Which is correct: lightning travels downward from the cloud or lightning travels upward from the earth?

Very good question and here is the scientific answer. Each of your other readers are half correct. When negative charge near the bottom of the cloud becomes large enough to overcome the air's resistance, electrons (called the step leader) begins to flow downward toward the ground. When these approach the ground a region of positive charge moves up into the air to meet the downward step leader. When they meet a strong current or return stroke surges upwards into the cloud. The amperage of a typical thunderstorm may vary from 10,000 to 200,000 amps, with a potential difference of several hundred million volts. The power generated by one thunderstorm may be in the neighborhood of several hundred megawatts. As one questioner pondered several weeks ago "if only we could harness this energy". Now you should have a little better understanding of this process. It is both from the cloud and from the ground. There is also cloud to cloud lightning, but I'll leave that for another day.

There is a famous picture of a bolt of lightning hitting a tree. Surrounding this bolt, you can actually see about a half dozen of these weak current moving out from the ground, a telephone pole, the fence, and the roof of the house. According to the NASA lightning web page, "This ground-to-cloud flash generally transfers a net positive charge to Earth and is characterized by upward pointing branches."

http://www.highvoltagephotography.com/

http://www.lightningsafety.noaa.gov/multimedia.htm

These weak currents from the earth to air may start even before the the current starts from the cloud. There is a another well know picture of two kids smiling with their hair standing up a few seconds before a lightning bolt strikes the photographer. I also remember when I was young, my friend noticed during a storm that all the kids hair started stand up. The soccer coach quickly told the kids to run to shelter. However, lightning from cloud to ground never occur even though there were weak ground to air current noted by the players. So it really depends on which current or part of the current you would define as lightning. In my opinion, I would count this "ground to air" as lightning just as we count the cloud to air or cloud to cloud as lightning. But there is more...

Just as we thought we understand lightning, something new has been comfirmed by NASA's Shuttle missions over the past decade or so...Space Lightning. This is lightning from the top of a large CB cloud that shoots far up into space and may not fit the classical reasoning of why we think lightning occurs. See the following link...

http://www.ghcc.msfc.nasa.gov/skeets.html

Both are true really...

Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud from an upward-moving leader stroke. These thunderstorm clouds are formed wherever there is enough upward motion, instability in the vertical, and moisture to produce a deep cloud that reaches up to levels somewhat colder than freezing. These conditions are most often met in summer. Lightning occurs less frequently in the winter because there is not as much instability and moisture in the atmosphere as there is in the summer. These two ingredients work together to make convective storms that can produce lightning. Without instability and moisture, strong thunderstorms are unlikely. Lightning originates around 15,000 to 25,000 feet above sea level when raindrops are carried upward until some of them convert to ice. For reasons that are not widely agreed upon, a cloud-to-ground lightning flash originates in this mixed water and ice region. The charge then moves downward in 50-yard sections called step leaders. It keeps moving toward the ground in these steps and produces a channel along which charge is deposited. Eventually it encounters something on the ground that is a good connection. The circuit is complete at that time, and the charge is lowered from cloud-to-ground. The return stroke is a flow of charge (current) which produces luminosity much brighter than the part that came down. This entire event usually takes less than half a second.

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. One special type of cloud-to-ground lightning is anvil-to-ground lightning, a form of positive lightning, since it emanates from the anvil top of a cumulonimbus cloud where the ice crystals are positively charged. In anvil-to-ground lightning, the leader stroke issues forth in a nearly horizontal direction until it veers toward the ground. These usually occur miles ahead of the main storm and will strike without warning on a sunny day. They are signs of an approaching storm and are known colloquially as "bolts out of the blue".

I think it can be either. The reason I think this is because lightening goes between clouds so there could a net charge in either state.

What you need to consider is the catalyst of the event that starts the ionization of the air to form the conductor and whether this is asymmetric.

Guessing:

I think the electrons go up to the clouds more, --but I have no reason to think this except a minute advantage caused by ionized air being heated and having an assist from convection.

The other way the electrons are more mobile so I cannot say.

But I maintain there probably are examples, however rare, from both directions.

the two, sorta, yet downwards is the final selection. as a results of way that water droplets distribute themselves in a cloud, the strategies-blowing of the cloud is useful and the backside is damaging. while a spark jumps interior the cloud, you get intra-cloud lightning. because of the fact the backside of the cloud is damaging, it has a extensive far extra desirable than electrons. those electrons create an electric powered field by way of the air that pushes on the undertaking below, which includes a tree, a metallic tower, or a park ranger. because of the fact damaging (electrons) repels damaging (different electrons), the cloud pushes all your electrons down into the earth, giving you a internet useful fee (induction). Opposites charm to, and a spark jumps. A spark contains a process freely flowing electrons in plasma. electrons will continuously pass from damaging to useful (because of the fact they're damaging, so they're repelled via the damaging pole). because of the fact of this they pass from the cloud to the floor. Down. in spite of the indisputable fact that, each so often it is going to seem that lightning strikes up, because of the fact the damaging interior the cloud relatively "pulls" a bolt of useful fee out of you and into the cloud by way of the air. in spite of the actuality that this journey, referred to as an excellent streamer, strikes upwards, the present nevertheless flows downwards.

It travels downward from the clouds. In a cloud, when the positive and negative charges meet it creates friction which creates static electricity which is what lightning is. So it comes down from the clouds.

Upwards from the Earth.

downwards, because earth is a better conductor than atmosphere, charges always want to be earthed.