Interactions entre activité électrique, microphysique et pollution dans les nuages d'orage

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Activité d'éclairs et paramètres physiques issus de l'observation radar dans les orages (application au projet HyMeX)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Corona emission from raindrops in strong electric fields as a possible discharge initiation: comparison between horizontal and vertical field configurations

The purpose of this work is to determine which electric field configuration (vertical or horizontal) produces corona emission from raindrops for the lowest ambient electric field. For that, a numerical modeling of the distortion of uncharged raindrops falling at terminal velocity in quiescent air in a horizontal electric field is performed. The results are compared with previous numerical study involving a vertical electric field. It is shown that the fall velocity is quite unaffected by ambient field intensities lower than 200 kV/m. The disruption and the corona onset fields are lower than those corresponding to the vertical field configuration and the larger the drop the larger the difference. For a given altitude the difference between the corona onset fields in both configurations can reach about 100 kV/m; meanwhile for a given ambient field intensity, the difference in altitude of corona emission can rise to about 1 km. These onset field intensities are, though, too high for allowing drop breakup and corona emission from an uncharged drop in permanent field conditions below 12 km height. An estimation of the critical onset field (disruption and/or corona emission) is carried out for charged drops in the horizontal field configuration. For a drop 2 mm in spherical equivalent radius carrying the quarter of its Rayleigh maximum net charge, the critical onset field is approximately equal to 290 kV/m below 7.4 km height and decreases down to 110 kV/m at 10 km. Given that present modeling does not take into account the effect of turbulence that could induce drop oscillations, the critical field intensities calculated here may be considered as upper limits

Influence of water conductivity on micro-discharges from raindrops in strong electric fields

International audienceThe influence of water conductivity on micro-discharges from raindrops has been studied by submitting water drops of different conductivities, falling at terminal velocity, to strong horizontal electric fields. The discharge onset field remains quite unchanged but the micro-discharges characteristics are clearly affected by the nature of water—scarce high amplitude pulses for low water conductivity and numerous low amplitude pulses for higher water conductivity. The influence of water conductivity on the onset streamer pulse mode of discharge is analysed. It is thought that the negative charge at the head of the positive avalanche is faster absorbed by the drop surface with rainwater, thus the reactivation of the pulses is faster. Possible implications of such behaviour are discussed in the light of recent studies on the influence of pollution on lightning activity

Multi-instrumental observation of an upward cloud-to-air discharge above a Mediterranean storm

On the night of November 1st, 2022, a luminous discharge was produced above a storm over the northwestern Mediterranean Sea. An unprecedented set of optical and electrical data makes it possible to characterize this event. It is embedded in a lightning flash which starts with a positive discharge producing a high-power VHF source at 6 km followed by VHF sources at 10 and 4 km within the cloud. The luminous event above the cloud is identified as a negative leader emerging from the cloud and reaching 14.2 km, topped with streamers up to about 17.2 km, and followed by channel rebrightening phases connected to the negative charge of a positive dipole. It is preceded by a convective surge and a production of positive flashes within the same storm region. Its polarity and its triggering conditions show similarities with those of gigantic jets

Multi‐Instrumental Observation of an Upward Cloud‐To‐Air Discharge Above a Mediterranean Storm

Abstract On the night of 1 November 2022, a luminous discharge was produced above a storm over the northwestern Mediterranean Sea. An unprecedented set of optical and electrical data makes it possible to characterize this event. It is embedded in a lightning flash which starts with a positive discharge producing a high‐power very high frequency (VHF) source at 6 km followed by VHF sources at 10 and 4 km within the cloud. The luminous event above the cloud is identified as a negative leader emerging from the cloud and reaching 14.2 km, topped with streamers up to about 17.2 km, and followed by channel rebrightening phases connected to the negative charge of a positive dipole. It is preceded by a convective surge and a production of positive flashes within the same storm region. Its polarity and its triggering conditions show similarities with those of gigantic jets

Concurrent satellite and ground-based lightning observations from the Optical Lightning Imaging Sensor (ISS-LIS), the low-frequency network Meteorage and the SAETTA Lightning Mapping Array (LMA) in the northwestern Mediterranean region

International audienc

Two Propagation Scenarios of Isolated Breakdown Lightning Processes in Failed Negative Cloud‐to‐Ground Flashes

International audienc

Lightning ground flash patterns over Paris aera between 192 and 2003: influence of pollution

International audience12 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

Lightning ground flash patterns over Paris aera between 192 and 2003: influence of pollution

International audience12 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