Establishing a national standard methodology for operational mixing height determination

Resultant smoke from wildland fire and prescribed burning in the United States is important in terms of human health and environmental safety. Local dispersion is a major concern for many wildland fire and air quality agencies that participate in wildfire and prescribed fire activities (e.g., U.S. and State Forest Services, Bureau of Land Management (BLM), and National Weather Service Forecast Offices (NWSFOs), and state and local air quality agencies). Prediction of smoke dispersion indices (e.g., mixed layer height and ventilation index) is a major component of operational fire weather forecasts issued by NWSFOs. For the past several years, the user community (e.g., local and state land managers, foresters, and personnel from the aforementioned agencies) has expressed concern over the accuracy and consistency of the mixing height methodologies employed, in particular the soundness of the widely used Holzworth method. Hence, this study revisited this technique and three alternatives including the Stull method, numerical Turbulent Kinetic Energy (TKE), and Richardson number. Methods were intercompared amongst each other and against lidar-derived mixing height estimates from NASA CALIPSO lidar. A series of diagnostic analyses were also conducted over space and time for point locations and spatial extent where topographic features and airmass exposure are highly variable. The primary objective of this study was to determine which methodology proved to be the most robust and promising as a consistent national standard.