Observed characteristics of luminous variation events during the initial stage of upward positive leaders

Abstract

We have measured the correlated sub-microsecond E-fields and high-speed images of the luminous variation events during the initial stage of three upward positive leaders initiated from a high tower. We found that each of the luminous variation events is composed of many electrical breakdowns. We classified the luminous variation events into the following two types: (1) they appear with an initial dominant pulse and their propagations can be identified from high speed images; (2) there is not an initial dominant pulse and their propagations can not be clearly identified. We inferred that in terms of propagation the luminous variation events are similar to ICC (initial continuous current) pulses and M-components. Based on the measured results and as an extension, we have discussed the contradicted propagation characteristics of M-components, an issue which has remained confusing in literatures for many years. We speculated that (1) an M-component is a composition of many waves occurring at different times and different locations, and those waves may interfere each other complicatedly; (2) an M-component may involve some waves excited locally anywhere along its continuous current channel through concentrating or absorbing electrical energy from ambient electric field; (3) the speed of an M-component, if measured optically by assuming that it is a process of only one or two waves , may be , in most of cases, just a kind of apparent and artificial (not real in physics) speed produced by many factors such as instrument sensitivity, and at which channel section and how the speed is measured. All these aspects together account for the contradicted propagation characteristics of M-components.