In this study, fine-scale numerical simulations using the Advanced Regional Prediction System (ARPS) are performed to examine the impact of vegetation on diurnal cold-air pool development inside an idealized valley. Recently, the Advanced Regional Prediction System (ARPS) atmospheric model has been modified to allow simulation of flow through a multi-layer canopy (ARPS-CANOPY). The effects of vegetation elements (e.g., branches, leaves) on drag, turbulence production/dissipation, radiation transfer, and the surface energy budget are accounted for through modifications to the original ARPS model equations and physical parameterization schemes.
We examine the impact of vegetation cover inside an idealized valley on cold-air pool evolution in four cases: (i) vegetation along the lower valley sidewall, (ii) vegetation along the upper valley sidewall, (iii) both lower and upper valley sidewall vegetation, and (iv) no vegetation. For each vegetation case, profiles of frontal area density (Af) are specified, where Af is defined as the frontal area of canopy elements (e.g., leaves, needles) per unit ground area per unit vertical distance in the canopy. Cold-air pool characteristics are compared between cases during the development of the cold-air pool and once the cold-air pool reaches maturity. Findings gleaned from this study have relevance to numerical prediction of cold pool development as well as air quality prediction.