The general conceptual model of the diurnal cycle of the CBL is well-known, as described by Stull (1988) for example, and computer simulations of the decay of convective turbulence during the afternoon and early evening have been conducted since the early 1970s. However these simulations usually implement simplified or unrealistic conditions, such as the absence of cloud, or a step change in surface fluxes.
This study uses 915 MHz profiler data obtained during the 1995 and 1996 Flatland boundary layer experiments, located near Champaign-Urbana, Illinois during August-September 1995 and June-August 1996. The profiler, ceilometer, and surface instruments were situated at the Flatland Atmospheric Observatory (FAO) and there were at least daily radiosonde launches during the campaigns.
We have examined the profiler data during the afternoon transition and
identified several different categories of behavior. These are analysed in conjunction with the surface, radiosonde, and ceilometer data to determine the effect of surface and boundary layer conditions on the characteristics of the transition. An understanding of the conditions controlling the behavior during this time is of practical interest in fields such as air pollution and visibility modeling since the spread of chemicals and pollutants released into the boundary layer is dependent on whether they remain within the mixed layer