LES Study of Atmospheric Boundary Layer Conditions During the Mosquito Wildland Fire Event and Implications for Smoke-Plume Transport

Large eddy simulation (LES) within a weather research and forecasting (WRF) model coupled with an active scalar transport equation was used to simulate Atmospheric Boundary Layer (ABL) conditions during the Mosquito wildland fire, the largest wildland fire in California during September of 2022. The simulations were conducted with realistic boundary conditions derived from the NOAA High Resolution Rapid Refresh (HRRR) model, with the aim of better understanding the two-way coupling between atmospheric boundary layer (ABL) and plume dynamics. The terrain was extremely inhomogeneous and the topography varied quite significantly within the numerical domain. Initially, LES of the smoke-free ABL were conducted on nested domains, and detailed ABL data were gathered from 08-09 September, 2022. LES simulations were validated using 4 ASOS stations and NOAA-MET Twin Otter measurements and the desired accuracy has been established. The smoke plume was then released into the ABL at noon on 09 September, 2022 and the plume simulations were conducted for a period of one hour from the release. During this period, the ABL transitioned from convective to buoyancy-shear-driven regimes. Late-night and early-morning conditions are influenced by the complex topography and low-level jet, whereas buoyancy and shear control the ABL dynamics during the morning and afternoon hours. The plume vertical transport is influenced by the ABL-depth and the size of the vertical turbulence structures during that time, whereas, the wind conditions and turbulent kinetic energy within the ABL dictate the horizontal transport scales of the plume. In addition, the results demonstrate that the plume modifies the microclimate along its path.