Electrical structure of the lightning-channel corona sheath

Expansion of positive (return-stroke) corona sheath inside the negative (leader) corona sheath is examined. It is shown that the positive corona sheath radius is smaller than that of the negative corona sheath. As a result, the overall corona sheath during the return-stroke stage is composed of two concentric zones: inner zone with net positive charge and outer one with negative charge. Corresponding radial electric field profiles are presented and compared to measurements.