The global circulation system (GCS) is a model that explains how heat, wind and precipitation are found in different parts of the world. It also explains why different ecosystems and biomes are located where they are and why tropical storms are only found in certain areas.
There are 5 key ideas you need to understand to fully understand the GCS.
The first is how latitude works. Latitude is a set of imaginary lines that run around the Earth from east to west. They can be used for locating places, in this case, we use them for showing how far away we are from the equator.
The equator is a line that runs around the centre of the Earth and runs through countries such as Brazil, the Democratic Republic of Congo and Indonesia.
The equator is written as 00 and as you move away from the equator (either north or south) the number increases. The north pole is at 900 N and the south pole is at 900 S. (it is 900 because it is at right angles to the equator if you imagined cutting through the world).
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Earned Point(s): 0 of 0, (0) What part of the Earth does the GCS work in?
In which direction are lines of latitude?
If person A is stood at 300 N and person B is stood at 500 S, who is further from the equator?
Match up the definitions of these places on Earth
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For the next section, we are going to look at two opposite places in the world, the equator and the poles (north or south, it doesn’t really matter at this point!)
The climate and surface temperature at the equator and the poles are very different, this is due to the suns insolation (the amount of solar energy hitting an area) being different between these two places. The equator gets a higher level of insolation as the solar insolation is more concentrated at the sun is directly overhead. The poles get much less insolation due to the curve of the earth, making the same amount of insolation spread over a larger area.
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Earned Point(s): 0 of 0, (0) Which country would receive the higher amount of solar insolation?
The equator is warmer because it is closer to the sun, true or false?
Fill in the blanks for this paragraph about solar insolation The equator experiences much solar insolation than the . This is due to the spreading out of the at higher .
Sort these latitudes into order of most solar insolation to the least:
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Air pressure is the next step in understanding the Global atmopsheric circulation model. When we talk about air pressure we are talking about how much air is at the surface.
How do we get areas of high and low pressure?
Remembering back to how the sun heats at different latitudes, the equator gets most solar insolation which warms the air, causing it to expand and rise away from the surface, this leaves low pressure at the surface as some of the air has risen up. As this air rises it cools, and condenses to form clouds, which causes rainfall. This effect causes tropical rainforests (which are located on the equator) to have a warm and wet climate.
In areas of high pressure, the air sinks to the ground so no clouds can form, causing these areas to have very little rainfall. This causes deserts to form where areas of high pressure occur.
Key points:
Low pressure: rising air, less air at the surface and clouds form
High pressure: sinking air, more air at the surface, no clouds can form.
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Earned Point(s): 0 of 0, (0) High pressure causes which type of weather in the UK?
Low pressure causes which type of weather in the UK?
Tropical rainforests have warm wet weather due to which factors combining?
Air pressure is measured at what level?
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To understand how high and low pressure work together to form the GCS model, we go back to the equator again! Air rises and when it hits the top of the atmosphere, it has to move apart. Some goes north, and some goes south. It then moves until it reaches approximately 30° N or S where it cools and sinks back to Earth, causing areas of high pressure (deserts). Trade winds pull most of this air back towards the equator causing a loop of moving air that is called a Hadley cell. There is a separate Hadley cell north and south of the equator.
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Air rises and when it hits the top of the , it has to move apart. Some goes north, and some goes south. It then moves until it reaches approximately 30° N or S where it cools and sinks, causing areas of high pressure. pull most of this air back towards the equator causing a loop of moving air that is called a . There is a separate Hadley cell and of the equator.
What type of biome is found at 30° N or S of the Equator?
The final idea of the GCS is the ferrel and polar cells. Some of the heat energy from the Hadley cells is pulled north or south by winds known as westerlies. The westerlies pull the air from 30° to approximately 60° north or south. Here it mixes with colder polar air which forces the warmer (less dense) air to rise and condense to form clouds around this area. Some of the warmer air returns towards the equator forming the next cell called a ferrel cell.
Between 60° and 90° there is less heat energy being transferred so the final cell of the three cell model, the polar cell is cooler than the ferrel and Hadley cells. Winds in this cell often stay circulating around the poles.
The UK sits underneath where the ferrel and polar cells meet and as the cells move slightly over time, the weather conditions can change depending on which cell is determining the weather at the time. This gives the UK a varied climate compared to some other areas around the world.
Key points:
Hadley cell: nearest the equator, largest heat energy, creates deserts and tropical rainforests.
Ferrel cell: middle cell, medium heat energy, variable climate areas.
Polar cell: highest latitude cell, low heat energy, creates polar conditions.
The three cells combine together to form a conveyor belt that moves heat energy from the equator to the poles and controls the wind and rainfall patterns around the world.
How these can combine to form extreme weather is the subject of the next lesson.
Explain how the Hadley cell works and why air sinks at 30 degrees N/S, what this causes (high pressure) and how high solar insolation gives high temperatures, forming an area of dry, warm deserts.
Tropical rainforests
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What is the name of the winds that pull warm air from the Hadley cells to the Ferrel cells?
Starting at the equator, put the climate cells in the correct sequence
Match these terms with the correct definitions
High pressure
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Low pressure
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Hadley cell
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Climate zones
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Global circulation system
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Which direction does air move at the equator?
Describe the climatic conditions of a desert at 30 degrees North or South of the equator (pick 2)
Describe the climatic conditions of a tropical rainforest on or near the equator (pick 2)
Fill in the blanks
circulation system is driven by air rising and cool air sinking. When air sinks, it presses down on the Earth, creating pressure. When it rises it causes pressure and condenses to form .
Put these cells in order of heat content, starting with the warmest
True or false, the cells always stay in exactly the same place?
Which two cells does the UK sit under?