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.

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A statistical study of two groups of storms that occurred in the Paris area (France) during summer 2000 has been realized. The first group includes 26 high radar reflectivity (HRR) storms with radar reflectivity values exceeding 60 dBZ while the second one includes 19 moderate radar reflectivity (MRR) storms with a maximum radar reflectivity value between 50 and 55 dBZ. The radar reflectivity was provided by a C-band radar and the total lightning activity (cloud-to-ground (CG) and intra-cloud (IC) flashes) was provided by the French Météorage network and a Safir device. HRR storms seem to be characterized by a longer lifetime, and a more extended convective area. On average, they produce more CG and IC flashes than MRR storms. However, a large variability in the number, the rate, and the type of flashes is observed. The HRR storms producing the highest IC flash rates (above 100 min − 1 ) exhibit the lowest CG flash proportion (1.2 and 4.3%). Most of the HRR storms exhibit a peak lightning activity when the radar reflectivity is strong at low level within the cloud. However, several cases of these storms show a large time lag between the strong lightning production and the presence of high radar reflectivity values at low level. Some possible explanations of these observations, taking into account cloud dynamics, microphysics and lightning initiation, are discussed.

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