Lightning ground flash patterns over Paris area between 1992 and 2003: Influence of pollution?

12 summers of cloud-to-ground (CG) lightning flashes data over a 200 km × 200 km domain centered on Paris (France) have been analyzed to infer the possible influence of pollution on lightning activity. Lightning flashes densities are calculated on a 5 km × 5 km grid, filtered for discarding extremely high events, and differentiated from weekdays to week-end days, with a specific insight upwind, over, and downwind Paris. Lightning flashes are more numerous in the North-East part of the domain and increasingly large events progressively concentrate over Paris and over some hills around. The former result indicates a possible influence of pollution on lightning activity downwind of Paris; the latter probably illustrates the influence of the urban heat island and of the relief on the convection strengthening. Furthermore, the number of positive CG flashes is rather uniformly distributed on the whole domain, except in the North-East where it appears somewhat relatively lower meanwhile negative CG are relatively more numerous in that region. This corresponds to a reduction in the percentage of positive CG downwind of Paris. Additionally, lightning activity appears weaker downwind of Paris during weekend days. A specific daily analysis of the lightning density in circles distributed along the direction of prevailing wind through Paris shows that the lightning activity appears higher downwind during the days most worked as Tuesday, Wednesday and Thursday. This higher electric activity persists up to about 40 km on Wednesday, and up to about 80 km on Tuesday and Thursday (most days worked). The electrification seems therefore more important downwind of Paris during the more polluted days.