Abstract
The VHF broadband digital interferometer (DITF) observed two- (2D) and three-dimensional (3D) developments of summer positive cloud-to-ground (CG) lightning flashes with high time resolution. The characteristics of summer positive CG lightning flashes attract a great deal of interest. In the first stage, the in-cloud negative breakdown progresses about 15 km horizontally between 6 and 10 km high. In the next stage, the lightning location and protection system (LLS) detects the positive lightning stroke near the initiation point of the preceding negative breakdown. In the last stage, the negative breakdown runs through the channel of the first negative breakdown. For the positive return stroke to run through the first negative channel, the positive leader, which is not visualized by the DITF, progresses from the initiation point of the first negative channel and touches to the ground. The return stroke current propagates and penetrates in the opposite direction as visualized subsequent negative breakdown. This suggests the negative and positive breakdown progress together. To realize this situation, we conclude the necessity to apply the bi-directional leader progression concept. In a word, we observed bi-directional leaders in summer nature positive CG lightning flashes.
