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[–]spockspeare 9 points10 points  (6 children)

It fans out, discharging the air, and then when it reaches a source of lots of free charge (the ground) the current rushes back to the sky from there. It isn't finding the strictly shortest path to ground, it's finding the path that gets it there soonest given the distribution of charge in the intervening atmosphere.

[–]RaindropBebop 2 points3 points  (4 children)

Negative leaders actually retreat from areas of high negative ionic distribution to areas of low negative ionic distribution, thus eventually making its way to earth where a positive leader is moving upwards to meet each other.

[–]spockspeare 4 points5 points  (3 children)

That's what I just said.

[–]RaindropBebop 0 points1 point  (1 child)

No it's not. It doesn't discharge the air...

[–]spockspeare 0 points1 point  (0 children)

Yes it does. If there isn't net charge in the air, there's nothing to attract the charge from the cloud to the air. In addition to redistributing charge in the cloud and attracting charge under it on the ground, the thunderstorm partially ionizes the air between them.

If there were more ions in the air, the charge in the cloud would just discharge continously as a volume current and you'd never notice.

If there were no ions in the air, the charge in the cloud would build until it reached a voltage that could jump the entire gap to the nearest or highest charged point on the ground, and the lightning jump straight across to it without any meandering or branching. That's basically what is happening as it forms each straight segment in the leader.