Radiation, Insolation, and
Energy Transfer
Solar Radiation: Sun to Earth
• Speed of light:
300,000 km/second
(186,000 miles/sec.)
• Distance to Earth:
150 million km (93
million miles)
• Radiation reaches us in
about 8.3 minutes
Radiation
• Radiation: energy transferred in
the form of electromagnetic waves
– no transfer of matter
– no material medium needed
Solar Constant =
2 calories/cm2/minute
Classifying Radiation
• Classified based on
wavelength, 
The Electromagnetic Spectrum
Micrometers or microns (µ) = 1/1 000 000 or 0.000 001 or 10-6
Hence Microwaves are about 1mm - long.
Radio waves are about a meter to 1000 meters long.
The sun’s energy distribution:
UV and shorter = 7%
Visible light = 50%
Infrared (IR) = 43%
Insolation
Thermal Infrared, the longest infrared, = heat.
Microwaves (1 mm – 30 cm) are used for long
distance communications.
Radar is portion of microwave. Microwave cooking
discovered on Navy ships. Takes 1/2 the energy of
conduction or convection ovens - more efficient.
Why doesn’t microwave pass through window of
oven?
Gamma - used for food safety. Discovered after
nuclear blasts.
Radiation Laws
• All objects emit radiation.
more radiation
less radiation
• Hot objects emit more radiation
(per unit area) than cold objects.
(Wein’s Law) The hotter the radiating
body,
the shorter the wavelength of
maximum radiation.
Sun: 6000ºC (11,000ºF)
Earth: 15ºC (60ºF)
Getting
through the
atmosphere:
•
•
•
•
•
Transmission
Scattering
Reflection
Absorption
Refraction
Energy pathways
and principles
Direct
radiation
Transmission
Direct
radiation
• Energy is passed through the atmosphere
• Energy/heat provided to the Earth system
Scattering
Scattering
(diffuse radiation)
Backscattering
(albedo)
• Energy “bounces off” particles in the atmosphere.
Scattering
Rayleigh Scattering: selective scattering if dust
is about 1/10 the wavelength of light (.5 micron)
VIB G YOR
4x
1x
Scattering &
light
short  ,
scatter
• result?
1. sun appears yellow as VIB is scattered out.
2. sky is blue: VIB is down-scattered and
becomes prominent.
Mie Scattering: white scattering, non-
selective, occurs with bigger particles,
about 30x the wavelengths of light.
1. salt crystals: things whiter at distance
2. bluer sky at high elevation - less white
3. white clouds.
 distance ,
scatter
• result?
Albedo ()
Reflection
• reflective quality
of a surface
Light color  high 
Dark color  low 
• Energy is bounced directly back
out to space (energy loss to Earth’s system)
Absorption
• ozone
• oxygen
• carbon dioxide
• water vapor
• liquid water / clouds
• Energy is absorbed by the atmosphere or the
surface
• Thermal (heat) energy created.
Refraction
• Change in direction
direction of radiation, by
wavelength, in response
to change in density of
medium.
Refraction
Change in direction
direction of radiation, by
wavelength, in response
to change in density of
medium.
Four Heat Transfer
Mechanisms
•
•
•
•
Conduction
Convection
Adiabatic Cooling and Warming
Latent Heat in Phase Changes of H2O
Conduction
Molecule to molecule energy transfer
When molecules collide, higher energy
molecules excite lower temperature
molecules, thereby transferring kinetic
(heat) energy.
Convection
Heat is transferred by the movement, from
place to place, of a gas or liquid. The
principal motion is vertical. All heated gases
and liquids experience this kind of “mixing”
heat exchange.
Adiabatic Cooling and Warming
When air rises it expands and cools as its pressure is
decreased. Thus, when it descends, it is warmed, as pressure
increases. This change takes place without the addition or
subtraction of energy from another source.
Adiabatic Cooling and
Warming
Phase Changes (Latent Heat)
Ice
Melting
Water
585 calories/gram
Evaporation
Water Vapor
Releases Energy
80 calories/gram
Freezing
Condensation
100 Units Outgoing
100 Units
30 Units
6 Units
64 Units
64 Units
Longwave
3 Ozone
19 direct
absorb
48 Units
6 Units
Conduction/
Convection
22 Latent Heat
14 Units
Greenhouse
Key Points
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•
•
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Electromagnetic radiation and spectrum
Radiation laws and solar radiation
Energy pathways and transfer principles
Earth energy budget