Cloud to Ground
This is the discharge from the negative lower part of the cloud to the positively charged earth. This is the most common form thought of when lightning is mentioned to people however it only constitutes 25% of all lightning however it is also the type that causes the most damage and so effects our lives the most.
The least common is the strike between the positive and negative charges within separate clouds where the strike travels in the air between them.
Intra-cloud lightning is the most common form of lightning. It appears as a flash within the cloud occurring between the positive and negative charges that are within the same thunder cloud.
Although this is the most common due to it causing very little danger or damage not alot of research has been carried out on it in comparison to cloud to ground.
This appears in the form of a glowing sphere which drifts horizontally in the air usually only lasting a few seconds.
It is still not fully understood why this occurs, one interesting theory that was recently found was by Abrahamson and Dinniss in 2000 is to do with the soil type at the place of the strike. This idea comes in three parts.
1. A heated mixture with more carbon content than silicon can cause the silicon to separate out into a very light fluffy form which is capable of floating in air.
2. The temperature of approximately 3000C where the lightning strikes.
3. The mixture of carbon and silicon found in the soil.
So, bearing in mind the previous elements if lightning strikes in an area where the soil has the correct make up then a ball of silicon would be created and due to its light nature would hover in the air. The light emitted then is believed to be the oxidization of the silicon which would explain why the ball gives off such light and the fades away, as this would occur when the oxidization is complete.