3.3.1 Global atmospheric circulation
Definitions of weather and climate; the structure and composition of the atmosphere and
the role different gases play in climate
Weather: the short-term state of the atmosphere, including temperature, atmospheric
pressure, wind, humidity, precipitation, and cloud cover
Climate: the long-term pattern of weather in a particular area. Weather is tracked for at
least 30 years.
Structure and composition of the atmosphere
The atmosphere can be divided into 5 distinct layers (lowest layer to highest layer):
o Troposphere
o Stratosphere
o Mesosphere
o Thermosphere
o Exosphere
Troposphere · Contains 90% of the Earth’s air – where weather occurs
· Extends 7-20km above sea level from Earth’s surface(widest at the
equator and narrowest at the poles)
· Air pressure and density decreases as you travel higher through the
troposphere
· Temperature gradient (15ºC to -57ºC: warmest ground level and the
coolest at the tropopause)
o Tropopause: the boundary between the troposphere and
the stratosphere)
What determines the height of the troposphere
· Depends on the latitude, season, day or night
· Near the equator – the troposphere is about 20km above sea level
· In winter, the tropopause is much lower near the poles
Winds and the troposphere
· Troposphere is heated from below
· Solar radiation warms the grounds and ocean → radiates heat back
into the air above → Warm air rises → convection, updrafts and
downdrafts mix the air.
· Due to uneven heating of the various regions of the troposphere by
the sun (warmest at the equator, coolest at the poles) convection
currents are produced = large-scale wind patterns that distribute
heat and moisture around the earth
· Earth’s rotation causes the air to be deflected since it moves from
the poles to the equator → causes belts of surface winds to move
from east and west in tropical and polar regions, and from west to
east in the mid latitude
· Jet streams form below here (400km/h)
,Stratosphere · Second layer of the atmosphere extends from the troposphere to an
altitude of about 50km
· At the equator, bottom is around 16km ; 10km in the mid-latitudes ;
8km at the poles
· Slightly lower in winter at mid and high latitudes, slightly higher in
summer
· Boundary between the stratosphere and the mesosphere is the
stratopause
· Area is very dry – the air contains little water vapour → few clouds
Mesosphere · Sits above the stratosphere and extends 50km above the Earth’s
surface to an altitude of 85km (ends at mesopause – boundary
between this layer and the thermosphere)
· Temperature gets colder as altitude increases
· Top of the mesosphere is the coldest part of the Earth’s atmosphere
and can be as low as -120ºC
· Temperature here is very low and air is very thin
Thermosphere · Lies directly above the mesosphere, extends from 90km to between
500 and 1000km in altitude
· Temperature in the upper thermosphere can range from 500ºC to
2000ºC
· Air would still feel cold because the hot gas particles (oxygen,
hydrogen, helium) are so far apart
Exosphere · Top layer of the atmosphere → extends to an altitude of 1000km
above Earth
· Contains very atmosphere particles → atoms molecules escape into
space
· Hydrogen and helium are the main components, present in
extremely low densities
· Area where many satellites orbit earth
Composition of atmosphere:
,The general circulation of the atmosphere, and ocean circulation, redistributes heat
energy across the planet and influences the locations of high and low pressure areas
Global atmospheric circulation:
· In the atmosphere above the earth, air masses circulate around the globe
· This circulation occurs in ‘cells’
· The different cells help to determine the climate and winds at different
latitudes
· Atmospheric circulation is the basis for our everyday weather, and it is driven
by the sun
· The circulation of the atmosphere, and ocean, redistributes heat energy
across the planet
Sun’s ray
· The sun’s rays are most direct and are concentrated over a smaller area
· Sunlight is also known as insolation (incoming solar radiation)
· So, the equator heats up more than other latitudes further north or south
· There are therefore hot climates at the equator
, What affects the distribution of heat energy?
Curvature of the Insolation at the Arctic Circle is stretched and therefore
Earth
weaker
Thickness of the The further from the equator, the greater the amount of
Earth atmosphere the radiation has to penetrate
Therefore more heat is lost through scattering, absorption,
reflection etc
Albedo The poles have a high albedo, due to the ice caps being
light/white in colour
Tilt of earth - As the earth tilts on its axis, the angle of the sun’s rays
seasonal changes throughout the year
The sun is directly over the equator at the equinoxes (this
means a peak of insolation at the equator)
June 21st the sun is over the Tropic of Cancer and December
21st over the Tropic of Capricorn
Definitions of weather and climate; the structure and composition of the atmosphere and
the role different gases play in climate
Weather: the short-term state of the atmosphere, including temperature, atmospheric
pressure, wind, humidity, precipitation, and cloud cover
Climate: the long-term pattern of weather in a particular area. Weather is tracked for at
least 30 years.
