Cloud-topped continental boundary layer structure and behavior

Many days of the 1999 Southern Oxidant Study Nashville Intensive campaign, and most of the days when the chemical sampling aircraft flew, had deep fair-weather cumulus atop the daytime boundary layer. The cloud layer, as deep or deeper than the sub-cloud layer but not precipitating, strongly affects dynamical and radiative conditions and greatly complicates the determination of parameters such as the mixing depth that are critical for chemical calculations and modeling. Such boundary layers have not received a great deal of attention in the literature, and there is no generally accepted theoretical or empirical framework for understanding them. In this presentation, we show observations from wind profilers and ceilometers. We also describe the boundary layers in terms of velocity and time scales, and attempt to provide guidance for modeling of the structure of and transport in these layers.