ELECTRIC-FIELD AND IONIC CONCENTRATION VARIATIONS OBSERVED AT GROUND-LEVEL IN STORM CONDITIONS

A study of simultaneous variations, at ground level and under storms, of the electric field and of the concentration of small positive ions has been realized during experiments which took place in Cote d'Ivoire in June 1981 and 1986. This study confirms the importance of the "electrode effect" phenomenon, especially during the "end of storm oscillation" (E.O.S.O), and those of the corona effect during times of high static electric field. It points out that corona ions created before a lightning flash go back to the ground when the lightning flash reverses the electric field at ground level. The amount of ions going back is mainly related to the value of the electric field before the flash and to the electric field jump associated with the lightning flash. Quantitative estimations show that about 20 to 60% of the corona ions created before the flash go back to the ground. So, they remain trapped into a thin layer close to the ground where their recombination probability increases, preventing their conduction movement upward to the cloud.