Temporal behaviour of lightning HF radiation at 3 MHz near the time of first return strokes

Simultaneous recordings of the electric field and high frequency emissions (HF) at 3 MHz at times close to the first return stroke are presented. It is shown that there is no time delay between the beginning of the return stroke electric field and the build up of the HF. The delay observed in previous studies may be due to propagation effects. The results in turn suggest that the first return stroke from the very beginning is a strong source of HF at 3 MHz.