Observation and simulation of boundary layer coherent roll structures and their effect on pollution dispersion

Coherent roll structures are often observed in the atmospheric boundary layer during strong wind shears and pre-convective situations. Data collected from in situ and remote observations at a coastal site under the presence of the rolls are analyzed which confirm the typical characteristic features coherent roll structures. A mesoscale simulation study with WRF shows that the structures could be simulated only when the spatial domain is configured in high resolution. The limiting criteria as an indicator of the rolls based on the stability parameter is investigated and found to fail as similarly pointed out by a few other researchers. The effect of rolls on the dispersion of a passive tracer plume is simulated by a Lagrangian particle dispersion model (FLEXPART). The plume is seen confined between two rolls for a significant downwind distance and shows alternative high and low areas of concentration.

► The coherent structure called rolls were observed under strong wind shear and convectively unstable condition.
► The ability of a weather forecast model to simulate the same was proved when the spatial domain was finely resolved.
► The usual limit for identification of rolls using Zi/L failed in this case.
► The effect of rolls in atmospheric dispersion showed that the horizontal width of the plume is confined between two rolls.
► The maximum ground level concentration occurs at a point away from the usually expected place by a simple Gaussian model.