Making Connection With the Ground
During the development of the stepped leader, the positive charge on the ground increases. As the branches of the stepped leader approach the ground, the electrical forces between the leader tips and the tops of tall objects on the ground also continues to increase.
Eventually, these forces cause the air above the taller objects to become more conductive, to ionize. As it does, negative charge starts moving from the air to the taller objects and into the ground. The result of the negative charge moving toward the ground, is that the channel of air directly above the taller objects becomes positively charged. This is usually referred to as an upward streamer. Eventually, the negatively-charged, downward-moving stepped leader makes contact with one of the upward developing positive streamers.
When this contact is made, the lightning channel is complete and charges can flow rapidly from the cloud toward the ground. It takes only a fraction of a second to go from the stepped leader initiation to the final connection.
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