Belts around the Earth

The idea

Uneven heating forms pressure belts: rising warm air makes the equatorial low, sinking air near 30° the sub-tropical highs, rising air near 60° the sub-polar lows, sinking cold air the polar highs; air moving between them forms planetary winds.

A journey of air

Imagine air near the equator, heated strongly by the Sun.

What will it do?

• Rise and move toward the poles high above
• Sink straight down
• Stay still

Follow the air

Northern half only. Press Next step.

Rise, sink, and flow

Where air rises the pressure is low. Where air sinks the pressure is high. Over long distances, air flowing along the surface from the high belts toward the low belts gives rise to the planetary winds.

Uneven heating forms pressure belts: rising warm air makes the equatorial low, sinking air near 30° the sub-tropical highs, rising air near 60° the sub-polar lows, and sinking cold air the polar highs. Air moving between them forms planetary winds.

Notes

Uneven heating makes low pressure belts where air rises (equator, 60°) and high pressure belts where air sinks (30°, poles). Air flowing between them forms planetary winds.

Check yourself

What forms near the equator, where intense heating makes warm air rise?

Around which latitudes does cooled air sink, forming the sub-tropical high pressure belts?

What forms near 60° where rising air meets the cold air from the polar regions?

Why is there a high pressure belt over the polar regions?

• The sub-tropical high pressure belt. The sub-tropical high forms near 30° where cooled air sinks.
• The polar high pressure belt. The polar high forms around 90° where cold air sinks.
• The equatorial low pressure belt — correct. Yes!
• About 30° North and South — correct. Yes!
• About 60° North and South. Near 60° air rises and forms the sub-polar low pressure belts.
• About 90° North and South. Around 90°, in the polar regions, cold air sinks to form the polar high pressure belts.
• The sub-tropical high pressure belt. The sub-tropical high forms near 30° where air sinks.
• The sub-polar low pressure belt — correct. Yes!
• The equatorial low pressure belt. The equatorial low forms near the equator.
• Intense heating makes warm air rise. Rising warm air makes a low pressure belt, as at the equator.
• The air is blown away by planetary winds. The chapter explains the polar high by cold, dense air sinking.
• Very low temperature makes cold, dense air sink — correct. Yes!