A study of a free convective boundary layer using a parcel-based Lagrangian model

We study the development of a dry convective boundary layer forced by surface heating and growing into a stably stratified atmosphere above. This is already a well-studied problem, and the novelty here is the application of a radically new, Lagrangian-based numerical approach. We employ the “Elliptical Parcel-In-Cell” (EPIC) method, which represents all prognostic quantities (e.g., vorticity and buoyancy) as a set of space-filling deformable ellipsoidal parcels. Mixing occurs via the splitting and merging of these parcels, which we view as turbulent mixing (it is localised in space, and is not like any existing eddy viscosity model). We compare our results with several recent comprehensive direct numerical simulation (DNS) studies and find broad agreement, and often close quantitative agreement, despite fundamental differences in the numerical methods employed. In particular, we reproduce the two-layer structure of the interface between the boundary layer and the free atmosphere.