Transport and diffusion processes in the PBL over complex terrain using a model system: application to the TRACT experiment

The transport and diffusion processes of a tracer gas released near the
ground in the Rhine valley region, in Central Europe,during the 1992
TRACT field experiment, are simulated by a computational model system for
complex terrain. This system (RMS)is composed of the prognostic mesoscale
model RAMS, the Lagrangian stochastic dispersion model SPRAY and the
interface code MIRS,which links RAMS to SPRAY. Three flow simulations
were performed, with different initialisations and the one showing the
best agreement with the measured flow was selected for the simulation of
the TRACT tracer experiment. Tracer concentrations measured by an array
of samplers at ground level and by an airplane aloft, are used to
evaluate the 3-D concentration field simulated by the model system. The
analysis of the simulation results generated by RMS shows that our model
system very well reproduces the general behaviour of the contaminant
plume, the temporal and spatial distribution of the concentration and the
location of the concentration maxima.