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Earth’s Global Energy Balance Overview

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Presentation on theme: "Earth’s Global Energy Balance Overview"— Presentation transcript:

1 Earth’s Global Energy Balance Overview
Electromagnetic Radiation Radiation and temperature Solar Radiation Longwave radiation from the Earth Global radiation balance Geographic Variations in Energy Flow Insolation over the globe Net radiation, latitude and energy balance Sensible and latent heat transfer

2 Overview The global energy system
Solar energy losses in the atmosphere Albedo Counterradiation and the greenhouse effect Global energy budgets of the atmosphere & surface Climate & global change

3 What is light? Newton showed that white light is composed of all the colors of the rainbow.

4 Light is an Electromagnetic Wave & a Particle
Photons: “pieces” of light, each with precise wavelength, frequency, and energy. Our eyes recognize frequency (or wavelength) as color! Use this slide to define wavelength, frequency, speed of light.

5 Photons Photons – are little packets of energy.
The energy carried by each photon depends on its frequency (color) Blue light carries more energy per photon than red light.

6 Electromagnetic Spectrum

7 Electromagnetic Radiation
Energy constantly emitted from every surface Can be in many different forms, e.g. light or heat

8 What happens when light gets absorbed?

9 What causes the atmosphere to be opaque?

10 Solar Radiation Shortwave Radiation from Sun (dark purple)
Absorption of UV by O3 Absorption by CO2 and water vapor (H2O↑) shown as valleys Longwave Radiation from Earth (dark red) Much absorbed by CO2 & H2O↑

11 Scattering Solar radiation can be scattered by atmosphere
Deflected off a molecule, cloud droplet, or particle May go up toward space, or down toward Earth Scattering most prevalent in blue wavelengths Thus, clear, blue skies Some solar radiation goes directly to surface Called transmission Solar radiation arrives as 0.3μm to 3μm wavelengths This is shortwave radiation

12 Remember you live on a rotating sphere

13 Geographic Variation in Solar Energy
Insolation – Incoming solar radiation More intense where sun angle is highest Less intense with lower sun angle Same energy spread over a larger area

14 Insolation Daily insolation – avg radiation total in 24 hours
Depends on : Sun angle – higher sun angle → greater insolation Length of day – higher latitudes get long summer days Annual insolation – avg radiation total for year Also depends on sun angle and length of day Both of these determined by latitude So, latitude determines annual insolation

15 Net Radiation Energy not usually balanced at any location
Net Radiation - Difference between incoming and outgoing radiation Between 40°N and 40°S, incoming > outgoing Creates energy surplus Poleward of 40°N & S, outgoing > incoming Creates energy deficit Deficit = Surplus, so net radiation for Earth = 0

16 Poleward Heat Transport
Surplus energy moves toward poles (deficit regions) Carried by: Warm, moist air Warm sea water Tropical cyclones Poleward heat transport is driving force behind: Global atmospheric circulation Weather systems Ocean currents

17 Why are there seasons? The Earth is tilted 23.5° from it orbital plane
Combine tilt with orbit Northern hemisphere gets more direct Sun part of year (northern summer) Southern hemisphere gets more direct Sun part of year (northern winter) Tilt & orbit create seasons, not distance to Sun

18 Northern Summer

19 Northern Winter

20 Solstices & Equinoxes

21 Path of the Sun in the Sky
40° North June solstice: Sun rises north of east & sets north of west Peaks at 73.5° above horizon at noon 15 hours of daylight Highest daily insolation of year

22 Path of the Sun in the Sky (40° North)
Date Noon Sun Angle Daylight Daily Insolation June Solstice 73.5° 15 hrs 460 W/m2 Dec. Solstice 26.5° 9 hrs 160 W/m2 Equinoxes 50° 12 hrs 350 W/m2

23 Path of the Sun in the Sky (Equator)
Date Noon Sun Angle Daylight Daily Insolation June Solstice 66.5° 12 hrs ~400 W/m2 Dec. Solstice Equinoxes 90° 440 W/m2

24 Path of the Sun in the Sky (North Pole)
Date Noon Sun Angle Daylight Daily Insolation June Solstice 23.5° 24 hrs 500 W/m2 Dec. Solstice No Sun 0 hrs 0 W/m2 Equinoxes Horizon 12 hrs ~0 W/m2

25 Daily Insolation through the Year
Yearly change in insolation greatest toward poles In Arctic & Antarctic Circles, Sun is below horizon part of year At Equator, 2 maxs & 2 mins for daily insolation At equinoxes & solstices Between tropics, also 2 maxs & 2 mins per year Yearly insolation change important to climate Insolation at equinox

26 Annual Insolation by Latitude
Tilted Earth shown as red line Equator greatest annual insolation Considerable insolation at highest latitudes Untilted Earth (blue line) Highest latitudes little insolation Big changes in climate Very cold pole Massive poleward heat transport

27 Heat Transfer: Surplus energy is transported in two forms
Sensible Heat – can be felt & measured Transferred by conduction (touching surface) Transferred by convection (carried by rising air) Example: Moving air masses Latent Heat – cannot be felt or measured Stored as molecular motion when water changes phase Absorbed in evaporation, melting, and sublimation Released in condensation, freezing, and deposition Very important form of heat transfer over long distances Example: Storm systems, hurricanes Conduction Convection Latent heat absorbed in evaporation

28 Solar energy losses in the atmosphere
Scattering due to: Gas molecules Dust or other particles O2, O3, & H2O↑ most important absorbers of insolation Global avg – 49% of insolation makes it to surface

29 Once at the surface what happens? Albedo
Proportion of shortwave radiation reflected Shown as a proportion (0-1) Examples: Snowfield Black pavement 0.03 Clouds Water (calm, high angle 0.02), (low angle 0.80) Avg for Earth and atmosphere

30 So what happens to all the energy absorbed by these various processes?
Counterradiation – heat absorbed by atmosphere reflected down to surface A – energy radiated to space from surface B – energy from surface absorbed by atmosphere C – energy radiated to space from atmosphere D – Counterradiation

31 Part of Counterradiation is the “Greenhouse Effect”
Longwave radiation absorbed & re-radiated to surface by atmosphere Lower atmosphere acts like blanket

32 Global Energy Budget Energy balanced for each level: surface, atmosphere, & space

33 Climate & Global Change
Quantifying human impacts on climate difficult Climate and society have complex relationship e.g., Industrial processes add CO2 to atmosphere (warming) add aerosols to atmosphere (cooling)

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