The impact of mesoscale PBL parameterizations on the evolution of mixed-layer processes important for fire weather

The surface-based mixed layer can profoundly impact fire–atmosphere interactions since wind, temperature, moisture, and turbulence characteristics within the mixed layer strongly affect the evolution of a wildland fire. Since mesoscale models are important tools for fire-weather forecasting and research, it is important to understand how simulations of the surface-based mixed layer are influenced by planetary boundary layer (PBL) parameterizations employed in the models. Within a mesoscale model, mixed-layer processes are simulated using a subgrid-scale parameterization that generates PBL structures based on model-resolved atmospheric conditions and surface characteristics. This study will investigate PBL structures simulated by a mesoscale model, and assess the performance of different PBL parameterizations employed in operational and research mesoscale models applied to fire-weather problems.

We will identify one or several wildland fire events in the eastern United States wherein the impact of mixed-layer processes on the evolution of the fire can be established. Weather Research and Forecasting (WRF) model simulations of the meteorological conditions associated with the event(s) will document the sensitivity of the simulated PBL structures to different PBL parameterizations. The PBL parameterizations to be considered include the Mellor–Yamada–Janjic (MYJ), the MRF, the Quasi-Normal Scale Elimination (QNSE), the Mellor–Yamada Nakanishi–Niino (MYNN), and the Bougeault and Lacarrere (BouLac) schemes. The performance of the PBL schemes and their respective effects on the evolution of the lower atmosphere will be addressed.

By employing observations from available surface stations, wind profilers, and atmospheric soundings, we will determine how the choice of PBL parameterization affects the ability of the WRF model to reproduce observed atmospheric conditions during wildland fire events. The Double Trouble State Park (New Jersey, 2002) and Warren Grove (New Jersey, 2007) wildfires have been selected as candidate test cases for assessing the performance of the PBL parameterizations. The wind, temperature, moisture, and turbulence characteristics within the mixed layer will be examined, as well as the mixed-layer depths yielded by the parameterizations.