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.
InsolationThe sun’s energy distribution:UV and shorter = 7%Visible light = 50% Infrared (IR) = 43%
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.
• Hot objects emit more radiation (per unit area) than cold objects.
less radiationmore radiation
Rad
iati
on
Law
s(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:
Energy pathways and
principles• Transmission
• Scattering
• Reflection
• Absorption
• Refraction
Transmission
• Energy is passed through the atmosphere• Energy/heat provided to the Earth system
Direct radiation
Direct radiation
Scattering
• Energy “bounces off” particles in the atmosphere.
Backscattering (albedo)Scattering
(diffuse radiation)
ScatteringRayleigh Scattering: selective scattering if dust is about 1/10 the wavelength of light (.5 micron)
VIB G YOR 4x 1x
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 distance2. bluer sky at high elevation - less white 3. white clouds.
distance , scatter
• result?
Scattering & light
short , scatter
• result?
Reflection
• Energy is bounced directly back out to space (energy loss to Earth’s system)
Albedo ()
• reflective quality of a surface
Light color high
Dark color low
Absorption
• Energy is absorbed by the atmosphere or the surface
• Thermal (heat) energy created.
• ozone
• oxygen
• carbon dioxide
• water vapor
• liquid water / clouds
Refraction• Change in direction
direction of radiation, by wavelength, in response to change in density of medium.
RefractionChange in direction
direction of radiation, by wavelength, in response to change in density of medium.
• Conduction
• Convection
• Adiabatic Cooling and Warming
• Latent Heat in Phase Changes of H2O
Four Heat Transfer Mechanisms
Molecule to molecule energy transfer
When molecules collide, higher energy molecules excite lower temperature molecules, thereby transferring kinetic (heat) energy.
Conduction
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.
Convection
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
Adiabatic Cooling and Warming
Ice80 calories/gram
Water
585 calories/gram
Water Vapor
Phase Changes (Latent Heat)
Rele
ase
s En
erg
ySto
res E
nerg
y
Freezing
Condensation
Melting
Evaporation
Su
bli
mat
ion S
ub
lima tio n
30 Units
64 Units Longwave
22 Latent Heat
6 Units
48 Units
64 Units
14 Units Greenhouse
6 Units Conduction/Convection
19 direct absorb
3 Ozone
100 Units
100 Units Outgoing
Key Points• Electromagnetic radiation and spectrum
• Radiation laws and solar radiation
• Energy pathways and transfer principles
• Earth energy budget
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