RADIATION
Insolation
intercepted solar radiation
Earth intercepts 0.0000000005 of the sun’s radiation
Solar constant
amount of radiation received at the top
of the atmosphere (on a plane surface
perpendicular to sun’s rays)
= 1372 Watts/m2
(reduced by half by the time it reaches surface of earth)
energy per unit area
amount of energy received at earth’s
surface per unit of area (square meter,
square inch, etc.)
surface receives
more energy per unit
area (more
concentrated) when
the sun’s rays are
vertical (direct)
less energy per unit
area (less concentrated)
when sun’s rays are
oblique (slanted)
Electromagnetic Radiation
• Radiant energy
• Earth, sun, everything! radiates energy
– tropical zones receive more energy
than they radiate
– polar zones radiate more energy than
they receive
– excess heat transfer:
• ocean currents, winds
• Sun’s energy from atomic fusion:
hydrogen atoms fused into helium atoms
– lost mass converted to energy
• Electromagnetic radiation (EMR)
– travels at speed of light
(93 million miles in 8.5 minutes)
– travels in waves
Wavelength: size of wave
electromagnetic spectrum
• “ruler” to measure different types of energy
Solar (Sun) vs. Terrestrial (Earth) Radiation:
• sun’s SHORTWAVE :
– gamma , X-ray, UV, visible, infrared
• earth’s LONGWAVE :
– infrared
Absorption of radiation in the
atmosphere:
• Shortwave absorbers:
• ozone, water vapor
• Longwave absorbers:
• water vapor, carbon dioxide, ozone
• “The atmosphere is relatively
transparent to shortwave radiation and
opaque to longwave radiation”
Types of heat energy
• Sensible heat
• thermometer
• Latent heat
• released or stored in a phase
change
• First Law of Thermodynamics:
• energy cannot be created or destroyed,
but can be:
CONVERTED
TRANSFERRED
Energy Transfer Mechanisms:
• Conduction
• energy transmitted within a substance
by collision of molecules
• Convection
• vertical motion of energy from one place
to another through physical motion of air
Energy Budget/Balance
• Exchange of energy between the sun,
the earth, and the atmosphere
– balance between incoming and
outgoing
• radiation entering the atmosphere can
be:
• absorbed
• transformed, re-emitted
• reflected
• “albedo” : percentage of incoming
radiation that is reflected;
• earth/atmosphere albedo = 31 %
Incoming solar shortwave
radiation
Longwave exchanges between surface,
atmosphere, and space:
The Balancing Act
• 95+48 = 143
• energy leaves
surface as:
– radiation
– latent heat
(evaporation)
– sensible heat
(conduction)
• losses: 114+23+7=
144
Counterradiation by the
atmosphere:
Greenhouse Effect
• atmosphere admits most shortwave;
absorbs and counterradiates longwave
• allows average surface temperature to
be 59oF rather than - 4oF
Review of energy balance
Latitudinal differences in
net radiation
Seasonal and Diurnal (daily)
differences in insolation
Seasonal and Diurnal (daily)
differences in net radiation