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The Structure of the Atmosphere

Weather can be defined as the state of the atmosphere on a local scale over a
short period of time.
Climate refers to the average atmospheric conditions over a larger time scale and
area. It is often defined as the average weather…

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While atmospheric pressure decreases rapidly with increasing altitude, changes in
temperature are more complex and is divided into 4 main layers:

The zone closest to the Earth and where most weathering takes place.
Exhibits the highest temperatures as radiation from the sun warms the Earth's
surface which then warms…

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Temperature decreases rapidly (similarly to in the troposphere) but this time
to much cooler temperatures of 90°C.
Here there is no water vapour or dust to absorb radiation.
Very strong winds of 3,000 kmph.
Culminates in another isothermal layer called the mesopause.

So named due to the increase…

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Not all radiation that approaches the planet actually reaches the surface.
Absorption of radiation by ozone, water vapour, carbon dioxide, ice particles and
dust reduces the amount that reaches the Earth, as does reflection from clouds.
Some radiation is also reflected back from the Earth itself.
The relationship between…

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This results in major heat transfers:
Horizontal. 80% of heat transferred away from the tropics is carried by winds
in the jet stream (an intense thermal wind in the upper troposphere),
hurricanes and depressions. The remaining 20% is transferred by the
movement of warmer ocean currents towards the poles.

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As the temperature of an air mass is determined by the area over which it
originated and the surfaces over which it has passed, winds blowing in from
the sea tend to be cooler in summer and warmer in winter than winds that
have travelled over land.


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The General Atmospheric Circulation

Winds are caused by differences in air pressure with air moving from areas of high
pressure to areas of low pressure.
Variations in air pressure occur because of changes in temperature and altitude.
Air pressure decreases with increasing height from the surface of the Earth.

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This frictional force is less pronounced than over the surfaces of the smoother
At higher altitudes, frictional forces are reduced and the effect of the pressure
gradient dominates with winds travelling from high to low pressure across the

The TriCellular Model

Differences between the amount of solar radiation…

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The remaining air travels towards the poles.
These winds pick up moisture when they cross the ocean and are responsible for
bring a lot of wet weather.
When these winds meet the colder air of the Arctic at the polar front they rise up to
form the boundary between the…

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Relief rainfall occurs when moist air that has been travelling over the sea is
forced to rise over upland areas.
As it rises and cools, the air reaches dew point (the point where air becomes
saturated) and then condenses which leads to rainfall.
Warmer air can hold more moisture.


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