Validation of the atmospheric dispersion model NAME against long-range tracer release experiments

The UK Met Office’s atmospheric dispersion model NAME (Numerical Atmospheric-dispersion Modelling Environment) is validated against controlled tracer release experiments, considering the impact of the driving meteorology and choices in the parametrization of unresolved motions. CAPTEX (Cross-Appalachian Tracer Experiment) and ANATEX (Across North America Tracer Experiment) were long-range dispersion experiments in which inert tracers were released and the air concentrations measured across North America and Canada in the 1980s. NAME simulations of the experiments have been driven by both reanalysis meteorological data from ECMWF (European Centre for Medium-Range Weather Forecasts) and data from the Advanced Research version of the WRF (Weather Research and Forecasting) Model. NAME predictions of air concentrations are assessed against the experimental measurements using a ranking method composed of four statistical parameters. Differences in the performance of NAME according to this ranking method are compared when driven by different meteorological sources. The effect of changing parameter values in NAME for the unresolved mesoscale motions parametrization is also considered, in particular, whether the parameter values giving the best performance rank are consistent with values typically used. The performance ranks are compared with analyses in the literature for other particle dispersion models, namely HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory), STILT (Stochastic Time-Inverted Lagrangian Transport) and FLEXPART (FLEXible PARTicle). It is found that NAME performance is comparable to the other dispersion models considered, with the different models responding similarly to differences in driving meteorology.