One of the key factors in fighting forest fires is the ability to predict the spread of the fire. Human experience and empirical spread models provide important tools, but they are not always accurate enough. In particular, they are often inadequate for large, intense wildfires. In the future, however, firefighters might get more reliable, hi-tech help predicting the flames and the smoke.

photographer Kari Greer

Two FSU scientists, CSIT professor Yousuff Hussaini and meteorology professor Phil Cunningham, are using computer models to try to understand the course of wildfires, hoping to be able to develop predictive tools that can be used in real life situations. The core of their research is not the chemistry of the combustion itself, but the fluid mechanics describing how the fire interacts with the surrounding air. Some major questions are: Where is the hot air going, and how does it interact with the atmospheric winds to feed back on the fire?

The FSU scientists work with Dr. Rodman Linn of Los Alamos National Laboratory, who developed one of the models that the group currently runs on the FSU supercomputers, and Dr. Scott Goodrick of the USDA Forest Service. Linn's model, called FIRETEC, is a coupled fire-atmosphere model, meaning that at every instant it calculates the interactions between the chemical reactions and the atmospheric flow to provide predictions of fire behavior.

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The intense buoyancy forces associated with the heat from the fire result in a column of rapidly rising air, causing the predominantly horizontal winds in the atmosphere to be diverted around the fire and to bend back in its wake, only to be swept up into the rising column of air. This effect results in a pair of vortices on the downstream edge of the fire, one rotating clockwise and the other rotating counter-clockwise, that can have major impact both on the spread of the fire and the transport of smoke away from the fire in the plume.

In addition to the work on fire spread, Phil Cunningham has adapted a model of the atmosphere to look specifically at the plumes. While most tools currently used to predict smoke concentrations downwind of a fire assume that the plume spreads like a cone with the highest concentration of smoke in the middle, this is not always the case. Occasionally the counter-rotating vortices are intense enough to entrain smoke-free air between them, causing the plume to split into two branches.

Beyond its immediate impact on air quality, the smoke from fires plays an important role in the carbon cycle and on the climate, and authorities concerned with air quality management are very interested in both short and long term effects of the smoke. In fact, despite the threatening nature of the fire itself, the fact is that smoke impacts the well being of a larger number of people over a much larger area.

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Caption: Simulation from the FIRETEC coupled fire-atmosphere model showing temperature, air flow streamlines and fuel depletion. (Image courtesy Wilfredo Blanco, FSU Visualization Lab, and Chunmei Xia.)