Further characteristics of positive radiation fields from lightning in sweden

Characteristics of the fields radiated by lightning in Sweden have been reported recently by Cooray and Lundquist (1982). That study is supplemented here by presenting additional characteristics of those fields that are hypothesized to be produced by positive return strokes. The new data presented here indicate that the currents in the sources of these radiation fields are either similar in duration to the currents in negative return strokes or of longer duration. This is based on the observation that the duration of these radiation fields are either similar to that of negative return strokes or of longer duration. During the first 50–100 μs both normal and long-duration waveforms, and hence the inferred currents, seem to behave in a similar manner. That is, there is an initial peak in the first few tens of microseconds and then a decay. After this the field and the inferred currents in some positive strokes continue to decay and in others start to increase again and reach a second peak in a few hundred microseconds. While the current is flowing, in some cases, a burst of electromagnetic pulses with a separation between pulses of about 3 μs or less occur. The shape of the inferred long-duration currents are similar to the shapes of the positive return stroke currents measured in lightning strikes to high towers.