Modeling the Diurnal Cycle of Conserved and Reactive Species in the Convective Boundary Layer

We report on continued development of a numerical model of the convective boundary layer (CBL) which we call the Second-Order Model for Conserved and Reactive Unsteady Scalars (SOMCRUS). It is a one-dimensional second-order closure model that combines a simple mixed-layer model of the diurnally-varying CBL from which we obtain the CBL depth and temperature jump across the CBL top, with a second-order model of the turbulence and mean CBL structure for both conserved and reactive species with surface sources and sinks, and turbulent entrainment of free-tropospheric air across the top of the CBL. Here we consider a shear-free CBL and use free-convection surface-layer scaling, but our scheme can easily be modified to run other parameterized boundary layers (e.g. incorporating shear and canopy structure). We then apply SOMCRUS first to a conserved species with differing surface and entrainment fluxes, and second to the O3–NO–NO2 triad, and compare the results with LES.