Multi ground termination upward flash in winter lightning at the coastal area of the Sea of Japan

Upward lightning flashes have been observed during winter at Nikaho Kougen Wind Farm in the coastal area of the Sea of Japan. From the observations, we found many multi-ground-termination upward flashes in winter lightning. These flashes involve at least two upward lightning flashes at different termination points in a short time. Current waveforms show that the time difference between two such lightning flashes ranges from 0.3 to 273 ms. Video images show that upward leaders are initiated from different wind turbines after the occurrence of another nearby lightning flash. This suggests that the first upward lightning flash triggers subsequent upward lightning flashes.