Energy Pathways at Earths surface

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Energy Pathways at Earths surface

• Refraction
• Change in speed and direction of light
• Reflection (albedo)
• Energy that bounces directly back into space
  without being absorbed or doing any work
• Absorption
• Assimilation of radiation by matter and its
  conversion from one form of energy to another

2
Refraction bending of light caused by its
change in speed when it passes from one medium
into another
www.mic-d.com/curriculum/lightandcolor/refraction.
html
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Refraction
Figure 4.3
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Refraction

• We actually see sunrise 4 minutes early because
  the light is bent as it hits the atmosphere and
  we watch the sun go down 4 minutes late.
• The amount of refraction depends on atmospheric
  conditions
• Temperature
• Moisture
• Pollutants

5
why do we see rainbows after storms?
Forms when light is refracted (bent) by the water
droplets in the air Different wavelengths are
bent at different angles A full rainbow is a
circle, but on Earth we only see part of it The
center of the circle (antisolar point) is at a
point below the horizon equal to the altitude of
the sun
6
Path of one light ray entering a raindrop at
point A. As the light beam enters the surface of
the rain drop, it is bent (refracted) a little
and instead of continuing to point D, strikes the
inside wall of the raindrop at point B, where it
is reflected back to point C. As it emerges from
the raindrop, it is refracted (bent) again into
the direction E. The angle created at point D is
42o.
www.unidata.ucar.edu/staff/blynds/rnbw.html
Much of the sunlight that is refracted and
reflected through the raindrop is focused along
this path
Since the raindrop is circular, the reflection it
creates is also circular.
Although each droplet reflects an entire spectrum
of colours, we will see only one of the colours
from any given droplet. Which colour we see
depends on the angle at which we are viewing that
dropletin other words, its position in the sky
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Albedo - the reflectiveness of a surface
Figure 4.5
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Albedo

• Albedo reflectivity of a surface
• Measured as of insolation reflected (0 total
  absorption, 100 total reflection)
• Affects the ability of the Earth to absorb the
  sun's energy
• Albedo values
• Snow 50 95
• Grass 25 30
• Roads 5 10
• Oceans 0 60 (depends on the angle of
  sunlight, with lower angles producing
  greater reflection)
• Forests 10 20
• Earth average 31

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Energy Pathways
69 of sun's energy is absorbed and converted to
either infrared radiation or chemical energy by
photosynthesis in plants
Figure 4.1
Absorption raises the temperature of surface,
which radiates more energy at shorter wavelengths
than otherwise
10
Earth's radiation budget Includes the balance
between incoming shortwave radiation (from the
sun) and outgoing longwave radiation (from the
Earth)
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Earth- Atmosphere radiation balance

• Average annual energy balance is positive for
  Earth's surface (energy surplus)
• Earth's surface absorbs more energy in the
  tropics than in the polar regions

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• TROPICS
• angle of insolation is high
• daylength is constant
• more energy is gained than lost
• POLAR REGIONS
• angle of insolation is low
• surfaces covered in ice have high albedo (high
  reflectivity)
• up to 6 months of year no insolation is
  received
• more energy lost than gained

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Balance occurs around 36 degrees latitude Spatial
imbalance in energy causes energy transfer from
equator to poles It is ultimately responsible for
all weather patterns
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• Balance is negative for the atmosphere
• The atmosphere radiates heat to space (energy
  deficit)
• But add together Earths surface and atmosphere
  and the annual average balances

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Net radiation is greatest near the equator and
decreases to negative values in the midlatitudes
Earth's climate loses more energy to space than
it receives from the sun So why aren't we
freezing here in Memphis? Heat in our atmosphere
is transported by wind and convection Heat is
distributed more evenly near the surface than it
is at the top of the atmosphere
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Maximum temperature is somewhat later than noon
because temperature is a measure of how much
insolation is absorbed and reradiated from the
ground, not the amount of insolation itself
Figure 4.15