Structure and composition of the atmosphere
The atmosphere can be divided into 5 distinct layers (lowest layer to highest layer):
o Troposphere
o Stratosphere
o Mesosphere
o Thermosphere
o Exosphere
Troposphere · Contains 90% of the Earth’s air – where weather occurs
· Extends 7-20km above sea level from Earth’s surface(widest at the
equator and narrowest at the poles)
· Air pressure and density decreases as you travel higher through the
troposphere
· Temperature gradient (15ºC to -57ºC: warmest ground level and the
coolest at the tropopause)
o Tropopause: the boundary between the troposphere and
the stratosphere)
What determines the height of the troposphere
· Depends on the latitude, season, day or night
· Near the equator – the troposphere is about 20km above sea level
· In winter, the tropopause is much lower near the poles
Winds and the troposphere
· Troposphere is heated from below
· Solar radiation warms the grounds and ocean → radiates heat back
into the air above → Warm air rises → convection, updrafts and
downdrafts mix the air.
· Due to uneven heating of the various regions of the troposphere by
the sun (warmest at the equator, coolest at the poles) convection
currents are produced = large-scale wind patterns that distribute
heat and moisture around the earth
· Earth’s rotation causes the air to be deflected since it moves from
the poles to the equator → causes belts of surface winds to move
from east and west in tropical and polar regions, and from west to
east in the mid latitude
· Jet streams form below here (400km/h)
,Stratosphere · Second layer of the atmosphere extends from the troposphere to an
altitude of about 50km
· At the equator, bottom is around 16km ; 10km in the mid-latitudes ;
8km at the poles
· Slightly lower in winter at mid and high latitudes, slightly higher in
summer
· Boundary between the stratosphere and the mesosphere is the
stratopause
· Area is very dry – the air contains little water vapour → few clouds
Mesosphere · Sits above the stratosphere and extends 50km above the Earth’s
surface to an altitude of 85km (ends at mesopause – boundary
between this layer and the thermosphere)
· Temperature gets colder as altitude increases
· Top of the mesosphere is the coldest part of the Earth’s atmosphere
and can be as low as -120ºC
· Temperature here is very low and air is very thin
Thermosphere · Lies directly above the mesosphere, extends from 90km to between
500 and 1000km in altitude
· Temperature in the upper thermosphere can range from 500ºC to
2000ºC
· Air would still feel cold because the hot gas particles (oxygen,
hydrogen, helium) are so far apart
Exosphere · Top layer of the atmosphere → extends to an altitude of 1000km
above Earth
· Contains very atmosphere particles → atoms molecules escape into
space
· Hydrogen and helium are the main components, present in
extremely low densities
· Area where many satellites orbit earth
Composition of atmosphere:
,The general circulation of the atmosphere, and ocean circulation, redistributes heat
energy across the planet and influences the locations of high and low pressure areas
Global atmospheric circulation:
· In the atmosphere above the earth, air masses circulate around the globe
· This circulation occurs in ‘cells’
· The different cells help to determine the climate and winds at different
latitudes
· Atmospheric circulation is the basis for our everyday weather, and it is driven
by the sun
· The circulation of the atmosphere, and ocean, redistributes heat energy
across the planet
Sun’s ray
· The sun’s rays are most direct and are concentrated over a smaller area
· Sunlight is also known as insolation (incoming solar radiation)
· So, the equator heats up more than other latitudes further north or south
· There are therefore hot climates at the equator
, What affects the distribution of heat energy?
Curvature of the Insolation at the Arctic Circle is stretched and therefore
Earth
weaker
Thickness of the The further from the equator, the greater the amount of
Earth atmosphere the radiation has to penetrate
Therefore more heat is lost through scattering, absorption,
reflection etc
Albedo The poles have a high albedo, due to the ice caps being
light/white in colour
Tilt of earth - As the earth tilts on its axis, the angle of the sun’s rays
seasonal changes throughout the year
The sun is directly over the equator at the equinoxes (this
means a peak of insolation at the equator)
June 21st the sun is over the Tropic of Cancer and December
21st over the Tropic of Capricorn
