Use of a statewide mesoscale automated weather station network for real-time operational assessment of near-surface dispersion conditions

Operational since 1994, the Oklahoma Mesonet is a statewide automated weather station network operated jointly by Oklahoma State University and the University of Oklahoma. Covering the state of Oklahoma, the Mesonet is a mesoscale network in both space and time. There are currently 116 remote monitoring stations, with at least one in every county. Using an already existing statewide telecommunications network, weather observations are reported in real-time every 5 minutes, while soil observations are reported every 15 to 30 minutes. This weather and soil data, in the form of various products, is available to users over the Internet only minutes after it is received.

The Oklahoma Dispersion Model (ODM), developed in the late 1990s, is a value-added operational product which utilizes the Oklahoma Mesonet to assess atmospheric dispersion conditions in the near-surface (10-m) boundary layer. In addition, it utilizes a 60-hour forecast to predict conditions over the next several days. The ODM has been used in the agricultural and natural resources arena to assess dispersion conditions for prescribed burning (smoke), pesticide application, and animal odor drift. However, it also has seen other uses (e.g., for debris burning after the Oklahoma City F5 tornado of May 3, 1999).

The Oklahoma Dispersion Model (http://agweather.mesonet.org/models/dispersion) generates both graphical and text output that depict current and future conditions for atmospheric dispersion (dilution of plume) and transport direction (direction of plume movement). Statewide maps showing current dispersion conditions and transport direction are generated every 15 minutes using Oklahoma Mesonet weather data. The latest 60-hour NGM (Nested Grid Model) MOS (Multiple Output Statistics) forecasts for specific sites within and surrounding Oklahoma are used to generate similar maps valid at 3-hour increments throughout the duration of the 60-hour period; these maps are updated every 12 hours. In addition to graphical output, tabular output for specific MOS sites is available.

Horizontal and vertical dispersion in the ODM is estimated using the traditional Gaussian plume model. Pasquill stability class is calculated in two ways: for current conditions, Mesonet weather data (wind speed, standard deviation of wind direction, vertical temperature gradient, and solar radiation) is used in conjunction with EPA recommended algorithms; for forecast conditions, the Turner (1964) method for calculating stability classes is used. Rural sigma-y and sigma-z values are calculated using the Briggs equations (1973). A scheme is used (to be described in detail in the paper) which breaks the atmosphere into five dispersion categories. The resulting dispersion maps feature a five-color classification scheme, ranging from excellent (dark green) to very poor (red). Corresponding maps for transport direction utilize a station plot of temperature, relative humidity, wind speed, and wind direction.

In summary, the Oklahoma Dispersion Model is an operational management tool which combines the traditional Gaussian plume model with a mesoscale automated weather station network to produce real-time maps of atmospheric dispersion conditions across the state of Oklahoma. This paper will discuss details of the model itself as well as present examples of graphical and text output from the Web site.