Title: The height of the atmospheric planetary boundary layer: 
state of the art, new developments, and remaining problems 

Abstract:
 
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 other pollutants 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 climate system through turbulent entrainment 
("ventilation") at the PBL upper boundary that essentially controls 
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.