A novel method to identify the radiation fields produced by positive return strokes and their submicrosecond structure

The submicrosecond structure of the positive return stroke radiation fields, together with the temporal behavior of HF at 3 MHz measured simultaneously with the electric fields, are presented. It is shown that (1) positive return strokes in the range of 25–100 km over land can be identified by studying the temporal behavior of the HF radiation, (2) the positive return stroke from its very beginning is a strong source of HF radiation, and (3) radiation fields from positive return strokes exhibit large submicrosecond components, which in turn suggest that currents in positive return strokes also contain a large submicrosecond component.