Characterizing the Preceding Discharges of the Positive Cloud-to-Ground Lightning First Strokes in Winter Thunderstorms in Japan

Inhalt:
We have successfully located in 3 dimensions the first return stroke preceding discharges of 78 positive cloud-to-ground (+CG) lightning flashes in Hokuriku winter thunderstorms in Japan using a discone-antenna lightning mapping array (DALMA). We found that among these flashes, 49 (63%) can be characterized with an upward preliminary breakdown (PB) process, while 29 (37%) with a downward preliminary process. Compared with those summer positive CG lightning flashes, the proportion of downward develop PB increased significantly. A statistical study shows that the development directions of PB will not affect the peak currents of the following return strokes. Also, the relationship between the peak current of +CG and the development speed and development distance of PB is not obvious. However, the peak current is inversely proportional to the time when the return stroke occurs. The earlier the return stroke occurs after the PB, the greater the probability of a strong positive return stroke.