Does Lightning Travel up or Down?

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. This phenomenon 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 charge can move.

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.

Lightning can travel both from the sky to the ground and from the ground to the sky. The most common type, cloud-to-ground lightning, initiates in a cloud and connects with the ground. However, the visible flash we see is due to the return stroke, which travels upward from the ground to the cloud, following a channel of ionized air created by a stepped leader moving downward.

A stepped leader is a preliminary discharge of electrons that moves in steps from the cloud towards the ground. It creates a conductive path for the subsequent return stroke. As it progresses downward in a series of rapid, intermittent bursts, it ionizes the air, forming a channel through which the bright return stroke will travel.

Lightning is an incredibly fast phenomenon. The stepped leader advances at speeds of about 220,000 km/h (136,700 mph), while the return stroke can reach speeds of up to 140,000 km/s (87,000 miles/s), according to the National Severe Storms Laboratory. This makes the return stroke, the main lightning flash, one of the fastest-moving processes in nature.

Positive and negative lightning refer to the charge of the originating part of the cloud. Negative lightning, which accounts for about 95% of all cloud-to-ground lightning strikes, originates from the negatively charged bottom of the storm cloud. Positive lightning, which is less common but more powerful, originates from the positively charged upper regions of the cloud.

Yes, lightning can travel horizontally. This is known as cloud-to-cloud or intra-cloud lightning and occurs within a single storm cloud or between different storm clouds. It is more common than cloud-to-ground lightning and is responsible for the majority of lightning occurrences. These horizontal flashes can extend for tens of miles.

The direction of a lightning strike is influenced by the distribution of charges within the storm cloud and the surrounding environment. The stepped leader will seek out the path of least resistance, which is often towards the ground where positive charges have accumulated on the surface. However, topography, the presence of tall objects, and variations in the electrical field can all affect the path lightning takes.