The point discharge streamers are continually fed by an intense ground charge that is deficient in electrons and usually follows right below the center of the storm cloud. When the leader stroke is a step or more above effective ground, a positive streamer shoots upward from a dominant pointed object. This streamer may be joined at its base by lesser streamers from nearby points. When the positive stream hits the negative stream, an ionized path is formed between the earth and the cloud. Most of these types of flashes are negatively charged.
Most people feel that the earth atmosphere is completely homogeneous.
This is not the case as many scientist's have found out first hand. The atmosphere actually forms pockets that contain about one liter of air. These pockets of air vary from pocket to pocket. The varying of these pockets is due to the fact that some have more molecules and particles than others. Imagine a thunder cloud, the earth's surface, and in between a bunch of one liter red and blue balloons that are stacked on one another in a checkered fashion.