VHF/UHF Radiation from Positive and Negative Lightning

Measurements of VHF/UHF radiation from positive and negative lightning flashes were made for close lightning in summer and winter together with the electric field change measurements. Strong radiations are associated with return strokes of a ground flash in summer, but in winter more than 50% of return strokes are not followed by detectable VHF/UHF radiation. The radiation intensity from positive return strokes in winter is several times as small as that from negative ones in summer. The time delay of VHF/UHF bursts from the onset of the electric field change due to a return stroke is found to be related to the distance to the flash. In winter, the radiation from other processes than the return stroke in the negative ground flash is more intensive than that in the positive ground flash.