Abstract
Investigation of the field-change due to cloud flash and junction process in the multiple ground flash leads to the conclusion that they progress continuously in the cloud without repeating any stepping process involved essentially in the negative streamer such as the stepped or dart leader. They are both positive streamers and are considered to have a similar nature to the continuous current observed in lightning to the Empire State Building.
Small rapid discharges overlap this continuous discharge at irregular time intervals. These phenomena are considered to be caused by the inhomogeneous distribution of negative charge in the cloud, i.e. the small rapid discharge occurs every time when the top of the positive streamer reaches the region where negative charge is densely concentrated. It is probable that the small rapid discharge refreshes the part of the ionized path previously made by the positive streamer, preceding stroke, etc. and has the same nature as that of the dart leader. In case of the flash to the ground, the negative charge consumed by the small rapid discharge may not be enough to refresh the whole path and consequently the return stroke does not occur.
Analysis of the intervals of small rapid discharges shows that such dense concentrations of negative charge in the cloud are distributed with spatial intervals of some 500 m (range 100∼1000 m), coinciding with the dimensions of the sub-cell of the thundercloud.
