A 3D Lagrangian stochastic particle model for the concentration variance dispersion

Abstract

A new scheme for the concentration variance calculation is assessed using field experiment data. The scheme is introduced in a Lagrangian stochastic particle model. The model provides run-time mean concentrations and concentrations’ variance 3D fields; thus, it does not need any off-line post-processing. The model is tested against the FFT-07 field experiment which involves a series of tracer releases. It is a short-range (500 m) highly instrumented experiment. In this work, measurement of tracer concentrations, emitted from a ground level point source is used to assess the ability of the new model in predicting the mean concentration, concentration variance, and the concentration fluctuation intensity at the ground level with a high spatial resolution. The results of the intercomparison are shown and discussed in terms of statistical plots and indices.

Exact nonlinear mountain waves propagating upwards

“…After recalling the governing equations in section 2, we present an explicit solution from the Lagrangian perspective, by providing in section 3 explicit formulas for the motion of individual air particles in the adiabatic dry flow of an upwards propagating mountain wave. Note that the unwieldiness of the Lagrangian approach compared to the Eulerian viewpoint of fluid flows owes precisely to the richness of its kinematical information [2,13]. In our setting it offers detailed insight into basic features of the flow pattern, revealing its organising structures (see section 4).…”