THE LIGHTNING HF RADIATION AT 3 MHZ DURING LEADER AND RETURN STROKE PROCESSES

Simultaneous recordings of the broadband electric field and HF radiati on at 3 MHz were obtained at times before and after the onset of first and subsequent lightning strokes. Data are presented for several hund red negative ground flashes observed in Sri Lanka within a range of 40 km over the land and sea. The stepped leader gave rise to strong 3 MH z radiation, but the peak amplitude of the radiation was less than tha t of the return stroke. In the return stroke phase, 3 MHz radiation wa s strongest at the beginning of the first return stroke and gradually decayed completely. The mean duration of the 3 MHz continua of 346 fir st strokes was 190 mus (S.D. = 69 mus). In about 99% of the cases 3 MH z radiation in the return stroke phase was accompanied by a burst of m ultitudinous, fine oscillatory pulses on the broadband electric field. Subsequent strokes, in general, had no 3 MHz radiation in their retur n stroke phases.