A positive lightning discharge that caused severe damage to the blade of a windmill

The optical progression characteristics of an upward connecting negative leader and a downward positive dart leader contained in a positive lightning discharge that hit on the blade tip of a windmill have been reported. The pulse discharges in the negative leader are found to propagate backward usually with a distance of a few tens of meters. Their propagation speeds tend to be around 1.0×10
⁸
m/s initially and soon drop to a stable value of about 2.0×10
⁷
m/s. The downward positive dart leader also exhibited a speed of about 2.0×10
⁷
m/s. The plasma formed on the windmill blade tip by the lightning tends to be much brighter than the free space lightning channel.