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© 2007, John Wiley and Sons, Inc.
Physical GeographyPhysical Geographyby Alan Arbogastby Alan Arbogast
Chapter 4Chapter 4
The Global Energy System
Lawrence McGlinnDepartment of GeographyState University of New York - New Paltz
© 2007, John Wiley and Sons, Inc.
The Global Energy SystemThe Global Energy System
• The Electromagnetic Spectrum and Solar Energy
• Composition of the Atmosphere
• The Flow of Radiation on Earth
• The Global Radiation Budget
© 2007, John Wiley and Sons, Inc.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
• Radiation – Electromagnetic (EM) energy transmitted as a wave
• Wavelength
• Amplitude
© 2007, John Wiley and Sons, Inc.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
• The entire wavelength range of EM energy
Electromagnetic Spectrum
The Electromagnetic The Electromagnetic SpectrumSpectrum
• Sun radiates shortwave energy
• Shorter wavelengths have higher energy
• Earth radiates re-radiates longwave energy
• Solar Radiation-
• Terrestrial Radiation-
• Electromagnetic Spectrum-
© 2007, John Wiley and Sons, Inc.
Shortwave RadiationShortwave Radiation
• Emitted by “hot” objects, i.e. the Sun, 6000ºC surface temperature
• Gamma radiation, X-rays, Ultraviolet, Visible light and Near-infrared
• Hot objects emit much more radiation than cooler objects
© 2007, John Wiley and Sons, Inc.
Longwave RadiationLongwave Radiation
• Emitted by “cool” objects, i.e. those on Earth’s surface, even objects hot to the touch, or too hot to touch
• Avg temp of Earths surface 16ºC
• Thermal infrared wavelength
InsolationInsolation• Incoming solar radiation
• A measure of solar radiation (power) received per unit area at a given time
• Contains all of the various wavelengths of energy from the Sun
• Average of 1372 W/m^2 (watts per meter squared) at outer surface of Earth’s atmosphere
• Max: 1412 W/m^2 in January
• Min: 1321 W/m^2 in July
• Average of 250 W/m^2 at surface
Distribution of InsolationDistribution of Insolation
• Tropics receive more concentrated insolation due to the Earth’s curvature
• Tropics receive 2.5x more than poles
• Why is this the case??
– The subsolar point
Angle and distance through atmosphere
© 2007, John Wiley and Sons, Inc.
Earth’s AtmosphereEarth’s Atmosphere
• Medium solar energy passes through• Unique in solar system – provides O2 and
CO2 for respiration and photosynthesis• Shields Earth from UV radiation• Flows like a liquid with currents and eddies• 3 Basic components : constant gases,
variable gases, and particulates.
© 2007, John Wiley and Sons, Inc.
Atmospheric CompositionAtmospheric Composition
• Constant Gases
- Always present in same proportion
- N2 O2 Ar
• Variable Gases -Differ from place
to place
- CO2 O3 H2O
© 2007, John Wiley and Sons, Inc.
Water Vapor (HWater Vapor (H22OO↑)↑)
• Least over deserts, most over tropical forests
• Absorbs and stores heat from Sun and from surface – Greenhouse Effect
• Warmer air can hold more water vapor
• Sticky or muggy air has a great deal of water vapor
© 2007, John Wiley and Sons, Inc.
Carbon Dioxide (COCarbon Dioxide (CO22))
• 368 parts per million (ppm) in atmosphere
• Absorbed by plants which release oxygen
• Significant contributor to greenhouse effect
• Steady increase in atmosphere since mid-1800s
• 50 ppm increase in atmosphere since 1958
© 2007, John Wiley and Sons, Inc.
Greenhouse EffectGreenhouse Effect
• The process through which the atmosphere traps longwave radiation
• Regulates Earth’s temperature
• Enhanced by higher levels of CO2 and other greenhouse gases
The Greenhouse Effect and The Greenhouse Effect and Atmospheric WarmingAtmospheric Warming
• Atmosphere absorbs heat energy
• A real greenhouse traps heat inside
• Atmosphere delays transfer of heat from Earth into space
© 2007, John Wiley and Sons, Inc.
