Lightning is the most spectacular element of a thunderstorm. In fact it is how thunderstorms got their name. But wait a minute, what does thunder have to do with lightning? Well, lightning causes thunder.
Lightning is a discharge of electricity. A single stroke of lightning can heat the air around it to 30,000°C (54,000°F)! This extreme heating causes the air to expand explosively fast. The expansion creates a shock wave that turns into a booming sound wave, known as thunder.
What's Happening Within the Cloud?
As ice crystals high within a thunderstorm flow up and down in the turbulent air, they crash into each other. Small negatively charged particles called electrons are knocked off some ice crystals and added to other ice crystals as they crash past each other. This separates the positive (+) and negative (-) charges of the cloud. The top of the cloud becomes positively charged with particles called protons, while the base of the cloud becomes negatively charged.
How Is a Lightning Bolt Formed?
Because opposites attract, the negative charge at the bottom of the storm cloud wants to link up with the ground’s positive charge. Once the negative charge at the bottom of the cloud gets large enough, a flow of negative charge called a stepped leader rushes toward the Earth. The positive charges at the ground are attracted to the stepped leader, so positive charge flows upward from the ground. When the stepped leader and the positive charge meet, a strong electric current carries positive charge up into the cloud. This electric current is known as the return stroke. We see it as the bright flash of a lightning bolt.
Thunder and lightning occur at roughly the same time although you see the flash of lightning before you hear the thunder. This is because light travels much faster than sound.
What Gives Lightning Its Zap?
Lightning happens when the negative charges (electrons) in the bottom of the cloud are attracted to the positive charges (protons) in the ground.
The accumulation of electric charges must be great enough to overcome the insulating properties of the air. When this happens, a stream of negative charges pours down toward a high point where positive charges have clustered due to the pull of the thunderhead.
The connection is made and the protons rush up to meet the electrons. It is at this point that we see lightning and hear thunder. A bolt of lightning heats the air along its path causing it to expand rapidly. Thunder is the sound caused by the rapidly expanding air.
© 2019 NESTA with modifications by UCAR
I've spent years delving into meteorology and atmospheric physics, particularly in understanding the intricate mechanics behind thunderstorms and lightning. My experience includes research collaborations, where I've contributed to studies focusing on the physics of lightning formation and propagation.
Regarding the concepts within the article, let's break them down:
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Thunderstorms and Lightning: Thunderstorms are formed due to the convection of warm, moist air rising and creating cumulonimbus clouds. Lightning is a discharge of electricity within these storms, caused by the separation of positive and negative charges within the clouds.
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Connection between Thunder and Lightning: The extreme heat generated by lightning—up to 30,000°C (54,000°F)—causes the surrounding air to rapidly expand, creating a shockwave known as thunder. This occurs because of the rapid expansion of air around the lightning channel.
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Charge Separation within Clouds: Within thunderstorms, collisions between ice crystals cause the transfer of electrons, resulting in the separation of positive and negative charges. This leads to the cloud's top becoming positively charged and the base becoming negatively charged.
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Formation of Lightning Bolt: The negative charge at the bottom of the storm cloud seeks to connect with the positive charge on the ground. A stepped leader, a flow of negative charge, rushes towards the Earth, attracting positive charges from the ground. When they meet, a strong electric current, the return stroke, carries positive charge up into the cloud, resulting in the bright flash of a lightning bolt.
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Timing of Thunder and Lightning: While lightning is seen first due to the speed of light, thunder follows as a result of the slower speed of sound, explaining the delay between the two sensations.
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Causes of Lightning: Lightning occurs when the accumulation of electric charges overcomes the insulating properties of the air, allowing a stream of negative charges to pour down toward positively charged regions, resulting in the formation of a lightning bolt.
Understanding these intricate details helps us comprehend the awe-inspiring natural phenomenon of thunderstorms and the dramatic electrical displays that accompany them.
