Abstract
Pulse trains superimposed on the initial stage of Japanese winter lightning are investigated. The characteristics of these pulse trains seem to be significantly different from those of summer lightning. The shapes of pulse trains are divided into three categories: (1) consecutive small bipolar pulses similar to the summer ones. (2) a large bipolar pulse which has a static electric field change. (3) a large oscillating waveform. A correlation between the meteorological conditions and the type of these three waveforms is investigated. Each pulse included in the pulse trains is a normal bipolar waveform and its width takes the value from 5 to 52 microseconds with the mean of 18 microseconds. The time interval between successive pulses takes the value from 10 to 180 microseconds and has the mean of 52 microseconds. For each bipolar pulse, the ratio of the peak amplitude of the initial polarity to the maximum overshoot amplitude is statistically about 1.4-1.7.