Ozone (OOzone (O33))• Combination of free oxygen
atom and O2 molecule
• Forms in two layers:
1. Upper atmosphere - ozone layer, natural, absorbs UV radiation
2. Surface – respiratory irritant from industrial and automobile gases in urban areas
© 2007, John Wiley and Sons, Inc.
Ozone DepletionOzone Depletion
• Refrigerant CFC reacts with ozone, producing simple oxygen (O2)
• More UV radiation passes through layer, harming aquatic life, vegetation, and human skin (cancer)
• Depletion most severe over high latitudes, especially Antarctica
• Montreal Protocol of 1987 – CFC phase out
• Ozone depletion appears to be slowly easing
© 2007, John Wiley and Sons, Inc.
Heat TransferHeat Transfer
• Heat – energy of motion of molecules and atoms in a substance
• 3 ways to transfer heat:
1. Radiation – electromagnetic waves
2. Conduction – substances in contact
3. Convection – upward movement of warm air or liquid
© 2007, John Wiley and Sons, Inc.
Solar Radiation through AtmosphereSolar Radiation through Atmosphere
• Absorption – gases and particulates interrupt solar radiation, gain heat
• Reflection – radiation returns to space
• Scattering – redirection & deflection of radiation
When shining a light at an object, it can When shining a light at an object, it can illustrate the three options that radiation illustrate the three options that radiation
hashas
© 2007, John Wiley and Sons, Inc.
Solar Radiation through AtmosphereSolar Radiation through Atmosphere
• Direct radiation - direct from Sun to Earth’s surface – average <30% of solar radiation
• Over 70% of solar radiation absorbed, reflected, or scattered by atmosphere
• Indirect radiation - approx 20% of solar radiation reflected or scattered makes it to Earth’s surface
© 2007, John Wiley and Sons, Inc.
Solar Radiation through AtmosphereSolar Radiation through Atmosphere
© 2007, John Wiley and Sons, Inc.
Solar Radiation and Earth’s SurfaceSolar Radiation and Earth’s Surface
• Either:
1. Absorbed, 96%
or
2. Reflected, 4%, depending on surface albedo
© 2007, John Wiley and Sons, Inc.
Absorbed RadiationAbsorbed Radiation
• Stored in Earth’s land and water surfaces as sensible heat which can be felt & measured
• Stored heat can be released from surface by:• Radiation to atmosphere or to space• Conduction to atmosphere• Evaporation/latent heat to atmosphere
Why is the albedo of a forest so low, relatively?
A. Its surfaces, in general, are relatively dark.B. It needs to absorb energy for photosynthesis.C. It is trying to reflect as much radiation as possible.D. Both A and B.E. Answers A, B, and C are all correct.
Answer: D
© 2007, John Wiley and Sons, Inc.
Evaporation/Latent HeatEvaporation/Latent Heat
• Liquid water → Water vapor (gas)
• Latent heat
• Heat absorbed in evaporation
• Breaks molecular bonds of liquid
• Cannot be felt or measured
• Released when condensation occurs
© 2007, John Wiley and Sons, Inc.
Reflected RadiationReflected Radiation
• Depends on surface albedo and angle of incidence • Albedo – reflectance of a surface
• Low albedo (closer to 0%) – dark surfaces• High albedo (closer to 100%) – light surfaces
• Angle of incidence - Sun angle• High (closer to 90 degrees) – little reflectance• Low (closer to 0 degrees) – high reflectance, esp. water
Angle of Incidence
© 2007, John Wiley and Sons, Inc.
Global Radiation BudgetGlobal Radiation Budget
• Balance between incoming and outgoing on Earth
• Net Radiation – difference between incoming and outgoing radiation
Global Energy Budget
© 2007, John Wiley and Sons, Inc.
Global Radiation BudgetGlobal Radiation Budget• Over time, global radiation budget is balanced
© 2007, John Wiley and Sons, Inc.
Global Radiation BudgetGlobal Radiation Budget• Major variations in net radiation by latitude• Surplus vs. Deficit
© 2007, John Wiley and Sons, Inc.
Global Radiation BudgetGlobal Radiation Budget• Seasonal variation in net radiation