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Physical GeographyPhysical Geographyby Alan Arbogastby Alan Arbogast

Chapter 4Chapter 4

The Global Energy System

Lawrence McGlinnDepartment of GeographyState University of New York - New Paltz

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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

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The Electromagnetic SpectrumThe Electromagnetic Spectrum

• Radiation – Electromagnetic (EM) energy transmitted as a wave

• Wavelength

• Amplitude

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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-

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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

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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

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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.

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Atmospheric CompositionAtmospheric Composition

• Constant Gases

- Always present in same proportion

- N2 O2 Ar

• Variable Gases -Differ from place

to place

- CO2 O3 H2O

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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

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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

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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

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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

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Ozone Depletion ProcessOzone Depletion Process

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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

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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

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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

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Solar Radiation through AtmosphereSolar Radiation through Atmosphere

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Solar Radiation and Earth’s SurfaceSolar Radiation and Earth’s Surface

• Either:

1. Absorbed, 96%

or

2. Reflected, 4%, depending on surface albedo

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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

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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

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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

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Global Radiation BudgetGlobal Radiation Budget

• Balance between incoming and outgoing on Earth

• Net Radiation – difference between incoming and outgoing radiation

Global Energy Budget

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Global Radiation BudgetGlobal Radiation Budget• Over time, global radiation budget is balanced

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Global Radiation BudgetGlobal Radiation Budget• Major variations in net radiation by latitude• Surplus vs. Deficit

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Global Radiation BudgetGlobal Radiation Budget• Seasonal variation in net radiation

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Daily InsolationDaily Insolation•Yearly pattern •Variation by latitude