Chapter 2: The global ledger of radiation and heat PROPERTIES OF - - PowerPoint PPT Presentation

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Chapter 2: The global ledger of radiation and heat PROPERTIES OF - - PowerPoint PPT Presentation

Aug 14, 2023 628 likes •986 views

Chapter 2: The global ledger of radiation and heat PROPERTIES OF RADIATION Everything radiatesat all wavelengths ! This includes the Sun, Earth, a candy bar, even us Fortunately, most objects dont radiate a lot of X-rays, gamma

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Chapter 2: The global ledger of radiation and heat

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Everything radiates…at all wavelengths!

 This includes the Sun, Earth, a candy bar, even us  Fortunately, most objects don’t radiate a lot of X-rays, gamma rays, etc...

PROPERTIES OF RADIATION

 However, different objects:

 Emit different amounts of radiation, and….  Emit their maximum radiation at different wavelengths  (don’t confuse these two differences)

 So what’s the determining factor?

 TEMPERATURE!

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 2 EASY RULES:

 1. The higher the temperature, the more radiation an object will emit (Stephan-Boltzman Law) 2. Higher temperature result in radiation being concentrated at shorter wavelength (Wien’s Law)

PROPERTIES OF RADIATION

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Radiation Energy Transfer by Electromagnetic Waves

WAVELENGTH FREQUENCY

RED VIOLET IR

UV

Electromagnetic Spectrum ENERGY

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  Sun: 10,000°F (solar, shortwave

radiation)  1. lots of radiation;  2. peak radiation in visible range

 Earth: 60°F (terrestrial, longwave

radiation)  1. some (but much less) radiation;  2. peak radiation in infrared range

PROPERTIES OF RADIATION

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LOWER HIGHER

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“Transparency” of the atmosphere by wavelength and atmospheric “windows”

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SOLAR RADIATION & GEOMETRY

  • Not all parts of Earth receive the same

amounts of radiation. Why?

  • TILT of our planet, 23.5
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SOLAR RADIATION AND TILT

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SOLAR RADIATION AND TILT

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EARTH’S SEASONS

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LAND OF THE MIDNIGHT SUN

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Mechanisms of Energy Transfer (Heating):

(Heat describes energy flow from hot -> cold, not amount of energy and object has) Conduction: Transfer of kinetic or vibrational energy by direct molecular

  • collisions. What could maximize

conduction efficiency? Convection: Spontaneous transfer of thermal energy by turbulent mixing in

  • fluids. What conditions might

maximize convection? Radiation: Transfer of energy by electromagnetic waves. Only mechanism that doesn’t need a medium for transfer. What could prevent radiative transfer?

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?

How does direct radiation from the sun warm a cup of water (PS 2) ?

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T mc Q

a) (power/are density radiation solar incoming

2

m W A P

Q(in J)=Total Energy= Power x time x area P( in W) = Power = Energy / time

1

A t A P Q c m A t A P T

1

Simple Thermodynamic Relationships

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Assumptions in calculating Temp. warming:

  • No significant net heat lost by conduction, convection, or radiation

(this is BS except for rare special circumstances)

  • All incident solar radiation is absorbed
  • Uniform temperature of object
  • Perfect styrofoam insulator

Typical Heat Capacities:

Substance J/kg/oC

  • r J/kg/K

cal/g/oC

  • r cal/g/K

Water (0 oC to 100 oC) 4186 1.000 Methyl Alcohol 2549 0.609 Ice (-10 oC to 0 oC) 2093 0.500 Steam (100 oC) 2009 0.480 Benzene 1750 0.418 Wood (typical) 1674 0.400 Soil (typical) 1046 0.250 Air (50 oC) 1046 0.250 Aluminum 900 0.215 Marble 858 0.205 Glass (typical) 837 0.200 Iron/Steel 452 0.108 Copper 387 0.0924 Silver 236 0.0564 Mercury 138 0.0330 Gold 130 0.0310 Lead 128 0.0305

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EARTH’S ENERGY BUDGET

  • Energy from the Sun reaches the top of Earth’s

atmosphere

  • Does all of it reach the surface?
  • NO
  • For example Ozone (O3) absorbs UV
  • Clouds and gases scatter, absorb, reflect other types
  • f radiation
  • Still, a lot of radiation (energy) reaches the surface of
  • ur planet.
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EQUATOR

SOUTH POLE NORTH POLE

Most of the incoming solar radiation is absorbed at the Tropics

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TERRESTRIAL RADIATION

 Amount of terrestrial radiation emitted from Earth’s

surface and atmosphere is dependent on temperature

 More terrestrial radiation emitted near equator (warmer)  Less terrestrial radiation emitted near poles (colder)

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EQUATOR

SOUTH POLE NORTH POLE

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Earth’s Annual Energy Budget

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EARTH’S ENERGY BUDGET

 Because of the differences in

incoming/outgoing radiation on the Earth, we have an energy imbalance between the polar regions and the Tropics.

 So… winds and ocean currents exist to

transport heat from the equator to the poles.

TO CREATE AN ENERGY BALANCE

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EQUATOR

SOUTH POLE NORTH POLE

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Average Emitted infrared radiation

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Incoming solar radiation for August

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Solar radiation absorbed yesterday

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August solar radiation absorbed by surface

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Sea Surface Temperatures

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Sea Surface Temperature Anomaly

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