How a cyclone forms

The idea

Over warm oceans, moist air rises and its vapour condenses, releasing heat that warms the air further and deepens the low pressure; surrounding air rushes in and Earth's rotation makes it spin, building a very low-pressure system with high-speed winds.

Over a warm ocean

The ocean water is heated. The warm, moist air above it starts to rise.

What does the rising air leave behind?

• A low pressure area
• A high pressure area
• No change in pressure

Build a cyclone

Press Next step. Each step adds to the picture.

Heat feeds the low

Warm, moist air rises over the ocean. Its vapour condenses and releases heat, which warms the air more, so it rises further and the pressure gets lower still. Surrounding air rushes in and Earth's rotation makes it spin. The spinning system of clouds, winds and rain is a cyclone.

A cyclone forms over warm ocean water: rising moist air, very low pressure, air rushing in and spinning because of the Earth's rotation, with high-speed winds.

Notes

A cyclone is a spinning system of clouds, winds and rain over warm ocean water, with very low pressure.

Check yourself

Cyclones form over …

When water vapour condenses into raindrops, heat is …

This released heat makes the rising air …

What makes the moving air spin in a cyclone?

• cold mountains. Cyclones are large storms that form over warm ocean waters.
• warm ocean waters — correct. Yes!
• deserts. They form over warm ocean waters.
• taken from the air. Condensation releases heat back into the air.
• lost for ever. Heat is released into the air.
• released into the air — correct. Yes!
• rise even further, with even lower pressure — correct. Yes!
• sink. The warmed air rises further.
• stand still. The heat makes it rise even further, lowering the pressure more.
• The moon's colour. The Earth's rotation makes the air spin.
• The Earth's rotation — correct. Yes!
• A fan. It is the Earth's rotation that makes the air spin.