Uploaded by johnny black

The Global Energy Balance 2.1

advertisement
The Global
Energy Balance
A. Ismail Jolboldin
B. 20212001
PLANETARY EMISSION TEMPERATURE
• Sun emits energy at a rate of Q = 3.87 × 1026 W
• The flux of solar energy at the Earth, called the solar constant depends on the distance of the Earth from
the Sun, r, and is given by the inverse square law, S0 = Q/4πr2.
• The way radiation interacts with
an
atmosphere depends on the
wavelength as
well as the intensity of the
radiative flux.
• Sun emits radiation that is primarily in the
visible part of the spectrum, energy flux
decreasing toward longer (infrared, IR) and
shorter (ultraviolet, UV) wavelengths.
Why does the spectrum have this
pattern?
• Such behavior is characteristic of the
radiation emitted by incandescent
material, as can be observed for example
in a coal fire.
• The hottest parts of the fire are almost
white and emit the most intense radiation,
with a wavelength that is shorter than that
coming from the warm parts of the fire,
which glow red.
• Incandescence is a natural phenomenon in which a hot object emits electromagnetic
radiation, including visible light, due to its high temperature. This process occurs
because as an object gets hotter, the thermal energy of its atoms and molecules
increases. When this thermal energy reaches a certain level, it causes the electrons
within the atoms to become excited and move to higher energy levels.
• As these excited electrons return to their lower energy levels, they release energy in the
form of photons, which are packets of electromagnetic radiation. The energy of these
photons can fall within the visible light spectrum, and this is what we perceive as
incandescent light. The specific color and intensity of the emitted light depend on the
temperature of the object.
Why does the spectrum have this
pattern?
• Experiment and theory show that the wavelength
at which the intensity of radiation is maximum,
and the flux of emitted radiation, depend only on
the temperature of the source.
Note that the hotter the radiating body, the more energy it
emits at shorter wavelengths.
Flux: refers to the flow or transfer of a quantity through a surface, a unit area, or a unit volum
Blackbody: which is an idealized substance that absorbs all incident radiation and
emits radiation across a continuous range of wavelengths or frequencies.
Albedo
The ratio of
reflected to incident solar energy is called
the albedo,
-In equilibrium, the total terrestrial flux
radiated to space must balance the solar
radiation absorbed by the Earth-
Earth intercepting the solar energy flux and
radiating terrestrial energy. If at the location
of the (mean) Earth orbit, the incoming solar
energy flux is S0 = 1367 Wm−2, then, given
that the cross-sectional area of the Earth
intercepting the solar energy flux is πa2,
where a is the radius of the Earth
Albedo
• If in total the spinning Earth radiates in all directions like a blackbody of uniform temperature Te (known as
the emission temperature of the Earth) the Stefan-Boltzmann law gives:
->
Earth
Emission
temp = 255K
Download