In this video, around 2:24, one can see a flash of lightning that keeps the same form for a little time span. Does this mean that it takes a while before the discharge is complete (which I can't imagine) or that the electrons move to and fro between the Earth and cloud (or between the clouds themselves) before the discharge is complete? I can imagine that extra electrons move behind the discharge which on arrival on Earth flash back, taking extra electrons back, etc. But in this case, the flash should dim over time. So why the flash remains in a steady shape that long?
Lightning is a rapid transition from a non-conducting to a conductive state.lightning creates an ionized, electrically conductive channel through air inside the cloud,between clouds or between cloud and earth.The high electric field accelerates the electrons between the channel.When they collide with air molecules, they create additional ions and newly freed electrons which are also accelerated.So it takes some time.Electrons will only flow against the electric field.they don't oscillate.
Once the gap breaks down, current flow is limited by the available charge (for an electrostatic discharge) or by the impedance of the external power supply. If the power supply continues to supply current, the spark will evolve into a continuous discharge called an electric arc