What are “positive” and “negative” strikes?
The sign–or polarity–of a lightning strike depends on what type of charge is lowered to ground. A negative cloud-to-ground flash means that negative charge is lowered to ground. In this case, excess negative charge occurred aloft in a thunderstorm, often at about 20,000 feet above sea level, and negative charge was brought down to the ground by the flash to try to equalize the electrical imbalance. Usually, the layering of charge is such that negative charge builds up closer to the ground than positive charge, so negative charge lowers more readily to the earth’s surface. About 95% of all cloud-to-ground flashes worldwide are negative. In the case of positive charge, the positive charge is brought to ground, but this usually happens near the end of storms, in winter storms, and on the edge of large thunderstorm complexes. Although less frequent, positive strokes generally contain more current and are more apt to catch more people by surprise.
