ATMOSPHERIC CIRCULATION AND
CLIMATE CHANGE
GCSE SUMMARY
ATMOSPHERIC CIRCULATION
WIND
Wind is the largescale movement of air. It is caused by differences in air pressure, which are
caused by variations in temperature. Winds move from an area of high pressure to an area
of low pressure.
Westerlies – surface winds which blow from 30 degrees north towards the north pole, or
from 30 degrees south towards the south pole.
- In the northern hemisphere: blow SW -> NE
- In the southern hemisphere: blow NW -> SE
Trade winds – surface winds that blow from 30˚ north or 30˚ south towards the equator.
- In the northern hemisphere: blow NE -> SW
- In the southern hemisphere: blow SE -> NW
GLOBAL ATMOSPHERIC CIRCULATION MODEL
The global atmospheric circulation model describes how air circulates between belts of low
pressure and belts of high pressure as a result of differing
conditions at different latitudes. This includes the transfer
of heat via circulation cells.
The cells at the poles are called Polar cells.
The cells between the Polar cells and the Tropics are called
Ferrell cells.
The cells between the tropics and the equator are called
Hadley cells.
Air circulates around the earth following these steps;
(1) The Earth’s surface is warmed by the sun at the equator. The Earth transmits this
heat to the air. The air gets hotter and rises. Rising hot air forms a low pressure, high
rainfall belt at the equator.
(2) Rising air cools and moves away from the equator towards 30˚ north and 30˚ south.
(3) At 30˚ north and 30˚ south, air cools and falls as it is further from the equator. This
causes a high pressure belt with minimal rainfall and little cloud cover.
, (4) Cool air reaches the Earth’s surface and is blown either by westerlies towards the
poles, or by trade winds back towards the equator.
(5) At 60˚ north and 60˚ south, cold air from the poles meets warm air surface winds.
Warm air is less dense, so it rises to from another low pressure belt with high
precipitation.
(6) Here, the air will split again, with some going towards the poles, and some returning
to the equator.
CLIMATE ZONES
ARID
Arid climate zones occur when cool air sinks (where the Hadley and Ferrell cells meet at 30˚
north and where the Polar cells meet at the poles). There is little rain due to high pressure.
TROPICAL
Tropical climate zones occur where the Hadley cells from each hemisphere meet (along the
equator). Air rises causing low pressure which results in high rainfall and high temperatures.
OCEAN CURRENTS
Ocean currents are large scale movements of water which transfer heat from warmer to
cooler areas.
Surface currents – currents on the surface of the water caused by the wind. They transfer
heat from the equator to cooler regions
For example: warm water is transferred from the Caribbean to Europe by the Gulf Stream.
Deep ocean currents – currents caused by differences in water density. They work via a
process called Thermohaline Circulation;
Water freezing in polar regions causes the surrounding water to become saltier
and denser.
The sinking of this dense water lets warm water flow in near the surface. This
warm water will then cool and sink, continuing the cycle.
CLIMATE CHANGE
The global climate has been changing since time began. Currently, we are in the Quaternary
period. It has lasted for the past 2.588 million years. The period before this was the
Neogene period, which lasted for 21.4 million years.
The Neogene period was warmer than the current Quaternary period.
LAST 300,000 YEARS
Over the past 300,000 years, there has been a cycle between interglacial and glacial periods.
Glacial -> cold periods which last for roughly 100,000 years
Interglacial -> periods around 7˚ warmer which last around 8,000-12,000 years
CLIMATE CHANGE
GCSE SUMMARY
ATMOSPHERIC CIRCULATION
WIND
Wind is the largescale movement of air. It is caused by differences in air pressure, which are
caused by variations in temperature. Winds move from an area of high pressure to an area
of low pressure.
Westerlies – surface winds which blow from 30 degrees north towards the north pole, or
from 30 degrees south towards the south pole.
- In the northern hemisphere: blow SW -> NE
- In the southern hemisphere: blow NW -> SE
Trade winds – surface winds that blow from 30˚ north or 30˚ south towards the equator.
- In the northern hemisphere: blow NE -> SW
- In the southern hemisphere: blow SE -> NW
GLOBAL ATMOSPHERIC CIRCULATION MODEL
The global atmospheric circulation model describes how air circulates between belts of low
pressure and belts of high pressure as a result of differing
conditions at different latitudes. This includes the transfer
of heat via circulation cells.
The cells at the poles are called Polar cells.
The cells between the Polar cells and the Tropics are called
Ferrell cells.
The cells between the tropics and the equator are called
Hadley cells.
Air circulates around the earth following these steps;
(1) The Earth’s surface is warmed by the sun at the equator. The Earth transmits this
heat to the air. The air gets hotter and rises. Rising hot air forms a low pressure, high
rainfall belt at the equator.
(2) Rising air cools and moves away from the equator towards 30˚ north and 30˚ south.
(3) At 30˚ north and 30˚ south, air cools and falls as it is further from the equator. This
causes a high pressure belt with minimal rainfall and little cloud cover.
, (4) Cool air reaches the Earth’s surface and is blown either by westerlies towards the
poles, or by trade winds back towards the equator.
(5) At 60˚ north and 60˚ south, cold air from the poles meets warm air surface winds.
Warm air is less dense, so it rises to from another low pressure belt with high
precipitation.
(6) Here, the air will split again, with some going towards the poles, and some returning
to the equator.
CLIMATE ZONES
ARID
Arid climate zones occur when cool air sinks (where the Hadley and Ferrell cells meet at 30˚
north and where the Polar cells meet at the poles). There is little rain due to high pressure.
TROPICAL
Tropical climate zones occur where the Hadley cells from each hemisphere meet (along the
equator). Air rises causing low pressure which results in high rainfall and high temperatures.
OCEAN CURRENTS
Ocean currents are large scale movements of water which transfer heat from warmer to
cooler areas.
Surface currents – currents on the surface of the water caused by the wind. They transfer
heat from the equator to cooler regions
For example: warm water is transferred from the Caribbean to Europe by the Gulf Stream.
Deep ocean currents – currents caused by differences in water density. They work via a
process called Thermohaline Circulation;
Water freezing in polar regions causes the surrounding water to become saltier
and denser.
The sinking of this dense water lets warm water flow in near the surface. This
warm water will then cool and sink, continuing the cycle.
CLIMATE CHANGE
The global climate has been changing since time began. Currently, we are in the Quaternary
period. It has lasted for the past 2.588 million years. The period before this was the
Neogene period, which lasted for 21.4 million years.
The Neogene period was warmer than the current Quaternary period.
LAST 300,000 YEARS
Over the past 300,000 years, there has been a cycle between interglacial and glacial periods.
Glacial -> cold periods which last for roughly 100,000 years
Interglacial -> periods around 7˚ warmer which last around 8,000-12,000 years
