Pressure, Winds, Storms, and Cyclones · Lesson 6 of 8
How Storms Produce Thunder and Lightning
“Follow rising moist air into clouds, rain, separated charges, lightning, and thunder.”
• Trace how warm moist air and replacement flow develop a storm. • Explain cooling, condensation, cloud formation, and rain, hail, or snow. • Describe the chapter’s model of charge separation and electrical discharge. • Explain why thunder follows lightning and identify safe shelter and the role of a lightning conductor.
Rising moist air builds storm clouds
A hot surface warms the moist air just above it. This warmer air is less dense than neighbouring cooler air and rises, leaving lower pressure near the surface. Cooler air flows in from surrounding higher-pressure regions, warms, and can rise in turn. The repeated upward movement and replacement create a circulation of air. These movements are much stronger in some storms than in an ordinary breeze.
As moist air rises, it expands and cools. Water vapour condenses into tiny droplets, forming clouds. Droplets can join into larger, heavier drops, which fall as rain. In some cold parts of a cloud, water may form ice particles, and precipitation may also arrive as hail or snow. A storm combines strong winds with rain or other precipitation. Hot, humid regions often supply the moisture and rising air that favour storms.
Problem
On a hot humid day, warm air rises repeatedly and a cloud grows. What turns invisible water vapour into droplets?
- 1.The moist air rises to lower-pressure surroundings and expands.
- 2.It cools as it rises; vapour condenses into tiny liquid droplets.
- 3.Many droplets together form a visible cloud; larger merged drops may fall as rain.
Electric charges inside a thundercloud
Inside a vigorous storm cloud, up-and-down winds move water droplets and ice particles past one another. Interactions and collisions help separate electric charges. The chapter depicts lighter positively charged ice particles high in the cloud and more negative charge lower down. A negatively charged cloud base can also cause the ground and objects below to become positively charged.
Air normally resists the movement of electric charge: it acts as an insulator. When the separation of charge becomes sufficiently large, a sudden electrical discharge can pass through the air. We see the bright flash as lightning. A discharge may happen within one cloud, between clouds, or between a cloud and the ground.
Problem
A student thinks lightning only travels from a cloud to the ground. Explain the three arrangements in the chapter.
- 1.Opposite charges may build up in different parts of the same cloud.
- 2.They may also differ between two clouds or between a cloud and ground.
- 3.A discharge can occur within a cloud, between clouds, or between cloud and ground.
Why we hear thunder
The electrical discharge heats nearby air very rapidly. That air expands suddenly, creating a sound wave. We call the sound thunder. Lightning is the flash and thunder is the sound produced by the rapid heating and expansion. The light arrives sooner than the sound because light travels far faster through air than sound.
A storm accompanied by lightning and thunder.
Problem
You see a flash and then hear a rumble. Explain the sequence without assuming two separate events.
- 1.An electrical discharge produces the flash.
- 2.It rapidly heats neighbouring air; the air expands and sends out a sound wave.
- 3.The light reaches you before the slower sound, so thunder is heard after the flash.
Some local thunderstorms have regional names. Before the monsoon, Kalboishakhi is a name used in West Bengal, Bihar, and Jharkhand, while Bordoisila is known in Assam. Mango showers in parts of southern India can help mangoes ripen; local pre-monsoon rain can support kharif crops and coffee plants. Such rain can be useful to farming, even though lightning and strong gusts remain hazardous.
Protection during lightning
Lightning can cause injury, fire, and damage. At the first thunder, go to a substantial enclosed building or a hard-topped vehicle with its windows closed. Leave water and avoid isolated trees, open fields, metal umbrellas, and contact with plumbing or electrical equipment during the storm. No outdoor position is safe from lightning; a crouched posture should not be presented as a substitute for shelter.
A lightning conductor is a metal rod installed on a building, with its top above the roof and a connection leading into the ground. Its purpose is to provide a planned, lower-resistance path for charge to reach the ground, reducing damage to the building. It does not prevent clouds from forming or make it safe to stand outside in a storm.
A car or bus with a closed hard top is generally safer than remaining outside. Do not lie flat on the ground or wait under a lone tall tree. Seek a sturdy enclosed shelter promptly.
Check your thinking
Separate the weather process from the electrical process: rising moist air builds the cloud, then charge separation and discharge make lightning, whose heat generates thunder.
Quiz
What first helps warm moist air rise over heated land?
What produces cloud droplets from water vapour in rising air?
What is lightning in this chapter’s model?
What makes thunder?
Where should a person go after hearing thunder?
What does a lightning conductor do?
Practice Problems
- Trace the steps from hot moist surface air to cloud and heavy rain.
- Explain why cooler nearby air flows toward a region where warm air rises.
- Describe how up-and-down motion in a storm cloud contributes to charge separation.
- List three places in which a lightning discharge may occur.
- Distinguish lightning from thunder and explain why one is seen before the other is heard.
- Describe how a lightning conductor helps protect a building, including its upper and lower ends.
- A friend suggests crouching in an open field when thunder begins. Give a safer action and explain why.
Key Takeaways
• Warm moist air rises; cooler air replaces it, and rising air cools into cloud droplets. • Strong storm-cloud motion helps separate electric charges; a sudden discharge is lightning. • Lightning rapidly heats air, whose expansion produces thunder. • Seek sturdy enclosed shelter when thunder is heard; a lightning conductor directs charge toward the ground.