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This presentation describes a coupled atmosphere-fire model that uses a sophisticated high-resolution meteorological numerical model to predict the local winds which are then used as input to the prediction of fire spread. The heat and moisture fluxes from the fire are then fed back to the atmospheric dynamics allowing the fire to influence its own mesoscale winds that in turn affect the fire behavior. This full coupling is necessary because the energy released by a fire can be large enough to drive the atmospheric dynamics over a wide range of spatial scales, from fine-scale vortices along the fire line to firestorms. This model is viewed primarily as a research tool designed for understanding fire dynamics. Each atmospheric grid cell is subdivided into fuel cells, which have characteristics of fuel type, load, moisture content, depth, etc. Four tracer particles per fuel cell define the area of burning fuel. while a local contour advection scheme maintains consistency between fuel cells. Using the dynamically predicted winds along with the terrain slope and fuel characteristics, algorithms from the BEHAVE system are used to predict the spread rates. A mass loss calculation based on results of the BURNUP fuel burnout model is used to treat post-flaming front heat release to the atmosphere. Results of recent experiments will be presented. As with previous experiments, these results show a number of features common to real fires. For example, we show how the well-recognized elliptical fire line shape is a direct result of fire-atmosphere interactions that produce the heading, flanking, and backing regions of a wind-driven fire with their expected behavior - it is produced by the model, not assumed. And, we see how perturbations upon this shape sometimes amplify to become fire whirls along the flanks, which are transported to the head of the fire where they may interact to produce erratic fire behavior. Another application is to a Colorado wildfire, where we examine the spatial scales and meteorological processes that direct fire progressions. |