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

The 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.