A discussion of traveling waves involved in the lightning return stroke process

Abstract

In this paper, we have presented the measured common features of return stroke optical traveling waves and offered some hypothetical interpretations. We suggest that a return stroke may be a cumulative effect of many waves. Of these waves, a kind of "precursor" wave induced by the electric field change of the return stroke may exist. This wave forms the return stroke tip. The tip is followed by the main disturbance wave which forms the initial sharp rise of the return stroke waveform. Both these "precursor" and main-disturbance waves propagate upward. The main disturbance wave is followed by waves that.are produced in neutralizing the space charge in the leader corona sheath and in the thundercloud. These waves propagate to the return stroke channel core and then downward to the ground. As a cumulative effect of these waves, the decaying part of the return stroke waveform is formed. The return stroke tip may attempt to travel at the speed of light, but in reality the tip speed should be smaller than the speed of light. In order to perform a direct measurement of return stroke speed using high-speed imaging systems, some kind of subjective judgment in identifying the starting points of return stroke waves at various heights is unavoidable. The resultant speed could only be an apparent and approximate speed depending on instrument sensitivity and many other factors.