Lightning branching and other questions

[Baby Astronaut]

http://www.space.com/scienceastronomy/lightning_backgrounder.html

 

I have some questions from the article linked above.

 

1. If lightning seeks an easy path to the ground, why does it branch, rather than stay as one thicker bolt?

 

2. If lightning is seeking a path to strike ground, does that mean the positive charge higher in the cloud has been depleted?

 

3. If lightning sends out a stepped leader, then how does a multi-branching occur?

 

4. The article mentions one return stroke from the ground, but how is that possible on a multi-branched lightning? Wouldn't that be several return strokes occur from various locations at once?

 

5. If lightning heats the air to 54,000 degrees Fahrenheit (five times hotter than the sun), how is it that any lightning strike victim can survive heat heat of that magnitude?

[Gilded]

1. The electrons follow the path where there is least resistance. As more and more electrons take one path in a resisting environment the resistance increases and it is easier for some electrons to arc from the main path wherever there might be less resistance (some ionized molecules in the air etc.)

5. The heat is very localized and of course lasts for a very brief while. It's not like everything around you is that hot if you get hit by a lightning. Also, the heat is more extreme in cases where resistivities are much larger than in the human body. Lightning can melt sand into glass but such extreme heat rarely occurs in the immediate vicinity of a human. In many cases some charring is evident, and clothes and hair can catch fire, but I haven't heard of anyone being vaporized by lightning. Also, it is rare to be directly hit by lightning. A direct hit is likely to cause heavy damage but most lightning victims are subjected to just a fraction of the energies involved.

 

(At this point Gilded had a kebab. It was quite tasty.)

 

Btw one thing one should realize is that only some lightning strikes hit the ground. There are potential differences in the atmosphere and some of them are evened out without anything having to reach the ground.

 

2. Not really. Lightning strikes happen because the potential difference between charges gets large enough to overcome the atmosphere's resistance. This can happen between any sufficiently large opposite charges anywhere, and after the arc the charges are mostly evened out. I wouldn't call it depletion as it's essentially an exchange of charges (although the only particles exchanged are electrons).

 

3. The paths of ionized air that form before the actual lightning strike aren't too linear. It's just a matter of where the atmosphere is most prone to breaking down, and as most atmospheric processes it can be considered quite random, so it's not just one apparent stepped leader that acts as a "feeler" for the potential difference.

 

4. The branches rarely hit the ground to the extent that the main bolt(s) does. I'd imagine the returning arc is a simple if extreme case of electric feedback.

Edited September 29, 2008 by Gilded
multiple post merged

[Baby Astronaut]

(Mmmm, kebabs)

 

Thank you much Gilded, that practically answers everything but one little detail. The article claims that a return stroke causes the flash we see. Yet if the lightning branches don't reach the ground, I assume that return strokes couldn't have reached the branches, so how do they light up?

[YT2095]

5. If lightning heats the air to 54,000 degrees Fahrenheit (five times hotter than the sun), how is it that any lightning strike victim can survive heat heat of that magnitude?

 

the better and larger the conductor, the less it heats up.