Global Atmospheric Circulation

Question 1

What is a hadley cell?

Answer 1

A Hadley Cell is formed when:

• The air separates and starts to move both north and south towards the poles.
• When it reaches about 30° north and south, the air cools and sinks towards the ground forming the subtropical high-pressure zone.
• As the air sinks, it becomes warmer and drier. This creates an area of little cloud and low rainfall, where deserts are found.
• The Hadley cell is then complete. The air completes the cycle and flows back towards the equator as the trade winds.
• In the northern hemisphere, the winds flow to the right and are called northeast trade winds. In the southern hemisphere the winds flow to the left and are called the southeast trade winds.

Question 2

What is a ferrel cell?

Answer 2

A ferrel cell is formed when:

• Air on the surface is pulled towards the poles, forming the warm south-westerly winds in the northern hemisphere and north-westerly winds in the southern hemisphere.
• These winds pick up moisture as they travel over the oceans. At around 60 degrees N and 60 degrees S, they meet cold air, which has drifted from the poles.
• The warmer air from the tropics is lighter than the dense, cold polar air and so it rises as the two air masses meet.
• This uplift of air causes low pressure at the surface and the unstable weather conditions that are associated with the mid-latitude depressions.

Question 3

What is a polar cell?

Answer 3

A Polar cell is formed when:

• At the poles, air is cooled and sinks towards the ground forming high pressure, this known as the Polar high.
• It then flows towards the lower latitudes. At about 60 degrees N and S, the cold polar air mixes with warmer tropical air and rises upwards, creating a zone of low pressure called the subpolar low.
• The boundary between the warm and cold air is called the polar front. It accounts for a great deal of the unstable weather experienced in these latitudes.

Question 4

What is a cumulo-nimbus cloud?

Answer 4

These are much deeper clouds that climb high into the atmosphere. They often contain a lot of heavy rain and are associated with thunder and lightning storms.

Question 5

What are trade winds?

Answer 5

The trade winds or are the permanent east-to-west prevailing winds that flow in the Earth’s equatorial region. The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth’s equatorial region.

Question 6

What is High air pressure?

Answer 6

The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth’s equatorial region.