Synoptic controls on boundary layer structure

Boundary layer characteristics are known to be strongly affected by the surface, the diurnal cycle and other small scale processes. It is also known that the boundary layer can affect large scale circulations; it determines how air masses are modified by the surface, and modulates how much energy and momentum is available to the troposphere. Synoptic-scale weather systems can also alter the characteristics of the boundary layer. Therefore, we develop a conceptual model of boundary layers driven by synoptic-scale forcings to complement pre-existing small scale conceptual models. To attribute changes in boundary layer structure to different physical processes, and identify where mass is exchanged between the boundary layer and free troposphere, we evaluate individual terms of a boundary layer mass budget. We do this, and quantify boundary layer variables, by simulating idealised baroclinic systems with a boundary layer present. This idealised approach, especially in terms of quantifying the boundary layer structure, differs considerably to previous approaches, for example case studies or climatologies. Results show that the largest increases in boundary layer column integrated mass occur during the passage of cold fronts. This contradicts the common assumption that entrainment in anticyclonic regions is the dominant process / location of mass transfer into the boundary layer.