The Electromagnetic Spectrum

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The Electromagnetic Spectrum
The Electromagnetic Spectrum describes how
radiation occurs in different forms, distinguished
by their wavelengths. The interaction of
electromagnetic radiation with matter depends on
wavelength. For example, some atmospheric gases
such as carbon dioxide absorb longwave radiation,
while others, such as ozone, absorb ultraviolet.
See animation on the Electromagnetic Spectrum in
the geodiscoveries section of your texts
website.
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The Global Radiation Balance
The Earth constantly absorbs solar shortwave
radiation and emits longwave radiation. In the
long run, the gain and loss of radiant energy
remains in balance and the Earth's average
temperature remains constant.
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The Global Radiation Balance
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The Suns Angle and the Length of the Day
The angle of the Sun in the sky at a particular
location depends on the latitude of the location,
the time of day, and the time of year.
See movie on the suns angle in the
geodiscoveries section of your texts website.
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The Suns Angle and the Length of the Day
Insolation and Sun angle. The angle of the Sun's
rays determines the intensity of insolation on
the ground. The energy of vertical rays A is
concentrated in square a by c, but the same
energy in the slanting rays B is spread over a
larger rectangle, b by c.
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The Path of the Sun in the Sky
How does the angle of the Sun vary during the
day? The angle depends on the Sun's path in the
sky. When the sun is high above the horizon, the
Sun's angle is greater, and so insolation will be
greater.
See movie on the suns path in the sky in the
geodiscoveries section of your texts website.
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The Path of the Sun in the Sky
The Sun's path in the sky changes greatly in
position and height above the horizon from summer
to winter. This diagram is for a location at lat.
40N (New York or Denver). At the winter
solstice, the Sun is low in the sky, and the
period of daylight is short. At the summer
solstice, the Sun is high, and the daylight
period is long.
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A Geographer's System of Latitude Zones
The seasonal pattern of daily insolation can be
used as a basis for dividing the globe into broad
latitude zones.
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A Geographer's System of Latitude Zones
World latitude zones. These zones are based on
the seasonal patterns of insolation observed over
the globe.
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Latent Heat
Latent heat, or hidden heat, is heat that is
taken up and stored when a substance changes
state from a solid to a liquid, from a liquid to
a gas, or from a solid directly to a gas. It
cannot be measured by a thermometer.
See movie on the suns path in the sky in the
geodiscoveries section of your texts website.
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The Composition of the Earth's Atmosphere
The composition of the lowest layer of the
Earth's atmosphere is fairly uniform up to around
80 kilometers altitude (50 miles). The most
dominant gases are nitrogen (78) and oxygen
(21). Less than 1 is comprised of argon, and
around 0.035 is taken up by carbon dioxide.
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The Composition of the Earth's Atmosphere
Component gases of the lower atmosphere. Values
show percentage by volume for dry air. Nitrogen
and oxygen form 99 percent of our air, with other
gases, principally argon and carbon dioxide,
accounting for the final 1 percent.
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Ozone in the Upper Atmosphere
The composition of the Earth's atmosphere
generally focuses upon the gases of the lowest
layer, the troposphere. However, gases higher in
the atmosphere also play a role in the Earth's
environment. Ozone is especially important
because of its role in absorbing ultra-violet
radiation, and so reducing the amount that
reaches the ground surface. Declining ozone
concentrations may lead to more cases of skin
cancers, the reduction of crop yields, and the
death of some forms of aquatic life.
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Albedo
The albedo of a surface describes the proportion
of radiation that is reflected away from that
surface. The average albedo of the Earth is
around 0.3 or 30, which means that 30 of
incoming solar radiation is reflected away and
back into space without contributing to the
heating of the planet's system. This measure is
also an average, and different surfaces on the
Earth have different albedos. Ice and snow
generally have a high albedo of anywhere between
40 for old snow to 95 for new, fresh snow.
Desert surfaces generally have albedos between
20 and 45. Vegetated surfaces generally have a
much lower albedo. Deciduous forests in leaf may
have albedos of around 20.
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Global Net Radiation
The flow of energy from the Sun to the Earth and
then back out into space is a complex system
involving not only radiation, but also energy
storage and transport.
See movie on the suns path in the sky in the
geodiscoveries section of your texts website.
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Global Net Radiation
Fate of incoming solar radiation. Losses of
incoming solar energy are much lower with clear
skies (left) than with cloud cover (right).
Diagram of the global energy balance. Values are
percentage units based on total insolation as
100. The left figure shows the fate of incoming
solar radiation. The right figure shows longwave
energy flows occurring between the surface and
atmosphere and space. Also shown are the
transfers of latent heat, sensible heat, and
direct solar absorption that balance the budget
for Earth and atmosphere.
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Earth's Energy Balance
Annual surface net radiation from pole to pole.
Where net radiation is positive, incoming solar
radiation exceeds outgoing longwave radiation.
There is an energy surplus, and energy moves
poleward as latent heat and sensible heat. Where
net radiation is negative, there is an energy
deficit. Latent and sensible heat are lost in the
form of outgoing longwave radiation.
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