Why does lightning strike from the ground-up?
The enlightening image below is of a lightning strike slowed down at 10,000 frames per second. It can be seen that the most intense flash produced from the lightening occurs in the direction from the ground up. Why does this final "ground-up" strike occur and why is it so much brighter and faster than the initial part of strike heading towards the ground?
Those initial streamers are looking for a path of least resistance. When they find it; that stroke comes up from the ground.
With 2018 4k video technology, you can see the same thing in high definition. https://youtu.be/nBYZpsbu9ds?t=12
I do want to answer this question and i can't !!! It is a highly active questionand needs 10 points experience to earn to answer this! Anyway the question is "Why does lightning strike from the ground-up" the most voted answer starts with "Does lightning strike from the sky down, or the ground up". Nice wiki answer but the question should be "Why does lightning strike from the ground up at this particular location in Earth and has it happened before?" Or "why does the downwards strike breaks into several paths but the upwards strike has a single path?"
consider also two things, electrical current is described as the flow from positive to negative but the opposite happens, electrons move. In addition electrical current when flowing metal resistors can heat up the metal (if the resistance is high) and change the color from a starting color of red until it reaches color white. Why do you actually think this does not happen to air? the more bright the spot the higher the resistance of the spot.
Does lightning strike from the sky down, or the ground up?
The answer is both. Cloud-to-ground lightning comes from the sky down, but the part you see comes from the ground up. A typical cloud-to-ground flash lowers a path of negative electricity (that we cannot see) towards the ground in a series of spurts. Objects on the ground generally have a positive charge. Since opposites attract, an upward streamer is sent out from the object about to be struck. When these two paths meet, a return stroke zips back up to the sky. It is the return stroke that produces the visible flash, but it all happens so fast - in about one-millionth of a second - so the human eye doesn't see the actual formation of the stroke.
The reason is that when cloud-to-ground strike approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field and the "downward leader" strike creates bridge for the "return stroke"; this per the wiki page for Lightning.
Cloud to cloud and Intra-Cloud Lightning
Might be worth also noting that cloud-to-ground is not as common as Cloud to cloud (CC) and Intra-Cloud (IC):
Lightning discharges may occur between areas of cloud without contacting the ground. When it occurs between two separate clouds it is known as inter-cloud lightning, and when it occurs between areas of differing electric potential within a single cloud it is known as intra-cloud lightning. Intra-cloud lightning is the most frequently occurring type.
Appears that ground-to-cloud is possible, though normally only a result of a man-made object creating "unnatural" electric potential, and is the least common type of lightning.
+1 thanks for your answer. I'll wait a few days to accept in case I get more specific answers on why the return flash is brighter and faster however.
Appears that the reason is that when cloud-to-ground strike approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field and the "downward leader" strike creates bridge for the "return stroke"; this per the wiki page for Lightning. Also, appears that ground-to-cloud is possible, though normally only a result of man-made object creating "unnatural" electric potential.
although i do agree that cloud-to-ground lightnings are rarer, it seems a bit bold to affirm that they are "**normally only** a result of a man-made object creating "unnatural" electric potential". Do you have any sources for that affirmation?
@plannapus: See Upward-moving lightning from TV towers, skyscrapers and other tall structures - also, FYI, you mean ground-to-cloud, not cloud-to-ground, right?
ah no i misread your sentence as talking about cloud-to-ground and not ground-to-cloud, my apologies.
This also explains why when you hair starts standing up on its own in a storm that is signalling it is time to go elsewhere (that E field has to come from somewhere, and you don't want to be in the vicinity of upward streamers that have the potential to become a CG strike).
This answer (and the other answers) don't seem to explain why the first movement is slow and downward, while the second movement is fast, bright and upward. There's interesting information there, but it doesn't seem to answer the question.
You actually see a ground to cloud lightning in this image? no such case here, sorry. Still ground to cloud do exist and many more fancy types of lightning, but not here. Take a better look in image please, don't be fooled by the light cause it only means more electrical resistance on that part of the ALREADY ESTABLISHED PATH.