Mixed Layer Height Estimates – A Statistical Analysis of Algorithm Performance

The Air Force Technical Applications Center (AFTAC) conducts dispersion transport modeling as part of their mission support for the United States Atomic Energy Detection System. Part of that modeling effort requires knowledge of the height of the mixed layer in the lower atmosphere to determine the vertical extent through which particulates can be distributed. The mixed layer can be estimated by analyzing atmospheric profiles of parameters obtained from observations (e.g., upper air soundings) or atmospheric models. Six mixed layer algorithms were evaluated: Gradient Richardson Number (RICH), Potential Temperature (POTEMP), Potential Instability Mixing Depth (PIMIX), and three variations of the PIMIX algorithm that have never been statistically tested. The purpose of the research was to evaluate algorithm performance when observed and model-generated soundings were used to determine the height of the mixed layer. The research was divided into two sections: observed and forecast. In the observed section, observed soundings were hand-analyzed to obtain subjective mixed layer heights, which were compared to the algorithm heights. In the forecast section, soundings generated by the Regional Atmospheric Modeling System (RAMS) were subjectively analyzed, and the results were compared to the algorithms\u27 output. Additionally, the algorithms were evaluated to determine if their performance varied temporally (i.e., was algorithm performance dependent on observation time). Finally, the algorithms\u27 root mean square errors (RMSE) compared to the subjective heights were calculated