HF RADIATION AT 3 MHZ ASSOCIATED WITH POSITIVE AND NEGATIVE RETURN STOKES

HF radiation at 3 MHz generated by positive and negative return stroke s is presented along with the associated broadband electric fields. Th e mean duration of the HF associated with negative return strokes was about 140 mus, with minimum and maximum values of 60 and 600 mus, resp ectively. The durations of the HF associated with the positive return strokes ranged from 5 to 25 ms which is much longer than the duration of HF radiation associated with negative return strokes. It is suggest ed that at least part of the HF radiation emitted by the return stroke is generated in the collapse of the leader corona sheath during the r eturn stroke.