A 3D planet boundary layer scheme for the representation of dispersion processes in sub-kilometer horizontally non-homogeneous flows

The simulation of dispersion processes over complex terrain is challenging as it directly relies on the availability of accurate meteorological fields, particularly in terms of wind velocity and direction, atmospheric stability, including thermal structure and turbulence. Over complex terrain, these fields are typically strongly non-homogeneous and an inaccurate estimate of their distribution has a direct impact on the fidelity of pollutant dispersion prediction. To properly describe meteorological fields over complex terrain, mesoscale models may be run with a sub-kilometer horizontal resolution, to allow for an accurate description of the topography. However, high-resolution simulations may not satisfy the underlying assumptions supporting the design of mesoscale parameterizations. Specifically, the assumption of horizontal homogeneity for mixing schemes is violated as grid spacing decreases. In order to overcome this issue, a new three-dimensional (3D) Planet Boundary Layer (PBL) parameterization is under developement within the Weather Research and Forecasting (WRF) model. This new parameterization will be particularly suitable for applications at a local scale and over complex terrain, as it introduces a calculation of 3D turbulent fluxes and the divergence. In this analysis we present preliminary tests run with the WRF model (Skamarock et al., 2008) and the CALPUFF puff-Gaussian model (Scire et al., 2000) and the SPRAYWEB Lagrangian dispersion model (Tinarelli et al. 2000; Alessandrini and Ferrero 2009), assessing the ability of the already available Nakanishi and Niino (2004) 1D PBL scheme, showing some of its deficiencies. For the evaluation of the PBLscheme, near-ground concentration observations are considered from the Bolzano Tracer EXperiment (BTEX – February 2017).