Four models will be tested and evaluated. The first model is the WRF-FLEXPART model, which couples the next generation Weather Research and Forecast (WRF) model with an existing community Lagrangian particle dispersion model FLEXPART. The coupled WRF-FLEXPART system has been successfully employed to simulate atmospheric dispersion from local to regional scales. Although WRF-FLEXPART can be run at fine scales that resolve details of local topography and vegetation, it currently does not contain a sophisticated canopy-layer model that takes into account canopy effects on the mean and turbulent flows.

WRF-FLEXPART simulated surface CO concentrations during the October 2007 southern California wildfires.

The second model to consider is the A2C (Atmosphere to CFD) model. Developed by the Yamada Science and Art Corporation, A2C is a next-generation atmospheric model designed as a meso-to-microscale forecasting system for air flow and dispersion of pollutants. With its ability to capture multiple scale motions, to resolve atmospheric circulations within vegetation layers, and to simulate atmospheric boundary-layer turbulence, A2C is particularly useful in simulating dispersion over areas of complex terrain and in the vicinity of forest vegetation. Despite these advantages, the ability of A2C to simulate smoke dispersion within and above forest vegetation layers has yet to be evaluated.

A2C simulated emission concentration. A2C simulated smoke plume.
A2C simulated smoke plume and emission concentration.

A third model to consider is the Regional Atmospheric Modeling System (RAMS) based, Forest Large Eddy Simulation (RAFLES) model. RAFLES has been used to simulate biological dispersal in forest canopies. The model will be adapted to simulate smoke dispersion from prescribed/wildland fires and the effects of canopy structure on the dispersion.

RAFLES simulations of circulations (ejection-sweep dynamics) and humidity within and above a forest vegetation layer. Green surface in figures represents the canopy top; tree stems are represented by brown; temperature on the back "wall." (Courtesy of Gil Bohrer)

Lastly, the fourth model to be considered is the Advanced Regional Prediction System (ARPS). ARPS is used for applications involving numerical weather prediction, mesoscale meteorology, and computational fluid dynamics. Like WRF-FLEXPART above, ARPS currently does not contain a sophisticated canopy-layer model. Also, ARPS currently does not have its own capability to calculate smoke dispersion, but FLEXPART can be revised for use with ARPS output.

Cross section of ARPS temperature perturbations resulting from a simulated fire situation.