Why does sinking air at about 30° north and south produce such extreme dryness?

As the air descends it warms, so it can hold more water vapour and cloud cannot form, leaving clear skies, fierce daytime heat and almost no rain.

How does the rotation of the Earth change the direction of surface winds?

It deflects them to the right in the northern hemisphere and to the left in the southern, so they curve rather than blowing straight towards low pressure.

What is the jet stream?

A narrow ribbon of very fast wind high in the atmosphere at the boundary between circulation cells, which steers depressions across the mid-latitudes.

OCR GCSE Geography A J383

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Environmental Threats to Our Planet

Topic overview Climate change through the Quaternary, and since 1000AD The evidence for climate change Natural causes of climate change, and the enhanced greenhouse effect The consequences of climate change The world’s climatic regions and global atmospheric circulation How global circulation produces extreme weather Tropical storms: causes, distribution and frequency A drought caused by El Niño or La Niña

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Environmental Threats to Our Planet

How global circulation produces extreme weather

3 things to know
Component 02

Overview

Why land near the equator is so wet and land near 30° so dry, the trade winds, how the Earth's rotation deflects surface winds, why the polar regions are dry, the jet stream and the extremes it brings, the seasonal shift of the rain belt, and changeable mid-latitude weather.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why does the land near the equator receive such extreme rainfall totals?

Key term

What are the trade winds and why are they so persistent?

Key term

Why are the polar regions among the driest places on Earth?

Questions from this subtopic

Each one with the model answer underneath.

1
Why does the land near the equator receive such extreme rainfall totals?
Model answer
Constant strong heating makes moist air rise, cool and condense every afternoon, giving towering cloud and torrential convectional downpours.
2
Why does sinking air at about 30° north and south produce such extreme dryness?
Model answer
As the air descends it warms, so it can hold more water vapour and cloud cannot form, leaving clear skies, fierce daytime heat and almost no rain.
3
What are the trade winds and why are they so persistent?
Model answer
Surface winds blowing from the high pressure near 30° towards the low pressure at the equator, kept steady by the permanent pressure difference between the two belts.
4
How does the rotation of the Earth change the direction of surface winds?
Model answer
It deflects them to the right in the northern hemisphere and to the left in the southern, so they curve rather than blowing straight towards low pressure.
5
Why are the polar regions among the driest places on Earth?
Model answer
Cold dense air sinking over the poles gives permanent high pressure, and such cold air holds almost no moisture, so very little precipitation falls.
6
What is the jet stream?
Model answer
A narrow ribbon of very fast wind high in the atmosphere at the boundary between circulation cells, which steers depressions across the mid-latitudes.

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The trade winds drive warm surface water .

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