Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere
The Atmosphere
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere
• How big is the atmosphere? • Why is it cold in Geneva? • Why do mountaineers need oxygen on Everest?
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere
• A relatively thin layer of gas over the Earths surface
• Earth’s radius ~ 6400km • Atmospheric thickness ~ 100km http://www.alpix.com/3d/worldwin/ WW_Atmosphere_1_m.jpg
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 36
Air Pressure and Altitude
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• Pressure decreases as you • The change in is pressure is not linear. Pressure decreases exponentially with altitude.
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Altitude (km)
go up in height.
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20 16 12 8
Height of Mt Everest
50% of air below this altitude
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0
200
400
600
Pressure (mb)
800
1000
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Air Density and Altitude
• Gravity pulls all particles down
• More particles at the
bottom of the air column
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 500
400
Altitude (km)
Air Molecules
•
As gravity pulls gas molecules to the Earths surface an pressure of 100Kpa is exerted at sea level
•
1013.25mb
300
Air Density 200
100
Air Pressure
0 Low
6
High Increasing
Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Layers and Temperature
• The atmosphere can be divided into layers based on temperature characteristics
• The layering creates real physical barriers. • Mixing occurs within layers but not between layers 7
Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 120
Layers of the atmosphere
• • Stratosphere • Mesosphere • Thermosphere
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Troposphere
Thermosphere Mesopause
Altitude (km)
80 Mesophere 60 Stratopause 40 Stratosphere 20 Tropopause Troposphere 0
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 120
Layers of the atmosphere
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Thermosphere 0.001mb Mesopause
Altitude (km)
•
80
Four layers are defined by trends in average air temperature
0.01mb Mesophere 0.1mb
60 Stratopause
1mb
40 Stratosphere 20 Tropopause Troposphere
10mb
100mb 1000mb
0 -100 -80 -60 -40 -20
0
20
40
60
Temperature oC
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Troposphere The habitable layer of the atmosphere
• • • • •
Contains 80% of the atmospheres mass Between 8-16 km deep Deeper at equator than at the poles The part of the atmosphere that contains weather
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Stratosphere
• • •
Contains the ozone layer
•
The stratosphere is warmer than the top of the troposphere because of the energy absorbed
Where ultra-violet radiation is absorbed Protects us from harmful high-energy radiation from the sun
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120
Topic 3: Global Cycles and Physical Systems 100
Thermosphere 0.001mb
Mesopause
Altitude (km)
3.1: 80The Atmosphere
0.01mb
Mesophere
Stratosphere 60
0.1mb
Stratopause
1mb
40 Stratosphere 20 Tropopause Troposphere
10mb
Warming in the Stratosphere
100mb 1000mb
0 -100 -80 -60 -40 -20
0
20
Temperature oC
40
60
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Ozone
• •
Highly reactive molecule oxygen O3 Two types - Stratospheric and Surface ozone O
O
O
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Surface Ozone
•
Result of chemical reactions between a variety of polluting gases
• •
Mainly from vehicle emissions An irritant
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Stratospheric Ozone
• • •
Beneficial - absorbs ultra-violet radiation Protects us from this harmful radiation Gets down by chemical reactions with chlorine containing gases (chlorofluorocarbons – CFCs): Manmade compounds used in aerosol sprays, refrigerators and air-conditioners
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Mesosphere
• • •
Between an altitude of 50 - 85 km
•
This results in no heating taking place
Temperature drops with altitude to about -90oC Little or no gases, particles or water vapour to absorb UV
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Thermosphere
• •
Extends to the exosphere at about 110km
• •
Thin layer that contains many ions (charged)
The upper layer of the mesosphere and the thermosphere are called the ionosphere
Responsible for the Northern and Southern Lights and the reflection of radio waves
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Lapse Rate
• • •
In the troposphere temperature decreases with altitude
•
Averaged as the Environmental Lapse Rate (ELR)
This varies from place to place and season to season The amount of moisture in the air has a large effect on the lapse rate
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Lapse Rate
• • •
ELR is around 6.5oC / 1000m This works for about the first 11 km of atmosphere But the idea that temperature falls in the troposphere is important
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Atmospheric Energy Budget
•
Sunlight (short wave radiation)
• •
Controls weather and climate Drives photosynthesis
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere
ENERGY IN THE ATMOSPHERE Incoming solar Radiation Reflected Solar Radiation
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Outgoing Longwave Radiation
342 Reflected by Clouds and Atmosphere
Emitted by Atmosphere
77
165
Atmospheric window
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Absorbed by
67 Atmosphere 78
Greenhouse Gases
40
Latent Heat
350
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Back Radiation
Reflected by Surfaces
30 168
390
Thermals
Surface Radiation
Absorbed by surfaces
78
Evapotranspiration
324
Absorbed back Radiation
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Energy in the Atmosphere
•
Solar radiation can take several paths within the atmosphere
• • •
30% reflected by the atmosphere 19% absorbed by the atmosphere 51% absorbed by Earth’s surfaces
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 100% Solar Radiation 6% Reflected by atmosphere 20% reflected by clouds
19% absorbed by the atmosphere and clouds
4% reflected from surfaces
51% absorbed at the surface
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Energy in the Atmosphere
•
UV absorption by ozone, water vapour carbon dioxide and dust and ice particles
• •
Reflection by clouds and surfaces The remainder heats up the Earth in the natural greenhouse effect
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Differences in Solar energy across the Earths surface
•
Because of the curve of the Earth different values of solar energy/unit area occur
•
Least solar energy / unit area is at the poles
•
Most solar energy / unit area is at the equator
Solar Radiation
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Differences in Solar energy across the Earths surface
•
Albedo effect is the balance between a surfaces ability to absorb or reflect
Surface type
Albedo (%)
Fresh snow
95
Dark rock
10
Desert sand
35
Urban areas
12-18
Grassland and forest
10-25
Dry ploughed fields 10-12 Water
8
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Latent and Sensible heat
•
Heat is redistributed over the Earths surface by three main processes
• • •
Latent Heat Flux Sensible Heat Flux Surface Heat Flux
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Latent heat flux
• •
Conversion of solid and liquid water into vapour
• •
Circulation by the atmosphere
Needs a large amount of heat energy to break bonds in water
Condensation to rain or snow release stored energy
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Sensible heat flux
•
Transfer of energy from surface to atmosphere by conduction and convection
• • •
Energy moved by advection from tropics to poles Creates atmospheric circulation Moves warm air to poles and cool air to tropics
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Surface heat flux
• • •
Energy transfered into tropical oceans from sun
•
Horizontal transfer of warm water (heat) from equator to poles and back again
Conversion of solar radiation to heat energy Conduction and convection transfer heat down water column
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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere
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