Influence of Stability on Canopy Flow and Fluxes over Forested Hills Using a Newly Developed Multiple-Layer Canopy Model in WRF-LES

Forest canopies play a critical role as the bottom boundary of atmosphere, acting as sources/sinks for atmospheric flow. Although there have been recent advances in numerical simulation of turbulent flows over forest canopies, few models have included the full physical processes within forest canopies. In this study, we have implemented an advanced multiple layer canopy model into the Weather Research and Forecasting model with large-eddy simulation (WRF-LES). Our canopy model includes full representation of the important physical processes within canopies, including radiative transfer, leaf photosynthesis, leaf surface energy balance, momentum drag, and heat and water transport between multiple canopy and soil layers. Based on validation using one month of data from the CHATS site, the model demonstrates good performance compared with observations. The model is then applied over idealized hills to investigate the effects of complex topography and atmospheric stability conditions on canopy flows. In this study, two idealized hills with a gentle slope and a steep slope are considered, as well as both neutral and unstable atmospheric stability conditions. Our focus is on scalar (i.e., CO₂) distribution and transportation over forested hills. The mean, flux, and advection fields of CO₂ will be carefully examined in this study.