Observed characteristics of upward leaders that are initiated from a windmill and its lightning protection tower

[1] We have analyzed the electric field changes of 14 upward leaders that were initiated from a windmill and its lightning protection tower. We found that these upward leaders can be sub-classified into two types according to whether they are triggered by nearby lightning discharge activity or they are initiated without any nearby preceding discharge activities. We have also obtained evidence of upward aborted leaders that are initiated from high-grounded objects in response to nearby lightning. All these results suggest that once the electric field which surrounds the high-grounded object is large enough, an upward leader can be initiated no matter whether the electric field is built up slowly or created rapidly by a nearby lightning discharge, although the later appears to be more efficient in triggering the leader. In addition, we found that without the assistance of a rising electric field produced by a nearby lightning discharge, compared to a stationary windmill and a tower with a similar height, a rotating windmill tends to have a bigger chance of initiating an upward leader.