Over the last year, Terry Clark and colleagues continued their studies using a coupled mesoscale-fire model to study the dynamics of forest fires. Two papers were published, one in the Journal of Applied Meteorology and the second in the International Journal of Wildland Fire, on the topic of how the simulated interactions account for some common fire shapes. Primarily, the fire line interacts with the updraft ahead of it, causing the fire line to curve forward into a conical shape. In the presence of vertical wind shear, a pair of rotating updrafts at the curved fire front can touch down within the fire and break up the line. These features that evolved in our simulations have been observed in situ.
Work has continued over the last year on improving the model. This effort concentrated on the formulation of the fire line tracers using quadrilateral tracers confined to each grid cell. This new technique, which is proving successful, is passing a number of important tests. It now enables us to use a significant range of horizontal resolutions within both the mesoscale model and the fuel (or fire) model, and also enables us to control the fire width and areal extent without concern about discrete fuel cell sizes producing sudden bursts of sensible heat flux. Probably more important, this formulation will enable us to assign the partitioning of convective and radiant heat flux in a physically meaningful manner. We expect this model to totally replace the original fire model early in FY97. Some of the predictions from this new model will be flame height and convective/radiant heat flux, which can be compared with observations for model validation.
Systematic studies on the effects of ambient wind shear, both positive and negative, continued over the last year, with results published in the two papers mentioned above. Ambient negative shear will be investigated this coming year along with more detailed tests of the new fire model.
As a result of this modeling activity, Terry Clark was invited to give a keynote talk at the International Fire Meteorology Conference in Lorne, Victoria, Australia held in the fall of 1996. A VIS5D visualization of some of the modeling results was displayed at this conference and also at Supercomputing 1996. This visualization, resulting from a collaboration with NCAR's Scientific and Computing Division (SCD), was produced by SCD's Don Middleton-Link. Other collaborations have included: NCAR's Research Applications Program (RAP), York University in Toronto, Canadian Department of Forestry, U.S. Department of Agriculture, and the Australian Bureau of Meteorology and Commonwealth Scientific and Industrial Research Organization (CSIRO).