When Does Lightning Occur and Why?

When a thunderstorm occurs lightning also exists. This is because a thunderstorm is classified by lightning. In order for either of the two to be present in the atmosphere, clouds must first form. The clouds form when air near the earth's surface is warmed, causing it to rise since warm air rises. Think of a marshmallow in a microwave; as the microwave heats the marshmallow it begins to expand. This is similar to most things, like air. When air heats up it expands and this expanding air has to go somewhere because it is taking up more space, just as the marshmallow does, so this expanding warm air rises.

So what does this have to do with the cloud? Well, as the air rises it is losing its heat and cooling. When things cool, they condense; think of the marshmallow again as it cools when you take it out of the microwave (it shrinks, or condenses). In a general sense, to give you a brief idea of how clouds form, when condensation occurs, clouds take shape; you must keep in mind, however, that there is much more involved in cloud formation, but this was just to get you thinking and give a place for the lightning to happen.

The most common thunderstorm cloud is a tall cloud which is precipitating, called a cumulonimbus cloud (cumuli- meaning tall, high altitude, and nimbus meaning precipitation). These clouds form when conditions include upward winds, rather moist air, and cooling temperatures. Within this cloud, there are many electrons giving off their charges. The tendency of charges within a cloud is to have positive charges gather toward the upper portion and negative charges in the bottom of the cloud.

When the difference between these charges is great enough to overcome the air's natural insulation, which keeps these charges from mixing, a lightning flash can take place. This charge difference builds up to millions of volts before the stoke of lightning takes place. The lightning bolt actually happens because nature tries to maintain equilibrium, a state of balance between all things. This is why the lightning that you see is a discharge of energy in the form of electricity.


Where Does Lightning Strike?

The Cloud to Ground Striking Process


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Amber Wozniak: awozniak@nmu.edu