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Topic 3

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  • 1. Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere The Atmosphere 1 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? 2 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 3 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 36 Air Pressure and Altitude 32 • Pressure decreases as you 28 24 go up in height. Altitude (km) 20 • The change in is pressure 16 12 is not linear. Pressure 8 50% of air below this Height of Mt Everest decreases exponentially 4 altitude with altitude. 0 200 400 600 800 1000 Pressure (mb) 4
  • 2. 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 5 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 500 400 • Air Molecules As gravity pulls gas molecules 300 to the Earths surface an pressure of 100Kpa is exerted Altitude (km) Air Density at sea level 200 • 1013.25mb 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 100 Thermosphere • Troposphere 80 Mesopause • Stratosphere Altitude (km) Mesophere 60 Stratopause • Mesosphere 40 Stratosphere 20 • Thermosphere 0 Tropopause Troposphere 8
  • 3. Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 120 Layers of the atmosphere 100 Thermosphere 0.001mb Mesopause 80 0.01mb • Four layers are Altitude (km) Mesophere 0.1mb 60 defined by trends in Stratopause 1mb average air 40 temperature Stratosphere 10mb 20 100mb Tropopause Troposphere 1000mb 0 -100 -80 -60 -40 -20 0 20 Temperature oC 40 60 9 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 10 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Stratosphere • Contains the ozone layer • Where ultra-violet radiation is absorbed • Protects us from harmful high-energy radiation from the sun • The stratosphere is warmer than the top of the troposphere because of the energy absorbed 11 120 Topic 3: Global Cycles and Physical Systems 100 Thermosphere 0.001mb Mesopause 3.1: The Atmosphere 80 0.01mb Altitude (km) Mesophere Stratosphere 60 0.1mb Stratopause 1mb 40 Warming in the Stratosphere 10mb Stratosphere 20 100mb Tropopause Troposphere 1000mb 0 -100 -80 -60 -40 -20 0 20 40 60 Temperature oC 12
  • 4. 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 13 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 14 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): Man- made compounds used in aerosol sprays, refrigerators and air-conditioners 15 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Mesosphere • Between an altitude of 50 - 85 km • Temperature drops with altitude to about -90oC • Little or no gases, particles or water vapour to absorb UV • This results in no heating taking place 16
  • 5. Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Thermosphere • Extends to the exosphere at about 110km • The upper layer of the mesosphere and the thermosphere are called the ionosphere • Thin layer that contains many ions (charged) • Responsible for the Northern and Southern Lights and the reflection of radio waves 17 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 18 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Lapse Rate • In the troposphere temperature decreases with altitude • 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 • Averaged as the Environmental Lapse Rate (ELR) 19 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 20
  • 6. Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Atmospheric Energy Budget • Sunlight (short wave radiation) • Controls weather and climate • Drives photosynthesis 21 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere ENERGY IN THE ATMOSPHERE Incoming solar Radiation Reflected 107 Solar Radiation Outgoing Longwave Radiation 342 Reflected by Clouds and Atmosphere Emitted by 77 Atmosphere 165 30 Atmospheric window Absorbed by 67 Atmosphere Greenhouse 40 Gases 78 Latent Heat 24 350 Back Radiation Reflected by Surfaces 30 390 168 22 Thermals Absorbed by surfaces Surface Radiation 324 Absorbed back 78 Evapotranspiration Radiation 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 23 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 100% Solar Radiation 6% Reflected by atmosphere 20% reflected 19% absorbed by by the atmosphere clouds and clouds 4% reflected from surfaces 51% absorbed at the surface 24
  • 7. 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 25 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 Solar Radiation • Least solar energy / unit area is at the poles • Most solar energy / unit area is at the equator 26 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Differences in Solar energy across the Earths surface • Albedo effect is the Surface type Albedo (%) balance between a Fresh snow 95 surfaces ability to Dark rock 10 absorb or reflect Desert sand 35 Urban areas 12-18 Grassland and 10-25 forest Dry ploughed fields 10-12 Water 8 27 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 28
  • 8. Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Latent heat flux • Conversion of solid and liquid water into vapour • Needs a large amount of heat energy to break bonds in water • Circulation by the atmosphere • Condensation to rain or snow release stored energy 29 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 30 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Surface heat flux • Energy transfered into tropical oceans from sun • Conversion of solar radiation to heat energy • Conduction and convection transfer heat down water column • Horizontal transfer of warm water (heat) from equator to poles and back again 31 Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 32

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