Does lightning travel down or up?

Answer 1

This is somewhat of a trick question - technically lightning does both. Let's take a look at the process through which lightning is known to be formed. Lightning occurs because of a difference in charge between a storm cloud and the ground.

First, the base of a cloud sends down a little electric discharge, called a stepped leader. It descends to the ground in steps, each about 50 yards (about 46 meters) in length. This process is extremely fast and impossible to see with the naked eye. Each step is less than a millionth of a second long. The interval between steps works out to about fifty-millionths of a second. This process can only be observed with the assistance of extremely quick-exposure cameras.

The stepped leader generally moves at about 75 miles per second (120 km/s) towards the ground. A typical trip duration is 20 milliseconds. Atoms pass along electrical charge much more quickly than sound vibrations.

The stepped leader carries tons of negative charge. As it nears the ground, it induces enormous quantities of positive charge in the earth, especially at the tips of tall objects. Because opposites attract, the stepped leader and the negative charge at the ground reach towards each other and quickly meet. The path from storm cloud to the surface is complete and "the floodgates are open", so to speak.

Because the cloud is filled with negative charge, it has a lot of current to offer to the newly created discharge path. This charge quickly moves from being distributed throughout the cloud to being concentrated at the point where the stepped leader first dropped from the cloud, into the ground or an elevated object. This discharge is called the return stroke, and is what we think of when we hear the word "lightning".

The return stroke takes around 100 millionths of a second to reach the ground. The immense flash generated is enough to leave an afterimage in our eyes for seconds at a time, giving us the illusion that the lightning flash is longer than it really is. In reality, our eyes cannot resolve any of the steps involved. We only see the final product - a lightning bolt.

So, to answer the original question - put roughly, lightning does move from cloud to ground - if you consider only the return stroke. The whole process begins in the cloud, goes to the ground, then goes back to the cloud, then goes from the entire cloud to the ground. That's how lightning works.

Answer 2

I'm going to try to offer something for the lay-person, because I'm not sure you care how fast a stepped-leader travels.

Lightning is the by-product of charge seperation within a cloud. Since you didn't ask how the charge seperation occurs, I won't get into it, but this division of a cloud into positively and negatively charged regions is where we start.

The cloud doesn't want to be divided into areas of different electrical charges and so it looks to nuetralize it's electric field by discharging an electric current which we call lightning. The cloud does this by breaking down the electric resistance of the air in a channel called a stepped-leader.

This stepped-leader can go either up, down, or from one cloud to another, but I'm assuming you're asking about the lightning that strikes the ground. So as the stepped-leader gets near the ground, opposite charges attract and the cloud induces a small pos or neg charge on the earth - this is why you see people with their hair standing up when lightning is about to kill them.

When the stepped-leader from the cloud and the"streamer" from the earth connect, the electricity in the stepped-leader is discharged UP the channel to the cloud, and then the lightning strike occurs and the clouds electricity is discharged DOWN the channel to the ground.

Answer 3

It can go either way:

Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud from an upward-moving leader stroke.

Cloud-to-ground lightning is a great lightning discharge between a cumulonimbus cloud and the ground initiated by the downward-moving leader stroke. This is the second most common type of lightning, and poses the greatest threat to life and property of all known types.

Answer 4

...both,up and down.........
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