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Since the 1960s the Holzworth method has remained a primary tool for operational mixed-layer height determination. The air volume through which ground-based pollutants vertically disperse defines the mixed layer. The appeal of this method rests on the simple mechanics of making a forecast where knowledge of the surface air temperature in concert with the background vertical structure is sufficient. The National Weather Service routinely issues forecasts using this method for air-quality and wildland fire activities. Methods of this type that are based principally on the static stability structure of the atmosphere and exclude vapor content or dynamical processes (e.g., advection and wind shear) can misrepresent the mixing height calculation. Systematic errors, such as the height being too low or high, can complicate wildland fire activities (e.g., go/no-go burn decisions). Motivation for the present study emerges from this premise, and thus examines the mixing height computed from four methods. Mixing height methods employed in this study include Holzworth, Stull, bulk Richardson number, and turbulent kinetic energy—where the latter two include dynamical processes. Mixing height also was derived from satellite-based lidar data to provide an observed proxy and validation. Results from a method intercomparison show that turbulent kinetic energy is the most robust and well suited as a national standard method for operational use—having both thermodynamic and dynamic processes incorporated. The bulk Richardson number and Stull methods are other possibilities because their calculations are not model dependent and heights are consistent with those from turbulent kinetic energy.

Establishing a national standard method for operational mixing height determination