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.