What causes lightning?

Nature is full of all kinds of amazing and interesting phenomena that has fascinated humans over the centuries right up to this very day. One such phenomenon is lightning. The bolt of a lightning takes the appearance of a zigzagging pattern that usually takes less than half a second to produce a luminosity that is so bright that it lights up its surrounding in the blink of an eye. While this is a fascinating sight it also drives fear in humans. With its burst of intense energy it could cut down a tree, start a fire and even cause death, if struck by one. This fear can even be greatly intensified by the loud frightening sound of thunder which adds to this effect, depending how close one is to the origin of the sound. Due to this mysterious, unexplainable yet fascinating phenomena in ancient times, humans from many cultures such as the Greeks, Romans and Norsemen thought these events were from gods who ruled the earth with lightning rods and thunder. Consequently, these cultures told stories of Zeus the king of the gods in Greek (name Jupiter for Romans) and Thor the Norse god of thunder. Today, even though lightning is just as fascinating and dangerous, with the advancement of our knowledge in science this can now be explained. Therefore, removing the mystery and thus, the folklore stories of ancient ancestors.

What is lightning?
Lightning simple, is electricity formed during a thunderstorm by the build up of large electrical fields in high anvil shaped cumulonimbus clouds (thunderstorm clouds) about 15,000 to 25,000 feet above sea level. This is accompanied by the emission of light which we see as flashes of light in the sky. The temperature inside a lightning bolts are extremely hot, with temperatures of 30,000 to 50,000 degrees F, hotter than that of the surface of the sun. However, to get a better understanding of what causes lighting we will need to take a more detail look at how it is formed.

What causes lightning?
Click to enlarge image
When water evaporates from the surface of earth from lakes, land, river, streams, ocean, ponds and from trees by transpiration, this rises into the atmosphere in the form of a gas by convection. As this warm air rises, cold air moves in and meets the warm moist air which causes the warm air to rise rapidly forming large, dense, tall towers of anvil shaped cumulonimbus clouds commonly known as thunderstorm clouds. Formed at a height between 15,000 to 25,000 feet above sea level, the water droplets are carried upward to a much cooler region until some of them are converted into ice (snow) particles.

During the thunderstorm, precipitation particles (water droplets and ice crystals) in the higher region of the clouds will then collide with each other as they rub against each other in strong currents of air. This strong air current here is due to the ascending (rising) and descending air in the updrafts and downdrafts of the storm (click here for diagram). As a result, this colliding and rubbing of many water droplets and ice crystals creates a static electrical charge. Thus, causing areas of negative and positive charge to develop within the thunderstorm. Some of the ice (snow) crystals and water droplets will therefore become positively charged (+ plus sign), while others become negatively charged( - minus sign). The positive and negative electrical charges in the cloud then separate from each other where the positively charged snow crystals moves to the upward top section of the storm cloud while the heavier negative charge ice crystal and water droplets drops to the lower section of the cloud.

Click to enlarge image

When the difference in the charges at the lower section of the cloud becomes large enough, whereby reaching a certain strength, a giant "spark" occurs causing the flow of electricity (electrical energy ) to be released through the air to another point that has an opposite charge. This release of electrical energy is called a leader stroke which may be from one cloud to another (Cloud-to-Cloud Lightning) or from one section of the cloud to another (In-Cloud Lightning) or from cloud to the ground (Cloud-to-Ground Lightning). Once a connection is made and the path is complete, a surge of electrical current moves in the opposite direction back to the cloud and produce a flash of light which we call lightning. This process is called the main stroke.

How lightning works
Now from the information provided above we will take a closer look at how lightning works using for example the Cloud-to-Ground Lightning. First, due to the colliding and rubbing of many water droplets and ice crystals in thunderstorm cloud this creates a static electrical charge. Thus, causing areas of negative and positive charges to develop within the thunderstorm. The positive and negative electrical charges in the cloud then separate from each other, where the positively charged snow crystals moves to the upward top section of the storm cloud while the heavier negative charge ice crystals and water droplets drop to the lower section of the cloud. The negative charges (-) in the lower part of the thunderstorm cloud causes positive charges (+) to build up on the ground directly beneath the cloud and in the area immediately surrounding the cloud. Thus, as the cloud becomes negatively charged (building up more and more electrons) these electrons cause the electrons on the ground to be pushed away (like charges repel) and therefore leaving the ground positively charged. This means the ground now becomes positively charged and the cloud is negatively charged.

{Click links to veiw diagarm. This is done to reduce loading time of site}

Diagarm A - Showing cloud with separtion of charges

Diagarm B - Showing how ligthning works


Now, when the lower section of the negatively charged cloud reaches a certain strength, the huge charges in the cloud cause the air to be ionized making the air a good conductor of electricity causing the air around them to act as a bridge. This now means that the electrical path is complete between the ground, air and cloud. After this happens, a giant "spark" occurs causing the rapid flow of electricity (electrical energy ) to be released through the air to the ground such as houses, buildings or other ground objects ( see diagrams above ) that have an opposite charge. This is called the leader stroke. As the negative charges from the cloud flows down, the positive charges (streamers) on the ground leap upward to meet them. This causes a surge of electrical current to move from the ground to the cloud causing the visible "return stroke" (main stroke) of electricity. As a result of this main stroke, the zigzagged path of negative charges suddenly lights up with a brilliant flash of light. This heats the air which becomes very hot, causing it to expand rapidly causing an explosion, making the well know sound we all know as thunder. It is also important to note that the zigzagged path (appearance) is due to the fact that air does not ionize equally in all directions.

Related Articles:
What are clouds and how are they formed?
Why is the sky blue?