A Case Study of the Morning Evolution of the Convective Boundary Layer Depth

Because of the importance of the convective boundary layer depth (CBLD) in determining pollutant concentrations near the surface, a study of the morning evolution of the convective boundary layer was carried out at the Central Nuclear de Almaraz, Almaraz, Spain, from 25 to 29 September 1995, with a tethersonde and a meteorological mast equipped with a sonic anemometer. The CBLD was estimated from the potential temperature and wind profile obtained with the tethersonde using a 0.5 critical bulk Richardson number criterion. Also, the evolution of the CBLD was studied using three different theoretical zero-order jump models. The results given by the models show that, even with far from homogeneous surfaces, the models fit the observed CBLD very well by tuning the parameters conveniently. The entrainment coefficient that relates the heat flux at the top of the CBL with the heat flux at the surface was almost entirely responsible for the goodness of the fit. The encroachment model works best during situations in which the rate of entrainment is relatively small.