- Climate System. Where is the energy driving the Earth's atmospheric
circulation and ocean currents derived originally from?
- A significant process of atmosphere heat transfer is radiation -- the
transfer of energy by means of electromagnetic waves.
- Absolute zero:
Temperature of - 273.15 degrees
Celsius. At this temperature
atomic motion stops.
- All objects with a temperature above absolution zero emit radiation at
a rate proportional to the fourth power of their absolute temperature.
- The higher an object's temperature, the greater the amount of
radiation emitted per unit surface area and the shorter the wavelength of
maximum emission.
- Visible light has wavelengths between 0.4 and 0.8 micrometer, and
dominates solar radiation output.
- The sun behaves as a blackbody, which can be defined as any object
which both absorbs and emits radiation with maximum efficiency.
- The earth's surface behaves as a blackbody, making it a much better
absorber and emitter of radiation than the atmosphere. (This latter
part will be explained further in next lecture.)
- The energy output of any blackbody radiator can be calculated from its
temperature using the Stefan-Boltzmann Law (i.e., page 36 in Ahrens'
book) .
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- Solar constant -- At the top of the atmosphere, solar energy received
on a surface perpendicular to the sun's rays appears to remain fairly
constant at nearly two calories on each square centimeters each minute or
1367 Watts per square meter -- a value called the solar constant. [Note
that solar "constant" changes with time, see Figure 19.15, pages 534-535
in Ahrens' book. Solar constant varies by only about 0.1% over an 11-year
sunspot cycle.]
- Planetary albedo -- the Earth and its atmosphere behave like a partial
mirror, and reflect about 31% of the incoming solar radiation back to
space. This amount is termed the planetary albedo.
- Whereas the hot sun emits the majority of its radiation between at
wavelengths less than 2 μm [with maximum radiation near 0.5 μm], the relatively cool earth emits almost all of its
energy at wavelengths between about 5-25 μm [with maximum radiation near
10 μm].
- The earth absorbs solar radiation only during the daylight hours;
however, it emits infrared radiation continuously, both during the day and
at night.
- Over the earth as a whole, outgoing infrared energy equals incoming
solar energy. [Also called radiative equilibrium]
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