Dispersion Simulations Using Inline WRF-HYSPLIT for Atmospheric Studies in Complex Terrain (ASCOT) Experiment

Abstract:

Dispersion simulations were conducted for the Atmospheric Studies in Complex Terrain (ASCOT) experiment using the newly developed inline model framework in which HYSPLIT, a Lagrangian dispersion model, was coupled (inline) to the WRF-ARW meteorological model. ASCOT comprised a series of field tracer experiments designed to study transport and dispersion of pollutant associated with nocturnal drainage flows in mid-September of 1980. A perfluorcarbon tracer was released for 1 hour at the Anderson Creek valley in northern California and more than 50 sampling sites were placed in an area of 10 by 10 km southeast from the release site. The dispersion calculation was run inline the WRF-ARW calculation taking advantage of the fine spatial scale (333.3 m for horizontal grid and ~14 m thickness for the 1^st model layer) and the higher temporal frequency (in second interval) of the meteorological variables, as well as using the same vertical coordinate as the meteorological model. The results were evaluated by comparing inline and offline model simulations with measured tracer concentrations from the controlled tracer experiments. The rank, a cumulative statistical score, of the inline dispersion simulations was better than offline runs in four out of five releases during the ASCOT campaign. The inline version showed better spatial coverage of the plumes but a larger difference between the cumulative concentration distributions than the offline approach. The inline coupling system is especially beneficial for this type of application because the drainage flow occurred over an area of complex terrain area, over a short time period (less than 10 hours), and in fine spatial resolution, which required a very detailed depiction of changes in the wind vectors and mixing parameters to accurately model the tracer’s transport and dispersion. The improvement of the inline calculation is attributed to the elimination of temporal and vertical interpolation of the meteorological data when compared to the offline version.