Using Large-eddy-simulation at event-scale to evaluate the ABL-widllandfire-plume interactions of Mosquito Wildland Fire

Wildland fire smoke transport is governed by a complex interplay between fire heat release, atmospheric boundary layer (ABL) turbulence, synoptic forcing, and terrain. Despite substantial advances in coupled fire–atmosphere modeling, the role of the ambient, evolving ABL state in controlling plume rise and transport under realistic fire conditions remains insufficiently resolved, largely due to the extreme computational demands of event-scale large-eddy simulation (LES). This study addresses this gap by conducting a high-resolution LES of the atmospheric boundary layer over complex terrain during the Mosquito Wildland Fire (California, September 2022), followed by a plume simulation whose forcing is constrained by satellite observations.

We perform a multi-domain Weather Research and Forecasting (WRF-LES) simulation spanning 24 hours (08–09 September 2022) over the Sierra Nevada, capturing the diurnal evolution of boundary-layer depth, turbulence intensity, wind shear, and regime transitions under realistic synoptic and topographic forcing. The ABL simulation is validated against four ASOS surface stations and NOAA Twin Otter airborne observations, demonstrating accurate reproduction of near-surface thermodynamics and vertical wind shear. The results reveal pronounced transitions from convective to shear–buoyancy-driven regimes, strong inversion-layer shear, terrain-modulated low-level jets, and vertically coherent turbulent structures extending several kilometers above the surface.

Using the resolved ABL state at noon local time, we then simulate the release of a buoyant plume for one hour using an active-scalar LES formulation. The plume is represented as an idealized, steady circular heat source at the ground, with surface heat flux prescribed to match satellite-derived fire radiative power (FRP) from MODIS. This approach isolates the influence of the ambient ABL on plume evolution while maintaining physically realistic forcing. Independent evaluation against MISR stereo plume-height retrievals shows strong consistency between simulated and observed plume-top heights (~3–4 km), vertical gradients, wind shear, and downstream transport pathways. Importantly, MISR plume heights reflect time-integrated plume evolution over several hours of advection, allowing meaningful comparison with the short-duration LES plume simulation.

The results demonstrate that plume rise, vertical penetration, and horizontal transport are primarily controlled by the evolving ABL structure—specifically boundary-layer depth, inversion-layer shear, turbulent kinetic energy distribution, and terrain-induced flow modulation—once the fire heat release is constrained to realistic values. Sensitivity analysis shows that while plume source size and buoyancy magnitude influence near-source behavior, ABL regime and shear dominate plume fate at kilometer scales.

This study provides one of the first event-scale demonstrations that resolving the real atmospheric boundary layer under complex terrain is a prerequisite for physically meaningful wildfire plume simulation. By combining validated ABL LES with satellite-constrained plume forcing, the work establishes a robust foundation for future fully coupled fire–atmosphere modeling and advances understanding of two-way ABL–buoyancy interactions in wildfire environments