Stepped leader characteristics in developing horizontally within thunderclouds and in descending out of thunderclouds

We examine VHF and optical images of cloud-to-ground flashes to study IC leaders that propagated within thunderclouds and CG leaders that descended outside thunderclouds. It is shown that IC leaders developed smoothly and CG leaders propagated in a heavily branched manner. We speculate that, in the case of IC leaders, only the leader tip having the highest charge density in the channel could propagate in E-field intensified by local positive charge. In the case of CG leaders, not only leader tips but also lower parts of the leader could initiate new branches due to higher charge density.