Dispersion Model Evaluation using the 1996 Model Validation Program Tracer Study

The 1996 Model Validation Program (MVP) provides an extensive atmospheric tracer database containing over two hundred tracer releases covering three seasons for the Cape Canaveral Air Force Station (CCAFS). Tracer experiments included both ground-level and elevated releases of SF6, consisting of instantaneous and continuous releases. In this study, Trials 308 on May 1^st, 1996, from Session Three of the MVP were evaluated. The objective of this study is to demonstrate the feasibility of using the 1996 MVP study to develop a database to support the evaluation of the performance of both the numerical weather prediction models and the transport and dispersion models used to assess potential accident scenarios which might pose a threat from the atmospheric release of hazardous materials for the CCAFS. We used the WRF model to generate the meteorological fields to drive NOAA/ARL's HYSPLIT model to simulate the transport and dispersion of the tracer releases. The coastal characteristics of these experiments add complexities to the meteorological and dispersion modeling. For reducing meteorological model bias, the model temperature and wind were nudged toward the observations collected during the experiment. Sensitivity tests on the nudging parameters were conducted to improve the meteorological simulation, which further has a positive impact on the tracer dispersion simulation. We found that differences between modeled and observed concentrations decrease from a factor-of-ten under-prediction to roughly a factor of three under-prediction when transitioning from using the WRF data with no observational nudging to nudging with both surface and upper-air measurements. While we only utilized a small set of tracer releases, we conclude that given the appropriate numerical weather simulation, the 1996 MVP Study could provide a rich database for evaluation, verification, and validation of numerical modeling of the potential release of hazardous materials within the environment of the CCAFS.