A study of dispersion in complex terrain under winter conditions using high-resolution mesoscale and Lagrangian particle models

Abstract

A mesoscale model (MM5), a dispersive Langrangian particle model (FLEXPART),and intensive meteorological and COrrelation SPECtrometer (COSPEC)measurements from a field campaign are used to examine the advectionand turbulent diffusion patterns associated with interactions andforcings between topography, synoptic atmospheric flows and thermally-drivencirculations. This study describes the atmospheric dispersion ofemissions from a power plant with a 343-m tall chimney, situatedon very complexterrain in the North-East of Spain, under winter conditions. Duringthe field campaign, the plume was transported with low transversaldispersion and deformed essentially dueto the effect of mechanical turbulence. The main surface impacts appearedat long distances from the emission source (more than 30 km). Theresults show that the coupled models(MM5 and FLEXPART) are able to predict the plume integral advectionfrom the power plant on very complex terrain. Integral advectionand turbulent dispersion are derived fromthe dispersive Lagrangian model output for three consecutive daysso that a direct quantitative comparison has been made between thetemporal evolution of the predicted threedimensional dispersive conditionsand the COSPEC measurements. Comparison between experimental andsimulated transversal dispersion shows an index of agreement between80% and 90%, within distance ranges from 6 to 33 km from the stack.Linked to the orographic features, the simulated plume impacts onthe ground more than 30 km away from the stack, because of the leewaves simulated by MM5.