DISPERSION OVER AND AROUND A STEEP OBSTACLE FOR VARYING THERMAL STRATIFICATION - NUMERICAL SIMULATIONS

A rather steep dump of an open-cast working area for lignite is situated close to the nuclear research installation of Juelich. This dump is more than 200 m high; under light wind conditions the air flow goes around this obstacle during night-time (stable stratification) and over it in the early morning hours when the stratification is destabilized. This air flow is simulated by the non-hydrostatic mesoscale numerical model FITNAH; for the time 0500-0900 LST the concentration field (of a point source) is simulated with a Lagrangian particle model. The computed flow behaviour causes a bifurcation of the plume during night while after 0900 LST dispersion is nearly unaffected by topography.