TABLE OF CONTENTS The main difference between the ground flashes and cloud flashes is that the ground flashes neutralise the charge centre in an intermittent manner in a number of high current events, that is, subsequent strokes, whereas in a cloud flash a continuous current may flow from one charge centre to the other during the initial and active part of the cloud flash. Only in the latter part of the cloud flash do intermittent breakdowns transfer charge from the negative to the positive. This difference is probably caused by the fact that in ground flashes the presence of the ground will lead to a rapid neutralisation of the leader channel, giving rise to return strokes, whereas no good conductor is involved in cloud flashes and the neutralisation process should take place slowly in comparison with the return strokes. An interesting comparison can be made between the lightning flashes and laboratory discharges. Discharge between two metal electrodes takes place in one burst of return stroke, whereas a discharge between two nonconducting materials takes place intermittently in a series of discharges with low current amplitude [165]. The reason for this is that, in the case of nonconducting electrodes, the charges transported along the discharge channel will accumulate at its extremities, thereby reducing the electric field and choking the discharge. As the charges dissipate slowly, the electric field recovers and reignites the discharge channel. In ground flashes the problem of charge dissipation is encountered only...
