The Oklahoma Dispersion Model: Use of the Gaussian plume model as an operational smoke management tool

The Oklahoma Dispersion Model (ODM) represents a current innovative application of the classic Gaussian plume model in an operational setting. Using a statewide mesoscale network of 120 weather monitoring stations (the Oklahoma Mesonet) for current and past weather conditions and 84-hour forecast output from the North American Model (NAM), the ODM is a web-based smoke management tool that can be used to assess recent, current, and future dispersion conditions across Oklahoma for near-surface releases of gases and small particulates.

The Oklahoma Dispersion Model is designed to qualitatively assess smoke concentrations at ground level near the plume centerline at downwind distances of up to several miles. The Gaussian plume model is used in conjunction with rural Briggs (1973) sigma-y and sigma-z coefficients to estimate horizontal and vertical dispersion. Pasquill stability class is calculated in two ways: for current conditions, Oklahoma Mesonet weather data (wind speed, standard deviation of wind direction, vertical temperature gradient, and solar radiation) are used in conjunction with EPA-recommended algorithms; for forecast conditions, NAM forecast data are used in conjunction with the Turner (1964) method. A method is then employed at each Oklahoma Mesonet location which assigns the atmosphere one of six dispersion categories, ranging from very poor to excellent.

Products of the Oklahoma Dispersion Model are available on the OK-FIRE web site (http://okfire.mesonet.org) and include dynamic maps (capable of animation and zooming) and site-specific charts and tables. Dispersion conditions are shown as well as wind conditions for plume transport. Mesonet-based products are updated every 5 minutes, while NAM-based products are available at hourly intervals through the 84-hour forecast period and are updated every 6 hours with each new NAM model run.

In summary, the Oklahoma Dispersion Model is an operational management tool which integrates the traditional Gaussian plume model with a mesoscale automated weather station network and 84-hour forecast output from the NAM model. The ODM is utilized by OK-FIRE users to plan suitable times for prescribed burns as well as assess smoke dispersion conditions for existing wildfires. Besides smoke dispersion, the model has seen other applications such as pesticide application and animal odor drift. The presentation will discuss details of the model itself, provide examples of products from the OK-FIRE web site, and indicate how the model is used.