Lightning travels both ways.
Lightning is a huge electrical discharge that results from vigorous motions that occur in thunderstorms. Lightning can travel from cloud to cloud, within the same cloud, or between the cloud and ground. In-cloud lightning discharges are more common than cloud-to-ground discharges and are not as hazardous. Cloud-to-ground is the best known type of lightning and it poses the greatest risk.
A typical cloud-to-ground flash begins as negative charges travel toward the ground in a sequence of spurts. This makes the ground positively charged. As the negative charges approach the ground, there is an upward stream of positive charges. When the two streams meet an initial flash occurs and a channel forms so that electricity can flow between the cloud and ground. This occurs so quickly that it looks like a single brilliant flash but high speed photography shows several bolts.
Cloud-to-ground lightning starts from the sky and heads downward but what we see can travel from the ground upward.
Over the last twenty years scientists have discovered that lightning also shoots upward out of the top of thunderstorms into the upper atmosphere. These lightning types are known as red sprites, elves and blue jets. We still lack full knowledge about these forms of lightning. We do know that red sprites and elves occur over cloud-to-ground lightning bolts. Blue jets occur in the stratosphere and have been observed by pilots.
