Comparison of the ACM2 vertical mixing scheme with observations taken during the TexAQS II field study
Preliminary results have shown good agreement between the WRF model, using ACM2, and estimates derived from radar wind profilers. Recently compiled data sets from both the TexAQS II and the Moody Tower TRAMP (TexAQS II Radical Measurement Project) Houston, TX field studies provide an opportunity to further evaluate this scheme in a complex meteorological environment. First, micropulse LIDAR data taken at Moody Tower during the TRAMP experiment was used to determine PBL heights based on aerosol backscatter during September of 2006. Second, mixing heights identified from radiosonde balloon data, courtesy of the University of Houston, are available for August and September of 2006. Lastly, hourly radar wind profiler-based mixing heights created independently by Sonoma Technologies, Inc. are available for August and September of 2006. The above observational data sets will be used to compare the model-derived mixing heights from a 12 km and 4 km horizontal resolution WRF model runs with the ACM2 mixing scheme. These WRF modeling runs were developed by the EPA, and represent the current state of knowledge for the region.
Knowing the accuracy of model-simulated mixing heights is crucial to the continued development of regulatory air quality models. Mischaracterization of the depth and evolution of the PBL and intensity of turbulent transport can lead to severe errors in both meteorological and chemical simulations. PBL processes greatly influence chemical concentrations and reactions within the lowest kilometer of the atmosphere. With the release of a new combined local and nonlocal closure atmospheric boundary layer model, ACM2, and several observational data sets from the TexAQS II field campaign, a comprehensive evaluation is necessary.