The planetary boundary layer (PBL) is defined as the strongly turbulent atmospheric layer immediately affected by dynamic, thermal and other interactions with the Earth’s surface. It essentially differs in nature from the weakly turbulent and persistently stably-stratified free atmosphere. To some extent the PBL upper boundary acts as a lid preventing dust, aerosols, gases and any other admixtures released from ground sources to efficiently penetrate upwards, thus blocking them within the PBL. It is conceivable that the air pollution is especially hazardous when associated with shallow PBLs. Likewise, positive or negative perturbations of the heat budget at the Earth’s surface immediately impact on the PBL and are almost completely absorbed within the PBL through the very efficient mechanism of turbulent heat transfer. Determination of the PBL height is, therefore, an important aspect of modelling and prediction of air-pollution events and extreme colds or heats dangerous for human health. Because of high sensitivity of shallow PBLs to thermal impacts, variability of the PBL height is an important factor controlling fine features of climate change. Deep convective PBLs strongly impact on the climate system through turbulent entrainment (“ventilation”) at the PBL upper boundary, and thus essentially control development of convective clouds. This paper outlines modern knowledge about physical mechanisms and theoretical models of the PBL height and turbulent entrainment, and presents an advanced model of geophysical convective PBL.